Dual Functional Molecular Engineering Utilizes Synergistic Effects to Enhance Hole Transport in Inverted Perovskite Solar Cells

ABSTRACT Energy losses and interfacial defects at the buried interface of perovskite thin films represent significant impediments to achieving high‐performance devices. These issues are typically attributed to nonuniform, poorly hole‐transporting self‐assembled monolayers (SAMs). Addressing these challenges is crucial for advancing perovskite solar cell (PSC) technology. In this work, we designed a novel molecule based on dimethyl‐substituted spirofluorene, in which the inherent three‐dimensional rigid structure of the spirofluorene skeleton provides large steric hindrance to the molecule, promoting the dense and ordered arrangement of SAMs on the substrate surface. The introduction of methyl groups on both sides amplifies the steric hindrance effect, further improving the uniformity of the film. Meanwhile, methyl groups open up high‐speed channels for charge carriers through C─H···π interactions. The synergistic effect of the two significantly reduces the density of interface defect states while maintaining excellent charge transport performance, providing a new approach for optimizing the buried interface. Consequently, we report a laboratory‐measured power conversion efficiency (PCE) of 26.62%. Furthermore, the devices exhibit excellent operational stability, retaining approximately 90% of their initial PCE after 1000 h of light soaking under maximum power point (MPP) tracking in nitrogen atmosphere.