Phosphorescent OLED device lifetime

Ren, X., Tyan,Y.-S., Madaras, M. et al. 2008. High-efficiency long-lifetime phosphorescent OLED devices based on electron-trapping iridium(III) complexes. SID Inti. Symp. Dig. Tech. Papers 39 864. 

Another large band-gap electron transport host is 3-phenyl-4-(l -naphthyl)-5-phenyl-1,2,4-triazole (TAZ), which has a HOMO (-6.6 eV) and LUMO (-2.6 eV). Using TAZ1 (109) as the host, a maximum EQE (ext) of 15.5% and a luminous power efficiency of 40 lm/W can be achieved in a phosphorescent OLED the value of phosphorescent decay lifetime of 7% Ir(ppy)3 in the TAZ (t-650 ns) is longer than that in CBP (t-380 ns) and the phosphorescence efficiency is approximately proportional to the excited state lifetime [174]. 

Other work by Tsuboyama et al. reported a very highly efficient red PHOLED with power efficiency of 8.0 lm/W at 100 cd/m2 using Ir(piq)3 as a dopant [362], Most exciting, however, is the relatively recent demonstration of exceptional lifetimes for these materials in OLED devices where work from UDC has claimed a 14 cd/A red CIE (0.65, 0.35) with a lifetime of 25,000 h at 500 nit. Such performance promises much for phosphorescent red emitters in commercial devices and even higher efficiencies have been realized in systems that compromise the chromaticity toward the deep red with CIE (0.67, 0.33) and lifetimes >100,000 h at 500 cd/m2 [363],... 

It is clear from the discussion in this section that red phosphorescent OLEDs show excellent device efficiency and operational lifetime and are consequently good candidates for application as red pixels in OLED displays. 

Various high triplet energy ETM such as phenanthrolines and benzimidazoles have been tested in the HBL in CBP + Ir(ppy)3 green phosphorescent OLEDs. 5 However, use of these materials usually resulted in poor device stability. In contrast, green triplet OLEDs with BAlq in the HBL demonstrated long lifetimes vide infra). Similar results were reported for red phosphorescent OLEDs (see Section 14.4.2.1). 

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