AgGaS2 (AGS) thin films were deposited onto glass substrates by sequential thermal evaporation of AgGaS2 single crystalline powder and excess silver (Ag) interlayer. Systematic optimization to obtain single phase AgGaS2 thin films was carried out by changing the thickness of the excess silver layer. The structure and composition of as-grown and annealed films were studied by means of X-ray diffraction and energy dispersive X-ray analysis, respectively. The optical properties of AGS thin films determined by transmittance and reflection measurements showed that they had quite high absorption coefficient with the values around 10(4) (cm(-1)). The calculated band gap values were found to be between 2.30 and 2.75 eV depending on annealing temperature. The refractive index (n) and extinction coefficient (k) of the films were determined by the envelope method. Finally, photo-electrical measurements under different illumination intensities were carried out, and different sensitizing and recombination centers were defined. (C) 2010 Elsevier B.V. All rights reserved.