Schottky/p-n Cascade Heterojunction Constructed by Intentional n-Type Doping Perovskite Toward Efficient Electron Layer-Free Perovskite Solar Cells

Electron transport layer (ETL)-free perovskite solar cells (PSCs) are getting much more attention with their simpler structure and potentially low cost as well as higher stability. However, the elimination of ETL (such as TiO2) with intrinsically deep valance band level leads to the absence of the hole blocking mechanism and thus serious charge recombination at the FTO/perovskite interface compared with ETL-based devices. An interface band bending associated built-in electric field is an essential driving force of charge separation. Here, by intentional polarity tailoring of perovskite via incorporation of Sb as a shallow donor, ETL-free PSCs with optimized energy level alignment both at the front and rear interfaces are constructed, resulting in an enhanced built-in electric field and thus efficient majority carrier collection and minority blocking as well as reduced interfacial charge recombination at both interfaces. Device simulation calculations also confirm the importance of polarity control for device performance improvement. The effect of doping on the perovskite films properties and device performance are systematically demonstrated. Correspondingly, ETL-free PSCs with a champion power conversion efficiency of 12.62% is achieved.