Multi-functional interface modification and/or passivation materials in inverted perovskite solar cells

The performance and stability of perovskite solar cells are significantly hampered by the inherent deficiencies at their interfaces. In inverted perovskite solar cells, issues such as mismatched energy levels at each interface obstruct efficient charge carrier transfer; the poor surface wettability of the anode and hole-transporting layer (HTL) like PTAA adversely affects the growth of perovskite crystalline films and the interface contact; ion defects on both the buried and upper surfaces of perovskites form heavy carrier recombination centers; the inherent nature of undesirable Schottky contact between organic electron-transporting layer (ETL) and metal cathode causes the large interface resistance; ion migration across the device layers accelerates device degradation. To overcome these challenges, various interface modification and/or passivation materials have been developed, some of which offer multiple functions. These functions mainly include passivating ion-related defects in the perovskite, optimizing energy-level alignment, adjusting wettability, improving interfacial contact, and protecting interfaces from degradation. This review explores these materials across four key interfaces: anode/HTL, HTL/perovskite, perovskite/ETL, and ETL/cathode. We categorize the materials based on their functional and structural characteristics, discussing their modification and/or passivation effects and mechanisms. Finally, we identify future opportunities and challenges for these materials in advancing the practical application of inverted perovskite solar cells.