Robust self-assembled monolayer enables ultraviolet stable perovskite photovoltaics.

Self-assembled monolayers (SAMs) have boosted perovskite solar cell (PSCs) efficiencies, but their ultrathin nature causes structural vulnerability under outdoor solar illumination, particularly in the ultraviolet (UV) regime, limiting long-term operation and practical deployment of PSCs. Extensive experiments with ab initio molecular dynamics reveal conventional SAMs undergo rapid structural degradation under UV irradiation, leading to molecular desorption and film collapse. Here, we introduced a SAM featuring dual-dimensional reinforcement. Vertically, multiple anchoring sites and flexible π-conjugated framework enable strong adhesion to bidirectional adjacent layers, providing exceptional interfacial UV durability. Horizontally, intrinsically structural stability and interlocked networks further prevent the film collapse caused by high-energy UV invasion. The champion device achieved a power conversion efficiency of 27.10% (certified 26.90%). After 2100 hours of maximum power point tracking (ISOS-L-2) at 65 °C, only 2% of the efficiency was lost. Moreover, the devices retained 86.7% of initial PCE after 2200 hours under high-intensity UV light (1.73-fold the intensity of natural sunlight), and 90.5% after 2035 hours of outdoor exposure, representing the highest UV stability of SAM-based PSCs.