Unraveling the Growth of Hierarchical Quasi-2D/3D Perovskite and Carrier Dynamics.

The construction of hybrid perovskites (both two-dimensional (2D) and three-dimensional (3D)) has attracted intensive research interest recently. Here, a facile, two-step consecutive deposition method was developed for the first time to grow a hierarchical quasi-2D/3D perovskite superstructure, with an oriented quasi-2D ((BA)2(MA)n-1PbnI3n+1) perovskite nanosheet (NS) perpendicularly aligned on 3D perovskites. The superstructures are found to be mixtures of multiple perovskite phases, with n = 2, 3, 4 and 3D perovskite; however, the n value was naturally increased from top to the bottom, which is distinct from many other works. We found that the concentration gradient, namely, the initial ratio and amount of BAI/MAI, collectively contributes to the spatially confined nucleation and growth of oriented quasi-2D superstructure perovskite on 3D perovskites. An efficient charge carrier transfer was demonstrated from small-n to large-n phases in this perovskite superstructure, indicating a different type of energy funnel from top to bottom.