Homogenized Self‐Assembled Molecules for Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) have rapidly improved, driven by advancements in self‐assembled molecules (SAMs). However, achieving homogeneous SAM coverage on substrates remains challenging, directly impacting device performance and stability. Here, we present (4‐(pyren‐1‐yl)phenyl)phosphonic acid (PhPAPy), a SAM with a rigid aromatic ring structure. Ab initio molecular dynamics (AIMD) simulations reveal that this rigidity limits rotational freedom, promoting a near‐vertical molecular orientation on the substrate. Additionally, π‐π interactions between the planar pyrene rings enhance molecular packing, forming a homogeneous and dense SAM layer. As a result, the uniform PhPAPy effectively minimizes perovskite‐substrate direct contact, enhance the interfacial properties, reduces buried interface defects, and improves both efficiency and stability. With PhPAPy SAM, the assembled inverted PSCs achieve a certified reverse‐scanning power conversion efficiency (PCE) of 26.74% and a certified stabilized power output (SPO) efficiency of 26.12% (from National Institute of Metrology in China). These devices retain 95% of their initial efficiency after 2,000 hours of maximum power point tracking (MPPT) under continuous AM 1.5G illumination at 65 °C and ambient humidity (ISOS‐L‐2).