Balancing transformation and dissolution–crystallization for pure phase CH3NH3PbI3 growth and its effect on photovoltaic performance in planar-structure perovskite solar cells

Abstract In situ transformation and dissolution–crystallization mechanisms play a competing role in determining the characteristics of perovskite films that greatly affect the device performance of perovskite solar cells in the sequential two-step process. Herein, we develop a facile solution engineering to balance the transformation from PbI 2 to CH 3 NH 3 PbI 3 and dissolution–crystallization of CH 3 NH 3 PbI 3 crystal growth, producing pure phase CH 3 NH 3 PbI 3 crystals for high-efficient planar-structure solar cells. Low concentration of CH 3 NH 3 I in a mixed solvent of isopropanol/cyclohexane with low polarity is applied to suppress dissolution–crystallization (Ostwald ripening growth) of perovskite, while increases the transformation time from PbI 2 to CH 3 NH 3 PbI 3 . Combination of porous PbI 2 and temperature-assistance effectively promote the transformation from PbI 2 to CH 3 NH 3 PbI 3 and reduce the time of Ostwald ripening growth of perovskite. This solution engineering reconciles the complete PbI 2 transformation and dissolution–crystallization of CH 3 NH 3 PbI 3 , resulting in a pure phase perovskite without any residual PbI 2 in a short time. This strategy exemplified here can serve in the design and development of more sophisticated perovskites based on planar-structure applications without mesoporous TiO 2 scaffold.