Devices with hole- and electron-transporting mixed host profiles with narrower band-gap materials showed lower driving voltage behavior as well as improved efficiency, where the charge-trapping issue due to host-dopant energy level offset is not significant and efficient Förster energy transfer is satisfied.
The device characteristics of blue phosphorescent organic light-emitting diodes (PHOLEDs) with mixed host structure were investigated by changing the combination and the composition of host materials in emissive layer.
The distributed recombination zone and balanced charge carrier injection within emissive layer were achieved through mixed host optimization with a hole transport-type and an electron transport-type host materials, therefore the device performances were greatly enhanced, with external quantum and power efficiencies of 21.8% and 53 lm/W.
We report an effective means to greatly improve the performance of blue phosphorescent organic light-emitting devices by doping well-known electron- or hole-transporting triplet host material, specifically, 3- 4-biphenyl -4-phenyl-5- 4-tert-butylphenyl -1,2,4-triazole (TAZ) or 4,4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA), into emissive layer to form mixed host structures.
Results are presented both for elastic and inelastic host materials.
Precisely defined heterostructured mixed layer profile, composed of hole-transporting/mixed/electron-transporting host (three layer), showed further improvement of luminous efficiency at high brightness maintaining driving voltage as low as that of simple mixed host device.
Recently the organic electrophosphorescent host materials have attracted increasing attention.
As a novel Mn3+-Mn4+ mixed valence system, hollandite-type compounds with chemical formula A x Mn8O16 (A = K, Rb, Ba, or Pb, etc. and x ≤ 2) have been enthusiastically pursued for their applications in fast ionic conductors, solid state electrolytes, oxidation catalysts, and stable host materials for radioactive ions from nuclear wastes [9 12].
A mixed layer of hole and electron transport materials was used as a host material and an interlayer, reducing the driving voltage of WOLEDs.
The mixed hosts for a new composite electrode can offer an initial efficiency close to 100%.
