Manipulating Interlayer Carrier Relaxation Dynamics in Type‐II Heterostructures of 2D Hybrid Perovskites Through Organic Spacer Engineering

Abstract Type‐II heterostructures are crucial components in optoelectronic devices such as photovoltaics and photodetectors. Previous studies have shown that interlayer charge transfer (CT) is the dominant carrier relaxation mechanism in type‐II heterostructures of 2D materials. In this study, it is demonstrated that in type‐II heterostructures composed of 2D organic–inorganic hybrid perovskites (OIHPs), the conventional CT process can transition to an energy transfer (ET) process without requiring an additional charge‐blocking interlayer. The results indicate that CT predominates in heterostructures in which both layers have the same organic spacer, particularly in BA 2 PbI 4 /BA 2 MA 2 Pb 3 I 10 . Notably, when the organic spacer BA is replaced with PEA in one layer of the heterostructure, that is BA 2 PbI 4 /PEA 2 MA 2 Pb 3 I 10 , the carrier relaxation process shifts from CT to ET. Although both BA 2 PbI 4 /BA 2 MA 2 Pb 3 I 10 and BA 2 PbI 4 /PEA 2 MA 2 Pb 3 I 10 exhibit type‐II band alignment, density functional theory calculations reveal that the substitution of BA with PEA creates a novel type‐II band alignment. This new alignment inhibits electron and hole separation, thereby favoring ET over CT. This study not only provides significant insight into the interlayer carrier relaxation dynamics but also is crucial for the future deterministic design of 2D OIHPs heterostructure‐based optoelectronic devices.