Solution-Processed, Visible-Light-Emitting Diodes Based on Colloidal Two-Dimensional Materials

Two-dimensional (2D) direct-bandgap semiconductors are highly promising for ultrathin, flexible light emitters. To enable scalable device fabrication beyond mechanically exfoliated flakes, we demonstrate light-emitting diodes based on colloidal 2D semiconductors (c2D-LEDs). Monolayer MoS2 produced via electrochemical exfoliation is employed as a model system for visible-light emission, and its colloidal dispersity and solution processability are systematically investigated. Dimethylformamide is identified as the optimal processing solvent that fulfills the orthogonal solvent requirement in solution-processed vertical heterostructured devices. A nanocomposite light-emissive layer incorporating poly(N-vinylcarbazole) is designed and integrated into the LED architecture, effectively suppressing electrical leakage while enhancing the light-outcoupling efficiency. This device architecture can be extended to colloidal monolayers produced from synthetic crystals. The resulting devices exhibit stable electroluminescence and maintain operation under cycles of mechanical stress. While device efficiencies remain below those of mature 2D-material LEDs based on mechanically exfoliated or epitaxial materials, the significance of this work lies in establishing a fully solution-processable and orthogonally fabricated device architecture for colloidal 2D semiconductors. The strategies developed here for ink formulation, multilayer deposition, carrier confinement, and light extraction provide a general platform for future optimization of scalable and flexible 2D-material optoelectronics.