Although the electroluminescence (EL) stability of phosphorescent organic light-emitting devices (PHOLEDs) has long been known to depend on the stability of the phosphorescent guest emitter, we recently found that the host also plays an important role. More specifically, we found that interactions between excitons and polarons to result in molecular aggregation of the host material, a phenomenon that appears to play a significant role in the deterioration in efficiency with electrical aging in these devices. The question of whether it is the guest or the host that plays the more leading role in device stability becomes therefore quite relevant. In this work we present data from a comparative systematic study on various host and guest materials used in PHOLEDs. The host materials include CBP, 26DCzPPy and TAPC, and the guest materials include Ir(ppy)3, Ir(ppy)2(acac), Ir(piq)3 and FIrpic. Changes in EL and time resolved photoluminescence characteristics are used in order to understand the interplay between the host and the guest under various electrical and thermal stress conditions. Results suggest that the host plays a more dominant role in determining PHOLED stability. They also shed some light on the interplay between host and guest materials and the effect on device stability. Results from this work will be presented and analyzed.

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Yingjie Zhang and Hany Aziz, "The role of the host versus the guest in the electroluminescence degradation of PHOLEDs (Conference Presentation)," Proc. SPIE 9941, Organic Light Emitting Materials and Devices XX, 99410Q (Presented at SPIE Organic Photonics + Electronics: August 29, 2016; Published: 4 November 2016); https://doi.org/10.1117/12.2237857.5167077770001.