Investigation of optical properties of the sulfosalt new absorber Sn2Sb2S5 thin films using Photothermal Deflection Spectroscopy

The thin Sn2Sb2S5 films which are new absorber material useful for photovoltaic cells are studied in this paper by the photothermal deflection spectroscopic method. Our study consists to draw the experimental normalized amplitude and phase of the photothermal signal versus wavelength at a fixed modulated monochromatic light pump beam frequency. The phase curves are independent of wavelength which is predicted theoretically. However the amplitude ones show saturated regions for high and low absorption coefficient and great variations in the vicinity of the energy gap. These curves show two energy gaps which may be explained by the coexistence of two phases. By comparison of the experimental and theoretical normalized amplitude of the PDS signal one can deduce the optical absorption coefficient and then the energy gaps. The obtained values of the energy gaps are in good agreement with those obtained by reflectivity and transmission measurements.