Amphoteric molecular Engineering of the Buried SnO₂/Perovskite Interface toward Efficient and Durable Solar Cells

Abstract

Interfacial optimization at the buried SnO2/perovskite junction is essential for advancing perovskite solar cells (PSCs). However, this interface commonly suffers from high defect densities, energy-level mismatch, and inefficient charge extraction, severely limiting the device efficiency and stability. Molecular passivation has emerged as a promising strategy, yet many reported ionic modifiers introduce mobile ions that increase ion-migration risk and undermine long-term stability. Here, we introduce the amphoteric small molecule dichloro(diethylamino)phosphine (DDP) to simultaneously regulate the SnO2 surface and perovskite crystallization. DDP effectively passivates oxygen vacancies in SnO2 and neutralizes undercoordinated Pb2+/I- defects at the buried interface, while promoting enlarged grains, suppressing trap-assisted recombination, and optimizing band alignment. As a result, DDP-modified PSCs delivered a champion PCE of 25.54% substantially outperforming the unmodified devices (23.63%). Remarkably, unencapsulated devices retained 78% of their initial efficiency after nearly 1300 h under ambient conditions and over 85% of their initial efficiency after 400 h of thermal aging at 70 °C in a N2 atmosphere. This work demonstrates a robust buried-interface molecular engineering strategy that substantially boosts both the efficiency and durability, offering broad implications for stable high-performance PSCs.