EFFECT OF SUBSTRATE TEMPERATURE ON THE OPTICAL, STRUCTURAL AND MORPHOLOGICAL PROPERTIES OF In2Se3 THIN FILMS GROWN BY A TWO-STEP PROCESS

Polycrystalline gamma-In(2)Se(3) 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 alpha-In(2)Se(3) phase in a first step followed by thermal annealing in Se ambient to activate the formation of the gamma-In(2)Se(3) 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 degrees C the indium selenide grow in the alpha-In(2)Se(3) phase, whereas the samples deposited at temperatures between 300 and 550 degrees C grow with a mixture of the alpha-In(2)Se(3) and gamma-In(2)Se(3) phases. The alpha-In(2)Se(3) samples change into the gamma-In(2)Se(3) phase when subjected to heat treatment around 550 degrees 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 alpha-In(2)Se(3) and gamma-In(2)Se(3) films respectively, indicating that this gamma-In(2)Se(3) 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.