Browsing by Author "Niu, Mu-Chun"

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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
;
Yang, Lan-Sheng
;
Su, Hsiao-Tso
;
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.
High-mobility polymer space-charge-limited transistor with grid-induced crystallinity
(2011-01-01)
Chao, Yu-Chiang
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Niu, Mu-Chun
;
Zan, Hsiao-Wen
;
Meng, Hsin-Fei
;
Ku, Ming-Che
The vertical mobility of a polymer film prepared on a textured substrate is enhanced from 10 (5) cm(2)/Vs to 10 (3) cm(2)/Vs by a slow drying process which is unattainable in planar substrate. Highly ordered structure is observed for polymer film treated with high-boiling-point solvent and slow solvent annealing. The enhanced vertical mobility enables the polymer space-charge-limited transistor (SCLT) capable of outputting current density as high as 100 mA/cm(2) while maintaining good current gain and on-off ratio. Such vertical transistor is able to drive high-power devices or mechanical actuator in large-area and flexible array. (C) 2010 Elsevier B. V. All rights reserved.
Leakage-free solution-processed organic light-emitting diode using a ternary host with single-diode emission area up to 6 x 11.5 cm(2)
(2019-01-01)
Liao, Si-Yi
;
Su, Hsiao-Tso
;
Hsiao, Yung-Hung
;
Chang, Yu-Fan
;
Chang, Chiung-Wen
The electrical current leakage and stability are studied for solution-processed OLEDs with areas of 4.45 mm(2), 3 x 3.2 cm(2), and 6 x 11.5 cm(2). The emission layer of the OLED has a ternary or binary mixed host with hole-transporting molecules tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), together with the electron-transporting molecule 2,7-bis(diphenylphosphoryl)-9,9-spirobi[fluorene] (SPPO13). The phosphorescent emitters are Ir(mppy)(3) for green and bis[4-(4-tert-butylphenyl)thieno[3,2-c]pyridine][N,N-diisopropylbenamidinato]iridium(iii) (PR-02) for orange. Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-sec-butylphenyl))diphenylamine)] (TFB) is used as the hole transport layer and PEDOT:PSS is used as the hole injection layer. On top of the emission layer, CsF/Al is deposited by thermal evaporation as the cathode. All organic layers are deposited by blade coating and the initial current leaking defects can be avoided by careful control of the coating conditions. The detrimental burning point caused by a local current short developed after long-time operation can be avoided by reducing the operation voltage using a ternary mixed host. The operation voltage is only 4 V at 100 cd m(-2) and 5 V at 250 cd m(-2) for the green emitting device. Furthermore, the crystallization defect is reduced by the ternary host. For the orange emitting device, the binary host is good enough with an operating voltage of 5 V at 100 cd m(-2). For an area as large as 6 x 11.5 cm(2), the OLED shows good stability and there is no burning point after an operation of over 1600 hours.