Effect of crystal structures on the stability of CH3NH3PbI3 under humidity environment

The efficiency of organic-inorganic hybrid perovskite (CH3NH3PbI3, MAPbI3) solar cells has been dramatically increased from 3.8% to 20.1% in the past five years, which is close to its theoretical limit. Nevertheless, the stability of perovskite solar cells remains a major hurdle for its commercialization. Here, we investigated the morphology and structure of MAPbI3 films with different preparation conditions, and reported the existence of orthorhombic structure in tetragonal MAPbI3 cuboids at room temperature. More interestingly, a special orthorhombic-to-tetragonal phase transition could lead to intensity oscillations in the time evolution of photoluminescence (PL), and increased the films stability in a high humidity (∼50%) environment. Furthermore, we used the films to prepare photovoltaic devices with a half-life over 200 h, and showed the potential of the phase transition to improve the lifetime and practical application for perovskite solar cells.