Separating Grain-Boundary And Bulk Recombination With Time-Resolved Photoluminescence Microscopy

Two-photon excitation (2PE) microscopy allows contactless and non-destructive cross-sectional analysis of grain-boundary (GB) and grain-interior (GI) properties in polycrystalline solar cells, with measurements of doping uniformity, space-charge field distribution, and carrier dynamics in different regions of the device. Using 2PE time-resolved microscopy, we analyzed charge-carrier lifetimes near the GBs and in the GI of polycrystalline thin-film CdTe solar cells doped with As. When the grain radius is larger than the minority-carrier diffusion length, GI lifetimes are interpreted as the bulk lifetimes tau(B), and GB recombination velocity S-GB is extracted by comparing recombination rates in the GI and near GBs. In As-doped CdTe solar cells, we find tau(B) = 1.0-2.4 ns and S-GB = (1-4) x 10(5) cm/s. The results imply the potential to improve solar cell voltage via GB passivation and reduced recombination center concentration in the GI. Published by AIP Publishing.