Bandgap Engineering in Indium SulfideThin Films by Tin Mixing

Abstract

AbstractIn2S3 thin films appear to be a promising candidate for photovoltaic applications due to its stability, wide band gap and photosensitivity. The optical band gap value of Indium sulfide (In2S3) thin films reported in the literature varies from 2.0 eV to 2.4 eV following their synthesis process. These values are too small for an application as buffer layer in solar cells. In Present work, we report that incorporation of Sn using [SnCl4.5H2O] could increase the bandgap to wider ranges. In2S3/Sn thin films were deposited on soda lime glass substrate using chemical spray pyrolysis (CSP) technique. The spraying solution contained indium chloride (InCl3), thiourea [CS(NH2)2] and [SnCl4.5H2O]. Studies were done on films prepared using different Sn/In ratios. Depth profile using x-ray photoelectron spectroscopy showed that incorporation of Sn increased the concentration of oxygen in the samples. Band gap of the films increased with increase in Sn/In ratios. Depending on the ratios, bandgap could be varied from 2.72 eV to 3.78 eV. At lower mixing levels wide band gap low resistive In2S3/Sn films could be obtained which is highly useful for buffer layer applications. Low resistive buffer layer will decrease the series resistance of the cell and wider band gap will improve light transmission in the blue wavelength, both these factors help in increasing the short circuit current of the photovoltaic cell. Samples having higher Sn/In ratios showed wider band gap (up to3.78 eV).Though the samples had very high bandgap and high resistivity these samples were highly photosensitive [(IL-ID)/ID = 11,000]. The results proved that tin incorporation modified the band gap and electrical properties of the In2S3/Sn films favorably over wider ranges making it highly suitable for different optoelectronic applications.