Formation Mechanism of Freestanding CH3NH3PbI3 Functional Crystals: In Situ Transformation vs Dissolution-Crystallization

To date, the formation mechanism of organolead halide CH3NH3PbI3 perovskites based on the efficient sequential reaction route has remained virtually unexplored. Such a synthetic method usually yields high-performance solar cells with an efficiency over 15%, and the identification of the crystal growth mechanism is crucial for understanding the chemical reaction process and further improving the light converting efficiency. Herein, we develop a versatile and facile approach based on sequential reaction to produce freestanding CH3NH3PbI3 crystals as a model for crystal growth mechanism studies. It was found that the in situ transformation and dissolutioncrystallization mechanisms play competing roles in determining the characteristics of products that are largely depend on the chemical reaction kinetics. Such a method can also be readily used for synthesis of freestanding CH3NH3PbI3 crystals with controllable morphological characteristics, such as cuboids, rods, wires, and plates. The synthetic strategy as well as the crystal growth mechanisms exemplified here can also serve in the design and development of more sophisticated organolead halide perovskites as well as further optimization across a range of possible domains of applications.