Two-dimensional (2D) semiconductors have attracted intense interest for their unique photophysical properties, including large exciton binding energies and strong gate tunability, which arise from their reduced dimensionality. Despite considerable efforts, a disconnect persists between the fundamental photophysics in pristine 2D semiconductors and the practical device performances. Here, I will discuss how our work using time-resolved photoluminescence spectroscopy along with photocurrent imaging allows us to correlate the intrinsic photophysics with the device performance in 2D semiconductor diodes. We observe a decrease of the exciton lifetime with increasing charge density from electrostatic doping due to increased exciton–charge Auger recombination. Using an exciton-diffusion-limited model we show how this explains the short-circuit photocurrent as function of charge density and the importance of Van der Waals contacts to achieve intrinsic behavior.

Photocurrent imaging and photoluminescence lifetimes reveal intrinsic excitonic 2D pn junction behavior

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