Thiocyanate Ionic Liquids for High‐Performance Ultra‐Wide‐Bandgap Perovskite Solar Cells

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Ultra‐wide‐bandgap (UWBG) perovskite solar cells are critical for constructing high‐efficiency multi‐junction tandem devices, yet their performance is constrained by severe nonradiative recombination and disorder in phase growth arising from high bromine content. Here, we report a rational anion‐cation pairing strategy using thiocyanate‐based ionic liquids to simultaneously modulate crystallization kinetics and passivate multidimensional defects in 1.93 eV UWBG perovskites. By co‐introducing formamidinium thiocyanate (FASCN) and 1‐ethyl‐3‐methylimidazolium thiocyanate (EImSCN), we achieve synergistic effects: the pseudohalide SCN − fills halide vacancies and suppresses ion migration, FA + compensates for volatile loss during annealing, and EIm + coordinates with the Pb‐I framework while hydrogen‐bonding with FA + . This integrated approach prolongs the crystal growth window, enlarges grain size, releases residual tensile strain, and reduces trap density. The resulting inverted devices deliver a champion power conversion efficiency of 16.76% with an open‐circuit voltage of 1.41 V and an exceptional fill factor of 83.37%. Moreover, unencapsulated devices retain 95% of their initial efficiency after 1500 h storage in N 2 , and large‐area modules (28.79 cm 2 ) achieve 13.80% efficiency, demonstrating scalability. This work provides a molecular‐level design route to high‐quality UWBG perovskite for commercial perovskite‐based tandem photovoltaics.