Engineering of sub-bandgap using intermediate states in a wide bandgap semiconductor is promising for high-efficiency photovoltaic technology. The direct bandgap of 2.46 eV in the green part of the visible spectrum attracts the chalcopyrite CuGaS_2 (CGS) as a host for Intermediate Band solar cell applications. Pristine and tin (Sn) doped CGS (CuGa_(1-x)Sn_xS_2) crystalline thin films were deposited using chemical spray pyrolysis method, and their structural and optical properties are characterized.CuGa_(1-x)Sn_xS_2 were subjected to XRD, DRS absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements.The measured XRD diffraction peaks of the thin films revealed chalcopyrite tetragonal structure without any presence of secondary phases (Cu_2S, CuO, SnO_2, and Ga_2S_3). The substitutional doping of Sn is evidenced by a lower 2θ angle shift of XRD peaksFig.1Absorbance spectra of CuGa_(1-x)Sn_xS_2 films due to the larger atomic radius of Sn (0.69 Å) than that of Ga (0.62 Å). The Sn doping has affected the sub-bandgap absorption spectra and bandgaps of CGS films. Apart from primary strong absorbance edges at 490 nm (Fig.1), strong shoulder absorbance edges are also observed in the NIR region between 1000 to 1600 nm for the Sn doped films, and Tauc-plot analyses revealed below-bandgap responses at around 1.25 eV while the host bandgaps were estimated at 2.49 eV.
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