Preparation, structure, composition, optical and photoelectrochemical properties of vacuum annealed In-Se thin films

Abstract

In2Se3 thin films have been prepared by sequentially evaporating In and Se followed by vacuum annealing at different temperatures. X-ray diffraction studies of the annealed films indicate the presence of β-In2Se3 along with free Se in the deposit. Rutherford backscattering spectrometry (RBS) analysis gave the In to Se ratio as 0.676 but it changed with annealing temperature. Proton-induced X-ray emission (PIXE) analysis of the annealed films gave an In to Se ratio lower than that of the RBS value. The discrepancy in the RBS and PIXE results has been discussed in terms of the inhomogeneity present in the In-Se film. The (KβKα) X-ray intensity ratios of In and Se in In-Se film have been estimated and found to be lower than their respective elemental values. The results have been attributed to the chemical/environmental changes in the electronic structure of In-Se films. The band gap has been estimated from the optical absorption studies and found to be ∼ 1.8 eV but changes with annealing temperature. A film formation mechanism involving the reaction between In and Se under thermal treatment has been described. Finally, photoelectrochemical solar cells have been fabricated and the results are discussed.