Surface passivation engineering strategy to fully-inorganic cubic CsPbI₃ perovskites for high-performance solar cells

Owing to inevitable thermal/moisture instability for organic-inorganic hybrid perovskites, pure inorganic perovskite cesium lead halides with both inherent stability and prominent photovoltaic performance have become research hotspots as a promising candidate for commercial perovskite solar cells. However, it is still a serious challenge to synthesize desired cubic cesium lead iodides (CsPbI₃) with superior photovoltaic performance for its thermodynamically metastable characteristics. Herein, polymer poly-vinylpyrrolidone (PVP)-induced surface passivation engineering is reported to synthesize extra-long-term stable cubic CsPbI₃. It is revealed that acylamino groups of PVP induce electron cloud density enhancement on the surface of CsPbI₃, thus lowering surface energy, conducive to stabilize cubic CsPbI₃ even in micrometer scale. The cubic-CsPbI₃ PSCs exhibit extra-long carrier diffusion length (over 1.5 μm), highest power conversion efficiency of 10.74% and excellent thermal/moisture stability. This result provides important progress towards understanding of phase stability in realization of large-scale preparations of efficient and stable inorganic PSCs.