Directional Exciton-Energy Transport in a Lateral Heteromonolayer of WSe2–MoSe2

Controlling the direction of exciton-energy flow in two-dimensional (2D) semiconductors is crucial for developing future high-speed optoelectronic devices using excitons as the information carriers. However, intrinsic exciton diffusion in conventional 2D semiconductors is omnidirectional, and efficient exciton-energy transport in a specific direction is difficult to achieve. Here we demonstrate directional exciton-energy transport across the interface in tungsten diselenide (WSe₂)-molybdenum diselenide (MoSe₂) lateral heterostructures. Unidirectional transport is spontaneously driven by the built-in asymmetry of the exciton-energy landscape with respect to the heterojunction interface. At excitation positions close to the interface, the exciton photoluminescence (PL) intensity was substantially decreased in the WSe₂ region and enhanced in the MoSe₂ region. In PL excitation spectroscopy, it was confirmed that the observed phenomenon arises from lateral exciton-energy transport from WSe₂ to MoSe₂. This directional exciton-energy flow in lateral 2D heterostructures can be exploited in future optoelectronic devices.