The effect of pH and selenization on the properties of CuInSe₂ thin films prepared by electrodeposition technique for device applications

Abstract

We have synthesized CuInSe₂ (CIS) thin films from an aqueous electrolyte by potentiostatic electrochemical technique at room temperature. The effects of pH and selenization on the properties of CIS layer have been thoroughly investigated. The studies were carried out on the samples prepared in as-prepared bath with pH 2.5 and later adjusted to 1.2. Cyclic voltammetry (CV) was studied at slow scan rate to optimize the deposition parameters. The prepared thin films were selenized in a tubular furnace at 400 °C for 20 min in selenium atmosphere. Structural, optical, compositional, morphological, and electrical properties were studied with the help of X-ray diffractometer, Uv-vis absorption spectroscopy, energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), and current–voltage (I–V) measurements. The prominent reflections (112), (204/220), and (312/116) of tetragonal CIS have been exhibited for all as-deposited and selenized samples. The energy band gap of the selenized CIS thin film was found to be ~1.03 eV. Granular, uniform, and densely packed surface morphology was observed for as-deposited and selenized samples electrodeposited at −0.6 and −0.8 V versus Ag/AgCl for the pH of bath 1.2 and 2.5, respectively. EDAX result reveals the stoichiometric CIS films can be electrodeposited at −0.6 and −0.8 V with pH of the bath 1.2 and 2.5, respectively. The ideality factor (η) deducted from I–V measurements was found to be reduced from 1.6 to 1.3 and 1.9 to 1.2 after selenization of samples grown at −0.6 and −0.8 V, respectively, revealing the formation of ideal diode due to elimination of surface leakage current. Photoelectrochemical (PEC) measurement confirms the growth of p-type CIS thin film.