Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics (2018) 29:4065–4074 https://doi.org/10.1007/s10854-017-8350-z Electrolyte pH dependent controlled growth of co-electrodeposited CZT flms for application in CZTS based thin flm solar cells Amrut Agasti 1  · Sudhanshu Mallick 1  · Parag Bhargava 1 Received: 22 August 2017 / Accepted: 28 November 2017 / Published online: 18 December 2017 © Springer Science+Business Media, LLC, part of Springer Nature 2017 Abstract Understanding Cu–Zn–Sn co-electrodeposition is important from the view point of developing high quality CZTS (Cu 2 ZnSnS 4 ) absorber layer for thin flm solar cells. One of the major issue during electrodeposition is hydrogen evolution which can severely afect the growth of the depositing flm. In the present study, the hydrogen evolution is controlled by systematically varying electrolyte pH during co-electrodeposition of Cu–Zn–Sn flms. Cu–Zn–Sn metal precursor flms were co-electrodeposited using electrolytic baths with pH varying from 4 to 8 and conditions for obtaining dense and stoi- chiometric Cu–Zn–Sn flms were evaluated. Films electrodeposited with electrolyte pH of 6, 7 and 8 produced dense and continuous electrodeposited flms in contrast to those deposited using electrolyte pH of 4 and 5. Films deposited with dif- ferent electrolyte pH were sulphurized in Argon atmosphere and their physical characterization was carried out in order to fnd out conditions to obtain a dense and compact CZTS flm having phase purity with appropriate stoichiometry resulting in a band gap of 1.45 eV. 1 Introduction Thin film solar cells based on Cu 2 InGaSe 4 (CIGS) and CdTe absorbers have reached efciencies beyond 20% on laboratory level and have reached a stage of commerciali- zation [1]. But, the toxicity of Cd and Se and scarcity of In, Ga and Te have prompted researchers to look for the use of non-toxic and easily available elements for develop- ing absorber material into thin flm solar cells. Cu 2 ZnSnS 4 (CZTS) has emerged as an attractive alternative absorber material for thin flm solar cells as it contains earth abundant and non-toxic elements, has a high absorption coefcient (> 10 4  cm −1 ) and a direct band gap of 1.5 eV falling within the range of optimal values for single junction solar device [2]. There are several vacuum based techniques like sput- tering [3], thermal evaporation [4], pulsed laser deposition [5] and non-vacuum based techniques like hydrazine slurry approach [6], electrodeposition [7–12], etc. used for produc- tion of CZTS. Electrodeposition is a promising technique for the development of CZTS, due to its cost efectiveness and faster large area deposition. Deposition of Cu–Zn–Sn layer as an intermediate step to formation of CZTS layer can be done in two ways: (i) Sequential electrodeposition, in which diferent metal layers are deposited sequentially (ii) Co-electrodeposition, in which deposition is carried out with all the constituents provided from the same electrolyte. Sequential or co-electrodeposition is usually followed by annealing in inert atmosphere in the presence of H 2 S or S powder to form crystalline CZTS. Unlike conventional elec- trodeposition, pulse electrodeposition uses square or sinu- soidal pulses of current or voltage. Although, there are very few reports available on pulse electrodeposition of CZT, it can be used to deposit CZT flms with desired morphology by controlling deposition rates of individual metal ions by optimizing parameters such as duty cycle, pulse duration and amplitude of pulse [9, 13]. Co-electrodeposition of Cu–Zn–Sn can be controlled by several factors like concentration of metal (Cu, Zn, Sn) salts [14], concentration and type of complexing agents [15–17], pH of the electrolyte [18], deposition potential [19] etc. All these factors can be used to control the fnal composition of the CZTS flm as stoichiometry of CZTS plays important Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10854-017-8350-z) contains supplementary material, which is available to authorized users. * Parag Bhargava pbhargava@iitb.ac.in 1 Department of Metallurgical Engineering and Materials Science, IIT Bombay, Powai, Mumbai 400076, India