In situ diagnostics of photoinduced processing and exciton diffusivity enhancement in two-dimensional semiconductors

Exciton transport is a fundamental process of energy conversion in semiconductors. The strong interaction of light with two-dimensional (2D) semiconductors provides the opportunity to optimize exciton transport for 2D optoelectronic devices. However efficient exciton transport in atomically thin 2D semiconductors is still challenging due to various scattering sources such as defects and traps. Here we show that photoinduced processes can achieve a giant enhancement in exciton diffusivity (from 1.5 to 22.5 cm2/s in monolayer MoS2 crystals)[1] and can be revealed by in situ optical spectroscopy monitoring. The mechanism of the enhancement is revealed: the scattering of excitons is screened by trapped charges generated by a photoinduced electron-hole plasma. This understanding of how to improve and control exciton transport in 2D semiconductors opens new avenues for the development of high-performance excitonic and photovoltaic devices. [1] Y. Yu et al., Sci. Adv., 2020, eabb4823.