A chemical-dedoping strategy to tailor electron density in molecular-intercalated bulk monolayer MoS 2

Molybdenum disulfide (MoS 2 ) is an extensively studied two-dimensional layered semiconductor with interesting electronic and optical properties. Monolayer MoS 2 features strong light–matter interactions due to its direct bandgap, whereas multilayer MoS 2 is an indirect bandgap semiconductor and optically inactive. The molecular intercalation of MoS 2 with organic cations offers a strategy to decouple the interlayer interaction, producing a bulk monolayer material, but is usually accompanied by a heavy electron doping effect that can diminish the intrinsic semiconductor properties or induce a phase transition. Here we report a chemical-dedoping strategy to tailor electron density in molecular-intercalated MoS 2 , thereby retaining monolayer semiconductor properties. By introducing a poly(vinylpyrrolidone)–bromine complex during the electrochemical intercalation process, we show that bulk monolayer MoS 2 thin film can be produced with decoupled interlayer interaction and reduced electron concentration. The resulting thin films display strong excitonic emission, 20 and >400 times stronger than the exfoliated monolayer and multilayer material, respectively, high valley polarization and an enhanced photoelectric response. Our study opens a scalable path to large-area bulk monolayer MoS 2 thin films with monolayer-like optical properties and greatly increased optical cross-sections, presenting an attractive material platform for both fundamental photophysics studies and scalable optoelectronic applications.