In recent years, inverted (p-i-n) perovskite solar cells (PSCs) employing self-assembled monolayers (SAMs) at their bottom interface have been widely investigated owing to their low-temperature processing, high fabrication reproducibility, ever-increasing power conversion efficiency (PCE) and long-term damp-heat stability.[1,2] In comparison to the functionalization of the bottom contact interface by SAMs, the top interface presents more challenging issues because solution-processed perovskite thin films tend to lost volatile species from the upward side during high-temperature annealing. These compositional variations lead to defect generation and, in turn, to non-ideal charge carrier dynamics. This, in addition to the formation of energetic barriers due to poor energy level alignment, hinder efficient electron extraction from the perovskite to the electron transport layer (ETL). Therefore, tailored interlayers at the top interface between the perovskite and the ETL, C60 or its derivatives (e.g., [6,6]-phenyl-C₆₁-butyric acid methyl ester, PCBM), are crucial for improving the performance and stability of inverted perovskite solar cells (PSCs).

Indeed, surface modification plays a pivotal role in developing state-of-the-art inverted perovskite solar cells (PSCs).[3-5] However, the functional specificity of amine-based compounds often results in selective passivation, leading to inconsistent device performance improvements. In this study, by combining the analysis of the quasi-Fermi level splitting (QFLS) [6] and surface photovoltage (SPV) by absolute photoluminescence and Kelvin probe measurements, we systematically investigate three cyclic-structured amine salts (benzene-, thiophene-, and piperazine-based) to elucidate their distinct enhancement mechanisms via defect passivation and thus suppression of non-radiative recombination. Our results reveal that the benzene and thiophene functional groups effectively passivate defects at grain interiors and boundaries owing to their conjugated structure, thereby improving the interfacial contact and reducing the defect density. Meanwhile, the piperazine-based molecules exhibit a superior hole-blocking capability, effectively repelling minority carriers back into the perovskite bulk and thus improving charge transfer kinetics. These mechanistic insights inspired the development of a bimolecular passivation strategy that simultaneously addresses surface defect mitigation and charge carrier management. By implementing this bifunctional approach combining piperazine- and thiophene- iodate, we achieved a champion device efficiency exceeding 25% (mask area: 0.152 cm²) with exceptional operational stability. The encapsulated devices maintained over 85% of their initial performance after 600 hours of continuous operation at 50°C under ambient conditions (ISOS-L-1 protocol).