Photoinduced charge transfer from vacuum-deposited molecules to single-layer transition metal dichalcogenides

Abstract Variations of photoluminescence (PL) and Raman spectra of single-layer MoS 2 , MoSe 2 , WS 2 , and WSe 2 due to the vacuum deposition of C 60 or copper phthalocyanine (CuPc) molecules have been investigated. PL spectra are decomposed into two competitive components, an exciton and a charged exciton (trion), depending on carrier density. The variation of PL spectra is interpreted in terms of charge transfer across the interfaces between transition metal dichalcogenides (TMDs) and dopant molecules. We find that deposited C 60 molecules inject photoexcited electrons into MoS 2 , MoSe 2 , and WS 2 or holes into WSe 2 . CuPc molecules also inject electrons into MoS 2 , MoSe 2 , and WS 2 , while holes are depleted from WSe 2 to CuPc. We then propose a band alignment between TMDs and dopant molecules. Peak shifts of Raman spectra and doped carrier density estimated using a three-level model also support the band alignment. We thus demonstrate photoinduced charge transfer from dopant molecules to single-layer TMDs.