Two-dimensional/three-dimensional (2D/3D) hierarchical structure has attracted extensively attention in recent years due to their stability and the enhanced open-circuit voltage of perovskite solar cells. However, the solution processed thin 2D perovskite layers on the surface of 3D perovskites would lead to undesirable intermixing between the two phases, impeded carrier transport. Here, we present a novel approach for fabricating 2D perovskite on 3D perovskite using vapor-assisted solution deposition. Unlike what is normally observed in solution-processed 3D/2D systems, a flat interface formed in the 2D/3D bilayer heterostructure. The vapor-deposited 2D perovskite capping layer promotes efficient electron and hole separation processes and significantly restrain non-radiative charge recombination. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells.