Carrier-Transport Imaging of Cadmium Telluride Intra- and Inter-Grains

Inhomogeneous local minority-carrier transport in thin-film solar cells is a critical aspect for the device operation. In this work, we applied a transport imaging (TI) technique to the intra- and inter-grain carrier-transport properties of cadmium telluride (CdTe) solar cell materials. We compared the TI results with cathodoluminescence and electron backscatter diffraction (EBSD) on the same CdTe thin film. The diffusion lengths of two distinct grain interiors were measured directly, and the values are significantly different. Three types of grain boundaries (GBs) determined by EBSD were studied by TI, and they have different decays, suggesting that different GB structure can be responsible for carrier-transport properties. Further, we did a 2D analytical simulation of carrier diffusion across GBs with varying GB lifetimes. The results suggest that GB lifetimes affect the carrier transport. Comparison of multiple technique results, together with numerical simulation, provides a deeper understanding of carrier-transport properties.