Research Article Enhanced Photoelectrochemical Response from … · 2019. 7. 31. · sulfurization...

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 154694 7 pageshttpdxdoiorg1011552013154694

Research ArticleEnhanced Photoelectrochemical Responsefrom Copper Antimony Zinc Sulfide Thin Filmson Transparent Conducting Electrode

Prashant K Sarswat and Michael L Free

Department of Metallurgical Engineering University of Utah Salt Lake City UT 84112 USA

Correspondence should be addressed to Prashant K Sarswat saraswatpgmailcom

Received 31 May 2013 Revised 10 August 2013 Accepted 11 August 2013

Academic Editor Leonardo Palmisano

Copyright copy 2013 P K Sarswat and M L Free This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Copper antimony sulfide (CAS) is a relatively new class of sustainable absorber material utilizing cost effective and abundantelements Band gap engineered modified CAS thin films were synthesized using electrodeposition and elevated temperaturesulfurization approach A testing analog of copper zinc antimony sulfide (CZAS) film-electrolyte interface was created in orderto evaluate photoelectrochemical performance of the thin film of absorber materials Eu3+Eu2+ redox couple was selected for thispurpose based on its relative band offset with copper antimony sulfide It was observed that zinc has a significant effect on CASfilm properties An enhanced photocurrent was observed for CAS film modified with zinc addition A detailed investigation hasbeen carried out by changing stoichiometry and corresponding surface and optical characterization results have been evaluated Asummary of favorable processing parameters of the films showing enhanced photoelectrochemical response is presented

1 Introduction

Sulphosalt group compounds such as chalcostibite (CuSbS2)

famatinite (Cu3SbS4) and tetrahedrite (Cu

12Sb4S13) are part

of a relatively new class of material containing antimonyThis class can be utilized for thin film solar cell photo-electrochemical hydrogen production and thermoelectric-ity production as well as its application as a topologicalinsulator [1ndash4] The sulphosalts containing Cu Sb and Sare commonly known as ldquoCASrdquo which is generally a p-typesemiconducting material [1ndash3] It is worth noting that mostof these elements are cost effective and abundantThis class ofcompounds (or minerals) was widely explored during 1960sand 1980s and it was found that their electronic propertiesare highly dependent on valance electrons in unit cells [5 6]It was reported that some CAS sulphosalts act as large bandgap semiconductors while some are metallic compoundsdepending on the number of valence electrons and thestoichiometry Interestingly ab initio calculations suggest thepresence of a ldquonontrivial 3D topological insulatingrdquo phase [4]It was also anticipated that the electronic properties of such a

class of materials can be tuned by changing various cationsand anions Recently optical properties of these materialshave been explored and it was observed that CAS compoundswith different stoichiometry exhibit different band gaps Theband gap of Cu

12Sb4S13is sim172 eV CuSbS

2shows a band gap

of 138 eV and Cu3SbS3has a band gap of 184 eV [1ndash4] It was

concluded that the band gap of this class of compounds is tun-able and can be varied between 09 and 19 eV [1 4]This rangeof band gap is perfectly suitable for thin film photovoltaiccells and solar hydrogen splitting [1ndash4] Recently varioussolution-processed and vacuum based techniques have beenutilized to grow thin films of CAS such as solvothermal(nanocrystal ink printing) electrodeposition-sulfur anneal-ing and heat treatment of Sb

2S3-CuS layer [1ndash3 7] In most

cases assessments of the photovoltaic properties of thesethin films were conducted using a photoelectrochemical cellEarlier published reports suggest that photoelectrochemicalresponse for chalcostibite thin film coated on ITO electrodewas sim009mAcm2 at saturation whereas film synthesizedusing electrodeposition annealing shows the change in offsetcurrent of sim008mAcm2 [2 7] It is important to note that

2 International Journal of Photoenergy

this change in photocurrent is relatively low compared toother types of chalcogenide films [8] Such inefficiency canhinder the sufficient utilization of CAS for solar cell appli-cations It is highly essential therefore to make additionalefforts for the enhancement of photovoltaic properties ofCASmaterial One of the approaches can be the modificationof film stoichiometry and experimental parameters It wasreported that zinc is one of the common substitutes forcopper antimony sulfide sulphosalt [5 6] For tetrahedrite(also a class of copper antimony zinc (or iron) sulfide)it was reported that up to sim30 of copper substitution ispossible with zinc or iron [5 6] Phase relations of quaternaryCu-Zn-Sb-S or Cu-Fe-Sb-S were discussed by Tatsuka andMorimoto [5] It was reported that tetrahedrite is more stablewhen it contains a relatively high amount of copper It wasconcluded that tetrahedrite decomposes into iron (or zinc)rich tetrahedrite antimony famatinite and digenite It wasalso reported that the Cu-Sb-S alloy system is less stablecompared to the iron (or zinc) bearing CAS alloy system atroom temperature [5] Hence in view of this information wehave systematically synthesized and investigated Cu-Zn-Sb-S (CZAS) type of thin films which is a modification of CASfilms on an FTO substrate

2 Experiments

Electrodeposition of Cu-Zn-SbThin Films and Subsequent Sul-furizationThinCZAS filmswere electrochemically grown ona fluorinated tin oxide (FTO) substrate using a bath contain-ing ions of interest (Cu2+ Zn2+ and Sb3+) Coelectrodepo-sition was done using a 3-electrode cell connected to GamryInstruments Reference 600 potentiostat operated by VirtualFront Panel software For synthesis of zinc-copper-antimonyalloy thin as-deposited film we utilized 50mL of electrolytecontaining copper sulfate pentahydrate zinc sulfate and anti-mony trichloride It was reported that an excess of antimonyis required in order to produce famatinite with low CuS[1 5] In light of this information three different experimentswere conducted for synthesis of as-deposited film (sample1 0016M CuSO

4sdot 5H2O 0043M SbCl

3 0062M ZnSO

4

sample 2 0016M CuSO4sdot 5H2O 00172M SbCl

3 0094M

ZnSO4 sample 3 0016M CuSO


3

0038M ZnSO4) The pHs of these baths were 157 23

and 19 respectively To mitigate preferential electroplatingpotassium sodium tartrate was used as a complexing orchelating agent It is a very common method to modifythe electrode potential of different metal ions closure in theelectrolyte (or plating solution) by conversion of simple ionsinto complex ions [9] The electrodepositions were carriedout at simminus16V Time of electrodeposition was limited tosim160ndash180 s in order to obtain 1ndash15 120583m thick as-depositedfilm The precursorrsquos films were annealed (duration sim2 h) inan evaporated sulfur environment to get CZAS thin filmSulfurization was carried out in a tube furnace (temperaturesim450∘ C) in an argon environment Photoelectrochemicalstudy was conducted using a Gamry PCI4750 Potentiostatand a three-electrode system containing CZAS electrodesaturated calomel reference electrode (SCE) and a platinum

counter electrode which were immersed in an aqueoussolution of 007M Eu(NO

3)3sdot 6H2O The advantages of

europium nitrate have been discussed elsewhere [10] Toexamine the photoelectrochemical responses of the CZASfilms the change in transient photocurrents was monitoredwhich were generated during alternating illumination from ahigh-intensity white light optical illuminator

21 Film Characterization Thin films were investigatedby X-ray diffraction (XRD) scanning electron microscopy(SEM) X-ray photoelectron spectroscopy (XPS) Ramanspectroscopy and UV-Vis spectroscopy in order to evaluatephase and structure oxidation state and morphologicalfeatures XRD patterns were obtained using a Philips XrsquoPertXRD diffractometer with Cu K120572 radiation over the 2120579range 20ndash80∘ For high resolution small step sizes and areceiving slit size of 18∘ were used SEM was performedusing an FEI Quanta 600 scanning electron microscopeRaman spectra were obtained by using anR 3000QEportableRaman spectrometer (made by Raman Systems) A 785 nmlaser with a power of sim140mW was used for excitationOptical transmittance measurements were performed usingan Ocean Optics spectrophotometer equipped with OOIBase 32 software X-ray photoelectron spectroscopy (XPS)measurements were carried out using the monochromaticAlK120572source equipped Kratos Axis Ultra DLD instrument

The spot size was sim400120583m dwell time was sim200ms and stepsize was kept sim1 eV

3 Results and Discussion

Figures 1(a) and 1(b) show the X-ray diffractograms of CZASthin films deposited on FTO substrate It can be seen thatapart from main characteristics peaks SnO

2peaks are also

prominent in this diffractogram for sample from experi-ment 1 (see Figure 1(a)) This diffraction analysis suggeststhe presence of famatinite CAS (strong peaks at sim2867∘and 337∘) as well as peak at sim56∘ [1] Sample 2 showsone distinct peak at sim297∘ and two low-intensity peaks atsim34∘ and 50∘ respectively These peaks closely match withdiffraction pattern of tetrahedrite [3 11] Sample 3 showsalmost amorphous behavior hence most of the analysis wasfocused on sample 1 and sample 2 Further investigation wasalso conducted to confirm phase and purity of these samplesWe have synthesized some filmswith a relatively high amountof antimony hence the possibility of binary sulfide will beinvestigated in XPS analysis

Raman spectra of thin films are shown in Figure 2 Itcan be seen that for sample 1 two distinct peaks at sim335and 365 cmminus1 are present For sample 2 an intense peakwas found at sim362 cmminus1 Sample 3 shows a low-intensitypeak at sim305 cmminus1 For reference and comparison we haveinvestigated Raman spectra of copper antimony chalcogenideminerals [12] It was found from the literature that chalcostib-ite shows a strong Raman peak at sim337 cmminus1 tetrahedrite atsim351 cmminus1 and famatinite at sim333 cmminus1 (strong peak) 283and 369 cmminus1 (low-intensity peak) [12] Based on these valuesand our observation it can be said that experiment 1 results in

International Journal of Photoenergy 3

20 30 40 50 60

Cou

nts (

au)

(312)

(112)

(200)

2120579 (deg)

SnO2

SnO2SnO2

(a)

(222)

(400) (440)

Cou

nts (

au)

2120579 (deg)20 30 40 50 60

(b)

Figure 1 X-ray diffraction pattern of modified copper antimony sulfide thin film (a) sample 1 and (b) sample 2

250 300 350 400 450 500Wavenumber (1cm)

Cou

nts (

au)

Experiment 1Experiment 2

Experiment 3FTO sample

335 cmminus1 362 cmminus1

Figure 2 Raman spectra of copper antimony sulfide thin films ofdifferent stoichiometry and FTO coated glass sample

the formation of famatinite phase It was observed that ourRaman peaks show a shift (from the standard peak positionof undoped Cu

3SbS4) towards higher frequency for CZAS

film Such an observation can be explained Analysis of BilbaoCrystallographic Server suggests that for famatinite119860

1mode

is Raman active and strong very similar to that for a kesteritecrystal structure [13 14] For a structurally similar compoundCZTS it was reported that 119860

1symmetry mode which is

a vibrational mode shift in the frequencies of these peaksis only due to different force constants fMminusS and free fromchange in reduced mass effects [15] The larger force constantgenerally results in higher Raman frequencies Famatinite isa class I-V-VI type of semiconductor and it crystallizes in anordered sphalerite superstructure with a 142119898 space groupwith lattice parameters 119886 = 119887 = 5391 A and 119888 = 10764 A[1] In randomly substituted CAS Zn solid solution zinc

occupies a copper position in the lattice [5 6] Hence there isa possibility of newZn-S bonds in a lattice As themass of zincis greater than copper which indicates fZn-S gt fCu-S hence itresults in the shifting of a strong Raman peak It is very likelythat the strong Raman peak from sample 2 is characteristicof a tetrahedrite peak which is possibly shifted due tostoichiometry modifications Such modification often causesa change in bonding interaction Both samples 1 and 2 wereprepared from the electrochemical bath containing similarconcentrations of copper but bath 1 contained a relatively lowamount of zinc Sample 2 contains high zinc hence moreshift in Raman peak position is expected Raman spectra ofsamples were also compared with standard samples of Sb

2S3

from the database It was concluded that the presence of Sb2S3

results in strong peaks at sim270 and 305 cmminus1 [12] howeverwe did not observe strong peaks at these wavenumbersfor samples 1 and 2 Such observation also eliminates thepossibility of enhanced presence of Sb

2S3for samples 1 and

2 On the other hand sample 3 shows a low-intensity peak atsim306 cmminus1 which indicates the presence of antimony sulfideThis investigation also suggests that there is less possibility of120573-Cu3SbS3as there is an absence of a strong peak atsim321 cmminus1

[16] It is essential to note that sample 1 (famatinite rich filmdoped with zinc) and sample 2 (tetrahedrite rich film dopedwith zinc) are more photoactive The formation of Cu

3SbS3

(famatinite) at 400∘C is more spontaneous compared toCuSbS

2 Cu2S and Sb

2S3[17] It was concluded that the

formation of Cu3SbS3and CuSbS

2from the parent elements

is more favorable rather than from secondary sulfide phase[5 6 17] The formation of famatinite from tetrahedrite isalso spontaneous and remains up to temperature sim770∘C Itis important to mention that no strong Raman peaks of FTOwere obtained in Raman spectra of CZAS film In contrastvery strong peaks which correspond to FTO were observedinXRDAn investigation of FTO coated glass sample suggeststhat its Raman intensity is very low compared toCZAS coatedsample (see Figure 2) In this situation there are variousRaman peaks of FTO between 250 and 500 cmminus1 althoughthey are not visible in CZAS spectra


20 120583m

(a)

20 120583m

(b)

5 120583m

(c)

5 120583m

(d)

20 120583m

(e)

5 120583m

(f)

Figure 3 Scanning electron micrograph of modified copper antimony sulfide coated substrate (a) low-magnification image of sample 1 (b)low-magnification image of sample 1 (different area) (c) high-magnification image of sample 1 (d) high-magnification image of sample 1showing flower-like structures (e) low-magnification image of sample 2 and (f) high-magnification image of sample 2

The SEM images of CZAS samples are shown in Figures3(a)ndash3(f) KCN etching was not performed in any of oursamples presented and evaluated in this report A low-magnification SEM image (sample 1) suggests that CZAS filmforms over the entire FTO substrate (see Figure 3(a)) Nopeel or cracking is observed Figure 3(b) shows an imagefrom another area which suggests that film is rough Italso can be seen that film contains a spherical-globulartype of grains in most places Grain size of film extendsfrom 500 nm to 1120583m High-resolution imaging (Figure 3(c))suggests that most of the grains are adjacent to each other

and in many cases they form clusters of grains Anotherhigh-resolution image (Figure 3(d)) suggests that thin filmfrom sample 1 contains flake- and flower-like crystals Theaverage diameters for these crystals are sim100 nm A low-magnification image (Figure 3(e)) of sample 2 suggests thatgrains are more uniform compared to sample 1 Althoughmost of the grains and film composition are uniform at someplaces a few grains with different texture (Figure 3(f)) canbe seen Such texture indicates the possibility of secondaryphase traces It can be observed that most portions of the filmare crack free however some pinholes are present Such an


920930940950960970

Inte

nsity

(au

)

Binding energy (eV)

2p12

2p32

(a)

Inte

nsity

(au

)

520525530535540545Binding energy (eV)

3d32

3d52

(b)

Inte

nsity

(au

)


2p32

(c)

1015102510351045

Inte

nsity

(au

)

Binding energy (eV)

2p12 2p32

SbMNNa and SbMNNb

(d)

Figure 4 X-ray photoelectron spectroscopy of sample 1 (a) Cu 2p peaks (b) Sb 3d doublet (c) S 2p peaks and (d) Zn 2p doublet

observation suggests that zinc has a significant effect on filmmorphology which subsequently affects device performanceRecent investigation by Warren et al [18] indicates that highphoton to current efficiency can be due to many factorsbut spatial distribution of current carrying domains in thecrystals plays an important role It is very likely that high-structural complexity results in high photocurrent

Sample showing highest photocurrent response (fromexperiment 1) was chosen for XPS analysis A 2p doublet forcopper at 9323 and 9521 eV (2p

32and 2p

12) was separated

by a gap of 198 eV (see Figure 4(a)) These positions andgap are indications of the Cu(I) oxidation state [19 20] Wedid not observe any satellite peaks which correspond to theCu(II) oxidation state The antimony lines are found at 5308and 540 eV (see Figure 4(b)) and are separated with a gapof 92 eV which perfectly matches with 3d doublet (3d

52

and 3d32

) [19] Careful observation indicates that each ofthese peaks is overlapped with peaks at 5296 and 539 eVThis observation suggests the presence of Sb(III) oxidationstate It was reported that a controlled sample of amorphousSb2S3also shows peaks at very similar positions sim52960 and

53897 eV [21] A shift towards higher binding energy was

found which indicates that Sb is present in the form of Sb5+It suggests the presence of A

3

IBVX4type crystal structure

One of the doublets (Figure 4(c)) of S 2p perfectly matcheswith the reported value of 2p

12at sim1629 eV [19] The S

2p line also shows asymmetry which is due to spin orbitcoupling In XPS spectra Zn 2p doublet (see Figure 4(d)) wasobserved at sim1022 eV (2p

32) and 1045 eV (2p

12) which was

consistent with the standard splitting sim229 eV It suggestsZn(II) oxidation state [19] Elemental analysis suggests thatthe atomic ratio of Cu Zn Sb S is 118 040 190 72

The optical properties of CZAS thin films (samples1 and 2) were analyzed using Ultra Violet-Visible opticaltransmission spectroscopy The transmittance of a CZASfilm was examined as a function of wavelength Using thetransmittance data from the absorption spectra the energygap of thin film can be determined as follows

120572 = 119860(ℎ] minus 119864119892)

12 (1)

where 120572 is the absorption coefficient 119860 is a constant ℎ]is the incident photon energy and 119864

119892is the energy gap

Figure 5 shows squared absorption coefficient and incident


195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2

Figure 5 (1205722) versus photon energy ℎ] for CZAS films

Potential (V)

Sample 1Sample 2Sample 3

Change in

Light on

minus09 minus08 minus07 minus06 minus05 minus04 minus03minus00005

minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)

Figure 6 Photoelectrochemical response of CZAS thin films(grownonFTO substrate) immersed in europiumnitrate electrolytesolution

photon energy relationship for CZAS films deposited onFTO coated glass By extrapolating the squared absorptioncoefficient versus photon energy curve to zero the band gapwas evaluated to be sim220 eV (sample 1) and sim225 eV (sample2)

The current density potential plots obtained after pho-toelectrochemical examination for three different samplesare shown in Figure 6 119869-119881 curves were recorded duringwhite LED illumination (incident illuminance on substratesim32 times 10

4 lux at wavelength of sim550 nm) and in the dark

The photocurrent was recorded during chopping illumina-tion and change in photocurrent was evaluated for relativephotovoltaic performanceThe highest photoelectrochemicalresponse of the film (experiment 1) is sim015mA The darkcurrent was very insignificant up to the biased potential ofsimminus06V (SCE) but started increasing beyond a potential simminus07V It should be noted that this photocurrent responseis relatively high (sim17 times greater) compared to earlierreported values [2 7] Sample 2 which was prepared fromthe bath of depleted antimony and high zinc showed arelatively low current response Highest current responsefor this sample was sim008mA which is approximately halfof the first sample The lowest current response (overall)was obtained for sample 3 which contains the highestlevel of antimony Dark current for this sample was alsohigher The high photocurrent response from sample 1can be explained based on the presence of a more stablecrystalline phase structural complexity relatively low-bandgap of film and more uniform and interconnected grainsOn the other hand sample 2 shows some secondary phasetraces on SEM which can create a trap or recombinationcenters throughout the filmvolume Such a phenomenonmaydiminish the photovoltaic performance Another possibilityof reduced photoelectrochemical performance of sample2 is a relatively high band gap compared to sample 1More analysis such as simulations using density functionaltheory tools and finite-difference time-domain methods arerequired to explain such behavior in detail This work is inprogress

4 Conclusions

In summary modified copper antimony sulfide thin filmswere synthesized using electrochemical growth of ldquoCu-Sb-Znrdquo alloy and subsequent elevated temperature sulfurizationThese films were investigated for phase and structural analy-ses as well as for photoelectrochemical performance RamanandXRDcharacterizations suggest that film grownon sample1 is a famatinite rich while sample 2 contains a tetrahedriterich film High-zinc content results in the strengthening ofthe force constant which subsequently causes shifting of theRaman peak towards higher frequency The band gap ofthe film deposited on sample 1 (moderate antimony) was sim220 eV whereas band gap of the sample 2 (zinc rich film) wassim225 eVThin film synthesized from an electrochemical bathcontaining a moderate level of antimony chloride shows thehighest photocurrent response However film from bath withexcess antimony exhibits very poor photoelectrochemicalresponse Enhanced photoelectrochemical response of themodifiedCAS filmwas explained on the basis of amore stablecrystalline phase a low-band gap of film and more uniform-interconnected grains

References

[1] J V Embden and Y Tachibana ldquoSynthesis and characterisationof famatinite copper antimony sulfide nanocrystalsrdquo Journal ofMaterials Chemistryno vol 22 no 23 pp 11466ndash11469 2012


[2] C Yan Z Su E Gu et al ldquoSolution-based synthesis ofchalcostibite (CuSbS

2) nanobricks for solar energy conversionrdquo

RSC Advances vol 2 no 28 pp 10481ndash10484 2012[3] C An Y Jin K Tang and Y Qian ldquoSelective synthesis

and characterization of famatinite nanofibers and tetrahedritenanoflakesrdquo Journal of Materials Chemistry vol 13 no 2 pp301ndash303 2003

[4] Y JWang H Lin T DasM ZHasan andA Bansil ldquoTopolog-ical insulators in the quaternary chalcogenide compounds andternary famatinite compoundsrdquo New Journal of Physics vol 13no 8 Article ID 085017 2010

[5] K Tatsuka and N Morimoto ldquoTetrahedrites stability relationsin the Cu-Fe-Sb-S systemrdquo American Mineralogist vol 62 pp1101ndash1109 1977

[6] R O Sack and R R Loucks ldquoThermodynamic properties oftetrahedrite-tennanites constraints on the interdependence ofthe Ag 999445999468 Cu Fe 999445999468 Zn Cu 999445999468 Fe and As 999445999468 Sb exchangereactionsrdquo American Mineralogist vol 70 no 11-12 pp 1270ndash1289 1985

[7] D Colombara L M Peter K D Rogers J D Painter and SRoncallo ldquoFormation of CuSbS

2and CuSbSe

2thin films via

chalcogenisation of Sb-Cu metal precursorsrdquo Thin Solid Filmsvol 519 no 21 pp 7438ndash7443 2011

[8] S C Riha S J Fredrick J B Sambur Y Liu A L Prietoand B A Parkinson ldquoPhotoelectrochemical characterizationof nanocrystalline thin-film Cu

2ZnSnS

4photocathodesrdquo ACS

Applied Materials and Interfaces vol 3 no 1 pp 58ndash66 2011[9] L J Durney Grahamrsquos Electroplating Handbook Springer New

York NY USA 1984[10] P K Sarswat and M L Free ldquoAn evaluation of depletion layer

photoactivity in Cu2ZnSnS

4thin filmrdquo Thin Solid Films vol

520 no 13 pp 4422ndash4426 2012[11] X Lu and D T Morelli ldquoNatural mineral tetrahedrite as a

direct source of thermoelectric materialsrdquo Physical ChemistryChemical Physics vol 15 no 16 pp 5762ndash5766 2013

[12] httprruffinfo (data base)[13] M I Aroyo A Kirov C Capillas J M Perez-Mato and H

Wondratschek ldquoBilbao crystallographic server II Representa-tions of crystallographic point groups and space groupsrdquo ActaCrystallographica A vol 62 no 2 pp 115ndash128 2006

[14] P K Sarswat M L Free and A Tiwari ldquoTemperature-dependent study of the Raman A mode of Cu

2ZnSnS

4thin

filmsrdquo Physica Status Solidi B vol 248 no 9 pp 2170ndash2174 2011[15] C Huang Y Chan F Liu et al ldquoSynthesis and characterization

of multicomponent Cu2(Fe119909Zn1minus119909

)SnS4nanocrystals with tun-

able band gap and structurerdquo Journal of Material Chemistry Avol 1 no 17 pp 5402ndash5407 2013

[16] A Pfitzner ldquo(CuI)2Cu3SbS3 copper iodide as solid solvent for

thiometalate ionsrdquoChemistry vol 3 no 12 pp 2032ndash2038 1997[17] J R Craig and W R Lees ldquoThermochemical data for sulfosalt

ore minerals formation from simple sulfidesrdquo Economic Geol-ogy vol 67 no 3 pp 373ndash377 1972

[18] S C Warren K Voıtchovsky H Dotan et al ldquoIdentifyingchampion nanostructures for solar water-splittingrdquo NatureMaterials vol 12 pp 842ndash849 2013

[19] ldquoNIST X-ray Photoelectron Spectroscopy Database Version41rdquo National Institute of Standards and Technology Gaithers-burg httpsrdatanistgovxps 2012

[20] P K Sarswat and M L Free ldquoUtility of by-product quantumdots obtained during synthesis of Cu

2ZnSnS

4colloidal inkrdquo

Ceramics International 2013

[21] H Yang M Li L Fu A Tang and S Mann ldquoControlledassembly of Sb

2S3nanoparticles on silicapolymer nanotubes

insights into the nature of hybrid interfacesrdquo Scientific Reportsvol 3 no 1336 2013

Submit your manuscripts athttpwwwhindawicom

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this change in photocurrent is relatively low compared toother types of chalcogenide films [8] Such inefficiency canhinder the sufficient utilization of CAS for solar cell appli-cations It is highly essential therefore to make additionalefforts for the enhancement of photovoltaic properties ofCASmaterial One of the approaches can be the modificationof film stoichiometry and experimental parameters It wasreported that zinc is one of the common substitutes forcopper antimony sulfide sulphosalt [5 6] For tetrahedrite(also a class of copper antimony zinc (or iron) sulfide)it was reported that up to sim30 of copper substitution ispossible with zinc or iron [5 6] Phase relations of quaternaryCu-Zn-Sb-S or Cu-Fe-Sb-S were discussed by Tatsuka andMorimoto [5] It was reported that tetrahedrite is more stablewhen it contains a relatively high amount of copper It wasconcluded that tetrahedrite decomposes into iron (or zinc)rich tetrahedrite antimony famatinite and digenite It wasalso reported that the Cu-Sb-S alloy system is less stablecompared to the iron (or zinc) bearing CAS alloy system atroom temperature [5] Hence in view of this information wehave systematically synthesized and investigated Cu-Zn-Sb-S (CZAS) type of thin films which is a modification of CASfilms on an FTO substrate

2 Experiments

Electrodeposition of Cu-Zn-SbThin Films and Subsequent Sul-furizationThinCZAS filmswere electrochemically grown ona fluorinated tin oxide (FTO) substrate using a bath contain-ing ions of interest (Cu2+ Zn2+ and Sb3+) Coelectrodepo-sition was done using a 3-electrode cell connected to GamryInstruments Reference 600 potentiostat operated by VirtualFront Panel software For synthesis of zinc-copper-antimonyalloy thin as-deposited film we utilized 50mL of electrolytecontaining copper sulfate pentahydrate zinc sulfate and anti-mony trichloride It was reported that an excess of antimonyis required in order to produce famatinite with low CuS[1 5] In light of this information three different experimentswere conducted for synthesis of as-deposited film (sample1 0016M CuSO


3 0062M ZnSO

4

sample 2 0016M CuSO4sdot 5H2O 00172M SbCl

3 0094M

ZnSO4 sample 3 0016M CuSO


3

0038M ZnSO4) The pHs of these baths were 157 23

and 19 respectively To mitigate preferential electroplatingpotassium sodium tartrate was used as a complexing orchelating agent It is a very common method to modifythe electrode potential of different metal ions closure in theelectrolyte (or plating solution) by conversion of simple ionsinto complex ions [9] The electrodepositions were carriedout at simminus16V Time of electrodeposition was limited tosim160ndash180 s in order to obtain 1ndash15 120583m thick as-depositedfilm The precursorrsquos films were annealed (duration sim2 h) inan evaporated sulfur environment to get CZAS thin filmSulfurization was carried out in a tube furnace (temperaturesim450∘ C) in an argon environment Photoelectrochemicalstudy was conducted using a Gamry PCI4750 Potentiostatand a three-electrode system containing CZAS electrodesaturated calomel reference electrode (SCE) and a platinum

counter electrode which were immersed in an aqueoussolution of 007M Eu(NO

3)3sdot 6H2O The advantages of

europium nitrate have been discussed elsewhere [10] Toexamine the photoelectrochemical responses of the CZASfilms the change in transient photocurrents was monitoredwhich were generated during alternating illumination from ahigh-intensity white light optical illuminator

21 Film Characterization Thin films were investigatedby X-ray diffraction (XRD) scanning electron microscopy(SEM) X-ray photoelectron spectroscopy (XPS) Ramanspectroscopy and UV-Vis spectroscopy in order to evaluatephase and structure oxidation state and morphologicalfeatures XRD patterns were obtained using a Philips XrsquoPertXRD diffractometer with Cu K120572 radiation over the 2120579range 20ndash80∘ For high resolution small step sizes and areceiving slit size of 18∘ were used SEM was performedusing an FEI Quanta 600 scanning electron microscopeRaman spectra were obtained by using anR 3000QEportableRaman spectrometer (made by Raman Systems) A 785 nmlaser with a power of sim140mW was used for excitationOptical transmittance measurements were performed usingan Ocean Optics spectrophotometer equipped with OOIBase 32 software X-ray photoelectron spectroscopy (XPS)measurements were carried out using the monochromaticAlK120572source equipped Kratos Axis Ultra DLD instrument

The spot size was sim400120583m dwell time was sim200ms and stepsize was kept sim1 eV

3 Results and Discussion

Figures 1(a) and 1(b) show the X-ray diffractograms of CZASthin films deposited on FTO substrate It can be seen thatapart from main characteristics peaks SnO

2peaks are also

prominent in this diffractogram for sample from experi-ment 1 (see Figure 1(a)) This diffraction analysis suggeststhe presence of famatinite CAS (strong peaks at sim2867∘and 337∘) as well as peak at sim56∘ [1] Sample 2 showsone distinct peak at sim297∘ and two low-intensity peaks atsim34∘ and 50∘ respectively These peaks closely match withdiffraction pattern of tetrahedrite [3 11] Sample 3 showsalmost amorphous behavior hence most of the analysis wasfocused on sample 1 and sample 2 Further investigation wasalso conducted to confirm phase and purity of these samplesWe have synthesized some filmswith a relatively high amountof antimony hence the possibility of binary sulfide will beinvestigated in XPS analysis

Raman spectra of thin films are shown in Figure 2 Itcan be seen that for sample 1 two distinct peaks at sim335and 365 cmminus1 are present For sample 2 an intense peakwas found at sim362 cmminus1 Sample 3 shows a low-intensitypeak at sim305 cmminus1 For reference and comparison we haveinvestigated Raman spectra of copper antimony chalcogenideminerals [12] It was found from the literature that chalcostib-ite shows a strong Raman peak at sim337 cmminus1 tetrahedrite atsim351 cmminus1 and famatinite at sim333 cmminus1 (strong peak) 283and 369 cmminus1 (low-intensity peak) [12] Based on these valuesand our observation it can be said that experiment 1 results in


20 30 40 50 60

Cou

nts (

au)

(312)

(112)

(200)

2120579 (deg)

SnO2

SnO2SnO2

(a)

(222)

(400) (440)

Cou

nts (

au)

2120579 (deg)20 30 40 50 60

(b)


250 300 350 400 450 500Wavenumber (1cm)

Cou

nts (

au)








1mode





2S3






3SbS3


2 Cu2S and Sb






20 120583m

(a)

20 120583m

(b)

5 120583m

(c)

5 120583m

(d)

20 120583m

(e)

5 120583m

(f)





920930940950960970

Inte

nsity

(au

)

Binding energy (eV)

2p12

2p32

(a)

Inte

nsity

(au

)


3d32

3d52

(b)

Inte

nsity

(au

)


2p32

(c)

1015102510351045

Inte

nsity

(au

)

Binding energy (eV)

2p12 2p32

SbMNNa and SbMNNb

(d)




32and 2p

12) was separated


52

and 3d32




3





32) and 1045 eV (2p

12) which was



120572 = 119860(ℎ] minus 119864119892)

12 (1)





195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2


Potential (V)


Change in

Light on


minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)






4 Conclusions


References











2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


20 30 40 50 60

Cou

nts (

au)

(312)

(112)

(200)

2120579 (deg)

SnO2

SnO2SnO2

(a)

(222)

(400) (440)

Cou

nts (

au)

2120579 (deg)20 30 40 50 60

(b)


250 300 350 400 450 500Wavenumber (1cm)

Cou

nts (

au)








1mode





2S3






3SbS3


2 Cu2S and Sb






20 120583m

(a)

20 120583m

(b)

5 120583m

(c)

5 120583m

(d)

20 120583m

(e)

5 120583m

(f)





920930940950960970

Inte

nsity

(au

)

Binding energy (eV)

2p12

2p32

(a)

Inte

nsity

(au

)


3d32

3d52

(b)

Inte

nsity

(au

)


2p32

(c)

1015102510351045

Inte

nsity

(au

)

Binding energy (eV)

2p12 2p32

SbMNNa and SbMNNb

(d)




32and 2p

12) was separated


52

and 3d32




3





32) and 1045 eV (2p

12) which was



120572 = 119860(ℎ] minus 119864119892)

12 (1)





195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2


Potential (V)


Change in

Light on


minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)






4 Conclusions


References











2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


20 120583m

(a)

20 120583m

(b)

5 120583m

(c)

5 120583m

(d)

20 120583m

(e)

5 120583m

(f)





920930940950960970

Inte

nsity

(au

)

Binding energy (eV)

2p12

2p32

(a)

Inte

nsity

(au

)


3d32

3d52

(b)

Inte

nsity

(au

)


2p32

(c)

1015102510351045

Inte

nsity

(au

)

Binding energy (eV)

2p12 2p32

SbMNNa and SbMNNb

(d)




32and 2p

12) was separated


52

and 3d32




3





32) and 1045 eV (2p

12) which was



120572 = 119860(ℎ] minus 119864119892)

12 (1)





195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2


Potential (V)


Change in

Light on


minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)






4 Conclusions


References











2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


920930940950960970

Inte

nsity

(au

)

Binding energy (eV)

2p12

2p32

(a)

Inte

nsity

(au

)


3d32

3d52

(b)

Inte

nsity

(au

)


2p32

(c)

1015102510351045

Inte

nsity

(au

)

Binding energy (eV)

2p12 2p32

SbMNNa and SbMNNb

(d)




32and 2p

12) was separated


52

and 3d32




3





32) and 1045 eV (2p

12) which was



120572 = 119860(ℎ] minus 119864119892)

12 (1)





195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2


Potential (V)


Change in

Light on


minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)






4 Conclusions


References











2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


195 255205 215 225 235 245Energy (eV)

Squa

red

Abs

Coe

ff

Sample 1Sample 2


Potential (V)


Change in

Light on


minus00007

minus00009

minus00011

minus00013

minus00015

currentCurr

ent (

Ac

m2)






4 Conclusions


References











2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










2and CuSbSe

2thin films via



2ZnSnS











2ZnSnS

4thin











2ZnSnS

4colloidal inkrdquo














Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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