Methylammonium lead triiodide (MAPbI3)-based perovskite solar cells potentially have potential advantages such as high efficiency and low-cost manufacturing procedures. However, MAPbI3 is structurally unstable and has low phase-change temperatures (30°C and 130°C); it is necessary to solve these problems. We investigated the crystal structure and phase separation using real-time temperature-change X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. MAPbI3 has a tetragonal structure, and at about 35°C the c-axis contracts, transforming MAPbI3 into the related cubic crystal structure. In addition, at 130°C, phase separation occurs in which CH3NH2 and HI at the center of the unit cell of the perovskite structure are extracted by gas, leavingand only PbI2 of the three-component structure, is produced as the final solid product.
