Molecular tailoring of 2PACz SAMs via substituent design enables efficient inverted p–i–n perovskite solar cells†

Perovskite solar cells (PSCs) have gained considerable attention due to their promising optoelectronic properties. This study systematically investigates the critical role of substituent engineering in self-assembled monolayers (SAMs) for optimizing interfacial charge dynamics in inverted p–i–n structured PSCs. We designed and synthesized [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and its derivatives (X-2PACz, X = NO₂, Br, MeO, and MeS) by introducing electron-donating and electron-withdrawing substituents on the carbazole unit. These molecular modifications tune the energy levels of the SAMs, facilitating optimized energy alignment between the NiOx hole transport layer and the MAPbI₃ perovskite, thereby influencing charge extraction performance. Among them, MeO-2PACz exhibited the most favorable energy level alignment, enabling a maximum power conversion efficiency (PCE) of 21.67% with significantly enhanced operational stability in PSCs (a T₈₀ lifetime of 17 hours under continuous UV illumination). This study highlights the potential of carbazole-based phosphonic acid SAMs as efficient interfacial modifiers and provides strategic insights into the molecular engineering of SAMs for high-performance PSCs.