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IEEE JOURNAL OF PHOTOVOLTAICS 1
Insigh s in Pe o ski e Sola Cell Fab ica ion:
Un a eling he Hidden Challenges o Each Laye
1
2
Ve ena S ockhausen, Isabel Mesqui a, Lu´
ısa And ade, and Ad´
elio Mendes3
Abs ac —Pe o ski e sola cells (PSC) a e undoub edly he4
mos ac i e esea ch a ea in pho o ol aics a his momen .5
Ac ually, since 2009 his eme ging echnology passed om 3.8%6
o he p esen >22% o ene gy con e sion e iciency. Along wi h7
ha , a huge amoun o some imes con adic ing and incomple e8
in o ma ion abou how o p epa e and cha ac e ize PSC is9
p o ided, which makes i di icul o no ge los . This pape is10
mainly di ec ed owa d newcome s in his a ea, wi h he goal o11
gi e o ien a ion o PSC ab ica ion p o ocols ha a e quickly12
implemen able and ha lead o eliable and accep able e iciencies.13
The e o e, a s ep-by-s ep analysis o each laye is p o ided and,14
wi hin his scope, se e al ab ica ion echniques a e compa ed in15
e ms o e iciency op imiza ion. Fu he mo e, a new and e sa ile16
al e na i e o lase -assis ed sc ibing o subs a e pa e ning is17
p esen ed. Elec ochemical cha ac e iza ion o dummy cells as an18
easy and e sa ile ool o isola ed laye cha ac e iza ion is demon-19
s a ed o TiO2blocking laye s. A e op imiza ion o each laye ,20
PSC wi h an a e age e iciency o (14.8 ±1.0)% was ob ained.21
Index Te ms—Blocking laye , ab ica ion de ails, pe o mance,22
pe o ski e sola cells.23
I. INTRODUCTION24
GLOBAL ene gy consump ion is p ojec ed o aise by 48%25
om 2012 o 2040 [1], which makes he in ensi ica ion o 26
enewable ene gy implemen a ion una oidable. Among hem,27
sola ene gy p oduc ion has been he as es g owing sec o 28
wi h he bigges sha e in newly c ea ed jobs in he pas ew29
Manusc ip ecei ed Decembe 22, 2017; e ised Ap il 4, 2018; accep ed
Ap il 6, 2018. This wo k was suppo ed in pa by he Eu opean Union’s Ho i-
Q1
zon 2020 P og amme, h ough a FET Open esea ch and inno a ion ac ion unde
G an 687008, in pa by he P ojec POCI-01-0145-FEDER-006939 (LEP-
ABE - Labo a o y o P ocess Enginee ing, En i onmen , Bio echnology and
Ene gy – UID/EQU/00511/2013), unded by he Eu opean Regional De elop-
men Fund, h ough COMPETE2020 – P og ama Ope acional Compe i i idade
e In e nacionalizac¸˜
ao (POCI) and by na ionals unds h ough FCT (Fundac¸˜
ao
pa a a Ciˆ
encia e a Tecnologia), and in pa by NORTE-01-0145-FEDER-000005
– LEPABE-2-ECO-INNOVATION, suppo ed by No h Po ugal Regional
Ope a ional P og amme (No e 2020), unde he Po ugal 2020 Pa ne ship
Ag eemen , h ough he Eu opean Regional De elopmen Fund. The wo k o
V. S ockhausen was suppo ed by he Eu opean Commission h ough he Se -
en h F amewo k P og am, he Speci ic P og am “Ideas” o he Eu opean Re-
sea ch Council o esea ch and echnological de elopmen as pa o an Ad-
anced G an unde G an 321315 (BI-DSC). The wo k o I. Mesqui a was
suppo ed by he FCT o he Ph.D. ellow ( e .: PD/PB/105985/2014). The
wo k o L. And ade was suppo ed by he FCT (IF/01331/2015). (Co espond-
ing au ho : Ad´
elio Mendes.)
The au ho s a e wi h he Faculdade de Engenha ia, Uni e sidade do
Po o, Po o 4200-465, Po ugal (e-mail:,[email p o ec ed]; [email p o ec ed];
[email p o ec ed]; [email p o ec ed]).
Colo e sions o one o mo e o he igu es in his pape a e a ailable online
a h p://ieeexplo e.ieee.o g.
Digi al Objec Iden i ie 10.1109/JPHOTOV.2018.2826055
yea s [2], [3]. Besides he ma u e silicon echnology, ad anced 30
coppe indium gallium selenide and CdTe sola cells la ely en e - 31
ing he ma ke , pe o ski e sola cells (PSC) ha e been ea ning 32
a lo o a en ion due o hei s iking pe o mance e olu ion 33
since 2012 [4]. Since hen, PSC e iciencies ha e been amp- 34
ing up quickly, eaching ce i ied eco d e iciencies o 22.7% 35
o labo a o y de ices [5]; mo e ecen ly, in Feb ua y 2018, 36
G ¨
a zel epo ed 23.3% a ABXPV con e ence, Rennes [6]. De- 37
spi e he as p og ess in ab ica ing PSC wi h high e iciency, 38
s abili y has been a limi ing ac o so a . Thus, a emp ing o 39
add ess e iciency and s abili y, a huge a ie y o o mula ions 40
and cell a chi ec u es has been published. I includes plana de- 41
ices using an in e ed p-i-n a chi ec u e and PSC employing 42
a mesopo ous s uc u e ha can ei he ac i ely pa icipa e in 43
he elec on ans e (ac i e mesopo ous laye ) o me ely se e 44
as sca old s uc u e (passi e mesopo ous laye ). Wi hin pe - 45
o ski es, chemical enginee ing has o igina ed a huge quan i y 46
o mixed s uc u es, employing mixed ca ions and anions. Many 47
labo a o ies ha e been deciding o di ec esea ch e o s owa d 48
his “shoo ing s a ,” bu no all o hem we e capable o ep o- 49
duce he ou s anding esul s published in he li e a u e. E en 50
wi hou ega ding long- e m s abili y, e iciencies o en emain 51
below expec a ions because usually, c ucial echnical de ails e- 52
main ba ely explained o e en unmen ioned in esea ch a icles. 53
Thus, li le ab ica ion e o s wi hin each laye o he PSC will 54
sum up and lead o an o e all e iciency d op. The e o e, me ely 55
conside ing e iciencies o en i e de ices makes ep oduc ion o 56
published esul s a ha d ask. 57
In his pape , a s ep-by-s ep analysis o he echnical p oblems 58
o each laye is p o ided and a possible impac o hei modi i- 59
ca ion on he cell pe o mance will be assessed. In he end, he 60
cha ac e iza ion o he en i e de ice is discussed. As eco d e i- 61
ciency PSC’s gene ally possess a cell a chi ec u e wi h an ac i e 62
mesopo ous laye [7], ocus will lie on his PSC s uc u e. Fo a 63
deepe discussion abou al e na i e cell a chi ec u es, in e es ed 64
eade s a e e e ed o he in o ma i e e iew o Salim e al.[8], 65
Mesqui a e al. [9] o he ecen book w i en by Pa k e al. [10]. 66
II. MATERIALS AND METHODS 67
Fig. 1 shows a schema ic ep esen a ion o he PSC. On op o 68
a anspa en conduc i e oxide (TCO) subs a e ha was sc ibed 69
in o de o impede sho ci cui ing (g ey line), a dense TiO2laye 70
is deposi ed, ollowed by a mesopo ous laye . The adjacen pe - 71
o ski e laye pa ially in il a es in o he mesopo ous s uc u e 72
and o ms a capping laye . I is ollowed by a laye o hole 73
2156-3381 © 2018 IEEE. Pe sonal use is pe mi ed, bu epublica ion/ edis ibu ion equi es IEEE pe mission.
See h p://www.ieee.o g/publica ions s anda ds/publica ions/ igh s/index.h ml o mo e in o ma ion.
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Fig. 1. Schema ic ep esen a ion o a mesoscopic PSC in c oss sec ion (le ) and op iew ( igh ).
anspo ma e ial (HTM); inally, a nanome ic me allic laye 74
se es as a cu en collec o .75
In he ollowing, laye ab ica ion de ails and, when applica-76
ble, al e na i e ab ica ion me hods a e p esen ed. Fu he mo e,77
i will be discussed wha equipmen is equi ed o cell ab ica-78
ion and which equipmen acquisi ion can be pos poned, hanks79
o al e na i e ab ica ion p o ocols.80
A. Subs a e P epa a ion81
Fluo ide-doped in oxide (FTO) subs a es (2.2 mm hick-82
ness, TEC7, Sola onix) we e pa e ned ia Ve saLase (VLS83
2.30, Uni e sal Lase Sys ems, USA) o c ea e wo sepa a e84
cha ge collec ion a eas on he FTO subs a e—me hod (A). As85
an al e na i e o lase sc ibing, which equi es he a ailabili y86
o such an equipmen , an elec ochemical educ i e ea men 87
can be pe o med o emo e selec i ely he conduc i e laye —88
me hod (B). Keep in o conside a ion ha he chemicals used89
o ha pu pose a e highly co osi e, which equi es adequa e90
p o ec ion and ca e. In o de o do so, he subs a e a ea o TCO91
emo al was delimi ed by Kap on ape and exposed oa3M92
HCl solu ion. A cons an po en ial o −2.4 V was applied un il93
ca hodic cu en dec ease s a ed o la en. Meanwhile, he in94
oxide o he FTO u ned g ey and s a ed o peel o ; samples95
we e emo ed om he solu ion and insed wi h wa e . Wi h96
a co on swab dipped in a dilu ed ni ic acid solu ion (0.5 M),97
emaining in esidues we e cleaned o . Then, Kap on ape was98
emo ed and samples we e abundan ly insed wi h wa e .99
In a nex s ep, samples we e mechanically cleaned, using a100
oo hb ush and a 10 % Hellmanex III (Hellma GmbH, Ge many)101
solu ion. Subsequen ly, subs a es we e abundan ly insed wi h102
wa e and sonica ed in e hanolic KOH solu ion o 5 min. The103
subs a es we e again abundan ly insed wi h wa e and son-104
ica ed in wa e o 5 min, be o e being insed wi h ace one105
and d ied in ni ogen lux. P io o blocking laye deposi ion,106
subs a es we e addi ionally cleaned o 20 min by an ozone107
cleane (UVO-Cleane , Jeligh Company Inc., USA). Al e na-108
i ely o an ozone cleane , plasma ea men can be applied [11],109
among o he e icien me hods.110
B. Elec on Blocking (BL) and Mesopo ous Laye P epa a ion111
TiO2blocking laye was deposi ed by wo di e en me hods.112
Me hod (A) was done by spincoa ing o a comme cial solu ion113
(Ti-Nanoxide BL/SC, Sola onix, Swi ze land) (5000 /min, 30 s, 114
2000 ( /min)/s). Be o e ilm deposi ion, he a ea o pho oan- 115
ode con ac was p o ec ed by adhesi e s ip (Sco ch Magic 116
Tape, 3M) and he ilms we e subsequen ly calcined a 550 °C117
o 1 h, unde applica ion o a s epwise empe a u e inc ease 118
o 100 °C each 10 min. Me hod (B) employed sp ay py ol- 119
ysis o a p ecu so solu ion con aining 0.56 M ace ylace one 120
(Sigma-Ald ich, 99.6%) and 0.18 M i anium diisop opoxide 121
bis(ace ylace ona e) (Sigma-Ald ich, 75 w .% in isop opanol) 122
in 7 mL isop opanol (Sigma-Ald ich, anhyd ous, 99.5%) ha 123
was su icien o 64 samples. He e, subs a es we e p ehea ed 124
a 450 °C and he pho oanode a ea was p o ec ed wi h a glass 125
s ipe be o e applying he sp ay ia an a omize , using ei he ai 126
o oxygen as ca ie gas. A e wa d, samples we e le o 45 min 127
mo e a ha empe a u e. Fo applica ion o mesopo ous TiO2,128
a comme cial pas e (gene ally 30-NR-D, Dyesol, Aus alia, un- 129
less o he wise s a ed) was dilu ed in pu e e hanol (1:6 w/w) and 130
applied on he subs a es ia spincoa ing (5000 /min, 10 s, 2000 131
( /min)/s). P io o deposi ion, pho oanode con ac had been 132
p o ec ed by adhesi e s ipes. Samples we e hen immedia ely 133
ans e ed on a hea pla e a 100 °C o p ed ying be o e being 134
calcined in a u nace a 500 °C o 30 min. Subsequen ly, sam- 135
ples we e ans e ed o oxygen- ee and d y condi ions (glo e 136
box) be o e allowing o cool below 100 °C. 137
C. Pe o ski e Ac i e Laye P epa a ion 138
The pe o ski e p ecu so solu ion was p epa ed acco ding o 139
he ollowing condi ions published by Saliba e al. [12]: 1.1 M 140
PbI2(Sigma-Ald ich, 99.999% ace me al basis), 0.2 M PbB 2141
(Sigma-Ald ich, 99.999% ace me al basis), 0.2 M me hylam- 142
monium b omide (Dyesol), and 1.0 M o mamidinium iodide 143
(Dyesol) we e dissol ed in 1 mL o a DMF/DMSO mix u e (8:2 144
/ , bo h Sigma-Ald ich, 99.8 and ࣙ99.9%, espec i ely). F om Q2145
his solu ion, 0.95 mL we e added o 0.05 mL o a 1.5 M CsI 146
s ock solu ion in DMSO (Sigma-Ald ich, 99.999% ace me als 147
basis). This inal solu ion was deposi ed on he subs a es by 148
applying a wo-s ep spincoa ing p og am (s ep 1: 1000 /min, 149
10 s, 200 ( /min)/s, s ep 2: 6000 /min, 30 s, 2000 ( /min)/s). 150
A e 25 s, 100 µL chlo obenzene was pou ed on o he spinning 151
subs a e, a p ocedu e which is known as an isol en echnique. 152
Ca e ul adjus men o d ipping speed and ip- o-sample dis ance 153
had o be ained o ab ica e samples in a ep oducible manne . 154
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STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 3
Samples appea ed b own immedia ely a e spincoa ing and155
we e subsequen ly sin e ed a 100 °C o 40 min be o e be-156
ing allowed o cool down. A e each deposi ion, he in e io o 157
he spin coa e was cleaned wi h a clo h o emo e he condensed158
chemicals.159
D. Hole Conduc ing Laye and Cu en Collec o 160
Two di e en hole conduc o s we e es ed: me hod161
(A) spi o-OMeTAD solu ion con ained 75 mM spi o-162
OMeTAD (Chembo un, 99.7% sublimed g ade), 0.24 M163
4- e -bu ylpy idine (Sigma-Ald ich, 96 %), 41 mM li hium164
bis i luo ome hanesul onimida e (Li-TFSI, Ac os O ganics)165
ha was ob ained om a 1.8 M s ock solu ion in ace oni ile166
(Sigma-Ald ich, 99.999 % elec onic g ade), and 27 mM FK167
209 Co(III) TFSI sal (Dyesol) ha was ob ained om a 0.27168
M s ock solu ion in ace oni ile. The solu ion was deposi ed169
ia spincoa ing (4000 /min, 20 s, 2000 ( /min)/s). Me hod (B):170
P3HT solu ion was ab ica ed om 15 mg/mL P3HT (Chem-171
bo un China), 23 mM 4- e -bu ylpy idine, and 0.7 mM Li-172
TFSI. I was deposi ed by spincoa ing (3000 /min, 30 s, 2000173
( /min)/s). A e wa d, pho oanode con ac s co e ed wi h pe -174
o ski e and hole conduc o we e mechanically cleaned wi h175
a scalpel and co on swabs dipped in ace oni ile. Finally, a176
60-nm- hick gold laye as cu en collec o was applied h ough177
a s ainless s eel mask by wo di e en me hods: 1) by he -178
mal e apo a ion on a Vapo S a ion 4 (Ox o d Vacuum Science,179
U.K.), applying a deposi ion a e o 0.01 nm/s o he i s 4 nm,180
ollowed by 0.1 nm/s o he emaining hickness; and 2) by181
spu e ing using a Leica EM ACE200 (Leica Mic osys ems,182
Ge many) and applying a cu en o 60 mA and a deposi ion183
du a ion o 360 s. A mask o adhesi e black ape wi h an ac i e184
a ea o 0.2 cm2was applied on he glass side o he cell p io o185
pho oelec ochemical cha ac e iza ion.186
E. Dummy Cell P epa a ion187
The p epa a ion was analogous o PSC, howe e , applying188
me ely blocking laye , hole anspo laye , and gold laye by189
he mal e apo a ion.190
F. Cha ac e iza ion191
Fo pho oelec ochemical cha ac e iza ion, a 150-W sola 192
simula o O iel class A sola simula o , (Newpo , USA) using193
a 1.5 ai mass il e (Newpo , USA) was employed. The e ec-194
i e i adia ion in ensi y was measu ed wi h a single c ys al Si195
pho odiode (Newpo , USA). I–V cu es we e eco ded wi h a196
po en ios a (Zennium, Zahne -Elek ik GmbH, Ge many) a a197
scan a e o 10 mV/s, sweeping om open-ci cui o sho -ci cui 198
po en ial (backwa d scan). Be o e each measu emen , he open-199
ci cui po en ial VOC was allowed o s abilize unde i adia ion,200
which gene ally ook less han a minu e. Ca e was aken ha 201
s a ing po en ials we e chosen o be no mo e han 20 mV su-202
pe io o VOC in o de o p o ec he cell [13]. A leas h ee203
cells o each ype we e es ed o a e aged e iciencies. SEM204
images we e eco ded wi h a Quan a 400 FEG (FEI, USA) a 205
he CEMUP ma e ials analysis cen e o he Uni e si y o Po o.206
III. RESULTS AND DISCUSSION 207
FTO on glass is usually employed as anspa en conduc i e 208
subs a e, due o i s s abili y owa d ele a ed empe a u es. Se - 209
e al shee esis ances a e a ailable on he ma ke and gene ally 210
FTO wi h a shee esis ance o 7–10 Ω/sq is chosen, as i is a 211
good comp omise in e ms o conduc i i y e sus anspa ency. 212
Tho ough subs a e cleaning is an essen ial s ep and o en unde - 213
a ed; howe e , i plays a pi o al ole as he pe o ski e sola cell 214
is cons i u ed by se e al laye s ha a e all wi hin he nanome e 215
scale and any con amina ion o he subs a e will hus lead o 216
ilm de ec s ha lowe o e all cell e iciency. The sc ibing o he 217
subs a e locally emo es he TCO laye and impedes he elec- 218
ic sho ci cui h ough he subs a e o he pho oanode and he 219
ca hode. I is o en ob ained by lase abla ion o he conduc i e 220
laye bu no e e y labo a o y possesses a sui able equipmen . 221
A low-cos al e na i e is chemical e ching o he conduc i e 222
laye [14], hough i leads o a he inhomogeneous FTO e- 223
mo al. A e y e sa ile and inno a i e, ye low-cos s a egy is 224
he elec ochemical educ i e ea men o he FTO, which leads 225
o a clean and comple e FTO emo al on he exposed a eas [15]. 226
The compac n- ype i anium dioxide ilm ac s as an elec on- 227
selec i e laye and hus p e en s he ecombina ion o exci ons 228
a he TCO su ace. I his laye is absen , no dense enough 229
o possesses pinholes, he ab ica ed cells will show dec eased 230
e iciencies due o ecombina ion e en s. A he same ime, i 231
has o be hin enough o p o ide e icien elec on anspo by 232
minimizing cha ge accumula ion and he e o e ecombina ion. 233
The so-called blocking laye can be ab ica ed by se e al ways, 234
including, bu no es ic ing o chemical ba h deposi ion [16], 235
spincoa ing [4], [17], sp ay py olysis [12], [18], [19], spu e ing 236
[20], [21], elec on-beam e apo a ion [22], and a omic laye de- 237
posi ion [23], [24]. We decided o compa e TiO2blocking laye s 238
ob ained by sp ay py olysis and spincoa ing o a comme cial so- 239
lu ion (Ti-Nanoxide BL/SC, Sola onix, Swi ze land). An easy 240
means o check i he elec ochemical beha io o he blocking 241
laye ollows a diode-like beha io is o ab ica e dummy cells. 242
Such cells a e composed o he compac TiO2laye on op o he 243
TCO subs a e, a hole- anspo laye like spi o-OMeTAD and 244
a gold con ac , hus simila o a pe o ski e cell, howe e wi h- 245
ou any pho oac i e laye . Cyclic ol amme y (CV) has been 246
pe o med on dummy cells wi h di e en BL and he esul s a e 247
shown in Fig. 2(a). In he case o a BL made by sp ay py olysis, 248
he CV shows ze o anodic cu en and a s eep inc ease o he 249
ca hodic cu en which sugges s a dense and pinhole- ee laye 250
wi h high elec onic conduc i i y. In case o he BL o med by 251
spin coa ing, he CV shows, in addi ion o he ca hodic cu en 252
inc ease a lowe po en ial, a sluggish ca hodic and anodic cu - 253
en e olu ion ac oss he en i e po en ial window, which is an 254
indica ion o pinholes. Fo compa ison, he CV o a dummy 255
cell wi hou any blocking laye demons a es a ypical ohmic 256
beha io , p o ing he absence o any blocking e ec a posi i e 257
po en ial. The PSC co esponding o he BL ab ica ion me hods 258
show I–V cu es ha unde line he ex emely impo an ole o 259
he blocking laye . The cell wi h he BL made by sp ay py oly- 260
sis shows bes e iciencies, whe eas ha made wi h spincoa ed 261
blocking laye pe o ms wo se. The cell wi hou any BL shows 262
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Fig. 2. (a) CV o dummy cells wi hou blocking laye (g ey diamonds), blocking laye made by spincoa ing ( ed ci cles) and by sp ay py olysis (black squa es).
(b) I–V cu es o PSC wi h a blocking laye made by sp ay py olysis (black squa es), spincoa ing o a comme cial solu ion ( ed ci cles) and wi hou any blocking
laye (g ey diamonds) a 0.95 sun.
Fig. 3. (a) Scanning elec on mic oscopy images ( op- iew) o a ba e TCO subs a e. (b) TiO2compac laye deposi ed by sp ay py olysis. (c) Spincoa ing o a
comme cial solu ion. Black ba s co espond o 2 µm.
TABLE I
EFFICIENCIES AND I–V CHARACTERISTICS OF PSC WITH COMPACT TIO2MADE BY SPRAY PYROLYSIS USING DIFFERENT CARRIER GASES
he lowes e iciencies ha , howe e , a e no ze o. The eason263
is ha he pe o ski e laye i sel is an elec on anspo e [17]264
as well as i is capable o anspo holes [25], [26]. This en-265
de s he TCO-pe o ski e in e ace in o a nonselec i e con ac 266
ha p omo es ecombina ion and he e o e leads o dec eased267
e iciencies.268
Images o he di e en blocking laye s eco ded by scanning269
elec on mic oscopy show some undamen al di e ences, see270
Fig. 3. The laye deposi ed by sp ay py olysis is a he hin and271
homogeneous, whe eas he laye deposi ed by spin coa ing is272
hicke and shows c acks, see Fig. 3(c) (uppe igh co ne ). I 273
can be concluded ha PSC wi h a BL ab ica ed by sp ay py-274
olysis show supe io e iciencies and he e o e, his ab ica ion275
me hod migh be ecommended. The in luence o he ca ie gas276
on cell e iciencies was u he es ed bu i came ou ha pu e277
oxygen did no imp o e cell e iciencies, see Table I. Due o 278
lack o deposi ion con ol, BL hickness may a y be ween 30 279
and 80 nm, as occasional SEM c oss sec ions showed. Howe e , 280
no co ela ed impac on PSC e iciency could be s a ed. 281
Mesopo ous i ania laye has been employed in dye-sensi ized 282
sola cells (DSSC), wi h he unc ion o inc ease he ac i e su - 283
ace a ea and anspo elec ons unde ligh exci a ion [27]. As 284
he ini ial pe o ski e sola cells we e hough as a con inui y o 285
DSSC, a mesopo ous i ania ilm also was applied he e, e en i 286
he ex inc ion coe icien o pe o ski es such as (CH3NH3)PbI3287
is abou en imes highe han ha o N719 dye [28]. As 288
a consequence, he necessi y o ac i e su ace inc ease is 289
u ned obsole e. Thus, PSC wi hou mesopo ous laye , so-called 290
plana de ices, ha e been de eloped, hough hei e iciencies 291
we e lagging behind hose employing a mesopo ous laye o 292
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STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 5
Fig. 4. I–V cu e o cells wi h a mesopo ous TiO2 laye made om 30NR-
D pas e (a e age pa icle size o 30 nm, black squa es) and om 18-NR-T
pas e (a e age pa icle size o 20 nm, ed ci cles) a 0.94 sun. Bo h pas es we e
pu chased om Dyesol L d.
a long ime [7]. Only ecen ly, he e iciency gap has become293
a he small, which is due o imp o ed in e ace enginee ing [7],294
[18], [29]. Beside highe e iciencies, PSC wi h a mesopo ous295
laye show educed e iciency de ia ion be ween o wa d and296
backwa d scan, a phenomenon desc ibed as hys e esis [19], [30],297
[31]. When Snai h e al. demons a ed ha e en wi h meso-298
po ous laye s o alumina, a ma e ial ha canno pa icipa e in299
elec on ans e due o band ene gy misma ch, high e iciencies300
o 15.9% could be ob ained [32], i was deduced ha he meso-301
po ous laye mainly ul ills a s uc u al ole o c ys al g ow h302
and geome y de e mina ion, e en i e icien elec on injec ion303
om he pe o ski e in o he TiO2mesopo ous laye was epo ed304
[33]. Howe e , la es esul s demons a e ha ionic mig a ion a 305
he pe o ski e/TiO2in e ace, which is esponsible o cha ge306
accumula ion and he e o e ecombina ion e en s, is educed o 307
e en supp essed in he p esence o he TiO2mesopo ous laye 308
[34]. As hys e esis also depends on ionic mig a ion [35]–[38],309
i s educ ion in he p esence o mesopo ous TiO2is he conse-310
quence. Pu ing all oge he , bes esul s ha e been achie ed so311
a using a hin TiO2mesopo ous laye and a pe o ski e cap-312
ping laye ha p e en s ecombina ion be ween TiO2and he313
hole anspo laye [33], [34].314
The e exis se e al comme cial pas es wi h di e en sizes o 315
TiO2pa icles and he e o e, i was decided o compa e wo316
di e en pa icle sizes, namely one possessing 20 nm and one317
wi h 30 nm a e age pa icle diame e . The same pas e dilu ion318
a io in pu e e hanol (1:6) as well as he same deposi ion and319
sin e ing condi ions we e applied. Fig. 4 shows ha bo h meso-320
po ous laye s lead o e y compa able cell e iciencies ha a e321
wi hin he e o scale. This poin s owa d a highe ole ance and322
owa d a mesopo ous laye a chi ec u e, as long as he pa icle323
size emains simila .324
Wi hin pe o ski e ma e ials, he e exis s a huge a ie y o 325
ecipes and deposi ion echniques, which a e well summa ized326
in he book by Pa k e al. [10] and in he e iew by Song e al.327
[39]. I migh be no an easy ask o decide o he sui able328
pe o ski e ype and ab ica ion p ocess. The name pe o ski e329
e e s o a c ys alline s uc u e o he ype ABX3, A and B be-330
ing ca ions and X an anion. The pe o ski e class sui able o 331
sola cells is an o ganic lead halide, wi h A being gene ally an 332
o ganic ca ion, B being he lead ion, and X being a halogen, 333
usually b omine, iodide, chlo ine, and mix u es he eo . Lead 334
subs i u ion by in and ge manium analogs leads o pe o ski es 335
wi h se e e s abili y p oblems [32], [40], [41] and he e o e will 336
no be add essed he e. Ou ocus was o de e mine a pe o ski e 337
o mula ion easy o implemen and ha esul s in ep oducible 338
pe o ski e laye s wi h enhanced s abili y. Many esul s ha e 339
been published wi h monoca ionic pe o ski es, howe e , wi h 340
some inhe en limi a ions ha a e b ie ly exposed he e: MAPbI3341
has been in ensi ely s udied [42] bu has some d awbacks such 342
as weak s abili y owa d mois u e [43], [44] and empe a u e 343
[45]. Fo mamidinium (FA) was p oposed as al e na i e ca ion; 344
howe e , i s pe o ski e analog FAPbI3c ys allizes in he pho- 345
oinac i e phase below 60 °C [46], such as he ino ganic ca ion 346
analog CsPbI3[47]. Whe eas se e al g oups obse ed imp o ed 347
s abili y o he pho oac i e phase upon using bina y mixed ca ion 348
pe o ski es [48]–[52], Saliba e al. decided o combine he h ee 349
ca ions in a pe o ski e and achie ed high e iciencies (>20%) 350
on a e y ep oducible basis [12]. 351
Se e al me hods exis o solu ion-p ocessed ilm ab ica ion, 352
he mos common being simple sp eading o he pe o ski e p e- 353
cu so solu ion on he subs a e, also known as one-s ep depo- 354
si ion. Howe e , ilms wi h poo su ace con ol and he e o e 355
huge e iciency a ia ions gene ally eme ge [42]. A mo e so- 356
phis ica ed app oach is he sequen ial s ep deposi ion, whe e 357
he me al halide is i s deposi ed and annealed be o e being 358
b ough in con ac wi h he ammonium sal as apo o in solu- 359
ion [42], [53]. Ne e heless, se e al d awbacks o his deposi- 360
ion me hod we e expe ienced in ou g oup, such as incomple e 361
con e sion o he me al halide o pa ial dissolu ion o he pe - 362
o ski e du ing he subsequen washing s ep. Fu he mo e, i is 363
mo e ime-consuming as i equi es wo sin e ing s eps. The 364
an isol en echnique was in oduced in 2014 by he g oup o 365
Seok [19] and since hen, i has been he me hod o choice o 366
subsequen ly published eco d e iciencies [7]. I is qui e simple 367
o implemen and equi es only one p ecu so solu ion, whe eas 368
he c ys alliza ion o he pe o ski e is ini ia ed by adding a so- 369
called an isol en . This an isol en is chosen no o dissol e he 370
pe o ski e on one side and o displace he sol en o he la e on 371
he o he side. The main d awback o his deposi ion me hod is 372
i s a isanal aspec , equi ing a ce ain deg ee o aining be o e 373
eaching enhanced ep oducibili y. Howe e , smoo h pe o ski e 374
ilms wi h homogeneous composi ion and la ge g ain bounda ies 375
a e ob ained a e a sho aining ime. Fig. 5(a) shows a c oss 376
sec ion o a PSC wi h he monoli hic pe o ski e capping laye 377
on op o he mesopo ous TiO2laye wi h g ains g owing om 378
he bo om o he op and which a e hough o enhance cha ge 379
anspo , acco ding o Saliba e al. [12]. The op iew o he 380
pe o ski e laye [see Fig. 5(b)]shows g ains possessing diame- 381
e s be ween 200 and 500 nm, which is in good ag eemen wi h 382
he o iginal epo [12]. 383
One o he bigges de imen al ac o s o pe o ski e ab- 384
ica ion and s abili y is a mosphe ic humidi y, oge he wi h 385
oxygen [54]. PSC ha a e mean o exhibi p olonged s abili y 386
equi e ab ica ion and s o age in ine a mosphe e o de ice 387
encapsula ion a e ab ica ion [55], [56]. The e o e, PSC a e 388

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6IEEE JOURNAL OF PHOTOVOLTAICS
TABLE II
BEST AND AVERAGE EFFICIENCIES FOR PSC, WHILE THE PEROVSKITE LAYER WAS FABRICATED WITHIN DIFFERENT CONDITIONS
Fig. 5. SEM images. (a) C oss sec ion o he en i e PSC de ice showing he
compac TiO2laye (ca. 80 nm), ollowed by he mesopo ous laye o 150–
200 nm. The adjacen pe o ski e laye pa ially in il a es in o he mesopo ous
s uc u e and i s capping laye has a hickness o 200–300 nm. The spi o-
MeOTAD hole anspo laye (da k g ey) has a hickness o 130–190 nm,
ollowed by a 60-nm- hick gold laye as cu en collec o (ligh g ey). (b) Top
iew o he pe o ski e laye , showing g ains wi h ca. 200–500 nm diame e . The
issu es e ol ed du ing image cap u e and he e o e a e belie ed o be due o
imaging. Ba s co espond o 1 µm.
gene ally ab ica ed in glo e boxes wi h d y and oxygen- ee389
a mosphe e. And no only ha , also he subs a es should be390
absolu ely mois u e- ee. A e sin e ing he mesopo ous laye ,391
subs a es should hus be handled only in d y a mosphe e o 392
ans e ed o d y a mosphe e such as a glo e box be o e cooling393
below 150 °C. Wi hin he deg ada ion mechanism o pe o ski eQ3 394
s uc u es, oxygen only in e e es subsequen ly o hyd a a ion395
[56] and can he e o e be conside ed less c i ical i mois u e is396
absen o e y low. Labo a o ies ha a e newcome s in his a ea397
o esea ch migh no possess a glo e box in as uc u e. Low398
a mosphe ic humidi y le els a e assumed o be less c i ical o399
pe o ski e ab ica ion bu hese condi ions depend s ongly on400
he geog aphic localiza ion, he season, and some mo e inhe -401
en ac o s. To demons a e he e ec o mois u e and oxygen402
a mosphe e on pe o ski e o ma ion, a compa a i e es o PSC403
de ices ha we e ab ica ed inside and ou side he glo e box404
( ela i e humidi y ou side he glo e box: 58%) was pe o med.405
The esul s a e displayed in Fig. 6 and Table II and i can be406
obse ed ha in case o pe o ski e being ab ica ed in ambi-407
en a mosphe e, he ac i e laye showed a ligh e colo and he408
co esponding PSC showed a bo h lowe VOC and JSC, whe eas409
he ill ac o emained a he unin luenced. As a s a egy o410
minimize wa e up ake by he subs a e, samples we e hea ed411
o 100 °C immedia ely be o e he pe o ski e p ecu so solu-412
ion was deposi ed. Co esponding PSC showed an imp o ed413
VOC and JSC, howe e he ill ac o dec eased. This is likely414
due o inhomogeneous c ys al g ow h, induced by he ele a ed415
empe a u e o he subs a e. Fo he bes cells ob ained, a li -416
Fig. 6. I–V cu es o PSC ab ica ed in a glo e box wi h 0% ela i e humidi y
a 25 °C (black squa es), a ambien humidi y (58% ela i e humidi y) a 25 °C
(g ey diamonds), and a ambien humidi y wi h subs a e p ehea ing a 100 °C
( ed ci cles) wi h an inciden ligh in ensi y o 0.94 sun. Image: Sample wi h
pe o ski e p oduced inside (le ) and ou side he glo e box ( igh ) a 25 °C.
le imp o emen can be s a ed when ho subs a es we e used, 417
hough a e age e iciencies came ou o be e y simila o hose 418
wi hou hea ea men . 419
This s udy shows ha i is highly ecommended o wo k 420
wi h a glo e box, p o iding e y low humidi y (<0.002% el. 421
humidi y) and oxygen le els. Ano he possible s a egy migh 422
be he use o a pe o ski e o mula ion ha is op imized owa d 423
enhanced esis ance a ele a ed humidi y le els [57]. 424
A op he pho oac i e laye , he hole conduc ing laye selec- 425
i ely anspo s he holes o he cu en collec o and he e o e 426
ul ills he complemen a y ole o he TiO2laye . I has o be 427
pinhole- ee o inhibi con ac o he cu en collec o wi h he 428
pe o ski e laye , o he same easons ha we e al eady s essed 429
ou conce ning he elec on conduc ing laye . Gene ally, a o - 430
mula ion using spi o-OMeTAD is used ha con ains, among o h- 431
e s, he ionic liquid LiTFSI o inc ease hole conduc i i y. How- 432
e e , bo h LiTFSI and spi o-OMeTAD ha e hyd ophilic p ope - 433
ies and p omo e humidi y inges ion, leading o poo humidi y 434
s abili y o he en i e de ice. A empe a u es abo e 55 °C, he 435
molecula hole anspo e c ys allizes, which se e ely a ec s 436
cell e iciencies. Two di e en hole conduc o laye s we e com- 437
pa ed owa d hei s abili y, namely spi o-oMeTAD as molecula 438
HTL and poly(3-hexyl hiophene) (P3HT) as polyme ic HTL. 439
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STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 7
Fig. 7. (a) I–V cu es o PSC employing spi o-OMeTAD (black squa es) and P3HT ( ed ci cles) as HTL a 0.95 sun. (b) No malized e iciency s abili y o PSC
using wo PSC wi h spi o-OMeTAD (black squa es and g ey diamonds) and wo wi h P3HT ( ed ci cles and blue iangles). The ha ched g een a ea indica es a
de ia ion less han 5% om he ini ial e iciency.
Fig. 8. I–V cu es o PSC possessing a gold cu en collec o made by he mal
e apo a ion (black line) and by spu e ing ( ed line) a 0.93 sun.
I u ns ou ha spi o-OMeTAD leads o be e e iciencies,440
see Fig. 7(a), showing be e cu en densi y, open-ci cui po-441
en ial, and ill ac o al oge he . A po en ial ad an age could442
lie in an enhanced s abili y despi e lowe e iciency when P3HT443
is employed, bu he expe imen al da a could no con i m his444
assump ion, see Fig. 7(b), wi hin he limi ed ime ame.445
Gene ally, cu en collec o s a e made o gold despi e i s446
highe cos , as al e na i e me als such as Ag and Al ha e been447
demons a ing weak s abili ies [58]–[60]. Among gold depo-448
si ion me hods, one o he mos common ones a e spu e ing449
and he mal e apo a ion. Howe e , almos all published wo ks450
use he mal e apo a ion. We decided he e o e o compa e gold451
ilms wi h simila hickness ha we e ab ica ed by hese wo452
echniques. Indeed, he mal e apo a ion leads o a be e o e all453
cell pe o mance, see Fig. 8.454
The eason o he wo se pe o mance o PSC wi h spu e ed455
cu en collec o was e idenced by doing a sco ch es . While456
in case o he mal e apo a ion, he gold laye could be easily 457
s ipped o , in case o spu e ing deposi ion, he gold emained 458
s uck in o HTM. E en a e dissol ing he HTM laye , gold 459
aces we e s ill de ec ed wi h he naked eye inside he pe - 460
o ski e laye . This means ha du ing he gold laye deposi ion, 461
su ace bomba dmen p o okes pene a ion o gold deep in o 462
he de ice s uc u e, c ea ing ecombina ion cen e s. Thus, a 463
he mal e apo a o is needed o e icien pe o ski e sola cell 464
ab ica ion, e en i his s ep conside ably inc eases he ene gy 465
payback ime o PSC [61]. 466
Following all he laye ab ica ion s eps men ioned be o e, 467
i was possible o ab ica e PSC wi h an a e age e iciency o 468
(14.8 ±1.0)% o a se o 49 cells, see Fig. 9 le . 469
In labo a o y condi ions, cell e iciencies a e gene ally mea- 470
su ed o cell ac i e a eas in e io o 1 cm2. The cell a ea de- 471
limi ed by he deposi ion o he cu en collec o should be only 472
sligh ly supe io o he ac i e cell a ea (delimi ed by a mask) o 473
a oid ecombina ion e en s. Ins ead o using c ocodile clamps 474
a bi a ily connec ed o he cell, a sui able sample holde is 475
p e e able, see Fig. 9 igh , o maximal ep oducibili y. Among 476
all ac o s ha desc ibe he cell’s pe o mance, he maximum 477
powe poin (MPP) is he mos aluable in o ma ion in e ms o 478
applicabili y in sola de ices as i desc ibes bes he ope a ing 479
pa ame e s o he cell [7], [13], [62]. The MPP is ob ained ia 480
ma hema ic ex ac ion om I–Vcu es and su p isingly has no 481
ye gained big a en ion in published scien i ic wo ks. I–Vcu es 482
a e gene ally ob ained by dynamic scanning o ex e nal loads 483
hough ca e mus be aken ha he scan a e does no o e pass 484
he dynamic elec ochemical e en s inside he pe o ski e cell. 485
An example is gi en in Fig. 10, whe e a PSC was measu ed 486
a se e al scan a es. I me ely he I–V cu e is conside ed o 487
e iciency de e mina ion, bes esul s a e ob ained wi h a scan 488
a e o 1 V/s. Bu i CV o he same cell a e eco ded a 10 mV/s 489
and a 1 V/s, a s iking di e ence is obse ed conce ning he 490
hys e esis, see Fig. 11. Whe eas hys e esis is a he low in he 491
o me case, i conside ably inc eases in he la e case. This 492
IEEE P oo
8IEEE JOURNAL OF PHOTOVOLTAICS
Fig. 9. E iciency dis ibu ion o all cells ab ica ed in s anda d condi ions (le ) and cell a chi ec u e wi h es ing de ice o ep oducible es ing condi ions
( igh ).
Fig. 10. I–V cu es and e iciencies o a PSC eco ded a di e en scan a es
a 0.98 sun: 10 mV/s (black squa es), 100 mV/s ( ed ci cles), 1 V/s (g ey
diamonds).
Fig. 11. Hys e esis o a PSC eco ded a a scan a e o 10 mV/s (black squa es)
and 1 V/s ( ed ci cles) a 0.98 sun.
means ha i he I–V cu e is eco ded in backwa d scan in such 493
condi ions, he ob ained esul s do no e lec he cell’s eal be- 494
ha io and he e o e lead o o e es ima ion o cell pe o mance 495
[7], [13]. Lacking so a easily implemen able measu emen 496
p o ocols o MPP acking, condi ions o I–V cu e eco ding 497
should be ca e ully chosen, wi h he goal o no o e es ima e 498
eal cell cha ac e is ics. 499
IV. CONCLUSION 500
PSC ep esen a e y a ac i e pho o ol aic echnology, as 501
innume ous publica ions ha e demons a ed, howe e ini ia ing 502
in his a ea may be a ha d ask. PSC a e made o se e al hin 503
laye s and no only each laye , bu also each in e ace plays 504
an impo an ole o he manu ac u ing o e icien de ices. 505
This pape is mainly di ec ed owa d esea ch g oups and sci- 506
en is s ha a e beginne s in his ac i e ield o esea ch and as 507
such, i was in ended o poin ou ab ica ion de ails ha emain 508
ba ely discussed in mos publica ions, bu ha a e signi ican 509
o he p epa a ion o e icien cells. I was e idenced ha be- 510
sides he usual equipmen o hin- ilm p epa a ion (ho pla e, 511
spin coa e , p og ammable u nace, e c.) and pho oelec ochem- 512
ical cha ac e iza ion (po en ios a o a iable ex e nal load, sola 513
simula o ), a glo e box and a he mal e apo a o o he depo- 514
si ion o he gold cu en collec o a e s ongly ad ised. The 515
goal o his pape is o analyze and op imize each laye and, as 516
a consequence, demons a e hei in luence on he en i e PSC 517
de ice. 518
I was e idenced by expe imen s ha o PSC pe o ming 519
bes , blocking laye has o be ab ica ed ia sp ay py olysis, 520
whe eas compa able esul s we e ob ained when pu e oxygen o 521
ai was used as ca ie gas. Fo he mesopo ous laye , no di e - 522
ence could be s a ed o bo h pa icle sizes used (20 and 30 nm); 523
howe e , i is likely ha a bigge di e ence in size may be o 524
ma e . Ou expe ience showed ha bes esul s o pe o ski e 525
ilms we e ob ained by applying he an isol en echnique wi h 526
a iple ca ion o mula ion. I was demons a ed ha conce ning 527
he adjacen hole anspo laye , spi o-OMeTAD was esul ing 528
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STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 9
in cells wi h supe io e iciency compa ed wi h he polyme ic529
analog P3HT. Finally, wo echniques o he ab ica ion o gold530
cu en collec o we e p esen ed and i was demons a ed ha 531
he mal e apo a ion leads o be e PSC han spu e ing, as in532
case o he la e he ene ge ic su ace bomba dmen p o oked533
gold pa icle pene a ion un il he pe o ski e ac i e laye , hus534
c ea ing ecombina ion cen e s. Inco po a ing all he discussed535
op imiza ions, PSC wi h an a e age e iciency o (14.8 ±1.0)%536
we e ab ica ed. Fu he mo e, an inno a i e, e sa ile, and quick537
me hod o elec ochemical subs a e e ching was applied in538
PSC, making lase -assis ed sc ibing and he e o e he neces-539
si y o such an equipmen obsole e. Dummy cells as selec i e540
elec ochemical cha ac e iza ion me hod o single laye s we e541
in oduced and yielded e sa ile esul s o he quali a i e com-542
pa ison o TiO2blocking laye s. I is belie ed ha his pape 543
con ibu es o a as e implemen a ion o PSC ab ica ion in544
esea ch g oups wi h ew expe ience in his a ea, hanks o a545
deepe unde s anding o ab ica ion de ails and use ul analysis546
ools ha a e easily a ailable.547
ACKNOWLEDGMENT548
The au ho s would like o hank M. G ¨
a zel o hos ing549
I. Mesqui a a EPFL o deepen he knowledge abou PSC ab-550
ica ion and O. Bellon om G ea cellsola L d. o ui ul551
discussions.552
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[17] M. Liu, M. B. Johns on, and H. J. Snai h, “E icien plana he e ojunc ion 598
pe o ski e sola cells by apou deposi ion,” Na u e, 501, pp. 395–398, 599
2013. 600
[18] D. Bi e al., “Polyme - empla ed nuclea ion and c ys al g ow h o pe - 601
o ski e ilms o sola cells wi h e iciency g ea e han 21%,” Na u e 602
Ene gy, ol. 1, 2016, A . no. 16142. 603
[19] N. J. Jeon, J. H. Noh, Y. C. Kim, W. S. Yang, S. Ryu, and S. I. Seok, 604
“Sol en enginee ing o high-pe o mance ino ganic–o ganic hyb id pe - 605
o ski e sola cells,” Na u e Ma e , ol. 13, pp. 897–903, 2014. 606
[20] D. Yang, Z. Yang, W. Qin, Y. Zhang, S. Liu, and C. Li, “Al e na ing 607
p ecu so laye deposi ion o highly s able pe o ski e ilms owa ds e - 608
icien sola cells using acuum deposi ion,” J. Ma e . Chem. A, ol.3, 609
pp. 9401–9405, 2015. 610
[21] D. Yang e al., “Su ace op imiza ion o elimina e hys e esis o eco d 611
e iciency plana pe o ski e sola cells,” Ene gy En i on. Sci., ol.9, 612
pp. 3071–3078, 2016. 613
[22] K. Wang e al., “CO2 Plasma- ea ed TiO2 ilm as an e ec i e elec on 614
anspo laye o high-pe o mance plana pe o ski e sola cells,” ACS 615
Appl. Ma e . In e aces, ol. 9, pp. 33989–33996, 2017. 616
[23] W. Yongzhen e al.,“Highly compac TiO 2 laye o e icien hole- 617
blocking in pe o ski e sola cells,” Appl. Phys. Exp ess, ol. 7, 2014, 618
A . no. 052301. 619
[24] H. Hu e al., “A omic laye deposi ion o TiO2 o a high-e iciency hole- 620
blocking laye in hole-conduc o - ee pe o ski e sola cells p ocessed in 621
ambien ai ,” ACS Appl. Ma e . In e aces, ol. 8, pp. 17999–18007, 2016. 622
[25] L. E ga , Hole T anspo Ma e ial (HTM) F ee Pe o ski e Sola Cell, 623
Hole Conduc o F ee Pe o ski e-Based Sola Cells. Cham, Swi ze land: 624
Sp inge , 2016, pp. 9–24. 625
[26] L. E ga e al., “Mesoscopic CH3NH3PbI3/TiO2 he e ojunc ion sola 626
cells,” J. Ame . Chem. Soc., ol. 134, pp. 17396–17399, 2012. 627
[27] A. Hag eld , G. Boschloo, L. Sun, L. Kloo, and H. Pe e sson, “Dye- 628
sensi ized sola cells,” Chem. Re ., ol. 110, pp. 6595–6663, 2010. 629
[28] J.-H. Im, C.-R. Lee, J.-W. Lee, S.-W. Pa k, and N.-G. Pa k, “6.5% e - 630
icien pe o ski e quan um-do -sensi ized sola cell,” Nanoscale, ol.3, 631
pp. 4088–4093, 2011. 632
[29] E. H. Ana aki e al., “Highly e icien and s able plana pe o ski e so- 633
la cells by solu ion-p ocessed in oxide,” Ene gy En i on. Sci., ol.9, 634
pp. 3128–3134, 2016. 635
[30] H. J. Snai h e al., “Anomalous hys e esis in pe o ski e sola cells,” J. 636
Phys. Chem. Le ., ol. 5, pp. 1511–1515, 2014. 637
[31] B. Chen, M. Yang, S. P iya, and K. Zhu, “O igin o J–V hys e esis in 638
pe o ski e sola cells,” J. Phys. Chem. Le ., ol. 7, pp. 905–917, 2016. 639
[32] K. Wojciechowski, M. Saliba, T. Leij ens, A. Aba e, and H. J. Snai h, “Sub- 640
150 [deg ee]C p ocessed meso-supe s uc u ed pe o ski e sola cells wi h 641
enhanced e iciency,” Ene gy En i on. Sci., ol. 7, pp. 1142–1147, 2014. 642
[33] T. Leij ens, B. Laube , G. E. Epe on, S. D. S anks, and H. J. Snai h, 643
“The impo ance o pe o ski e po e illing in o ganome al mixed halide 644
sensi ized TiO2-based sola cells,” J. Phys. Chem. Le ., ol. 5, pp. 1096– 645
1102, 2014. 646
[34] M. Anaya e al., “Elec on injec ion and sca old e ec s in pe o ski e 647
sola cells,” J. Ma e . Chem. C, ol. 5, pp. 634–644, 2017. 648
[35] E. L. Unge e al., “Hys e esis and ansien beha io in cu en - ol age 649
measu emen s o hyb id-pe o ski e abso be sola cells,” Ene gy En i on. 650
Sci., ol. 7 pp. 3690–3698, 2014. 651
[36] W. T ess, N. Ma ino a, T. Moehl, S. M. Zakee uddin, M. K. Nazee uddin, 652
and M. G a zel, “Unde s anding he a e-dependen J-V hys e esis, slow 653
ime componen , and aging in CH3NH3PbI3 pe o ski e sola cells: The 654
ole o a compensa ed elec ic ield,” Ene gy En i on. Sci., ol. 8, pp. 995– 655
1004, 2015. 656
[37] S. Meloni e al., “Ionic pola iza ion-induced cu en – ol age hys e esis 657
in CH3NH3PbX3 pe o ski e sola cells,” Na u e Commun., ol. 7, 2016, 658
A . no. 10334. 659
[38] G. Richa dson e al., “Can slow-mo ing ions explain hys e esis in he 660
cu en - ol age cu es o pe o ski e sola cells?” Ene gy En i on. Sci.,661
ol. 9, pp. 1476–1485, 2016. 662
[39] Z. Song, S. C. Wa hage, A. B. Phillips, and M. J. Heben, “Pa hways owa d 663
high-pe o mance pe o ski e sola cells: Re iew o ecen ad ances in 664
o gano-me al halide pe o ski es o pho o ol aic applica ions,” J. Pho on. 665
Ene gy, ol. 6, 2016, A . no. 022001. 666
IEEE P oo
STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 5
Fig. 4. I–V cu e o cells wi h a mesopo ous TiO2 laye made om 30NR-
D pas e (a e age pa icle size o 30 nm, black squa es) and om 18-NR-T
pas e (a e age pa icle size o 20 nm, ed ci cles) a 0.94 sun. Bo h pas es we e
pu chased om Dyesol L d.
a long ime [7]. Only ecen ly, he e iciency gap has become293
a he small, which is due o imp o ed in e ace enginee ing [7],294
[18], [29]. Beside highe e iciencies, PSC wi h a mesopo ous295
laye show educed e iciency de ia ion be ween o wa d and296
backwa d scan, a phenomenon desc ibed as hys e esis [19], [30],297
[31]. When Snai h e al. demons a ed ha e en wi h meso-298
po ous laye s o alumina, a ma e ial ha canno pa icipa e in299
elec on ans e due o band ene gy misma ch, high e iciencies300
o 15.9% could be ob ained [32], i was deduced ha he meso-301
po ous laye mainly ul ills a s uc u al ole o c ys al g ow h302
and geome y de e mina ion, e en i e icien elec on injec ion303
om he pe o ski e in o he TiO2mesopo ous laye was epo ed304
[33]. Howe e , la es esul s demons a e ha ionic mig a ion a 305
he pe o ski e/TiO2in e ace, which is esponsible o cha ge306
accumula ion and he e o e ecombina ion e en s, is educed o 307
e en supp essed in he p esence o he TiO2mesopo ous laye 308
[34]. As hys e esis also depends on ionic mig a ion [35]–[38],309
i s educ ion in he p esence o mesopo ous TiO2is he conse-310
quence. Pu ing all oge he , bes esul s ha e been achie ed so311
a using a hin TiO2mesopo ous laye and a pe o ski e cap-312
ping laye ha p e en s ecombina ion be ween TiO2and he313
hole anspo laye [33], [34].314
The e exis se e al comme cial pas es wi h di e en sizes o 315
TiO2pa icles and he e o e, i was decided o compa e wo316
di e en pa icle sizes, namely one possessing 20 nm and one317
wi h 30 nm a e age pa icle diame e . The same pas e dilu ion318
a io in pu e e hanol (1:6) as well as he same deposi ion and319
sin e ing condi ions we e applied. Fig. 4 shows ha bo h meso-320
po ous laye s lead o e y compa able cell e iciencies ha a e321
wi hin he e o scale. This poin s owa d a highe ole ance and322
owa d a mesopo ous laye a chi ec u e, as long as he pa icle323
size emains simila .324
Wi hin pe o ski e ma e ials, he e exis s a huge a ie y o 325
ecipes and deposi ion echniques, which a e well summa ized326
in he book by Pa k e al. [10] and in he e iew by Song e al.327
[39]. I migh be no an easy ask o decide o he sui able328
pe o ski e ype and ab ica ion p ocess. The name pe o ski e329
e e s o a c ys alline s uc u e o he ype ABX3, A and B be-330
ing ca ions and X an anion. The pe o ski e class sui able o 331
sola cells is an o ganic lead halide, wi h A being gene ally an 332
o ganic ca ion, B being he lead ion, and X being a halogen, 333
usually b omine, iodide, chlo ine, and mix u es he eo . Lead 334
subs i u ion by in and ge manium analogs leads o pe o ski es 335
wi h se e e s abili y p oblems [32], [40], [41] and he e o e will 336
no be add essed he e. Ou ocus was o de e mine a pe o ski e 337
o mula ion easy o implemen and ha esul s in ep oducible 338
pe o ski e laye s wi h enhanced s abili y. Many esul s ha e 339
been published wi h monoca ionic pe o ski es, howe e , wi h 340
some inhe en limi a ions ha a e b ie ly exposed he e: MAPbI3341
has been in ensi ely s udied [42] bu has some d awbacks such 342
as weak s abili y owa d mois u e [43], [44] and empe a u e 343
[45]. Fo mamidinium (FA) was p oposed as al e na i e ca ion; 344
howe e , i s pe o ski e analog FAPbI3c ys allizes in he pho- 345
oinac i e phase below 60 °C [46], such as he ino ganic ca ion 346
analog CsPbI3[47]. Whe eas se e al g oups obse ed imp o ed 347
s abili y o he pho oac i e phase upon using bina y mixed ca ion 348
pe o ski es [48]–[52], Saliba e al. decided o combine he h ee 349
ca ions in a pe o ski e and achie ed high e iciencies (>20%) 350
on a e y ep oducible basis [12]. 351
Se e al me hods exis o solu ion-p ocessed ilm ab ica ion, 352
he mos common being simple sp eading o he pe o ski e p e- 353
cu so solu ion on he subs a e, also known as one-s ep depo- 354
si ion. Howe e , ilms wi h poo su ace con ol and he e o e 355
huge e iciency a ia ions gene ally eme ge [42]. A mo e so- 356
phis ica ed app oach is he sequen ial s ep deposi ion, whe e 357
he me al halide is i s deposi ed and annealed be o e being 358
b ough in con ac wi h he ammonium sal as apo o in solu- 359
ion [42], [53]. Ne e heless, se e al d awbacks o his deposi- 360
ion me hod we e expe ienced in ou g oup, such as incomple e 361
con e sion o he me al halide o pa ial dissolu ion o he pe - 362
o ski e du ing he subsequen washing s ep. Fu he mo e, i is 363
mo e ime-consuming as i equi es wo sin e ing s eps. The 364
an isol en echnique was in oduced in 2014 by he g oup o 365
Seok [19] and since hen, i has been he me hod o choice o 366
subsequen ly published eco d e iciencies [7]. I is qui e simple 367
o implemen and equi es only one p ecu so solu ion, whe eas 368
he c ys alliza ion o he pe o ski e is ini ia ed by adding a so- 369
called an isol en . This an isol en is chosen no o dissol e he 370
pe o ski e on one side and o displace he sol en o he la e on 371
he o he side. The main d awback o his deposi ion me hod is 372
i s a isanal aspec , equi ing a ce ain deg ee o aining be o e 373
eaching enhanced ep oducibili y. Howe e , smoo h pe o ski e 374
ilms wi h homogeneous composi ion and la ge g ain bounda ies 375
a e ob ained a e a sho aining ime. Fig. 5(a) shows a c oss 376
sec ion o a PSC wi h he monoli hic pe o ski e capping laye 377
on op o he mesopo ous TiO2laye wi h g ains g owing om 378
he bo om o he op and which a e hough o enhance cha ge 379
anspo , acco ding o Saliba e al. [12]. The op iew o he 380
pe o ski e laye [see Fig. 5(b)]shows g ains possessing diame- 381
e s be ween 200 and 500 nm, which is in good ag eemen wi h 382
he o iginal epo [12]. 383
One o he bigges de imen al ac o s o pe o ski e ab- 384
ica ion and s abili y is a mosphe ic humidi y, oge he wi h 385
oxygen [54]. PSC ha a e mean o exhibi p olonged s abili y 386
equi e ab ica ion and s o age in ine a mosphe e o de ice 387
encapsula ion a e ab ica ion [55], [56]. The e o e, PSC a e 388

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6IEEE JOURNAL OF PHOTOVOLTAICS
TABLE II
BEST AND AVERAGE EFFICIENCIES FOR PSC, WHILE THE PEROVSKITE LAYER WAS FABRICATED WITHIN DIFFERENT CONDITIONS
Fig. 5. SEM images. (a) C oss sec ion o he en i e PSC de ice showing he
compac TiO2laye (ca. 80 nm), ollowed by he mesopo ous laye o 150–
200 nm. The adjacen pe o ski e laye pa ially in il a es in o he mesopo ous
s uc u e and i s capping laye has a hickness o 200–300 nm. The spi o-
MeOTAD hole anspo laye (da k g ey) has a hickness o 130–190 nm,
ollowed by a 60-nm- hick gold laye as cu en collec o (ligh g ey). (b) Top
iew o he pe o ski e laye , showing g ains wi h ca. 200–500 nm diame e . The
issu es e ol ed du ing image cap u e and he e o e a e belie ed o be due o
imaging. Ba s co espond o 1 µm.
gene ally ab ica ed in glo e boxes wi h d y and oxygen- ee389
a mosphe e. And no only ha , also he subs a es should be390
absolu ely mois u e- ee. A e sin e ing he mesopo ous laye ,391
subs a es should hus be handled only in d y a mosphe e o 392
ans e ed o d y a mosphe e such as a glo e box be o e cooling393
below 150 °C. Wi hin he deg ada ion mechanism o pe o ski eQ3 394
s uc u es, oxygen only in e e es subsequen ly o hyd a a ion395
[56] and can he e o e be conside ed less c i ical i mois u e is396
absen o e y low. Labo a o ies ha a e newcome s in his a ea397
o esea ch migh no possess a glo e box in as uc u e. Low398
a mosphe ic humidi y le els a e assumed o be less c i ical o399
pe o ski e ab ica ion bu hese condi ions depend s ongly on400
he geog aphic localiza ion, he season, and some mo e inhe -401
en ac o s. To demons a e he e ec o mois u e and oxygen402
a mosphe e on pe o ski e o ma ion, a compa a i e es o PSC403
de ices ha we e ab ica ed inside and ou side he glo e box404
( ela i e humidi y ou side he glo e box: 58%) was pe o med.405
The esul s a e displayed in Fig. 6 and Table II and i can be406
obse ed ha in case o pe o ski e being ab ica ed in ambi-407
en a mosphe e, he ac i e laye showed a ligh e colo and he408
co esponding PSC showed a bo h lowe VOC and JSC, whe eas409
he ill ac o emained a he unin luenced. As a s a egy o410
minimize wa e up ake by he subs a e, samples we e hea ed411
o 100 °C immedia ely be o e he pe o ski e p ecu so solu-412
ion was deposi ed. Co esponding PSC showed an imp o ed413
VOC and JSC, howe e he ill ac o dec eased. This is likely414
due o inhomogeneous c ys al g ow h, induced by he ele a ed415
empe a u e o he subs a e. Fo he bes cells ob ained, a li -416
Fig. 6. I–V cu es o PSC ab ica ed in a glo e box wi h 0% ela i e humidi y
a 25 °C (black squa es), a ambien humidi y (58% ela i e humidi y) a 25 °C
(g ey diamonds), and a ambien humidi y wi h subs a e p ehea ing a 100 °C
( ed ci cles) wi h an inciden ligh in ensi y o 0.94 sun. Image: Sample wi h
pe o ski e p oduced inside (le ) and ou side he glo e box ( igh ) a 25 °C.
le imp o emen can be s a ed when ho subs a es we e used, 417
hough a e age e iciencies came ou o be e y simila o hose 418
wi hou hea ea men . 419
This s udy shows ha i is highly ecommended o wo k 420
wi h a glo e box, p o iding e y low humidi y (<0.002% el. 421
humidi y) and oxygen le els. Ano he possible s a egy migh 422
be he use o a pe o ski e o mula ion ha is op imized owa d 423
enhanced esis ance a ele a ed humidi y le els [57]. 424
A op he pho oac i e laye , he hole conduc ing laye selec- 425
i ely anspo s he holes o he cu en collec o and he e o e 426
ul ills he complemen a y ole o he TiO2laye . I has o be 427
pinhole- ee o inhibi con ac o he cu en collec o wi h he 428
pe o ski e laye , o he same easons ha we e al eady s essed 429
ou conce ning he elec on conduc ing laye . Gene ally, a o - 430
mula ion using spi o-OMeTAD is used ha con ains, among o h- 431
e s, he ionic liquid LiTFSI o inc ease hole conduc i i y. How- 432
e e , bo h LiTFSI and spi o-OMeTAD ha e hyd ophilic p ope - 433
ies and p omo e humidi y inges ion, leading o poo humidi y 434
s abili y o he en i e de ice. A empe a u es abo e 55 °C, he 435
molecula hole anspo e c ys allizes, which se e ely a ec s 436
cell e iciencies. Two di e en hole conduc o laye s we e com- 437
pa ed owa d hei s abili y, namely spi o-oMeTAD as molecula 438
HTL and poly(3-hexyl hiophene) (P3HT) as polyme ic HTL. 439
IEEE P oo
STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 7
Fig. 7. (a) I–V cu es o PSC employing spi o-OMeTAD (black squa es) and P3HT ( ed ci cles) as HTL a 0.95 sun. (b) No malized e iciency s abili y o PSC
using wo PSC wi h spi o-OMeTAD (black squa es and g ey diamonds) and wo wi h P3HT ( ed ci cles and blue iangles). The ha ched g een a ea indica es a
de ia ion less han 5% om he ini ial e iciency.
Fig. 8. I–V cu es o PSC possessing a gold cu en collec o made by he mal
e apo a ion (black line) and by spu e ing ( ed line) a 0.93 sun.
I u ns ou ha spi o-OMeTAD leads o be e e iciencies,440
see Fig. 7(a), showing be e cu en densi y, open-ci cui po-441
en ial, and ill ac o al oge he . A po en ial ad an age could442
lie in an enhanced s abili y despi e lowe e iciency when P3HT443
is employed, bu he expe imen al da a could no con i m his444
assump ion, see Fig. 7(b), wi hin he limi ed ime ame.445
Gene ally, cu en collec o s a e made o gold despi e i s446
highe cos , as al e na i e me als such as Ag and Al ha e been447
demons a ing weak s abili ies [58]–[60]. Among gold depo-448
si ion me hods, one o he mos common ones a e spu e ing449
and he mal e apo a ion. Howe e , almos all published wo ks450
use he mal e apo a ion. We decided he e o e o compa e gold451
ilms wi h simila hickness ha we e ab ica ed by hese wo452
echniques. Indeed, he mal e apo a ion leads o a be e o e all453
cell pe o mance, see Fig. 8.454
The eason o he wo se pe o mance o PSC wi h spu e ed455
cu en collec o was e idenced by doing a sco ch es . While456
in case o he mal e apo a ion, he gold laye could be easily 457
s ipped o , in case o spu e ing deposi ion, he gold emained 458
s uck in o HTM. E en a e dissol ing he HTM laye , gold 459
aces we e s ill de ec ed wi h he naked eye inside he pe - 460
o ski e laye . This means ha du ing he gold laye deposi ion, 461
su ace bomba dmen p o okes pene a ion o gold deep in o 462
he de ice s uc u e, c ea ing ecombina ion cen e s. Thus, a 463
he mal e apo a o is needed o e icien pe o ski e sola cell 464
ab ica ion, e en i his s ep conside ably inc eases he ene gy 465
payback ime o PSC [61]. 466
Following all he laye ab ica ion s eps men ioned be o e, 467
i was possible o ab ica e PSC wi h an a e age e iciency o 468
(14.8 ±1.0)% o a se o 49 cells, see Fig. 9 le . 469
In labo a o y condi ions, cell e iciencies a e gene ally mea- 470
su ed o cell ac i e a eas in e io o 1 cm2. The cell a ea de- 471
limi ed by he deposi ion o he cu en collec o should be only 472
sligh ly supe io o he ac i e cell a ea (delimi ed by a mask) o 473
a oid ecombina ion e en s. Ins ead o using c ocodile clamps 474
a bi a ily connec ed o he cell, a sui able sample holde is 475
p e e able, see Fig. 9 igh , o maximal ep oducibili y. Among 476
all ac o s ha desc ibe he cell’s pe o mance, he maximum 477
powe poin (MPP) is he mos aluable in o ma ion in e ms o 478
applicabili y in sola de ices as i desc ibes bes he ope a ing 479
pa ame e s o he cell [7], [13], [62]. The MPP is ob ained ia 480
ma hema ic ex ac ion om I–Vcu es and su p isingly has no 481
ye gained big a en ion in published scien i ic wo ks. I–Vcu es 482
a e gene ally ob ained by dynamic scanning o ex e nal loads 483
hough ca e mus be aken ha he scan a e does no o e pass 484
he dynamic elec ochemical e en s inside he pe o ski e cell. 485
An example is gi en in Fig. 10, whe e a PSC was measu ed 486
a se e al scan a es. I me ely he I–V cu e is conside ed o 487
e iciency de e mina ion, bes esul s a e ob ained wi h a scan 488
a e o 1 V/s. Bu i CV o he same cell a e eco ded a 10 mV/s 489
and a 1 V/s, a s iking di e ence is obse ed conce ning he 490
hys e esis, see Fig. 11. Whe eas hys e esis is a he low in he 491
o me case, i conside ably inc eases in he la e case. This 492
IEEE P oo
8IEEE JOURNAL OF PHOTOVOLTAICS
Fig. 9. E iciency dis ibu ion o all cells ab ica ed in s anda d condi ions (le ) and cell a chi ec u e wi h es ing de ice o ep oducible es ing condi ions
( igh ).
Fig. 10. I–V cu es and e iciencies o a PSC eco ded a di e en scan a es
a 0.98 sun: 10 mV/s (black squa es), 100 mV/s ( ed ci cles), 1 V/s (g ey
diamonds).
Fig. 11. Hys e esis o a PSC eco ded a a scan a e o 10 mV/s (black squa es)
and 1 V/s ( ed ci cles) a 0.98 sun.
means ha i he I–V cu e is eco ded in backwa d scan in such 493
condi ions, he ob ained esul s do no e lec he cell’s eal be- 494
ha io and he e o e lead o o e es ima ion o cell pe o mance 495
[7], [13]. Lacking so a easily implemen able measu emen 496
p o ocols o MPP acking, condi ions o I–V cu e eco ding 497
should be ca e ully chosen, wi h he goal o no o e es ima e 498
eal cell cha ac e is ics. 499
IV. CONCLUSION 500
PSC ep esen a e y a ac i e pho o ol aic echnology, as 501
innume ous publica ions ha e demons a ed, howe e ini ia ing 502
in his a ea may be a ha d ask. PSC a e made o se e al hin 503
laye s and no only each laye , bu also each in e ace plays 504
an impo an ole o he manu ac u ing o e icien de ices. 505
This pape is mainly di ec ed owa d esea ch g oups and sci- 506
en is s ha a e beginne s in his ac i e ield o esea ch and as 507
such, i was in ended o poin ou ab ica ion de ails ha emain 508
ba ely discussed in mos publica ions, bu ha a e signi ican 509
o he p epa a ion o e icien cells. I was e idenced ha be- 510
sides he usual equipmen o hin- ilm p epa a ion (ho pla e, 511
spin coa e , p og ammable u nace, e c.) and pho oelec ochem- 512
ical cha ac e iza ion (po en ios a o a iable ex e nal load, sola 513
simula o ), a glo e box and a he mal e apo a o o he depo- 514
si ion o he gold cu en collec o a e s ongly ad ised. The 515
goal o his pape is o analyze and op imize each laye and, as 516
a consequence, demons a e hei in luence on he en i e PSC 517
de ice. 518
I was e idenced by expe imen s ha o PSC pe o ming 519
bes , blocking laye has o be ab ica ed ia sp ay py olysis, 520
whe eas compa able esul s we e ob ained when pu e oxygen o 521
ai was used as ca ie gas. Fo he mesopo ous laye , no di e - 522
ence could be s a ed o bo h pa icle sizes used (20 and 30 nm); 523
howe e , i is likely ha a bigge di e ence in size may be o 524
ma e . Ou expe ience showed ha bes esul s o pe o ski e 525
ilms we e ob ained by applying he an isol en echnique wi h 526
a iple ca ion o mula ion. I was demons a ed ha conce ning 527
he adjacen hole anspo laye , spi o-OMeTAD was esul ing 528
IEEE P oo
STOCKHAUSEN e al.: INSIGHTS IN PSC FABRICATION: UNRAVELING THE HIDDEN CHALLENGES OF EACH LAYER 9
in cells wi h supe io e iciency compa ed wi h he polyme ic529
analog P3HT. Finally, wo echniques o he ab ica ion o gold530
cu en collec o we e p esen ed and i was demons a ed ha 531
he mal e apo a ion leads o be e PSC han spu e ing, as in532
case o he la e he ene ge ic su ace bomba dmen p o oked533
gold pa icle pene a ion un il he pe o ski e ac i e laye , hus534
c ea ing ecombina ion cen e s. Inco po a ing all he discussed535
op imiza ions, PSC wi h an a e age e iciency o (14.8 ±1.0)%536
we e ab ica ed. Fu he mo e, an inno a i e, e sa ile, and quick537
me hod o elec ochemical subs a e e ching was applied in538
PSC, making lase -assis ed sc ibing and he e o e he neces-539
si y o such an equipmen obsole e. Dummy cells as selec i e540
elec ochemical cha ac e iza ion me hod o single laye s we e541
in oduced and yielded e sa ile esul s o he quali a i e com-542
pa ison o TiO2blocking laye s. I is belie ed ha his pape 543
con ibu es o a as e implemen a ion o PSC ab ica ion in544
esea ch g oups wi h ew expe ience in his a ea, hanks o a545
deepe unde s anding o ab ica ion de ails and use ul analysis546
ools ha a e easily a ailable.547
ACKNOWLEDGMENT548
The au ho s would like o hank M. G ¨
a zel o hos ing549
I. Mesqui a a EPFL o deepen he knowledge abou PSC ab-550
ica ion and O. Bellon om G ea cellsola L d. o ui ul551
discussions.552
REFERENCES553
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o gano-me al halide pe o ski es o pho o ol aic applica ions,” J. Pho on. 665
Ene gy, ol. 6, 2016, A . no. 022001. 666
IEEE P oo
10 IEEE JOURNAL OF PHOTOVOLTAICS
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Na u e Pho on., ol. 8, pp. 489–494, 2014.669
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CH3NH3PbI3 pe o ski e sola cells a high empe a u es and humidi y,”719
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pp. 75–81, 2016.723
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A . no. 091901.729
Ve ena S ockhausen ecei ed he B.S. deg ee in 730
chemis y and biochemis y and he M.S. deg ee 731
in chemis y om Ludwig Maximilians Uni e si y, 732
Munich, Ge many, in 2005 and 2007, espec i ely, 733
and he Ph.D. deg ee in analy ical physical chem- 734
is y om Denis Dide o Uni e si y, Pa is, F ance, 735
in 2011. 736
In 2013 and om 2015 o 2017, she was a Pos - 737
doc Fellow wi hin he g oup o P o . Ad´
elio Mendes. 738
He esea ch in e es s include pho o ol aic sys ems 739
such as dye-sensi ized sola cells and pe o ski e so- 740
la cells, as well as pho oelec ochemical sys ems o wa e spli ing. 741
742
Isabel Mesqui a was bo n in Po o, Po ugal, in 1988. 743
She ecei ed he M.S. deg ee in chemical enginee - 744
ing om he Uni e si y o Po o, Po o, in 2011. She 745
is cu en ly wo king owa d he Ph.D. deg ee a he 746
Facul y o Enginee ing, Uni e si y o Po o, ocusing 747
in he pe o ski e sola cells and hei s abili y. 748
F om Sep embe o 2011 o Ma ch 2015, she 749
was a Resea ch Fellow wi h LEPABE—Labo a o y 750
o P ocess Enginee ing, En i onmen , Bio echnol- 751
ogy and Ene gy wo king in me hanol uel cells and 752
dye-sensi ized sola cells. . 753
754
Lu´
ısa And ade ecei ed he Ph.D. deg ee om he 755
Uni e si y o Po o, Po o, Po ugal, in 2010, wi h 756
he hesis “S udy and Cha ac e iza ion o G ¨
a zel 757
Sola Cells.” 758
She is cu en ly an Assis an Resea che wi h LEP- 759
ABE, Facul y o Enginee ing, Uni e si y o Po o, 760
wo king wi h dye-sensi ized sola cells and pe - 761
o ski e sola cells. She wo ked di ec ly wi h P o . 762
G ¨
a zel a he Labo a o y o Pho onic and In e aces, 763
Lausanne, Swi ze land. 764
D . And ade was he ecipien o he ACP Diogo 765
Vasconcelos awa d in 2011, he Sol ay&Ho ione Inno a ion Challenge awa d 766
in 2011 and 2012, and he Ramos Ca a ino awa d in 2012. 767
768
Ad´
elio Mendes was bo n in 1964. He ecei ed he 769
Ph.D. deg ee om he Uni e si y o Po o, Po o, Po - 770
ugal, in 1993. 771
He is a Full P o esso wi h he Chemical Enginee - 772
ing Depa men , Facul y o Enginee ing, Uni e si y 773
o Po o. He coo dina es a la ge esea ch eam wi h e- 774
sea ch in e es s mainly including dye-sensi ized sola 775
cells and pe o ski e sola cells, pho oelec ochemi- 776
cal cells, including wa e spli ing and sola edox 777
low cells, edox low ba e ies, PEMFC, me hanol 778
s eam e o ming, memb ane, and adso ben -based 779
gas sepa a ions. He ecei ed an Ad anced Resea ch G an om he ERC on 780
dye-sensi ized sola cells o building in eg a ed o ca. 2 MEu os. He is cu - 781
en ly he Coo dina o o CEne -FEUP, he Compe ence Cen e o Ene gy o 782
he Facul y o Enginee ing a he Uni e si y o Po o. 783
784

IEEE P oo
GENERAL INSTRUCTION 785
Au ho s: Please no e ha we canno accep new sou ce iles as co ec ions o you pape . I possible, please anno a e he PDF 786
p oo we ha e sen you wi h you co ec ions, using Adobe Ac oba edi ing so wa e, and upload i ia he Au ho Ga eway. 787
Al e na i ely, you may send us you co ec ions in a simple . x ile, u ilizing he line numbe s in he ma gins o he p oo o 788
indica e exac ly whe e you would like o us o make co ec ions. You may, howe e , upload e ised g aphics ia he Au ho 789
Ga eway. 790
QUERIES 791
Q1. Au ho : Please check whe he he unding in o ma ion is co ec . 792
Q2. Au ho : Please p o ide he expansion o DMF, DMSO, and HTL. 793
Q3. Au ho : Please check he usage o he e m “hyd a a ion” in he sen ence “Wi hin he deg ada ion mechanism o pe o ski e 794
s uc u es . . . ”. 795
Q4. Au ho : Please p o ide missing yea o Re s. [5]and [6].796
Q5. Au ho : Please p o ide page age o Re . [54].797