Charge photogeneration in few-layer MoS2

The 2D semiconductor MoS in its mono- and few-layer form is expected to have a significant exciton binding energy of several 100 meV, suggesting excitons as 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. Here, modulation spectroscopy in the sub-ps and ms time scales is used to study the photoexcitation dynamics in few-layer MoS. The results suggest that the primary photoexcitations are excitons that efficiently dissociate into charges with a characteristic time of 700 fs. Based on these findings, simple suggestions for the design of efficient MoS photovoltaic and photodetector devices are made. Few-layer MoS flakes are intermediates between conventional semiconductors and excitonic nanomaterials. By femtosecond optical pump-probe spectroscopy it is shown that photoexcitation creates excitons as the primary species. The excitons efficiently dissociate into charge carriers with a time constant of 700 fs, making few-layer MoS an excellent candidate for efficient photodetectors and photovoltaic devices.