A Multifunctional Coumarin‐Based Additive for Defect Passivation in Perovskite Solar Cells

Perovskite solar cells (PSCs) have become a promising next‐generation photovoltaic technology, owing to their excellent optoelectronic properties. However, solution‐processed perovskite films inevitably generate numerous intrinsic defects that cause nonradiative recombination, thus reducing device efficiency and stability. Therefore, selecting multifunctional, low‐cost, and low‐toxic additives is crucial to improve perovskite film quality. Herein, a coumarin‐based multifunctional additive, 7‐(diethylamino)coumarin‐3‐carboxylic acid (7‐DCCA), was incorporated into the perovskite precursor to optimize device performance. The introduction of 7‐DCCA effectively reduced the defect density, improved film crystallinity and surface morphology, and optimized the energy level alignment. Consequently, the champion device incorporated with 7‐DCCA achieved a power conversion efficiency (PCE) of 23.75%, outperforming the control device (21.84%). Notably, the 7‐DCCA‐treated device still maintained 87% of its initial efficiency after 480 h at 30%–40% relative humidity (RH). This study provides a simple and effective defect passivation strategy for high‐performance PSCs.