Alloy-mediated phonon-assisted ultrafast charge transfer in transition metal dichalcogenides heterostructures

Understanding and controlling interlayer charge transfer is critical for advancing the performance of van der Waals (vdW) heterostructures in optoelectronic applications. Despite extensive studies demonstrating ultrafast charge transfer across vdW interfaces, the microscopic mechanisms remain under debate. Here, we report an experimental test of phonon-assisted interlayer charge transfer using a MoSe 2 /MoSSe/MoS 2 trilayer heterostructure. By inserting an alloy MoSSe monolayer between MoSe 2 and MoS 2 , we demonstrate that the electron transfer process becomes significantly faster than in a direct MoSe 2 /MoS 2 bilayer, despite increased spatial separation and reduced band offsets. This result provides support to the phonon-assisted charge transfer model, where the alloy layer enhances phonon-assisted charge transfer from MoSe 2 to MoS 2 layers by offering compatible phonon modes. This finding also offers a new design principle for controlling ultrafast processes in vdW heterostructures and demonstrates that alloy engineering is a powerful strategy to modulate interfacial interactions and unlock novel functionalities in vdW heterostructures.