Jinsoo Joo

Interlayer excitons (IXs) at the interface of heterostructures (HSs) with a staggered band alignment are fascinating quantum quasi‐particles with light‐emitting and long‐lifetime characteristics. In this study, the energy band alignments (EBAs) of the HS of MAPbI 3 perovskite thin sheets with CdSe‐ZnS core–shell quantum dot (QD) layers are modulated by using different diameters of the QDs. Far‐red IX emission is observed at 1.42 eV from the HS of MAPbI 3 /CdSe‐ZnS‐QD ( λ em = 645 nm) with type‐II EBA owing to charge transfer. The lifetime of the far‐red IXs is estimated to be 5.68 µs, which is considerably longer than that (0.715 ns) of the intralayer excitons from CdSe‐ZnS‐QD. With increasing incident excitation power, the PL peak and its intensity of IXs are blue‐shifted and linearly increased, respectively, indicating a strong dipole alignment of far‐red IXs at the heterojunction. Back focal plane imaging suggests that the directions of dipole moments of the IXs are relatively out‐of‐plane compared to those of the intralayer excitons (MAPbI 3 and CdSe‐ZnS‐QD). Notably, the abnormal behavior of the optical characteristics is observed near the phase transition temperature (90 K) of MAPbI 3 . MAPbI 3 /CdSe‐ZnS‐QD HS photodetectors show the increase in photocurrent and detectivity compared to MAPbI 3 at IX excitation.