Side‐Group‐Mediated Small Molecular Interlayer to Achieve Superior Passivation Strength and Enhanced Carrier Dynamics for Efficient and Stable Perovskite Solar Cells

Abstract Considering the high surface defects of polycrystalline perovskite, chemical passivation is effective in reducing defects‐associated carrier losses. However, challenges remain in promoting passivation effects without compromising the carrier‐extraction yield at the perovskite interfaces. In this work, interlayer molecules functionalized with different side groups are rationally designed to investigate the correlation between defect‐passivation strength and interfacial carrier dynamics. It is revealed that Cl‐grafted molecules impose destructive effects on the perovskite structure due to its lower electronegativity and mismatched spatial configuration. The introduction of cyanide (CN) as a side group in molecules also leads to perovskite deformation and unfavorable hole collection. After the molecular optimization, the incorporation of carbonyl (C═O) as the side group (TPA─O) simultaneously promotes the carrier‐collection yield as well as sufficient defect passivation. As a consequence, the devices based on TPA─O yield a champion PCE of 23.25%, along with remarkable stability by remaining above 88.5% of initial performance after 2544 h storage in the air. Furthermore, this interlayer based on TAP─O enables flexible devices to achieve a high efficiency of 21.81% and promising mechanical stability. This work paves the way for further improving the performance of perovskite solar cells.