title: Metal oxide induced charge transfer doping and band alignment of graphene electrodes for efficient organic light emitting diodes.
abstract: The interface structure of graphene with thermally evaporated metal oxide layers, in particular molybdenum trioxide (MoO3), is studied combining photoemission spectroscopy, sheet resistance measurements and organic light emitting diode (OLED) characterization. Thin (<5 nm) MoO3 layers give rise to an 1.9 eV large interface dipole and a downwards bending of the MoO3 conduction band towards the Fermi level of graphene, leading to a near ideal alignment of the transport levels. The surface charge transfer manifests itself also as strong and stable p-type doping of the graphene layers, with the Fermi level downshifted by 0.25 eV and sheet resistance values consistently below 50 Ω/sq for few-layer graphene films. The combination of stable doping and highly efficient charge extraction/injection allows the demonstration of simplified graphene-based OLED device stacks with efficiencies exceeding those of standard ITO reference devices.
authors.affiliation: Philips Research, Philipsstrasse 8, 52068 Aachen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Meyer
authors.affiliation: Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK.
authors.forename: Piran R
authors.initials: PR
authors.lastname: Kidambi
authors.affiliation: Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK.
authors.forename: Bernhard C
authors.initials: BC
authors.lastname: Bayer
authors.affiliation: Philips Research, Philipsstrasse 8, 52068 Aachen, Germany.
authors.forename: Christ
authors.initials: C
authors.lastname: Weijtens
authors.affiliation: Philips Research, Philipsstrasse 8, 52068 Aachen, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Kuhn
authors.affiliation: Graphenea S.A, Tolosa Hiribidea 76, E-20018 Donostia San Sebastian, Spain.
authors.forename: Alba
authors.initials: A
authors.lastname: Centeno
authors.affiliation: Graphenea S.A, Tolosa Hiribidea 76, E-20018 Donostia San Sebastian, Spain.
authors.forename: Amaia
authors.initials: A
authors.lastname: Pesquera
authors.affiliation: Graphenea S.A, Tolosa Hiribidea 76, E-20018 Donostia San Sebastian, Spain.
authors.forename: Amaia
authors.initials: A
authors.lastname: Zurutuza
authors.affiliation: Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK.
authors.forename: John
authors.initials: J
authors.lastname: Robertson
authors.affiliation: Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, UK.
authors.forename: Stephan
authors.initials: S
authors.lastname: Hofmann