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Spray pyrolysis approach to CZTSSe thin films. Influence of solvents on film characteristics

The Cu2ZnSnS4 (CZTS) thin films were deposited by means of spray pyrolysis technique on the Mo/glass substrate, which was heated in the air at a temperature of 320 °C. Samples were prepared using solutions with different solvents: dimethylsulfoxide (DMSO), dimethylformamide (DMF) and water–alcohol (H2O–EtOH). Further, the CZTS films were selenized at a temperature of 540 °C. The influence of the solvents on the crystalline structure, phase composition and optical properties of the CZTS and CZTSSe films were investigated using XRD, scanning electron microscopy with EDX, Raman spectroscopy and UV–vis spectroscopy. The photo-activity of CZTSSe films was assessed by measuring the open-circuit potential (Eoc) values under illumination in an aqueous solution of 0.5 M Na2SO4. Pure kesterite phase Cu2ZnSnSe3.2S0.8 (CZTSSe) with the p-type conductivity and an optical band gap in the range of 1.21–1.31 eV was obtained after the selenization. The CZTSSe films prepared using the DMF as a solvent showed the best phase purity, the lowest density of voids, the highest stability of photoelectrochemical response and the highest power conversion efficiency of fabricated photovoltaic device.