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Syn hesis and Cha ac e iza ion o CuSe Thin Films ia
Chemical Vapo Deposi ion o Enhanced Pho oca aly ic
Wa e Spli ing
Sana Ta iq (Co esponding Au ho )
Uni e si y o Managemen and Technology (UMT), Laho e, Punjab 54770, Pakis an
Email: sana a [email protected]
I am Shahzadi
Depa men o Chemis y, Laho e College o Women Uni e si y, Laho e, Pakis an
Email: [email p o ec ed]
Nadeem Jan
Depa men o Chemis y, Beijing Uni e si y o Chemical Technology, Beijing,
China Email: [email p o ec ed]
Syed Amee Tahi
Depa men o Biomedical Enginee ing, NED Uni e si y o Enginee ing and
Technology, Ka achi, Pakis an Email: sye[email p o ec ed]
One o he key echnologies in he pu sui o clean hyd ogen p oduc ion is
pho oca aly ic wa e spli ing. High su ace ac i i y and app op ia e band gaps a e
essen ial o his p ocedu e in semiconduc o ma e ials. Due o i s ad an ageous
elec ical s uc u e, adjus able op oelec onic cha ac e is ics, and en i onmen al
s abili y, coppe selenide (CuSe) s ands ou as a ype o semiconduc o . The
ab ica ion o CuSe hin ilm This pape p o ides a de ailed examina ion o he
chemical apo deposi ion (CVD), i s ma e ial p ope ies, and i s e ec i eness in
pho oca aly ic wa e spli ing applica ions. All o his is co e ed in de ail in his,
including doping, nanos uc u ing, and he e ojunc ion enginee ing, o e ing a
ho ough assessmen o he s a e-o - he-a om 2018 o 2025 as well as po en ial
u u e pa hs.
Keywo ds: Coppe Selenide (CuSe), Thin Films, Chemical Vapo Deposi ion (CVD),
Pho oca alysis, Wa e Spli ing, Pho oelec ochemical (PEC) Hyd ogen E olu ion,
Bandgap Enginee ing, He e ojunc ions, Cha ge Ca ie Sepa a ion, Semiconduc o
Pho oca hodes.
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In oduc ion
Con e ing o clean and enewable ene gy sou ces has eme ged as a op wo ldwide
p io i y due o he accele a ion o clima e change, he deple ion o ossil uels, and he
ising need o sus ainable ene gy. Because o i s high g a ime ic ene gy densi y,
s o abili y, and he ac ha he only esul o bu ning is wa e , hyd ogen (H₂) is seen
as a possible ze o-ca bon uel among o he ene gy ca ie s. The ene gy-in ensi e and
signi ican CO₂ emissions o con en ional hyd ogen p oduc ion echniques, like
s eam me hane e o ming, jeopa dize sus ainabili y objec i es.
In his ega d, he p oduc ion o g een hyd ogen di ec ly om wa e and sunligh —a
plen i ul, clean, and enewable esou ce iad—has become appealing h ough he use
o pho oca aly ic and pho oelec ochemical (PEC) wa e spli ing. The c ea ion o
ex emely e ec i e, inexpensi e, and eadily a ailable semiconduc o pho oca alys s
ha can cap u e isible ligh and ca alyze edox p ocesses in mild en i onmen s is
essen ial o his echnology.
Coppe selenide (CuSe), a membe o he semiconduc o ma e ial amily, has d awn
in e es la ely because o i s
Di ec and na ow bandgap (1.4–1.7 eV), pe ec o abso bing isible ligh
High abso p ion coe icien , which makes ligh ha es ing mo e e ec i e
Sui able o pho oca hodic wa e spli ing, p- ype conduc i i y
Low oxici y and ea h abundance in con as o semiconduc o s based on hea y
me als.
CuSe's conduc ion band edge is mo e nega i e han he hyd ogen e olu ion po en ial,
which allows p o ons o spon aneously educe in o H₂ when exposed o ligh . This
p ope y gi es i he po en ial o be a pho oca hode ma e ial. I may also o m
he e ojunc ions wi h n- ype semiconduc o s (such as ZnSe and TiO₂) due o i s band
alignmen , which imp o es cha ge anspo and sepa a ion.
Al hough hese ad an ages exis , CuSe's pe o mance is hea ily elian on he calibe
o i s hin- ilm p oduc ion, speci ically ega ding shape, c ys allini y, and
s oichiome ic con ol. Chemical Vapo Deposi ion (CVD) becomes ex emely
impo an in his si ua ion.
CVD is a lexible, scalable, and con ollable syn hesis me hod ha enables:
P ecise s oichiome ic egula ion using p ecu so s in he gas phase
Uni o m coa ing o in ica e subs a es
G ain bounda ies and ilm mo phology cus omiza ion
Inco po a ion o doping and nanos uc u ing echniques
Al hough CVD has been widely used o hin ilms o oxides and sul ides (such as
CuFeO₂ and CuWO₄), i s use in chalcogenide sys ems, such as CuSe, is s ill in i s
in ancy. Ne e heless, p elimina y e idence sugges s ha CuSe hin ilms gene a ed
by CVD can p o ide be e PEC pe o mance han ilms made using adi ional
solu ion-based me hods.
Li e a u e e iew
Chopade e al. (2025) in es iga ed. The impac o phase composi ion and
s oichiome ic de ia ion on he elec oca aly ic ac i i y o coppe selenide
(Cu<sub>x</sub>Se) ma e ials o wa e spli ing applica ions was in es iga ed.
Using a cus omized sol o he mal syn hesis p ocess, he s udy me hodically examined
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se e al non-s oichiome ic phases, including CuSe, Cu<sub>1.8</sub>Se, and
Cu sub>2</sub>Se. High- esolu ion ansmission elec on mic oscopy (HRTEM) and
X- ay di ac ion (XRD) we e used by he au ho s o con i m unique c ys allog aphic
inge p in s and nanoscale mo phologies linked o each phase.
Za a , e al. (2023) in his wo k, sul u -doped CuSe ilms p oduced ia chemical ba h
deposi ion (CBD) we e examined. Unde AM 1.5G illumina ion, he addi ion o
sul u imp o ed ligh abso p ion and cha ge ca ie sepa a ion, yielding a
pho ocu en densi y o abou 1.8 mA/cm². I p o ed ha basic doping echniques can
g ea ly imp o e PEC pe o mance.
Ghobadi, Nade , e al. (2020). To asce ain he op ical bandgap and ecombina ion
cha ac e is ics o CuSe hin ilms, he scien is s conduc ed UV-Vis DRS and
pho oluminescence esea ch. Band gaps be ween 1.45 and 1.68 eV we e obse ed.
The s udy shed ligh on he ecombina ion p ocesses associa ed wi h de ec s and
elec onic ansi ions. Cell
Chen e al. (2022) hyd o he mally p oduced ZnSe/CuSe he e os uc u es wi h ype-II
band alignmen . The composi e's e ec i e cha ge sepa a ion a he he e ojunc ion
in e ace esul ed in no able inc eases in pho ocu en . I demons a ed how CuSe and
n- ype semiconduc o s can be coupled.
Lai, W., e al. (2022) In his s udy, yolk-shell nanos uc u es made o gold
nanopa icles enclosed in a Cu₂Se shell we e p esen ed. Gold's plasmonic impac
imp o ed elec on injec ion and isible ligh abso p ion, inc easing H₂ gene a ion by
mo e han 40%. A hyb id nanopho onic me hod o sola uel applica ions was
demons a ed.
Pee e s, M. E., e al. (2018). In his wo k, he easibili y o using a mosphe ic p essu e
chemical apo deposi ion (APCVD) o deposi Cu-based oxide semiconduc o s was
con i med. Despi e being cen e ed on CuWO₄, i c ea ed s anda ds o hin- ilm
homogenei y and p ecu so con ol ha apply o CuSe.
Yengan iwa , A., e al. (2018). CuFeO₂ pho oca hodes we e c ea ed by he au ho s
using chemical apo deposi ion. The s udy ad anced knowledge o Cu-based e na y
oxides and p oposed ha CuSe hin ilms could bene i om simila echniques o
inc ease PEC du abili y and c ys allini y.
He, J., e al. (2019) Cu-based chalcogenides we e among he many hin- ilm ma e ials
o wa e spli ing ha we e co e ed in his ho ough e iew. I o e ed heo e ical
amewo ks o CuSe- ela ed band alignmen , cha ge anspo , and e iciency-
boos ing echniques.
Ikeda, S. (2021) This wo k, which ocused on in e ace enginee ing, highligh ed he
signi icance o passi a ion and su ace ea men s in p ese ing he long- e m PEC
s abili y o Cu-based pho oca hodes. The obse a ions ha e di ec ele ance o he
endu ance o CuSe ilms.
Chen, Q., e al. (2023). CuSe combined wi h me al oxide co-ca alys s h ough
sol o he mal syn hesis was demons a ed in his wo k. Co-ca alys s inc eased
ca aly ic ac i i y and cha ge ca ie li espan, acili a ing he c ea ion o CuSe hyb id
sys ems.
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Scope o This Re iew
The objec i e o his e iew pape is o p esen a ho ough and c i ical e alua ion o
CuSe hin ilms p oduced h oughou he p e ious i e yea s (2018–2025) u ilizing
CVD and associa ed echniques. I emphasizes:
CuSe phase s uc u es and ma e ial cha ac e is ics ha a e pe inen o pho oca alysis,
Pa ame e s, di icul ies, and p ospec s o CVD syn hesis,
Thin ilm s uc u al, op ical, and PEC cha ac e isa ion,
Techniques o imp o e wa e -spli ing pe o mance include doping, nanos uc u ing,
and he e ojunc ion enginee ing.
Analysis in compa ison o o he Cu-based and non-Cu ma e ials
Fu u e di ec ions o esea ch, especially in andem de ices, compu a ional design,
and low- empe a u e CVD
This e iew seeks o expedi e he logical design o CuSe-based pho oca alys s o
nex -gene a ion sola hyd ogen p oduc ion sys ems by using echnical analysis wi h
insigh s om he li e a u e.
The de elopmen o enewable hyd ogen p oduc ion me hods has inc eased due o
en i onmen al conce ns and global ene gy demands. One o he mos e ec i e and
en i onmen ally iendly me hods is pho oelec ochemical (PEC) wa e spli ing,
which uses sola ene gy o sepa a e wa e in o hyd ogen and oxygen.
Fo his pu pose, hin- ilm semiconduc o s a e becoming mo e popula , pa icula ly
ansi ion me al chalcogenides (TMCs). CuSe is a s ong con ende o usage as a
pho oca hode in PEC sys ems due o i s ideal bandgap (1.4–1.7 eV), high abso p ion
coe icien , and ad an ageous band edge loca ions.
High-quali y CuSe ilms wi h adjus able shape and c ys allini y, which a e essen ial
o e icien ligh abso p ion and cha ge sepa a ion, may now be ab ica ed hanks o
ecen de elopmen s in deposi ion echnologies, especially CVD.
CuSe Ma e ial O e iew: Elec onic and Pho oca aly ic Rele ance
A membe o he bina y chalcogenide amily, coppe selenide (CuSe) has become a
ma e ial o in e es o pho oca aly ic applica ions because o i s isible-ligh ac i i y,
phase a ie y, and cus omizable elec onic s uc u e. I is pa icula ly p omising o
pho oelec ochemical (PEC) hyd ogen gene a ion due o i s ad an ageous ene gy
band alignmen and capaci y o c ea e he e ojunc ions wi h o he semiconduc o s.
Elec onic S uc u e and Band Alignmen
The in insic p- ype conduc i i y o CuSe is mainly asc ibed o he accep o s a es
known as coppe acancies (V_Cu). I s abili y o ac as a pho oca hode is c ucially
dependen on i s p- ype beha io , which pe mi s e ec i e hole anspo and hyd ogen
e olu ion a he semiconduc o –elec oly e in e ace.
F om he pe spec i e o he ene gy band:
CuSe's conduc ion band minimum (CBM) p o ides enough he modynamic d i ing
o ce o p o on educ ion o H₂ because i is loca ed abo e he hyd ogen e olu ion
po en ial (0 V s. RHE).
When combined wi h a pho oanode in a andem PEC cell, he alence band maximum
(VBM), which is loca ed below he oxygen e olu ion po en ial (1.23 V s. RHE),
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educes he likelihood o pho oco osion.
The isible spec um (~400–850 nm) may be e icien ly ha es ed hanks o he
bandgap ene gy, which no mally anges be ween 1.45 and 1.7 eV. This maximizes he
e iciency o sola - o-hyd ogen (STH) con e sion.
Addi ionally, CuSe's band o ien a ion can be e icien ly adjus ed by doping, alloying,
o he e ojunc ion c ea ion, which helps o imp o e ca ie sepa a ion and educe
cha ge ecombina ion, wo c ucial pho oca aly ic pe o mance bo lenecks.
Phase Di e si y
The pho oca aly ic beha io o Cu–Se compounds is g ea ly in luenced by hei many
s oichiome ic phases, each o which has unique c ys allog aphic s uc u es and
op oelec onic cha ac e is ics. These consis o :
Phase
C ys al S uc u e
Bandgap (eV)
Rele ance o PEC
Cu₂Se
Cubic o e agonal
~1.2–1.5
Good conduc i i y,
al hough appa en
abso p ion is limi ed
by a small bandgap.
CuSe
Monoclinic o
hexagonal
~1.5–1.7
Pe ec o balanced
edox po en ials and
abso p ion o isible
ligh
CuSe₂
O ho hombic
~1.7–1.9
G ea e sui abili y o
UV-d i en ca alysis
due o i s wide
bandgap
Monoclinic CuSe is hough o be he mos app op ia e o hem o PEC applica ions
because
Di ec bandgap (1.5–1.7 eV): P omo es he p oduc ion o elec on–hole pai s and
pho on abso p ion.
High pho oconduc i i y: Unde ligh , i enables quick cha ge ansmission.
Longe di usion leng hs a e suppo ed, and bulk ecombina ion is dec eased by
enhanced ca ie mobili y.
The space g oup P2₁/c is whe e monoclinic CuSe c ys allizes. I s laye ed s uc u es
encou age aniso opic cha ge mig a ion, which can be used o align ilms du ing CVD
and o he deposi ion p ocedu es.
Fu he mo e, ecen esea ch demons a es ha syn hesis pa ame e s, including
g ow h empe a u e, p ecu so a io, and gas low a es in CVD, can modi y he
mo phology and c ys allini y o hese phases, allowing o p ecise uning o
op oelec onic p ope ies o desi ed PEC pe o mance.
Depending on whe he he a mosphe e is coppe - ich o selenium- ich du ing
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syn hesis, a phase ansi ion be ween Cu₂Se ↔ CuSe may occu . Con olling he
p ecu so s oichiome y is he e o e essen ial o CVD de elopmen .
In con as o non-s oichiome ic Cu–Se phases, which could deg ade o expe ience
su ace oxida ion while in use, phase-pu e CuSe has supe io PEC s abili y.
This dual-axis g aph con as s he onse po en ial ( ed line) and bandgap ene gy (blue
ba s) o a ious CuSe-based pho oca aly ic sys ems. These a e impo an ac o s
in luencing how well hey di ide wa e .
Bandgap (eV):
The pa o he sola spec um ha a subs ance may abso b is de e mined by i s
bandgap.
E e y CuSe-based sys em alls be ween 1.45 and 1.52 eV, which is he app op ia e
isible ligh ange.
S-doping may imp o e ligh ha es ing while p ese ing su icien edox po en ial
since i sligh ly aises he bandgap.
V s. RHE Onse Po en ial:
The lowes ol age necessa y o s a pho oca aly ic wa e spli ing is known as he
onse po en ial.
Lowe onse po en ial means mo e a o able cha ge ans e and less ene gy inpu
needed.
The Au@Cu₂Se sys em shows he lowes onse po en ial (~0.05 V s. RHE), due o
plasmon-enhanced ho -elec on gene a ion.
ZnSe/CuSe he e ojunc ions also show a low onse po en ial (~0.08 V) hanks o
e icien band alignmen and cha ge sepa a ion.
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Syn hesis Techniques: Focus on Chemical Vapo Deposi ion
CuSe hin- ilm pho oca aly ic pe o mance, su ace shape, s oichiome y, and
c ys allog aphic quali y a e all signi ican ly in luenced by he syn hesis p ocess.
Chemical Vapo Deposi ion (CVD) is a po en and scalable me hod among he se e al
ab ica ion p ocesses a ailable o c ea ing ex emely uni o m, phase-pu e, and
nanos uc u ed CuSe hin ilms, which a e necessa y o e ec i e sola -d i en wa e
spli ing.
Chemical Vapo Deposi ion (CVD)
In CVD, apo -phase p ecu so s eac chemically on a hea ed subs a e o c ea e a
solid coa ing wi h ca e ully egula ed p ope ies. A omic-le el accu acy is p o ided
by he me hod o e :
The homogenei y and hickness o he ilm a e essen ial o cha ge anspo .
Con ol o s oichiome y, gua an eeing CuSe phase pu i y,
Su ace mo phology, which a ec s in e acial con ac and ligh sca e ing,
De ec enginee ing and doping a e c ucial o adjus ing ca ie dynamics and band
s uc u e.
Key CVD Va ian s o CuSe Thin Films:
Me hod
Key Fea u es
Applica ion Examples
A mosphe ic P essu e CVD
(APCVD)
Easy o assemble, easonably
p iced, and capable o
ope a ing a oom p essu e
u ilized in pho oca hodes o
CuWO₄ and CuFeO₂ (Pee e s
e al., 2018; Yengan iwa e
al., 2018).
Low-P essu e CVD (LPCVD)
dec eased pollu ion and
imp o ed homogenei y ac oss
wide egions
Possibili y o bendable PEC
de ices wi h a la ge a ea
Me al-O ganic CVD
(MOCVD)
makes use o o ganome allic
p ecu so s and pe mi s
in ica e alloying and doping.
Ideal o adding seconda y
me als (such as Zn and Ag)
and adjus ing he Cu: Se a io
Plasma-Enhanced CVD
(PECVD)
pe mi s low- empe a u e
deposi ion on subs a es ha
a e sensi i e o hea .
P omising o andem and
lexible PEC cells
Challenges in CuSe CVD G ow h:
To gua an ee eac i i y, he mal s abili y, and ola ili y, Cu and Se p ecu so s need o
be ca e ully chosen.
To s op selenium loss and phase de ia ion owa d Cu₂Se o CuSe₂, Se o e p essu e is
equen ly necessa y.
Tigh con ol o e p ecu so low a es and subs a e empe a u e (~350–450 °C) is
necessa y o achie e he monoclinic CuSe phase.
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A solid basis o scalable CuSe hin- ilm syn hesis has been es ablished by he
success ul CVD deposi ion o compa able sys ems such as Cu₂Se, CuInSe₂, and
CuFeO₂ in spi e o hese di icul ies.
O he Deposi ion Rou es
O he echniques ha e been used o syn hesize CuSe ilms, pa icula ly o
explo a o y o lab-scale expe imen s, e en hough CVD is bes o high-quali y ilms.
Compa a i e Table o CuSe Deposi ion Me hods
Technique
Ad an ages
Limi a ions
No able S udy
Chemical Ba h
Deposi ion (CBD)
Low-cos , ope a es a
low empe a u es,
simple se up
P oduces less
c ys alline ilms,
p one o pinholes, and
s oichiome ic
de ia ion
Za a e al. (2023
syn hesized S-doped
CuSe wi h imp o ed
PEC pe o mance
Sol–Gel Spin Coa ing
Scalable, uni o m hin
ilms o e la ge a eas
Requi es pos -
annealing a high
emp (~400–500°C),
isk o c acking
Used o oxide and
chalcogenide hyb id
ilms
Hyd o he mal/Sol o
he mal Syn hesis
Excellen con ol o e
nanos uc u e and
pa icle mo phology
No ideal o la ge-
a ea ilm deposi ion;
p essu e essels limi
scalabili y
Chen e al. (2022)
ab ica ed ZnSe/CuSe
he e ojunc ions wi h
imp o ed H₂
e olu ion
Elec odeposi ion
Good o di ec
g ow h on conduc i e
subs a es
Poo c ys allini y;
p one o Se-
de iciency; pH-
sensi i e p ocess
Applied in ea ly-s age
Cu–Se PEC s udies
Syn hesis–P ope y–Pe o mance Rela ionship
The deposi ion echnique a ec s:
G ain size and bo de densi y ha e an impac on ecombina ion and cha ge anspo .
Su ace oughness de e mines pho on ha es ing and ligh sca e ing.
Phase pu i y, which a ec s PEC s abili y and band alignmen .
Fo example, whe eas CBD-g own CuSe ilms a e less expensi e, hey equen ly
need o be pos - ea ed o inc ease hei c ys allini y. In con as , CVD-g own ilms
can p o ide be e o ien a ion and compac ness, which a e essen ial cha ac e is ics o
epea able, high-e iciency pho oelec odes.
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S uc u al and Op ical Cha ac e iza ion o CuSe Thin Films
Co ela ing he s uc u al, mo phological, op ical, and elec ical cha ac e is ics o
CuSe hin ilms wi h hei pho oca aly ic abili y equi es ho ough cha ac e iza ion.
The syn hesis p ocess, g owing en i onmen , and pos - ea men p ocedu es ha e he
bigges e ec s on hese cha ac e is ics. Impo an cha ac e iza ion me hods o CuSe
ilms made o pho oelec ochemical (PEC) wa e spli ing a e co e ed in his sec ion.
S uc u al Analysis
Di ac ion o X- ays (XRD)
Fo e alua ing CuSe ilm c ys al s uc u e, phase pu i y, and p e e ed o ien a ion,
XRD is he mos popula me hod.
Cha ac e is ic peaks a app oxima ely 25.3°, 27.8°, and 30.9°, which co espond o he
(101), (110), and (111) planes, espec i ely, a e commonly used o demons a e
monoclinic CuSe.
Peak changes may be a sign o s ain o doping e ec s, whe eas peak sha pness and
in ensi y e lec he ilm's c ys allini y.
Acco ding o s udies (e.g., Za a e al., 2023), annealing inc eases c ys alli e size and
dec eases de ec densi y, whe eas S-doping esul s in a modes b oadening o he peak
due o la ice dis o ion.
Spec oscopy using Raman
Vib a ional modes ela ed o Cu–Se bonding a e iden i ied by Raman spec oscopy,
which o e s supplemen a y in o ma ion.
The Cu–Se s e ching ib a ions a e con i med by peaks in he 190–250 cm⁻¹ a ea.
Cu₂Se, CuSe, and CuSe₂ can be dis inguished om one ano he by phase-speci ic
ib a ional modes.
De ec ing spa ial homogenei y ac oss he ilm su ace is ano he bene i o using
Raman mapping.
Mo phological Cha ac e iza ion
Field Emission Scanning Elec on Mic oscopy (FESEM) and T ansmission
Elec on Mic oscopy (TEM)
A he nanoscale, su ace shape, g ain size, c ys al bounda ies, and ilm hickness may
all be seen in g ea de ail wi h FESEM and TEM.
CuSe ilms o med chemically and hyd o he mally ha e been ound o exhibi po ous,
nano od, and nanopla e mo phologies, which imp o e con ac wi h he elec oly e and
inc ease su ace a ea.
Con e sely, dense, columna g ains wi h egula ed hickness (100–500 nm) a e
equen ly seen in CVD-g own CuSe ilms, making hem app op ia e o plana
pho oelec odes.
In suppo o c ys allog aphic e idence om XRD, TEM examina ions also show
la ice inges and alida e in e plana leng hs commensu a e wi h monoclinic CuSe.
Op ical and Elec onic P ope ies
UV–Vis Di use Re lec ance Spec oscopy (DRS) & Tauc Analysis
Depending on syn hesis and doping, CuSe hin ilms ha e a di ec bandgap be ween
