Spatial Control of Dynamic p–i–n Junctions in Transition Metal Dichalcogenide Light-Emitting Devices

Emerging transition metal dichalcogenides (TMDCs) offer an attractive platform for investigating functional light-emitting devices, such as flexible devices, quantum and chiral devices, high-performance optical modulators, and ultralow threshold lasers. In these devices, the key operation is to control the light-emitting position, that is, the spatial position of the recombination zone to generate electroluminescence, which permits precise light guides/passes/confinement to ensure favorable device performance. Although various structures of TMDC light-emitting devices have been demonstrated, including the transistor configuration and heterostructured diodes, it is still difficult to tune the light-emitting position precisely owing to the structural device complexity. In this study, we fabricated two-terminal light-emitting devices with chemically synthesized WSe2, MoSe2, and WS2 monolayers, and performed direct observations of their electroluminescence, from which we discovered a divergence in their light-emitting positions. Subsequently, we propose a method to associate spatial electroluminescence imaging with transport properties among different samples; consequently, a common rule for determining the locations of recombination zones is revealed. Owing to dynamic carrier accumulations and p–i–n junction formations, the light-emitting positions in electrolyte-based devices can be tuned continuously. The proposed method will expand the device applicability for designing functional optoelectronic applications based on TMDCs.