We have presented a physical concept for enhancing efficiency and lifetime of doped electrophosphorescent organic light-emitting devices. In order to provide a control parameter for higher device performance, a stepwise doping concentration profile at the emission layer was prepared. A more than 30% improvement of power efficiency was obtained for green electrophosphorescent device with a higher doping ratio at the emission layer-hole transport layer interface. We explained the carrier trapping and transport mechanism with direct recombination of an exciton in an iridium-based dopant system. When compared to green device, phosphorescent red devices showed a more significant charge trapping effect at low doping concentration, which is responsible for shifting the recombination zone far from the emission layer-hole transport layer interface. Therefore, charge trapping by doping control in an emission layer could be utilized for a charge-balancing technique for the confinement of a triplet exciton.
[5] Decreasing the temperature, two regimes are successively observed: i) a one-dimensional regime where the physics of the electron gas presents a lack of quasi-particle states at the Fermi energy accompanied by the existence of separate collective modes for spin and charge degrees of freedom: a) J. Voit, Rep. Prog. Phys. 1995, 58, 977; and ii) a temperature domain where interchain couplings become relevant leading to long range ordered phases: b) T. Lorenz, M. Hofmann, M. Grüninger, A. Freimuth, G. S. Uhrig, M. Dumm, M.
The addition of methacryloxypropyltrimethoxysilane to poly(3,4‐ ethylenedioxythiophene) has enabled laser‐induced thermal imaging (LITI) of polymer light‐emitting materials on a hole‐transport layer (see Figure for example). The I–V–L (current–voltage–luminance) performances of the device patterned by the LITI process are comparable to those of typical spin‐coated devices.
We have developed a novel color patterning method for the fabrication of large format full‐color OLEDs. Laser Induced Thermal Imaging (LITI) is a laser addressed high resolution thermal patterning process with unique advantages such as excellent transfer film thickness uniformity, multilayer stack transfer ability, and scalability to large‐size mother glass. LITI patterning of small molecule materials produces OLEDs that are comparable in performance to conventional evaporated devices. Using the technology, we fabricated 2.2″ full color active matrix OLEDs.
We have developed a new color patterning method for the patterning of full color polymer light-emitting devices. Laser Induced Thermal Imaging (LITI) involves the imagewise exposure of a thermal transfer film with a scanning near infrared laser. During the process, light emitting polymer (LEP) is transferred from a thermal film to a circuitized substrate. Using the technology, we fabricated a 3.6" QVGA full color active matrix polymer light-emitting device (PLED).
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