Phase Distribution in Quasi‐2D Dion Jacobson Perovskite Dictates Ultrafast Energy Transfer and Directional Charge Transport

Abstract The efficient and rapid charge transfer at the interface of heterostructures plays a crucial role in optoelectronic applications. Quasi‐2D perovskites accompanying randomly dispersed various layer thickness (n) phases can introduce multiple interfaces with specific potential barriers, obstructing the charge transport and energy transfer processes. Herein, the strategic spatial distribution of various n phases and enhanced energy transfer, accompanied by the narrow‐band emission in the high n phases, is achieved. The additive, i.e., Cesium Iodide (CsI), is found to alter the phase distribution across the films. The pronounced radiative emissions from low n phases are observed at low temperatures despite their absence at room temperature. The phenomenon of ultrafast energy transfer in consecutive phases has been observed in quasi‐2D perovskite thin films using transient absorption spectroscopy. The photocurrent reduction in quasi‐2D perovskite thin films has verified anisotropic charge transport. The local surface potential reduction on illumination corroborates the spatial phase distribution and promotes directional charge transport. The results provide important implications for the effects of phase distribution in lateral and vertical directions on the performance of 2D perovskite optoelectronic devices.