Chemically Driven Tunable Light Emission of Charged and Neutral Excitons in Monolayer WS₂

Abstract

Monolayer (1L) semiconducting transition metal dichacogenides (TMDs) possess remarkable physical and optical properties, promising for a wide range of applications from nanoelectronics to optoelectronics such as light-emitting and sensing devices. Here we report how the molecular adsorption can modulate the light emission and electrical properties of 1L WS2. The dependences of trion and exciton emission on chemical doping are investigated in 1L WS2 by microphotoluminescence (μPL) measurements, where different responses are observed and simulated theoretically. The total PL is strongly enhanced when electron-withdrawing molecules adsorb on 1L WS2, which is attributed to the increase of the exciton formation due to charge transfer. The electrical transport measurements of a 1L WS2 field effect transistor elucidate the effect of the adsorbates on the conductivity, which give evidence for charge transfer between molecules and 1L WS2. These findings open up many opportunities to manipulate the electrical and optical properties of two-dimensional TMDs, which are particularly important for developing optoelectronic devices for chemical and biochemical sensing applications.

Effects of substrate type and material-substrate bonding on high-temperature behavior of monolayer WS2

“…The higher ), also known as a trion. Trions results from n-type doping due to either charge transfer from the substrate or defects in the film [38,39]. The variation in the A exciton peak position among these samples is likely due to strain.…”

Understanding Solvent Effects on the Properties of Two-Dimensional Transition Metal Dichalcogenides

“…[13][14][15][16][17][18][19][20][21] Given the scalability and simplicity, solution-based molecular adsorption (i.e., chemical doping) has been widely investigated, which exploits surface charge transfer between adsorbates and TMDCs. Adsorbed molecules such as 2,3,5,6-tetrafluoro- 7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ), 16,17 cesium carbonate, 18 benzyl viologen, 19 1,2-3 dichloroethane, 20 and benzimidazoline 21 withdraw or donate electrons, resulting in the enhancement or quenching of TMDC PL. Such molecular interactions may also control carrier density or contact resistance in the field-effect transport.…”

Photoluminescence from Liquid‐Exfoliated WS2Monomers in Poly(Vinyl Alcohol) Polymer Composites

“…However, in the liquid state, this is partly overcompensated by the surrounding water acting as p-type dopant giving initial trion/exciton areas of ~1. 61,67 As the water is evaporated, the actual n-type doping effect of PVA begins to dominate, resulting in broadened, red-shifted photoluminescence and an increased trion/exciton ratio. While the water has mostly evaporated after 20 minutes, we suggest that there is a residual portion of water, perhaps interacting strongly with the PVA, which evaporates more slowly over the 20-80 minute period.…”