Characterization, modelling and optimization of industrial silicon thin film solar cells

Author: Rodríguez González, José Antonio

Year: 2013

Source: https://minerva.usc.es/bitstreams/30c035e5-6863-4a81-be2b-d16ae8b31601/download

UNIVERSIDADE DE SANTIAGO DE COMPOSTELA
Depa amen o de Elec ónica e Compu ación
Doc o al hesis
CHARACTERIZATION, MODELLING AND OPTIMIZATION OF
INDUSTRIAL SILICON THIN FILM SOLAR CELLS
Submi ed by:
José An onio Rod íguez González
Supe ised by:
D . An onio J. Ga cía Lou ei o
D . Ing. Michael Ve e
San iago de Compos ela, Sep embe 2013
D . An onio J. Ga cía Lou ei o, P o eso Ti ula del Á ea de Elec ónica de la Uni e sidade de
San iago de Compos ela
D . Ing. Michael Ve e , Di ec o del Labo a o io de I+D de la emp esa T-Sola Global S.A.
HACEN CONSTAR:
Que la memo ia i ulada CHARACTERIZATION, MODELLING AND OPTIMIZATION OF
INDUSTRIAL SILICON THIN FILM SOLAR CELLS ha sido ealizada po D. José An onio
Rod íguez González bajo nues a di ección en el Depa amen o de Elec ónica e Compu ación de la
Uni e sidade de San iago de Compos ela, y cons i uye la Tesis que p esen a pa a op a al í ulo de
Doc o .
San iago de Compos ela, sep iemb e de 2013
D . An onio J. Ga cía Lou ei o
Codi ec o de la esis
D . Ing. Michael Ve e
Codi ec o de la esis
José An onio Rod íguez González
Au o de la esis
A mis pad es

No podemos esol e p oblemas pensando de la
misma mane a que cuando los c eamos.
Albe Eins ein
Casi odo lo que ealice se á insigniﬁcan e, pe o es
muy impo an e que lo haga.
Maha ma Gandhi
Acknowledgmen s
Fis o all, I wan o kindly hank my PhD supe iso s, Michael Ve e and An onio Ga cía
Lou ei o, o hei cons an help, suppo and encou agemen , which ha e allowed me o ca y
ou his PhD. As well, o hei abili y o success ully manage hei espec i e eams and hei
mo i a ion and passion showed a wo k. I would also hank Jo di And eu o his conﬁdence.
To my T-Sola wo kma es om all he depa men s bu especially om he Labo a o y:
Ca los, Jacin o, Flo en , José Manuel, Miguel, Ósca , Bo is, Te esa and Luis. The wo king
en i onmen was eally nice and o wo k wi h you a ewa ding expe ience. I wan o also
hank you o he good momen s in Ou ense playing oo ball, ennis, going o he swimming
pool o making pa y a "Vinos". Pa icula ly, I wan o hank o E a, Mon se and Amau y, o
wo k in g oup wi h you has been e y easy and you mo i a ion a pleasu e.
To my CITIUS wo kma es, whe e I ha e pe o med he simula ions and w o e his
memo y, especially o En ique o his help wi h he simula ions and compu e p oblems.
I canno o ge Pablo, which has been my "b o he " in Ou ense du ing he las ou yea s.
We o m a nice " andem" and I hope i is going o con inue in he u u e wi h ou jump o he
business wo ld.
To my pa en s and my b o he San i o hei cons an suppo , help and hei sac iﬁce o
le me s udy wha e e I wan ed and o le me pa icipa e in he E asmus in e nship p og am.
To my iends o being always he e and o so many un o ge able momen s.
Finally, I acknowledge he unding o he Spanish Minis y o Economics and
Compe i i eness in he ame o he p og am "To es Que edo" (Con ac No. PTQ-10-03524)
and unde p ojec TEC2010-17320. This wo k was suppo ed by he FP7 Eu opean P ojec
HELATHIS (G an Ag eemen No. 241378) and he egional go e nmen o Galicia (P ojec s
No. IN841D-2010/14 and IN841C 2011/231).
San iago de Compos ela, Sep embe 2013
x i Lis o Figu es
Fig. 1.19 PECVD ool chambe usage o he p-i-n deposi ion ............. 29
Fig. 1.20 a-Si:H lase sc ibing s ep, P2 ......................... 30
Fig. 1.21 PVD spu e ing ool .............................. 31
Fig. 1.22 a-Si:H and back con ac lase sc ibing s ep, P3 ................ 31
Fig. 1.23 P1, P2 and P3 sc ibes (mic oscope iew) ................... 32
Fig. 1.24 Final module s uc u e which allows he cu en o ﬂow among he cells . . . 32
Fig. 1.25 T-Sola p oduc ion line is eady o p oduce modules o ou di e en sizes . 33
Fig. 1.26 Buss ool pic u e and clean oom o handle he PVB ............. 34
Fig. 1.27 Lamina ion ool and au ocla e ool o e all iew ............... 35
Fig. 1.28 Junc ion box ool and in-line sola simula o ool ............... 35
Fig. 1.29 Finished ull and qua e size modules ..................... 36
Fig. 1.30 Con ol plan scheme wi h all he con ols made in-line and o -line ..... 38
Fig. 2.1 Gene a ion o elec on-hole pai s due o he pho on incidence in a p-n junc ion 45
Fig. 2.2 Sola cell IV cu e as esul o he diode IV cu e minus he Iph ....... 46
Fig. 2.3 Equi alen ci cui o an a-Si:H sola cell ................... 47
Fig. 2.4 p-i-n s uc u e ................................. 48
Fig. 2.5 Amo phous silicon s uc u e ( andom ne wo k) showing a bond wi h a
hyd ogen a om ................................. 48
Fig. 2.6 DOS dis ibu ion model o in insic a-Si:H laye on a linea scale ...... 51
Fig. 2.7 DOS dis ibu ion model o in insic a-Si:H laye on a loga i hmic scale . . . 51
Fig. 2.8 Di e en ypes o localized s a es in he band gap o a-Si:H and models ha
a e used o calcula e he ecombina ion a e and cha ge occupa ion ..... 55
Fig. 2.9 Elec onic ansi ions in he ecombina ion p ocess be ween a single ene gy
le el in he band gap o a semiconduc o and he ene gy bands ........ 56
Fig. 2.10 Possible elec onic ansi ions in he ecombina ion p ocess be ween he
ene gy bands and an ampho e ic R-G cen e ep esen ed by wo ene gy le els
in he band gap ................................. 59
Fig. 2.11 Band diag am o he a-Si:H p-i-n laye s unde 1 sun illumina ion and
wi hou pola iza ion (V=0V) ........................ 63
Fig. 2.12 S uc u e o he simula ed a-Si:H sola cell .................. 65
Fig. 2.13 Pho on ﬂux in o a semiconduc o ....................... 67
Fig. 2.14 Op ical abso p ion coe ﬁcien o di e en PV ma e ials ........... 68
Fig. 2.15 Complex e ac i e index o ou a-Si:H laye s ................ 69

Lis o Figu es x ii
Fig. 2.16 SEM pic u e o an indus ial TCO sample AN10 om AGC showing ﬁne
su ace oughness o he c ys al g ains .................... 71
Fig. 2.17 AFM pic u e o an indus ial TCO sample AN10 om AGC ......... 71
Fig. 2.18 Sola spec um AM0, AM1.5G and AM1.5D ................. 73
Fig. 2.19 Simpliﬁed ﬂow cha o he me hod used o he nume ical esolu ion .... 75
Fig. 2.20 Ene gy band diag am o a ypical single junc ion a-Si:H sola cell unde
equilib ium condi ions ............................. 77
Fig. 3.1 Schema ic ep esen a ion o he glow-discha ge deposi ion p ocess ..... 87
Fig. 3.2 PECVD chambe diag am ........................... 88
Fig. 3.3 Fo me T-Sola coupon wi h 1 cm2sola cells and sample holde o MCs
measu emen s o IV cu es and SR wi h he swi ch box o choose he sola
cell o be measu ed ............................... 90
Fig. 3.4 Sc a ch mask, sc a ch pencils and Combi mask wi h hei ou pieces .... 92
Fig. 3.5 Back con ac side and glass side o a coupon p oduced a FZJ wi h a
magne ized mask (Combi mask) ........................ 92
Fig. 3.6 Posi ion o he coupons wi h MCs along he ull size panel .......... 93
Fig. 3.7 Back con ac side and glass side o a coupon p oduced a TS h ough lase
sc ibe ...................................... 94
Fig. 3.8 Posi ion o he MMs along he ull size panel ................. 95
Fig. 3.9 10 cm x 10 cm o al a ea MM p oduced a TS h ough LSR sc ibe ...... 95
Fig. 3.10 A c lamp and monoch oma o ......................... 97
Fig. 3.11 Incoming beam di ided by he beam-spli e ................. 98
Fig. 3.12 Two lock-in ampliﬁe s and cold ligh sou ce wi h i s illumina ion sys em . . 99
Fig. 3.13 SR equipmen and links be ween he di e en de ices ............ 103
Fig. 3.14 Conﬁgu a ion o a Cze ny-Tu ne monoch oma o .............. 104
Fig. 3.15 The beam-spli e wi h he wo a ms ...................... 104
Fig. 3.16 Op ical pa h o he ligh h ough he sys em .................. 105
Fig. 3.17 Rela ionship be ween ha dwa e and so wa e o he CSR equipmen .... 106
Fig. 3.18 Compa ison o he EQE p o ided by he manu ac u e and he a e age EQE
measu ed in he T-Sola equipmen o he e e ence sola cell WPVS Cell
06-2008 .................................... 107
Fig. 3.19 Expe imen al IV cu e and DC bias poin o 4 ep esen a i e LEDs ..... 111
x iii Lis o Figu es
Fig. 3.20 Peak wa eleng h and FWHM o a LED wi h na ow band wid h and o a
LED wi h wide band wid h .......................... 112
Fig. 3.21 Expe imen al spec al i adiance o 23 selec ed LEDs in he ange 370 nm -
1000 nm .................................... 112
Fig. 3.22 Decomposi ion o a pe iodic signal in i s di e en ha monics ........ 113
Fig. 3.23 Sine wa e in he ime-domain and, a e FFT analysis, sine wa e in he
equency-domain ............................... 114
Fig. 3.24 MM wi h e e y cell connec ed indi idually wi h a conduc ing adhesi e side
buss....................................... 115
Fig. 3.25 Diag am o he VFSR measu emen sys em .................. 116
Fig. 3.26 Time dependen cu en densi y cu e ..................... 117
Fig. 3.27 Cu en densi y cu e in he equency-domain as esul ing om FFT analysis 117
Fig. 3.28 EQE measu ed in a CSR equipmen wi h monoch oma o and in a VFSR
equipmen ................................... 118
Fig. 3.29 Sola simula o and he o he pa s o IV cu e measu emen de ices .... 120
Fig. 3.30 Equi alen ci cui o an a-Si:H PV sola cell ................. 122
Fig. 3.31 Typical illumina ed IV cu e and PV cu e o a pho o ol aic sola cell . . . 124
Fig. 3.32 Typical da k IV cu e o a pho o ol aic sola cell ............... 125
Fig. 3.33 Spa ial mapping esul o he calib a ion done on 29/11/2011 ........ 127
Fig. 3.34 LabVIEW on panel o he IV cu e ace ................. 129
Fig. 4.1 Design o he o me T-Sola sola cells p oduced wi h shadow mask .... 133
Fig. 4.2 JV cu es o sola cells on Asahi U TCO-glass ................ 138
Fig. 4.3 Illumina ed JV cu e o h ee cells be o e and a e pe o ming shun bus ing
o a coupon sen o FZJ wi hou back con ac (ﬁ s shipmen ) ........ 141
Fig. 4.4 Da k JV cu e o he bes cell (C17) be o e and a e pe o ming shun
bus ing o a coupon sen o FZJ wi hou back con ac (ﬁ s shipmen ) .... 141
Fig. 4.5 JV cu e compa ison o he bes cells be ween he samples p oduced on
04/02/10 only wi h p-i-n, wi h back con ac laye s added on 18/03/10:
p-i-n wi hou any ea men , p-i-n ea ed wi h HF e ching and p-i-n + AZO . 144
Fig. 4.6 Da k JV cu es o wo sola cells sen wi h and wi hou back con ac .... 144
Fig. 4.7 EQE compa ison be ween he samples p oduced on 04/02/10 wi h back
con ac laye s deposi ed on 18/03/10: p-i-n wi hou any ea men , p-i-n
ea ed wi h HF e ching, p-i-n + AZO ..................... 145
Lis o Figu es xix
Fig. 4.8 To al ansmission o ﬁ e TCO ypes wi h di e en ca ie mobili y,
hickness and esis i i y ............................ 148
Fig. 4.9 Co ela ion be ween Jsc measu ed in he SS and TCO-glass abso bance o
ﬁ e TCO-glass ypes wi h di e en ca ie mobili y, hickness and esis i i y 148
Fig. 4.10 JV cu e o ﬁ e TCO ypes wi h di e en ca ie mobili y, hickness and
esis i i y .................................... 150
Fig. 4.11 EQE cu e o ﬁ e TCO ypes wi h di e en ca ie mobili y, hickness and
esis i i y .................................... 150
Fig. 4.12 To al ansmission o h ee indus ial TCO-glasses and one labo a o y
TCO-glass (Asahi U) .............................. 152
Fig. 4.13 JV cu e o wo TCO-glass ypes wi h di e en o al ansmission, ca ie
mobili y and hickness ............................. 153
Fig. 4.14 EQE cu e o wo TCO-glass ypes wi h di e en o al ansmission, ca ie
mobili y and hickness ............................. 154
Fig. 4.15 S uc u e o an a-Si:H sola cell including he placemen o wo ARC a
in e aces ai /glass and TCO/p-laye ...................... 155
Fig. 4.16 JV cu e o ou sola cells wi h NTO in e ace laye wi h di e en hickness
and doping concen a ion deposi ed on Asahi U TCO-glass ......... 157
Fig. 4.17 EQE cu e o ou sola cells wi h NTO in e ace laye wi h di e en
hickness and doping concen a ion deposi ed on Asahi U TCO-glass .... 157
Fig. 4.18 Reﬂec ion o ou sola cells wi h NTO in e ace laye wi h di e en
hickness and doping concen a ion deposi ed on Asahi U TCO-glass .... 158
Fig. 4.19 To al and di use ansmission o a SnO2TCO deposi ed on ﬂoa glass o
3.2 mm and a ZnO TCO deposi ed on Co ning glass o 1.0mm ....... 159
Fig. 4.20 Haze o a SnO2TCO deposi ed on ﬂoa glass o 3.2 mm and a ZnO TCO
deposi ed on Co ning glass o 1.0mm..................... 160
Fig. 4.21 JV cu e o h ee sola cells wi h ZnO on TCO p oduced a FZJ wi h
di e en doping concen a ion and deposi ion p ocess ............ 161
Fig. 4.22 EQE cu e o h ee sola cells wi h ZnO on TCO p oduced a FZJ wi h
di e en doping concen a ion and deposi ion p ocess ............ 162
Fig. 4.23 JV cu e o wo sola cells wi h ZnO on TCO p oduced a FZJ and
Asahi U (SnO2) on TCO. Bo h samples ha e μc-Si p-laye ........ 163
xx Lis o Figu es
Fig. 4.24 EQE cu e o wo sola cells wi h ZnO on TCO p oduced a FZJ and
wi h Asahi U (SnO2) on TCO. Bo h samples ha e μc-Si p-laye and a e
compa ed wi h a sola cell wi h ZnO on TCO wi h a-Si:H p-laye ..... 163
Fig. 4.25 Typical hickness mapping o a n- ype a-Si:H con ol laye .......... 165
Fig. 4.26 Va ia ion o he main elec ical pa ame e s o ou coupons placed along he
diagonal F-I o he panel ............................ 165
Fig. 4.27 EQE cu e o wo coupons o he same panel, one placed in he cen e and
he o he one in a co ne ............................ 166
Fig. 4.28 Deg ada ion ac o s o Jsc o sola cells p epa ed wi h di e en i-laye
hicknesses in di e en labo a o ies ...................... 168
Fig. 4.29 Deg ada ion ac o s o Voc and FF o sola cells p epa ed wi h di e en
i-laye hicknesses in di e en labo a o ies .................. 168
Fig. 4.30 E ﬁciency o qua e size modules in he ini ial and s abilized s a e and η
deg ada ion ac o s ............................... 169
Fig. 4.31 Rela ion be ween i-laye hickness educ ion and h oughpu inc ease o he
PECVD machine and ex apola ion o he annual p oduc ion capaci y .... 169
Fig. 4.32 JV cu e o h ee sola cells which ep esen he main h ee e olu ions
pe o med a T-Sola du ing he h ee yea s o he HELATHIS p ojec .... 172
Fig. 4.33 EQE cu e o h ee coupons which ep esen he main h ee e olu ions
pe o med a T-Sola du ing he h ee yea s o he HELATHIS p ojec . The
EQE o he wo ld eco d sola cell o Oe likon Sola -Lab is also p esen ed . 173
Fig. 4.34 Gain o he main elec ical pa ame e s (in s abilized s a e) espec o
e olu ion No. 4 o he main ou e olu ions pe o med a T-Sola du ing
he h ee yea s o he HELATHIS p ojec ................... 173
Fig. 4.35 EQE cu e o wo sola cells, one wi h Al back con ac and ano he one wi h
Ag back con ac , bo h deposi ed by spu e ing a UU ............. 175
Fig. 4.36 Reﬂec ance o ﬁ e di e en Ag and/o Al back eﬂec o s .......... 175
Fig. 4.37 EQE o wo SJ sola cells wi h di e en i-laye hickness, bo h measu ed
wi h ou CSR equipmen and he new VFSR equipmen ........... 176
Fig. 4.38 EQE o wo SJ sola cells wi h di e en BKM e olu ions (No.4 s. No.8),
bo h measu ed wi h he CSR and VFSR equipmen .............. 178
Fig. 4.39 Jsc spa ial mapping along a 10 x 10 cm2size mini module measu ed wi h he
VFSR equipmen ................................ 179
Lis o Figu es xxi
Fig. 4.40 Va ia ion o sho ci cui cu en densi y and open ci cui ol age wi h he
i-laye hickness o h ee di e en p-laye hicknesses ............ 180
Fig. 4.41 Va ia ion o e ﬁciency and ﬁll ac o wi h he i-laye hickness o h ee
di e en p-laye hicknesses .......................... 181
Fig. 4.42 Va ia ion o sho ci cui cu en densi y and open ci cui ol age wi h he
i-laye hickness o h ee di e en p-laye doping concen a ions ...... 181
Fig. 4.43 Va ia ion o e ﬁciency and ﬁll ac o wi h he i-laye hickness o h ee
di e en p-laye doping concen a ions .................... 182
Fig. 4.44 Ligh apping in he ac i e laye (i-laye ) o an a-Si:H sola cell ....... 183
Fig. 4.45 Rep esen a ion o he ex u e in e ace pa ame e s .............. 184
Fig. 4.46 Simula ed JV cu es o ﬂa and ex u ed in e aces wi h di e en heigh s . . 185
Fig. 4.47 Simula ed EQE o ﬂa and ex u ed in e aces wi h di e en heigh s .... 186
Fig. 4.48 Expe imen al and simula ed JV cu e in he ini ial and deg aded s a e .... 187
Fig. 4.49 Expe imen al and simula ed EQE in he ini ial and deg aded s a e ...... 187
Fig. 4.50 E ﬁciency e olu ion in modules in he las ou yea s ............. 188
Fig. 4.51 E ﬁciency his og am o simila p oduc ion pe iods o 5.72 m2a-Si:H
modules om 2009 o 2012 .......................... 189
Fig. 4.52 E olu ion o he T-Sola p oduc ion capaci y and h oughpu du ing he
pe iod 2009 - 2012 ............................... 190

Lis o Tables
Tabla 1.1 An o e iew o majo PV echnologies ................... 10
Tabla 1.2 E olu ion o he cumula i e sola elec ical capaci ies un il 2035 ...... 21
Tabla 2.1 Time a es o change in he ca ie concen a ions o ansi ions in ol ing
VB and CB ail s a es a an a bi a y ene gy le el ETin he band gap .... 56
Tabla 2.2 T ansi ion a es o change in he ca ie concen a ions o ecombina ion
p ocesses in ol ing DB s a es. ........................ 59
Tabla 2.3 Baseline inpu pa ame e s used in he simula ion .............. 66
Tabla 3.1 IV cu e pa ame e s o he calib a ed sola cell (4 cm2) om FHG-ISE
measu ed unde STC ............................. 99
Tabla 3.2 Compa ison o he echnical da a shee alues wi h he expe imen al da a
ob ained a ou lab o he 24 selec ed LEDs ................. 110
Tabla 3.3 Resul s o all he calib a ion con ols done o he h ee lamps used un il
he momen in he sola simula o ...................... 128
Tabla 4.1 Elec ical pa ame e s compa ison o he old (shadow mask) and new (lase
sc ibe) T-Sola sola cell design ....................... 134
Tabla 4.2 Elec ical pa ame e s compa ison o h ee di e en ypes o annealing
pe o med in h ee coupons which we e loca ed side by side in he same
panel. Top: Resul s be o e and a e annealing and a e 300 kWh/m2o
ligh soaking. Middle: Va ia ion o he h ee coupons be o e and a e
pe o ming annealing. Bo om: LID o he h ee coupons ......... 135
xxi Lis o Tables
Tabla 4.3 Elec ical pa ame e s a e age o he bes 5 cells o a coupon wi hou
ea men , a e shun bus ing and a e shun bus ing and annealing ( op).
Va ia ion espec o alues wi hou ea men (middle). Numbe o good
cells in ou di e en coupons wi hou ea men , a e annealing, a e
shun bus ing o a e shun bus ing and annealing (bo om) ......... 136
Tabla 4.4 Elec ical pa ame e s compa ison o 1 cm2sola cells and 5.72 m2 ull size
modules p oduced on 16/06/2011 ...................... 137
Tabla 4.5 Elec ical pa ame e s o sola cells on Asahi U TCO-glass p oduced wi h
di e en p oduc ion me hods and ea men s ................. 139
Tabla 4.6 A e age elec ical pa ame e alues be o e and a e pe o ming shun
bus ing o a coupon sen o FZJ wi hou back con ac (ﬁ s shipmen ) . . . 140
Tabla 4.7 A e age elec ical pa ame e alues o he measu ed sola cells in each
expe imen (p-i-n: 8 cells, p-i-n + HF: 12 cells, p-i-n + AZO: 8 cells) . . . 143
Tabla 4.8 Elec ical pa ame e alues o he bes cell o he h ee expe imen s and
a e age alues o 1 cm2cells p oduced (wi h mask) wi h he T-Sola
s anda d p ocess ............................... 143
Tabla 4.9 Summa y o he main cha ac e is ics o he di e en TCO ypes ...... 146
Tabla 4.10 T ansmission, abso p ion and shee esis ance o ﬁ e TCO-glass ypes wi h
di e en ca ie mobili y, hickness and esis i i y .............. 147
Tabla 4.11 Elec ical pa ame e s o ﬁ e TCO ypes wi h di e en ca ie mobili y,
hickness and esis i i y ........................... 149
Tabla 4.12 In eg a ed o al ansmission in he ange 400 nm - 800 nm o h ee
indus ial TCO-glasses and one labo a o y TCO-glass (Asahi U) and hei
gain wi h espec o AN10 .......................... 151
Tabla 4.13 Elec ical pa ame e s o wo TCO-glass ypes wi h di e en o al
ansmission, ca ie mobili y and hickness ................. 153
Tabla 4.14 Thickness and doping condi ions o ou di e en in e ace laye s o NTO
deposi ed on Asahi U ............................. 155
Tabla 4.15 Elec ical pa ame e s (ini ial s a e) o wo e e ences and ou sola cells
wi h NTO in e ace laye wi h di e en hickness and doping concen a ion
deposi ed on Asahi U TCO-glass ....................... 156
Tabla 4.16 Ma e ial p ope ies o a SnO2TCO deposi ed on ﬂoa glass o 3.2 mm and
a ZnO TCO deposi ed on Co ning glass o 1.0mm ............. 158
Lis o Tables xx
Tabla 4.17 Elec ical pa ame e s (ini ial s a e) o h ee sola cells wi h ZnO on TCO
p oduced a FZJ wi h di e en doping concen a ion and deposi ion p ocess 160
Tabla 4.18 Elec ical pa ame e s (ini ial s a e) o wo sola cells wi h ZnO on TCO
p oduced a FZJ and Asahi U (SnO2) on TCO. Bo h samples ha e μc-Si
p-laye .................................... 162
Tabla 4.19 Elec ical pa ame e s s a is ics o ou coupons o he same panel placed
along he diagonal .............................. 166
Tabla 4.20 LID o hi een coupons p oduced a di e en labo a o ies (2 a UU, 3 a
FZJ and 8 a TS) wi h di e en i-laye hicknesses ............. 167
Tabla 4.21 Main BKM e olu ion ela ed o he PECVD p ocess since he T-Sola
p oduc ion s a ................................ 170
Tabla 4.22 Elec ical pa ame e s o ﬁ e coupons wi h sola cells which ep esen he
main ﬁ e e olu ions pe o med a T-Sola du ing he h ee yea s o he
HELATHIS p ojec .............................. 171
Tabla 4.23 Gain in he s abilized s a e espec o e olu ion No. 4 ............ 174
Tabla 4.24 Elec ical pa ame e s o he s abilized eco d T-Sola sola cell and wo ld
eco d sola cell o Oe likon Sola -Lab ................... 174
Tabla 4.25 Jsc de e mined om SR wi h he VFSR and CSR equipmen o sola cells
wi h i-laye hickness (di)o 260nmand200nm.............. 177
Tabla 4.26 Jsc de e mined om SR wi h he VFSR and CSR equipmen o sola cells
wi h di e en BKM e olu ion s eps (No.4 s. No.8) ............ 177
Tabla 4.27 S a is ical pa ame e s ob ained om he mapping in Fig. 4.39 (VFSR
equipmen ) and he same mapping ob ained wi h he CSR equipmen . . . 179
Tabla 4.28 Simula ed elec ical pa ame e s depending on he βangle in he deg aded
s a e ...................................... 185
Tabla 4.29 Elec ical pa ame e s o an expe imen al and simula ed sola cell in he
ini ial and deg aded s a e ........................... 186
xxxii Lis o Ac onyms
PV powe - ol age
PVB poly inyl bu y al
PVD physical apou deposi ion
QASR quali y assu ance and shun emo al
QE quan um e ﬁciency
eﬂec ion
R-G ecombina ion-gene a ion
RF adio equency
ROW es o he Wo ld
Rsse ies esis ance
Rsh shun esis ance
Rsq shee esis ance
SB shun bus ing
SCPI s anda d commands o p og ammable ins umen s
SEM scanning elec on mic oscopy
Si silicon
SiF4silicon e aﬂuo ide
SIGMA "SIs ema de Ges ión y Moni o ización A anzado"
SiH4silane
SiO2silicon oxide
SJ single junc ion
SnO2 in oxide

Lis o Ac onyms xxxiii
SnO2:F ﬂuo ine-doped in oxide
SR spec al esponse
SRH Shockley Read Hall
SS sola simula o
STC s anda d es condi ions (1000 W/m2,25oC and AM1.5G spec al dis ibu ion)
SWE S aeble -W onski e ec
T empe a u e
T-Sola T-Sola Global S.A.
TCO anspa en conduc i e oxide
TCS he mal condi ioning s a ion
TiO2 i anium oxide
TJ andem junc ion
TMM ans e ma ix me hod
TS T-Sola Global S.A.
UB Uni e si y de Ba celona
USC Uni e si y o San iago de Compos ela
UU Uni e si y U ech
UV ul a iole
UVI Uni e si y o Vigo
VB alence band
VBT alence band ail
VFSR e y as spec al esponse
xxxi Lis o Ac onyms
VI i ual ins umen
Vmpp ol age a maximum powe poin
Voc open ci cui ol age
WP wo k packages
ZnO zinc oxide
In oduc ion
Nowadays he mos o he ene gy consump ion is p o ided om ossil uels as oil, na u al
gas o coal. Ne e heless, in he las yea s, he wo ld-wide ene ge ic policies a e changing and
enewable ene gies a e inc easing apidly hei quo a in he ene gy mix. The main easons o
his modiﬁca ion a e, on one hand, ha ossil uel p ices a e aising due o he dec easing
a ailabili y o his sou ces. On he o he hand, he consume coun ies a e dependen o he
p oduce coun ies. In addi ion, he massi e use o hem is p oducing he clima e change.
The Eu opean Union (EU) clima e and ene gy a ge s, known as he "20-20-20" a ge s,
se h ee key objec i es o 2020 [1]: A 20% educ ion in EU g eenhouse gas emissions om
1990 le els ( o come back o 450 ppm - 550 ppm ange), o aise he sha e o EU ene gy
consump ion p oduced om enewable esou ces o 20% and a 20% imp o emen in he EU’s
ene gy e ﬁciency.
Du ing he las yea s he in es men s in o enewable ene gy and ene gy e ﬁciency sec o s
has been inc easing. In 2011, wo ld-wide new in es men s in o hese sec o s inc eased o a
new eco d o e202 billion, including e19.8 billion esea ch and de elopmen spending.
Mo e han 85% (e173 billion) o hese in es men s we e non-go e nmen al, non- esea ch
clean ene gy in es men s [2]. This esul ed in a eco d o 83.5 GW o new clean ene gy
gene a ion capaci y, b inging he o al o mo e han 565 GW (50% mo e han he ins alled
nuclea gene a ing capaci y wo ld-wide).
Speciﬁcally o sola ene gy, in 2011 ( o he second yea in a ow) a ac ed he
la ges amoun o new in es men s in o enewable ene gies [2]. The e was a 44% inc ease
( espec i ely o 2010) in sola ene gy in es men s o e98.5 billion [2].
Nowadays, elec ici y p oduc ion om pho o ol aic (PV) sola sys ems has shown ha i
can be cheape han peak p ices in he elec ici y exchange. The elec ici y gene a ion cos s
2In oduc ion
a e al eady a he le el o esiden ial elec ici y p ices in se e al coun ies, depending on he
ac ual elec ici y p ice and he local sola i adiance le el.
Pho o ol aic sola ene gy will con inue o g ow a high a es in he coming yea s
accele a ing i s consolida ion because i is conside ed o be he mos powe ul ene gy sou ce
in he u u e since i joins op imal condi ions such as sola ene gy is an unlimi ed esou ce
( he sun supplies 1000 imes mo e ene gy han he wo ld ene gy consump ion) o i is a clean
ene gy. Fu he mo e, he cu en sola module echnologies a e well es ablished and p o ide
a eliable p oduc , wi h su ﬁcien e ﬁciency and ene gy ou pu o a leas 25 yea s li e ime.
The de elopmen and ecen as g ow h o he PV indus y has esul ed in module
o e supply and a as dec ease o module p ices in he las yea s, demanding now on all
ac o s in he PV sec o an impo an inc ease in R&D ac i i ies o be compe i i e in he
u u e. The in es iga ions o his PhD hesis we e pe o med in ha ame. I was ﬁnanced
by he High E ﬁcien e y LA ge a ea THIn ﬁlm Silicon pho o ol aic modules (HELATHIS)
p ojec and he "To es Que edo" p og am. The ac i i y in ol ed he Technology and R&D
Depa men o he T-Sola Global S.A. (T-Sola ) company and he Depa men o Elec onics
and Compu e Science o he Uni e si y o San iago de Compos ela.
This PhD hesis is s uc u ed in ou chap e s and is based on he op ical and elec ical
cha ac e iza ion o sola cells wi h di e en ma e ials and deposi ion p ocess condi ions, he
op imiza ion and modelling o hese cells and he de elopmen o me ology equipmen s.
The ﬁ s chap e p esen s a gene al iew on he pho o ol aic s a us analysing he di e en
pho o ol aic echnologies and i s applica ions, as well we will ake a glance on he e olu ion
o he wo ld-wide pho o ol aic p oduc ion capaci y and ins alled capaci y since 2000 and he
o ecas un il 2017. Nex , we will ocus in T-Sola and i s hyd ogena ed amo phous silicon
(a-Si:H) pho o ol aic module ac o y. Finally, he main aims o he op imiza ion o a-Si:H
sola cells in he ame o he FP7 Eu opean P ojec HELATHIS a e exposed.
In he second chap e he elec ical model ha go e ns he a-Si:H sola cells is p esen ed,
as well as hei equi alen ci cui , bo h ob ained om he ideal diode model and deduced
om he c ys alline silicon (c-Si) sola cell model. Then, he physical model is explained
emphasising in he di e ences be ween he p ope ies o a-Si:H and c-Si. The mos
impo an changes esul om he densi y o s a es (DOS), he ecombina ion-gene a ion
s a is ics, he g aded laye s and he ligh induced deg ada ion p oduced in a-Si:H due o he
S aeble -W onski e ec (SWE). Nex , i is explained how he op ical gene a ion is p oduced in
a-Si:H sola cells, how he spec al i adiance is conside ed and how he op ical ansmission,
In oduc ion 3
eﬂec ion and abso p ion wo ks in he di e en sola cell laye s. As well, we poin ou he
di e en me hods adop ed in he he e used Sen au us (Synopsys) simula ion ool o simula e
bo h models, wi h ﬂa o ex u ed laye s. Finally, a summa y is p esen ed abou how he
semiconduc o equa ions a e sol ed. Tha sec ion in oduces he equa ions and bounda y
condi ions ha he Sen au us so wa e sol es o ge , e.g., he cu en - ol age (IV) cu es
o ex e nal quan um e ﬁciency (EQE) cu es. The simula ed de ice is meshed o ming
housands o nodes and he espec i e equa ions desc ibing he de ice and he bounda y
condi ions a e disc e ised in e e y o hese nodes, hen, he esul ing sys em o equa ions
is linea ised and sol ed wi h he Gummel o New on-Raphson me hods.
The hi d chap e p esen s how he plasma enhanced chemical apou deposi ion
(PECVD) p oduc ion p ocess wo ks, as well as how we ab ica e R&D sola cells o 1 cm2
(o 4cm
2) o mini modules in he indus ial p oduc ion line. La e , he equipmen ins alled in
he labo a o y a e shown. Conce ning his hesis, he mos impo an ones a e a con en ional
spec al esponse (CSR) and a e y as spec al esponse (VFSR) equipmen , which a e used
o de e mine he EQE cu es, and a sola simula o (SS) equipmen wi h i s IV ace o
measu e he illumina ed o da k IV cu es. The h ee equipmen we e de eloped in ou
labo a o y. The de elopmen o p oduce R&D sola cells and mini modules in he T-Sola
p oduc ion line as well as he de elopmen o he measu emen equipmen ha e been c ucial
o imp o e he p oduc ion module e ﬁciency.
In he ou h chap e we mainly p esen wo k pe o med in he ame o he Eu opean
p ojec HELATHIS. One o i s objec i es is he op imiza ion o he sola cell s uc u e
implemen ed in T-Sola ’s indus ial p oduc ion p ocess o e y la ge a ea (2.6mx2.2m)
a-Si:H PV modules. In he op imiza ion no only he achie emen o he physical e ﬁciency
limi o he sola cells has o be aken in o accoun , bu also aspec s like sola cell ab ica ion
ime (impac ing on ac o y h oughpu ), he ma e ial and ene gy consump ion (impac ing on
p oduc ion cos ), e c. In e e ence o his we epo he e, ﬁ s ly, on he e olu ion o ab ica e
highly e ﬁcien and eliable a-Si:H es sola cells in he indus ial en i onmen o T-Sola
and he p epa a ion o samples wi h sola cells o shipmen s o p ojec pa ne s. Nex ,
we in es iga e he cell s uc u e de elopmen s, epo ing on he on anspa en conduc i e
oxide (TCO) laye and glass de elopmen s, p-i-n s uc u e de elopmen s and back con ac
de elopmen s. Nex , we analyse he esul s ob ained wi h he VFSR equipmen and simula ion
s udies on he p-i-n s uc u e and he on TCO laye ex u e. To conclude his chap e , he

4In oduc ion
imp o emen s in he indus ial p oduc ion line o T-Sola since he beginning in he yea 2008
a e shown.
Finally, he conclusions and he main ad ances achie ed du ing his PhD hesis a e
indica ed.
CHAPTER 1
PHOTOVOLTAICS STATUS AND T-SOLAR’S
THIN FILM SILICON FACTORY
Pho o ol aic (PV) sola ene gy is expec ed o be he mos powe ul ene gy sou ce in he
u u e since i ga he s he op imal condi ions o his. Fo ins ance, sola ene gy is an unlimi ed
esou ce ( he sun supplies 1000 imes mo e ene gy han he wo ld ene gy consump ion) and
u he mo e, i is a clean ene gy. In ac , he cu en sola module echnologies a e well
es ablished and p o ide a eliable p oduc , wi h su ﬁcien e ﬁciency and ene gy ou pu o ha e
a leas a 25-yea -long li e ime. In addi ion, he inc easing amoun o elec ici y in e up ions
(due o g id o e loads), oge he wi h he con inuous p ice ise o elec ici y coming om
con en ional ene gy sou ces, add a ac i eness o he PV sys ems.
This chap e p esen s a gene al o e iew o he s a us o pho o ol aics, analysing he
di e en pho o ol aic echnologies and hei applica ions. Likewise, we will ake a glance on
he e olu ion o he wo ld-wide pho o ol aic p oduc ion capaci y and he ins alled capaci y
om yea 2000 o he p esen , and he o ecas un il yea 2017. Nex , we will ocus on he
company T-Sola Global S.A. and i s hyd ogena ed amo phous silicon (a-Si:H) pho o ol aic
module ac o y. Finally, he main aims o he op imiza ion o a-Si:H sola cells in he ame
o he FP7 Eu opean P ojec HELATHIS a e exposed.
6Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
1.1 Pho o ol aic echnologies
The e a e a wide ange o PV cell echnologies on he ma ke oday, using di e en ypes
o ma e ials, and e en a la ge numbe will be a ailable in he u u e. PV cell echnologies a e
usually classiﬁed in o h ee gene a ions, depending on he ma e ial on which hey a e based
and on hei le el o comme cial ma u i y [3].
1.1.1 Fi s gene a ion PV echnologies: C ys alline silicon sola cells
Silicon is one o he mos abundan elemen s in he ea h’s c us . C ys alline silicon is he
ma e ial mos commonly used in he PV indus y, he e o e wa e -based c ys alline silicon
(c-Si) PV cells and modules domina e he cu en ma ke . This is a ma u e echnology ha
employs he accumula ed knowledge basis de eloped in he elec onic indus y. This ype o
sola cell is p oduced in mass, indi idual companies p oduce hem a a a e o se e al hund ed
MW pe yea , eaching in some cases he GW-scale. In Fig. 1.1 he manu ac u ing p ocess
o wa e -based silicon PV modules is p esen ed. I comp ises ou main s eps: poly-silicon
p oduc ion, ingo /wa e p oduc ion, cell p oduc ion and module assembly.
Figu e 1.1: C ys alline silicon module p oduc ion chain [4].
1.1. Pho o ol aic echnologies 7
C ys alline silicon sola cells a e classiﬁed in o h ee main ypes depending on how he Si
wa e s a e made [3]. They a e:
– Mono-c ys alline (c-Si).
– Mul i-c ys alline (mc-Si).
– Edge-deﬁned ﬁlm- ed g ow h (EFG) ibbon silicon.
C ys alline silicon echnologies accoun ed abou 85% o he global PV sales in 2012 [5].
The e ﬁciency o c ys alline silicon modules anges om 15% o 21% [6]. Since i is a ma u e
echnology, con inued cos educ ions a e possible h ough imp o emen s in ma e ials and
manu ac u ing p ocesses. F om he economies o scale, one can p edic ha when he ma ke
con inues o g ow, mo e high- olume manu ac u e s will eme ge.
1.1.2 Second gene a ion PV echnologies: Thin ﬁlm sola cells
Thin ﬁlm sola cells could po en ially p o ide lowe cos elec ici y han c-Si wa e -based
sola cells. Howe e , his is no ce ain. The lowe capi al cos s (due o lowe p oduc ion
and ma e ials cos s) a e o se , o some ex en , by he lowe e ﬁciencies o his echnology.
Besides, he educ ion o c-Si modules’ cos s will make he economics e en mo e challenging.
Thin ﬁlm sola cells do no use wa e s o p oduce he semiconduc o , in con as , hey
consis o successi e hin laye s (o abou 1 μm o4μm hick) deposi ed on a la ge
inexpensi e subs a e, such as: glass, polyme , o me al. As a consequence, hey equi e
a lo less semiconduc o ma e ial o abso b he same amoun o sunligh (up o 99% less
ma e ial han c ys alline sola cells). In addi ion, hin ﬁlms can be packaged in o ﬂexible
and ligh weigh s uc u es which can be easily in eg a ed in o building componen s, such as
oo s o acades (building in eg a ed pho o ol aics (BIPV)). The h ee p ima y comme cially
de eloped echnologies employed in hin ﬁlm sola cells a e: amo phous silicon; cadmium
ellu ide (CdTe); and coppe , indium, gallium, selenium (CIGS)[3]. They a e ho oughly
explained in he ollowing pa ag aphs:
–Amo phous silicon sola cells (a-Si:H and a-Si:H/μc-Si:H): Amo phous silicon
can be deposi ed on cheap and e y la ge subs a es (up o 5.7m
2o glass) based
on con inuous deposi ion echniques, hus conside ably educing manu ac u ing cos s.
Cu en ly, amo phous silicon PV module e ﬁciencies a e in he ange om 5%
14 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
–G id-connec ed powe plan s: Can be g ound-moun ed, o loca ed on la ge
indus ial/comme cial buildings such as shopping malls, ai po e minals o ailway
s a ions. These p oduce a la ge quan i y o PV elec ici y a a single poin .
–O -g id sys ems o u al elec iﬁca ion: Can be a small sola PV sys em co e ing
he basic elec ici y needs o a household, o a la ge sola mini-plan , p o iding enough
powe o se e al homes. These sys ems b ing access o elec ici y o emo e a eas
(moun ain hu s, illages in de eloping coun ies o small islands).
–O -g id indus ial applica ions: Ve y equen in he elecommunica ions and
anspo ﬁelds. Fo example o epea e s a ions o mobile phones, a ﬁc signals,
ma ine na iga ion aids, secu i y phones, emo e ligh ing, highway signs, e c. These
b ing cos -e ec i e powe o a eas a away om he elec ici y g id, a oiding he high
cos o ins alling cabled ne wo ks.
–Consume goods: Many e e yday elec ical appliances use PV sola cells: wa ches,
calcula o s, oys, ba e y cha ge s, wa e sp inkle s, ligh ing, e c.
1.3 E olu ion o pho o ol aic p oduc ion and ins alled capaci y
The da a p esen ed in his sec ion is mainly ob ained om he epo s "Global ma ke
ou look o pho o ol aics 2013 - 2017" o he Eu opean Pho o ol aic Indus y Associa ion
(EPIA) [5] and "PV s a us epo 2012" o he Join Resea ch Cen e (JRC) [2].
1.3.1 Pho o ol aic ma ke : Ins alla ions
The ins alled PV powe he e p esen ed includes only sys ems connec ed o he g id and
no hose ha ha e been ins alled bu no ye connec ed.
In Fig. 1.5 he annual PV ins alla ions om 2000 o 2012 a e p esen ed. PV echnology
has g own o e he pas decade a a ema kable a e and is on he way o becoming a majo
sou ce o powe gene a ion o he wo ld. The annual PV ins alla ions in 2012 we e abou
31 GW. A e he wo ld-wide PV ma ke mo e han doubled in 2010, he g ow h in 2011
was 80% compa ed o 2010, ne e heless, in 2012 he PV ma ke s abilized. The 2012 ma ke
olume was mainly led by Ge many (7.6 GW ins alled in 2012 / 32.4 GW cumula i e ins alled
capaci y), China (5.0GW/8.3 GW), I aly (3.4GW/16.4 GW), he USA (3.3GW/7.8 GW)
and Japan (2.0GW/6.9 GW).

1.3. E olu ion o pho o ol aic p oduc ion and ins alled capaci y 15
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The esul s in 2012 and he o ecas o he coming yea s indica e ha Eu ope’s leading
ole in he PV ma ke is coming o an end. In 2011, Eu ope accoun ed o 74% o he wo ld’s
new PV ins alla ions (22.4 GW); in 2012 his numbe was a ound 55% (17.2 GW) [5]. In
2013 i is almos ce ain ha he majo i y o new PV capaci y in he wo ld will be ins alled
ou side o Eu ope. The e o e, in he nex yea s he PV g ow h in Eu ope will occu a a mo e
s able – and sus ainable – a e han i has in he las ew yea s. In he u u e he d i ing o ces
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global.
As shown in Fig. 1.6, a he end o 2012 he o al cumula i e PV ins alla ions wo ld-wide
we e 102 GW. The 69% o he wo ld-wide ins alled capaci y (70 GW om he 102 GW) a e
ins alled in he Eu opean Union (EU). Mo eo e , Ge many coun s on 32 GW. In he pe iod
2000 - 2012, Eu ope has inc eased 540 imes ( om 129 MW o 70 GW) i s ins alled capaci y
[5], [16].
In 2012, o he second yea in a ow, PV was he numbe -one new sou ce o elec ici y
gene a ion ins alled in Eu ope. PV co e s 2.6% o he elec ici y demand in Eu ope [5]. The
de elopmen o PV elec ici y in Eu ope is occu ing a a as e a e han almos anyone had
expec ed. As shown in Fig. 1.7, in 2012 a o al o 44.9 GW o new powe capaci y was
connec ed in he EU while 15.8 GW we e decommissioned. This esul ed in 29.1GWo new
16 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
ne capaci y in he EU. F om his ﬁgu e, 16.7 GW (o 57%) o he new ne capaci y came
om PV and 30.8 GW (o 106%) co esponded o enewable ene gies. The ne capaci y om
non- enewable ene gies was nega i e [5].
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1.3. E olu ion o pho o ol aic p oduc ion and ins alled capaci y 17
Rega ding he u u e PV de elopmen , EPIA conside s wo scena ios o PV ma ke s. The
Business-as-usual scena io assumes a he pessimis ic ma ke beha iou . The Policy-d i en
scena io assumes a posi i e ma ke beha iou , conside ing PV as a majo powe sou ce in he
coming yea s [5].
Fo he ﬁ s ime in he las 12 yea s, he PV ma ke in Eu ope dec eased in 2012 in
e ms o new connec ed capaci y, as shown in Fig. 1.5. The u u e o he Eu opean ma ke
is unce ain o he coming yea s and he sho - e m p ospec s a e s able in he bes case o
declining.
In he Business-as-usual scena io, he expec ed g ow h o ma ke s ou side Eu ope is no
likely o compensa e as enough o he slowdown o he ma ke in Eu ope in he wo coming
yea s. Bu e en in his scena io, he global ma ke could be as high as 48 GW in 2017 as
indica ed in Fig. 1.8 [5].
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,ŝƐƚŽƌŝĐĂůĚĂƚĂ
W/ƵƐŝŶĞƐƐͲĂƐͲhƐƵĂů
W/WŽůŝĐǇͲƌŝǀĞŶ
Figu e 1.8: Annual PV ma ke scena ios un il 2017 - Bussiness-as-usual and Policy-d i en [5].
In he Policy-D i en scena io, he Eu opean ma ke would s abilise ﬁ s a ound 16 GW
- 17 GW in 2013 be o e g owing slowly again o a ound 25 GW - 28 GW ﬁ e yea s om
now. In ha case, he global ma ke could op mo e han 84 GW in 2017 (see Fig. 1.8),
wi h wo- hi ds o his coming om new ma ke s ou side Eu ope [5]. EPIA expec s he Asia
Paciﬁc (APAC) egion (wi hou China) o ep esen be ween 10 GW and 20 GW each yea
un il 2017. China alone could add 10 GW o PV ins alla ions each yea [5].
18 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
As shown in Fig. 1.9, in he Business-as-Usual scena io, he 200 GW ma k could be
eached in be ween 2014 and 2016, while in he Policy-D i en scena io, mo e han 420 GW
o PV sys ems could be connec ed o he g id o e he nex ﬁ e yea s [5].
Ϭ
ϱϬ
ϭϬϬ
ϭϱϬ
ϮϬϬ
ϮϱϬ
ϯϬϬ
ϯϱϬ
ϰϬϬ
ϰϱϬ
ϮϬϬϴ ϮϬϬϵ ϮϬϭϬ ϮϬϭϭ ϮϬϭϮ ϮϬϭϯ ϮϬϭϰ ϮϬϭϱ ϮϬϭϲ ϮϬϭϳ
WsĐƵŵƵůĂƚŝǀĞƐĐĞŶĂƌŝŽƐ;' Ϳ
,ŝƐƚŽƌŝĐĂůĚĂƚĂ
W/ƵƐŝŶĞƐƐͲĂƐͲhƐƵĂů
W/WŽůŝĐǇͲƌŝǀĞŶ
Figu e 1.9: Cumula i e PV ma ke scena ios un il 2017 - Bussiness-as-usual and Policy-d i en [5].
1.3.2 Pho o ol aic indus y
In 2012, he PV indus y wen again h ough a challenging pe iod, wi h poli ical, ma ke
and indus y ac o s a ec ing business along he whole alue chain. Impo an manu ac u e s
disappea ed, we e acqui ed o had o adap hei business plan, dec ease he u ilisa ion a e
and consequen ly educe signiﬁcan ly hei p oduc ion. The ough ma ke en i onmen in
Eu ope has o ced many impo an playe s ou o he PV business.
The PV global ma ke capaci y has e ol ed mainly in a con ex o p oduc ion o e capaci y.
In he las h ee yea s, module p oduc ion capaci y was in be ween 150% - 230% highe han
annual global ins alla ions [5]. This, esul ed in con inuous p ice p essu e in PV sys ems
ma ke . Howe e , he agg essi e educ ion o p ices also opened new ma ke s ge ing highe
g ow h o he indus y han hoped. This scena io beneﬁ s some PV companies and damages
o he s.
In Fig. 1.10 wo ld PV cell/module p oduc ion om 2009 o 2012, as well as he o ecas
om 2013 o 2017 is p esen ed (ba g aph). In he pe iod om 2000 o 2011, o al PV
1.3. E olu ion o pho o ol aic p oduc ion and ins alled capaci y 19
p oduc ion inc eased almos by wo o de s o magni ude wi h annual g ow h a es be ween
40% and 90% [2]. Acco ding o IHS Sola , he wo ld PV p oduc ion capaci y in 2012 eached
56.5 GW, inc easing 24% compa ed o 2011. Those capaci ies a e likely o g ow con inuously,
wi h a g ow h a e o a ound 6% un il 2017, eaching a p oduc ion capaci y up o 75 GW in
2017 [5].
Ϭй
ϭϬй
ϮϬй
ϯϬй
ϰϬй
ϱϬй
ϲϬй
ϳϬй
ϴϬй
ϵϬй
Ϭ
ϭϬ
ϮϬ
ϯϬ
ϰϬ
ϱϬ
ϲϬ
ϳϬ
ϴϬ
ϵϬ
ϮϬϬϵ ϮϬϭϬ ϮϬϭϭ ϮϬϭϮ ϮϬϭϯ ϮϬϭϰ ϮϬϭϱ ϮϬϭϲ ϮϬϭϳ
WsŵŽĚƵůĞƐƉƌŽĚƵĐƚŝŽŶƐŚĂƌĞ
WsŵŽĚƵůĞƐƉƌŽĚƵĐƚŝŽŶĐĂƉĂĐŝƚǇ;' Ϳ
KƚŚĞƌƐƚĞĐŚŶŽůŽŐŝĞƐ
dŚŝŶĨŝůŵƐŚĂƌĞ;ŽƌŐĂŶŝĐнŝŶŽƌŐĂŶŝĐͿ
ĐͲ^ŝƐŚĂƌĞ
Figu e 1.10: Wo ld PV cell/module p oduc ion capaci y om 2009 o 2012 and annual o ecas un il 2017 [5].
Since 2011, Eu opean indus y ep esen s only abou 8% - 13% o he global ma ke in
e ms o ac ual module p oduc ion. China and APAC coun ies supply abou 70% o he
global PV demand [2], [5], since his egion has expe ienced he mos apid g ow h in annual
p oduc ion o e he las yea s.
Rega ding he ep esen a ion pe echnology, he p edominan c-Si echnology is expec ed
o main ain i s ma ke sha e a le els sligh ly highe han 80% (blue line in Fig. 1.10). The
main ad an age o c-Si echnology is ha comple e p oduc ion lines can be bough , ins alled
and p oducing wi hin a ela i ely sho ime- ame. Howe e , he empo a y sho age in
silicon eeds ock and he ma ke en y o companies o e ing u n-key p oduc ion lines o hin
ﬁlm sola cells, led o a massi e expansion o in es men s in o hin ﬁlm capaci ies be ween
2005 and 2009 (mo e han 200 companies a e in ol ed) [2].
In 2005 he p oduc ion o hin ﬁlm sola modules eached mo e han 100 MW/yea . In
he pe iod 2005 - 2009, compound annual g ow h a e (CAGR) o hin ﬁlm sola module
p oduc ion was beyond ha o he o e all indus y inc easing he ma ke sha e o hin ﬁlm

20 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
p oduc s: 6% in 2005, 10% in 2007 and be ween 16% - 20% in 2009. Since hen, he hin
ﬁlm sha e (black line in Fig. 1.10) is dec easing slowly as hei amp up o new p oduc ion
lines did no ollow ha o wa e -based silicon due o he compe ing ma ke p ice o c-Si
echnology. Anyway, he o ecas o hin ﬁlm is o g ow a a lowe a e, and he e o e, hei
ma ke sha e will s abilise o e he nex ﬁ e yea s. I he o ecas p esen ed in Fig. 1.10 is
ulﬁlled, hin ﬁlm p oduc ion capaci y could be 10 GW o 13% o he o al 75 GW in 2017.
The g ow h a e o a-Si:H echnologies migh be educed by a ound 3% un il 2017 [5].
The eason o his nega i e CAGR is he lowe module e ﬁciency o a-Si:H in compa ison
wi h he apid e olu ion o CdTe and CIGS, limi ing he ma ke o hin ﬁlm modules wi h
e ﬁciencies below 10% on module le el.
Among eme ging echnologies, o ganic pho o ol aic (OPV) echnologies and especially
concen a ion pho o ol aic (CPV) echnologies a e expec ed o enjoy a ound 1% o he
ma ke sha e by 2017. The de elopmen o hese echnologies is accele a ed by he posi i e
de elopmen o he PV ma ke .
The exis ing PV echnology mix is a solid ounda ion o u u e g ow h o he sec o as a
whole. No single echnology can sa is y all he di e en consume needs.
1.3.3 Ou look
In 1996, he Di ec o a e-Gene al o Ene gy o he Eu opean Commission published he
s udy "Pho o ol aics in 2010" [17]. The medium scena io o ecas a cumula i e ins alled
capaci y o 3 GW in he EU by 2010. The mos agg essi e scena io in his epo p edic ed a
cumula i e ins alled PV capaci y o 27.3 GW wo ld-wide and 8.7 GW in EU o 2010. The
eali y check e eals ha e en he mos agg essi e scena io is lowe han wha we expec om
he cu en de elopmen s. A he end o 2010, PV sys ems wi h a cumula i e capaci y o o e
41 GW wo ld-wide and o e 30 GW in Eu ope we e gene a ing elec ici y ( he ins alla ions
inc eased u he o abou 102 GW wo ld-wide and 70 GW in Eu ope a he end o 2012).
Tu nkey sys em p ices as low as 1.0e/Wpha e been epo ed o p ojec s o be ﬁnished
in 2013 [18]. A e he massi e cos educ ions o he echnical componen s o PV sys ems
like modules and o he componen s (Balance O Sys em, BOS) he nex challenge is o lowe
he so cos s o PV sys em ins alla ions, like he pe mission o ﬁnancing cos s [2].
The di e en PV indus y associa ions, as well as G eenpeace, he Eu opean Renewable
Ene gy Council (EREC) and he In e na ional Ene gy Agency (IEA), ha e de eloped new
scena ios o he u u e g ow h o PV. Table 1.2 shows he di e en scena ios o he
1.3. E olu ion o pho o ol aic p oduc ion and ins alled capaci y 21
G eenpeace / EREC s udy, as well as he di e en 2011 IEA Wo ld Ene gy Ou look scena ios
and he IEA PV Technology Roadmap. I is in e es ing o no e ha he 2015 capaci y alues o
ou o he six scena ios p esen ed in he able (in ed) ha e al eady been eached o exceeded
in 2012. Wi h o ecas cumula i e PV ins alla ions (acco ding o 2013 EPIA scena ios in Fig.
1.9) be ween 198 GW o 264 GW in 2015, e en he G eenpeace e olu ion scena io is no
longe ﬁc ional hinking [18].
Table 1.2: E olu ion o he cumula i e sola elec ical capaci ies un il 2035. In ed, capaci y alues al eady eached
o exceeded. Sou ce: [2], [9], [19].
ƵŵƵůĂƚŝǀĞWsƉŽǁĞƌĐĂƉĂĐŝƚǇ;' Ϳ ϮϬϭϮ ϮϬϭϱ ϮϬϮϬ ϮϬϯϬ ϮϬϯϱ
ĐƚƵĂůŝŶƐƚĂůůĂƚŝŽŶƐ ϭϬϮ
'ƌĞĞŶƉĞĂĐĞͲZĞĨĞƌĞŶĐĞƐĐĞŶĂƌŝŽΎ ϴϴ ϭϮϰ Ϯϯϰ ϮϵϬ
'ƌĞĞŶƉĞĂĐĞͲ΀ƌ΁ĞǀŽůƵƚŝŽŶƐĐĞŶĂƌŝŽΎ Ϯϯϰ ϲϳϰ ϭϳϲϰ ϮϰϮϬ
/ͲƵƌƌĞŶƚƉŽůŝĐǇƐĐĞŶĂƌŝŽΎΎ ϲϬ ϭϲϭ Ϯϲϴ ϯϭϰ
/ͲEĞǁƉŽůŝĐǇƐĐĞŶĂƌŝŽΎΎ ϭϭϮ ϭϴϰ ϯϴϱ ϰϵϵ
/ͲϰϱϬƉƉŵƐĐĞŶĂƌŝŽΎΎ ϳϬ ϮϮϬ ϲϮϱ ϵϬϭ
/ͲWsƚĞĐŚŶŽůŽŐǇƌŽĂĚŵĂƉΎΎΎ ϳϲ ϮϭϬ ϴϳϮ ϭϯϯϬ
ΎϮϬϯϱǀĂůƵĞƐĂƌĞĞǆƚƌĂƉŽůĂƚĞĚĂƐŽŶůǇϮϬϯϬĂŶĚϮϬϰϬǀĂůƵĞƐĂƌĞŐŝǀĞŶ
ΎΎϮϬϭϱǀĂůƵĞƐĂƌĞĞǆƚƌĂƉŽůĂƚĞĚĂƐŽŶůǇϮϬϬϵĂŶĚϮϬϮϬǀĂůƵĞƐĂƌĞŐŝǀĞŶ
ΎΎΎϮϬϭϱΘϮϬϯϱǀĂůƵĞƐĂƌĞĞǆƚƌĂƉŽůĂƚĞĚĂƐŽŶůǇϮϬϭϬϮϬϮϬϮϬϯϬΘϮϬϰϬǀĂůƵĞƐĂƌĞŐŝǀĞŶ
The IEA’s Ene gy Technology Pe spec i es 2010 s a ed ha o hei cu en Baseline
Scena io, he o e all in es men s in ene gy supply and use, o he pe iod be ween 2010
and 2050, o als e208 illion [20]. The BLUE-Map scena io, which would limi he
concen a ion o G eenhouse Gases a 450 ppm, has an addi ional ﬁnancing need o e35.4
illion, bu a he same ime he cumula i e uel sa ings o his scena io compa ed o he
Baseline would be e86.2 illion, o mo e han wice he in es men cos . This clea ly
indica es he huge socie al beneﬁ o a mo e agg essi e clima e change app oach.
The pho o ol aic indus y has changed om a MW size indus y in o a mass-p oducing
indus y, aiming o mul i GW p oduc ion on he long e m. The de elopmen o economy
o scale ha comes wi h la ge p oduc ion olumes, allows new la ge sola cell companies o
use hei cos ad an ages o o e lowe -p iced p oduc s accele a ing he g ow h a e. On he
con a y, his de elopmen will inﬂuence nega i ely he small and medium companies. To
su i e hey ha e o specialise in niche ma ke s wi h high added alue in hei p oduc s.
22 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
Renewable ene gies a e, con a y o con en ional ene gy sou ces, he only ones o o e
a educ ion o p ices a he han an inc ease in he u u e. We see a con inuous dec ease in
p oduc ion cos s o enewable ene gy echnologies, as a esul o s eep lea ning cu es (see
Fig. 1.11). Despi e o his, enewable ene gies and pho o ol aics a e s ill pe cei ed as being
mo e expensi e in he ma ke han con en ional ene gy sou ces. This is due o he ac ha
ex e nal ene gy cos s, subsidies in con en ional ene gies and p ice ola ili y isks a e gene ally
no ye aken in o conside a ion. Ne e heless, elec ici y p oduc ion om pho o ol aic sola
sys ems has al eady p o ed o be cheape han esiden ial consume p ices in a wide ange o
coun ies.
Da a: Na i g an Co n su l in g ; EUPD m o d u l e p i ce (si n ce 2006) G ap h : PSE A G 2012
All PV Technologies
Mono-Si 24.5 GWp
Mul i-Si 31.6 GWp
(incl. Ribbon-Si)
Thin Film 8.5 GWp
all PV Technol. (1980-2011) LR 19.52
all PV Technol. (2006-2011) LR 26.93
Mono (2006-2011) LR 26.61
Mul i (2006-2011) LR 27.35
Thin Film (2006-2011) LR 20.51
Figu e 1.11: P ice lea ning cu e by echnology om 1980 o 2011 [21].
1.4 G oup T-Sola Global S.A.
T-Sola Global S.A. (T-Sola ) is a company dedica ed o hyd ogena ed amo phous silicon
(a-Si:H) PV module manu ac u e. I was ounded in Oc obe 2006 and is pa o T-Sola
G oup which i sel is a subsidy o he mul ina ional company Isolux. I s ﬁ s PV modules
we e ab ica ed in July 2008.
1.4. G oup T-Sola Global S.A. 23
T-Sola has implemen ed in i s p oduc ion line, which is ully au oma ed and in eg a ed,
he SunFab ac o y echnology om he Ame ican company Applied Ma e ials Inc. (AMAT).
T-Sola was he second cus ome o AMAT and i s ac o y he ﬁ s cons uc ed in Eu ope. I s
hin ﬁlm module ab ica ion p ocess was an inno a i e p ojec on wo ld-wide le el, due o
he low cos o he p oduc ion p ocess and he eno mous size o he modules wi h dimensions
o 2.2mx2.6 m and a maximum powe o abou 430 Wp(e ﬁciency o 7.52%) [22]. The
ac o y has an annual p oduc ion capaci y o abou 72 MWp, equi alen o abou 900.000 m2
o PV modules.
The ac o y is loca ed in he "Pa que Tecnolóxico de Galicia", pa o he San Cib ao das
Viñas indus ial a ea, in Ou ense, Spain. The p oduc ion plan and he o ﬁces ake up a plo
o 29.000 m2(see Fig. 1.12). The labo a o ies a e placed in he echnical annex, he o ange
pain ed pa o he building in he lowe igh side o Fig. 1.12.
Figu e 1.12: T-Sola Global S.A.’s a-Si:H PV module ac o y.
Apa om ab ica ion and comme cializa ion o PV modules, T-Sola G oup has also
buil la ge PV powe plan s. I s ands cu en ly as one o he la ges p oduce s o PV elec ici y
in Spain. In ac , i is one o he leading independen powe p oduce s (IPPs) o sola PV
ene gy wo ldwide. The g oup has an ins alled capaci y o 284 MWp h oughou Spain, I aly,
India, Pe u, Pue o Rico and Cali o nia.
30 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
Figu e 1.20: a-Si:H lase sc ibing s ep, P2 (c oss sec ion iew).
6. Back con ac deposi ion in physical apou deposi ion (PVD) 5.72 m2in-line
spu e ool: This las hin ﬁlm deposi ion on he glass panel c ea es he back con ac
ha consis s o h ee laye s which a e ob ained by PVD echnique (Fig. 1.21). In ou
case his is a plasma p ocess wi h pulsed di ec cu en (DC) spu e ing om ce amic
and me allic a ge s in A gon (A )-a mosphe e. The spu e compa men has a ca hode
( a ge ) ha is bomba ded by he plasma a oms (A ) o deposi me al on he glass. The
chambe is e acua ed wi h u bo pumps o achie e low base p essu e (in he ange
o 1 ×10−6mba - 10 ×10−6mba ), he deposi ion p ocess is ca ied ou a a ound
5×10−3mba o p essu e. The ollowing laye s a e implemen ed:
– Aluminium-doped zinc oxide (ZnO:Al o AZO): Ac s as anspa en back con ac
o imp o e he ligh eﬂec ion a he back me al laye and, hus, o imp o e he
op ical conﬁnemen . Laye hickness is abou 90 nm, deposi ed wi h a plana
a ge .
– Aluminium (Al): Reﬂec i e and conduc i e laye . I s hickness is abou 200 nm,
deposi ed simul aneously wi h dual o a able a ge s.
– Nickel anadium (NiV): P o ec i e and solde laye . I s hickness is abou 50 nm,
deposi ed wi h a single o a able a ge .
7. Thi d lase sc ibing, LSR3: The unc ion o his las lase sc ibing is, oge he wi h
LSR1, o isola e one cell om ano he a he back con ac . LSR3 applies a Nd:YVO4
ligh emission, wo ks in Q-swi ch pulse mode wi h a maximum powe o 16 W and
uses a wa eleng h o 532 nm (g een). I emo es he a-Si:H laye and wi h i , he back
con ac by abla ing hem as p esen ed in Fig. 1.22. The hickness o he lase line is
app oxima ely 40 μm and i is sepa a ed abou 110 μm om he second lase line. The
dea h a ea be ween ou side ex emes o he P1 and P3 lase sc ibes is abou 250 μm. In
Fig. 1.23 a mic oscope iew o he h ee lase sc ibes wi h he sepa a ion be ween hem
and he diame e o each one is p esen ed.

1.5. T-Sola p oduc ion line: Fab ica ion p ocess and p ocess con ol 31
Figu e 1.21: PVD spu e ing ool.
Figu e 1.22: a-Si:H and back con ac lase sc ibing s ep, P3 (c oss sec ion iew).
8. Tes s. Quali y assu ance and shun emo al: Once he module is elec ically
ﬁnished, some basic elec ical es s a e done on each module in he quali y assu ance
and shun emo al (QASR) ool. Fi s , a shun emo al s ep is applied o elimina e
shun s by e e se biasing he cells wi h a high cu en o a e y sho ime. Then,
he quali y assu ance checks he pe o mance o e e y single sola cell on he panel
by measu ing he shun esis ance (Rsh) and open ci cui ol age (Voc) unde low
illumina ion.
32 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
Figu e 1.23: P1 (le ), P2 (middle) and P3 ( igh ) sc ibes (mic oscope iew).
9. Final cell s uc u e: The ﬁnal s uc u e o each sola cell is shown in Fig. 1.24.
The gene a ed cu en in he p-i-n junc ion passes e ically o he on TCO laye
and i ﬂows la e ally om one cell o ano he h ough he P2 lase sc ibe a ea (LSR2
sc ibe) con ac ing he on TCO o he back con ac and allowing he se ies connec ion
be ween cells. Lase sc ibes 1 and 3 sepa a e and isola e consecu i e cells.
F on Glass
TCO
a-Si
Back Con ac
Figu e 1.24: Final module s uc u e which allows he cu en o ﬂow among he cells (c oss sec ion iew).
10. Panel cu ou (op ional): The cu ing able is used only when o he sizes, a he han
he ull size modules, a e equi ed (qua e size o hal size). Fig. 1.25 p esen s he ou
di e en sizes a ailable.
11. Edge dele ion by an au oma ic seaming: In he nex ab ica ion s ep, he laye s a
he glass edge a e emo ed o a wid h o abou 12 mm om he glass bo de . The
goal is o ge a module elec ically well isola ed and mo e esis an o me eo ological
1.5. T-Sola p oduc ion line: Fab ica ion p ocess and p ocess con ol 33
1.1 m 2.2 m 1.1 m 2.2 m
1.3 m
1.3 m
2.6 m
2.6 m
Figu e 1.25: T-Sola p oduc ion line is eady o p oduce modules o ou di e en sizes.
inclemency. Humidi y pene a ion caused by a mosphe ic exposu e is p e en ed, as
well as he cu en leaks a he bo de s and edges ha can induce elec ic shock ( he
modules ope a e a abou 200 V and 3 A). A e his seaming p ocess he module is
washed again.
12. Wi ing: The buss line a achmen ool (see he le side o Fig. 1.26) places buss wi es
on he panel o e ie e he cu en om he module. The side buss wi es a e solde ed
on he ﬁ s and las cell o he panel collec ing he cu en o he whole panel (due o he
se ies connec ion o he cells h ough he lase sc ibe). The c oss buss wi es a e used o
connec each side buss o he junc ion box.
13. Poly inyl bu y al (PVB) oil and on glass posi ioning: A PVB shee is placed on
he on panel o ensu e he me ge be ween he on and he back glass. The PVB
is a hyg oscopic ma e ial, hus i mus be s o ed a low empe a u e (cold oom) and
handled unde con olled empe a u e and humidi y condi ions (clean oom as he one
shown in he igh side o Fig. 1.26). Nex , he back glass is placed o e he PVB.
14. Module lamina ion. This p ocess consis s o wo s ages:
– P ehea ing a abou 140 oC wi h he subsequen p essu e olle lamina o . This
s ep deals he ai emo al.
– Hea ing a abou 230 oC wi h he subsequen p essu e olle . This s ep seals he
edges.
I is impo an o sepa a e hese wo s eps conside ing ha , o ob ain a good ai emo al
you canno apply high empe a u es, o he wise he sealing o edges would s a oo
34 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
Figu e 1.26: Buss ool pic u e (le ) and clean oom o handle he PVB ( igh ).
ea ly, enclosing inside some o he ai . Lamina ion ool is shown in he le side o Fig.
1.27.
15. Au ocla e (ACL): This p ocess occu s a high p essu e and empe a u e o ensu e he
comple e elimina ion o he emaining ai in he glass/PVB/glass sandwich. The p ocess
las s abou 3 h and eaches a p essu e o abou 12 ba - 13 ba and a empe a u e o
145 oC. The ope a ion is done in a amp o h ee s eps: Hea ing, s abiliza ion and
cooling. ACL ool is shown in he igh side o Fig. 1.27.
16. Junc ion box a achmen : The junc ion box is an elec ical connec o o ex ac he
cu en gene a ed by he module (see le side o Fig. 1.28). The box con ains wo
connec o s ha a e solde ed o he c oss buss wi es and a bypass diode o p e en
he a ay om ailing unde pa ial shadow condi ions since he panels a e usually
connec ed in se ies. I s placemen consis s o h ee phases:
– Adhesion o he box o he ea glass.
– Welding he pins o he junc ion box o he module wi es.
– Sealing and insula ion he connec ions using a polyme (po an ).
1.5. T-Sola p oduc ion line: Fab ica ion p ocess and p ocess con ol 35
Figu e 1.27: Lamina ion ool (le ) and au ocla e ool ( igh ) o e all iew.
17. In-line sola simula o : When he module is ﬁnished i passes h ough he sola
simula o in o de o be elec ically es ed (see igh side o Fig. 1.28). Modules a e
illumina ed wi h a xenon lamp unde s anda d es condi ions (STC, 1000 W/m2ligh
powe , AM1.5G spec um and 25 oC empe a u e) and hen, hei elec ical pa ame e s
a e measu ed (η,I
sc,V
oc, FF, Rs,R
sh,V
mpp,I
mpp and Pmpp). The da a is s o ed o
each module and is p in ed on a label ( oge he wi h he se ies numbe and a ba code)
which is glued on he backside o he module.
Figu e 1.28: Junc ion box ool (le ) and in-line sola simula o ool ( igh ).
18. Rail bonding: Fou ( wo) ails a e placed in he ull size modules (qua e size
modules) on he back side o he module o ﬁx i on he suppo s uc u es when hey
a e ins alled in he ﬁeld.

36 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ﬁlm silicon ac o y
19. So ing and packaging he PV modules: The modules pass he las quali y con ol,
whe e is checked isually i hey ha e any impe ec ion. Then, hey a e classiﬁed and
packaged depending on hei powe . The powe class achie ed in he las gene a ion o
5.72 m2 ull size modules is TS410, whose maximum powe is 410+20 W. Fig. 1.29
shows a ull and qua e size module as example.
The modules ha e been ce iﬁed acco ding o Eu opean s anda ds IEC 61646 and IEC
61730. In addi ion, he plan whe e hey a e manu ac u ed ulﬁls he s anda ds ISO
9001, ISO 14001, OHSAS 28001 and EMAS.
Figu e 1.29: Finished ull and qua e size modules (lowe le ).
Since he e y beginning o he p oduc ion line, 100% o modules a e handled in
au oma ic mode by he ma e ial handling sys em (MHS). The MHS is con olled by he
ac o y au oma ion so wa e (FAS) sys em, de eloped by AMAT. Ano he impo an ool
o au oma e he p oduc ion line is he "SIs ema de Ges ión y Moni o ización A anzado"
(SIGMA) ool (ad anced managemen and moni o ing ool), which is a powe ul in-home
1.5. T-Sola p oduc ion line: Fab ica ion p ocess and p ocess con ol 37
de eloped in e ace o da a collec ion and da a mining. SIGMA so wa e ool uploads
in-line and on eal ime da a ( om ools, inspec ion me ology, e c) o be u he s udied and
used o panel acking and aceabili y. The in o ma ion p o ided by SIGMA is commonly
used by se e al depa men s such as managemen , R&D, quali y, enginee ing, p oduc ion,
main enance, logis ics, e c. We di ide he mos impo an asks o SIGMA in o h ee ﬁelds:
–Line managemen : SIGMA o e s de ailed in o ma ion abou he ac ual and p e ious
s a us o all he p oduc ion line, e.g. ool s a us, ool speciﬁca ions, ma e ial a ailabili y,
panel loca ion wi hin he p oduc ion line, panel his o y, o cu en and p e ious ecipes
used in each panel.
–P oduc quali y and p ocess con ol: They a e done in-line and o -line. The
elec ical pa is checked in he in-line sola simula o (ISS) (illumina ed cu en - ol age
(IV) cu e), QASR ( ol age measu emen when he panel is elec ically ﬁnished)
and B igh iew (PECVD laye p ope ies). The op ical p ope ies con ol is mos ly
pe o med o -line in he labo a o y. The isual con ol is done in-line by he quali y
ope a o s which a oid ha sc ap panels wi h de ec s o go o wa d in he p oduc ion
line. In Fig. 1.30 a schema ic con ol plan wi h all he con ols made in-line and o -line
is p esen ed.
–Tool con ol: The di e en ools a e also moni o ed and con olled wi h SIGMA.
The e o e, all da a o senso s a ailable a he ools is s o ed.
38 Chap e 1. Pho o ol aics s a us and T-Sola ’s hin ilm silicon ac o y
TCO
• TCO RESISTIVITY: MANUAL
MEASUREMENT OF THE
CONDUCTIVITY (MATERIALS
CONTROL PLAN).
• TCO THICKNESS : 100% OF TCOS
MEASURED IN THE IN-LINE
BRIGHTVIEW TOOL (SIGMA ).
LASER-1 CVD LASER-2
J-BOX BUSS LASER-3
PVD
• HOT PANELS INTRODUCED IN-LINE FOR
A FAST FEEDBACK OF THE LASER SCBRIBE
QUALITY AT THE QASR.
• SAMPLING CHECK IN-LINE TO CONTROL
THE QUALITY OF THE LASER SCRIBES
(CONTROL PLAN).
• PANEL VOLTAGE VALUES MEASURED
100% AT THE QASR TOOL (SIGMA).
• ALL ELECTRICAL PARAMETERS, 100%
MEASURED AT SOL (SIGMA).
• PANEL VOLTAGE VALUES MEASURED 100%
AT THE QASR TOOL (IN SIGMA).
• ALL ELECTRICAL PARAMETERS, 100%
MEASURED AT SOL (DATA IN SIGMA).
• FILM THICKNESS (STACK) MEASURED AT
BRIGHTVIEW TOOL (100%).
• REFLECTED POWER BY CHAMBER
AVAILABLE IN SIGMA (100%).
• INDIVIDUAL DEPOSITED LAYERS ON
QUALIFICATION PANELS ARE MEASURED
INLINE (BRIGHTVIEW TOOL) & OFFLINE
(LAB).
• PANEL VOLTAGE VALUES
MEASURED 100% AT THE
QASR TOOL (IN SIGMA).
• ALL ELECTRICAL
PARAMETERS, 100%
MEASURED AT SOL (DATA IN
SIGMA).
• QUALIFICATION PANELS
FOR INDIVIDUAL LAYERS
DEPOSITED ARE MEASURED
OFFLINE (LAB).
• VOLTAGE MEASUREMENT IN A
„LIGHT BED“ DURING THE
TRIMMING PROCESS (SAMPLING
UNDER ENG. CONTROL).
• ALERT IN SIGMA WHEN LOOSING
VOLTAGE DUE TO A WRONG
SOLDERING PROCESS.
• OPTICAL INSPECTION (VISION
SYSTEM) TO CHECK THE CORRECT
SOLDERING PROCESS.
• POTTANT RATIO AND POTTANT
QUANTITY CHECK.
BRIGHTVIEW
- THICKNESS,
UNIFORMITY &
ROUGHNESS (TCO
AND a-SI).
QASR
- VOLTAGE
MEASUREMENT
SOLAR
SIMULATOR
- ELECTRICAL
PARAMETERS
• HOT PANELS INTRODUCED IN-LINE FOR A
FAST FEEDBACK OF THE LASER SCBRIBE
QUALITY AT THE QASR (QUALITY
ASURANCE TOOL).
• SAMPLING CHECK IN-LINE TO CONTROL
THE QUALITY OF THE LASER SCRIBES
(CONTROL PLAN).
• PANEL VOLTAGE VALUES MEASURED
100% AT THE QASR TOOL (IN SIGMA).
• ALL ELECTRICAL PARAMETERS, 100%
MEASURED AT SOL (DATA IN SIGMA).
• HOT PANELS INTRODUCED IN-LINE FOR
A FAST FEEDBACK OF THE LASER SCRIBE
QUALITY AT THE QASR (QUALITY
ASURANCE TOOL).
• SAMPLING CHECK IN-LINE TO CONTROL
THE QUALITY OF THE LASER SCRIBES
(CONTROL PLAN).
• PANEL VOLTAGE VALUES MEASURED
100% AT THE QASR TOOL (IN SIGMA).
• ALL ELECTRICAL PARAMETERS, 100%
MEASURED AT SOL (DATA IN SIGMA).
• EDGE DELETE WIDTH MEASURED
ON LINE
• EDGE DELETE STEP HEIGHT
MEASURED IN LINE AND ON THE LAB
USING A PROFILOMETER
SEAM-B
Figu e 1.30: Con ol plan scheme wi h all he con ols made in-line and o -line.
1.6 Technology and R&D Depa men
In o de o imp o e he e iciency and quali y o he modules and o de elop he echnology
in he ac o y, T-Sola has ins alled a scien i ic labo a o y. Wi h he pu pose o implemen ing
in a as and e icien way i s esea ch ac i i y, his depa men ope a es di ec ly beside he
p oduc ion line. In he o ganiza ional s uc u e o T-Sola , he labo a o y, whe e he he e
epo ed PhD ac i i y was ca ied ou , is loca ed wi hin he Technology and R&D Depa men .
Some objec i es o he Depa men a e:
– To imp o e he p ocess o each machine as well as o each p ocess s ep o he
p oduc ion line.
– To op imize he op ical and elec ical p ope ies o he modules, in o de o inc ease
hei e iciency.
– To minimize he a-Si:H deg ada ion due o illumina ion (S aeble -W onski e ec
(SWE)).
1.6. Technology and R&D Depa men 39
– To de elop and o implemen p oduc ion con ol echniques, such as new me ology
sys ems, wi h he objec i e o e i ying ha modules mee he design speciﬁca ions.
The asks ca ied ou by he labo a o y s a a e di ided in wo ﬁelds, con ol plan and
R&D ac i i ies. The con ol plan ac i i ies a e, on one hand, he con ol o he p ocess
pa ame e s. This includes di e en measu emen s such as hickness, esis i i y o op ical
p ope ies o TCO, PECVD and PVD indi idual laye s deposi ed on con ol panels. On he
o he hand, i consis s on he implemen a ion o he au oma ion o he con ol plan by, e.g.
de eloping in-line me ology equipmen s.
Conce ning he R&D ac i i ies, T-Sola is collabo a ing wi h di e en ins i u ions like he
Uni e si y o San iago de Compos ela (USC), he Uni e si y o Vigo (UVI) and Galician
esea ch cen e s such as "Labo a o io Oﬁcial de Me ología de Galicia" (LOMG) and
"Asociación de In es igación Me alú gica del No oes e" (AIMEN).
Besides his, he mos impo an esea ch ac i i y du ing he las h ee yea s, 2010-2012,
was pe o med in he ame o he Eu opean P ojec HELATHIS, which is he ac onym o
"High E ﬁcien e y LA ge a ea THIn ﬁlm Silicon pho o ol aic modules". This p ojec was
c ea ed in he p og am call "FP7 - ENERGY 2009.2.1.1: E ﬁciency and ma e ial issues o
hin ﬁlm pho o ol aics". T-Sola was he coo dina o , he o he pa ne s o he p ojec we e
he Belgian subsidia y o he mul ina ional glass p oduce AGC, AGC Fla Glass Eu ope
S.A. (AGC); he pho o ol aic depa men o he Resea ch Cen e Jülich GmbH (FZJ); he
Debye Ins i u e o he Uni e si y U ech (UU); and he Depa men o Applied Physics and
Op ics o he Uni e si y de Ba celona (UB). The pa icipan s co e he whole ab ica ion
chain om he TCO-glass (AGC) o he ﬁnal a-Si:H sola cells o small modules (UU, UB
and FZJ) and o he e y la ge a ea (5.72 m2) a-Si:H modules (T-Sola ). In ac , T-Sola was
he ﬁ s company in Eu ope ab ica ing modules wi h size la ge han 5 m2. Co e ing he
whole ab ica ion p ocess allowed he conso ium o implemen as op imiza ion cycles o
he TCO-glass/p-i-n/back eﬂec o sys em. In he nex sec ion, mo e abou he main aims o
his p ojec in he poin s ela ed wi h his hesis will be explained.
T-Sola also pa icipa ed in o he na ional and egional p ojec s such as he "To es
Que edo" p og am om he Spanish Minis y o Economics and Compe i i eness. The
in es iga ions o his PhD hesis we e pe o med in he ame o he HELATHIS p ojec and
he "To es Que edo" p og am.
Finally, i is no ewo hy o men ion ha a sophis ica ed Ou doo es s a ion was de eloped
o e he yea s by he labo a o y s a . I allows moni o ing and measu ing a la ge numbe
46 Chap e 2. Theo y and simula ion models o a-Si:H sola cells










Figu e 2.2: Sola cell IV cu e as esul o he diode IV cu e minus he Iph.
Fig. 2.3). Hence, in eq. 2.3, we ha e o subs i u e he ol age d op a he diode, V,byV−IRs
and o add he e m (V−IRs)/Rsh as a sum in he second pa o he equali y.
To ge he illumina ed IV cu e o a-Si:H p-i-n junc ion sola cells we ha e o add a e m
due o cu en loss by ecombina ion wi hin he i-laye , hus we ob ain [23]:
I=−Iph +Iph
d2
i
(μτ)e [Vbi −(V−IRs)] +I0expq(V−IRs)
nkT −1+V−IRs
Rsh
(2.5)
whe e Vbi (V) is he buil -in ol age, which is he di e ence be ween he elec on and hole
quasi-Fe mi le els unde illumina ed condi ions, i s alue depends on he illumina ion le el;
di(cm) is he p-i-n junc ion hickness o he sola cell; (μτ)e (cm2/V), whe e μ(cm2/(V·s))
is he e ec i e ca ie mobili y in he in insic egion and τ(s) he e ec i e ca ie li e ime in
he in insic egion. The equi alen ci cui is shown in Fig. 2.3.
Wi h his equa ion we ob ain he ypical IV cu e o an a-Si:H sola cell. The e m I ec =
Iph
d2
i
(μτ)e [Vbi−(V−IRs)] desc ibes he ecombina ion in he in insic egion. I is impo an o
conside his e m in he a-Si:H echnology due o he SWE (see subsec ion 2.2.5). This e m
exp esses a dec ease in he ca ie s mobili y and li e ime wi h illumina ion ime.

2.2. Physical model 47





Figu e 2.3: Equi alen ci cui o an a-Si:H sola cell. The cu en sink (I ec, dashed lines) akes in o accoun he
cu en loses due o ecombina ion in he i-laye o he de ice [23].
2.2 Physical model
Silicon (Si) belongs o IV g oup o he pe iodic elemen able and has ou elec ons in i s
alence band ha o m a e ahed al s uc u e h ough co alen bonds when i o ms a c ys al
o an amo phous s uc u e. When doped wi h a V g oup elemen , such as phospho us (P),
he e is an excess o elec ons and p o ides a n- ype semiconduc o ma e ial (dono ). On he
o he hand, i III g oup impu i ies a e in oduced, e.g. bo on (B), holes a e c ea ed in he
ne wo k o a oms, esul ing in a p- ype semiconduc o ma e ial (accep o ).
C ys alline semiconduc o s a e ma e ials wi h a e y low concen a ion o con aminan s
and a c ys alline s uc u e wi h a e y low densi y o s uc u al de ec s. The e o o
indus ialize sola cells a lowe cos s has led o he de elopmen o hin ﬁlm semiconduc o
de ices such as a-Si:H sola cells. The p ope ies o a-Si:H a e di e en om he ones o c-Si,
as a consequence, sola cells based on his ma e ial, need an special de ice s uc u e. Nex ,
we p esen he main di e ences in ma e ial p ope ies in e ms o de ice ea u es:
–Ca ie mobili y: Doped a-Si:H ﬁlms p esen a e y sho ca ie li e ime due o i s
high de ec densi y and he esul ing as ecombina ion p ocesses. The e o e, one
uses an in insic (non-doped) ma e ial wi h low de ec densi y as abso be laye ha
allows he gene a ed ca ie s (elec ons o holes) o ha e la ge li e ime. The ca ie s
a e sepa a ed due o he elec ic ﬁeld c ea ed by e y hin p and n-laye s deposi ed on
op and bo om o he in insic laye (see Fig. 2.4). The d i leng h p oduced by he
elec ic ﬁeld is longe han he wid h o he in insic egion. The e o e, he sola cell
s uc u e o amo phous silicon (a-Si:H) modules is gene ally p-i-n o n-i-p ype.
48 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
W/E
Figu e 2.4: p-i-n s uc u e.
–S uc u e: Amo phous silicon molecules ha e a local e ahed al bonding s uc u e
simila o c-Si, bu he amo phous s uc u e has an impo an amoun o si es wi h a
lowe elec onic coo dina ion, in hese si es a non-sa u a ed bond (o dangling bond)
appea s. These non-sa u a ed bonds p oduce elec onic s a es wi h ene gies close o he
middle o he gap ( ecombina ion cen es). The e o e, he amo phous silicon ﬁlms a e
deposi ed in a plasma con aining a silane (SiH4)/hyd ogen (H2) a mosphe e. Due o he
high amoun o hyd ogen in he plasma, hyd ogen is bonded o he silicon (Si) a oms
in he si es wi h lowe elec onic coo dina ion, sa u a ing he dangling bonds (see Fig.
2.5). This is an impo an p ocess o achie e amo phous silicon wi h elec onic de ice
quali y wi h a low de ec densi y and ca ie ecombina ion a e.






Figu e 2.5: Amo phous silicon s uc u e ( andom ne wo k) showing a bond wi h a hyd ogen a om.
–Elec onic s a es: E en wi hou long ange o de , a-Si:H p esen s band s a es simila
o he ones o c-Si. The alence band can be unde s ood as a p oduc o he bonding sp3
2.2. Physical model 49
o bi al and he conduc ion band as a p oduc o he an ibonding sp3. The unsa u a ed
bonds p oduce elec onic s a es wi h ene gies close o he middle o he gap. Fo
non-hyd ogena ed silicon he densi y o hese de ec s is abou 1020 cm−3, hyd ogen
in oduc ion dec eases his densi y o abou 1016 cm−3. The diso de also p oduces
exponen ial ails o localized s a es nea he edges o he conduc ion and alence bands.
The ene gy limi be ween ex ended and localized s a es is called he mobili y edge.
–Doping: Al hough a-Si:H can be doped wi h se e al a oms, he doping e ﬁciency is
much lowe han ha in c-Si. Fo n- ype doping he minimum sepa a ion be ween
Fe mi le el and conduc ion band is 0.25 eV. Fo p- ype doping he minimum dis ance
be ween alence band and Fe mi le el is 0.40 eV. The eason o lowe Fe mi le el shi
in compa ison o c-Si is because mos o he elec ons eleased by he dono s in n- ype
a-Si:H go o a de ec and do no con ibu e o ﬁll he conduc ion band. In he same way,
mos o he accep o s ake he elec on om a deep de ec s a e in p- ype a-Si:H and do
no come om he alence band.
Rega ding he simula ions, he e a e di e en so wa e packages a ailable o elec onic
de ice simula ion in he ma ke . Sen au us TCAD so wa e (Synopsys Inc.) is one o he
mos ad anced ools. We ha e chosen his ool o simula e complex 2D a-Si:H sola cell
s uc u es. Sen au us is basically designed o simula ion o elec onic de ices. The e o e, i
can be used o he simula ion o a-Si:H de ices since i is based on using physical models
o desc ibe he semiconduc o ma e ial p ope ies and sol ing he semiconduc o equa ions.
Howe e , o simula e a-Si:H de ices a lo o basic conﬁgu a ion wo k mus be done. Besides
he s anda d models and equa ions used o c-Si, he main ea u es o include in an a-Si:H
sola cell simula ion a e [24]:
– Theo e ical models o desc ibe a con inuous DOS dis ibu ion in he band gap o a-Si:H.
– Model o ecombina ion-gene a ion (R-G) a e and occupa ion in ol ing he localized
s a es in he mobili y gap o a-Si:H.
– Modelling o g aded laye s.
– In oduc ion o ex u ed laye s ( on TCO). Op ical modelling including sca e ing a
he ough in e aces.
50 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
In he nex sec ions he desc ip ion o he models o a-Si:H o he DOS dis ibu ion, R-G
s a is ics, g aded laye s and ex u ed laye s is in oduced.
2.2.1 Densi y o s a es models o amo phous silicon
The s anda d model o he DOS dis ibu ion consis s in a pa abolic conduc ion band (CB)
and alence band (VB) as in c-Si. In addi ion, in a-Si:H, he con inuous dis ibu ion o he
DOS in he band gap s ongly a ec s he apping and ecombina ion p ocesses and he e o e,
he apped cha ge in he localized s a es canno be igno ed. The localized s a es a e o med
by:
–Tail s a es: They a e modelled by an exponen ial dis ibu ion in he ene gy gap which
a e called conduc ion band ail (CBT) and alence band ail (VBT). They beha e like
o dina y accep o -like s a es (CB ail s a es) o dono -like s a es (VB ail s a es).
–Dangling bond s a es (DB+/0and DB0/−): They a e simula ed by adding wo equal
Gaussian dis ibu ions sepa a ed by an ene gy U. The dangling bond (DB) a e
ampho e ic s a es so hey can ac bo h as accep o -like and dono -like s a es and a e
ep esen ed by wo ene gy le els.
The di e en na u e o he localized s a es in compa ison o he ex ended s a es equi es
ha di e en models a e applied o calcula e R-G s a is ics h ough localized s a es. I is
assumed ha wi hin he mobili y gap he mobili y o cha ge ca ie s is ze o.
Nex , we show he s anda d model o he DOS dis ibu ion in a-Si:H on a linea scale
in Fig. 2.6 and on a loga i hmic scale in Fig. 2.7. I is assumed ha he mobili y edges o
conduc ion and alence band (Emob
Cand Emob
V) a e equal o he connec ion poin s (E ail
Cand
E ail
V), hus Emob
C=E ail
C,Emob
V=E ail
V. The alues o DOS a he mobili y edges Emob
Cand
Emob
Va e deno ed Nmob
Cand Nmob
V, espec i ely.
The ene gy le els ECand EV, in eV, de ine he band gap. In he case o a-Si:H i
co esponds o he so-called op ical band gap, Eop
gap (eV) (see Fig. 2.6):
Eop
gap =EC−EV(2.6)
When conside ing he anspo p ope ies o ca ie s in a-Si:H we ha e o di e en ia e
be ween he ex ended s a es and he localized s a es in he DOS dis ibu ion. The ene gy
le els Emob
Cand Emob
V, de ine he mobili y gap, Emob
gap (eV) (see Fig. 2.7):
Emob
gap =Emob
C−Emob
V(2.7)
2.2. Physical model 51
Ϭ
ϭнϮϮ
ϮнϮϮ
ϯнϮϮ
ϰнϮϮ
ͲϬϮϬϬϬϮϬϰϬϲϬϴϭϬϭϮϭϰϭϲϭϴϮϬ
EK^ ;ĐŵͲϯ ĞsͲϭͿ
ŶĞƌŐǇͲǀ;ĞsͿ
ŐĂƉŽƉƚсϭϳϲĞs 
s
ƚĂŝůEƚĂŝů
sƚĂŝůEsƚĂŝů
Figu e 2.6: DOS dis ibu ion model o in insic a-Si:H laye on a linea scale. The densi y in he conduc ion band
is lowe han in he alence band esul ing in a non-symme ic DOS dis ibu ion. The poin s (E ail
C,
N ail
C) and (E ail
V,N ail
V) a e he connec ion be ween he pa abolic dis ibu ion o ex ended s a es and he
exponen ial dis ibu ion o ails.
ϭнϭϰ
ϭнϭϱ
ϭнϭϲ
ϭнϭϳ
ϭнϭϴ
ϭнϭϵ
ϭнϮϬ
ϭнϮϭ
ϭнϮϮ
ϭнϮϯ
ͲϬϮϬϬϬϮϬϰϬϲϬϴϭϬϭϮϭϰϭϲϭϴϮϬ
EK^ ;ĐŵͲϯ ĞsͲϭͿ
ŶĞƌŐǇͲǀ;ĞsͿ
ŐĂƉŵŽďсϭϳϴĞs
ϬͲEϬͲ
нϬEнϬ
ŵŽďEŵŽď
sŵŽďEsŵŽď
h
Figu e 2.7: DOS dis ibu ion model o in insic a-Si:H laye on a loga i hmic scale. I is assumed ha he mobili y
edges a e equal o he connec ion poin s (Emob
C=E ail
C,Emob
V=E ail
V).
The ma hema ical desc ip ion o he DOS dis ibu ion in a-Si:H is gi en by he equa ions
p esen ed in he ollowing subsec ions [25].

52 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
Conduc ion and alence band s a es
The DOS dis ibu ion o he conduc ion band is gi en by:
NCB+CBT (E)=NCB(E) o E≥E ail
C
NCBT (E) o E≤E ail
C
(2.8)
NCB(E)=N0
C(E−EC)(1/2)(2.9)
NCBT (E)=N ail
Cexp−(E ail
C−E
E ail
C0
)(2.10)
The DOS dis ibu ion o he alence band is gi en by:
NVB+VBT(E)=NVB(E) o E≤E ail
V
NVBT(E) o E≥E ail
V
(2.11)
NVB(E)=N0
V(EV−E)(1/2)(2.12)
NVBT(E)=N ail
Vexp−(E−E ail
V
E ail
V0
)(2.13)
whe e N0
Cand N0
V,incm
−3, a e he pa ame e s which desc ibes he pa abolic dis ibu ion
o s a es in he conduc ion and alence band espec i ely; E ail
C0and E ail
V0, in eV, a e he
cha ac e is ic ene gies desc ibing he decay o he CB and VB ails espec i ely and (E ail
C,
N ail
C) and (E ail
V,N ail
V) a e he connec ion poin s o he pa abolic and exponen ial pa o he
conduc ion and alence band, espec i ely.
Dangling bond s a es
To desc ibe he con inuous dis ibu ion o he DB s a es in he band gap, a Gaussian
dis ibu ion is used. A DB can be in h ee cha ge s a es: posi i e (D+), neu al (D0) and
nega i e (D−). A de ec wi h h ee possible cha ge s a es ac s in good app oxima ion like
a g oup o wo de ec s consis ing o a dono -like s a e (DB+/0) and an accep o -like s a e
(DB0/−) and is he e o e ep esen ed by wo ene gy le els E+/0and E0/−in he band diag am,
espec i ely. These ene gy le els a e called he ansi ion ene gy le els, hey a e sepa a ed
om each o he by a co ela ion ene gy, U(eV), which is he ene gy needed o add he second
elec on o a singly occupied (neu al) DB. Uis assumed o be cons an and posi i e. Unde
hese assump ions he DB a e ep esen ed by wo equal Gaussian dis ibu ions in he band
2.2. Physical model 53
diag am sepa a ed om each o he by a dis ance U. The equa ions o ep esen he densi y o
DB s a es a e he ollowing:
NDB+/0(E)= N o
DB
σDB√2πexp−(E−E+/0
DB )2
2σ2
DB (2.14a)
NDB0/−(E)= N o
DB
σDB√2πexp−(E−E0/−
DB )2
2σ2
DB (2.14b)
whe e N o
DB (cm−3) is he o al densi y o de ec s, E+/0
DB and E0/−
DB , in eV, a e he ene gies o he
peaks o Gaussian dis ibu ions o he dono -like s a es DB+/0and he accep o -like s a es
DB0/−, espec i ely and σDB (eV) is he s anda d de ia ion o he dis ibu ion.
To co ela e NDB+/0and NDB0/−and E+/0
DB and E0/−
DB one uses he nex ela ions:
NDB0/−(E)=NDB+/0(E+U)(2.15)
E0/−
DB =E+/0
DB +U(2.16)
Concen a ion o cha ge ca ie s
The s a es in he conduc ion band abo e he mobili y edge Emob
Ca e ex ended s a es.
They a e popula ed wi h elec ons ha a e cha ac e ized by he concen a ion nand he
ex ended-s a e mobili y μn>0. The s a es in he alence band below he mobili y edge
Emob
Va e also ex ended s a es. They a e popula ed wi h holes ha a e cha ac e ized by he
concen a ion pand he ex ended-s a e mobili y μp>0.
In he ope a ional ange o a-Si:H sola cells he dominan elec ic anspo mechanism
is mul iple apping and elease. The anspo is hen cha ac e ized by he concen a ion o
ca ie s in he ex ended s a es (n,p) and he ex ended-s a e mobili ies (μn,μp). Fu he mo e,
i is assumed ha he mobili ies a e he same in he mal equilib ium and in s eady s a e
illumina ion condi ions. Fo he concen a ion o cha ge ca ie s we can w i e [25]:
n=Ne
Cmob expEFN −Emob
C
kT (2.17a)
p=Ne
Vmob expEmob
V−EFP
kT (2.17b)
whe e Ne
Cmob and Ne
Vmob ,incm
−3, a e he e ec i e densi y o s a es a he CB and VB mobili y
edge. In case o a-Si:H he e ec i e densi y o s a es NCand NVa e equal o Ne
Cmob and Ne
Vmob ,
espec i ely.
54 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
2.2.2 Recombina ion-gene a ion s a is ics in amo phous silicon
The ecombina ion p ocess in c ys alline semiconduc o s is ypically domina ed by a
single ene gy le el o a ecombina ion cen e in he band gap. Howe e , in he band gap
o a-Si:H he e is a con inuous densi y o allowed s a es which con ibu e o he ne R-G a e.
Hence, one needs o in eg a e he ecombina ion a e con ibu ions om he gap s a es o e
he whole band gap. Unde he assump ion ha he ecombina ion cen es a e non-in e ac ing,
he ne R-G a e, Rne (cm−3s−1), can be calcula ed om:
Rne =Emob
C
Emob
V
N(E)ηR(E)dE(2.18)
whe e ηR(E)is he ecombina ion a e con ibu ion o a s a e a ene gy Eand N(E)is he
DOS as unc ion o ene gy in he band gap.
The apped cha ge in ail s a es is calcula ed using he ollowing equa ions o o dina y
dono -like and accep o -like s a es, espec i ely:
ρD=qEmob
V
Emob
C
ND(E)[1− (E)]dE(2.19)
ρA=−qEmob
V
Emob
C
NA(E) (E)dE(2.20)
whe e (E)is he occupa ion unc ion [26] [27]. In case o he ampho e ic DB s a es he
space cha ge is gi en by:
ρDB =qEmob
V
Emob
C
NDB(E)[F+(E)−F−(E)]dE(2.21)
In his equa ion F+(E)and F−(E)a e he occupa ion unc ions o emp y and doubly
occupied DB, espec i ely.
The assump ion o non-in e ac ing cen es means ha he localized s a es in he band gap
can only in e ac wi h ca ie s in he ex ended s a es o he conduc ion and alence bands.
This assump ion allows o use he Shockley Read Hall (SRH) R-G s a is ics [28] o model
he ecombina ion p ocess h ough he single-le el s a es and he Sah and Shockley [29]
mul i-le el R-G s a is ics o he ampho e ic DB s a es. The di e en ypes o he localized
s a es in he band gap o a-Si:H and he models ha a e used o calcula e he ecombina ion
a e h ough hese s a es and hei cha ge occupa ion a e schema ized in Fig. 2.8.
2.2. Physical model 55
>ŽĐĂůŝǌĞĚƐƚĂƚĞƐŝŶƚŚĞďĂŶĚŐĂƉŽĨ ĂͲ^ŝ,
dĂŝůƐƚĂƚĞƐ ĂŶŐůŝŶŐďŽŶĚƐƚĂƚĞƐ
sƚĂŝůƐƚĂƚĞƐ
;ŽŶŽƌͲůŝŬĞƐƚĂƚĞƐͿ
ƚĂŝůƐƚĂƚĞƐ
;ĐĞƉƚŽƌͲůŝŬĞƐƚĂƚĞƐͿ
ŵƉŚŽƚĞƌŝĐ
ƐƚĂƚĞƐ
^ŚŽĐŬůĞǇͲZĞĂĚͲ,Ăůů
;ƐŝŶŐůĞͲůĞǀĞů ƐƚĂƚŝƐƚŝĐƐͿ
^ĂŚΘ^ŚŽĐŬůĞǇ
;ŵƵůƚŝͲůĞǀĞůƐƚĂƚŝƐƚŝĐƐͿ
Figu e 2.8: Di e en ypes o localized s a es in he band gap o a-Si:H and models ha a e used o calcula e he
ecombina ion a e and cha ge occupa ion [25].
R-G s a is ics o CB and VB ail s a es
In he ene gy band diag am, he dono and accep o R-G cen e is ep esen ed by a single
ene gy le el. The CB ail s a es beha e like o dina y accep o s a es and a e neu al (T0
A)o
nega i e (T−
A). The VB ail s a es beha e like o dina y dono s a es and a e neu al (T0
D)o
posi i e (T+
D). The heo y ha desc ibes he ecombina ion p ocess in ol ing a single ene gy
le el in he band gap o a semiconduc o was de eloped by Shockley and Read [28] and Hall
[30], [31].
The SRH heo y is based on ou possible ansi ions be ween an ene gy le el ETin he
band gap and he ex ended s a es o he CB and VB:
1. Elec on cap u e a an R-G cen e .
2. Elec on he mal emission om an R-G cen e .
3. Hole cap u e a an R-G cen e .
4. Hole he mal emission om an R-G cen e .
62 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
–Elec on and hole e ec i e masses: The elec on and hole e ec i e masses a e deﬁned
wi h he nex o mula [36]:
me
m0=NC,300
2.540×1019 2/3
(2.43a)
mh
m0=NV,300
2.540×1019 2/3
(2.43b)
whe e we se NC,300 =NV,300 =1.0×1020 (cm−3) which a e he e ec i e DOS in he
CB and VB, espec i ely a a empe a u e o 300 K. To know he e ec i e DOS a any
empe a u e we apply he nex equa ion:
NC(T)=NC,300 ·(T/300)3/2(2.44a)
NV(T)=NV,300 ·(T/300)3/2(2.44b)
–Band gap and elec on a ﬁni y: In c ys alline semiconduc o s, he band gap (EG)is
he di e ence be ween he lowes ene gy in he CB and he highes ene gy in he VB
(Eop
Gin Fig. 2.6). In a-Si:H based ma e ial he EG ep esen s he mobili y gap (Emob
Gin
Fig. 2.7). The elec on a ﬁni y (χ) is he di e ence be ween he lowes ene gy in he
CB and he acuum le el (E0).
Sen au us models he la ice empe a u e–dependence o he band gap as [37]:
EG(T)=EG(0)−αT2
T+β(2.45)
whe e we ha e chosen β=0 and α=0.0004 eV/K [38].
The e ec i e band gap esul s om he educ ion caused by he empe a u e and doping
concen a ion. I is p esen ed in he nex equa ion:
EG,e (T)=EG(T)−EBGN (2.46)
Ano he pa ame e ha can be ob ained om he p e ious ones is he in insic densi y:
ni(T)=NC(T)NV(T)·exp−EG(T)
2kT (2.47)

2.2. Physical model 63
The e ec i e in insic densi y (including doping-dependen band gap na owing) is:
ni,e =ni·exp−EBGN
2kT (2.48)
whe e EBGN (eV) is he ene gy educ ion in he band gap due o high doping le el.
Fig. 2.11 shows he band diag am o he a-Si:H p-i-n laye s unde illumina ion and
wi hou pola iza ion. One can app ecia e ha he doped laye s a e much hinne han he
in insic laye which has sloped ene gy bands as consequence o he elec ic ﬁeld c ea ed by
he doped laye s. One also sees a la ge ene gy gap o he p-laye due o i s ca bon con en
(a-SiC:H) which inc eases he ene gy band gap wi h he objec i e o abso b less pho ons in
his egion.
0
1
2
e
gy,E(eV)
Ec
E
E n
E p
Ͳ2
Ͳ1
0 50 100 150 200
En
e
Dep h,d(nm)
iͲlaye nͲlaye
pͲlaye
Figu e 2.11: Band diag am o he a-Si:H p-i-n laye s unde 1 sun illumina ion and wi hou pola iza ion (V=0 V).
The d op in EFN a he beggining o he p-laye is because he anode is placed a he TCO/p in e ace.
2.2.5 Ligh -induced deg ada ion. S aeble -W onski e ec
The a-Si:H p esen s a ligh -induced me as abili y o i s elec onic p ope ies (also known
as S aeble -W onski e ec , SWE) [39], [40]. I causes a educ ion o he con e sion e ﬁciency
o a-Si:H sola cells due o ligh exposu e. The a e o deg ada ion du ing con inuous
illumina ion a 1 sun (1000 W/m2) in ensi y is high du ing he ﬁ s ens o hou s, bu dec eases
o e ime. Finally, he cell pe o mance s abilizes a e se e al hund eds o hou s.
64 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
The ini ial e ﬁciency can be comple ely eco e ed by annealing o he de ice a abou
150 oC o se e al hou s. The e e sibili y o he de ice pe o mance shows ha he ini ial
loss is no due o di usion o ions o dopan s, no o o he i e e sible p ocesses, bu i is due
o he inc ease o DB de ec s c ea ed in he i-laye which ac as ecombina ion cen es o
he pho ogene a ed ca ie s. The me as able DBs ha e an ene ge ic and spa ial dis ibu ion,
which de e mines hei cha ge s a e. The space cha ge dis ibu ion o he cha ged s a es hen,
modiﬁes he in e nal elec ic ﬁeld p oﬁle which in u n has an e ec on he ca ie collec ion
in he de ice [25].
The main ma e ial p ope ies ha could play a ole in he SWE a e he concen a ion o
impu i ies, he hyd ogen concen a ion and i s complex bonding s uc u e and he diso de o
he Si ne wo k.
The mos commonly obse ed e ec s in he elec ical pa ame e s o p-i-n a-Si:H sola
cells a e:
– The bigges ela i e changes occu in he ﬁll ac o (FF), he ela i e changes in sho
ci cui cu en densi y (Jsc) and open ci cui ol age (Voc) a e signiﬁcan ly smalle .
– Sola cells wi h a hick in insic laye deg ade mo e han hose wi h a hin in insic
laye .
– Sola cells wi h a high impu i y concen a ion (abo e 1018 cm−3) in he i-laye deg ade
s onge han hose wi h high pu i y i-laye .
– Sola cells ope a ed a ele a ed empe a u es (60 oC-90oC) s abilize a a highe
e ﬁciency han hose ope a ed a oom empe a u e o below.
– Cyclic exposu e esul s in o a highe e ﬁciency s abiliza ion han con inuous exposu e.
– Exposu e a high in ensi y illumina ion causes s onge deg ada ion han 1 sun.
Illumina ion le els less han 1000 W/m2lead o educed deg ada ion.
In o de o educe he SWE ela ed deg ada ion o a-Si:H sola cells se e al me hods ha e
been in es iga ed, e.g.:
– To make he i-laye as hin as possible in o de o main ain a high elec ic ﬁeld a e
deg ada ion. A he same ime, he abso bed ac ion o he inciden ligh is maximized
by using op ical ligh conﬁnemen echniques made possible by ex u ed elec odes and
enhanced mul ilaye back eﬂec o s.
2.2. Physical model 65
– To assis he anspo o he mino i y ca ie s (holes) in he low ﬁeld egion by band
gap p oﬁling [41].
– To edis ibu e he ﬁeld by using g aded low-le el impu i y doping [42].
– To s ack laye s wi h di e en ca ie mobili ies, making a mobili y g ading [43].
2.2.6 Baseline inpu pa ame e s applied in he simula ion
The he e simula ed s uc u e is TCO/a-SiC:H/a-Si:H/a-Si:H/AZO/Al implemen ed in he
T-Sola module ab ica ion. In he simula ion we assume an ideal unnel con ac a he on
con ac and an ideal ohmic con ac a he back one. To implemen his, we ﬁx he on
con ac a he TCO/p-laye in e ace and he back con ac a he end o he Al laye . Hence,
he elec ical ea u es o he TCO a e no conside ed, only i s op ical cha ac e is ics a e aken
in o accoun . The p-i-n single junc ion sola cell is shown in Fig. 2.12.
TCO
F on con ac
i-laye
AZO
Al
Back con ac
p-laye
n-laye
Glass
Figu e 2.12: S uc u e o he simula ed a-Si:H sola cell.
66 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
Table 2.3 shows he baseline inpu pa ame e s o he ini ial s a e used in he simula ion.
The alues a e adjus ed o ﬁ he elec ical pa ame e s and he spec al esponse o ou ypical
1cm
2labo a o y a-Si:H sola cells p oduced in he T-Sola p oduc ion line. To simula e he
s abilized s a e (ligh -soaked s a e) we only need o inc ease he maximum densi y o dangling
bonds (NDB) in he i-laye [44].
Table 2.3: Baseline inpu pa ame e s used in he simula ion. Some pa ame e s we e aken om [25]
p-laye i-laye n-laye
MATERIAL PARAMETERS
d (nm) 10-30 200-300 10-20
Doping (cm−3)3×1018 1×1015 8×1018
ε 7.211.911.9
χ(eV) 3.90 4.00 3.99
Emob
gap (eV) 1.95 1.78 1.80
μn(cm2/(V·s)) 20 20 20
μp(cm2/(V·s)) 5 5 5
NC(cm−3)1×1020 1×1020 1×1020
NV(cm−3)1×1020 1×1020 1×1020
TAIL STATES PARAMETERS
N ail
C(cm−3/eV) 2×1021 8×1021 1×1021
N ail
V(cm−3/eV) 1×1021 4×1021 2×1021
E ail
C0(eV) 0.180 0.032 0.070
E ail
C0(eV) 0.090 0.047 0.160
C−
p,C+
n(cm3/s) 1×10−81×10−81×10−8
C0
p,C0
n(cm3/s) 1×10−10 1×10−10 1×10−10
DANGLING BOND STATES PARAMETERS
σ(eV) 0.144 0.144 0.144
N o
DB (cm−3)8×1018 5×1015 2×1019
E+/0
DB (eV) ( om CB) −0.70 −0.89 −1.40
U (eV) 0.20 0.20 0.20
C−
p,C+
n(cm3/s) 4×10−88×10−94×10−8
C0
p,C0
n(cm3/s) 4×10−98×10−10 4×10−9
2.3 Op ical model
The op ical model is based on he op ical gene a ion in he sola cell which depends on
he ansmission and eﬂec ion coe ﬁcien s o he di e en laye s o he sola cell, he ligh
2.3. Op ical model 67
sca e ing and ligh apping p ope ies o he de ice and he spec al i adiance o he sun o
an equi alen ligh sou ce.
2.3.1 Op ical gene a ion
The op ical gene a ion in a sola cell is exp essed by he numbe o elec ons and holes
gene a ed by he inciden pho ons pe cm3and second in a conc e e posi ion inside he de ice.
The amoun o pho ons pene a ing he abso be ma e ial decay exponen ially when going
deepe in o he semiconduc o as we see in Fig. 2.13.




 












Figu e 2.13: Pho on ﬂux in o a semiconduc o .
The pho on ﬂux, φpho ons
cm2s, is gi en by he Lambe law as shown in he nex equa ion:
φ(x,λ)=φ(0,λ)exp−α(λ)x(2.49)
whe e α(cm−1) is he abso p ion coe ﬁcien which is di e en o e e y semiconduc o (see
Fig. 2.14). The e ec i e ange o abso p ion o a-Si:H is om abou 300 nm o 800 nm.

68 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
The op ical gene a ion, Gop 1
cm3s, o a semiconduc o , depending on he posi ion and
he wa eleng h, esul s in:
Gop (x,λ)=−dφ(x,λ)
dx =α(λ)φ(0,λ)exp−α(λ)x(2.50)
ϭнϬϭ
ϭнϬϮ
ϭнϬϯ
ϭнϬϰ
ϭнϬϱ
ϭнϬϲ
ϮϬϬ ϰϬϬ ϲϬϬ ϴϬϬ ϭϬϬϬ ϭϮϬϬ ϭϰϬϬ ϭϲϬϬ ϭϴϬϬ
ďƐŽƌƉƚŝŽŶĐŽĞĨĨŝĐŝĞŶƚα
α
α
α;ĐŵͲϭͿ
ĂǀĞůĞŶŐƚŚλ
λλ
λ;ŶŵͿ
^ŝ
'Ğ
Ě^
ĂͲ^ŝ,
'ĂƐ
Figu e 2.14: Op ical abso p ion coe ﬁcien o di e en PV ma e ials.
Conce ning he complex e ac i e index (n), i is used o desc ibe he p opaga ion and
abso p ion o ligh in a media:
n=n−ik (2.51)
The e ac i e index (n) ela es he speed o ligh in acuum (c) and in he media ( ):
n=c
(2.52)
The ex inc ion coe ﬁcien (k) desc ibes he abso p ion o he ligh in he media:
k=αλ
4π(2.53)
We ha e added in he ma e ial lib a y o e e y laye in Sen au us a able wi h he complex
e ac i e index in he a-Si:H wa eleng h ange o in e es (300 nm - 800 nm). In Fig. 2.15
we see he e ac i e index and he ex inc ion coe ﬁcien o he h ee p-i-n laye s. We canno
measu e he coe ﬁcien s in he ange 300 nm - 400 nm he e o e, we ex apola e he end o
each one o ge he da a.
2.3. Op ical model 69
3
4
5
6
d
ex(n)andex inc ion
e
icien (k)
n o 
p
Ͳla
y
e
0
1
2
300 400 500 600 700 800
Re ac i ein
d
co
e
Wa eleng h,
O
(nm)
p
y
n o iͲlaye
n o nͲlaye
k o pͲlaye
k o iͲlaye
k o nͲlaye
Figu e 2.15: Complex e ac i e index o ou a-Si:H laye s.
2.3.2 Imp o emen o ligh apping and sca e ing h ough ex u ed
in e aces
A c ucial aspec o imp o e he cu en gene a ion in he sola cell ha ing hin in insic
laye s is he high dispe sion a he on TCO, which is desc ibed by he haze ac o . The haze
is he a io be ween he di use ansmission (Tdi ) and he o al ansmission (T), as indica ed
in Eq. 2.54. Thus, a on TCO wi h high haze will lead o mo e sca e ed ligh in he de ice
and longe abso p ion, inc easing he p obabili ies o pho ons o be abso bed in he sola
cell. This is achie ed by ex u ing he on TCO laye which esul s in ex u ed in e aces as
shown in Fig. 2.12. Apa o good sca e ing, o inc ease he cu en gene a ion in he 550 nm
- 800 nm wa eleng h ange, we need a highly eﬂec i e back eﬂec o o ake ad an age o
he non-abso bed pho ons in he i-laye which could be abso bed a e ebounding in he back
eﬂec o . This imp o emen would no be possible in he long wa eleng h ange wi hou bo h
he ex u ed on TCO and he back eﬂec o .
Haze =Tdi
T(2.54)
To simula e he ex u e we ha e used wo op ions: he Hegedus model (assuming a ligh
enhancemen ac o , which is an app oxima ion) and o build a egula iangula s uc u e
(which is a mo e p ecise me hod).
70 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
–Hegedus model: To simula e he ligh apping e ec we use a me hod o calcula e
an op ical pa h enhancemen ac o m(λ)depending on he wa eleng h ange using
he model de eloped by Hegedus e al. [45]. Thus, he abso p ion o he i-laye (Ai)
changes om Eq. 2.55a o 2.55b. This p o ides an adjus men o he spec al esponse
o he espec i e expe imen al da a in he long wa eleng h ange.
Ai(λ)=1−exp[−α(λ)·di](2.55a)
Ai(λ)=1−exp[−α(λ)·m(λ)·di](2.55b)
The use o non- ex u ed su aces/in e aces implies he o ma ion o in e e ences in he
spec al esponse depending mainly on he TCO and i-laye hickness. The e o e, o
supp ess he in e e ence e ec s coming om he TCO, we implemen a e y hin TCO
laye (d=75 nm, when usually d≈700 nm - 1000 nm). We also applied a espec i ely
enhanced ex inc ion coe ﬁcien (k) o app oxima e he eal abso p ion p ope ies o he
TCO in he de ice.
–Geome y wi h ex u e: We ook he on TCO AGC AN10 as expe imen al ex u e
e e ence. This TCO ype is no any mo e he s anda d TCO a T-Sola , which now is
ANS10ME. Howe e , he ex u e o bo h can be conside ed nea ly iden ical. Scanning
elec on mic oscopy (SEM) and a omic o ce mic oscopy (AFM) pic u es o he AN10
TCO ex u e ha e been s udied [46]. One example o hese measu emen s is p esen ed
in Figs. 2.16 and 2.17. They show how he ex u e is i egula ha ing, in gene al,
py amidal shape. To simula e he ex u e in 2Dwe ha e employed, o he in e ace
TCO/p-laye , a egula iangula s uc u e wi h heigh and base using he a e age
pa ame e s ob ained om he AFM da a. In he in e aces i-laye /n-laye and AZO/Al
we ha e applied a scaled coe ﬁcien o sligh ly educe he heigh o he ex u e [47],
[48], [49], [50].
2.3. Op ical model 71
Figu e 2.16: SEM pic u e o an indus ial TCO sample AN10 om AGC showing ﬁne su ace oughness o he
c ys al g ains [46].

Figu e 2.17: AFM pic u e o an indus ial TCO sample AN10 om AGC [46].
78 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
ηn=EFn −EC
kT (2.66a)
ηp=EV−EFp
kT (2.66b)
in he equa ions abo e NCand NV,incm
−3, a e he e ec i e DOS in he CB and VB. Thei
alues a e gi en by Eq. 2.44; F1/2is he Fe mi in eg al o o de 1/2; EFn =qφnand EFp =qφp
a e he quasi-Fe mi ene gies o elec on and holes, and φnand φp, in V, a e he quasi-Fe mi
po en ials o elec on and holes.
Al e na i ely, one can w i e he equa ions 2.64 as:
n=γn·NC·expEFn −EC
kT =γn·NC·expEFn −E0+qψ+χ
kT (2.67a)
p=γp·NV·expEV−EFp
kT =γp·NV·expE0−qψ−χ−EG−EFp
kT (2.67b)
whe e γnand γpa e unc ion o ηnand ηp:
γn=F1/2(ηn)
exp(ηn)(2.68a)
γp=F1/2(ηp)
exp(ηp)(2.68b)
Wo king ou he alue o EFn and EFp, espec i ely, we ob ain:
EFn =EC+kT lnn
γnNC=E0−qψ−χ+kT lnn
γnNC(2.69a)
EFp =EV−kT lnp
γpNV=E0−qψ−χ−EG−kT lnp
γpNV(2.69b)
Cu en anspo . D i -Di usion model
Using equa ions 2.69a and 2.69b in equa ions 2.61a and 2.61b, espec i ely, and a e
a manipula ion which makes use o he Eins ein ela ions o he di usion coe ﬁcien o
elec ons and holes:
Dn=kT
qμn(2.70a)
Dp=kT
qμp(2.70b)
and he ac ha dE0
dx =0, we ﬁnd:

2.4. Nume ical me hods and sol e s 79
Jn=qDn
dn
dx
 
Elec on di usion cu en
+μnn−qdψ
dx −dχ
dx −kT
NC
dNC
dx 
 
Elec on d i cu en
(2.71a)
Jp=−qDp
dp
dx
 
Hole di usion cu en
+μpp−qdψ
dx −dχ
dx −dEG
dx +kT
NV
dNV
dx 
 
Hole d i cu en
(2.71b)
In Equa ions 2.71 he ﬁ s e m ep esen s he cu en due o di usion o he ca ie s and
he second e m ep esen s d i anspo . The e ms in he squa e b acke s a e conside ed o
be he e ec i e d i ﬁelds. In he case ha he de ice is made o spa ially uni o m ma e ial
(homojunc ion de ice), we ob ain:
dχ
dx =dEG
dx =dNC
dx =dNV
dx =0 (2.72)
The e o e, he Eqs. 2.71 esul in he classical cu en densi y exp essions o elec on
and hole, which a e used in c-Si homojunc ion non-degene a ed de ices analysed wi h
Maxwell-Bol zmann s a is ics.
2.4.3 Bounda y condi ions
The e a e wo bounda ies in he de ice, he on and he back con ac . The implied
condi ions a he con ac s ﬁx he alues o he independen model a iables a hese poin s.
The bounda y condi ions depend on how he con ac s o a de ice a e modelled. Gene ally,
wo ypes o con ac s a e dis inguished: Ohmic con ac s and Scho ky con ac s.
Ou de ice is modelled wi h Ohmic con ac s whe e he elec os a ic po en ial and elec on
and hole concen a ions a he bounda ies o he de ice (x=0, anode and x=L, ca hode,
whe e Lis he de ice hickness) a e ﬁxed, o he mino i y ca ie concen a ions a e
de e mined by su ace ecombina ion. I is assumed ha he majo i y ca ie concen a ion
is independen o he injec ion le el. In case o ideal Ohmic con ac s inﬁni e su ace
ecombina ion, equilib ium and cha ge neu ali y a he con ac s is assumed:
ρ(0,y)=0⇒n0(0,y)−p0(0,y)=ploc −nloc +ND−NA(2.73a)
ρ(L,y)=0⇒n0(L,y)−p0(L,y)=ploc −nloc +ND−NA(2.73b)
n0(0,y)·p0(0,y)=n2
i,e (2.74a)
n0(L,y)·p0(L,y)=n2
i,e (2.74b)
80 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
The space cha ge densi y ρ(x)is gi en by Eq. 2.60. The ollowing condi ions a e
in oduced o he elec os a ic po en ial ψand quasi-Fe mi po en ials φFn and φFp a he
bounda ies:
ψ(0,y)=ψ0(0,y)+Vapp (2.75a)
ψ(L,y)=ψ0(L,y)(2.75b)
φFn(0,y)=φFp(0,y)=Vapp (2.76a)
φFn(L,y)=φFp(L,y)=0 (2.76b)
whe e ψ0(0,y)and ψ0(L,y)a e he solu ions o equa ions 2.73 andVapp is he applied ex e nal
ol age.
Fo Bol zmann s a is ics, hese condi ions can be exp essed analy ically. Fo Fe mi
s a is ics his is no possible, hence, Sen au us De ice compu es he equilib ium solu ion
nume ically.
Fu he mo e, o Ohmic con ac s he su ace ecombina ion eloci ies o elec ons, νn
and holes, νp, in cm/s, de e mine he ca ie concen a ions a he bounda ies. I hey a e
speciﬁed, Sen au us De ice uses he ollowing cu en densi y bounda y condi ions:

Jn·ˆn=qνn·(n−n0)(2.77a)

Jp·ˆn=qνp·(p−p0)(2.77b)
whe e nand pa e he elec on and hole concen a ions a he on and back con ac s, n0and
p0a e he elec on and hole concen a ions in he modynamic equilib ium a he on and
back con ac s and ˆnis he no mal ec o o he con ac .
Replacing he gene al poin xby x=0 and x=L, we ﬁnd:

Jn(0,y)·ˆn=q·νn0·[n(0,y)−n0(0,y)] (2.78a)

Jn(L,y)·ˆn=q·νnL ·[n(L,y)−n0(L,y)] (2.78b)

Jp(0,y)·ˆn=q·νp0·[p(0,y)−p0(0,y)] (2.79a)

Jp(L,y)·ˆn=q·νpL ·[p(L,y)−p0(L,y)] (2.79b)
whe e νn0and νnL a e he su ace ecombina ion eloci ies o elec ons a he on and back
con ac , espec i ely, and νp0and νpL a e he su ace ecombina ion eloci ies o holes a
he on and back con ac , espec i ely. By de aul , n=n0and p=p0a e applied o
concen a ions a he Ohmic con ac s since 
Jn,p=0 a he bounda ies.
2.4. Nume ical me hods and sol e s 81
2.4.4 Disc e iza ion
The model desc ibed p e iously is o med by he di e en ial equa ions which model he
beha iou o he co esponding semiconduc o . To sol e he model we need o look o a
nume ical solu ion o he sys em o equa ions oge he wi h hei bounda y condi ions. This,
esul s in a non-linea sys em o pa ial di e en ial equa ions. The p ocedu e used o sol e
his sys em o a simula ed semiconduc o de ice is he ollowing [59]:
– To disc e ise he sys em o non-linea equa ions. Hence, he con inuous p oblem is
eplaced by a disc e e non-linea sys em o equa ions.
– To apply any linea iza ion me hod o he non-linea p oblem.
– To sol e a sys em o linea and dispe se equa ions in o de o ge he wished solu ion.
To sol e he non-linea sys em o 3N(whe e Nis he numbe o nodes) di e en ial
equa ions o med by he Poisson and he con inui y ca ie equa ions (2.57, 2.58 and 2.59)
one needs o disc e ise he sys em o equa ions. In spi e ha ou simula ion is in 2D, we a e
going o simpli y in he ollowing he disc e iza ion o 1D since he esolu ion me hods a e
no he aim o his hesis, hey a e p esen ed jus o cla i y how he simula ions s eps a e.
The disc e iza ion s a s di iding he de ice in cells. In e e y cell he e a e wo kinds o
poin s: he cell edges which a e called io x(i)and he cen al poin s i+1/2o x(i+1/2). The
anode (posi i e elec ode) o on con ac is placed a he poin 0 and he ca hode (nega i e
elec ode) o back con ac is placed a he poin N−1.
The equa ions ela e h ee a iables a he poin i:ψ(i),n(i)and p(i). The e o e, he e
a e 3N a iables wi h 3Nequa ions in o al. In addi ion, he h ee equa ions a each iposi ion
depend no only on he h ee a iable alues a his loca ion bu also on he a iable alues a
he adjacen poin s i−1 and i+1.
To ob ain he disc e ised equa ions a a poin i(which is no a con ac ) o he ci ed
equa ions 2.57, 2.58 and 2.59 we ha e o in eg a e hem wi h limi s i−1/2 and i+1/2,
conside ing hi=x(i+1)−x(i)and hi−1=x(i)−x(i−1), we ge :
εi+i/2
ψi+1−ψi
hi−εi−i/2
ψi−ψi−1
hi−1=hi+hi−1
2(n−p+NA−ND)|i(2.80)
Jn(i+1/2)−Jn(i−1/2)=IR(i)(2.81)
Jp(i+1/2)−Jp(i−1/2)=−IR(i)(2.82)
82 Chap e 2. Theo y and simula ion models o a-Si:H sola cells
whe e IR(i) is he in eg al o he ne ecombina ion (Rne ) which was ob ained in Eq. 2.41,
esul ing in:
IR(i)=i+1/2
i−1/2(R o
CB +R o
VB+R o
DB)dx (2.83)
2.4.5 Linea iza ion o he disc e ised sys em
The coupled non-linea sys em o 3Nequa ions, disc e ised in he p e ious sec ion, is
sol ed using he New on me hod [60].
To ob ain he linea sys em we ha e o ake in o accoun ha in e e y poin i he e a e 3
disc e ised equa ions (Poisson and con inui y ca ie equa ions). They can be w i en equalling
hem o ze o: Gi
1=0, Gi
2=0 and Gi
3=0. Due o he disc e iza ion, he equa ions only depend
on h ee a iables (ψ,nand p) in h ee poin s (i−1, iand i+1). We name Wi he ec o
whose componen s a e he a iables in his poin (Wi=(ψi,ni,pi)) and dWii s di e en ial
ec o . Then, we apply he Taylo se ies de elopmen o he unc ions Gi
1,Gi
2and Gi
3 o a
ange o alues o he a iables oge he wi h he New on me hod. I leads in each i e a ion o
h ee linea equa ions which can be ep esen ed in ma ix as ollow:
⎛
⎜
⎜
⎝
∂Gi
1
∂Wi−1
∂Gi
1
∂Wi
∂Gi
1
∂Wi+1
∂Gi
2
∂Wi−1
∂Gi
2
∂Wi
∂Gi
2
∂Wi+1
∂Gi
3
∂Wi−1
∂Gi
3
∂Wi
∂Gi
3
∂Wi+1
⎞
⎟
⎟
⎠·⎛
⎜
⎝
dWi−1
dWi
dWi+1⎞
⎟
⎠=⎛
⎜
⎝
−Gi
1
−Gi
2
−Gi
3
⎞
⎟
⎠(2.84)
2.4.6 Nume ical esolu ion o he non-linea equa ions
To sol e he sys em 2.84, coming om he d i -di usion model, wo app oxima ion
me hods a e usually employed [61] [59] [62], he New on-Raphson me hod (coupled) and
he Gummel me hod (uncoupled). To choose be ween bo h me hods, one has o conside he
ope a ion cha ac e is ics o he de ice, he algo i hms used o sol e he linea ised sys em o
equa ions o he amoun o memo y o he compu a ional sys em whe e he simula ions a e
un.
New on-Raphson me hod
The New on-Raphson me hod consis s in sol ing he comple e sys em o 3Nequa ions
simul aneously by applying any i e a i e me hod o ype New on [63]. This me hod is e y
obus and p o ides a e y accu a e solu ion. Howe e , i may need a lo o ime and memo y
2.4. Nume ical me hods and sol e s 83
esou ces since i sol es a non-linea and non-symme ic sys em o equa ions wi h high
numbe o dimensions.
Gummel me hod
The Gummel me hod [59] [64] uses an i e a ion ype Gauss-Seidel/Jacobi which
uncouples he equa ions G1,G2and G3, so ha i is only necessa y o sol e h ee sys ems
o equa ions o dimension N. Hence, he Poisson equa ion and he con inui y equa ions o
elec on and holes a e sol ed sepa a ely. This me hod is e y use ul since i is possible o
each he con e gence e en s a ing wi h poo ini ial condi ions and i is a as me hod.
Ne e heless, o some applica ions such as e y high injec ion le el in he semiconduc o
o high ecombina ion, he me hod could ha e con e gence p oblems. In addi ion, in some
cases he Gummel me hod con e ges e y as in he ﬁ s i e a ions bu la e he con e gence
u ns slowe . In his case, one can combine he Gummel and New on-Raphson me hods.
Thus one can app oxima e he solu ion by using he Gummel me hod and la e change o he
New on-Raphson me hod in o de o ake ad an age o i s quad a ic con e gence p ope ies
nea he solu ion.

CHAPTER 3
INDUSTRIAL PRODUCTION PROCESS AND
BASIC EQUIPMENT SET-UPS OF A-SI:H
SOLAR CELLS
This chap e p esen s how he PECVD p oduc ion p ocess wo ks, as well as how we
ab ica e R&D sola cells o 1 cm2(o 4 cm2) o mini modules in he indus ial p oduc ion
line. La e , he equipmen ins alled in he labo a o y a e shown. Conce ning his hesis, he
mos impo an ones a e he con en ional spec al esponse and he e y as spec al esponse
equipmen , which a e used o de e mine he ex e nal quan um e ﬁciency (EQE) cu es; and
he sola simula o equipmen wi h i s cu en - ol age (IV) ace o measu e he illumina ed
o da k IV cu es. The h ee equipmen we e de eloped in ou labo a o y. The de elopmen o
R&D sola cells and mini modules in he T-Sola p oduc ion line as well as he measu emen
equipmen ha e been c ucial o imp o e he p oduc ion modules’ e ﬁciency.
3.1 Plasma enhanced chemical apou deposi ion
As explained in sec ion 1.5, he sola cell ab ica ion p ocess is based on he deposi ion o
a-Si:H laye s by PECVD in a 7 chambe clus e ool on a 2.2mx2.6 m subs a e. The ﬁ s
laye deposi ion is a p- ype laye doped wi h ime hyl bo ane (TMB, B(CH3)3), he second
one is an in insic laye and, a las , a n- ype laye doped wi h PH3. The p-laye is deposi ed
in one chambe while he o he wo a e deposi ed oge he in ano he chambe o p e en
86 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
c oss con amina ion. The a-Si:H laye s a e o med h ough deposi ion o SiH4and H2. This
deposi ion o a p-i-n s uc u e allows he gene a ion o he cu en in he cell when he module
is exposed o he ligh .
The hin ﬁlm deposi ion p ocess esul s om he decomposi ion o SiH4,H
2and o he
gases c ea ing a plasma a mode a e subs a e (glass ﬁlm) empe a u es, a ound 200 oC
(PECVD). In his p ocess he silicon o ms an amo phous laye mixed wi h hyd ogen in a
andom bond ne ( andom ne wo k, see Fig. 2.5). PECVD uses elec ical powe coupled in o
he plasma a a adio equency (RF) o 13.56 MHz o c ea e adicals and ions o incoming
gases, so ha hey can eac o o m silicon laye s on he subs a e glass. The whole sys em is
kep in acuum by a mechanical oughing sys em. The chambe s a e cleaned by dissocia ing
ni ogen iﬂuo ide (NF3) which emo es Si emaining in he chambe . The ﬂuo ine (F) a oms
o med in he plasma eac wi h Si o a ola ile molecule, silicon e aﬂuo ide (SiF4), which
hen, a e pumped ou o he chambe .
The deposi ion p ocess by an RF discha ge can be desc ibed as a ou s ep p ocess [25], i
is schema ically ep esen ed in Fig. 3.1 [65]:
– The p ima y eac ions in he gas phase a e elec on-impac exci a ion, dissocia ion
and ioniza ion o SiH4molecules. The plasma hus, consis s o neu al adicals and
molecules, posi i e and nega i e ions and elec ons.
– Seconda y eac ions, be ween molecules and ions o adicals, a e e y impo an as hey
p edominan ly con ol he elec onic and s uc u al ﬁlm p ope ies. Reac i e neu al
species mo e o he subs a e by di usion, posi i e ions bomba d he g owing ﬁlm
and nega i e ions a e apped wi hin he shea hs [66] o he coun e elec ode and may
e en ually o m small pa icles o dus .
– The hi d s ep consis s o su ace eac ions, such as hyd ogen abs ac ion, adical
di usion and chemical bonding.
– The ou h s ep is he subsu ace elease o hyd ogen molecules and elaxa ion o he
silicon ma ix.
The deposi ion p ocess is a e y complica ed ma e as he physical and chemical
in e ac ions in he plasma and a he g owing ﬁlm su ace a e dependen on he RF powe
and equency, he subs a e empe a u e, he gas p essu e and composi ion, he magni ude
and he pa e n o he gas ﬂow, he elec ode geome y, e c.
3.1. Plasma enhanced chemical apou deposi ion 87
ZĞĐŽŵďŝŶĂƚŝŽŶ
^ŝ,ϰн,Ϯ
^ŝ,ϰ,Ϯ
ĐƚŝǀĞƐ
Ɖ
ĞĐŝĞƐ
;ǇсϬ ϭϮϯͿ
;ǆфϭϬǇф΀ϮǆͲϭ΁Ϳ
;ǌсϭϮͿ
;ǇсϬ ϭϮϯͿ
ŚĞŵŝĐĂůĂĚƐŽƌƉƚŝŽŶŽĨƌĂĚŝĐĂůƐĂƚŽŵƐ
,ͲĂƚŽŵƌĞĂĐƚŝŽŶƐ
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/ŶƐĞƌƚŝŽŶ
^ƵƌĨĂĐĞƌĞĂĐƚŝŽŶƐĚŝĨĨƵƐŝŽŶ
^ƵďƐƵƌĨĂĐĞƌĞĂĐƚŝŽŶƐ,ϮƌĞůĞĂƐĞ^ŝƌĞůĂǆ ^ŽůŝĚ
WůĂƐŵĂ
ƚĐŚŝŶŐ
ĚĞƐŽƌƉƚŝŽŶ
ůĞĐƚƌŽŶŝŵƉĂĐƚĚŝƐƐŝŽŶŝǌ
,ͲĂƚŽŵĂďƐƚƌĂĐƚŝŽŶ
/ŽŶͲŶĞƵƚƌĂůƌĞĂĐƚŝŽŶƐ
+
y
SiH
y
SiH
yx HSi
+
yx
HSi
H
+
z
H
Figu e 3.1: Schema ic ep esen a ion o he glow-discha ge deposi ion p ocess [25].
In Fig. 3.2 we see he main pa s o a PECVD chambe as well as hei dis ibu ion and
he place o he subs a e.
94 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Figu e 3.7: Back con ac side (le ) and glass side ( igh ) o a coupon p oduced a TS h ough lase sc ibe.
high e ﬁciency bu o en in bad cell yield. Howe e , combining SB and annealing we
achie e high e ﬁciency, high yield and low dispe sion in elec ical pa ame e s. Toge he
wi h he e y accu a e cell a ea deﬁni ion on coupons, MCs p oduced wi h LSR sc ibe
me hod e u n e y eliable da a.
The p oduc ion p ocess can be summa ized as:
Glass →TCO (SnO2)→a-Si:H →LSR sc ibe (P2) o g ids →ZnO
→Al →NiV →LSR sc ibe (P3) o pads →SB →Annealing
The design h ough LSR sc ibe allows a ﬂexible design, which ﬁnally has pe mi ed
he ab ica ion o MC sizes wi h 1 cm2and4cm
2, as well as MMs o se e al sizes
(usually 10 x 10 cm2and 20 x 20 cm2o o al o ac i e su ace). As an example, Fig.
3.8 p esen s he loca ion o 18 MMs 20 x 20 cm2and 18 MMs 10 x 10 cm2in he
ull size panel. The o e all design o hese MMs is he same as he one o ull size
modules ha ing he same measu emen s o he edge dele e a ea and he con ac cells a
he module bo de . An example o a 10 x 10 cm2MM design is p esen ed in Fig. 3.9.
To measu e he MMs we do no use a sample holde . We solde side buss on he con ac
cells o make he connec ion and hen we pe o m he SB. P e iously o hese wo s eps,

3.2. P oduc ion p ocess o ob ain mini cells and mini modules: lase sc ibe p ocesses, shun bus ing
and annealing 95


ϵϯ ϲ ϵ
ϴ
ϳϮ ϱ ϴ
ϲ
ϱϭ ϰ ϳ
ϰ
ϯ
Ϯ
ϭ


ϵ
ϴ
ϳ
ϲ
ϱ
ϰ
ϯ
Ϯ
ϭ
ϭϮϯϰϱϲϳϴϵϭϮϯϰϱϲϳϴϵ
ϭϲ
ϭϭ ϭϰ ϭϳ
ϯϲϵ
ϮϲϬϬŵŵ
ϮϮϬϬŵŵ
Ϯϱϴ
ϭϰϳ
ϭϮ ϭϱ ϭϴ
ϭϬ ϭϯ
ϭϮ ϭϱ ϭϴ
ϭϰ
ϭϭ
ϭϬ ϭϯ ϭϲ
ϭϳ
&^
Ǉ
ǆ
Figu e 3.8: Posi ion o he MMs along he ull size panel.
C1 C2 C3 C4 C5 C6
Poin
(0,0)
Edge
dele e
Dea h
cell Ac i e a ea Dea h
cell
Edge
dele e
Ac i e a ea
Edge
dele e
Edge
del.
Figu e 3.9: 10 cm x 10 cm o al a ea MM p oduced a TS h ough LSR sc ibe. Dis ances in mm.
96 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
we dele e he edges by manual g inding. Mos o he imes, we lamina e hem ollowing
a p ocess simila o he one pe o med in-line and we make he annealing placing he
MMs in he ACL.
3.3 Con en ional spec al esponse equipmen
Wi h he SR equipmen we measu e he gene a ed cu en in he sola cells o a
de e mined wa eleng h and o he wa eleng h ange whe e he sola cell is sensi i e o ligh .
This ange depends on he kind o semiconduc o used and on he sola cell s uc u e. Fo SJ
a-Si:H p-i-n s uc u es, he in e es ing wa eleng h ange goes om 300 nm o 800 nm.
3.3.1 Componen s o he con en ional spec al esponse sys em
The con en ional spec al esponse (CSR) equipmen is made up o he ollowing de ices:
– A c lamp: This lamp is a Newpo 300 W Xenon Ozone ee lamp supplied by a powe
con olle o ha e s able illumina ion condi ions (see le side o Fig. 3.10). This kind
o lamp deli e s s able adia ion, om UV o nea in a ed (NIR) adia ion wi h a
a iable in ensi y. Howe e i s ou pu spec um p esen s some peaks ha could a ec
he accu acy o he ﬁnal measu emen .
– Choppe wheel: I con e s con inuous ligh (p o ided by he a c lamp) in o pulsed ligh
wi h a cons an equency ha we se .
– Fil e wheel: This ﬁl e wheel allows o use and o change au oma ically di e en
ﬁl e s when measu ing o e he wa eleng h spec um. These ﬁl e s a e used o a oid
illumina ion e ec s a second o de wa eleng hs caused by he di ac ion g a ing in
he monoch oma o . Fo example, i he di ac ion g a ing is in he posi ion o ansmi
ligh a 800 nm wa eleng h, he monoch oma o will also ansmi a small 400 nm
componen whe e ou sola cell is also sensi i e. This would induce a cu en highe
han he ue cu en gene a ed a 800 nm. The ﬁl e s elimina e second o de ligh by
jus ansmi ing abo e he wa eleng h ange o in e es . As an example, i we wan o
scan om 400 nm o 900 nm, we will use a ﬁl e om 800 nm on, ha will ansmi
only om wa eleng hs g ea e han 400 nm.
3.3. Con en ional spec al esponse equipmen 97
– Monoch oma o : I is shown in he igh side o Fig. 3.10, i is he main componen
o he CSR equipmen . I supplies he sys em wi h monoch oma ic ligh . The
monoch oma o ecei es a la ge band spec um ligh o he a c lamp which is ocused
on a g a ing which only ansmi s a ce ain wa eleng h o he monoch oma o ou pu
depending on he incidence angle o he g a ing. Changing he incidence angle and
changing o di e en g a ings, a wide ange o wa eleng hs can be selec ed. All he
mechanical manipula ions in he monoch oma o used o selec he wa eleng h, a e
ope a ed by a compu e p og am de eloped in he labo a o y ( o be explained in sec ion
3.3.6).
Figu e 3.10: A c lamp (le ) and monoch oma o ( igh ).
– Beam-spli e : I is used o di ide he main incoming beam in o wo beams o ligh
wi h an angle o 90o. One is called ﬁb e op ic ou pu (whe e he sola cell unde es
is placed) and he o he one is he e e ence ou pu (whe e he e e ence pho odiode is
placed). By using di e en semi anspa en ma e ials, e.g. pa ially co e ed glasses o
mi o s, a beam-spli e has di e en ansmissions p ope ies and he e o e di e en
ligh in ensi ies o he wo ou pu beams. I is impo an o op imize he ligh di ision
o ha e adequa e ligh in ensi ies in bo h, he e e ence pho odiode and he sola cell
unde es .
– Re e ence pho odiode and calib a ed pho odiode: Two pho odiodes a e used in he
spec al esponse measu emen p inciple. In he calib a ion p ocedu e a calib a ed
pho odiode, wi h known SR, is loca ed a he ﬁb e op ic ou pu ( eplacing he sola cell
98 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Figu e 3.11: Incoming beam di ided by he beam-spli e .
unde es ) and he signal is measu ed a he same ime wi h he e e ence pho odiode
(whose SR is also known). F om his measu emen we ob ain he calib a ion ac o (F)
o each wa eleng h o he op ical assembly. The F is used la e o calcula e he SR o
he sola cell unde es compa ing i s in ensi y wi h he one o he e e ence pho odiode
which s ays always a he e e ence ou pu o he beam spli e .
– Op ical ﬁb e: This op ical ﬁb e bundle anspo s he ligh om he beam-spli e o he
sola cell unde es . We use a ﬁb e bundle o ha e mo e ﬂexibili y o illumina e easily
di e en pa s o he coupon.
– Lock-in ampliﬁe s: The small cu en s gene a ed by he sola cell and he pho odiode
a e measu ed wi h wo lock-in ampliﬁe s (see le side o Fig. 3.12). A lock-in ampliﬁe
uses a e e ence equency p o ided by he choppe wheel o s imula e he es sample
and phase locked loop echnology. I is able o de ec e y small signals (a he same
equency as ha o he e e ence equency) in a noisy signal backg ound. The wo
lock-in ampliﬁe s a e used o simul aneously measu e he small cu en s gene a ed by
he momoch oma ic ligh o he e e ence pho odiode and he sola cell unde es .
– Cold ligh : This ligh sou ce, used as a bias ligh , illumina es he es cell wi h a whi e
ligh du ing he measu emen (see igh side o Fig. 3.12). This illumina ion adjus s he
cell o ope a ing condi ions simila o s anda d es condi ions (1000 W/m2,25oC and
AM1.5G spec al dis ibu ion) (STC). I is called cold ligh because he lamp ﬁl e s he
3.3. Con en ional spec al esponse equipmen 99
in a ed (IR) ligh so ha i does no c ea e hea du ing he illumina ion and, he e o e,
does no ansmi hea o he illumina ed sola cell.
Figu e 3.12: Two lock-in ampliﬁe s (le ) and cold ligh sou ce wi h i s illumina ion sys em ( igh ).
O he de ices/equipmen s linked o he CSR equipmen a e:
– Re e ence sola cell: The calib a ed ﬁl e ed sola cell ( ab ica ed and calib a ed by he
FHG-ISE Callab F eibu g, Ge many) is used o check i we a e wo king unde an
i adiance o 1000 W/m2wi h he sola simula o (SS) and o know he e o o ou
SR equipmen . We know i s SR and EQE in 10 nm s eps o a spec um om 280 nm
o 930 nm, as well as i s IV cu e in he ﬁ s quad an unde STC. The main elec ical
pa ame e s a e exposed in Table 3.1:
Table 3.1: IV cu e pa ame e s o he calib a ed sola cell (4 cm2) om FHG-ISE measu ed unde STC [68].
Elec ical pa ame e s
η(%) 7.6±0.2
Isc (mA) 61.0±1.5
Jsc (mA/cm2)15.23±0.38
Voc (mV) 624.2±3.1
FF (%) 80.1±0.8
Impp (mA) 57.0
Vmpp (mV) 532.9
Pmpp (mW) 31.0

100 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
– Spec opho ome e: The Pe kin Elme LAMBDA 950 spec opho ome e is an
ins umen ope a ing om he UV o he NIR spec al ange. I is made up o wo
monoch oma o s, wo adia ion sou ces (a deu e ium lamp and a halogen lamp) and a
de ec o compa men . In he labo a o y, his equipmen allows measu ing he di use
and o al ansmission and eﬂec ion o hin ﬁlms and hus, i can calcula e he di ec
ansmission and abso p ion. Rela ed o he SR, we de e mine he in e nal quan um
e ﬁciency (IQE) by measu ing he sola cell eﬂec ion (as explained in he nex sec ion).
3.3.2 Spec al esponse and quan um e ﬁciency
The spec al esponse (SR, exp essed in A/W) ep esen s he in ensi y o he pho o ol aic
e ec depending on he incoming ligh o a gi en wa eleng h in a sola cell. I allows
o de e mine how much cu en is gene a ed by a sola cell o a speciﬁc i adiance and
o each wa eleng h o he whole spec um. The SR is also associa ed o he ex e nal
quan um e ﬁciency (EQE, dimensionless), which ep esen s he numbe o elec on/hole pai s
gene a ed in he cell by he inciden pho on ﬂux a each wa eleng h [69]. Bo h pa ame e s a e
linked by Eq. 3.1:
EQE(λ)=SR(λ)
q
hc
λ=1240SR(λ)
λ(3.1)
whe e qis he elec ic cha ge o one elec on (q=1.602×10−19 C), his he Planck’s cons an
(h=6.626×10−34 J·s), cis he speed o ligh in acuum (c=3×1017 nm/s) and λ(nm) is
he wa eleng h o he inciden ligh .
The SR is usually used o ex ac in o ma ion abou ecombina ion a on and ea
con ac s, di usion o d i leng hs o ca ie s, wid h o he deple ion egion and ligh apping
p ope ies among he mos impo an [70] [71]. In addi ion, i gi es de ailed in o ma ion abou
which wa eleng hs ha e mo e ca ie gene a ion in he sola cell and he e o e, i is essen ial
o op imize he modules.
The e is ano he pa ame e ela ed o he QE, he in e nal quan um e ﬁciency (IQE) which
conside s he eﬂec ion loss a he sola cell’s su ace. I ep esen s he numbe o ca ie s
gene a ed in he sola cell pe abso bed pho on. Knowing he EQE and he eﬂec ion ( ) o
he de ice we calcula e he IQE h ough he Eq. 3.2:
IQE(λ)=EQE(λ)
1− (λ)(3.2)
3.3. Con en ional spec al esponse equipmen 101
3.3.3 Di e en ial spec al esponse me hod
T adi ionally, he di e en ial spec al esponse (DSR) me hod is based on he de ec ion by
a lock-in ampliﬁe o he sola cell’s esponse (sola cell’s cu en ). The illumin a ion sou ce is
a modula ed (AC) monoch oma ic es ligh . The cell is simul aneous exposed o a whi e bias
(DC) ligh o i adiance in he ange o 1 sun illumina ion. Ano he a ia ion o his me hod is
o use an incandescen lamp, ﬁl e ed wi h a se o spec al ﬁl e s, o ob ain he monoch oma ic
ligh sou ce. In his e sion, a sola simula o is used as he bias ligh sou ce [72].
The p inciple o he DSR me hod [52] is o compa e he cu en o a e e ence pho odiode
and he cu en o he sola cell unde es illumina ed simul aneously by he same ligh sou ce
unde STC [73]. Moni o ing simul aneously hese wo cu en s o each wa eleng h, and
knowing he calib a ion ac o (F(λ)) o he e e ence cell, we can calcula e he SR o he
sola cell unde es and, hus, he EQE and he sho ci cui cu en (Isc) (see below).
3.3.4 De e mina ion o he calib a ion ac o , he spec al esponse
and he in eg a ed sho ci cui cu en densi y
Be o e measu ing he sola cell in he SR equipmen , we ha e o know a calib a ion ac o
(F(λ)) o he calcula ions o he sola cell SR. In he case o he CSR equipmen , he F is
de e mined by he ansmission and eﬂec ion cha ac e is ics o he beam spli e and by he
losses in he ﬁb e op ic. This ac o akes in o conside a ion he di e ence o ligh in ensi y
in he wo a ms o he beam spli e . To de e mine i , we use a second pho odiode (calib a ed
pho odiode) wi h a known SR. In he calib a ion measu emen he calib a ed pho odiode is
in he posi ion o he sola cell unde es . Consequen ly, we will measu e simul aneously he
signals o he e e ence and calib a ed pho odiodes o ob ain he a io be ween hem o each
wa eleng h. One has o pu special a en ion in he quan i y o inciden ligh eaching he
calib a ed pho odiode, so i is e y impo an o concen a e all he ligh in he ac i e a ea o
he pho odiode ( he same holds o he sola cells). The e o e, he beam is ocused by placing
a lens in he ﬁb e op ic ou pu .
Taking in o accoun he deﬁni ion o he EQE, we ge he ollowing equa ion:
EQE(λ)= Iph(λ)
q·φ o (λ)(3.3)
whe e Iph (A) is he gene a ed cu en o a sola cell and φ o (pho ons/s) is he inciden pho on
ﬂux.
102 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Applying Eq. 3.3 o he calib a ed pho odiode (cal), he e e ence pho odiode ( e ) and
he sola cell unde es (cell), we ge :
EQEcal(λ)= Ical
ph (λ)
q·φ o (λ)· (λ)(a ib e op ic ou pu )(3.4a)
EQE e (λ)= I e
ph (λ)
q·φ o (λ)· (λ)(a di ec ou pu )(3.4b)
EQEcell(λ)= Icell
ph (λ)
q·φ o (λ)· (λ)(a ib e op ic ou pu )(3.4c)
whe e φ o (pho ons/s) is he inciden pho on ﬂux on he beam-spli e , is he ansmi ance
o he beam spli e and is he eﬂec ion o he beam-spli e .
Combining he equa ions 3.4 and changing EQE o SR ollowing he Eq. 3.1 we ob ain
he SR o he sola cell unde es :
SRcell(λ)=Icell
ph (λ)
I e
ph (λ)·F(λ)·SRcal(λ)(3.5)
whe e he F is:
F(λ)=I e
ph (λ)
Ical
ph (λ)(3.6)
The SR equipmen is conﬁgu ed o measu e he samples in sho ci cui condi ions. So,
o calcula e he Isc o he sola cell om he spec al esponse measu emen one only has
o in eg a e o e he spec um o in e es he p oduc o he measu ed SR(λ), he i adiance
(G(λ)) o he AM1.5 spec um and he su ace o he sola cell unde es as shown in he
ollowing equa ion:
Isc =λ
λ0
Gi ad(λ)·SR(λ)·S·dλ(3.7)
whe e Gi ad (W/cm2/nm) is he i adiance p o ided by he sola spec um AM1.5 by uni o
su ace and wa eleng h and S (cm2) is he su ace o he sola cell.
3.3.5 Expe imen al se -up
In Fig. 3.13 he scheme o he expe imen al se -up o he CSR measu emen equipmen
is p esen ed. The ope a ion is based in he con e sion o con inuous ligh p o ided by
3.3. Con en ional spec al esponse equipmen 103
he a c lamp o pulsed ligh employing he choppe wheel. Then, he beam a i es o he
monoch oma o which con e s he pulsed ligh in monoch oma ic ligh depending on i s
wa eleng h. This beam o monoch oma ic ligh is sepa a ed in o wo by he beam spli e .
One beam goes di ec ly o he e e ence pho odiode and he o he one goes h ough a ﬂexible
op ical ﬁb e whose ou pu illumina es jus abo e he sola cell. A sample holde is used o
es ablish he elec ical con ac wi h he sola cell (see Fig. 3.3, igh ). Las ly, he wo lock-in
ampliﬁe s de ec and measu e he small cu en gene a ed pe wa eleng h.
Whi e
lamp
Beam
spli e
Choppe
Compu e
Lock-in
ampli ie 2
Sola cell unde es o
calib a ed pho odiode
Lock-in
ampli ie 1
Re e ence
pho odiode
Monoch oma o
Fil e
wheel
Ligh pa h
Figu e 3.13: SR equipmen and links be ween he di e en de ices.
The op ical uning du ing he ins alla ion o he equipmen is a challenge. The op ical
componen s o he equipmen mus be ins alled s ep by s ep by op imizing he beam a each
ansi ion poin , beginning a he a c lamp and ﬁnishing in he e e ence pho odiode and he
sola cell. One o he mos impo an s eps is o p ope ly ocus he collima ed beam p o ided
by he a c lamp on he inpu sli o he monoch oma o . This poin is i al o use he maximum
a ea o he di ac ion g a ing and o ha e he maximum amoun o ligh a he ou pu sli o
110 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Table 3.2: Compa ison o he echnical da a shee alues wi h he expe imen al da a ob ained a ou lab o he 24
selec ed LEDs.
LED
code S uc u e
V(V) I(mA) V(V) I(mA) V(V) I(mA)
L1 355 ͲͲ3.60 25 3.70 34.0 0.3 56 Ͳ
L2 370 376 11 3.90 10 3.50 30.5 0.3 23 AlGaN
L3 385 383 11 3.50 20 3.55 47.0 0.3 35 InGaN
L4 400 395 12 3.70 20 3.50 18.5 0.4 26 InGaN
L5 415 412 14 3.70 30 3.35 24.0 0.3 21 InGaN
L6 470 470 31 3.20 30 3.40 18.0 0.4 20 InGaN
L7 510 501 23 3.40 20 3.25 18.0 0.5 25 InGaN
L8 525 524 38 3.20 20 3.00 37.0 0.3 33 InGaN
L9 565 562 23 2.00 20 3.50 18.0 0.5 34 GaP
L10 596 593 15 2.10 20 2.00 14.0 0.3 25 AlGaInP
L11 625 641 16 2.20 20 2.45 35.0 0.5 41 AlGaInP
L12 660 653 21 1.90 20 2.05 32.0 0.5 40 GaAlAs
L13 670 672 25 1.80 20 1.80 22.0 0.2 31 GaAlAs/GaAlAs
L14 680 683 21 1.90 20 2.20 47.0 0.3 33 GaAlAs
L15 720 721 24 2.00 50 1.80 34.0 0.2 37 AlGaAs/AlGaAs
L16 760 755 25 1.20 20 1.65 26.0 0.3 57 AlGaAs/AlGaAs
L17 780 772 27 1.70 50 2.00 43.0 0.3 33 AlGaAs/AlGaAs
L18 800 795 30 1.80 50 1.65 66.0 0.3 67 AlGaAs
L19 820 819 30 1.60 100 1.55 42.5 0.1 43 AlGaAs
L20 840 827 31 1.60 100 1.60 47.5 0.4 74 AlGaAs
L21 870 859 49 1.50 100 1.45 58.5 0.1 49 AlGaAs
L22 910 914 57 1.40 100 1.40 47.0 0.2 44 AlGaAs
L23 950 941 44 1.40 100 1.35 80.0 0.1 100 AlGaAs/GaAs
L24 985 982 43 1.25 100 1.25 54.5 0.1 63 GaAs
Da ashee 
peak
wa eleng h
(nm)
Expe imen al
peak
wa eleng h
(nm)
FWHM(exp.)
(nm)
Da ashee DCbias Expe imen alDCbias Expe imen alACampli ude
o he ) is c ucial [74]. To iden i y his egion we measu ed he IV cu e o each LED by
in oducing ol age o i and measu ing (in se ies) he cu en ha c ossed.
In o de o au oma e he analysis, a p og am was de eloped in he isual pla o m
LabVIEW. The sou ce-mul ime e used o his pu pose was a Kei hley 2420. Fig. 3.19
shows he IV cu es o ou ep esen a i e LEDs. The ange o ope a ion is indica ed
as well as hei expe imen al di ec cu en (DC) ope a ing poin (chosen o be in he
middle o he expe imen al quasi linea ange). Each LED is supplied wi h a sinusoidal
ol age. I oscilla es in i s linea ange, he e o e he ope a ing poin is he DC bias and
he ampli ude o he sine wa e is deﬁned by he ex ension o he linea ange.
–Peak wa eleng h and spec al bandwid h: To minimize he measu emen e o in
ou equipmen we need o de e mine e y well he peak wa eleng h (λpeak) o emission
and o selec LEDs wi h na ow band wid h. Fig. 3.20 shows he spec a o wo
LEDs measu ed unde 25 oC p esen ing a la ge di e ence in he band wid h. The
ﬁgu e illus a es as well ha we ound some di e ences be ween he measu ed peak
wa eleng hs and he ones p o ided by he manu ac u e . We ha e disca ded LEDs wi h

3.4. Ve y as spec al esponse equipmen 111
Ϭ
ϮϬ
ϰϬ
ϲϬ
ϴϬ
ϭϬ ϭϱ ϮϬ Ϯϱ
ƵƌƌĞŶƚ/;ŵͿ
sŽůƚĂŐĞs;sͿ
ϲϳϬŶŵ
ϱϵϲŶŵ
ϳϲϬŶŵ
ϱϲϱŶŵ
ǆƉKƉĞƌĂƚŝŶŐWŽŝŶƚ
Figu e 3.19: Expe imen al IV cu e and DC bias poin o 4 ep esen a i e LEDs. Black lines indica e he AC
ampli ude.
ull wid h a hal maximum (FWHM) g ea e han 40 nm, in addi ion i is impo an o
know he exac peak wa eleng h, especially o LEDs illumina ing in he wa eleng h
ange a he ﬂanges o he SR cu e, o p e en la ge e o s [74].
The peak wa eleng hs we e de e mined using an Ocean’s Op ics USB2000+
spec ome e and supplying he LEDs wi h DC ol age using an Agilen N5771A. The
cu en a e sing he LED was measu ed connec ing in se ies a Fluke 287 mul ime e.
Since he sensi i i y o he men ioned spec ome e is limi ed om 360 nm o 1010 nm,
we expe ienced ce ain es ic ions while measu ing he λpeak o some UV and IR
LEDs. In addi ion, he λpeak and he FWHM we e ound o be independen om he
cu en a which he LED wo ks unde ou ope a ion condi ions. Howe e , he emission
o pho ons is p opo ional o he LEDs supply cu en [27].
The a ia ion among he spec a o LEDs o he same model was also measu ed,
obse ing a small de ia ion be ween he peak wa eleng hs (less han 2 nm). Since
hese esul s we e no signiﬁcan we con inued e alua ing one LED pe model.
Fig. 3.21 p esen s he indi idual spec a o he wen y- h ee selec ed LEDs o he
VFSR measu emen sys em. L1 a 355 nm canno be measu ed wi h ou spec ome e,
in his case we use he da a o he LED manu ac u e . The spec al i adiance alues
112 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
we e ob ained wi h LEDs ope a ing nea o he ecommended wo king poin o he
p o ide .
ϬϬϬ
ϬϬϮ
ϬϬϰ
ϬϬϲ
Ϭ
Ϯ
ϰ
ϲ
ϱϱϬ ϲϬϬ ϲϱϬ ϳϬϬ ϳϱϬ ϴϬϬ ϴϱϬ ϵϬϬ
>ƐƐƉĞĐƚƌĂů/ƌƌĂĚŝĂŶĐĞ; ŵϮŶŵͿ
>ƐƐƉĞĐƚƌĂůŝƌƌĂĚŝĂŶĐĞ; ŵϮŶŵͿ
ĂǀĞůĞŶŐƚŚʄ ;ŶŵͿ
>ϱϵϲŶŵΛϮϱŵ
>ϳϬϬŶŵΛϮϱŵ
ʄƉĞĂŬсϱϵϯŶŵ
ʄƉĞĂŬсϳϬϲŶŵ
& ,DсϲϲŶŵ
& ,DсϭϱŶŵ
Figu e 3.20: Peak wa eleng h (λpeak) and FWHM o a LED wi h na ow band wid h (22 nm, blue dashed cu e)
and o a LED wi h wide band wid h (66 nm, ed do ed cu e).
ϬϬϬ
ϬϬϰ
ϬϬϴ
ϬϭϮ
Ϭϭϲ
ϬϮϬ
ϬϮϰ
ϬϮϴ
Ϭ
Ϯ
ϰ
ϲ
ϴ
ϭϬ
ϭϮ
ϭϰ
ϯϱϬ ϰϬϬ ϰϱϬ ϱϬϬ ϱϱϬ ϲϬϬ ϲϱϬ ϳϬϬ ϳϱϬ ϴϬϬ ϴϱϬ ϵϬϬ ϵϱϬ ϭϬϬϬ
>ϵƐƉĞĐƚƌĂůŝƌƌĂĚŝĂŶĐĞ; ŵϮŶŵͿ
^ƉĞĐƚƌĂůŝƌƌĂĚŝĂŶĐĞ; ŵϮŶŵͿ
ĂǀĞůĞŐŚƚλ
λλ
λ;ŶŵͿ
>ϯ
>ϳ
>ϰ
>Ϯ
>ϱ
>ϲ >ϴ
>ϭϭ
>ϵ
>ϭϯ
>ϭϬ
>ϭϰ
>ϭϱ
>ϭϲ>ϭϳ
>ϭϴ
>ϭϵ
>ϮϬ
>Ϯϭ
>ϮϮ >Ϯϯ
>Ϯϰ
>ϭϮ
Figu e 3.21: Expe imen al spec al i adiance o 23 selec ed LEDs in he ange 370 nm - 1000 nm.
3.4. Ve y as spec al esponse equipmen 113
3.4.2 Sinusoidal gene a o s
In o de o educe signiﬁcan ly he measu emen ime, in he VFSR sys em all LEDs
wo k simul aneously and, o iden i y hem, hei ligh is modula ed a di e en equencies.
La e , he cu en gene a ed by each LED in he sola cell is de e mined by a FFT o he o al
gene a ed cu en .
Nowadays, we use eigh een/ wen y- ou sine-wa e gene a o s o SJ/TJ sola cell
measu emen s. The sine-wa e gene a o s exi simul aneously 24 indi idual ol age wa es o
±4.5 V o ampli ude. They p oduce an indi idually op imized wa e o each LED ( equency,
DC bias and AC ampli ude) acco ding o hei co esponding IV cu e. This illumina ion
gene a es sinusoidal cu en in he sola cell.
Conce ning he exci a ion equencies o hese signals, hey we e chosen o sweep be ween
100 Hz and 200 Hz wi h a s ep wid h o 4 Hz (a oiding mul iples o equencies o he LEDs
and o he 50 Hz equency o he elec ici y g id). The selec ion o he equency applied o
each LED is impo an o each a p ope equipmen ope a ion. The o e lap o he ha monics
wi h he main cu en peaks mus be a oided.
3.4.3 Fas Fou ie ans o m concep
The undamen al ool used in he VFSR equipmen is he FFT. This is widely u ilized
in digi al signal p ocessing (DSP). When signals a e exp essed in ime-domain some
in o ma ion such as equency and ampli ude a e coded. This da a becomes e iden
in equency-domain. Analy ically, Fou ie analysis p o ides he connec ion be ween
ime-domain and equency-domain. Using he Fou ie T ans o m a ime dependen pe iodic
unc ion ( )can be exp essed as he sum o di e en sinusoidal unc ions wi h di e en
equencies wn=(n+1)·w0(see Fig. 3.22). Fo n=0 we say ha i is he undamen al
equency. While, o n=1,2,3,4··· we say ha i is he n h ha monic.
Figu e 3.22: Decomposi ion o a pe iodic signal in i s di e en ha monics.
114 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Fas Fou ie ans o ma ion is a me hod ha allows sa ing calcula ions o ﬁnd he Fou ie
ans o m o a sampled signal. We can say ha o a sinusoidal wa e in he ime-domain he
FFT is a del a unc ion placed in he equency-domain o his signal (see Fig. 3.23). I has
no ha monics, jus he undamen al componen .
Figu e 3.23: Sine wa e in he ime-domain (le ) and, a e FFT analysis, sine wa e in he equency-domain ( igh ).
The i ual pla o m LabVIEW has implemen ed a ool o FFT calcula ion, using
di e en algo i hms. The FFT ool allows us o de e mine he spec um o he measu ed
pe iodical cu en and display he esul s in e ms o peak ampli ude. This means ha , a sine
one o ampli ude Ayields a spec al alue (magni ude) o Aa he sine one equency.
3.4.4 Measu emen p ocedu e o he e y as spec al esponse
equipmen
The VFSR equipmen allows he measu emen o MCs, MMs o ull size modules. In
he case o MCs, we es ablish he elec ical con ac wi h he sola cells by means o he
sample holde and i s swi ch, bo h p esen ed in sec ion 3.2. The e minals o his sample
holde a e connec ed o a digi al mul ime e o sampling. As o MMs, we ab ica ed special
es modules whe e e e y cell is connec ed indi idually wi h a side buss. This enables o
pe o m he measu emen s connec ing each cell di ec ly o connec ing he ex emes o he
mini module, as is he usual way o elec ically connec a module (see Fig. 3.24). In his las
case, he side buss is no solde ed as usual o p e en damaging he sola cells. The used buss
has a conduc ing adhesi e ha can be pas ed on o he sola cells’ back con ac wi hou losing
conduc i i y. The illumina ion is done placing he op ical coupling elemen di ec ly abo e
he espec i e sola cell illumina ing a small a ea (0.5 mm o diame e ). Simul aneously, he
e e ence pho odiode is li . We use a as and sensi i e cu en me e, an Agilen 34410A, o
di ec ly measu e he gene a ed cu en in bo h de ices (Icell( )and I e ( )). We use shielded
3.4. Ve y as spec al esponse equipmen 115
cables in he connec ions o minimize he noise. The nex s eps consis in p ocessing his da a
and a e explained in he ollowing sec ion.
Figu e 3.24: MM wi h e e y cell connec ed indi idually wi h a conduc ing adhesi e side buss.
To measu e he gene a ed cu en p ope ly, one has o ake in accoun ha o analyse an
analogue ( ime con inuous) signal i is necessa y o digi alise and sample i . When his is done,
a phenomenon known as aliasing can appea . This e ec causes di e en con inuous signals
o become indis inguishable once sampled. To a oid i , he Nyquis heo em es ablishes ha
he sampling a e (numbe o samples (S) aken by uni o ime) mus be a leas he double
o he equency o he sampled signal [80]. The equencies a which he LEDs a e d i en
a e be ween 100 Hz and 200 Hz. This means ha acco ding o ha heo em, he sampling
a e mus be a leas 400 S/s. In ou case, he sample equency a which he Agilen 34410A
wo ks is 1000 S/s, aking 5000 measu emen s (samples).
The schema ic diag am o he ope a ion o he whole sys em is shown in Fig. 3.25.
3.4.5 So wa e de eloped o he e y as spec al esponse
equipmen
As men ioned, we ha e implemen ed he VFSR p og am using he pla o m LabVIEW.
Fo his pu pose, we use s anda d commands o p og ammable ins umen s (SCPI)
ins uc ions in o de o con ol he digi al mul ime e. We measu e ol age in he on and

116 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
Figu e 3.25: Diag am o he VFSR measu emen sys em.
ea e minals, aking o each one 5000 samples (S) a a a e o 1000 S/s. The ansduc ion
o ol age o cu en is done digi ally knowing he alue o a esis ance placed pa allel o he
sola cell o pho odiodes.
I we a e doing a calib a ion o he equipmen , a calib a ed pho odiode is loca ed in he
place o he sola cell unde es . The e e ence pho odiode and calib a ed pho odiode cu en s
(Ical( )and I e ( )) a e measu ed as explained in he p e ious sec ion. Then, he FFT analysis
will be pe o med o e bo h cu en signals (ob aining equency-domain signals Ical(ν)and
I e (ν)). Subsequen ly, as he exci a ion equencies o he LEDs a e known, we can assign
a cu en alue o each wa eleng h (Ical (λ)and I e (λ)). Nex , he F(λ) ac o will be
calcula ed using Eq. 3.6. Finally, he F(λ) ac o will be sa ed in a . x ﬁle, oge he wi h he
I e (λ) alues du ing his calib a ion (I e cal (λ)), he da a shee EQE(λ) o bo h pho odiodes
and he spec um AM1.5(λ) o he gi en wa eleng hs. This ﬁle is used as inpu ﬁle when
measu ing a sola cell o module.
In he case o he SR measu emen o a sola cell, he e e ence pho odiode and sola cell
cu en s (Icell( )and I e ( )) a e measu ed in he ime-domain as explained in he p e ious
sec ion, esul ing in Fig. 3.26. Then, wi h he FFT analysis we ob ain he equency-domain
cu en signals (Icell(ν)and I e (ν)) as p esen ed in Fig. 3.27. In he ﬁgu e i is shown ha he
signal o noise a io is abou 2 – 4 o de s o magni ude which is su ﬁcien o de e mine he SR
o an indi idual sola cell. Apa om he peaks co esponding o he LEDs, peaks esul ing
om he noise p oduced by he elec ici y g id a e indica ed.
Once he cu en is de e mined in he equency-domain ( esolu ion 0.2 Hz) we analyse he
peak by sea ching he maximum in ±1.6 Hz o he e e ence equency o each LED and we
in eg a e he gene a ed cu en in ±0.4 Hz om he maximum o include small de ia ions
3.4. Ve y as spec al esponse equipmen 117
ϴϬ
ϵϬ
ϭϬϬ
ϭϭϬ
ϭϮϬ
ϭϯϬ
ϬϬϬϭϬϮϬϯϬϰϬϱ
ƵƌƌĞŶƚĚĞŶƐŝƚǇ:;μ
μ
μ
μĐŵϮͿ
dŝŵĞƚ;ƐͿ
WĞƌŝŽĚсϮϱϬŵƐ
Figu e 3.26: Time dependen cu en densi y cu e p esen s epe i ion pe iod o 250 ms due o he selec ed
equencies wi h highes common di iso o 4.
ϭͲϬϱ
ϭͲϬϰ
ϭͲϬϯ
ϭͲϬϮ
ϭͲϬϭ
ϭнϬϬ
ϭнϬϭ
Ϭ ϱϬ ϭϬϬ ϭϱϬ ϮϬϬ ϮϱϬ
ƵƌƌĞŶƚĚĞŶƐŝƚǇ:;μ
μ
μ
μĐŵϮͿ
&ƌĞƋƵĞŶĐǇν
νν
ν;,ǌͿ
ůĞĐƚƌŝĐŐƌŝĚ
&ƵŶĚΘϭƐƚ
,ĂƌŵŽŶŝĐ
&ƵŶĚĨƌĞƋŽĨ
ϭϬ>Ɛ
&ƵŶĚĨƌĞƋŽĨ
ϲ>Ɛ
ůĞĐƚƌŝĐŐƌŝĚ
ϮŶĚΘϯƌĚ
,ĂŵŽŶŝĐƐ
EŽŝƐĞ
ůĞǀĞů
Figu e 3.27: Cu en densi y cu e in he equency-domain as esul ing om FFT analysis.
in equency o he gene a ed signal [81]. Subsequen ly, as he exci a ion equencies
o he LEDs a e known, we can assign a cu en alue o each wa eleng h (Icell(λ)and
I e (λ)). Nex , he p og am accesses o he inpu ﬁle which con ains he da a o he e e ence
pho odiode cu en de e mined du ing he las calib a ion (I e cal (λ)). A compa ison is
done be ween I e cal (λ)and I e (λ), he di e ence mus no exceed ±5%. O he wise, he
118 Chap e 3. Indus ial p oduc ion p ocess and basic equipmen se -ups o a-Si:H sola cells
p og am will be s opped, since he de ice needs calib a ion. I he ac ual cu en o he
e e ence pho odiode (I e (λ)) is wi hin he ole ance ange, he calcula ion o he EQE will
be pe o med using he EQE o he calib a ed pho odiode and he calib a ion ac o o he las
calib a ion ( h ough Eqs. 3.1 and 3.5). Addi ionally, i he EQE da a measu ed wi h he CSR
equipmen is a ailable, a compa ison o he esul s can be done. Finally, he Isc is calcula ed
ollowing Eq. 3.7 and he esul s a e sa ed in a . x ﬁle.
In Fig. 3.28 he compa ison o he EQE measu ed wi h he CSR and VFSR equipmen
is p esen ed. The ed measu emen poin s ep esen he a e age da a o en epe i i e
measu emen s a each wa eleng h, o he poin a 593 nm ( he one wi h highe s anda d
de ia ion) an e o ba (s anda d de ia ion) is indica ed.
ϬϬ
ϬϮ
Ϭϰ
Ϭϲ
Ϭϴ
ϭϬ
ϯϬϬ ϰϬϬ ϱϬϬ ϲϬϬ ϳϬϬ ϴϬϬ
ǆƚĞƌŶĂůƋƵĂŶƚƵŵĞĨĨŝĐŝĞŶĐǇY
ĂǀĞůĞŶŐƚŚλ
λλ
λ;ŶŵͿ
^ZƵƐŝŶŐŵŽŶŽĐŚƌŽŵĂƚŽƌ
^ZƵƐŝŶŐs&^Z
ϯϳϱŶŵͲϴϬϬŶŵ
:ƐĐ ŵŽŶŽĐсϭϮϯϳŵĐŵϮ
:ƐĐ s&^ZсϭϮϯϯŵĐŵϮ
ƌƌŽƌďĂƌƐ
Figu e 3.28: The blue cu e p esen s he EQE measu ed in a CSR equipmen wi h monoch oma o (5 nm wa eleng h
s ep). Red do s ( he poin a 593 nm has an e o ba indica ing i s s anda d de ia ion) ep esen he
a e age o en EQE measu emen s wi h he VFSR measu emen sys em. In his case, he di e ence
be ween he Jsc de e mined wi h he CSR equipmen and he VFSR is 0.26%.
We ha e ound ha he s anda d de ia ion in epe i i e measu emen s is less han 2% o
e e y wa eleng h. Fo mos o he poin s he de ia ion om he adi ional me hod is small, a
la ge de ia ion is ound o he LEDs a 501 nm and 562 nm wa eleng hs. The eason o he
la ge de ia ion a 562 nm mos p obably is due o he small in ensi y o he LED illumina ion
a ha wa eleng h which is unde in es iga ion, also he la ge de ia ion a 501 nm is unde
in es iga ion bu no eason has been iden iﬁed so a . As shown in he inse o Fig. 3.28, he
sho ci cui cu en calcula ed in he wa eleng h ange om 375 nm o 800 nm is e y simila
3.5. Measu emen s o illumina ed and da k cu en - ol age cu es 119
o bo h me hods wi h a de ia ion o less han 1%, and compa able o alues ound by o he
esea che s [75], [76].
3.5 Measu emen s o illumina ed and da k cu en - ol age
cu es
Wi h he measu emen o illumina ed and da k IV cu es we a e going o cha ac e ise
elec ically he sola cells and mini modules. Nex , we p esen he main elec ical pa ame e s
o be conside ed and he equipmen s and p ocedu es needed o ob ain hem.
3.5.1 Equipmen
– Sola simula o : I is ins alled in he op ical labo a o y. I simula es he sola ligh in
a 20 cm x 20 cm a ea speciﬁcally, i p o ides a wide beam o collima ed and uni o m
ligh wi h an i adiance almos like he sun. The sola simula o (SS) equipmen consis s
mainly in a 1300 W ex e nal elec ic powe sou ce, an a c lamp compounded by high
p essu e noble gases, an ellipsoid mi o a ound he lamp o collima ion, a ﬂa mi o o
di ec he ligh o he sample h ough a lens and an AM1.5 spec um ﬁl e . I p o ides
class AAA ( he highes p ecision) illumina ion o a 20 cm x 20 cm a ea. Since we
ha e a a iable powe supply by he ex e nal sou ce, we could egula e he i adiance
in ou de ice changing he powe , howe e , ha could change he spec um. The e o e,
he illumina ion le el is usually ﬁne adjus ed by he lamp posi ion in espec o he
ellipsoid, e en i his could a ec sligh ly he o e all uni o mi y. To measu e he IV
cu es unde STC we se he SS ou pu i adiance o 1000 W/m2 ollowing he s eps
desc ibed in sec ion 3.5.4. In addi ion, he i adiance le el is con olled e e y ime we
use he SS by measu ing he Isc wi h a e e ence sola cell. Wi h his equipmen we
measu e he illumina ed IV cu es o small samples as ou 1 cm2and4cm
2sola cells
and ou 10 x 10 cm2and20x20cm
2MMs.
– Kei hley 2400 sou ce me e/mul ime e: We use his sou ce o injec cu en o o apply
ol age o he samples in which we measu e IV cu es unde illumina ion o da k
condi ions. The maximum powe , ol age and cu en pa ame e s o his sou ce a e:
Pmax =22W,V
max = 200 V, Imax = 1 A. Consequen ly, i we wo k wi h he maximum

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