In this work, thin films of phase-pure Cu 2 ZnSnS 4 (CZTS) were developed from a stack of binary metal sulfides by post-deposition thermal processing. The precursor stack SnS/Cu/ZnS was grown by sequential electrodeposition of SnS and Cu layers followed by thermal evaporation of ZnS layer. The transformation from binary/ternary composition to phase-pure CZTS was studied using different experimental tools such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The TEM images revealed the formation of tetragonal crystals with interplanar spacing 0.312 nm. Raman spectra of the films confirmed that annealing at 550 • C for 30 min under N 2 /S ambient resulted in the formation of phase-pure CZTS film. The bandgap estimated from the optical transmittance and reflectance spectra showed a direct transition at 1.59 eV. The films are photosensitive and the photo electrochemical measurements showed the p-type conductivity of the films. and a theoretical power conversion efficiency of 32.2%. [2][3][4][5] Moreover, the absence of toxic and expensive elements highlights CZTS as an alternative to CdTe and CIGS, which is important in high volume manufacturing of photovoltaic panels and its deployment.CZTS thin films have been deposited by several methods such as thermal evaporation, 6 sputtering, 7 RF magnetron sputtering, 8 electrodeposition, 9-12 sulfurization of the metals, binary sulfide or CZTS layers deposited by different methods 1,[13][14][15][16] etc. In majority of the cases, the films were subjected to post deposition thermal treatment to attain stoichiometry and improve the structural and optical properties.Devices with CZTS and CZTS/Se absorber layers developed by both chemical and physical methods have been reported earlier. [17][18][19][20][21][22] Among the vaccum based techniques, co-evaporated Cu 2 ZnSnSe 4 (CZTSe) and sputter deposited CZTS have attained device efficiencies of 9.15% and 9.3% respectively. 18,19 The films developed with chemical methods such as electrodeposition and nanoparticle based suspension are equally competent and economically attractive. Solar cells with 5.5% and 7% efficiencies were reported with CZTS and CZTS/Se absorber layers developed by electrodeposition technique.21,22 All these aforementioned results suggest a potential commercial interest behind sulfide/selenide based kesterite solar cells which need further optimization in the film synthesis and device fabrication steps to compete with established CdTe and CIGS technologies.In the present work we developed the CZTS films on SnO 2 :F substrates by the sulfurization of a stack of SnS/Cu/ZnS films under N 2 /S atmosphere. The SnS and Cu films were developed by electrodeposition whereas ZnS film was deposited by evaporation in the order shown for the stack. The films were annealed at different temperatures in presence of S to identify the optimum annealing temperature for the formation of phase pure CZTS. The cryst...
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