Cu(In, Ga)Se-2 (CIGS) thin films with thickness of 1 mu m and 2 mu m are prepared by co-evaporation process, and the different Ga/(Ga + In) are achieved by varying the temperature of Ga source. The morphology, structure, minimum band gap, and performance of solar cells are comparatively studied. As Ga/(Ga + In) increases, little changes can be observed in the crystal quality of 1 mu m CIGS films, while the grain size of 2 mu m films decreases significantly. (112) diffraction peak intensities of the 1 mu m and 2 mu m films decrease and increase, respectively. In the case of the same Ga/(Ga + In), the minimum band gap values of 1 mu m films are larger than that of 2 mu m films, and the difference becomes large with Ga/(Ga + In) increasing. The minimum band gap values of 1 mu m films are more sensitive to variation of the Ga/(Ga + In). As Ga/(Ga + In) increases, a more improvement of the efficiency of solar cells with thickness of 1 mu m is obtained due to the large enhancement of the open-circuit voltage, and the efficiency reaches the maximum value when Ga/(Ga + In) is about 0.37. (C) 2015 Elsevier B.V. All rights reserved.