Thin films of Tin Oxide (SnO 2 ), having thickness of 200 nm, were formed on to glass substrates by thermal evaporation of high-purity SnO 2 powder in vacuum at various substrate temperatures (T S ), ranging between 25 and 200C. SnO 2 films with varying thickness were also prepared for a fixed T S = 100C. Further, doping of SnO 2 films with Indium (In) was accomplished through solid state diffusion process by successive deposition of SnO 2 and In films and subsequent annealing at 200C for 10 minutes. Both undoped and doped films were characterized optically by UV-VIS-NIR spectrophotometry in the photon wavelength ranging from 300 to 2500 nm. In the visible photon wavelength range, the average optical transmittance (T%) of the films with varying T S was found to be 85%. The maximum value of T % was found to be 89 % around the wavelength of 700nm. The variation of absorption coefficient with photon energy in the fundamental absorption region is the steepest for T S = 100C. The sub-band gap (SBG) absorption is also minimum for this T s . A fluctuating behavior of the band gap energy (E g ) with T s is observed attaining the highest value of 3.59 eV for T s = 100C. The band gap energy increases with thickness but T% in the visible range decreases. The T% in the visible range varies inversely with indium doping, being highest for undoped films. The E g increases upto 2 wt% In doping and gradually decreases for enhanced doping. It seems reasonable to conclude that In doping does not bring favorable optical characteristics. Undoped SnO 2 films having thickness of 200 nm and formed at substrate temperature of 100C yield essential acceptable properties for photovoltaic applications.

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