Exploring the synthesis of Cu2(Zn,Cd)SnS4 at high temperatures as a route for high-efficiency solar cells

P og ess in Pho o ol aics: Resea ch and Applica ions, 2025; 0:1–16
h ps://doi.o g/10.1002/pip.3899
1 o 16
P og ess in Pho o ol aics: Resea ch and Applica ions
RESEARCH ARTICLE OPEN ACCESS
Explo ing he Syn hesis o Cu2(Zn,Cd)SnS4 a High
Tempe a u es as a Rou e o High- E iciency Sola Cells
Ou manElKhouja1,2 | YuancaiGong3,4 | AlexJimenez-A guijo3,4 | MaykelJimenezGue a3,4 | AxelGonMedaille3,4 |
RomainSca idi5,6,7,8 | A indamBasak9 | C is ianRadu1,10 | DenisFland e5,6,7,8 | Ba Ve mang5,6,7,8 | Se gioGi aldo3,4 |
Ma celPlacidi3,4 | Zacha ieJehlLi-Kao3,4 | Au elianCa alinGalca1,11 | Edga doSaucedo3,4
1Na ional Ins i u e o Ma e ials Physics, Magu ele, Il o , Romania | 2Facul y o Science, Ibn To ail Uni e si y, Campus Uni e si ai e, Keni a,
Mo occo | 3Uni e si a Poli ècnica de Ca alunya (UPC), Ba celona, Spain | 4Ba celona Cen e o Mul iscale Science & Enginee ing, Uni e si a
Poli ècnica de Ca alunya (UPC), Ba celona, Spain | 5IMO, Hassel Uni e si y, Diepenbeek, Belgium | 6IMOMEC, imec, Diepenbeek,
Belgium | 7Ene gyVille 2, Genk, Belgium | 8ICTEAM, UCLou ain, Lou ain- la- Neu e, Belgium | 9Thin Film Pho o ol aic Lab, School o
Elec onics Enginee ing, KIIT- Deemed o Be Uni e si y, Bhubaneswa , India | 10Facul y o Physics, Uni e si y o Bucha es , Magu ele, Il o ,
Romania | 11In e na ional Cen e o Ad anced T aining and Resea ch in Physics, Magu ele, Il o ,Romania
Co espondence: Au elian Ca alin Galca (ac_galca@in im. o) | Edga do Saucedo (edga [email protected])
Recei ed: 30 July 2024 | Re ised: 12 Decembe 2024 | Accep ed: 4 Feb ua y 2025
Funding: NIMP au ho s acknowledge unding om Minis e ul Ce ce ă ii, Ino ă ii și Digi aliză ii (Romanian Minis y o Resea ch, Inno a ion
and Digi aliza ion) h ough he Co e P og amme PC3- PN23080303 p ojec , and om Uni a ea Execu i ă pen u Finanța ea În ățămân ului
Supe io , a Ce ce ă ii, Dez ol ă ii și Ino ă ii (UEFISCDI) h ough PN–III–P4- ID- PCE- 2020- 0827 (Con ac no. PCE74 09/02/2021) and ERANET-
M- 3- ERANET- Lig hcell (Con ac No. 19/15.03.2024) p ojec s. Au ho s acknowledge he COST Ac ion Resea ch and In e na ional Ne wo king
p ojec “Eme ging Ino ganic Chalcogenides o Pho o ol aics (RENEW- PV),” CA21148, suppo ed by COST (Eu opean Coope a ion in Science and
Technology). This wo k ecei ed also unding om he Eu opean Union‘s Ho izon 2020 esea ch and inno a ion p og am unde g an ag eemen
numbe 952982 (CUSTOM- ART) and 866018 (SENSATE), and by he Science Minis y o Spain (Minis e io de Ciencia, Inno ación y Uni e sidades)
p ojec s numbe PID2020- 116719RB- C41 (MATER- ONE) and TED2021- 130265B- C21 (MIRACLE). A. J. A. hanks he Eu opean Social Fund+ o
he FI ellowship. S.G. hanks he Juan de la Cie a g an IJC2020- 044716- I unded by Minis e io de Ciencia, Inno ación y Uni e sidades (MCIN/
AEI/10.13039/501100011033) and by Eu opean Union‘s Ho izon 2020 esea ch and inno a ion p og am, Nex Gene a ionEU/PRTR. E. S. is g a e ul
o ICREA (Ins i ució Ca alana de Rece ca i Es udis A ança s) Academia p og am. R. S. hanks Fonds We enschappelijk Onde zoek (FWO) o he
unding h ough he Fundamen al Resea ch PhD Fellowship (1178024 N). A. B. hanks he g an SIR/2022/001011 by Science and Enginee ing
Resea ch Boa d (SERB) India. Ho izon 2020 F amewo k P og amme.
Keywo ds: CZCTS ilms| pho o ol aic op imiza ion| s uc u al cha ac e iza ion| sul u iza ion empe a u e uning
ABSTRACT
The p esen esea ch explo es o he i s ime he in ica e ela ionship be ween sul u iza ion empe a u e a unusual high
empe a u es (up o 700°C) and he s uc u al/op oelec onic p ope ies o Cu2(Zn,Cd)SnS4 (CZCTS) hin ilms, syn hesized ia
a wo- s ep sequen ial p ocess in ol ing he p ecu so ilm deposi ion using ap o ic molecula ink ollowed by he mal ea men
in sul u a mosphe e. X- ay di ac ion pa e ns con i ms he e agonal s uc u e. Scanning Elec on Mic og aphs e ealed sig-
ni ican g ain g ow h, wi h g ain sizes inc easing om ~0.3 μm a 620°C o ~1.5 μm a 680°C, e ec i ely educing g ain bound-
a y ecombina ion. Ene gy dispe si e X- ay spec oscopy demons a ed a Cu- poo and Zn- ich composi ion, wi h a consis en
Cd inco po a ion o ~3.7 a %. Raman spec oscopy showcases he homogenei y and pu i y o he CZCTS c ys alline s uc u e.
P ecise con ol o he sul u iza ion empe a u e plays a c ucial ole in de e mining he pho o ol aic cha ac e is ics o CZCTS-
based sola cells. By inc easing he g ain size and p e en ing he he mal decomposi ion o he CZTS phase, he pho o ol aic
pe o mance peaked a a sul u iza ion empe a u e o 680°C, achie ing a powe con e sion e iciency (PCE) o 10.4%, wi h an
open- ci cui ol age o 0.701 V, a sho - ci cui cu en densi y o 24.3 mA/cm2 and a ill ac o o 60.8%. Ex e nal quan um e i-
ciency eached a maximum o 83.3% a 580 nm. The bandgap o he CZCTS abso be was de e mined o be 1.48 eV, op imal o
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© 2025 The Au ho (s). P og ess in Pho o ol aics: Resea ch and Applica ions published by John Wiley & Sons L d.
2 o 16 P og ess in Pho o ol aics: Resea ch and Applica ions, 2025
pho o ol aic applica ions. Howe e , u he inc easing he sul u iza ion empe a u e o 700°C esul ed in a lowe PCE o 8.5%,
a ibu ed o in e ace deg ada ion and seconda y phase o ma ion. Tempe a u e- dependen cu en – ol age measu emen s e-
ealed a educ ion in ecombina ion losses, wi h an ac i a ion ene gy o 1.24 eV a he CZCTS/CdS in e ace, indica ing e ec i e
de ec passi a ion by Cd inco po a ion. The op imized ilms, sul u ized a 680°C, displayed an abso be hickness o ~1.2 μm
a e sul u iza ion, p o iding e icien ligh abso p ion and cha ge anspo . The indings no only emphasize he c i ical ole o
sul u iza ion empe a u e in enginee ing CZCTS ilm and subsequen ly hei unc ionali y bu also p o ide aluable insigh s o
ine uning hei pe o mance in he ield o pho o ol aic applica ions.
1 | In oduc ion
Eme ging enewable ene gy sou ces p esen a pionee ing solu ion
o mi iga e he challenges posed by he ene gy c isis and en i on-
men al pollu ion. Among hese, pho o ol aic powe gene a ion
echnology eme ges as a p ac ical and i al co ne s one o ealiz-
ing sus ainable en i onmen al conse a ion, ene gy e iciency, and
emission educ ion. This inno a i e app oach no only add esses
he p essing need o cleane ene gy al e na i es bu also shows a
signi ican leap owa d os e ing a g een, sus ainable u u e [1, 2].
Coppe zinc in sul oselenide (CZTSSe) sola cells, based on he
kes e i e c ys al s uc u e, s and ou as one o he mos p omising
eme ging echnologies in he ealm o pho o ol aics. Thei excep-
ional po en ial in he hi d gene a ion o sola echnologies comes
om a combina ion o ac o s, including ea h- abundan ma e i-
als, a unable di ec bandgap, high op ical abso p ion coe icien s,
en i onmen ally iendly cha ac e is ics, and a ela i ely cos -
e ec i eness. This con e gence o p ope ies posi ions CZTSSe
sola cells as a o midable candida e, cha ing a cou se owa d a
sus ainable and economically iable u u e o pho o ol aic ech-
nologies [3–7]. CZTSSe sola cells, e ol ed om 2nd gene a ion Cu
(In,Ga)(S,Se)2 (CIGS), ma k a signi ican s ide o wa d. I is no e-
wo hy ha he cu en pinnacle o powe con e sion e iciency
(PCE) o CIGS de ices s ands a 23.35%, achie ed h ough ac-
uum me hods [8]. In con as , CZTSSe de ices ha e demons a ed
compe i i e PCE alues using solu ion p ocessing echniques. The
acuum p ocesses inhe en o CIGS syn hesis demand subs an ial
ene gy inpu s, conside able capi al in es men , and esul in exces-
si e ope a ing cos s. Fu he mo e, unde lines he unique bene i s
o CZTSSe, which h ough solu ion p ocessing no only yields en-
cou aging esul s bu also p o ides a mo e e ec i e and econom-
ically iable al e na i e in he cons an ly changing ield o sola
cell echnology [9]. Mo eo e , he ansla ion o high- pe o mance
de ices om labo a o y se ings o la ge- scale comme cial p oduc-
ion encoun e s challenges like low yields, p ocess in icacies, and
ma e ial u iliza ion complexi ies. Fo una ely, he solu ion me hod
eme ges as a p omising way wi h as de elopmen al po en ial,
cha ac e ized by i s cos - e ec i eness, s aigh o wa d la ge- a ea
p epa a ion, and ep oducible PCE [10, 11]. In 2021, Xin's g oup
achie ed a ema kable PCE o 13.0% u ilizing a dime hyl sul oxide
(DMSO)- based p ocessing app oach [12]. Meng e al. [13] demon-
s a ed u he imp o emen s, achie ing an e iciency o 13.6%
h ough inno a i e solu ion me hods, ecen ly being epo ed an
upda ed alue o app oxima ely 15% [14]. Signi ican ly, he ce i-
ied e iciency o CZTSSe sola cells ab ica ed using he solu ion
me hod exceeded he highes e iciency o 12.62%, p e iously se
by Kim e al. [15] using acuum me hods. This highligh s he pi -
o al ole o solu ion p ocessing, no only in achie ing compe i i e
e iciencies bu also in su passing benchma ks es ablished by a-
di ional acuum me hods.
Cu en ly, he p oduc ion o CZTSSe abso be s h ough solu-
ion p ocessing ypically in ol es he ollowing s eps: (i) deposi
o a p ecu so laye o he subs a e and (ii) hea ea men o
he p ecu so laye unde sul u and/o an ine a mosphe e
o p oduce he inal polyc ys alline abso be s [16]. While he
highes e iciency eco ded o CZTSSe sola cells manu ac-
u ed h ough solu ion p ocessing is a an imp essi e 14.9%, i
is no ewo hy ha his igu e s ill signi ican ly lags behind he
heo e ical limi p edic ed by he Shockley–Queisse model,
which s ands a app oxima ely 32%. The dispa i y highligh s
he exis ing gap be ween eal- wo ld achie emen s and he he-
o e ical uppe bounds wi hin he ield o CZTSSe sola cell e i-
ciency. Subsequen ly, i emphasizes he signi icance o ongoing
esea ch and de elopmen s in ab ica ion echniques in o de o
b idge his gap and ge close o a aining he maximal e iciency
po en ial p edic ed by he Shockley–Queisse model. The key o
p oducing high- e iciency CZTSSe sola cells is ge ing op- ie
abso be ilms [17, 18].
The u iliza ion o a hyd azine- based p ecu so solu ion s ands
as he mos success ul me hod o CZTSSe sola cell p epa a ion
wi hin he solu ion p ocessing pa adigm. This inno a i e ap-
p oach, pionee ed by IBM in 2010, achie ed a g oundb eaking
ce i ied con e sion e iciency o 12.6% in 2013, a eco d e iciency
ha has se he s anda d o se e al yea s [19, 20]. Ne e heless,
hyd azine sol en s pose inhe en challenges due o hei highly
oxic and explosi e na u e, coupled wi h explici anspo a ion
and applica ion es ic ions in ce ain coun ies and egions.
These limi a ions ha e ca alyzed a apid shi owa d he de el-
opmen and widesp ead adop ion o solu ion me hods employing
non- hyd azine sol en sys ems. P esen ly, an a ay o en i on-
men ally iendly, s able, and high- e iciency sol en sys ems has
eme ged. No able examples include dime hyl sul oxide (DMSO),
N,N- dime hyl o mamide (DMF), e hylene glycol me hyl e he
(EGME), hioglycolic acid and ammonia (TGA), and he e hylene-
diamine/e hanedi hiol sys em (EN/EDT). This ans o ma i e
shi no only add esses sa e y conce ns bu also signi ies a pi o al
ad ancemen in he ield o CZTSSe sola cell ab ica ion, p omo -
ing sus ainabili y and wide accessibili y [21]. Table1 displays a
selec ed o e iew o he expe imen al se ings and de ice pe -
o mances o CZTS/CZTSSe based sola cells employing a ious
sol en - based solu ion- deposi ed abso be s.
Reducing he signi ican Voc losses ound in kes e i e sola cells
has mainly depended on imp o ing abso be quali ies h ough
echniques such con olling Cu- Zn diso de , educing su ace
and g ain bounda y impe ec ions, and con olling abso be
g ain de elopmen [58–60]. Se e al s udies ha e exhibi ed
s a egies o imp o e he abso be cha ac e is ics in kes e -
i e sola cells. Ex ended low- empe a u e annealing enhances
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3 o 16
TABLE 1 | O e iew o he expe imen al se ings and de ice pe o mances o CZTS/CZTSSe based sola cells employing a ious sol en - based
solu ion- deposi ed abso be s.
Sola
cell
Molecula ink
sol en
Dissolu ion
condi ion Hea ea men s Voc Jsc FF PCE Re .
CZTSSe N2H4N2, glo e
box
500°C 513.4 35.2 69.8 12.6 Wang e al.
(2014) [20]
CZTSSe N2H4N2, glo e
box
500°C 471 37.1 70.3 12.7 Kim e al.
(2014) [22]
CZTS MOE and MEA S i ing
(50°C)
580°C 664 14.8 58 5.7 Zhang e al.
(2014) [23]
CZTSSe C₆H₁₅N/C3H8S N2, glo e
box
500°C 382 34.4 60.1 7.86 K. W. B ew e al.
(2015) [24]
CZTS MOE S i ing
(50°C)
250°C + 580°C 581 24.1 66 9.82 Z. Su e al.
(2015) [25]
CZTSSe DMSO S i ing 540°C 449 38.8 68.1 11.8 Xin e al.
(2015) [26]
CZTSSe MOE S i ing 560°C 446 32.22 55.97 8.04 Y.- T. Hsieh
(2016) [27]
CZTSSe TGA, CH3NH2S i ed
(45°C)
510°C 378 28.17 65.4 6.96 Y. Yang e al.
(2016) [28]
CZTSSe C2H4(SH)2. and
C2H4(NH2)2
S i ing
(60°C)
480°C 448 35.19 65.66 10.36 Guchhai e al.
(2017) [29]
CZTS MOE S i ing
(50°C)
600°C 650 25 66.2 10.8 S. H. Hadke
e al. (2018) [30]
CZTSSe DMSO + Tu S i ing 550°C 463 33.4 65.5 10.1 C. M. Su e -
Fella e al.
(2018) [31]
CZTSSe DMSO S i ing 300°C, 500°C,
550°C
531 33.7 64.8 11.6 A. Cabas- Vidani
e al. (2018) [32]
CZTSSe EGME S i ing 540°C + 520°C 578 30.5 63 11.1 S.- H. Wu e al.
(2018) [33]
CZTSSe C2H4(SH)2. and
C2H4(NH2)2
S i ing 550°C 386 29.36 57.26 6.49 Q. Yan e al.
(2019) [34]
CZGTS DMF N2, glo e
box
540°C 583 33.60 55.9 11.0 J. A. Cla k e al.
(2019) [35]
CZTSSe DMSO S i ing 560°C 460 32.2 58.2 8.6 S. Ge e al.
(2019) [36]
CZTS MOE S i ing
(60°C)
200°C + 580°C 640 27.8 71 12.6 Z. Su e al.
(2020) [37]
CZTS MOE S i ing
(50°C)
600°C 670 21.5 57.22 8.24 A. Ib ahim e al.
(2020) [38]
CZTSSe MOE S i ing
(60°C)
550°C 465.1 39.33 66.51 12.18 X. G. Zhao e al.
(2020) [39]
CZTSSe MOE S i ing
(60°C)
555°C 507 33.97 65.36 11.1 G.- X. Liang e al.
(2021) [40]
CZTSSe 1 C2H4(SH)2. and
C2H4(NH2)2 + s abilize
S i ing
(70°C)
550°C 495 37.07 66.26 12.16 X. Chang e al.
(2021) [41]
(Con inues)
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4 o 16 P og ess in Pho o ol aics: Resea ch and Applica ions, 2025
Cu- Zn diso de and inc eases Voc o he de ice. SnOx is c ea ed
by hea ea men in ai , which passi a es laws a he g ain
bounda ies and abso be su ace and can achie e e iciencies o
up o 12.6%. G ain g ow h is managed by ca e ully con olled
sul o- seleniza ion p ocesses, which imp o es de ice e iciency
[15, 20, 61]. Cd alloying pu e sul ide kes e i e has an a ay o
bene i s, including s abilizing he conduc ion band o se , educ-
ing CuZn an isi e de ec s, and posi i ely modula ing he bandgap
[21, 37]. Th ough he use o se e al deposi ion p ocesses, includ-
ing co- e apo a ion and solu ion- based p ocedu es, he inco po-
a ion o Cd has esul ed in e iciency gains o up o 10% in CZTS
sola cells. No able imp o emen s, such as o e 12% e iciency
in CZCTS sola cells, ha e been epo ed; hese we e made
possible by in e ace de ec elimina ion and pos - annealing
[37, 62]. High- e iciency CZCTS sola cells o en equi e high-
empe a u e pos - annealing o CZTS/CdS he e ojunc ion hea
ea men [63]. The ull po en ial o Cd alloying in CZCTS e-
mains un apped. Recen indings e eal ha de ec clus e o -
ma ion, impac ing kes e i e band ailing, is ela ed o abso be
g ain g ow h mechanisms. Di ec - phase ans o ma ion g ain
g ow h, acili a ed by Cu+- Sn4+- based DMSO solu ions, shows
p omise in supp essing de ec o ma ion [64]. This app oach,
success ul in CZTSSe sola cells, holds he po en ial o enhanc-
ing CZCTS sola cell e iciency [12, 50].
This s udy explo ed, o he i s ime, he complex ela ionship
be ween sul u iza ion a unusually high empe a u es (up o
700°C) and he s uc u al and op oelec onic cha ac e is ics
Sola
cell
Molecula ink
sol en
Dissolu ion
condi ion Hea ea men s Voc Jsc FF PCE Re .
CZTSSe DMSO N2, glo e
box
550°C 540 32.1 72.3 12.5 Y. Gong e al.
(2021) [42]
CZTSSe C2H4(SH)2. and
C2H4(NH2)2
S i ing
(70°C)
300°C + 550°C 463 35.65 62.47 10.24 W. Xie e al.
(2022) [43]
CZTSSe DMF/DMSO
bina y sol en s
S i ing 530°C 493.5 33.89 73.30 12.26 Y. Sun e al.
(2022) [44]
CZTSSe DMF S i ing 550°C 501 35.36 66.4 11.76 Y. Cui e al.
(2022) [45]
CZTSSe DMSO N2, glo e
box
550°C 529 33.7 72.9 13.0 Y. Gong e al.
(2022) [12]
CZTSSe MOE S i ing
(60°C)
550°C 505.5 39.3 64.8 12.87 H. Geng e al.
(2022) [46]
CZTSSe DMF S i ing 550°C 520 39.08 63.32 12.86 M. Wang e al.
(2023) [47]
CZCTS DMSO S i ing 625°C 640 27.8 71.0 12.3 X. Pan e al.
(2023) [48]
CZTSSe MOE S i ing 550°C 526.1 36.37 66.52 13.02 Y. Qi e al.
(2023) [49]
CZTSSe MOE, DMSO, DMF S i ing
(60°C)
535 °C 551.20 35.74 71.73 13.8 J. Zhou e al.
(2023) [50]
CZTSSe C2H4(SH)2. and
C2H4(NH2)2
S i ing
(55°C)
550°C 513.85 38.69 69.27 13.77 L. Cao e al.
(2024) [51]
CZTSSe DMF No
men ioned
No men ioned 471.7 34.98 73.61 12.15 J. Zhou e al.
(2024) [52]
CZTSSe MOE S i ing 520°C 576.0 36.9 70.0 14.9 Y. Li e al.
(2024) [53]
CZTSSe MOE S i ing 560°C 573.0 35.1 70.1 14.1 Y. Gong e al.
(2024) [54]
CZTSSe MOE S i ing
(50°C)
540°C 555 36.7 71.2 14.5 J. Wang e al.
(2024) [55]
CZTSSe MOE S i ing 555°C 580 36.63 67.43 14.3 Y. Zhao e al.
(2024) [56]
CZTS MOE S i ing
(60°C)
620°C 664 24.28 62.33 10.0 F. Ye e al.
(2024) [57]
TABLE 1 | (Con inued)
1099159x, 0, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/pip.3899 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [21/03/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
5 o 16
o Cd- based CZTS hin ilms. By ab ica ing CZTS abso be s
using a Cu+- Sn4+- DMSO solu ion (suppo ing in o ma ion [SI],
Figu eS1), he p esen s udy demons a es he ans o ma i e
impac o p ecise empe a u e con ol on he p ope ies o he
CZTS and co esponding de ice. Pho o ol aic cells based on Cd
ee CZTS abso be laye s c ys allized a di e en empe a u es
had a maximum PCE o 4.08% and a Voc o 576 mV (Figu eS2 and
TableS1). The analysis e eals ha high sul u iza ion empe a-
u es induce a ans o ma ion in c ys allini y, d i ing he ansi-
ion om an amo phous o a c ys alline s uc u e. This p ocess
is accompanied by signi ican g ain g ow h, which e ec i ely
educes band ailing and enhances he op oelec onic p ope ies
o he ilms. By in oducing Cd in he CZTS, along wi h band
gap dec ease, he CdS/CZCTS in e ace change in posi i e man-
ne he pho o ol aic p ope ies. As a esul , he PCE inc eases,
peaking a 10.4% a an op imal sul u iza ion empe a u e o
680°C, unde sco ing he c i ical ole o g ain bounda y passi a-
ion and in e ace enginee ing. Howe e , u he inc easing he
sul u iza ion empe a u e o 700°C led o pe o mance deg ada-
ion, a ibu ed o seconda y phase o ma ion and in e ace deg-
ada ion, hus highligh ing po en ial ade- o s in op imizing
p ocessing condi ions. Impo an ly, he inco po a ion o 20% Cd
in o CZTS no only s abilized he conduc ion band o se bu also
signi ican ly educed he Voc loss o CZCTS de ices, e en wi h-
ou pos - hea ea men o he CZCTS/CdS he e ojunc ion. This
wo k es ablishes a no el app oach o uning kes e i e- based
hin ilms h ough a combina ion o Cd- alloying and sul u iza-
ion empe a u e op imiza ion, p o iding aluable insigh s in o
achie ing highe e iciencies and ad ancing he ield o scalable,
solu ion- p ocessed pho o ol aics.
2 | Ma e ials and Me hods
2.1 | Reagen s and Ma e ials
Dime hyl sul oxide (DMSO), Thiou ea (99%), CuCl (99.99%),
SnCl4 (99.998%), Zn (Ac)2 (99.99%), and CdCl2 (98%), all pu -
chased om Sigma- Ald ich, ha e been used as chemicals.
2.2 | CZCTS P ecu so Film P epa a ion
The p ecu so solu ion was p epa ed unde ambien ai condi-
ion, wi h all chemicals used as ecei ed wi hou u he pu i-
ica ion. The 6 mmol o CuCl, 3 mmol o SnCl4, 3.7 mmol o Zn
(Ac)2, 0.74 mmol o CdCl2 (co esponding o 20% o he o al
Zn + Cd mola con en ), and 27 mmol o hiou ea we e dissol ed
in 10 mL o dime hyl sul oxide (DMSO) and s i ed un il com-
ple e dissolu ion. The yellow and clea p ecu so solu ion was
ob ained a e 2- h s i ing. The ab ica ion p ocess desc ibed
in ol es he spin- coa ing o he ap o ic molecula ink on o Mo/
SiO2/Glass subs a e (Suzhou ShangYang Sola Technology Co.),
ollowed by annealing (300°C) o p oduce CZCTS ilms. The
wo- s ep sequence (spin- coa ing and annealing p ocess), is e-
pea ed se en imes o achie e a p ecu so ilm wi h a hickness
o app oxima ely 1 μm (Figu eS3). The sul u iza ion o p ecu -
so ilms was conduc ed in a ubula u nace unde p ecisely
con olled condi ions. The p ocess began wi h a empe a u e
amp- up a a a e o 10°C/min, leading o he a ge empe a-
u e, which anged be ween 620°C and 700°C (Figu eS4). Once
he desi ed empe a u e was eached, he ilms we e held a his
empe a u e o 15 min o allow ho ough sul u inco po a ion
and comple e he eac ion. The sul u iza ion p ocess was ca -
ied ou unde a mosphe ic p essu e wi hin a dedica ed g aphi e
box con aining sul u pelle s (0.1 g) as he sou ce ma e ial. The
g aphi e box was speci ically designed o es ablish an op imal
sul u - ich en i onmen , e ec i ely educing con amina ion
isks while ensu ing a uni o m dis ibu ion o sul u apo . This
se up acili a ed consis en sul u inco po a ion ac oss he ilm,
which is c ucial o achie ing homogenei y in he ma e ials
s uc u al and composi ional p ope ies.
2.3 | Film Cha ac e iza ion
XRD pa e ns we e collec ed using an X- ay di ac ome e ea-
u ing Cu Kα as he adia ion sou ce (Empy ean, PANaly ical).
Raman spec a we e ob ained using a Raman spec ome e
(Lab- RAM HR E olu ion, HORIBA) wi h a 532 nm lase diode
as he exci a ion sou ce. De ailed scanning elec on mic oscopy
(SEM) images we e cap u ed on a Hi achi S4800 SEM, u ilizing
a 10 kV accele a ing ol age. The mic os uc u e and elemen al
dis ibu ion o he sul u ized ilms we e analyzed using a JEOL-
F200CF STEM equipped wi h an ene gy dispe si e X- ay spec-
oscopy (EDS) sys em.
2.4 | De ice Fab ica ion and Cha ac e iza ion
Fo he de ice ab ica ion, ini ially, a 50 nm- hick CdS bu e
laye was deposi ed on o he sul u ized ilms (Figu eS5) using
he chemical ba h deposi ion me hod. Following his, adio e-
quency spu e ing was employed o deposi in insic ZnO (i- ZnO)
and indium in oxide (ITO) o o m he essen ial window laye .
The mal e apo a ion o Sil e (Ag) using mechanical masks
comple ed he en i e de ice. Mo e de ails a e p esen ed in he SI.
As men ion in he in oduc ion, he op imiza ion o he de ice
ab ica ion has been done on Cd- ee CZTS sola cells, s uc-
u al and pho o ol aic p ope ies being also e ealed in he SI.
The cu en densi y– ol age (J–V) cu es we e eco ded using
a Kei hley 2400 Sou ce Me e unde simula ed AM 1.5 sunligh
a 100 mW cm−2, calib a ed wi h a Si e e ence cell (12.8% e i-
ciency o e an ape u e a ea o 0.23 cm2). EQE measu emen s
we e conduc ed using he Enli ech QE- R es sys em, employing
calib a ed Si and Ge diodes as e e ences.
3 | Resul s and Discussion
The XRD pa e ns o p ecu so ilms subjec ed o a ying sul u -
iza ion empe a u es a e p esen ed in Figu e1a. Aside om he
peak o igina ing om Mo (110 e lec ion, 2θ = 40.5°, ICDD PDF
no. 00- 004- 0809), he ilms show peaks a app oxima ely 28.4°,
32.92°, 47.13°, 56.05°, and 58.71°, which co espond o e agonal
CZTS 112, 220 and 312 di ac ion lines (ICDD PDF no. 04- 015-
7542). The absence o signi ican de ia ions in he di ac ion
pa e n implies a high le el o s uc u al in eg i y and success ul
alignmen wi h p esen ab ica ion objec i es. Mo eo e , om
he obse ed pa e ns, he c ys alli e size e olu ion as unc ion
o sul u iza ion empe a u e p o ide use ul insigh s in o he
ilm p oduc ion p ocess (SI, Figu eS6). The g adual inc ease o
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6 o 16 P og ess in Pho o ol aics: Resea ch and Applica ions, 2025
he mean c ys alli e size ( he cohe ence leng h along he c ys al-
log aphic di ec ions) up o 700°C shows a link be ween highe
sul u iza ion empe a u es and ad an ageous mic o- c ys alli es
o ma ion. The subsequen dec ease in c ys allini y a 700°C
implies he onse o ad e se e ec s, po en ially linked o decom-
posi ion p ocesses. This nuanced ela ionship be ween sul u -
iza ion empe a u e and c ys allini y poin s ou he need o a
well unde s anding o he he mal ac o s du ing he ab ica ion
p ocess.
The p og essi e inc ease in g ain size wi h highe sul u iza ion
empe a u es (Figu e1b) indica es ha ele a ed empe a u es
p omo e enhanced c ys al g ow h and coalescence, leading o
he o ma ion o la ge , well- de ined g ains wi hin he CZCTS
ilms, as shown in SEM images p o ided in he Figu es1b and
S7. The imp o emen in g ain mo phology is i al o educing
g ain bounda y densi y, which di ec ly impac s he pe o mance
o CZCTS- based sola cells. G ain bounda ies a e signi ican e-
combina ion cen e s, and hei densi y di ec ly in luences he
ecombina ion a e. Since he ecombina ion a e is p opo ional
o he o al g ain bounda y a ea, educing he a ea inhe en ly
dec eases ecombina ion losses. This implies ha he ca ie
li e ime a he g ain bounda ies is in e sely p opo ional o he
g ain bounda y a ea. The e o e, by p omo ing la ge and mo e
uni o m g ains, he o al g ain bounda y a ea is minimized,
leading o enhanced ca ie li e imes and be e cha ge ans-
po . This imp o emen ansla es in o highe elec ical con-
duc i i y and supe io de ice e iciency. The SEM images e eal
ha a empe a u es up o 680°C, he ilms exhibi compac
and uni o m g ains, con ibu ing o supe io s uc u al in eg-
i y and op oelec onic p ope ies. Howe e , a 700°C, pinholes
become e iden in he ilm, sugges ing ha excessi e sul u iza-
ion empe a u es may induce localized he mal decomposi ion
o ma e ial de ec s, which comp omise he ilm's quali y. These
obse a ions align closely wi h he XRD esul s, whe e he in-
c ease in g ain size obse ed in SEM co ela es wi h he en-
hanced c ys alli e size and educed la ice s ain e iden in he
di ac ion pa e ns. Thus, he complemen a y SEM and XRD
analyses con i m ha op imizing sul u iza ion empe a u e is
c i ical o achie ing he desi ed balance be ween imp o ed c ys-
allini y and minimal de ec o ma ion, he eby op imizing he
CZCTS abso be 's pho o ol aic pe o mance.
The Raman spec oscopy analysis o CZCTS ilms p o ides
c ucial insigh s in o he s uc u al cha ac e is ics o he ma e-
ial (Figu e2). The A1 ib a ion mode in he Raman spec a is
FIGURE 1 | (a) XRD and (b) SEM images o CZCTS hin ilms sul u ized a di e en empe a u e. All ba s co espond o 1 μm (Mag = 10.00 KX).
[Colo igu e can be iewed a wileyonlinelib a y.com]
FIGURE 2 | Raman spec oscopy o CZCTS hin ilms. [Colo igu e
can be iewed a wileyonlinelib a y.com]
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7 o 16
obse ed as a dominan and well- de ined peak a 335.6 cm−1,
which con i ms he p esence o he CZCTS kes e i e c ys al
s uc u e, alida ing he success ul syn hesis o he desi ed
phase. The A1 mode is associa ed wi h S- only ib a ions, wi h
Cu- Sn and Cu- Zn ib a ions agains he [110] and [1–10] c ys al-
log aphic di ec ions, espec i ely, wi h a ne sul u con ibu ion.
The p esence o he A1 mode ac oss a ying sul u iza ion em-
pe a u es indica es he s abili y o he CZCTS phase h oughou
he empe a u e ange in es iga ed, wi h minimal s uc u al
changes. No ably, he e a e no signi ican shi s o b oadening
in he A1 mode, sugges ing ha sul u iza ion up o 700°C does
no induce no able he mal deg ada ion o phase ansi ions,
which is u he co obo a ed by he XRD da a showing s a-
ble c ys alli e sizes up o his empe a u e. Fu he mo e, a he
highe sul u iza ion empe a u e o 700°C, an addi ional dis-
inc peak eme ges a ound 407 cm−1, co esponding o he MoS2
phase, which indica es he p esence o his phase on o unde
he su ace o he CZCTS, which migh al e also he pho o ol-
aic p ope ies o he inal de ice.
Table2 summa izes alues o dis inc i e modes wi hin he KS
phase o CZCTS ilms ac oss a empe a u e spec um (620°C o
700°C). No ably, B (TO)269 cha ac e izes CZTS ca ions aligning
agains S a oms||[001], wi h epo ed alues spanning 250 o
252 cm−1. B (LO)285 signi ies he alignmen o all ca ions agains
S a oms||[001], exhibi ing alues om 285 cm−1 o 288 cm−1. In
E (TO)305/A305, Cu + Sn aligns agains [110], and Cu + Zn aligns
agains [11¯0], in ol ing a ne sul u con ibu ion in he (x- y)
plane, wi h epo ed alues anging om 302 o 306 cm−1. A335/B
(LO)335 cap u es S- only and ca ion ib a ions agains [110] and
[11¯0], espec i ely, wi h alues in he ange o 334 o 337 cm−1.
E (LO)341 e eals Zn aligning agains [110] wi h Cu opposi ely
posi ioned, inco po a ing speci ic S a oms agains Zn and Cu,
and epo s alues be ween 345 cm−1 and 349 cm−1. B (TO)354
ea u es Cu- Zn alignmen agains [001] wi h S in he (x- y) plane,
p esen ing alues om 355 o 367 cm−1.
Ac oss he empe a u e ange, he Raman peak loca ion o he
A335/B (LO)335 mode is compa a i ely consis en , wi h a sligh
TABLE 2 | Raman shi s (cm−1) co esponding o phonon modes iden i ied om he Lo en zian componen s (shown in Figu e2) o he CZCTS
ilms.
Row
CZCTS
620°C
CZCTS
635°C
CZCTS
650°C
CZCTS
680°C
CZCTS
700°C
Modes in
KS phase A omic Mo emen s
Expe imen al
epo ed alues
1255.69 251.71 255.60 250.99 251.10 B (TO)269 CZTS ca ions (Cu, Zn.
Sn)||[001], agains S
250 [65]
252 [66]
2287.93 288.03 285.50 288.29 286.75 B (LO)285 All ca ions||[001],
agains S
285 [66]
287 [67, 68]
288 [58, 69]
3303.51 302.11 307.06 — — E (TO)305
/A305
Cu + Sn||[110],
Cu + Zn||[1
1
0]; ne S
con ibu ion/S- only
in he (x- y) plane
302 [70]
303 [58]
305 [71]
306 [66, 72]
4335.16 335.10 335.06 335.15 335.37 A335
/B (LO)335
S- only/Cu- Sn||[110],
Cu + Zn||[1
1
0]; ne
S con ibu ion
334 [66]
335 [73]
336 [74]
337 [67, 75]
5349.24 348.79 346.03 —345.78 E (LO)341 Zn||[110], Cu oughly
opposi e; wo S
agains Zn and wo
o he S agains Cu
347 [66]
6363.70 365.60 363.19 362.66 B (TO)354 Cu- Zn||[001]; S
in (x- y) plane
355 [76]
364 [77]
366 [65, 71]
367 [58]
FIGURE 3 | FWHM and peak a ea o A335/B (LO)335 ib a ion mode
o he CZCTS samples. [Colo igu e can be iewed a wileyonlineli-
b a y.com]
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8 o 16 P og ess in Pho o ol aics: Resea ch and Applica ions, 2025
la ge Raman shi obse ed a 700°C. This end is simila o
wha has been epo ed in o he wo ks in es iga ing he em-
pe a u e dependence o ib a ional modes in CZTS and CZCTS
ilms [58]. The numbe o ac i e ib a ional modes is ep esen ed
by he a ea o he Raman peak, which inc eases ypically wi h
empe a u e. I eaches i s maximum a 680°C and hen s a s
o dec ease sligh ly a 700°C. Up o 680°C, his end sugges s
an imp o emen in c ys alline quali y o a dec ease in de ec
densi y, consis en wi h obse a ions om ecen s udies on he
impac o empe a u e on CZTS c ys allini y [78]. A highe em-
pe a u es, s uc u al deg ada ion o de ec o ma ion is likely, as
indica ed by he dec ease in peak in ensi y and he b oadening
o he ull wid h a hal maximum (FWHM). The FWHM, an in-
dica ion o c ys alline quali y ha is in e sely co ela ed, d ops
om 8.00 a 620°C o 6.15 a 650°C (Figu e3). None heless, a
mino ise in FWHM a 680°C and 700°C sugges s ha la ice
s ain o de ec de elopmen may be beginning a hese high
empe a u es. The in ensi y o he ib a ional mode is ep e-
sen ed by he heigh o he Raman peaks, which no mally ise
wi h empe a u e ( he a io A335/B285 ollows he same end).
The peak is eached a ound 650°C, and as empe a u es ise,
hey g adually dec ease. Up o 650°C, imp o emen s in c ys al-
lini y a e consis en wi h his pa e n; a highe empe a u es,
he e may be s uc u al al e a ions o he in oduc ion o de ec s.
Figu e4 shows he EDS coupled wi h SEM mapping, illus a ing
he uni o m dis ibu ion o elemen s ac oss he sample su ace.
The elemen al composi ion (Table3) con i ms a desi able Cu-
poo and Zn- ich p o ile in all ilms, which is known o a o
enhanced pho o ol aic pe o mance by educing deep- le el de-
ec s a es [79]. The Cd concen a ion emains consis en ac oss
all samples, while Zn con en is simila ly s able, suppo ing he
FIGURE 4 | EDS spec a, and he su ace EDS mapping o he componen s elemen s o he sample sul u ized a di e en empe a u e. [Colo
igu e can be iewed a wileyonlinelib a y.com]
TABLE 3 | Chemical elemen al composi ion (a %) o he CZCTS ilms.
Sample Cu (a .) Zn (a .) Cd (a .) Sn (a .) S (a ) Cu/(Zn + Cd + Sn) (Zn + Cd)/Sn S/ca ions
CZCTS 700°C 15.86 12.09 3.22 13.63 50.72 0.54 1.12 1.13
CZCTS 680°C 19.68 11.73 3.99 10.65 53.92 0.75 1.47 1.17
CZCTS 650°C 18.51 11.79 3.70 9.16 56.81 0.75 1.69 1.31
CZCTS 635°C 19.77 11.45 2.64 10.62 55.50 0.80 1.32 1.24
CZCTS 620°C 21.35 13.23 4.72 11.27 49.41 0.73 1.59 0.97
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9 o 16
ep oducibili y o he alloying s a egy. Howe e , he in concen-
a ion is ela i ely lowe a lowe sul u iza ion empe a u es
(620°C), while he sul u con en is also less a hese empe a-
u es, eaching a minimum a 635°C. In e es ingly, a he high-
es sul u iza ion empe a u e (700°C), he Cu/(Zn + Cd + Sn)
a io dec eases signi ican ly o app oxima ely 0.5, e lec ing
p onounced Cu deple ion and unexpec edly high Sn concen a-
ions. This anomalous composi ion a 700°C, which is ypi ied
by an excess o Sn and a Cu de iciency, may con ibu e o he
lowe pe o mance in hese samples. A highe empe a u es,
one migh no mally p edic Sn loss h ough di usion owa d
he su ace ollowing he e apo a ion, while he e apo a ed
Sn is eabso bed on he CZCTS su ace conside ing he closed
space ea u e o he g aphi e box. Al e na i ely, Cu may mig a e
o he MoS₂/Mo in e ace, as sugges ed by e idence om simi-
la sys ems, d i en by he modynamic a o abili y o in e acial
s abiliza ion. This mig a ion could also al e he s oichiome y
and accoun o he Cu de iciency.
The pe o mance o CZCTS based pho o ol aic de ices
(Figu e5), as de ailed in Table4, e eals a well- de ined end
wi h espec o sul u iza ion empe a u e. S a ing a 620°C,
he achie ed PCE was 5.14%, accompanied by an open- ci cui
ol age (Voc) o 0.480 V, a sho - ci cui cu en densi y (Jsc) o
18.97 mA cm−2, and a ill ac o (FF) o 56.75%. Subsequen ly,
inc easing he sul u iza ion empe a u e o 635°C esul ed in
an imp o ed PCE o 6.16%, d i en by a Voc o 0.608 V and a
Jsc o 22.03 mA cm−2, albei a sligh ly educed FF o 46.32%.
As he empe a u e u he ose o 650°C, he PCE con in-
ued inc easing, eaching 7.12% wi h a Voc o 0.608 V, Jsc o
19.79 mA cm−2, and an imp o ed FF o 59.32%. A 680°C,
he de ice achie ed he maximum pe o mance, wi h a PCE
o 10.4%, a ibu ed o a combina ion o he highes Voc o
0.701 V, a Jsc o 24.31 mA cm−2, and an FF o 60.81%. Howe e ,
a 700°C, he PCE declined o 8.51%, co esponding o a sligh
educ ion in Voc o 0.624 V, Jsc o 24.07 mA cm−2, while main-
aining a ela i ely high FF o 59.13%. This end aligns wi h
obse a ions epo ed in ecen s udies, whe e op imal sul-
u iza ion empe a u es imp o e g ain g ow h, c ys allini y,
and de ec passi a ion, con ibu ing o enhanced de ice pe -
o mance. Fo example, Pan e al. [48] obse ed a simila in-
c ease in PCE wi h highe sul u iza ion empe a u es due o
educed g ain bounda y ecombina ion, wi h diminishing e-
u ns a excessi ely high empe a u es a ibu ed o in e ace
deg ada ion and seconda y phase o ma ion. The ob ained
esul s co obo a e hese indings, pa icula ly he s ong co -
ela ion be ween la ge g ain size a 680°C and educed e-
combina ion losses.
The decline in PCE a 700°C can be asc ibed o a delica e
equilib ium be ween he bene icial and de imen al e ec s
o he sul u iza ion p ocess on he CZCTS abso be ilm.
While inc easing sul u iza ion empe a u es gene ally lead
o imp o ed c ys allini y, g ain size, and cha ge ca ie mo-
bili y, pushing he limi s o 700°C migh induce ad e se e -
ec s, such as in e acial decomposi ion, phase seg ega ion,
seconda y phase o ma ion, o de ec gene a ion, which com-
p omise elec onic p ope ies and o e all pho o ol aic pe o -
mance as simila ly epo ed in p e ious s udies [21, 80, 81].
Addi ionally, a highe empe a u es, he e is a likelihood
o enhanced g ain bounda y ecombina ion and inc eased
su ace oughness, nega i ely impac ing he cha ge anspo
p ope ies wi hin he ilm. The e o e, he decline in PCE a
700°C shows he c i ical impo ance o ca e ully op imiz-
ing sul u iza ion empe a u es, ecognizing ha exceeding
a ce ain limi can in oduce de imen al ac o s ha o se
he gains achie ed a lowe empe a u es, emphasizing he
nuanced balance equi ed o maximizing he e iciency o
CZCTS abso be ilms [21, 80, 81].
The c oss- sec ional SEM images depic ed in Figu e 6 o e
insigh s in o bo h he abso be and he de ices enginee ed
om he high- pe o mance CZCTS ilms, p epa ed a 680°C.
No ably, he images showcase a ypical la ge- g ain s uc u e,
wi h ce ain g ains ex ending seamlessly h oughou he en i e
hickness o he CZCTS laye . The s a egic p esence o such
la ge g ains holds in insic bene i s o de ice pe o mance,
e ec i ely minimizing he likelihood o ecombina ion o pho-
ogene a ed ca ie s a g ain bounda ies. This inhe en cha ac-
e is ic demons a es he po en ial o CZCTS ilms syn hesized
FIGURE 5 | J–V cu es o CZCTS based de ices. [Colo igu e can be
iewed a wileyonlinelib a y.com]
TABLE 4 | De ailed pa ame e s o pho o ol aic de ices based on he
CZCTS ilms.
Sample
Jsc (mA/
cm2)
Voc
(mV) FF (%)
PCE
(%)
CZCTS
700°C
23.1 624 59.1 8.5
CZCTS
680°C
24.3 701 60.8 10.4
CZCTS
650°C
19.8 608 59.3 7.1
CZCTS
635°C
22.0 608 46.3 6.2
CZCTS
620°C
18.8 480 56.7 5.1
1099159x, 0, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/pip.3899 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [21/03/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License
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Suppo ing In o ma ion
Addi ional suppo ing in o ma ion can be ound online in he
Suppo ing In o ma ion sec ion.
1099159x, 0, Downloaded om h ps://onlinelib a y.wiley.com/doi/10.1002/pip.3899 by Readcube (Lab i a Inc.), Wiley Online Lib a y on [21/03/2025]. See he Te ms and Condi ions (h ps://onlinelib a y.wiley.com/ e ms-and-condi ions) on Wiley Online Lib a y o ules o use; OA a icles a e go e ned by he applicable C ea i e Commons License