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

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 N₂, and large-area modules (28.79 cm²) 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.