A Lewis Base‐Assisted Passivation Strategy Towards Highly Efficient and Stable Perovskite Solar Cells

Organo‐metal halide hybrid perovskites with mixed cations and halides have become promising photovoltaic materials, showing extraordinary optoelectronic properties and excellent device performance. Herein, an organic semiconducting nonfullerene acceptor (NFA) molecule IT‐M is introduced as Lewis base to improve perovskite interfaces. This facile Lewis base‐assisted strategy effectively enhances the electronic properties of Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 thin films, passivates the perovskite surface defects and further boosts the performance of perovskite solar cells. With the reduced surface defects, this approach significantly enhances the charge transport properties and boosts the photogenerated photoluminescence lifetime from 1.46 to 2.20 µs. As a result, the n‐i‐p planar perovskite solar cell champion efficiency reaches 20.5% with a high FF of 81%. Moreover, the Lewis base molecule IT‐M can also passivate the under‐coordinated lead ions and enhance the durability of perovskite PbI 6 octahedra framework under an ambient environment with thermal stress and humidity. The results provide a simple while highly effective route of fabricating the high performance and stable planar perovskite solar cells.