Twist Angle-Dependent Exciton Mobility in WS2 Bilayers

Bilayer WS2 shows exceptional promise for excitonic devices due to its defect tolerance, high carrier density, and angle-tunable electronic properties. However, fundamental understanding of twist angle-dependent exciton transport remains limited due to challenges in sample preparation and interplays between interlayer coupling and moiré potential. Using transient reflection microscopy (TRM), we systematically studied exciton mobility in chemical vapor deposition-grown (CVD-grown) bilayer WS2 with different twist angles. At 0°, strong interlayer coupling without moiré potential effects yielded the highest exciton mobility (87.3 cm2/V s)- 10-fold greater than monolayer WS2-with a 1.06 μm diffusion length, while the 25° sample showed reduced mobility (44.5 cm2/(V s)) and shorter diffusion length (0.88 μm) due to weakened coupling and moiré potential effects, and the 60° case exhibited intermediate characteristics. This work demonstrates that interlayer coupling and moiré potential modulation critically determine exciton transport dynamics in layered two-dimensional semiconductors, providing essential guidelines for device engineering.