title: Interface Energy Alignment of Atomic-Layer-Deposited VOxon Pentacene: an in Situ Photoelectron Spectroscopy Investigation.
abstract: Ultrathin atomic-layer-deposited (ALD) vanadium oxide (VOx) interlayer has recently been demonstrated for remarkably reducing the contact resistance in organic electronic devices (Adv. Funct. Mater. 2016, 26, 4456). Herein, we present an in situ photoelectron spectroscopy investigation (including X-ray and ultraviolet photoelectron spectroscopies) of ALD VOxgrown on pentacene to understand the role of the ALD VOxinterlayer for the improved contact resistance. The in situ photoelectron spectroscopy characterizations allow us to monitor the ALD growth process of VOxand trace the evolutions of the work function, pentacene HOMO level, and VOxdefect states during the growth. The initial VOxgrowth is found to be partially delayed on pentacene in the first ∼20 ALD cycles. The underneath pentacene layer is largely intact after ALD. The ALD VOxis found to contain a high density of defect states starting from 0.67 eV below the Fermi level, and the energy level of these defect states is in excellent alignment with the HOMO level of pentacene, which therefore allows these VOxdefect states to provide an efficient hole-injection pathway at the contact interface.
authors.affiliation: School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, China.
authors.forename: Ran
authors.identifier: http://orcid.org/0000-0002-4689-1836
authors.initials: R
authors.lastname: Zhao
authors.affiliation: School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, China.
authors.forename: Yuanhong
authors.initials: Y
authors.lastname: Gao
authors.affiliation: School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Guo
authors.affiliation: School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, China.
authors.forename: Yantao
authors.initials: Y
authors.lastname: Su
authors.affiliation: School of Advanced Materials, Shenzhen Graduate School, Peking University , Shenzhen 518055, China.
authors.forename: Xinwei
authors.initials: X
authors.lastname: Wang
keywords: atomic layer deposition; defect states; interface energy alignment; photoelectron spectroscopy; vanadium oxide