Amphoteric Anion‐Mediated Crystallization and Universal Defect Passivation for High‐Efficiency and Stable Perovskite Solar Cells

Ionic liquids (ILs) have emerged as attractive bulk modifiers for perovskite absorbers in realizing long‐term operational stability; however, most IL anions are chemically “one‐sided”, typically neutralizing only cationic or anionic vacancies. Our study introduces a novel strategy using ILs with amphoteric anions—specifically tetramethylguanidine hydrogen sulfate (GUHS) and tetramethylguanidine dihydrogen phosphate (GUDHP)—to act as “universal passivators”. The amphoteric nature of HSO 4 − and H 2 PO 4 − anions passivate both Lewis acidic and Lewis basic defects via localized electron‐rich oxygen sites and electron‐deficient regions, while the guanidine cation anchor FA + /MA + cations through multiple N─H⋯N bonds, resulting in a high‐quality perovskite film with suppressed defect densities, enhanced crystallization, and relieved residual strain. The passivation effect is more pronounced in GUDHP than in GUHS due to the higher basicity of H 2 PO 4 − ‐derived PO 4 framework and presence of multiple P─OH functionalities. Consequently, the GUDHP‐modified PSCs achieve a PCE of 26.13% with an FF exceeding 85% for normal bandgap (1.56 eV) cells, and a remarkable 20.06% PCE with an impressive 85.74% FF for wide bandgap (1.84 eV) devices. In addition, the GUDHP‐modified devices maintained 93.6% of their initial PCE after 1000 h of continuous operation under the ISOS‐L‐1 protocol.