Temperature effect on the physical properties of CuIn11S17 thin films for photovoltaic applications

CuIn11S17 compound was synthesized by horizontal Bridgman method using high-purity copper, indium and sulfur elements. CuIn11S17 thin films were prepared by high vacuum evaporation on glass substrates. The glass substrates were heated at 30, 100 and 200 °C. The structural properties of the powder and the films were investigated using X-ray diffraction (XRD). XRD analysis of thin films revealed that the sample deposited at a room temperature was amorphous in nature while those deposited on heated substrates were polycrystalline with a preferred orientation along the (311) plane of the spinel phase. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of thin films. The results showed that CuIn11S17 thin films have high absorption coefficient α in the visible range (105–106 cm−1). The band gap Eg of the films decrease from 2.30 to 1.98 eV with increasing the substrate temperature (Ts) from 30 to 200 °C. We exploited the models of Swanepoel, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index n and the determination of the optical constants of the films. Hot probe method showed that CuIn11S17 films deposited at Ts=30 °C and Ts=100 °C are p-type conductivity whereas the sample deposited at Ts=200 °C is highly compensated.