Fast relaxation of interlayer excitons from the free to self-trapped states in lead halide perovskite van der Waals heterostructures

We study the thermal relaxation of interlayer excitons from the free to momentary self-trapped states in lead halide perovskite van der Waals heterostructures based on the well-known Huang-Rhys model. We find that these relaxation processes (self-trapped processes) are very fast ranging from nanoseconds to picoseconds. Moreover, the self-trapped time displays different variational trends by regulating three key structural parameters of the heterostructure, which could be intrinsically attributed to the modulation of exciton-phonon coupling by these structural parameters, resulting in the variation of the self-trapping depth. The underlying physical pictures that the changing of intersection points of two adiabatic potential between the free and momentary self-trapped states in the configuration coordinates are proposed to explain these relaxation processes. These results not only provide the significant enlightenments for analyzing the abnormal features of excitonic spectra in experiments but also present the practical ways to modulate the dynamical processes of excitons in two-dimensional structures.