Multifunctional Ionic Liquid Enabling Cation Homogenization and Lead Chelation for Pure‐Iodide Wide‐Bandgap Perovskite Solar Cells

ABSTRACT

Wide‐bandgap perovskite solar cells (WBG‐PSCs) are essential for high‐efficiency tandem photovoltaics, yet conventional mixed‐halide formulations suffer from photoinduced halide segregation. While pure‐iodide WBG‐PSCs offer a fundamental solution, their development is hindered by the distinct crystallization kinetics of A‐site cations, which lead to severe compositional inhomogeneity, coupled with lead toxicity. Herein, we report a multifunctional ionic liquid, 1‐propylsulfonate‐3‐methylimidazolium trifluoromethanesulfonate ([SO ₃ H‐PMIm][OTf]), that addresses these challenges. The additive interacts with CsI through sulfonate‐Cs ⁺ coordination bonds to increase CsI solubility, anchors methylammonium (MA) and dimethylammonium (DMA) cations via hydrogen bonding, and coordinates with undercoordinated Pb ²⁺ ions through the ─SO ₃ ⁻ . These synergistic interactions suppress colloidal aggregation in the precursor solution, while this coordination effect lowers the crystallization temperature of Cs‐based perovskites, enabling synchronous crystallization with their organic‐based counterparts. Consequently, homogeneous A‐site cation distribution across both in‐plane and out‐of‐plane dimensions is achieved. The resulting Cs _0.3 DMA _0.2 MA _0.5 PbI ₃ pure‐iodide WBG‐PSCs deliver a champion efficiency of 22.02% with an open‐circuit voltage ( V _OC ) of 1.231 V and retain 90% of initial efficiency after 3000 h under the ISOS‐D‐1 protocol. Pb ²⁺ chelation and hydrophobic ─CF ₃ mitigate lead leakage by over 58%. This strategy provides a versatile strategy for overcoming cation inhomogeneity and lead toxicity, enabling efficient, stable, and safe pure‐iodide perovskite photovoltaics.