Currently, Nanjing South Railway Station planning to implement slate roof renovation is integrating solar cell modules into traditional roof materials to generate clean energy. Copper–indium–gallium diselenide (CuIn1−xGa x Se2, CIGS) is one of the most promising materials for thin film solar cells. Cu(In1−xGa x )Se2 films were deposited by a one-step radio frequency magnetron sputtering process at low substrate temperature. X-ray diffraction, Raman, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electrical and optical measurements were carried out to investigate the deposited films. The results reveal that a temperature of 320 °C is critical for near-stoichiometric CIGS films with uniform surface morphology. Cu-rich phase particulates are found at less than this temperature. The sample deposited at 380 °C gives well-crystalline single-phase CIGS film. Furthermore, the electrical and optical performances of the absorber layer are improved significantly with the increasing substrate temperature.