No abstract

Multilayer organic light-emitting devices with phosphorescent guest emitter, tris(2-phenylpyridine) iridium doped in a host 4,4′-N,N′-dicarbazol-biphenyl layer were prepared. The device with the 6.5 wt% guest emitter exhibited external quantum efficiency and power luminous efficiency of 13.7% and 38.3 lm/W, respectively at the luminance of 105 cd/m2 driven at the voltage of 4.0 V and current density of 0.215 mA/cm2. The half decay lifetime under continuous constant-current driving for the initial luminance of 500 cd/m2 was 170 h.

No abstract

No abstract

Multilayer organic light-emitting device with phosphorescent guest emitter, tris(2-phenylpyridine)iridium (Ir(ppy)) doped in a host 4,4'-N,N'-dicarbazol-biphenyl (CBP) layer, exhibited very high luminous efficiency. A device having such phosphorescent guest emitter could not offer sufficiently long driving lifetime required by real products. On the other hand, phosphorescence in organic molecules rarely occurs at room temperature. We studied ways to increase driving lifetime by three types of experiments. First, we investigated to see whether the driving lifetime is dependent on guest molecule concentration. Second, we inserted Copper phtalocyanine (CuPc) between Indium Tin Oxide (ITO) anode and hole transport layer, 4,4'-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (NPB) to prevent driving voltage from rising during constant current operation. Finally, we exchanged the hole blocking layer, which is 2,9-dimethyl-4,7-diphenyl-1,1O-phenanthroline (BCP), for ((1 ,1 '-biphenyl)-4-olato)bis(2-methyl-8-quinolinolato N1,08)aluminum (BA1q). Optimizing all of the above mentioned steps, we can expect the half decay lifetime of 20000 hours or over at an initial luminance of lOOcd/m2 by constant current driving.