Highly efficient solution-processed phosphorescent multilayer organic light-emitting diodes based on small-molecule hosts

The authors report on highly efficient phosphorescent organic light-emitting diodes (OLEDs) based on a low-molecular weight electron-conducting, bis-spirobifluorene host doped with a soluble derivative of the green emitter fac-tris(2-phenylpyridine) iridium (III) [Ir(ppy)(3)]. All organic layers were spin coated and a strong improvement of performance was achieved by introduction of a hole-transporting double layer based on cross-linkable low-molecular weight molecules. The devices combine the easy fabrication procedure known from polymer-based OLEDs with the higher efficiency of small molecules. Maximum luminous and power efficiencies of 59 cd/A and 58 lm/W, respectively, are obtained, combined with a low driving voltage and high efficiencies even at high brightnesses. At 1000 cd/m(2) the efficiencies are as high as 55 cd/A and 49 lm/W. (C) 2007 American Institute of Physics.