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

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Abstract
Time-resolved photoluminescence measurements on polycrystalline Cu ( In , Ga ) Se 2 (CIGS) thin films corresponding to high-efficiency solar cells indicate recombination lifetimes as long as 250 ns , 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 ∕ Cd S ∕ Zn O 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.