Enhanced performance of MAPbI2.85Br0.15 perovskite solar cells via ionic liquid-induced surface passivation of perovskite films

Metal halide perovskite solar cells are considered as a competitive new force for next-generation photovoltaic, whereas the interfacial defect of perovskite films severely degrades the performance and stability of the devices. Herein, we introduce the 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) ionic liquid to passivate lead-related defect on the surface of the MAPbI 2.85 Br 0.15 perovskite films. The carbonyl groups of [EMIM]Ac coordinate with the uncoordinated lead ions on the perovskite surface, and meanwhile the [EMIM]Ac ionic liquid suppresses the formation of metallic lead, which effectively reduces the nonradiative recombination and improves the working stability. As a result, the power conversion efficiency of the solar cell with [EMIM]Ac treatment is improved from 16.95 % to 19.29 %. The unencapsulated device shows good stability and retains the initial efficiency of 95 % after being exposed in ambient environment for 240 h. Therefore, this ionic liquid surface passivation proposed in this work may shed light on the development and practical application of perovskite solar cells.