Far-Red Interlayer Excitons of Perovskite/Quantum-Dot Heterostructures

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 MAPbI₃ 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 MAPbI₃ /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 (MAPbI₃ and CdSe-ZnS-QD). Notably, the abnormal behavior of the optical characteristics is observed near the phase transition temperature (90 K) of MAPbI₃ . MAPbI₃ /CdSe-ZnS-QD HS photodetectors show the increase in photocurrent and detectivity compared to MAPbI₃ at IX excitation.