A Method for Improving the Color Purity and Angle-dependent Character of Red Top-emitting Organic Light-emitting Device

Ag was deposited onto Si/SiO2 substrate as anode,4,4,4-tris(3-methylphenylpheny-lamino)-triphenylamine(m-MTDATA):MoOx/m-MTDATA/N,N-bis-(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine(NPB) were used as hole-injected layer and hole-transporting layer,respectively.4,4-N,N-dicarbazole-biphenyl(CBP) doped with(1-(phenyl)isoquinoline) iridium(III) acetylanetonate(Ir(piq)2(acac)) was chosed as emitting layer.4,7-di-phenyl-1,10-phenanthroline(BPhen) worked as hole-blocking layer and electronic-transporting layer.LiF(1 nm)/Al(2 nm)/Ag(20 nm) were composite cathode.In order to improve the outcoupling character of the top-emitting device,an organic CBP layer was introduced above the cathode.Appropriate use of the optical outcoupling layer is helpful for improving the transmittance of the composit cathode film system,and caused the color of the emitting light moved to deep-red region.The angle-dependent properties of the devices were also investigated and the ones with optical outcoupling layer show better performance.And it is very meaningful to the production of high-quality displays.In further study,another 20 nm NPB doped with Ir(piq)2(acac) was introduced to form dual emitting-layer structure,and while the driving voltage of the devices did not significant increase due to the relative high hole mobility of NPB.Meanwhile efficient triplet energy transfer between the host and guest is obtained,the recombination zone is broadened and the non-radiative losses is reduced,seen from the experimental,the current efficiency and color purity are both improved for the dual emitting-layer devices compared with the single emitting-layer structures.