Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host
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RESEARCH ARTICLE
Improved stability of blue TADF organic electroluminescent diodes via OXD-7 based mixed host Weiguang LI1,2 , Jie TANG1,2 , Yanqiong ZHENG (✉)1, Junbiao PENG3, Jianhua ZHANG1, †
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Bin WEI (✉)1, Xifeng LI1
1 Key Laboratory of Advanced Display and System Applications of Ministry of Education, School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China 2 School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China 3 State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
© Higher Education Press 2020
Abstract Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have been demonstrated in applications such as displays and solid-state lightings. However, weak stability and inefficient emission of blue TADF OLEDs are two key bottlenecks limiting the development of solution processable displays and white light sources. This work presents a solution-processed OLED using a blue-emitting TADF small molecule bis[4-(9,9-dimethyl-9,10-dihydroacridine) phenyl]sulfone (DMAC-DPS) as an emitter. We comparatively investigated the effects of single host poly(Nvinylcarbazole) (PVK) and a co-host of 60% PVK and 30% 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)1,3,4-oxadiazole] (OXD-7) on the device performance (the last 10% is emitter DMAC-DPS). The co-host device shows lower turn-on voltage, similar maximum luminance, and much slower external quantum efficiency (EQE) rolloff. In other words, device stability improved by doping OXD-7 into PVK, and the device impedance simultaneously and significantly reduced from 8.6 103 to 4.2 103 W at 1000 Hz. Finally, the electroluminescent stability of the co-host device was significantly enhanced by adjusting the annealing temperature. Keywords blue thermally activated delayed fluorescence organic light-emitting diode (TADF OLED), 2,2′-(1,3phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS), stability Received July 14, 2020; accepted October 22, 2020 E-mails: [email protected] (Y. Zheng), [email protected] (B. Wei) †
These authors contribute equally to this work.
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Introduction
Since the first organic light-emitting diode (OLED) was reported by Tang and Vanslyke in 1987 [1], OLEDs have attracted much attention due to their high brightness, flexibility, relative ease of large-scale manufacturing, and potentially higher efficiency and lower cost. Thermally activated delayed fluorescence (TADF) materials have attracted more attention due to the nearly 100% internal quantum efficiency and reduced material price/toxicity. These types of materials are usually based upon donoracceptor units either in a single molecule or in two different molecules forming an exciplex. However, weak stability and inefficient emission of blue TADF OLEDs are two of the key bottlenecks limiting the development of solution processable displays and white light source
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