Dustin L. Comfort

Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes

We demonstrate highly efficient white and nonwhite hybrid organic light-emitting diodes (OLEDs) in which singlet and triplet excited states, generated in the recombination zone, are utilized by fluorescence and phosphorescence, respectively. The excited states are formed at a blue fluorescent light-emitting layer (LEL), and the triplets diffuse through a spacer layer to one or more phosphorescent LEL(s). A key feature enabling the triplet diffusion in such OLEDs is the use of a blue fluorescent emitter with triplet energy above, or not much below, that of the fluorescent host. Additional material properties required for triplet harvesting are outlined. At 1000 cd/m2 a blue and yellow harvesting OLED shows 13.6% external quantum efficiency, 3.8 V, 30.1 lm/W, and color characteristics suitable for display application. High-efficiency harvesting R+G+B white, and B+G and B+R nonwhite OLEDs are also demonstrated. The triplet-harvesting mechanism was verified in all devices by physical methods including spectra...

17.3: Highly Efficient Fluorescent/Phosphorescent OLED Devices Using Triplet Harvesting

We demonstrate efficient white and non-white hybrid OLED devices operating by a triplet harvesting mechanism to create light. Triplet excited states are generated in a blue fluorescent light-emitting layer (LEL) and utilized upon their diffusion to the phosphorescent LEL(s). At 1000 cd/m2 a blue/yellow hybrid OLED device shows external quantum efficiency (EQE) of 13.6%, 3.8 V, 30.1 lm/W, and excellent color characteristics suitable for display application. Performance of non-white-emitting hybrids, RGB white, and a tandem hybrid device is discussed. The triplet harvesting mechanism in all hybrid devices was verified by several experimental methods (spectral analysis, time-resolved electroluminescence (EL), magnetic field effect on EL).

23.3: Distinguished Paper: High‐Efficiency Tandem Blue OLEDs

Tandem blue OLEDs using different fluorescent dopants have achieved 20 cd/A (CIEx,y = 0.14, 0.18) and 38 cd/A (CIEx,y = 0.15, 0.42) with external quantum efficiencies higher than 11%. The tandem blue OLEDs include two electroluminescent units that are connected in series with an organic intermediate connector. At an initial brightness of 1,000 cd/m2, the drive voltage of the devices can be less than 6.5 V, and the operational lifetime (T 50) of the devices is estimated to be greater than 10,000 h. We also demonstrate that the selection of electron-transporting material and an intermediate connector have significant impact on the electroluminescence performance of the tandem blue OLEDs.

P-149: Effect of Organic Hole-Injecting Buffer Layer on Stability of Organic Light-Emitting Diodes

Lifetimes of blue fluorescent and red phosphorescent OLEDs are improved by the presence of an organic buffer layer between the oxygen-plasma-treated ITO and a hole-injecting layer of HAT-CN. Possible explanations are discussed.