Enhanced optoelectronic and photoelectrochemical characteristics of nebulised spray pyrolysed ‘Cu’ rich CuInS2 thin film

CuInS2 thin films are deposited by nebulised spray pyrolysis technique using the aqueous solutions of CuCl2, InCl3 and thiourea on a pre-heated glass substrate with different chemical compositions. The as-deposited films are vacuum annealed at 200 °C. In all cases, thin films are found to be crystallised in chalcopyrite phase with a preferential orientation along (112) direction. The crystalline quality of the films is further enhanced by heat treatment under vacuum. Cu rich CuInS2 film exhibited better crystallinity and high conductivity compared to CuInS2 and In rich CuInS2 thin films. The films exhibited net-like surface structure. The elemental composition of CuInS2 thin films is controlled by varying Cu/In ratios in precursor. Absorption co-efficient of the films is of the order of 104 cm−1 in the visible region and the films exhibited a band gap of 1.39–1.47 eV. Photoluminescence intensity of all the stoichiometric composition is drastically decreased upon vacuum annealing. This feature may be attributed to the vacation of carriers from shallow traps, thereby increasing the number of surface state densities. The solution resistance and charge transfer resistance of Cu rich CuInS2 electrode in dark and under light illumination are determined from electrochemical impedance spectroscopy and are found to be 10.22 Ω, 11.36 Ω and 471.6 Ω, 81.97 Ω respectively. The flat band potential and acceptor density of Cu rich CuInS2 electrode are determined from Mott-Schottky plot and are found to be 0.53 V and 9.25×1021 cm−3 respectively.