Charge photogeneration in few-layer MoS2

TL;DR

This study investigates charge photogeneration in few-layer MoS2, revealing mechanisms like hot exciton dissociation that enhance photovoltaic and photodetector performance.

Contribution

It uncovers the dynamics of charge carrier generation in MoS2, including energy-dependent hot exciton dissociation, informing better device design.

Findings

Charge photogeneration involves excitons and charge carriers.

Hot exciton dissociation is an energy-dependent process.

Implications for improved MoS2 photovoltaic devices.

Abstract

The two-dimensional semiconductor MoS2 in its mono- and few-layer form is expected to have a significant exciton binding energy of several 100 meV, leading to the consensus that excitons are the primary photoexcited species. Nevertheless, even single layers show a strong photovoltaic effect and work as the active material in high sensitivity photodetectors, thus indicating efficient charge carrier photogeneration (CPG). Here we use continuous wave photomodulation spectroscopy to identify the optical signature of long-lived charge carriers and femtosecond pump-probe spectroscopy to follow the CPG dynamics. We find that intitial photoexcitation yields a branching between excitons and charge carriers, followed by excitation energy dependent hot exciton dissociation as an additional CPG mechanism. Based on these findings, we make simple suggestions for the design of more efficient MoS2 photovoltaic and photodetector devices.