Ultrafast Hot-Carrier Photovoltaics of Type-I Monolayer Heterojunctions in the Broad Spectral Ranges

Strong interlayer photoresponses in monolayer (ML) semiconductor stacks, such as substantial light absorption and charge separation across interlayer band alignments, suggest potentials for two-dimensional photovoltaics (PVs). Here, we report an interlayer PV conversion in a type-I ML heterojunction by ultrafast interlayer transfer of photoexcited hot carriers in the broad spectral ranges. Specifically, low-energy photoexcitation on a stack of a narrow-band-gap (Eg) Bi2Te3 few-layer and a large-Eg MoS2 ML permits interlayer transfer of transient hot carriers from the Bi2Te3 layer to the excitonic states of the neighboring MoS2 ML within a time scale of ∼70 fs, producing interlayer charge separation. Thereby we achieve substantial conversion efficiency from a MoS2 ML with visible to infrared light illumination.