Optical Parameters of Thermally Evaporated SnO2 Thin Films

Abstract

Tin Oxide (SnO2) is a transparent metal oxide that is usually used as a fore contact in superstrate thin film solar cells such as CdS/CdTe solar cells. To increase the efficiency of the solar cell, it is necessary to optimize the optical properties of this layer. SnO2 thin films of comparable thickness (500 and 600 nm) were produced by thermal evaporation at ambient temperature. X-ray diffraction (XRD) measurements showed that the films are poorly crystallized. The transmittance of the films was measured at room temperature in the wavelength range (290-1100 nm) and used to deduce the optical parameters. The optical bandgap was estimated by assuming a direct transition. The reflectance was calculated and used to evaluate the extinction coefficient, refractive index, real and imaginary parts of the dielectric constant. The relations of these parameters with photon's energy were discussed and compared with the results obtained by other authors.