To investigate the process temperature on the growth of ultra-thin (<= 500 nm) Cu(In,Ga)Se-2 (CIGSe) absorbers and the corresponding performance of solar cells, the process temperature was set to 610 degrees C and 440 degrees C respectively. It was found that the low process temperature (440 degrees C) could reduce the inter-diffusion of Ga-In and thus result in a higher back [Ga]/([Ga]-[In]) ([Ga]/[III]) grading than at the temperature of 610 degrees C. The higher back [Ga]/[III] grading at 440 degrees C was evidenced to both electrically and Optically contribute to the efficiency enhancement of the solar cells in contrast to the lower back [Ga]/[III] grading at 610 degrees C It was also implied that the high back [Ga]/[III] grading was beneficial to the collection of carriers generated from the back-reflected light. (C) 2014 Elsevier B.V. All rights reserved.