title: Workfunction-tunable, N-doped reduced graphene transparent electrodes for high-performance polymer light-emitting diodes.
abstract: Graphene is a promising candidate to complement brittle and expensive transparent conducting oxides. Nevertheless, previous research efforts have paid little attention to reduced graphene, which can be of great benefit due to low-cost solution processing without substrate transfer. Here we demonstrate workfunction-tunable, highly conductive, N-doped reduced graphene film, which is obtainable from the spin-casting of graphene oxide dispersion and can be successfully employed as a transparent cathode for high-performance polymer light-emitting diodes (PLEDs) as an alternative to fluorine-doped tin oxide (FTO). The sheet resistance of N-doped reduced graphene attained 300 Ω/□ at 80% transmittance, one of the lowest values ever reported from the reduction of graphene oxide films. The optimal doping of quaternary nitrogen and the effective removal of oxygen functionalities via sequential hydrazine treatment and thermal reduction accomplished the low resistance. The PLEDs employing N-doped reduced graphene cathodes exhibited a maximum electroluminescence efficiency higher than those of FTO-based devices (4.0 cd/A for FTO and 7.0 cd/A for N-doped graphene at 17,000 cd/m(2)). The reduced barrier for electron injection from a workfunction-tunable, N-doped reduced graphene cathode offered this remarkable device performance.
authors.affiliation: Department of Materials Science and Engineering, KI for the Nanocentury, KAIST, Daejeon, 305-701, Republic of Korea.
authors.forename: Jin Ok
authors.initials: JO
authors.lastname: Hwang
authors.forename: Ji Sun
authors.initials: JS
authors.lastname: Park
authors.forename: Dong Sung
authors.initials: DS
authors.lastname: Choi
authors.forename: Ju Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Sun Hwa
authors.initials: SH
authors.lastname: Lee
authors.forename: Kyung Eun
authors.initials: KE
authors.lastname: Lee
authors.forename: Yong-Hyun
authors.initials: YH
authors.lastname: Kim
authors.forename: Myoung Hoon
authors.initials: MH
authors.lastname: Song
authors.forename: Seunghyup
authors.initials: S
authors.lastname: Yoo
authors.forename: Sang Ouk
authors.initials: SO
authors.lastname: Kim
mesh_terms: D004566:Electrodes; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006108:Graphite / Q000737:chemistry*; D008029:Lighting / Q000295:instrumentation*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D012666:Semiconductors
chemical_list: D011108:Polymers; D006108:Graphite