Multi-Level Passivation of MAPbI3 Perovskite for Efficient and Stable Photovoltaics

The photovoltaic performance and long-term stability of perovskite solar cells (PSCs) are greatly affected by trap states. Herein, a functional ionic liquid of 1-ethyl-3-methylimidazolium trifluoroacetate (EMIMTFA) is introduced, in which the 1-ethyl-3-methylimidazolium cations (EMIM + ) can interact with PbI 2 to form a stable one-dimensional (1D) perovskite of EMIMPbI 3 , and the trifluoroacetic acid anions (TFA − ) can passivate the interface between the electron transfer layer and the perovskite layer. Unlike, the widely studied low dimensional perovskite capping layers or quasi-2D configuration, the EMIM + cations not only distribute on the top surface and inside the bulk phase, but also accumulate at the buried interface of 3D perovskite film, achieving a multi-level distribution. The different defect states are successfully passivated by this distribution mode, leading to a significant decrease of non-radiative recombination. As a result, the methyammonium lead iodide-based PSCs with the EMIMTFA additive show an enhanced photovoltaic performance with a champion power conversion efficiency up to 22.14% and improved long-term stability. This work demonstrates that the formation of multilevel low-dimensional structure is a new strategy for the preparation of efficient and stable PSCs.