20 April 2006 High-efficiency white organic-light-emitting diodes combining fluorescent and phosphorescent emitter systems
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We report on white organic light emitting diodes with three stacked emitter layers comprising the fluorescent blue emitter Spiro-DPVBi, the phosphorescent green emitter system TCTA:Ir(ppy)3 and the phosphorescent red emitter system NPB:Ir(MDQ)2(acac). A thin additional layer of mixed TCTA and TPBi separates the fluorescent and phosphorescent emitting regions, simultaneously confining excitons efficiently and letting electrons and holes easily pass. Furthermore, phosphorescence quenching by Dexter transfer to the non-radiative triplet state of Spiro-DPVBi is suppressed. Devices were optimized to get color coordinates very close to the warm white standard illuminant A. Best devices have a current efficiency of 13.8 cd/A, CIE color coordinates of (0.45, 0.42), and a color rendering index of 91 at a brightness of 1000 cd/m2. Due to the use of electrically doped charge transport layers, the voltage needed for 1000 cd/m2 was only 3.0 V, which leads to a power efficiency of 14.4 lm/W assuming Lambertian emission.
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Gregor Schwartz, Karsten Walzer, Martin Pfeiffer, Karl Leo, "High-efficiency white organic-light-emitting diodes combining fluorescent and phosphorescent emitter systems", Proc. SPIE 6192, Organic Optoelectronics and Photonics II, 61920Q (20 April 2006); doi: 10.1117/12.660524; https://doi.org/10.1117/12.660524

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