Visualising and Mitigating Problematic Defects in Halide Perovskite Photovoltaic Absorbers

Halide perovskites are exciting materials showing high performance in photovoltaic devices, among other device platforms. This performance is in part due to the fact that many of the defects in halide perovskites appear to be electronically benign. However, there are still deep traps in halide perovskites that limit performance and need addressing.<br/><br/>Here, I will outline work where we have characterised deep trap states in halide perovskite absorber materials. We find that there are small nanoscale clusters of impurity phases including hexagonal polytypes that have high defect densities leading to deep trap states. Furthermore, these defective sites are where photo-instability pathways are seeded, realising a fundamental link between carrier traps and device stability. I will outline how managing these particularly problematic defects – through passivation and material composition control – will be key to further pushing device performance and stability.