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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 59cd∕A and 58lm∕W, respectively, are obtained, combined with a low driving voltage and high efficiencies even at high brightnesses. At 1000cd∕m2 the efficiencies are as high as 55cd∕A and 49lm∕W.
Rehmann et al. (Mon,) studied this question.