RESEARCH ARTICLE
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The Influence o Annealing on he Sb Laye in he Syn hesis
o [001]-O ien ed Sb2Se3Film o Pho oelec ochemical
Hyd ogen Gas Gene a ion
Magno B. Cos a, Moisés A. de A aújo, Joaquim Puigdolle s, Pablo O ega,
Te esa And eu, C is obal Voz, Edga do Saucedo,* and Lucia H. Masca o*
This wo k epo s a new he mal ea men app oach o ob ain [001]-o ien ed
Sb2Se3film, which consis s o p elimina y annealing o he Sb laye be o e i s
seleniza ion. Among he diffe en Sb annealing empe a u es assessed, he one
a 200 °C ollowed by seleniza ion (Sb2Se3(Sb-A200)) esul s in a conside ably
high ex u e coefficien a he [001] di ec ion, whe eas he Sb2Se3film ob ained
only by seleniza ion o he non-annealed Sb film (Sb2Se3(Sb-NA)) ea u es
p e e en ial o ien a ion a he [hk0] di ec ion. In e ms o pho oelec ochemical
(PEC) pe o mance o H2gene a ion, he Sb2Se3(Sb-A200)/CdS/TiO2/P
film deli e s a subs an ial pho ocu en densi y o −5.65 mA cm−2a 0 VRHE,
which is 10 imes highe compa ed o he Sb2Se3(Sb-NA)/CdS/TiO2/P film.
Addi ionally, he employmen o he Sb annealing s ep esul s in s able PEC
pe o mance o he Sb2Se3film o e 7000 s, meaning ha he pho oco osion
is minimized. The imp o ed PEC pe o mance o he Sb2Se3film is
a ibu ed o be e c ys allini y and composi ion close o he s oichiome ic
condi ion, as well as he p e e en ial o ien a ion a he [001] di ec ion
ha a o s cha ge ca ie s’ anspo a ion. A las , he findings o his wo k
ea u e an inno a i e he mal ea men app oach o ob ain [001]-o ien ed
Sb2Se3film o u he imp o e H2gene a ion om PEC wa e spli ing.
1. In oduc ion
The conce n o deple ion o ene gy esou ces based on ossil
uels has led la ely o a conside able inc ease in he sea ch o
M. B. Cos a, L. H. Masca o
Depa amen o de Química
Uni e sidade Fede al de São Ca los (UFSCa )
Rodo ia Washing on Luiz, km 235, São Ca los, São Paulo 3565-905, B azil
E-mail: lmasca o@u sca .b
M.A.deA aújo
Ins i u odeQuímicadeSãoCa los
Uni e sidadedeSãoPaulo(USP)
A enidaT abalhado Sanca lense,400,SãoCa los,SãoPaulo13566-590,
B azil
The ORCID iden ifica ion numbe (s) o he au ho (s) o his a icle
can be ound unde h ps://doi.o g/10.1002/ad m.202506401
© 2025 The Au ho (s). Ad anced Func ional Ma e ials published by
Wiley-VCH GmbH. This is an open access a icle unde he e ms o he
C ea i e Commons A ibu ion License, which pe mi s use, dis ibu ion
and ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly
ci ed.
DOI: 10.1002/ad m.202506401
enewable ene gy sou ces ha can po en-
ially eplace hem. Mo e wo ying is ha
ossil uel esou ces con ibu e abou 90%
o global ene gy consump ion, which im-
pac s he inc ease in he emission o ca bon
dioxide (CO2) in o he a mosphe e.[1]Al-
hough CO2is an essen ial gas o he main-
enance o li e, he e e -g owing elease
o his gas in o he a mosphe e, om os-
sil uel combus ion, can conside ably con-
ibu e o he in ensifica ion o he g een-
house effec and clima e changes, and hese
can cause an inc ease in he a e age empe -
a u e o he plane and affec he en i e exis -
ing ecosys em.[2]To ci cum en hese p ob-
lems, sunligh has become one o he mos
p omising al e na i e ene gy esou ces due
o being abundan and en i onmen ally
iendly, ease o usage/ha es , less o e all
cos , and e sa ile.[3,4]Addi ionally, sola en-
e gy can be con e ed o he mal ene gy ia
sola wa e hea e s, o elec ical and chem-
ical ene gy ia pho o ol aic and PEC de-
ices, espec i ely.[5]Thecon e siono sola
ene gy in o chemical ene gy consis s o s o ing ene gy in he
bonds o hyd ogen gas (H2) molecules, and his molecule is
known as a dense ene gy ca ie . H2has hea capaci y and en-
e gy densi y much highe han ba e ies,[6,7]and he ene gy yield
J. Puigdolle s, P. O ega, C. Voz, E. Saucedo
Elec onic Enginee ing Depa men
Uni e si a Poli ècnica de Ca alunya (UPC)
Mic o and Nano Technologies G oup (MNT)
Jo di Gi ona 31, Ba celona 08034, Spain
E-mail: [email p o ec ed]
M.B.Cos a,J.Puigdolle s,E.Saucedo
Ba celonaCen e o Mul iscaleScience&Enginee ing
Uni e si a Poli ècnicadeCa alunya(UPC)
A Edua dMa is any10-14,Ba celona08019,Spain
T.And eu
Depa amen deCiènciadelsMa e ialsiQuímicaFísica
Uni e si a deBa celona(UB)
Ma íiF anquès,1,Ba celona08028,Spain
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o H2is 2.75 imes highe compa ed o ha o hyd oca bon
uels.[8]One way o ob ain H2is ia sola wa e spli ing, which
can be ca ied ou in PEC cells o pho o ol aic panels coupled o
elec olyze s.[7]
To d i e sola wa e spli ing in o PEC cells, a a ie y o semi-
conduc o ma e ials ha e been unde in es iga ion, and among
hose an imony(III) selenide (Sb2Se3) hin film has s ood ou as a
p omising pho oca hode owing o i s adequa e in insic op oelec-
onic p ope ies, ea h-abundan elemen s, and low oxici y.[9,10]
To exempli y he op oelec onic p ope ies o Sb2Se3, his ma e-
ial has a high abso p ion coefficien , a, in he ul a iole and
he isible egion o he sola spec um (a>105cm−1),[11]sui -
able op ical bandgap ene gy, Eg, o 1.1–1.3 eV,[12–14]high mo-
bili y (≈10 cm2V−1s−1 o mino i y ca ie s),[15]long ca ie li e-
ime (≈60 ns),[15]and app op ia e ene gy band posi ion o d i e
hyd ogen e olu ion eac ion (HER) unde illumina ion.[14,16,17]
In addi ion, Sb2Se3has a single o ho hombic c ys alline phase
composed o quasi-1D (Q1D) pa allel ibbons o (Sb4Se6)nin
one spa ial di ec ion.[18,19]These Q1D (Sb4Se6)n ibbons p esen
co alen Sb−Se bonds along he [001] di ec ion, and he ib-
bons a e s acked along he [100] and [010] di ec ions, which a e
held oge he by an de Waals o ces.[20]The diffe en o ien-
a ion g ow h o he (Sb4Se6)n ibbons enables he exis ence o
aniso opic c ys allog aphic beha io , meaning ha any p e e ed
o ien a ion in he [001] di ec ion ( ibbons e ically o ien ed o
he subs a e) a o s he cha ge anspo , as he cha ge ca i-
e s a el mo e easily along he ibbon-like s uc u e. On he
o he hand, he (Sb4Se6)n ibbons ea u ing [100] and [010] di-
ec ions ( ibbons ho izon ally o ien ed o he subs a e) esul in
difficul y o cha ge ca ie s anspo due o he hopping mecha-
nism, ha is, cha ge ca ie s mus hop om one (Sb4Se6)n ibbon
o ano he .[20]Such an aniso opic cha ge ca ie s’ anspo a-
ion sugges s ha a p ope ly ex u ed Sb2Se3film (i.e., ea u ing
[hk1] di ec ion) is he ideal condi ion o sola ene gy con e sion
applica ions.[20–22]Addi ionally, he combina ion o all hese p op-
e ies makes Sb2Se3a e y p omising semiconduc o ma e ial o
be used as a pho oca hode o PEC cells when compa ed o o he
semiconduc o s.[23–25]
Al hough Sb2Se3has been ex ensi ely demons a ed o be an
excellen al e na i e as a pho oca hode o sola -d i en wa e
spli ing,[26,27] he elec on-hole ecombina ion p ocess in bulk,
and he p esence o in e acial de ec s a e ecu en issues[18]
ha limi o each sa is ac o y PEC pe o mance o his ma e ial
o comme cial applica ion.[28]To o e come hese issues, he im-
p o emen o c ys allini y and he con ol o elemen al composi-
ion o Sb2Se3ha e been a ibu ed as he main ac o s o enhance
he PEC pe o mance o Sb2Se3pho oca hode.[29,30]Rega ding,
pa icula ly he elemen al composi ion effec , Caño e al.[31]ha e
ecen ly shown ha nons oichiome ic Mo/Sb2Se3film gi es ise
o seconda y phases, ha is, Se- ich Mo/Sb2Se3film leads o he
o ma ion o MoSe2and Se phases, whe eas he Sb- ich condi-
ion a o s he occu ence o Sb2O3and m-Sb phases. In ano he
ecen s udy, Lian e al.[32]iden ified he p esence o deep-le el
de ec s in Sb- ich Sb2Se3film, which, based on expe imen al e-
sul s, we e cha ac e ized as ampho e ic SbSe de ec s. Mo eo e ,
acco ding o he au ho s, he ampho e ic de ec s in his ma e ial
can ap bo h elec ons and holes, esul ing e en ually in a e-
combina ion p ocess. I was also shown ha Se- ich Sb2Se3films
ha e ela i ely less de ec concen a ion as well as a educed num-
be o shallow ene gy le els. Besides he elemen al composi ion
effec , ano he limi ing ac o is ha he [hk1]-o ien ed Sb2Se3,
which is he ideal condi ion o PEC and pho o ol aic cells, is no
he modynamically a o able compa ed o ha o [hk0] o ien a-
ion, as he [hk0] leads o he o ma ion o Sb2Se3c ys al ace s
wi h a lowe o ma ion ene gy.[33]
To ackle his issue, s udies ha e ecen ly shown ha [hk1]-
o ien ed Sb2Se3film can be ob ained by op imizing he seleniza-
ion empe a u e o ei he he Sb o Sb2Se3film.[34,35]I is o en
epo ed ha he employmen o molybdenum (Mo) as he back-
con ac o g ow [hk1]-o ien ed Sb2Se3film du ing he seleniza ion
s ep, howe e , Liang e al.[36]demons a ed ha he in si u su -
ace seleniza ion o ungs en (W) can be used as a back-con ac
o enable he ob ainmen o Sb2Se3film ea u ing [hk1] p e e ed
o ien a ion. Fu he mo e, he au ho s epo ed ha he hin laye
o WSe2beha es as a hole anspo laye , which means ha his
ma e ial can collec he pho ogene a ed holes and block he pho-
ogene a ed elec ons om ans e ing o he back-con ac , hin-
de ing he elec on-hole ecombina ion p ocess.
He ein, i is conside ed an al e na i e he mal ea men ap-
p oach o ob ain [001]-o ien ed Sb2Se3film. Fo his s udy, a new
me hodology was de eloped consis ing o p elimina y annealing
o he Sb laye be o e he seleniza ion s ep. Pa icula ly, i was
aimed o in es iga e he influence o he diffe en annealing em-
pe a u es o he Sb laye and he diffe en seleniza ion condi-
ions (i.e., empe a u e and dwelling ime) o he annealed Sb
laye o p oduce [001]-o ien ed Sb2Se3film. I was also a ge ed
o assess how he c ys allini y and elemen al composi ion o he
[001]-o ien ed Sb2Se3film di ec ly affec he PEC pe o mance o
H2p oduc ion ia sola -d i en wa e spli ing. As will be shown
in he Resul s and Discussion sec ion, compa ed o he Sb2Se3
film ob ained only ia seleniza ion, he annealing o he Sb laye
be o e seleniza ion led o he o ma ion o Sb2Se3film wi h p e -
e en ial c ys allog aphic o ien a ion o he [001] di ec ion, be e
c ys allini y, and sui able elemen al composi ion. I will also be
demons a ed ha he Sb2Se3film ob ained ia annealing o Sb
be o e seleniza ion deli e s a subs an ial imp o emen o PEC
ac i i y and s abili y o H2gene a ion om he wa e spli ing
eac ion. All in all, he annealing s ep de eloped in his wo k p o-
ides an al e na i e app oach o conside ably enhance PEC ac i -
i y and s abili y o [001]-o ien ed Sb2Se3film o H2p oduc ion.
2. Resul s and Discussion
2.1. Cha ac e iza ion o Single-Laye ed Films
2.1.1. Seleniza ion o Non-Annealed Sb
In his ega d, he elemen al composi ion o he Sb2Se3(Sb-NA)
film submi ed o seleniza ion a 320 °C o 30 min was analyzed
by XRF. Acco ding o Figu e S3a, Suppo ing In o ma ion, he el-
emen al composi ion o he film was Se- ich, p esen ing a max-
imum a omic pe cen age a io o 3[Sb%]/2[Se%] ≈0.67, which
is a om he s oichiome ic alue (3[Sb%]/2[Se%] =1, co e-
sponding o 60 a .% Se and 40 a .% Sb). A b ie in es iga ion
was pe o med o e he ange o seleniza ion empe a u es o
320 ±20 °C (i.e., 300 and 340 °C o 30 min), howe e , he films
con inued o p esen a Se- ich composi ion. Se- ich Sb2Se3films
ha e also been epo ed as an effec i e s oichiome ic condi ion
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o pho o ol aic cell applica ion due o he p esence o benign de-
ec s, ha is, SeSb an isi es (shallow accep o s) and he difficul y
o de imen al de ec s o ma ion, such as selenium acancies and
SbSe an isi es (deep dono s).[37–39]
2.1.2. Annealing Tempe a u e Effec o Sb
In he a emp o find ou he eason o ob aining Se- ich
Sb2Se3(Sb-NA) films, XRD measu emen s we e pe o med o
he as-deposi ed Sb film no subjec ed o annealing s ep (labeled
as Sb-NA), as well as o hose annealed a 150, 200, and 250 °C
o 30 min (labeled as Sb-A150, Sb-A200, and Sb-A250, espec-
i ely). As shown in Figu e S3b, Suppo ing In o ma ion, i was
iden ified weak eflec ions o he (003), (006), and (202) planes
o he Sb-NA film, which we e assigned o he hombohed al Sb
phase (Powde Diff ac ion File (PDF) no. 35–732). These peaks
ea u ed low in ensi y, sugges ing poo c ys allini y o he Sb-
NA film. Tha may ha e p e en ed he o ma ion o a mo e s o-
ichiome ic Sb2Se3film and affec ed i s composi ion du ing he
seleniza ion p ocess. Howe e , he esul s o he as-deposi ed
Sb films annealed a he highes empe a u es, namely, Sb-A200
and Sb-A250 films, showed s ong eflec ions and he e o e mo e
c ys alline films compa ed o hose o he Sb-NA and Sb-A150
films, which ha e weak eflec ions.
As addi ional e idence o he annealing effec , i can be ob-
se ed ha a dec ease o up o 21.5% o he ull wid h a hal
maximum (FWHM) alues o he (006) plane (Figu e S3c,Sup-
po ing In o ma ion), indica ing an inc ease in he size o he
Sb c ys alli e as he annealing empe a u e inc eases. In e es -
ingly, he Sb-A200 and Sb-A250 films ea u ed a seconda y phase
o Sb2O3(PDF no. 75–1565) as no ed by he peaks indexed o
he (111), (222), and (444) planes, which a e indica ed by ci cled
egions in he XRD pa e ns (c . Figu e S3b, Suppo ing In o -
ma ion). Al hough he annealing was pe o med unde A a mo-
sphe e, his esul indica es ha he Sb films unde wen he mal
oxida ion a annealing empe a u es highe han 200 °C. Despi e
he p esence o he Sb2O3seconda y phase, he seleniza ion p o-
cess (pe o med a 320 °C) can con e all oxidized phases in o
Sb2Se3. Acco ding o Equa ions (1)and(2), which conside he
eac ion be ween Sb(s) and Se(g), and he eac ion o Sb(s) and
O2(g) bo h a 320 °C (co esponds o 593 K),[40,41] he o ma ion
o Sb2Se3is he modynamically mo e a o able han Sb2O3and
he seleniza ion also allows any oxide esidues o be con e ed
in o he Sb2Se3. Fu he mo e, elemen a y Se has a mel ing poin
o 221 °C,[42]and high apo p essu e,[43]which con ibu es o
he chalconiza ion in he absence o oxygen gas. The eade is
e e ed o he Suppo ing In o ma ion (SI) o de ails abou he
calcula ion o he alues o he mola Gibbs ene gy o eac ion a
593 K (∆ G(593 K)) o he eac ions in Equa ions (1)and(2).
2Sb(s)+3Se(g)→Sb2Se3(s)Δ G(593 K)=−670.9kJmol
−1(1)
2Sb(s)+3
2O2(g)→Sb2O3(s)Δ G(593 K)=−546.8kJmol
−1(2)
2.1.3. Seleniza ion o Sb Annealed a Diffe en Tempe a u es
The as-deposi ed Sb films annealed a diffe en empe a u es
we e subsequen ly submi ed o seleniza ion and assessed hei
elemen al composi ion by he XRF analysis (Figu e 1a). I is
possible o obse e ha he annealing o he Sb imp o ed he
s oichiome y o he Sb2Se3films, allowing he 3[Sb%]/2[Se%]
a omic a io o hese films o inc ease compa ed o hose o he
Sb2Se3films ob ained wi hou annealing he Sb. This is indica-
i e ha mo e c ys alline Sb films may lead o be e o ma ion
o Sb2Se3phase in he seleniza ion p ocess. The bes annealing
condi ion be o e seleniza ion was a 200 °C, as a o ed a maxi-
mum 3[Sb%]/2[Se%] a omic a io o ≈0.8. The imp o emen o
adjus ed chemical composi ion migh be a ibu ed o a lesse ex-
en elemen al Se condensa ion o e he su ace o he Sb2Se3(Sb-
A) films compa ed o hose o Sb2Se3(Sb-NA) films. The elemen-
al Se condensa ion may ha e occu ed du ing he seleniza ion
p ocess o he Sb-A and Sb-NA films.[44]The p esence o elemen-
al Se on he Sb2Se3(Sb-A) films’ su ace was e ified by XPS anal-
ysis (see discussion u he ). The minimized condensa ion o el-
emen al Se o he Sb2Se3(Sb-A) films migh be associa ed wi h
he c ys al s uc u e o he [001]-o ien ed Sb-A films (see discus-
sion o Figu e 1b,c) ha possibly a o s diffusion o sublima ed
Se a oms in o he [001]-o ien ed c ys al la ice o he Sb-A film
ha can subsequen ly eac o o m [001]-o ien ed Sb2Se3.[45]
The Sb2Se3films ob ained ia seleniza ion o annealed Sb,
as well as he Sb2Se3(Sb-NA) film, we e also cha ac e ized by
XRD measu emen s (see Figu e 1b). All he diff ac og ams ea-
u ed diff ac ion peaks indexed o he (020), (120), (220), (230),
(211), (221), (301), (311), (240), (231), (141), (411), (002) and
(061) planes, and hese peaks we e assigned o he o ho hom-
bic Sb2Se3phase (PDF no. 89–821). The diff ac ion peaks labeled
wi h as e isks (*) a e a ibu ed o he Mo-coa ed glass subs a es
(PDF no. 42–1120). Fu he mo e, i was no iden ified he diff ac-
ion peaks o he seconda y phase o Sb2O3, p o ed he efficacy
o he me hod o ully con e ing he Sb and Sb2O3phases in o
he Sb2Se3phase du ing seleniza ion, as shown in Equa ions (1)
and (2). Ano he in e es ing aspec om Figu e 1b is ha all he
Sb2Se3films ob ained ia seleniza ion o he annealed Sb showed
s ong eflec ions o he (002) plane compa ed o hose o he
Sb2Se3(Sb-NA) film, indica ing be e c ys allini y and p e e en-
ial o ien a ion in he [001] di ec ion. To be e unde s and he
p e e ed o ien a ion o he c ys allog aphic planes o he Sb2Se3
films, he ex u e coefficien o a gi en (hkl) plane, TC(hkl), was
calcula ed using Equa ion (3),[27]and he esul s a e displayed in
Figu e 1c.
TC (hkl)=I(hkl)
I0(hkl){1
N
N
∑
i=0
I(hkl)
I0(hkl)}−1
(3)
whe e I(hkl)and I0(hkl)a e he diff ac ion peak in ensi ies o a
gi en (hkl) plane measu ed om he XRD and he da abase o
XRD (Sb2Se3PDF no. 89–821) pa e ns, espec i ely, and Nis
he numbe o planes conside ed o he calcula ion (10 planes
in ha diff ac og am).
Acco ding o Figu e 1c, he TC o he (120), (301), (221), and
(211) planes ea u ed simila alues and we e lowe han 1, mean-
ing no p e e en ial c ys al o ien a ion o hese planes. Howe e ,
TC(230) >1 was achie ed o he Sb2Se3(Sb-NA) and Sb2Se3(Sb-
A150) films, sugges ing ha he c ys al o Sb2Se3has a p e e en-
ial g ow h o ien a ion pa allel o he subs a e ([100] and/o [010]
o ien a ion), which is no efficien o pho ogene a ed cha ge
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Figu e 1. a) A omic pe cen age a io ob ained om he XRF analysis, b) XRD pa e ns, and c) TC(hkl) alues o he Sb2Se3(Sb-NA) and he Sb2Se3(Sb-A)
films. XRD pa e ns o he PDF da abase o he o ho hombic Sb2Se3(PDF no. 89–821) and he cubic Mo (PDF no. 42–1120) phases a e displayed as
e ical lines a he bo om o he diff ac og ams. The diff ac ion peaks labeled wi h * we e assigned o he Mo back-con ac .
ca ie s anspo a ion due o in e - ibbons hopping mechanism.
Fo he (002) plane, he Sb2Se3(Sb-A200) film ea u ed he high-
es TC(002) alue (i.e., ≈3), indica ing he ibbons o he Sb2Se3
a e e ically g own o he subs a e ([001] o ien a ion), which a-
o efficien pho ogene a ed cha ge ca ie s anspo a ion owing
o he anspo o he ca ie s alongside he ibbons. I was also
no ed ha he Sb2Se3(Sb-A200) film has he lowes alue o he
TC(120), indica ing low con ibu ion o he pa allel o ien a ion
o he subs a e. This p e e en ial g ow h o he [001] di ec ion
o he Sb2Se3has likely occu ed due o he influence o he im-
p o ed in ensi y o he diff ac ion peaks o he (003) and (006)
planes ([001]-o ien ed Sb) o he Sb-A200 and Sb-A250 films com-
pa ed o hose o he Sb-A150 and Sb-NA films (c . Figu e S3b,
Suppo ing In o ma ion). The (003) and (006) planes enable con-
inuous diffusion o sublima ed Se o eac wi h [001]-o ien ed
Sb and o m column g ow h o [001]-o ien ed Sb2Se3.[45]To be -
e unde s and his phenomenon in e ms o a possible seleniza-
ion mechanism, he change in empe a u e du ing he anneal-
ing p ocess di ec ly influences he apo p essu e o Se a oms
and hei kine ic ene gy. A a gi en seleniza ion empe a u e, he
sublima ed Se a oms may adso b on he [001]-o ien ed Sb film
su ace wi h sufficien ene gy o eac and o m a Sb2Se3c ys-
al nucleus. The sublima ed Se a oms may con inue o diffuse
o he [001]-Sb/[001]-Sb2Se3in e ace along he an Waals gaps
o Sb2Se3 o ex end he leng h o he [001]-Sb2Se3p e e en ial
g ow h.[34,46]
Howe e , despi e he Sb-A250 film ea u ing he highes in en-
si y o he Sb’s diff ac ion peaks o he (003) and (006) planes,
he p esence o he Sb2O3phase may ha e minimized i s p e e -
en ial o ien a ion in he [001] di ec ion compa ed o ha o he
Sb2Se3(Sb-A200) film. The e o e, he expe imen al condi ion o
he p epa a ion o Sb2Se3(Sb-A200) film was chosen as he op i-
mum condi ion.
Addi ional cha ac e iza ion o he Sb2Se3(Sb-NA) and he
Sb2Se3(Sb-A) films was achie ed by Raman spec a, as shown in
Figu e 2. The main ib a ional modes o Sb2Se3a e ep esen ed
by well-defined bands wi hin a ange o 50 – 300 cm−1.[44]The
bands loca ed a 210 and 190 cm−1a e ela ed o he Agmode o
he Sb–Se–Sb bending ib a ions o he Sb2Se3, while he small
band ≈154 cm−1is assigned o he A2u ib a ion mode o he Sb–
Sb bond. The obse ed bands a 120 and 80 cm−1a e a ibu ed o
he Se–Se bending.[44,47]I is impo an o men ion ha none o
he samples displayed he cha ac e is ic bands o he Sb2O3sec-
onda y phase in he Raman spec a (co esponding o he main
bands a 254 and 450 cm−1[44]), howe e , all he samples p e-
sen ed low-in ensi y bands a 98 and 250 cm−1assigned o he
p esence o Se6 ing ( hombohed al Se).[44,48]I has also been e-
po ed ha Se- ich chalcogenide film can p o ide hombohed al
Se signals in ha egion, which a ise om he excess o Se de-
posi ed on he samples’ su ace.[49,50]The Raman spec a in his
wo k sugges ha he seleniza ion p ocess may ha e con ibu ed
o he occu ence o elemen al Se on he su ace o all he sam-
ples, and his ag ees wi h he XRF analysis, which indica es ha
he Sb2Se3a e Se- ich (c . Figu e 1a). Ne e heless, i was no
iden ified Se phase in he XRD da a (c . Figu e 1b), p obably in-
dica ing ha Se phase may be p esen in small quan i ies.
Figu e S4a,b, Suppo ing In o ma ion show he Tauc plo s as
(𝛼h )1/2 e sus Eph (indi ec ansi ion) and (𝛼ℎ𝜈)2 e sus Eph (di-
ec ansi ion), espec i ely.[51]Fo an indi ec and a di ec an-
si ion, he linea ex apola ion o he baseline ende ed op ical Eg
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Figu e 2. (on he le ) Raman spec a and hei co esponding (on he igh ) expanded egion o he spec a encompassing he main bands o Sb2Se3
o he Sb2Se3(Sb-NA) and he Sb2Se3(Sb-A) films.
alues o 1.33 and 1.34 eV, espec i ely, o all he samples. These
esul s a e sligh ly highe han hose epo ed in he li e a u e
(i.e., 1.1–1.3 eV[12–14]), howe e , i is also epo ed ha Sb2Se3wi h
highe op ical Eg o nano od[52,53]o nanowi es[54]mo pholo-
gies. In addi ion, i was also assessed he Euo he films, which
cha ac e izes he s uc u al diso de o he semiconduc o .[55]An
inc ease o Eu alue ep esen s an enla gemen o he wid h o
he bands’ edges ail, which means a mo e p onounced s uc-
u al diso de in he semiconduc o . This pa ame e can be un-
de s ood as he wid h o he ail o he conduc ion and alence
band edges associa ed wi h he localized de ec s a es wi hin he
Eg. Addi ionally, he p esence o he bands’ edges ailing co -
esponds o ansi ions be ween ex ended s a es o he alence
band and localized s a es o he conduc ion band.[56]Acco ding
o Figu e S4c, Suppo ing In o ma ion, i can be seen a na -
ow linea egion in he inse o he Euplo be o e he Eg al-
ues, which he Euwas es ima ed om he in e se o he slope
o he s aigh lines in he g aphs. Unlike he op ical Eg alue
in which he e was no diffe ence in compa ison wi h he diffe -
en samples, he Euhas shown a sligh diffe ence in hei al-
ues. The lowes alue o he Euwas 0.21 eV o he Sb2Se3(Sb-
A200) film compa ed o hose o he o he films. This indica es
ha he annealing a 200 °C o he Sb film has con ibu ed o
he dec ease o he s uc u al diso de and he localized de ec s
in he band edges o he Sb2Se3(Sb-A200) film. On he o he
hand, he Sb2Se3(Sb-A250) film ea u ed he highes alue o he
Eu(i.e., 0.32 eV), indica ing ha his film has a highe num-
be o localized de ec s in i s band edges compa ed o he o he
films.[57]
The Sb2Se3(Sb-A200) film, ha is, ep esen ing he op imum
condi ion, was chemically assessed by he XPS measu emen s,
and he spec a a e displayed in Figu e 3.AsshowninFigu e3a,
he su ey spec um exhibi s he main peaks o Sb, Se, O, and
C elemen s, co esponding o Sb 4p, Sb 3d, Sb 4s, Sb 4d, Se 3s,
Se 3p, Se 3d, O 1s, and C 1s co e le els, espec i ely. Rega ding
he high- esolu ion XPS spec a (Figu e 3b), he spec um o he
Sb 3d co e le el ea u es wo Sb 3d double s: he fi s one wi h
peaks a 529 (Sb 3d5/2) and 538.34 eV (Sb 3d3/2) a e assigned o
he Sb–Se bonds in Sb2Se3, whe eas he second one ha ing peaks
a 530 (Sb 3d5/2) and 539.34 eV (Sb 3d3/2) a e a ibu ed o he Sb–
O bonds.[58]Since XPS is a highly su ace-sensi i e echnique,
he p esence o an Sb–O signal is a esul o he sample being
exposed o ai be o e he XPS analysis,[59]and his has also been
epo ed in he li e a u e.[60–62]The p esence o Sb–O signal (pos-
sibly Sb2O3) migh be beneficial as i could passi a e de ec s (i.e.,
Se acancies) on he su ace o Sb2Se3films.[62]Mo eo e , bea -
ing in mind ha XPS is su ace-sensi i e (pene a ion dep h o
10 nm o less[63]), despi e he possibili y o supe ficial o ma ion
o Sb2O3, he bulk p ope ies o Sb2Se3films emain unal e ed,
as can be e ified om he discussion o XRD (c . Figu e 1)and
Raman (c . Figu e 2). S ill ega ding Figu e 3b, The O 1s peak a
531.7 eV is assigned o he ad en i ious oxygen weakly adso bed
on he su ace, which could also be a esul o a mosphe ic CO2
physiso p ion on he pho oelec ode su ace.[64]Conce ning he
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Figu e 3. a) The su ey and high- esolu ion XPS spec a o b) Sb 3d and c) Se 3d co e le els o Sb2Se3(Sb-A200) film.
high- esolu ion spec a o he Se 3d co e le el (Figu e 3c), one
no ices he p esence o wo Se 3d double s: he fi s one con ain-
ing peaks a 53.5 (Se 3d5/2) and 54.36 eV (Se 3d3/2) a e assigned
o he Se–Sb bonds in Sb2Se3, and he second one wi h peaks a
54.9 (Se 3d5/2) and 55.76 eV (Se 3d3/2) a e a ibu ed o he Se–Se
bonds in elemen al selenium.[58]As shown in he discussion o
he Raman spec a (c . Figu e 2), he p esence o elemen al se-
lenium a ises om he excess o Se in he o m o Se6 ings on
he samples’ su ace du ing he seleniza ion p ocess o e en as a
side-p oduc o he Sb2Se3ai oxida ion.
Besides he chemical assessmen , i has employed SEM anal-
yses (Figu e 4) o cha ac e ize he mo phology on he su ace
and a he c oss-sec ion o he Sb2Se3(Sb-NA) and he Sb2Se3(Sb-
A) films. As indica ed in Figu e 4a, i is possible o obse e
he o ma ion o od-like s uc u es wi h leng hs o mo e han
1μm, which a e andomly o ien ed in all di ec ions on he su -
ace o he Sb2Se3(Sb-NA) film. The p esence o hese od-like
s uc u es may indica e a p e e en ial o ien a ion o he Sb2Se3
c ys al. Since he Sb2Se3(Sb-NA) film ea u ed p e e en ial o i-
en a ion o he (230) plane (c . Figu e 1c), his implies ha
he od s uc u es migh be associa ed wi h he exis ence o
(Sb4Se6)n ibbons o ien ed a he [hk0] di ec ion (i.e., ibbons
ho izon ally o ien ed o he subs a e).[33]Fo he Sb2Se3(Sb-A)
films (c . Figu e 4a), he Sb2Se3(Sb-A150) film ea u es a mix o
mo phologies on i s su ace, anging om mic o ods o ound-
shaped s uc u es. The mo phology o he Sb2Se3(Sb-A200) film
mos ly consis s o compac ed i egula s uc u es, whose con-
ou s a e well-defined. On he o he hand, he mo phology o
he Sb2Se3(Sb-A250) film p esen s a less-defined shape, includ-
ing elonga ed and misshapen g ains. The c oss-sec ion mic o-
g aphs in Figu e 4b showed diffe ences in he films’ mo phol-
ogy. The Sb2Se3(Sb-NA) and Sb2Se3(Sb-A150) films show less-
defined g ains, whe eas he Sb2Se3(Sb-A250) film displays oids
be ween he Sb2Se3and he i-laye Mo. Fo he Sb2Se3(Sb-A200)
film, one no ices he p esence o homogeneous and well-defined
g ains e ically g own on he i-laye Mo wi h no oids be ween
hem. The o ma ion o hese e ically o ien ed s uc u es o
he Sb2Se3(Sb-A200) film sugges s o ma ion o [001]-o ien ed
(Sb4Se6)n ibbons,[33]as was also obse ed by he highes TC(002)
alue o ≈3 (see Figu e 1c). All he mo phological ea u es o
he Sb2Se3(Sb-A200) film can be be e obse ed in he mic o-
g aphs zoomed ou o he su ace and c oss-sec ion (Figu e 4c).
Rega ding he hickness o he films, al hough i is no possible
o accu a ely measu e he hickness due o he non-uni o mi y,
one no ices ha he hickness o he Sb2Se3(Sb-A) films is highe
compa ed o ha o Sb2Se3(Sb-NA) film (c . Figu e 4b). This ap-
pa en inc ease in hickness o he Sb2Se3(Sb-A) films is p ob-
ably due o enla ged c ys alli e size o Sb-A films upon he
annealing p ocess, which can be obse ed by he dec ease o
up o 21.5% o he FWHM alues o he (006) plane (Figu e
S3c, Suppo ing In o ma ion), ep esen ing an inc ease in
≈11 nm (acco ding o he Sche e equa ion) o he Sb c ys alli e
size.
2.1.4. Op imizing Seleniza ion o Annealed Sb
Acco ding o he esul s ha ha e been p esen ed so a , he op-
imum he mal ea men condi ion co esponded o he sam-
ple labeled as Sb2Se3(Sb-A200). Aiming o u he e alua e he
he mal ea men app oach o he Sb2Se3films, i has also
been assessed he effec o he seleniza ion on he Sb-A200
films a diffe en empe a u es (i.e., 280, 300, 320, and 340 °C)
and dwelling imes (i.e., 30 and 60 min). The Sb-A200 films
selenized a diffe en empe a u es and imes we e cha ac e -
ized in e ms o hei elemen al composi ion, c ys al s uc u e,
and pho oelec oca aly ic pe o mance owa d HER, as p esen ed
as ollows.
F om he XRF analysis (Figu e 5a), one no ices ha he Sb-
A200 films selenized a he lowes empe a u e and ime (i.e.,
280 °C and 30 min, espec i ely) ea u ed he highes a omic a-
io o 0.81, which is easonably close o he expec ed s oichiome -
ic alue. Addi ionally, he Se- ich condi ion became mo e p o-
nounced o he Sb-A200 films selenized a he highes empe -
a u e and ime (i.e., 340 °C and 60 min, espec i ely), leading o
a minimum alue o a omic a io o 0.69. Based on hese esul s,
one can in e ha longe dwelling imes and highe empe a u es
can lead o a sublima ed Se- ich a mosphe e and significan ly a -
ec he composi ion o he samples. This esul means ha he
employmen o he annealing s ep o he Sb film and he simple
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Figu e 4. FEG-SEM mic og aphs o he a) su ace (20k imes magnifica ion) and b) he c oss-sec ion (100k imes magnifica ion) o he Sb2Se3(Sb-NA)
and he Sb2Se3(Sb-A) films. c) FEG-SEM mic og aphs zoomed ou o he su ace (10k imes magnifica ion) and c oss-sec ion (50k imes magnifica ion)
o he Sb2Se3(Sb-A200) film.
adjus men o he seleniza ion empe a u e and ime play an im-
po an ole in imp o ing he s oichiome y o he Sb2Se3films.
Conce ning he XRD analysis (Figu e 5b), he diff ac ion peaks
o all he samples we e assigned o he o ho hombic Sb2Se3
phase (which ollows he PDF no. 89–821), and no seconda y
phase, such as elemen al Se and Sb2O3, was de ec ed. Addi ion-
ally, all he samples ha e shown s ong eflec ions in he diff ac-
ion peak indexed o he (002) plane as he mos in ense one,
indica ing be e c ys allini y and p e e en ial o ien a ion o he
Sb2Se3c ys al o he [001] di ec ion. As addi ional analysis om
he XRD pa e ns, i was also calcula ed he mean o c ys alli e
size, D, om he diff ac ion peak posi ions ia Equa ion (4)[65]
o he Sb2Se3(Sb-A200) films selenized a diffe en empe a u es
and dwelling imes.
D=K𝜆
𝛽cos 𝜃(4)
whe e Kis he shape ac o (0.9, conside ing he o ho hombic
na u e o Sb2Se3[65,66]), 𝜆is he X- ay wa eleng h (1.54 Å o Cu
K𝛼1 adia ion), 𝛽is he FWHM o a gi en diff ac ion peak, and
𝜃is he diff ac ion peak posi ion.
As shown in Figu e 5c, a sligh endency was no ed o he
D alues o he samples selenized a diffe en empe a u es and
dwelling imes. Fo he dwelling ime o 60 min, Dp esen ed
alues anging om 107.85 o 116.41 nm wi h inc easing sel-
eniza ion empe a u e, sugges ing an inc ease in he g ain size
as he empe a u e inc eases. This inc ease o Dmay indica e
ha he c ys allini y and g ain size o he Sb2Se3film a e a -
ec ed upon seleniza ion. Since he film becomes Se- ich as he
seleniza ion empe a u e inc eases, he a oms o Se may inco -
po a e in o he Sb2Se3s uc u e[66]and inc ease i s size. Con-
e sely, o he dwelling ime o 30 min, Dp esen ed a maxi-
mum alue o 112.61 nm o he seleniza ion empe a u e o
300 °C and hen his alue dec eased o highe seleniza ion
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Figu e 5. a) A omic pe cen age a io ob ained om he XRF analysis, b) XRD pa e ns, and c) D alues o he Sb2Se3(Sb-A200) films selenized a
diffe en empe a u es and dwelling imes. XRD pa e ns o he PDF da abase o he o ho hombic Sb2Se3(PDF no. 89–821) and he cubic Mo (PDF
no. 42–1120) phases a e displayed as e ical lines a he bo om o he diff ac og ams. The diff ac ion peaks labeled wi h * we e assigned o he Mo
om he Mo back-con ac .
empe a u es. This dec ease in he D alues o he Sb2Se3a sel-
eniza ion empe a u es >300 °C is p obably ela ed o he pa ial
decomposi ion o he Sb2Se3c ys alli es, as Sb2Se3can unde go
he mal decomposi ion and/o s uc u al ea angemen unde
high empe a u es.[47,67]
2.2. Cha ac e iza ion o Mul i-Laye ed Films
Aiming o ob ain a mul ilaye pho oca hode o he H2gene a-
ion ia sola -d i en wa e spli ing, he su ace o he Sb2Se3(Sb-
A200) film was ini ially e ched wi h he KCN solu ion ollowed
by he sequen ial deposi ion o he CdS and he TiO2laye s
on o hei films’ su ace o ob ain he Sb2Se3(Sb-A200)/CdS/TiO2
films. Rega ding he mo phological analysis o he mul ilaye
films, Figu e S5 shows he su ace mic og aphs ob ained by FEG-
SEM a 20k imes magnifica ion o each o he laye s p esen
in he sample. The su ace o he back-con ac ( i-laye Mo)
p esen ed a wo m-like mo phology, whe eas he Sb-A200 laye ,
which was deposi ed on o his back-con ac , exhibi ed a mo -
phology o i egula g ains closely packed. Fo he Sb2Se3(Sb-
A200) film, ob ained by selenizing he Sb-A200 film a 320 °C o
30 min, one no ices ha he pa icles ea u ed i egula shape and
once he Sb2Se3(Sb-A200) film was e ched wi h he KCN solu ion,
he i egula shape o he pa icles was d as ically affec ed by he
e ching p ocess, sugges ing a sligh dissolu ion o he pa icles
o his laye .[18]Fo he CdS laye , which was deposi ed o e he
KCN-e ched Sb2Se3(Sb-A200) film, i was no ed he p esence o
e ically g own pla e-like s uc u es and he occu ence o clus-
e s dis ibu ed h oughou he CdS film’s su ace. Fo he uppe
laye , ha is, TiO2, one no ices he p esence o a compac laye
co e ing he whole film’s su ace.
As addi ional SEM image analyses, i was also ob ained
he c oss-sec ion mic og aph o he SLG/Mo/Sb2Se3(Sb-
A200)/CdS/TiO2film o measu e he hickness o he laye s
(Figu e 6a). The i-laye Mo exhibi ed a o al hickness o
≈0.9 μm, which was comp ised o he denomina ed MoA
(≈0.6 μm, lowe egion o he back-con ac ), and MoB+MoA
(≈0.3 μm), co esponding o he po ous (in e media e egion o
he Mo laye ) and he sac ificial (uppe egion o he Mo laye )
laye s, espec i ely. I is wo h men ioning ha he difficul y in
diffe en ia ing he po ous and he sac ificial laye s does no allow
a p ope dis inc ion be ween hem, howe e , he mo phological
cha ac e is ics o hese laye s a e e y simila o ha epo ed in
he li e a u e.[68]I is also wo h poin ing ou ha he denomina-
ion o he laye s in he i-laye Mo (i.e., SLG/MoA/MoB/MoA)
was based on he wo k de eloped by Lopez-Ma ino e al.,[68]
who epo ed he i-laye Mo was comp ised o he MoAlaye
(back-con ac ), deposi ed a high powe and low p essu e, MoB
( esis an o seleniza ion), deposi ed a low powe and high
p essu e, and he MoAlaye (sac ificial laye ). The MoAlaye is
mo e compac and has excellen elec ical p ope ies, bu i is
easily o e selenized, whe eas he MoBlaye is mo e po ous and
has highe shun esis ance. The p esence o a hin MoAlaye
on he uppe egion ac s as a sac ificial laye o he o ma ion
o MoSe2, and he in e io seleniza ion o he back-con ac is
p e en ed by he MoBlaye , leading hus he hick MoAlaye on
he lowe egion unselenized, which ac s as he back-con ac o
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Figu e 6. a) FEG-SEM c oss-sec ion mic og aph (15k imes magnifica ion), b) EDS elemen al mapping, and c) hei espec i e elemen s o each laye
p esen in he SLG/Mo/Sb2Se3(Sb-A200)/CdS/TiO2film. d) EDS scan line p ofile o he i-laye Mo ha ing on i s su ace he Sb2Se3(Sb-A200) film.
he ligh abso be ma e ial. Rega ding he c oss-sec ion mic o-
g aph o he o he ma e ials deposi ed on he i-laye Mo, one
no ices a e y compac laye o he Sb2Se3(SbA200)/CdS/TiO2
h oughou he film’s c oss-sec ion wi h a hickness o ≈0.7 μm,
p esen ing no oids be ween he abso be and he i-laye Mo
and no appa en delamina ion. The XRF analysis was used o
es ima e he hickness o Sb2Se3, whose alue is ≈0.65 μm,
sufficien o abso b pho ons wi hin he wa eleng h ange o 400–
1000 nm.[11,69]The CdS laye was es ima ed wi h a hickness o
50 nm, while TiO2was es ima ed wi h a hickness o ≈26 nm.
The c oss-sec ion o he mul ilaye film was also chemically
cha ac e ized ia EDS elemen al mapping, i was possible o dis-
inguish he elemen s in he diffe en laye s (see Figu e 6b,c,and
Figu e S6a, Suppo ing In o ma ion). Addi ionally, acco ding o
he EDS scan line analysis (Figu e 6d) along he c oss-sec ion o
he film, one no ices he p esence o Se (blue line) loca ed wi hin
0.6 and 0.9 μm ( oughly below he Sb2Se3laye ). Tha is due o
he o ma ion o a hick laye o MoSe2 om he seleniza ion o
MoBand MoA(in e media e and uppe egion o Mo laye , e-
spec i ely). The massi e o ma ion o MoSe2is p one o occu
gi en ha he mola Gibbs ene gies o he eac ion o MoSe2and
Sb2Se3a e bo h nega i e (Equa ions (5)and(6)), conside ing he
eac ion be ween Mo(s) o Sb(s) wi h Se(g) a 320 °C (co esponds
o 593 K).[40,41]Fo mo e de ails abou he calcula ion o he al-
ues o he ∆ G(593 K) o hese eac ions, he eade is e e ed
o he SI. The p esence o an MoSe2in e laye can imp o e he
con ac quali y be ween he abso be (i.e., Sb2Se3) and he back
con ac by o ming a quasi-ohmic con ac , esul ing in a highe
open-ci cui ol age due o a educed con ac ba ie and mini-
mized se ies esis ance.[70]
S ill conce ning Figu e 6d, i is no ed ha he p esence o O
(g ay line) is loca ed close o he lowe egion o he i-laye
Mo, and i is belie ed ha his is om he glass subs a e (i.e.,
SiO2). Also, no O signal was iden ified wi hin he egion o he
Sb2Se3(Sb-A200) film, which ensu es he absence o Sb2O3a e
he seleniza ion p ocess.
Mo(s)+2Se(g)→MoSe2(s)Δ G(593 K)=−503.9kJmol
−1(5)
2Sb(s)+3Se(g)→Sb2Se3(s)Δ G(593 K)=−670.9kJmol
−1(6)
The emaining elemen s, such as Si, Cd, and Ti did no affec
he Sb2Se3laye , as can be seen in he EDS scan line comple e
analysis (Figu e S6b, Suppo ing In o ma ion). Conce ning he
S elemen , i canno be said how i affec s he Sb2Se3since Mo
and S elemen s ha e small ene gy diffe ences (14 eV) by ene gy
dispe si e X- ay, and i is ha d o dis inguish Mo and S elemen s
wi h he ene gy esolu ion in EDS.[71]As long as he subs a e is
a hick laye o Mo (0 o 0.9 μm), i can be in e ed ha he huge
signal in his ange is ela ed o he Mo elemen .
Addi ional chemical cha ac e iza ion was ca ied ou o
he Sb2Se3(Sb-A200)/CdS/TiO2film ha ing on i s su ace de-
posi ed P , which was used as a coca alys o u he imp o e
he HER unde illumina ion. The su ace o he Sb2Se3(Sb-
A200)/CdS/TiO2/P film was assessed ia EDS elemen al map-
ping, as shown in Figu e S6c, Suppo ing In o ma ion. The da a
e i y he p esence o P as well as Sb and Se, and hese elemen s
a e well-dis ibu ed h oughou he su ace o he samples.
2.3. PEC Assessmen
The PEC pe o mance o he Sb2Se3(Sb-A200) films ob-
ained om he seleniza ion o Sb-A200 films a diffe en
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