Multi-Resonance Emitters (MREs) are a promising candidate for fulfilling the harsh requirements of display applications due to their unique photophysical properties. Recently, MREs have been widely used as a Terminal Emitter (TE) in Hyper Fluorescence Organic Light-Emitting Diodes (HF-OLEDs); however, since MREs are always TADF-active, possessing long triplet lifetimes in milli-second order, they result in severe chemical degradation. The device lifetime of blue OLED is still a challenge. Here, instead of shortening the delayed lifetime of MREs by molecular design, we introduced a low-triplet pyrene unit into an MRE scaffold to achieve narrowband emission and quick removal of triplets in MREs simultaneously. Blue HF-OLED based on the non-TADF MRE demonstrated a high external quantum efficiency (EQE) of 20% and a ten-fold improvement in stability, compared to those of the HF-OLEDs with standard MREs.
Organic light-emitting diodes (OLEDs) are a promising light-emitting technology useful for various display applications1,2. Despite great progress in this field3-12, there is an ongoing challenge to realize high performance blue OLEDs with efficiency, good color purity, and device lifetime. Here, we report pure-blue (CIEx,y color coordinates of [0.13, 0.16]) OLEDs with high-efficiency (external quantum efficiency of 32 % at 1000 cd m–2 ), narrow-emission (full width half maximum of 19 nm), and good stability (LT95 of 18 hours at an initial luminance of 1000 cd m–2 ). The design is based on a two-unit stacked tandem hyperfluorescence (HF)-OLED with an improved singlet-excited energy transfer process from a sky-blue TADF assistant dopant (AD) (HDT-1) to a pure-blue terminal emitter (TE) (v-DABNA). Furthermore, the effect of dopant concentration of terminal emitter on the device performance of hyperfluorescence OLEDs is studied. Device shows a better color purity when dopant concentration is increased. On the other hand, new hyperfluorescence OLEDs have been fabricated, in which device stability has been extended with a new molecular design of TE.
Recently, we reported the accurate rate equation set to analyze the kinetics of three-state photophysics for the thermally activated delayed fluorescence (TADF) materials. The accurate rate constant could be estimated with the simple equation approximated to be no phosphorescence in emission, and the non-radiative decay rate was resulted to be 0. Therefore, the rate constants should be provided as the possible ranges when it is necessary to consider the non-radiative decay from triplet etc. In here, we introduce how analyze the actual emission decays profile which be fit with not only the bi- but also tri-exponential curves to analyze TADF.
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