Recombination kinetics and stability in polycrystalline Cu(In,Ga)Se2 solar cells

Time-resolved photoluminescence (TRPL) measurements indicate that bare Cu(In,Ga)Se2 (CIGS) films degrade when they are exposed to air or stored in nitrogen-purged dry boxes. The degradation significantly affects device performance and electro-optical measurements. Measuring films prior to degradation reveals long lifetimes and distinct recombination properties. For high-quality material, the surface recombination velocity at grain boundaries, bare CIGS surfaces, and CIGS/CdS interfaces is less than 103 cm/s, and lifetime values are often greater than 50 ns. In high injection, CIGS has recombination properties similar to GaAs. On completed devices, charge-separation dynamics can be characterized.