Tailoring Interfacial Energetics and Defect Landscapes with Polar Molecules for High‐Efficiency and Stable Perovskite Solar Cells

ABSTRACT The rapid progress of metal halide perovskite solar cells (PSCs) is hampered by intrinsic defects that lead to efficiency losses and poor stability. Surface passivation, particularly through the formation of quasi‐2D perovskites, offers a promising avenue to mitigate these challenges. Here, we developed a polarity‐enhanced surface passivation strategy by introducing fluorine atoms onto the passivation molecules. A stronger polarity could enhance interlayer interactions, reduce trap densities, improve interface charge transfer, suppress non‐radiative recombination, and improve energy band alignment at the interface. As a result, the S‐P‐F‐MBAI passivation process yielded a device with a PCE of 25.05% (23.67% for the flexible device). Benefiting from the enhanced structural stability conferred by strong polarity and the increased hydrophobicity imparted by aromatic backbone and fluorine atom, the S‐P‐F‐MBAI‐passivated device exhibited significantly improved environmental and performance stability, keeping more than 95% and 80% of its original PCE after 1000 h under environmental conditions and MPP tracking conditions with continuous illumination, respectively. This work underscores the importance of rational molecular design, leveraging polarity and hydrophobic functionalization, for realizing high‐efficiency and stable PSCs.