MAAc Ionic Liquid-Assisted Defect Passivation for Efficient and Stable CsPbIBr2 Perovskite Solar Cells

Cesium-based all-inorganic perovskite solar cells (PSCs), such as CsPbIBr2 PSCs, have attracted wide attention for good thermal and wet stability, but the low open-circuit voltage (V-oc) mainly caused by the inadequate coverage of CsPbIBr2 films is the main reason for limiting their development. The CsPbIBr2 films grown on TiO2 substrate directly have a large number of pinholes, which bring a lot of defects and lead to an increase of nonradiative recombination. In this work, a strategy extended for CsPbIBr2 films by precoating methylammonium acetate (MAAc) ionic liquid onto a TiO2 layer before depositing the CsPbIBr2 film is demonstrated. The uniformly distributed MA(+) will be the nucleation center at the bottom of the CsPbIBr2 film, which exhibited a notable impact on the crystallization kinetics of CsPbIBr2 films. This effect simultaneously enhanced the crystal quality of the CsPbIBr2 film and interfacial contact between the electron transporting layer (ETL) and CsPbIBr2 layer. It is instrumental in decreasing the trap state density, suppressing nonradiative recombination, and extracting the charge carriers. Therefore, the stability of the optimized device has been improved considerably, and the champion power conversion efficiency (PCE) is up to 8.85% with a high V-oc of 1.26 V. Benefiting from passivation, the PSC with 2 M MAAc IL interfacial modification remains 82% of its initial PCE after 30 days of exposing the device to ambient air at room temperature.