We present a comprehensive model to analyze, quantitatively, and predict the process of degradation of OLEDs considering polaron, exciton, exciton–polaron interactions, exciton–exciton interactions and a newly proposed impurity effect. The loss of efficiency during degradation is presented as a function of quencher density. The density and generation mechanisms of quenchers are extracted using a voltage rise model. The comprehensive model is applied to stable blue phosphorescent OLEDs, and the results show that the model describes the voltage rise and external quantum efficiency loss very well, and that the quenchers in emitting layer are mainly generated by polaron-induced degradation of dopants. Quencher formation was confirmed from a mass spectrometry. The polaron density per dopant molecule is reduced by controlling the emitter doping ratio, resulting in the highest reported LT50 of 431 hours at an initial brightness of 500 cd/m2 with CIEy<0.25 and high EQE>18%.
Recently all-organic thermally activated delayed fluorescent (TADF) emitters have attracted great attention. In TADF emitters, nonemissive triplet states can be also harvested via population of emissive singlet states through reverse intersystem crossing (RISC). The RISC can be induced by the small energy gap between the lowest singlet (S1) and triplet (T1) states. Due to this ability of TADF, 100% internal quantum efficiency and high maximum external quantum efficiency (EQEmax) comparable to those of phosphorescent organic light emitting diodes (OLEDs) have been already reported in TADF OLEDs. In this study, we demonstrate high efficiency TADF OLEDs which are attributed to employing triazine acceptor type TADF compounds having high RISC rates(kRISC).
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