Spatiotemporal Cooling and Diffusion of Hot Interlayer Excitons in Moiré-Potential-Suppressed WSe₂/WS₂...

Harnessing hot interlayer excitons (HIEs) in two-dimensional (2D) van der Waals (vdW) heterostructures offers a promising strategy for advancing hot-carrier optoelectronics beyond the Shockley-Queisser limit. However, the spatiotemporal diffusion dynamics and cooling behavior of HIEs remain poorly understood, particularly in transition metal dichalcogenide (TMD) bilayer heterostructures where moiré potentials significantly influence interlayer exciton transport. Here, we investigate a WSe₂/WS₂ bilayer heterostructure with a twist angle of ∼36°, a configuration that effectively suppresses moiré potential. We uncover a linear spatiotemporal diffusion behavior of interlayer excitons under weak moiré conditions─markedly different from the nonlinear dynamics typically observed in small-twist-angle systems (∼9°) dominated by strong moiré potentials. Furthermore, under above-bandgap excitation, we provide the direct experimental observation of the spatial diffusion of HIEs in a TMD bilayer heterostructure, a phenomenon that is difficult to observe in systems with strong moiré confinement. We demonstrate that the cooling time of HIEs is an order of magnitude longer than that of intralayer excitons in monolayer TMDs. This extended lifetime indicates the potential for efficient hot-carrier extraction in 2D heterostructures. Together, these findings offer insights into exciton transport and relaxation in moiré-engineered bilayer heterostructures and may inform the use of HIEs in optoelectronic and energy-harvesting applications.