Synchronous modulation of hole-selective self-assembled monolayer and buried interface for inverted perovskite solar cells

Modulating the hole transport layer (HTL) and its interface with perovskite is crucial to lower the interfacial losses and thereby achieve highly efficient inverted perovskite solar cells (PSCs). Here, we develop a mixed strategy for a self-assembled monolayer (SAM)-based HTL, where 2-mercaptoimidazole and 2-mercaptobenzimidazole are introduced as additives into [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz). It is revealed that the cluster formation during SAM adsorption leads to incomplete substrate coverage. However, these additives can effectively suppress the SAM aggregation by forming complexation with MeO-2PACz, affording homogeneous HTLs. The mixed HTLs exhibit better-matched energy bands with perovskite and improve the interface contact, resulting in denser and larger grains of the bottom perovskite. Moreover, some additives and MeO-2PACz molecules in HTL can enter the bottom of perovskite films to passivate interface defects. All of these positive results promote interfacial charge transfer and inhibit charge recombination, helping PSCs achieve a high power conversion efficiency of 24.38% with enhanced stability.