22 September 2015 Long-lived and highly efficient green and blue phosphorescent emitters and device architectures for OLED displays
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Abstract
In this paper, two OLED device concepts are introduced. First, classical phosphorescent green carbene emitters with unsurpassed lifetime, combined with low voltage and high efficiency are presented and the associated optimized OLED stacks are explained. Second, a path towards highly efficient, long-lived deep blue systems is shown. The high efficiencies can be reached by having the charge-recombination on the phosphorescent carbene emitter while at the same time short emissive lifetimes are realized by fast energy transfer to the fluorescent emitter, which eventually allows for higher OLED stability in the deep blue.

Device architectures, materials and performance data are presented showing that carbene type emitters have the potential to outperform established phosphorescent green emitters both in terms of lifetime and efficiency. The specific class of green emitters under investigation shows distinctly larger electron affinities (2.1 to 2.5 eV) and ionization potentials (5.6 to 5.8 eV) as compared to the "standard" emitter Ir(ppy)3 (5.0/1.6 eV). This difference in energy levels requires an adopted OLED design, in particular with respect to emitter hosts and blocking layers. Consequently, in the diode setup presented here, the emitter species is electron transporting or electron trapping.

For said green carbene emitters, the typical peak wavelength is 525 nm yielding CIE color coordinates of (x = 0.33, y = 0.62). Device data of green OLEDs are shown with EQEs of 26 %. Driving voltage at 1000 cd/m2 is below 3 V. In an optimized stack, a device lifetime of LT95 > 15,000 h (1000 cd/m2) has been reached, thus fulfilling AMOLED display requirements.
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Christian Eickhoff, Christian Eickhoff, Peter Murer, Peter Murer, Thomas Geßner, Thomas Geßner, Jan Birnstock, Jan Birnstock, Michael Kröger, Michael Kröger, Zungsun Choi, Zungsun Choi, Soichi Watanabe, Soichi Watanabe, Falk May, Falk May, Christian Lennartz, Christian Lennartz, Ilona Stengel, Ilona Stengel, Ingo Münster, Ingo Münster, Klaus Kahle, Klaus Kahle, Gerhard Wagenblast, Gerhard Wagenblast, Hannah Mangold, Hannah Mangold, } "Long-lived and highly efficient green and blue phosphorescent emitters and device architectures for OLED displays", Proc. SPIE 9566, Organic Light Emitting Materials and Devices XIX, 95662N (22 September 2015); doi: 10.1117/12.2199079; https://doi.org/10.1117/12.2199079
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