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Nano Lett. 2016 Apr 13;16(4):2786-91. doi: 10.1021/acs.nanolett.6b00536. Epub 2016 Mar 21.

Recombination Kinetics and Effects of Superacid Treatment in Sulfur- and Selenium-Based Transition Metal Dichalcogenides.

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Electrical Engineering and Computer Sciences, University of California , Berkeley, California 94720, United States.
Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Department of Materials Science and Engineering, University of Texas, Dallas , Richardson, Texas 75080, United States.


Optoelectronic devices based on two-dimensional (2D) materials have shown tremendous promise over the past few years; however, there are still numerous challenges that need to be overcome to enable their application in devices. These include improving their poor photoluminescence (PL) quantum yield (QY) as well as better understanding of exciton-based recombination kinetics. Recently, we developed a chemical treatment technique using an organic superacid, bis(trifluoromethane)sulfonimide (TFSI), which was shown to improve the quantum yield in MoS2 from less than 1% to over 95%. Here, we perform detailed steady-state and transient optical characterization on some of the most heavily studied direct bandgap 2D materials, specifically WS2, MoS2, WSe2, and MoSe2, over a large pump dynamic range to study the recombination mechanisms present in these materials. We then explore the effects of TFSI treatment on the PL QY and recombination kinetics for each case. Our results suggest that sulfur-based 2D materials are amenable to repair/passivation by TFSI, while the mechanism is thus far ineffective on selenium based systems. We also show that biexcitonic recombination is the dominant nonradiative pathway in these materials and that the kinetics for TFSI treated MoS2 and WS2 can be described using a simple two parameter model.


Transition metal dichalcogenide; biexcitonic recombination; quantum yield; radiative lifetime

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