Spatially and spectrally resolved defects in polycrystalline CdTe thin films revealed by quantitative cathodoluminescence
Bidaud Thomas1, Moseley John2, Al-Jassim Mowafak 2, Amarasinghe Mahisha 2, Metzger Wyatt K. 2, Collin Stéphane 1
1C2N/CNRS, Palaiseau, France
/2NREL, Denver, CO, United States

Increasing the grain size is a potential strategy to reduce grain-boundary recombination and improve performance of thin-film solar cells. Here, CdTe thin films with a range of grain sizes were produced by varying the CdCl2 post-deposition treatment (PDT) temperature. We use high-resolution cathodoluminescence (CL) microscopy to study recombination and shallow defect levels in detail. Intensities from room-temperature CL maps were compared across samples. We find that the CL intensity initially increases with grain size, as expected, but then plateaus as the grain size is increased further.  The plateau is correlated with decrease in the characteristic length—related to the carrier diffusion length—determined from CL intensity profiles near grain boundaries. Furthermore, low-temperature CL measurements demonstrate the evolution of the defect levels with PDT temperature.