Scalable synthesis of bulk monolayer molybdenum disulfide thin films with tailored electron doping

Molybdenum disulfide (MoS₂) is an extensively studied two-dimensional layered semiconductor with interesting electronic and optical properties. Monolayer MoS₂ features strong light-matter interactions due to its direct bandgap, whereas multilayer MoS₂ is an indirect bandgap semiconductor and optically inactive. The molecular intercalation of MoS₂ 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. Herein, we report a chemical-dedoping strategy to tailor electron density in molecular-intercalated MoS_2, therefore retaining monolayer properties. By introducing a poly(vinylpyrrolidone)-bromine complex during the electrochemical intercalation process, we show bulk monolayer MoS₂ 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, as well as high valley polarization and enhanced photo-electric response. Our study opens a scalable path to large-area bulk monolayer MoS₂ thin films with monolayer-like optical properties and greatly increased optical cross-section, presenting an attractive material platform for both fundamental photophysics studies and scalable optoelectronic applications.