CIGS thin film solar cells on polyimide foils

The influence of Ga content and substrate temperature on the device performance of CIGS thin film solar cells fabricated on polyimide foils has been investigated. It was found that the precise control of substrate temperature and Ga content in CIGS are important issues to achieve high-efficiency CIGS devices since these strongly affect the formation of double-graded bandgap structure. A desirable double-grading of Ga/(In+Ga) atomic ratio was formed with Ga/(In+Ga) = 0.27 at a substrate temperature of 480°C. By optimizing fabrication conditions a best flexible CIGS solar cell yielded a total-area efficiency of 15.7% with V_OC=0.605 V, J_sc=35.1 mA/cm², and FF=0.741.