Electrodeposition of Copper Tin Selenide Films from Aqueous Solution

Thin films of Cu2SnSe4 have been electrodeposited potentiostatically from aqueous solution containing CuCl2, SnCl4 and Na2SeO3 on titanium substrates at room temperature. The disodium salt of ethylenediaminetetraacetic acid (Na2-EDTA) was used as a complexant. Cyclic voltammetry was performed at room temperature to elucidate the electrodic processes occurred and to determine the potential range for electrodeposition. The effect of parameters such as deposition potential, electrolyte concentration, deposition time, bath temperature, annealing time and temperature and concentration of complexant on the film properties were studied. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS) and linear sweep photovoltammetry (LSPV) technique. The band gap energy and type of optical transition were determined from optical absorbance data. XRD studies confirmed the formation of polycrystalline Cu2SnSe4 on the titanium substrate and showed a cubic structure with strong (111) orientation. The films prepared in this study showed p-type semiconductor behaviour. SEM micrographs confirmed the polycrystalline nature of the deposit. The photoactivity, composition, grain size and shape of the film were dependent on the electrodeposition condition. Nearly stiochiometric for Cu2SnSe4 film was obtained from 0.02 M Cu-EDTA, 0.02 M Sn-EDTA and 0.02 M Na2SeO3 solution at potential -0.60 V vs Ag/AgCl. Further investigation at -0.50 V shows that this potential was not suitable for the deposition of copper tin selenide. Increasing the deposition time allowed more materials to be deposited onto the substrate and thicker films were formed. The electrodeposition of the Cu2SnSe4 film was most suitable to be carried out at room temperature. Increasing the bath temperature could not improve the crystallinity of Cu2SnSe4 compound, but lead to formation of binary phase, CuSe. Annealing also could not improve the crystallinity of film but other binary phases such as CuSe2 and Cu2Se appeared. Minimum concentration of EDTA obtained for Cu2SnSe4 film. The film thickness was controlled by the time of deposition and changing the concentration of the reaction. XPS spectrum confirms the presence of Cu, Sn and Se. The optical absorption studies revealed that the transition is direct and band gap energy Eg was 1.2 eV.

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