Zwitterionic Ionic Liquid Confer Defect Tolerance, High Conductivity, and Hydrophobicity toward Efficient Perovskite Solar Cells Exceeding 22% Efficiency

Defect passivation has been a promising route for enhancing the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, defect inhibition in two-step solution-processed (FAPbI 3 ) 1− x (MAPbBr 3 ) x films via a rationally designed zwitterionic ionic liquid (ZIL) with 4-fluoro-phenylammonium (4FB + ) as cations and tetrafluoroborate (BF 4 − ) as anions is demonstrated. First, 4FB + and BF 4 − can effectively fill vacancy defects caused by the migrated organic A-site cation and halogen anion, confirmed by X-ray photoelectron spectroscopy. Second, the 4FB + with π conjugated benzene ring can donate electrons for carrier extraction, whereas its fluorination of the phenyl ammonium could enhance moisture blocking through the molecular packing of C  F bond. The electrical characterization, including space charge limited current and Mott–Schottky measurement, proves the enhanced carrier extraction and photovoltaic performance. Third, the pseudohalogen anion BF 4 − with high ionic conductivity could significantly enhance the carrier lifetime and reduce the V OC loss. As a result, the ZIL-modified PSCs can achieve a high PCE of 22.5% with excellent long-term stability maintaining more than 80% of the initial efficiency after storing in an ambient condition for 2000 h. Herein, a new paradigm toward accelerating the development of efficient and stable PSCs is opened up.