Coordination Nanosheets‐Mediated Crystallization and Light Management for Efficient and Operationally Durable Methylammonium/Bromide‐Free Perovskite Solar Cells

ABSTRACT Methylammonium/bromide‐free perovskite solar cells (PSCs) with mixed A‐site cations of varying ionic radii often suffer from uncontrolled crystallization and a restricted spectral response, limiting further improvements in both power conversion efficiency (PCE) and stability. Herein, π‐conjugated terpyridine‐zinc(II) (ZnTPY) coordination nanosheets (CONASHs) are introduced as multifunctional additives for heterogeneous nucleation and down‐conversion, offering a versatile platform that simultaneously promotes the crystal quality of triple‐cation formamidinium/cesium/rubidium lead iodide perovskites and improves short‐wavelength photon utilization. Synthesized via bottom‐up liquid‐liquid interfacial coordination, ZnTPY CONASHs can be ultrasonically fragmented into pieces enriched with unsaturated terpyridine moieties, which form multidentate chelates with PbI 2 to generate ZnTPY‐[PbI 6‐x ] 4− octahedral heteronuclei. These adducts promote low‐barrier heterogeneous nucleation in perovskites, which synergistically suppresses defect densities and prolongs photocarrier lifetimes, thereby enhancing both crystallinity and environmental stability. In parallel, the intramolecular charge‐transfer absorption and subsequent visible emission of CONASHs facilitate down‐conversion, which augments the external quantum efficiency in the 300–590 nm range and optimizes ultraviolet light harvesting in the ZnTPY‐modified perovskites. Consequently, the PSCs with ZnTPY additive achieve a champion PCE of 22.50%, compared to 20.94% for the control, along with improved outdoor stability. These findings highlight the substantial practical potential of the CONASH‐induced strategy for future PSC applications.