Defect Passivation in Perovskite Solar Cells: From Trap Suppression to Stable Interfaces

Conspectus Halide perovskites combine strong light absorption and long carrier-diffusion lengths with an unusual tolerance to defects, which is commonly attributed to the predominantly shallow electronic states associated with many intrinsic defects. Nevertheless, defects at surfaces, grain boundaries, and buried interfaces continue to limit the efficiency and operational durability of perovskite solar cells. These defects can be electronically active, ionically charged, chemically reactive, and mobile under illumination, heat, and electrical bias. Passivation in perovskites therefore cannot be understood solely as the termination of dangling bonds. It must simultaneously address defect chemistry, local charge balance, interfacial energetics, carrier selectivity, and the persistence of these functions during device operation. In this Account, we trace the development of defect-passivation concepts through our group’s research and organize them into five principal mechanisms. First, Lewis acid–base interactions reduce trap activity through complementary chemical interactions: Lewis bases coordinate with electron-deficient, undercoordinated Pb2+ sites, whereas Lewis acids interact with electron-rich halide-related defects. Our early studies of fullerene and nonfullerene acceptors further demonstrated that chemical passivation can be coupled with selective electron extraction to suppress interfacial recombination and hysteresis. Second, ionic charge compensation uses complementary cationic and anionic species to neutralize defects of opposite polarity. Third, band-bending passivation, conceptually analogous to field-effect passivation in silicon heterojunction solar cells, uses interfacial doping, molecular dipoles, or nonuniform ion distributions to separate carriers from residual defects. Fourth, surface-phase conversion reconstructs a defective three-dimensional perovskite surface into a low-dimensional perovskite, lead oxysalt, or another robust wide-bandgap phase that provides both electronic passivation and chemical protection. Fifth, the charge recombination lifetime is extended by increasing surface strain which pushes deep traps into shallow ones. We further discuss how passivation can be extended from initial trap suppression to long-term stability enhancement. Bilateral molecular anchoring can improve the retention of passivators at surfaces and grain boundaries, whereas strongly bound buried interlayers can preserve energy alignment and carrier selectivity while suppressing detrimental interfacial reactions. Conversely, initially beneficial passivators may become degradation sources if they desorb, redistribute, deprotonate, react with the perovskite, or lose their electronic function during operation. These examples illustrate why improvements in fresh-device photoluminescence, open-circuit voltage, or power-conversion efficiency do not necessarily translate into durable device performance. Future passivators should therefore be evaluated according to whether their chemical, electrostatic, structural, and interfacial functions persist under simultaneous illumination, heat, electrical bias, ultraviolet exposure, and humidity. They must also remain compatible with scalable deposition and preserve their effects across large-area films and modules. We argue that the next stage of passivator development should prioritize persistent multifunctional interfaces and rigorous operational testing rather than further expand empirical libraries of additives that improve only initial performance.