Effect of thickness and substrate temperature on structure and optical band gap of hot wall-deposited CuInSe2 polycrystalline thin films

The copper indium di selenide (CuInSe2) compound was prepared by direct reaction of high-purity elemental copper, indium and selenium. CuInSe2 thin films were prepared on to well-cleaned glass substrates by hot wall deposition technique. The X-ray diffraction studies revealed that all the deposited films are polycrystalline in nature, single phase and exhibiting chalcopyrite structure. The crystallites were found to have a preferred orientation along the (1 1 2) direction. The SEM analysis indicated that the films are polycrystalline in nature. The composition of the chemical constituents present in the deposited CuInSe2 thin films has been determined using energy dispersive X-ray analysis (EDX). Structural parameters of CuInSe2 thin films coated with higher substrate temperatures were also studied. As the substrate temperature increases the grain size increases. Simultaneous TG-DTA analysis has been done for CuInSe2 bulk and an endothermic reaction is observed near the melting point of the compound. Optical transmittance spectrum of the hot wall-deposited CuInSe2 thin films of different thicknesses deposited at three different substrate temperatures were obtained. As the thickness of the film and the substrate temperature increases, the optical band gap decreases. The refractive index of the CuInSe2 thin films are found decreasing with the incident photon wavelength.