Phosphorescent OLED device green triplet

As an extension of the fluorescent sensitizer concept, Forrest et al. have applied this approach to phosphorescent OLEDs, in which the sensitizer is a phosphorescent molecule such as Ir(ppy)3 [342]. In their system, CBP was used as the host, the green phosphor Ir(ppy)3 as the sensitizer, and the red fluorescent dye DCM2 as the acceptor. Due to the triplet and the singlet state energy transfer processes, the efficiency of such devices is three times higher than that of fluorescent sensitizer-only doped device. The energy transfer processes are shown in Figure 3.21. 

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). 

Nakayama et al. reported highly efficient and stable single-stack white phosphorescent OLEDs based on blue triplet emitter KMBD-342 described in Section 14.4.2.3. Yellow-green (YD-85) and red (RD-61) dopants used in the device were provided by Universal Display Corporation. The device layer structure was as follows Light outcoupling film ITO HIL HTL green EML red EML I blue EML HBL n-doped ETL A1. At 1000cd/m the performance... 

In their follow-up paper, they also demonstrated 100% efficient energy transfer of both singlet and triplet excited states. The device exhibits peak external efficiency and power efficiency of 25 cd/A and 17 lm/W at 0.01 mA/cm2, respectively [343]. Liu demonstrated a high-efficiency red OLED employing DCJTB as a fluorescent dye doped in TPBI with a green phosphorescent Ir(ppy)3 as a sensitizer. A maximum brightness and luminescent efficiency of... 

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