Controlling Lattice Defects and Inter-Exciton Interactions in Monolayer Transition Metal Dichalcogenides for Efficient Light Emission

Monolayer transition metal dichalcogenides (1L-TMDs) have attracted tremendous attention as two-dimensional (2D) light-emitting semiconductors because the optical properties of 1L-TMDs are primarily determined by excitonic transitions, providing an ideal platform for the study or practical uses of 2D confined exciton systems. While pristine 1L-TMDs experience a low quantum yield (QY) due to the high density of lattice defects, significant advances have been made for increasing the QY based on various experimental approaches and theoretical understanding of modulating defect states of 1L-TMDs. Under the high exciton density condition, the strong interexciton interaction observed in 1L-TMDs was determined to be the primary limiting factor of QY. Here, we outline recent discoveries and efforts to overcome the lattice defects and exciton-exciton annihilation with the aim of improving the efficiency of light emission of 1L-TMDs. Along with perspectives on future research to realize the defect free and highly luminescent TMDs, we propose a simple scheme of suppressing the EEA effect to maintain the QY of 1L-TMDs in high exciton densities.