Thin film CuIn1-xGaxSe2 solar cells have been fabricated and studied over the range 0 less than or equal to x less than or equal to 1. X-ray diffraction analysis showed that the films with x less than or equal to 0.5 have a chalcoprite structure and the films with x greater than or equal to 0.5 have a zinc blende structure. The variation of lattice parameters with composition was found to obey Vegards law. The variation in band gap with composition was determined for these films from optical absorption measurement, which showed that the band gap varied linearly over composition range. Grain size was measured using scanning electron microscopy (SEM) where the grain size measured linearly with the Ga content.