title: Hot Carrier Extraction from Multilayer Graphene.
abstract: Hot carriers in semiconductor or metal nanostructures are relevant, for instance, to enhance the activity of oxide-supported metal catalysts or to achieve efficient photodetection using ultrathin semiconductor layers. Moreover, rapid collection of photoexcited hot carriers can improve the efficiency of solar cells, with a theoretical maximum of 85%. Because of the long lifetime of secondary excited electrons, graphene is an especially promising two-dimensional material to harness hot carriers for solar-to-electricity conversion. However, the photoresponse of thus far realized graphene photoelectric devices is mainly governed by thermal effects, which yield only a very small photovoltage. Here, we report a Gr-TiOx-Ti heterostructure wherein the photovoltaic effect is predominant. By doping the graphene, the open circuit voltage reaches values up to 0.30 V, 2 orders of magnitude larger than for devices relying upon the thermoelectric effect. The photocurrent turned out to be limited by trap states in the few-nanometer-thick TiOxlayer. Our findings represent a first valuable step toward the integration of graphene into third-generation solar cells based upon hot carrier extraction.
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Roberto
authors.initials: R
authors.lastname: Urcuyo
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Dinh Loc
authors.initials: DL
authors.lastname: Duong
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Sailer
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Marko
authors.initials: M
authors.lastname: Burghard
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, D-70569 Stuttgart, Germany.|Institut de Physique , Ecole Polytechnique de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Klaus
authors.initials: K
authors.lastname: Kern
keywords: F4-TCNQ; Gr−TiOx−Ti heterostructures; graphene; hot carrier; photovoltaic devices; two-dimensional (2D) materials