Formation of CuIn(S,Se)2 thin film by thermal diffusion of sulfur and selenium vapours into Cu–In alloy within a closed graphite container

The formation of CuIn(S,Se)2 thin films by thermal diffusion of sulfur (S) and selenium (Se) vapours into co-sputtered Cu–In alloy within a closed-space graphite container is reported. All films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Four-point-probe and hot-probe measurements. Cu–In alloy films with composition varying from Cu-rich to In-rich were deposited. The synthesized In-rich films yielded CuIn5(S,Se)8 spinel compound which gradually transformed into a single phase CuIn(S,Se)2 as the film composition approached the Cu-rich region. The morphology of the CuIn5(S,Se)8 was found to differ from the stoichiometric and Cu-rich CuIn(S,Se)2 as observed from SEM. EDX composition analysis of the films showed a Cu/In ratio varying from 0.36 to 1.54 and a (S+Se)/(Cu+In) varying from 0.97 to 1.32. The amount of S incorporated in the films was found to differ with changes in the composition. The resistivity of the films ranged between 10−1 and 107 Ω cm and it strongly followed the change in the alloy film composition.