Multiple Hot-Carrier Collection in Photo-Excited Graphene Moire Superlattices

TL;DR

This paper demonstrates multiple hot carrier collection in graphene-Moire superlattices, achieving high quantum efficiency and surpassing traditional limits, by leveraging enhanced Nernst effects due to Moire miniband formation.

Contribution

It reports the first observation of multiple hot carrier collection in graphene-Moire superlattices, enabled by Moire miniband-induced Nernst coefficient enhancement.

Findings

Achieved external quantum efficiency over 50%.

Demonstrated collection of at least 5 carriers per photon.

Linked enhanced Nernst effect to Moire miniband formation.

Abstract

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 the efficiency and possibly overcome this limit. Here, we report the observation of multiple hot carrier collection in graphene-boron-nitride Moire superlattice structures. A record-high zero-bias photoresponsivity of 0.3 ampere per watt, equivalently, an external quantum efficiency exceeding 50 percent, is achieved utilizing graphene photo-Nernst effect, which demonstrates a collection of at least 5 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 Moire minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures.