Observation of room-temperature long-lived trapped exciton in WS2/RGO heterostructure

In this Letter, we studied the nature of exciton interactions and lifetimes in the WS2/Reduced graphene oxide (WS2/RGO) heterostructure using femtosecond transient absorption spectroscopy. Our studies demonstrate that the key optoelectronic properties of the heterostructure in the strongly coupled regime are substantially different from those of the control WS2 and RGO, promoting the mixing of electronic states at the interfaces leading to the suppression of direct excitons. The combined effect of midgap states and donor levels induced by RGO below the conduction band of WS2 along with the charge transfer to these trap states forms long-lived non-decaying excitons existing more than 1.5 ns, an ultimate time limit in our experiment. These results identify the interfacial trap states as a useful degree of freedom to engineer the lifetime of trapped excitons.