Journal
NANOSCALE ADVANCES
Volume 3, Issue 14, Pages 4216-4225Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d0na01014f
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Funding
- EPSRC [EP/L015978/1, EP/L016087/1, EP/P027741/1, EP/M006360/1, EP/P005152/1]
- Royal Commission for the Exhibition of 1851
- Royal Society Dorothy Hodgkin Research Fellowship
- Swedish Research Council, Vetenskapsradet [2018-06610]
- European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme [758826]
- Winton Program for Physics of Sustainability
- EPSRC [EP/M006360/1, EP/P027741/1, EP/P005152/1] Funding Source: UKRI
- Swedish Research Council [2018-06610] Funding Source: Swedish Research Council
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The study demonstrates that treatment with oleic acid (OA) provides a simple wet chemical passivation method for monolayer MoSe2, significantly enhancing PL yields and improving spectral uniformity. The OA treated MoSe2 shows trap-free PL dynamics dominated by neutral exciton recombination, increased PL lifetimes, and reduced charge trap density in field effect transistors. This work confirms OA treatment as a simple solution-based chemical passivation protocol for improving PL yields and electronic characteristics in both selenide and sulphide TMDs, which has not been reported previously for other solution-based passivation schemes.
The inherently low photoluminescence (PL) yields in the as prepared transition metal dichalcogenide (TMD) monolayers are broadly accepted to be the result of atomic vacancies (i.e., defects) and uncontrolled doping, which give rise to non-radiative exciton decay pathways. To date, a number of chemical passivation schemes have been successfully developed to improve PL in sulphur based TMDs i.e., molybdenum disulphide (MoS2) and tungsten disulphide (WS2) monolayers. Studies on solution based chemical passivation schemes for improving PL yields in selenium (Se) based TMDs are however lacking in comparison. Here, we demonstrate that treatment with oleic acid (OA) provides a simple wet chemical passivation method for monolayer MoSe2, enhancing PL yields by an average of 58-fold, while also improving spectral uniformity across the material and reducing the emission linewidth. Excitation intensity dependent PL reveals trap-free PL dynamics dominated by neutral exciton recombination. Time-resolved PL (TRPL) studies reveal significantly increased PL lifetimes, with pump intensity dependent TRPL measurements also confirming trap free PL dynamics in OA treated MoSe2. Field effect transistors show reduced charge trap density and improved on-off ratios after treatment with OA. These results indicate defect passivation by OA, which we hypothesise as ligands passivating chalcogen defects through oleate coordination to Mo dangling bonds. Importantly, this work combined with our previous study on OA treated WS2, verifies OA treatment as a simple solution-based chemical passivation protocol for improving PL yields and electronic characteristics in both selenide and sulphide TMDs - a property that has not been reported previously for other solution-based passivation schemes.
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