Synthesis of Dendrimers and Copolymers Containing Benzimidazole-Based Iridium Complexes and Their Application of Organic Light-Emitting Diodes

• Main Authors: Huang, Wei-Sheng, 黃偉聖
• Other Authors: Lin, Hong-Cheu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/15952900048191782683

博士 === 國立交通大學 === 材料科學與工程系所 === 98 === The syntheses, physical properties and device characteristics of novel series of phosphorescent dendrimers and novel series copolymers of electroluminencent materials were discussed in this thesis. 1. Phosphorescent dendrimers A series of novel non-conjugated Fr�繁het-type functionalized benzimidazole-based dendrimers containing peripheral benzyl ether and fluorenyl surface groups have been synthesized and characterized. These compounds undergo cyclometalation with iridium trichloride to form iridium(III) complexes. These iridium dendrimers were green-emitting with high phosphorescence quantum yield, and can be spin-coated as films of good quality. With a device configuration of ITO/PEDOT:PSS/(G2)3Ir 20 wt% + CBP/TPBI/LiF/Al had a maximum external quantum efficiency (EQE) of 17.6% and a maximum current efficiency of 61.5 cd/A. Similar, the device structure with ITO/PEDOT:PSS/(G2F)3Ir 20 wt% + CBP/TPBI/LiF/Al has a maximum external quantum efficiency of 13.6% and a maximum current efficiency of 45.8 cd/A. Space-charge-limited current (SCLC) flow technique was used to measure the mobility of charge carriers in the blend films of the compounds in CBP. Blend films of higher generation dendrimers had lower hole mobility, albeit with higher device efficiencies. 2. Phosphorescent polymers Dibenzothiophene-co-fluorene (PFD), dibenzothiophene-S,S-dioxde-co-fluorene (PFDo) and 1,4-bis(9-octyl-9H-carbarzol-3yl)-2,5-dioctyloxy-benzene-co-fluorene (PFBCB) were synthesized by Suzuki coupling reaction. Some copolymers with various mol% of iridium complexes covalently bonded in polymer backbones were also synthesized. The efficiency of both intramolecular and intermolecular energy transfer was inefficient in the solution for Ir-copolymers. In contrast, there was efficient and prominent intermolecular energy transfer in the solid films. The relative intensities of phosphorescence and fluorescence were affected by the efficiency of energy transfer from copolymers to the iridium moiety. The efficiency of energy transfer appeared to be higher as D (Do) and BCB ratio in the polymer backbones increased. Compared with Ir-copolymers, the Ir-doped copolymers doped with a small iridium complex (compound 34) showed a better energy transfer efficiency, which suggested that intermolecular energy transfer was more facile than intramolecular energy transfer. PLED devices were fabricated using metal-free copolymers, Ir-copolymera, and Ir-doped copolymers with model iridium complexes, respectively. The EL efficiencies of phosphorescent devices increased with the host allowing efficient energy transfer from host to guest, and possessing higher triplet energy level to suppress the back energy transfer. With a device configuration: ITO/PEDOT:PSS/P3 dopant 10 mol% 34/TPBI/LiF/Al has a maximum external quantum efficiency (EQE) of 2.32% and a maximum current efficiency of 6.20 cd/A. With a device configuration: ITO/PEDOT:PSS/P17 dopant 5 mol% 34/TPBI/LiF/Al has a maximum external quantum efficiency (EQE) of 4.09% and a maximum current efficiency of 10.94 cd/A. Space-charge-limited current (SCLC) flow technique was used to measure the mobility of charge carriers in the solid film of these copolymers. The hole and electron mobility decreased with increasing content of the iridium complex.