Ideal host and guest system in phosphorescent OLEDs

Ideal host-guest system for emission in phosphorescent OLEDs with only 1% guest doping condition for efficient energy transfer have been demonstrated in the present investigation. Using a narrow band-gap fluorescent host material, bis(10-hydroxybenzoh] quinolinato)beryllium complex (Bebq₂), and red dopant bis(2-phenylquinoline)(acetylacetonate)iridium (Ir(phq)₂acac), highly efficient red phosphorescent OLEDs (PHOLEDs) exhibiting excellent energy transfer characteristics with a doping concentration of 1% were developed. Fabricated PHOLEDs show a driving voltage of 3.7 V, maximum current and power efficiencies of 26.53 cd/A and 29.58 lm/W, and a maximum external quantum efficiency of 21%. Minimized electron or hole trapping at the phosphorescent guest molecules and efficient Förster and Dexter energy transfers from the Bebq₂ host singlet and triplet states to the emitting triplet of Ir(phq)₂acac guest appear to be the key mechanism for ideal phosphorescence emission.