Electrodeposition of Nickel Tin Selenide Thin Film

Nickel tin selenide thin films have been potentiostatically electrodeposited on titanium substrate from aqueous solution consisting of nickel sulphate (NiSO4), tin chloride (SnCl2) and sodium selenide (Na2SeO3). Ethylenediaminetetraacetic acid (EDTA) was used as additive to improve the quality of deposit and longevity of the deposition bath. The electrodeposition potential was selected from the cyclic voltammetry (CV) experiment. The crystalline structure, morphology, composition and photoactivity of the films deposited were characterised by using X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy disperse analysis of X-rays (EDAX) and linear sweep photovoltammetry (LSPV). X-ray photoelectron spectroscopy (XPS) was performed to the selected sample. The band gap energy and type of optical transition were determined from optical absorbance data. The formation of polycrystalline NiSnSe4 was confirmed by comparing the XRD results to that of a powder which was synthesized by precipitation method. Elemental analysis of the powder determined from XPS spectrum showed the presence of nickel, tin and selenium as ternary compound. The stoichiometric ratio of 1:1:4 of nickel, tin and selenium has been confirmed by EDAX analysis and this value was used as reference. The deposition was carried out at varying parameters such as different potentials, bath temperatures, concentrations of electrolytes and complexing agent, and deposition times. The photoactivity, composition, grain size and shape of the films were dependent on the electrodeposition conditions. The electrodeposition of NiSnSe4 film is most suitable to be carried out at -0.5 V vs. Ag/AgCl with 0.02 MNiSO4, SnCl2, Na2SeO3 while the concentration of complexing agent, EDTA was 0.02 M. This film was obtained in p-type semiconductor. Shorter deposition time also effected the composition of the films which resulted in a non-stoichiometric selenium rich deposit. The best time to deposit nickel tin selenide thin film was obtained at 60 minutes. The optimum bath temperature was 45°C. Higher bath temperature could not improve the crystallinity, but also resulted in the formation of binary compound. The optical absorption studies revealed that the film has direct transition with band gap energy of 1.55 eV.

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