Tautomeric Molecule Acts as a "Sunscreen" for Metal Halide Perovskite Solar Cells.

UV light always does great harm to perovskite solar cells, relentlessly degrading perovskites and shortening the lifetime of perovskite devices. Meanwhile, surface defects in perovskite films further accelerate the degradation process and serve as nonradiative charge recombination centers to deteriorate device efficiency. Herein, we demonstrate that a "sunscreen" molecule, 2‐hydroxy‐4‐methoxybenzophenone, not only protects the perovskite solar cell from UV degradation but also enables molecular defect passivation through interaction between functional groups and defects by molecular tautomerism under UV light illumination. Therefore, the sunscreen strategy efficiently enhances the UV endurance of PSCs and improves defect formation energy to −1.35 eV. The perovskite solar cell with sunscreen (sunscreen PSC) exhibits outstanding efficiencies of up to 23.09 % (0.04 cm2) and 19.73 % (1.00 cm2) as well as long‐term UV (UVa: 365 nm and UVb: 285 nm) stability. [ABSTRACT FROM AUTHOR]