Exciton–exciton annihilation
(EEA) is a nonradiative process
commonly observed in excitonic materials at high exciton densities.
Like Auger recombination, EEA degrades luminescence efficiency at
high exciton densities and causes efficiency roll-off in light-emitting
devices. Near-unity photoluminescence quantum yield has been demonstrated
in transition metal dichalcogenides (TMDCs) at all exciton densities
with optimal band structure modification mediated by strain. Although
the recombination pathways in TMDCs are well understood, the practical
application of light-emitting devices has been challenging. Here,
we demonstrate a roll-off free electroluminescence (EL) device composed
of TMDC monolayers tunable by strain. We show a 2 orders of magnitude
EL enhancement from the WSe2 monolayer by applying a small
strain of 0.5%. We attain an internal quantum efficiency of 8% at
all injection rates. Finally, we demonstrate transient EL turn-on
voltages as small as the band gap. Our approach will contribute to
practical applications of roll-off free optoelectronic devices based
on excitonic materials.
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