Cathodoluminescence study of carrier transport across grain boundaries in CdTe

It is widely reported that polycrystalline CdTe thin films yield higher conversion efficiency than their single crystal counterparts. However, the mechanism that increases the efficiency is not well understood despite a large body of work on the subject. In particular, understanding how grain boundaries affect carrier transport is crucial to providing future pathways for engineering higher efficiency devices. In this work, we adapted a method for observing carrier transport based on cathodoluminescence that had previously been used to determine diffusion lengths in pc-CdTe films and various III-V alloys to study individual grain boundaries. Utilizing large-grained CdTe (tens of μm grain size) and site-specific specimen preparation, we observed how charge carriers interact with grain boundaries in CdTe. Our results suggest that carrier transport across grain boundaries in CdTe is influenced by the concentration of defect states in the material.