Surface Charge Transfer Doping of MoS₂ Monolayer by Molecules with Aggregation-Induced Emission Effect

Surface charge transfer doping has attracted much attention in modulating the optical and electrical behavior of 2D transition metal dichalcogenides (TMDCs), where finding controllable and efficient dopants is crucial. Here, 1,1,2,2-tetraphenylethylene (TPE) derivative molecules with aggregation-induced emission (AIE) effect were selected as adjustable dopants. By designing nitro and methoxyl functional groups and surface coating, controlled p/n-type doping can be achieved on a chemical vapor deposition (CVD) grown monolayer, MoS₂. We investigated the electron transfer behavior between these two dopants and MoS₂ with fluorescence, Raman, X-ray photoelectron spectra and transient absorption spectra. 1,1,2,2-Tetrakis(4-nitrophenyl)ethane (TPE-4NO₂) with a negative charge aggregation can be a donor to transfer electrons to MoS₂, while 1,1,2,2-Tetrakis(4-methoxyphenyl)ethane (TPE-4OCH₃) is the opposite and electron-accepting. Density functional theory calculations further explain and confirm these experimental results. This work shows a new way to select suitable dopants for TMDCs, which is beneficial for a wide range of applications in optoelectronic devices.