The self-trapped state (STS) of the interlayer exciton (IX) has aroused enormous interest owing to its significant impact on the fundamental properties of the van der Waals heterostructures (vdWHs). Nevertheless, the microscopic mechanisms of STS are still controversial. Herein, we study the corrections of the binding energies of the IXs stemming from the exciton−interface optical phonon coupling in four kinds of vdWHs and find that these IXs are in the STS for the appropriate ratio of the electron and hole effective masses. We show that these self-trapped IXs could be classified into type  with the increasing binding energy in the tens of millielectronvolts range, which are very agreement with the red-shift of the IX spectra in experiments, and type  with the decreasing binding energy, which provides a possible explanation for the blue-shift and broad line width of the IX's spectra at low temperatures. Moreover, these two types of exciton states could be transformed into each other by adjusting the structural parameters of vdWHs. These results not only provide an in-depth understanding for the self-trapped mechanism but also shed light on the modulations of IXs in vdWHs.

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Quantum defects are essential to understand the non-radiative recombination processes in metal halide perovskites-based photovoltaic devices, in which Huang–Rhys factor, reflecting the coupling strength between the charge carrier and optical phonons, plays a key role in determining the non-radiative recombination via multiphonon processes. Herein, we theoretically present multiphonon Raman scattering intermediated by defects arising from the charge carrier of defect coupled with the longitudinal optical (LO) phonon in the deformation potential and Fr o ̈ hlich mechanisms, respectively. We find that the Raman scattering shows multiple LO phonon overtones at equal interval LO phonons, where Huang–Rhys factor could be evaluated by the order of the strongest overtone. Meanwhile, we give the combinational multiphonon scattering between two mechanisms. Different types of the combinational modes with the weak scattering intensities provide a possible explanation for the long non-radiative charges-carrier lifetimes in metal halide perovskites.

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The systematical analysis for varieties of defects with different depths and lattice relaxation strengths in metal halide perovskites (MHPs) is a challenging task. Here, we study the energy shifts of the full-configuration defects due to the polaron effect based on the all-coupling variational method in MHPs, where these polaron states are formed stemming from different defect species coupling with the longitudinal optical phonon modes via Fröhlich mechanism. We find that the polaron effect results in defect levels varying from tens to several hundreds of meV, which are very close to the correction of defect levels due to the defect-polaron effect, especially for these migration defects proved in the recent experiments in MHPs. These results provide the significant enlightenment not only for analyzing the radiation and non-radiation processes of carriers mediated by defects, but also for optimizing defect effect in the photovoltaic and photoelectric devices based on MHPs materials.