Long lifetimes in high-efficiency Cu(In,Ga)Se2 solar cells

Abstract

Time-resolved photoluminescence measurements on polycrystalline Cu(In,Ga)Se2 (CIGS) thin films corresponding to high-efficiency solar cells indicate recombination lifetimes as long as 250ns, far exceeding previous measurements for this material. The lifetime decreases by two orders of magnitude when exposed to air. Charge separation effects can be observed on CIGS∕CdS∕ZnO devices in low-intensity conditions. The ZnO layer forms a robust junction critical for charge separation, whereas the CdS layer alone forms a much weaker junction. Recombination at the CIGS/CdS interface is negligible. The results significantly adjust the previous picture of recombination in CIGS solar cells.