Blue emitting exciplex for yellow and white organic light‑emitting diodes

White organic light-emitting diodes(WOLEDs)have several desirable features,but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures.Herein,we investigate a standard blue emitting hole transporting material(HTM)N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine(NPB)and its exciplex emission upon combining with a suitable electron transporting material(ETM),3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole(TAZ).Blue and yellow OLEDs with simple device structures are developed by using a blend layer,NPB:TAZ,as a blue emitter as well as a host for yellow phosphorescent dopant iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate(PO-01).Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units.The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer(CGL).Judicious choice of the spacer prevents exciton difusion from the blue emitter unit,yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation.This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission.The overall white light emission properties are enhanced,achieving CIE coordinates(0.36,0.39)and color temperature(4643 K)similar to daylight.Employing intermolecular exciplex emission in OLEDs simplifes the device architecture via its dual functionality as a host and as an emitter.

An external quantum efficiency of>20%from solutionprocessed poly(dendrimer)organic light-emitting diodes

Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode(OLED)research,with external quantum efficiencies(EQEs)of>30%being reported for phosphorescent emitters.These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III)complexes blended with a host and additional layers to balance charge injection and transport.Large area OLEDs for lighting and display applications would benefit from low-cost solution processing,provided that high EQEs could be achieved.Here,we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III)complexes forming the cores of firstgeneration dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices.Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of>20%at luminances of up to≈300 cd/m^(2),showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.