title: Red phosphorescent organic light-emitting diodes based on the simple structure.
abstract: We demonstrated that the simple layered red phosphorescent organic light-emitting diodes (OLEDs) are possible to have high efficiency, low driving voltage, stable roll-off efficiency, and pure emission color without hole injection and transport layers. We fabricated the OLEDs with a structure of ITO/CBP doped with Ir(pq)2(acac)/BPhen/Liq/Al, where the doping concentration of red dopant, Ir(pq)2(acac), was varied from 4% to 20%. As a result, the quantum efficiencies of 13.4, 11.2, 16.7, 10.8 and 9.8% were observed in devices with doping concentrations of 4, 8, 12, 16 and 20%, respectively. Despite of absence of the hole injection and transport layers, these efficiencies are superior to efficiencies of device with hole transporting layer due to direct hole injection from anode to dopant in emission layer.
authors.affiliation: Department of Information Display, Hongik University, Seoul 121-791, Korea.
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Seo
authors.forename: Seok Jae
authors.initials: SJ
authors.lastname: Lee
authors.forename: Bo Young
authors.initials: BY
authors.lastname: Kim
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Choi
authors.forename: Wone Keun
authors.initials: WK
authors.lastname: Han
authors.forename: Kum Hee
authors.initials: KH
authors.lastname: Lee
authors.forename: Seung Soo
authors.initials: SS
authors.lastname: Yoon
authors.forename: Young Kwan
authors.initials: YK
authors.lastname: Kim