Opto-optical edge defect mitigation in solution-processed WSe₂ thin films for high-efficiency optical modulation

Two-dimensional optical modulators often suffer from low efficiency due to defect-induced losses and light-matter interaction strength. Here we show that edge defects in solution-processed WSe₂ nanosheets, arising from metallic 1 T domains at the edges and semiconducting 2H interiors, can be dynamically saturated through carrier trap filling. By tuning the nanosheet lateral size and applying optical or electrical excitation, defect states are progressively saturated, reducing nonradiative recombination and reshaping the carrier distribution within the film. This process enhances the intrinsic excitonic response, as reflected by the improved photoluminescence peak modulation efficiencies of 0.025 eV·V^-1 (electro-optic) and 0.1 eV·mW^-1 (opto-optic). More importantly, the carrier redistribution and trap filling induce changes in the complex refractive index (Δn + iΔk) through defect-state modulation and free-carrier (Drude-like) effects. Integrated with lithium-niobate-on-insulator micro-ring resonators, solution-processed WSe₂ films deliver efficient C-band (1530-1565 nm) modulation with a tuning efficiency of 1.84 × 10^-5pm^-1·mW·m². Time-resolved measurements further confirm fast dynamics, with ~48.1 ns rise, ~79.4 ns fall, and sustained 200 ns operation ( ~ 5 MHz), which surpasses prior 2D-material OO modulators, establishing engineered defect regulation as a scalable route toward high-performance photonic integration.