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

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Original abstract

ABSTRACT 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.

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