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

Abstract

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 (FAPbI3)1−x(MAPbBr3)x films via a rationally designed zwitterionic ionic liquid (ZIL) with 4‐fluoro‐phenylammonium (4FB+) as cations and tetrafluoroborate (BF4−) as anions is demonstrated. First, 4FB+ and BF4− 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 BF4− with high ionic conductivity could significantly enhance the carrier lifetime and reduce the VOC 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.