Directional Exciton-Energy Transport in a Lateral Heteromonolayer of WSe 2 -MoSe 2 .

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 (WSe ₂ )-molybdenum diselenide (MoSe ₂ ) 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 WSe ₂ region and enhanced in the MoSe ₂ region. In PL excitation spectroscopy, it was confirmed that the observed phenomenon arises from lateral exciton-energy transport from WSe ₂ to MoSe ₂ . This directional exciton-energy flow in lateral 2D heterostructures can be exploited in future optoelectronic devices.