Growth of CuInS2 thin films by annealing Cu-In stack layers with elemental sulphur for photovoltaic applications

Abstract

Copper Indium Disulphide (CuInS2) is a promising material as an absorber layer in photovoltaic devices since it has a direct band gap of 1.5 eV and a high absorption coefficient. Among CuInS2 preparation techniques, annealing of Cu-In stack layers in hydrogen sulphide (H2S) gas is attractive because it produces high quality CuInS2 thin films. In this investigation, CuInS2 thin films were prepared by annealing sequentially electrodeposited Cu-In stack layers (copper plating followed by indium plating) in elemental sulphur without using toxic H2S gas.Thin films of copper were potentiostatically electrodeposited on smooth Ti substrates using an aqueous solution of 0.1 M sodium acetate and 0.01 M cupric acetate at ?800 mV Vs SCE for 20 min. Thin films of indium were potentiostatically electrodeposited on Ti/Cu films using an aqueous solution of 25 mM InCl3 at ?1.5 V Vs SCE for different durations, in order to change Cu/In atomic ratio of Cu-In stack layers. The temperature of the electrolyte was maintained at 55oC and it was stirred continuously using a magnetic stirrer. After each eposition, films were washed with distilled water. For the ulphidation, Cu-In stack layers were annealed at 550oC for 20 min with 0.08 g sulphur. Optoelectronic properties of the films were studied using I-V measurements and spectral response was obtained in a PEC containing an aqueous solution of polysulphide. Optoelectronic properties suggest that good n-CuInS2 thin films can be grown by maintaining Cu/In atomic ratio of ~ 0.7. The preliminary results of this study suggest the possibility of growing photoactive CuInS2 thin films by annealing electrodeposited Cu-In layers with sulphur.