Some physical investigations on Ag2S thin films prepared by sequential thermal evaporation

Ag2S thin films have been prepared on glass substrates by the sequential thermal evaporation technique. X-ray diffraction analysis shows that the films annealed at Ta = 250 °C in argon atmosphere are well crystallised in the β-Ag2S phase with crystallinity preferentially oriented towards (1¯03) direction. Microprobe analysis shows that a nearly stoichiometric composition is obtained under such annealing temperature. The optical properties of the films are investigated using spectrophotometric measurements of transmittance T(λ) and reflectance R(λ) in the wavelength range 500-2000 nm. The refractive and absorption indexes, n and k, of Ag2S thin films are calculated from the values of the measured transmittance and reflectance. The study of the absorption coefficient of these films versus incident energy revealed that the value of the band gap energy is of the order of 1.1 eV. For the first time, a photovoltaic effect is reported using Ag2S as absorber.