White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency
- PDF / 584,284 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 45 Downloads / 303 Views
1212-S02-06
White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency Sebastian Reineke1, Frank Lindner1, Gregor Schwartz1*, Nico Seidler1, Karsten Walzer1*, Björn Lüssem1, and Karl Leo1 1
Institut für Angewandte Photophysik, George-Bähr-Straße 1, 01062 Dresden, Germany.
ABSTRACT We discuss white organic light-emitting diodes (OLEDs) that have luminous efficacies comparable with fluorescent tubes. The emission layer comprises three phosphorescent emitters, of which the blue one is embedded in a host material having a resonant triplet energy with respect to the emitter level. This design leads to very low operating voltages. Using high refractive index glass substrates, thick electron transport layers, and a glass surface modification, white OLEDs are presented that reach 90 lm W-1 at an illumination relevant brightness of 1,000 cd m-2. INTRODUCTION Organic light-emitting diodes (OLEDs) bear great potential to become a next generation, highly efficient light source. In contrast to conventional inorganic LEDs, OLED are areaemitting and ultrathin devices consisting of different layers of functional organic materials sandwiched between two electrodes, with a total thickness in the order of a few hundred nanometers. Comprising different emitters, white light emission can be realized [1]. Using phosphorescent emitter molecules enables 100% internal quantum efficiency because all created excitons are directed to their radiative triplet state [2]. Here, we report on phosphorescent white organic LEDs with extremely high efficiency [3], reaching levels of fluorescent tubes, being the current benchmark for lighting technologies. This is achieved by a novel emission layer concept in connection with improved light outcoupling. EXPERIMENT The white OLED layer sequence is as follows: x nm N,N,N′,N′-tetrakis (4methoxyphenyl)- benzidine (MeO-TPD) doped with 4 mol.% NDP-2 (purchased from Novaled AG, Dresden) as hole-transport layer (HTL) / 10 nm N,N′-di(naphthalen-1-yl)-N,N′)-diphenylbenzidine (NPB) as the electron-blocker layer / emission layer (EML) / 10 nm 2,2′,2′′(1,3,5benzenetriyl) tris-(1-phenyl-1H-benzimidazole) (TPBi) as a hole-blocking layer / y nm Cs-doped 4,7-diphenyl-1,10-phenanthroline (Bphen) as an electron-transport layer (ETL) / 100 nm Ag cathode. The thickness of the HTLs and ETLs are adjusted for optimal light outcoupling. Two types of glass substrates are used. As a reference, conventional glass substrates with a refractive index of n=1.51 is used (Device LI). Additionally, OLEDs on high refractive index substrates *
current address: heliathek GmbH, Liebigstraße 26, 01187 Dresden, Germany.
with n=1.78 are prepared (Devices HI-1,-2 and-3). Device LI has a 60 nm thick HTL and a 40 nm thick ETL. For all HI OLEDs, the HTL thickness is 45 nm, the ETL thicknesses are varied from 45 nm (HI-1) to 205 nm (HI-2) and 210 nm (HI-3). The emission layer consists of a complex layer sequence: 6 nm of 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA): iridium (III) bis (2-methyldibenzo [f,h] quinoxaline) (acetylace
Data Loading...
