Effect of substrate temperature on the optical, structural and morphological properties of In2Se3 thin films grown by a two-step process

Polycrystalline γ – In2Se3 thin films with adequate properties to use them as buffer layer in solar cells, were grown on corning glass substrates using a novel procedure which includes the formation of the α- In2Se3 phase in a first step followed by thermal annealing in Se ambient to activate the formation of the γ- In2Se3 phase. X-ray diffraction (XRD) measurements revealed that the substrate temperature strongly affects the phase in which the indium selenide films grow; at substrate temperatures of around 300°C the indium selenide grow in the α-In2Se3 phase, whereas the samples deposited at temperatures between 300 and 550°C grow with a mixture of the α-In2Se3 and γ-In2Se3 phases. The α-In2Se3 samples change into the γ-In2Se3 phase when subjected to heat treatment around 550°C in Se ambient. Spectrophotometric measurements also revealed that the phase in which the indium selenide films grow, significantly affects the optical gap Eg. Eg values of 1.47 eV and 2.11 eV were determined for the α-In2Se3 and γ-In2Se3 films respectively, indicating that this γ-In2Se3 compound has better properties to perform as buffer layer in thin film solar cells. The effect of substrate temperature on the structural, optical and morphological properties was investigated using XRD, spectral transmittance and atomic force microscope (AFM) measurements. Theoretical simulation of the XRD pattern carried out with the help of the PowderCell package, allowed us to identify the phases associated to the X-Ray reflections, with a good degree of confidence.