Dual‐Interface Management Modulated by Functional Cationic Ligands Enables Robust and Efficient Perovskite Photovoltaics

Despite the effectiveness of surface passivation, simultaneous optimization of buried interface and top surface in perovskite solar cells (PSCs) remains challenging due to incompatible additive functions and uncontrolled crystallization kinetics. Here, we present a dual‐interface regulation strategy that deploys phenyltrimethylammonium chloride (THPA) treatment on the top surface and 5‐amino‐1‐pentanol (5‐APT) treatment at the buried interface of the perovskite film. This approach achieves multiple collaborative regulation effects of dual interfaces: (i) THPA reduces trap density at the top surface of perovskites and promotes n‐type character. (ii) 5‐APT forms hydrogen and ionic bonds with the substrate, enhancing bottom crystallinity via cation exchange with FA + /Cs + and facilitating hole extraction. Besides, in‐situ photoluminescence reveals that 5‐APT retards the crystallization process, promoting grain merging and yielding uniformly sized grains. As a result, the optimized PSCs achieve a power conversion efficiency of 26.24% with excellent stability. This straightforward strategy transcends conventional spacer cation engineering, bridging the efficiency‐stability divide and providing a generalizable paradigm for interface passivation in perovskite optoelectronics.