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Research On Device Structure And Fabrication Method Of Organic Light-emitting Diodes

Posted on:2017-03-13Degree:MasterType:Thesis
Country:ChinaCandidate:Y M XieFull Text:PDF
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Organic light-emitting diode(OLED) is an emerging flat-panel display and solid-state lighting technology, which have many advantages such as high efficiency, low power consumption, wide color gamut, ultra-thin structure, flexibility etc.. Therefore, OLED has a wide range of applications ranging from mobile and large-sized TV displays, wearable and flexible display to energy saving and healthcare oriented lighting. Though numerous OLED products(Samsung Galaxy smartphone and tablet series, Apple watches, LG curved TVs, etc.) are already available in the market, achieving high-efficiency, long-lifetime and low-cost white OLEDs(WOLEDs) are still challenging issues. To obtain high-efficiency devices, phosphorescent OLED(PhOLED) which fully utilizes both the triplet and singlet excitons and hence acquires 100 % of internal quantum efficiency is one of the best solutions. While green and red-emitting PhOLEDs have very high device efficiency and operational stability, blue-emitting PhOLED has drawbacks of moderate efficiency and very short lifetime. In order to achieve efficient blue emission, the blue phosphorescent emitters should have high triplet energy. As such, host materials with higher triplet energies than the blue guest materials are needed. Other crucial factors, such as the energy alignment with the neighboring charge-transport materials, thermal stability, etc., should also be considered. Therefore, design and synthesis of high-performance phosphorescent blue hosts are of urgent needs for the improvement of phosphorescent white OLEDs(PhWOLEDs).In the meantime, small-molecule based OLEDs are generally fabricated by thermal evaporation under ultra-high vacuum. The high manufacturing cost arisen from the expensive high-vacuum deposition equipment and relatively complex device fabrication process are the obstacles for OLED commercialization. Thus, exploring simple and low-cost OLED fabrication methods have long been the goals in the OLED community.In this project, device engineering of the newly synthesized hosts and exploration of a new and low-cost device fabrication method are of the main focuses.In order to improve the performance of blue and white-emitting PhOLEDs, a new host material based on bicarbazole group and triphenylsily moiety, BCz-Si, is designed. The BCz-Si based blue Ph OLED using FIrpic as the dopant material was fabricated. The device exhibited a maximum external quantum efficiency of 21 %, corresponding to a current efficiency and power efficiency of 46.5 cd/A and 45.8 lm/W, respectively. Two-color based and three-color based PhWOLEDs utilizing BCz-Si as the host material were also fabricated. They showed current efficiencies of 70.5 cd/A and 50.1 cd/A, respectively. To further optimize the material, two other new hosts, namely BCz-DBT and BCz-DBF, were also synthesized. The BCz-DBT and BCz-DBF based blue PhOLEDs exhibited external quantum efficiency of 25 % and 21.4 % respectively.In addition, this project explores dip-coating as a low-cost method to fabricate solution processed OLEDs. Highly efficient, large-area green-emitting fluorescent and thermally activated delayed fluorescent(TADF) OLEDs are successfully demonstrated. The device performance and morphology of the prepared films are correlated with the dipping rate. The devices based on dip-coating are benchmarked with those fabricated by traditional spin-coating method.
Keywords/Search Tags:organic light-emitting diodes, high efficiency, host material, dip-coating method, thermally activated delayed fluorescence, life-time
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