Proceedings Article | 20 October 2004
Proc. SPIE. 5530, Fourth International Conference on Solid State Lighting
KEYWORDS: Light sources, Organic light emitting diodes, Solid state lighting, Molecules, Energy transfer, Electrons, Quantum efficiency, Light sources and illumination, Excitons, Iridium
We demonstrate efficient (η<sub>p</sub>=11±1 lm/W at 1000 cd/m<sup>2</sup>), bright electrophosphorescent white organic light emitting devices (WOLEDs) employing three dopants in a 9-nm-thick inert host matrix. The emissive layer consists of 2 wt.% iridium (III) bis(2-phenyl quinolyl-N,C<sup>2'</sup>) acetylacetonate (PQIr), 0.5 wt.% <i>fac</i>-tris(2-phenylpyridine) iridium (Ir(ppy)<sub>3</sub>) and 20 wt.% bis(4’,6’-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) co-doped into a wide energy gap <i>p</i>-bis(triphenylsilyly)benzene (UGH2) host. Devices were characterized in terms relevant to both display and general lighting applications, and have a peak total power efficiency of 42±4 lm/W at low intensities, falling to 10±1 lm/W at a drive current of 20 mA/cm<sup>2</sup> (corresponding to 1.4 lm/cm<sup>2</sup> for an isotropic illumination source). The Commission Internationale de l’Eclairage coordinates shift from (0.43,45) at 0.1 mA/cm<sup>2</sup> to (0.38,0.45) at 10 mA/cm<sup>2</sup>, and a color rendering index >75 is obtained. Three factors contribute to the high efficiency: thin layers leading to low voltage operation, a high quantum efficiency blue dopant, and efficient confinement of charge and excitons within the emissive region. The highest occupied and lowest unoccupied energy levels of component layers will be discussed to elucidate charge and exciton confinement within the emissive layer. Additionally, we will explain energy transfer between dopants based on photoluminescent transient analysis of triple-doped thin films.
