Impact of Energy Level Mismatch on the Photostability of Wide Bandgap Perovskite Solar Cells

Halide segregation in wide bandgap (WBG) halide perovskites is an important bottleneck towards long operational lifetimes of perovskite-based multi-junction solar cells. To minimize this phenomenon, aside from other well-known strategies such as perovskite defect passivation, enhancing the charge carrier collection needs to be effectively addressed. Here, we will discuss the need to enhance hole and electron collection to minimize halide segregation in WBG perovskites. For this, we will elucidate systematically the impact of the valence band and the conduction band offsets and barriers formed at the hole transport layer (HTL) and electron transport layer (ETL) interfaces with the perovskite layer, its influence on halide segregation, and ultimately on WBG perovskite solar cell (PSC) photostability. In fact, we find that optimized interface energetic alignment significantly enhances the long-term photostability of the WBG PSCs under continuous AM1.5G illumination. By studying different perovskite compositions, we highlight the universality of our method. Furtherly, our results show that photostable devices can be predicted when comparing transport layer/perovskite interfaces using photoluminescence’s evolution and transient surface photovoltage spectroscopies, in correlation with halide segregation. We believe the methodology employed in this work can be used to accelerate the development of photostable WBG PSCs.