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

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 PbI2 to generate ZnTPY-[PbI6-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.