Browsing by Author "Yang, Lan-Sheng"

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All-Solution-Processed Red and Orange-Red Organic Light-Emitting Diodes with High-Efficiencies: The Effect of Mixed-Host Emissive Layers and Thermal Annealing Treatment
(2019-09-01)
Chang, Yu-Fan
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Yang, Lan-Sheng
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Su, Hsiao-Tso
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Liao, Si-Yi
;
Niu, Mu-Chun
The instability of the organic light-emitting diodes (OLEDs) during operation can be attributed to the existence of point defects on the organic layers. In this work, the effect of mixed-host emissive layer and the thermal annealing treatment were investigated to eliminate defects and to boost the device performance. The mixed-host system includes 4,4 ',4 ''-tri (9-carbazoyl) triphenylamine (TCTA) and 2,7-bis(diphenylphosphoryl)-9, 9 '-spirobi[fluorene] (SPPO13). The mixed-host emissive layer with thermal annealing treatment showed low roughness and few pinholes, and the devices fabricated from this emissive layer exhibited high efficiencies, high stabilities, and long lifetimes. The red and orange-red OLEDs exhibited efficiencies of 13.9 cd/A and 24.35 cd/A, respectively. The longest half-lifetime (L-0=500 cd/m(2)) of the red and orange-red OLEDs were 158 h and 180 h, respectively. Efforts were made to solve problems in large-area coating and to reduce the number of defects on in organic layer. Large-active-area (active area=3 cmx4 cm) red phosphorescent OLEDs (PhOLEDs) devices were realized with very high current efficiency up to 9 cd/A.
Stable and efficient blue fluorescent organic light-emitting diode by blade coating with or without electron-transport layer
(2017-12-01)
Yang, Lan-Sheng
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Meng, Hsin-Fei
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Chang, Yu-Fan
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Lien, Cheng-Hsin
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Zan, Hsiao-Wen
Multi-layer small-molecule blue fluorescent organic light-emitting diode (OLED) is fabricated by blade coating. The emission layer is based on a mixed host of 1-(7-(9,90-bianthracen-10-yl)-9,9-dioctyl-9H-fluoren- 2-yl) pyrene (PT-404) and electron-transport material 2,7-Bis(diphenylphosphoryl)-9,90 -spirobifluorene (SPPO13), and the blue guest emitter is 4-40-(1E, 10E)-2,20-(naphthalene-2,6-diyl) bis(ethane-2,1diyl) bis(N, N-bis(4-hexyl-Phenyl) aniline) (Blue D). A hole-transport layer of Poly-(9, 9-dioctylfluorenyl2, 7-diyl)-co-(4, 4-(N-(4-sec-butylphenyl)) diphenylamine) (TFB) is added on top of PEDOT: PSS anode. The electrons are blocked away from TFB by a layer of pure host emission layer of PT-404 between TFB and the mixed ehost emission layer. For the devicewith the electron transport layer of Tris(8-hydroxyquinolinato) aluminum (Alq3) blade-coated over the emission layer the efficiency and lifetime at initial brightness of 500 cd m(-2) are 7.5 cd A(-1) and 150 h for Alq3/CsF/Al cathode. When the Alq3/CsF/Al is replaced by simply CsF/Al over the mixed-host emission layer the efficiency and lifetime are 6.4 cd A(-1) and 300 h (2 times longer than that of the Alq3/CsF/Al cathode). The lifetime depends on the electron-hole balance tuned by the mixed-host blending ratio as well as the electron injection from the cathode. This work shows good stability is possible for all-solution-processed blue OLED. (C) 2017 Published by Elsevier B.V.
The influence of the interfacial layer on the stability of all-solution-processed organic light-emitting diodes
(2020-08-04)
Yang, Lan-Sheng
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Meng, Hsin-Fei
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Chao, Yu-Chiang
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Huang, Hu-Chi
;
Luo, Chih-Wei
Improving the stability of large-area organic light-emitting diodes is very important for practical applications. The interfacial layer plays a crucial role to improve the electron injection characteristic. In this work, devices prepared by various solution-processed interfacial materials and thermal-evaporated CsF were compared. In the devices with active area of 2.25 mm x 2.25 mm, we found that the performance and lifetime of the device with solution-processedLiqinterfacial layer was comparable with the device with thermal-evaporated CsF. However, for the devices with active area of 2.4 cm x 3.7 cm, the device based on thermal-evaporated CsF was the champion in both performance and lifetime. The influence of the thickness of CsF on the stability was investigated. The most stable blue fluorescent devices can be achieved when the thickness of CsF is about 0.1 nm, while the most stable green phosphorescent devices can be obtained by depositing 0.2 nm CsF. The best current efficiency for the blue fluorescent device is 4 cd A(-1), while the best one for the green phosphorescent device is 22 cd A(-1). Furthermore, burning points causing the failure of the devices were investigated by scanning electron microscopy, atomic force microscopy, thermography and secondary ion mass spectrometry. We demonstrated that burning points are defects, which can be observed after long-time operation, showing higher local temperature and fragmentary electrode.