Mechanistic insight into the chemical treatments of monolayer transition metal disulfides for photoluminescence enhancement
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Abstract: There is a growing interest in obtaining high quality monolayer transition metal disulfides for optoelectronic applications. Surface treatments using a range of chemicals have proven effective to improve the photoluminescence yield of these materials. However, the underlying mechanism for the photoluminescence enhancement is not clear, which prevents a rational design of passivation strategies. Here, a simple and effective approach to significantly enhance the photoluminescence is demonstrated by using a family of cation donors, which we show to be much more effective than commonly used p-dopants. We develop a detailed mechanistic picture for the action of these cation donors and demonstrate that one of them, bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI), enhances the photoluminescence of both MoS2 and WS2 to a level double that of the currently best performing super-acid trifluoromethanesulfonimide (H-TFSI) treatment. In addition, the ionic salts used in our treatments are compatible with greener solvents and are easier to handle than super-acids, providing the possibility of performing treatments during device fabrication. This work sets up rational selection rules for ionic chemicals to passivate transition metal disulfides and increases their potential in practical optoelectronic applications.
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Funder: RCUK | Engineering and Physical Sciences Research Council (EPSRC); doi: https://doi.org/10.13039/501100000266
Funder: funding from the Royal society through a Newton international fellowship
Funder: the Winton programme for the physics of sustainability
Funder: The Royal society and Tata group. The Royal society funding through a Newton international fellowship. The Winton programme for the physics of sustainability.
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Royal Society (UF150033)
EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council) (758826, 756962)