Ultrafast Electron Transfer with Long-Lived Charge Separation and Spin Polarization in WSe₂/C₆₀ Heterojunction

Abstract

The strong excitonic effect in monolayer transition-metal dichalcogenides (TMDs) endows them with intriguing optoelectronic properties but also short-lived population and valley polarization. Exciton dissociation by interfacial charge transfer has been shown as an effective approach to prolonging excited-state lifetimes. Herein, by ultrafast spectroscopy and building-block molecule C₆₀, we investigated exciton and valley polarization dynamics in the prototypical WSe₂/C₆₀ inorganic-organic hybrid. We show that excitons in WSe₂ can be dissociated through ultrafast (∼1 ps) electron transfer to C₆₀, with nanosecond charge separation due to thermally activated electron diffusion in C₆₀ film. Because of suppressed electron-hole exchange interaction after electron transfer, hole in WSe₂ exhibits a spin/valley polarization lifetime of ∼60 ps at room temperature, more than 2 orders of magnitude longer than that in WSe₂ monolayer. This study suggests exciton dissociation as a general approach to suppress electron-hole interaction and prolong the charge/spin/valley lifetime in TMDs.