Voltage reduction (2.4 V at 2 mA/cm 2 ) and efficiency improvement (7-times) were demonstrated in blue QLEDs by positive aging process, which came from (1) improvement of carrier injection at ZnO/QD interface and/or carrier transport in QD layer, and (2) enhancement of PLQY of QD emissive layer.
KeywordsQLED; blue emission; high efficiency; positive aging. P-108 / W.-C. Ding SID 2018 DIGEST • 1623
Optical sensors with high oxygen sensitivity and efficient deep-blue OLEDs with CIEy of 0.08 was developed using the simplicity in molecular design of di-tert-butyl-dimethylacridanyl disubstituted oxygafluorene.
We have demonstrated that degradation of the hole-transporting layer material in the blue quantum-dot light-emitting diode (QLED) is the main reason accounts for the efficiency loss operated under constant current driving, and the operation lifetime can be elongated by 85% under pulse-mode driving compared to DC case.Keywords QLED, blue emission, lifetime. Figure 3. (a) PL spectra of QLED excited at 340 nm. PL spectra of QLED excited at 420 nm with different HTL thickness: (b) 0 nm, (c) 7 nm, (d) 14 nm, and (e) 28 nm.Figure 4. Enhancement factor for the QLED drive by pulsemode with 10 kHz and different duty cycle.
We have demonstrated a high efficiency blue quantum‐dot light‐emitting diode (QLED) with positive aging treatment. While device was statically stored 602 hrs, the external quantum efficiency (EQE) of QLED increased from 4.8% to 7.8%, which resulted from the enhancement in electron injection at quantum dot (QD)/ electron transporting layer (ETL) interface. It was confirmed by the measurement of the depth profile of X‐ray photoelectron spectroscopy (XPS). It indicated that cathode material, aluminum (Al), diffused into ETL material, zinc oxide (ZnO), leading to aluminium zinc oxide (AZO) alloy, Al doped ZnO.
The carbazole of a model compound CPTBF was replaced by αand β-carboline to give donors α-CPTBF and β-CPTBF, respectively. The introduction of carboline leads the new donors to have deeper highest occupied molecular orbital (HOMO) energy levels. Different electron acceptors were tested, among them, a new acceptor, 3,4-CN, was found to give exciplexes with efficient green emissions that are blue-shifted as compared to that of model CPTBF:3,4-CN system. The exciplex formations of α-CPTBF:3,4-CN and β-CPTBF:3,4-CN blends were verified with the significantly red-shifted emissions different from those of constituent donor and acceptor together with the delayed fluorescent observed by time-resolved PL decay experiments. The organic light-emitting diode (OLED) devices with α-CPTBF:3,4-CN and β-CPTBF:3,4-CN blends as the emitting layer showed a maximum external quantum (EQE) of 7.57 and 7.34%, respectively, which is higher as compared to that (EQE = 6.87%) of the model device employing CPTBF:3,4-CN. These results were attributed to the higher exciplex photoluminescence quantum yields due to the higher delay fluorescence components, deeper HOMO, and higher triplet energy of the carboline donors. In addition, the β-CPTBF:3,4-CN exciplex-based OLED exhibited better efficiency roll-off at higher luminesce due to more charge balance with less polaron formation, which was analyzed with time-resolved EL.
High efficiency (EQE=30.15%) organic light emitting diode (OLED) was demonstrated by lightly doping the thermally activated delayed fluorescence (TADF) emitter (0.5%) into the TADF host, resulting from: (1) efficient energy transfer from host to dopant, (2) long exciton diffusion length in host, and (3) rare concentration quenching due to lightly-doped condition.
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