CuIn 1 - x Ga x Se 2 (0 ≤ x ≤ 0.25) films were deposited (on glass substrates at ∼ 770 K) by four source coevaporation 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 (O t ) at the grain boundaries varied from 7.2 10 9 to 1.3 10 1 1 cm - 2 . The corresponding variation in the average built electric field (F a v ) 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 Culn 1 - x Ga 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.