Transition metal dichalcogenides (TMDs), a
two-dimensional (2-D) semiconductor, are promising materials for
next-generation optoelectronic devices. They can emit strong light
due to the large binding energies of excitons, quasiparticles
composed of electron-hole pair, as well as an atomically thin
nature. In existing 2-D light emitting devices, however, the
simultaneous injection of electrons and holes into 2-D materials
has been challenging, which results in low light emission
efficiency.