Phase Engineering in Quasi-2D Ruddlesden-Popper Perovskites.

Quasi-2D Ruddlesden-Popper (RP) halide perovskites have drawn intensive research interest because they possess superior ambient stability while retaining excellent device performance as compared to their pure 2D or 3D counterparts. By phase engineering strategy, quasi-2D perovskites can fall into three types-large- n 2D perovskite, 2D:3D mixed perovskite, and 3D/2D bilayer perovskite. This Perspective discusses the modulation of phase composition, hierarchical distribution, and crystal orientation in quasi-2D perovskites, aiming to uncover the correlation between morphological structure, band alignment, and charge recombination. A perspective of phase engineering in 2D RP-type perovskite materials is then given toward the concurrent stability and device efficiency.