Electrical suppression of all nonradiative recombination pathways in monolayer semiconductors

Electrostatic doping boosts emission Although monolayers of transition-metal dichalcogenides such as molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) should exhibit strong photoluminescence, in practice, defects in these materials can lead to very low quantum yields (less than 1%). Lien et al. show that as-formed MoS 2 and WS 2 monolayers encapsulated in poly(methyl methacrylate) can be electrostatically doped to achieve quantum yields near unity. Under these conditions, instead of charged trion species that recombine nonradiatively, only neutral excitons that recombine emissively form. These results help explain why coating these materials with certain Lewis acids also boosts the quantum yield. Science , this issue p. 468