Rational Construction of Graded Heterojunction Buried Interfaces for Efficient and Stable Perovskite Solar Cells

Self-assembled monolayers (SAMs) employed as hole-transporting materials have driven significant advances in p-i-n-type perovskite solar cells (PSCs). However, inadequate SAM coverage and poor interfacial contact often result in inferior interface properties. Herein, a graded heterojunction buried interface for a perovskite film has been constructed to modify the perovskite/SAM interface via introducing an interfacial modifier of 3,6-dimethoxy-9-(4-vinylbenzyl)-9H-carbazole (MCz-V). The MCz-V molecule with carbazole-based core structures optimizes the surface properties of (2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl)phosphonic acid (MeO-2PACz)-based SAMs. Simultaneously, MCz-V molecules diffuse into the perovskite film, and a graded perovskite/MCz-V heterostructure near the perovskite buried interface is formed, thus promoting the carrier extraction process. Moreover, the in situ polymerization of MCz-V further enhances perovskite stability. Consequently, the MCz-V-modified PSCs achieve a champion power conversion efficiency (PCE) of 24.45% and a stabilized power output of 23.95%, retaining over 88% of their initial efficiency after over 2000 h of storage. This work provides an avenue for tackling buried interface issues in high-performance PSCs.