title: Effect of Injection Layer Sub-Bandgap States on Electron Injection in Organic Light-Emitting Diodes.
abstract: It is generally considered that the injection of charges into an active layer of an organic light-emitting diode (OLED) is solely determined by the energetic injection barrier formed at the device interfaces. Here, we demonstrate that the density of surface states of the electron-injecting ZnO layer has a profound effect on both the charge injection and the overall performance of the OLED device. Introducing a dopant into ZnO reduces both the energy depth and density of surface states without altering the position of the energy levels-thus, the magnitude of the injection barrier formed at the organic/ZnO interface remains unchanged. Changes observed in the density of surface states result in an improved electron injection and enhanced luminescence of the device. We implemented a numerical simulation, modeling the effects of energetics and the density of surface states on the electron injection, demonstrating that both contributions should be considered when choosing the appropriate injection layer.
authors.forename: Carsten
authors.initials: C
authors.lastname: Hinzmann
authors.affiliation: Sara and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology , Haifa 32000, Israel.
authors.forename: Osnat
authors.initials: O
authors.lastname: Magen
authors.forename: Yvonne J
authors.initials: YJ
authors.lastname: Hofstetter
authors.forename: Paul E
authors.initials: PE
authors.lastname: Hopkinson
authors.affiliation: Sara and Moshe Zisapel Nano-Electronic Center, Department of Electrical Engineering, Technion-Israel Institute of Technology , Haifa 32000, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Tessler
authors.forename: Yana
authors.identifier: http://orcid.org/0000-0002-0783-0707
authors.initials: Y
authors.lastname: Vaynzof
keywords: drift-diffusion Poisson; electron injection; modeling; organic light-emitting diode; surface states