Culn 1 − xGa xSe 2 (0 ≤ x ≤ 0.25) films were deposited (on glass substrates at ~ 770 K) by four source co-evaporation technique. The thickness and average grain size of the films varied within 3–3.5 μm and 0.2–0.5 μm, respectively, with small variation of surface roughness (18–24 nm). The films were characterized by measuring the microstructural, optical and mechanical properties. A new optical technique was used to estimate the strain/stress in the polycrystalline films from the broadening of the optical absorption band tail. Addition of Ga increased the stress from 1.37 × 10 8 to 2.78 × 10 8 dynes/cm 2 while the density of trap states (Q t) at the grain boundaries varied from 7.2 × 10 9 to 1.3 × 10 11 cm −2. The corresponding variation in the average built electric field (F av) at the grain-surfaces of the polycrystalline films was estimated to be 0.15 − 2.95 × 10 4 V/cm. Surface photovoltage (SPV) measurements of CuIn 1 − xGa x Se 2/CdS devices indicated minority carrier diffusion lengths (L n) to be ~ 1 μm and 0.7 μm, respectively, for x = 0 and x = 0.25.