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In conventional light-harvesting devices, the absorption of a single photon only excites one electron, which sets the standard limit of power-conversion efficiency, such as the Shockley-Queisser limit. In principle, generating and harnessing multiple carriers per absorbed photon can improve efficiency and possibly overcome this limit. We report the observation of multiple hot-carrier collection in graphene/boron-nitride Moiré superlattice structures. A record-high zero-bias photoresponsivity of 0.3 A/W (equivalently, an external quantum efficiency exceeding 50%) is achieved using graphene's photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We reveal that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities, which is an emergent phenomenon due to the formation of Moiré minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures.
Pubmed ID: 27386538
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Facility offers array of solid state, solution state, MRI/S (animal and human), MR microscopy and diffusion capabilities and techniques. Among their machines is 900 MHz 105 mm bore magnet. Techniques and instruments are available at two different MagLab facilities in Florida, NMR-MRI/S Facility at MagLab headquarters near Florida State University in Tallahassee and Advanced Magnetic Resonance Imaging and Spectroscopy Facility (AMRIS) housed within McKnight Brain Institute at University of Florida in Gainesville.
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