合成含benzimidazole配位基之銥金屬磷光體的樹枝狀分子以及高分子與其在有機發光二極體的應用

Abstract

本論文討論了兩個系列的樹枝狀磷光化合物以及兩個系列的磷光高分子的合成方法，物理性質，以及有機電機發光的元件特性。 1. 樹枝狀磷光化合物 首先我們合成一系列非共軛由Fr□chet-type dendrons構成含benzimidazoles片段的樹枝狀化合物作為配位基，這些化合物可以與三氯化銥以cyclometalation的方式配位，形成具有磷光性質的磷光銥金屬樹枝狀分子（Ir(III)）。儘管外圍片段不同，這些樹枝狀分子的放光皆來自於銥金屬中心的綠色光，並且有很高的磷光量子產率。以旋轉塗佈法製成DLED元件有不錯的成膜性質。當TPBI作電子傳輸層的條件下，可得到不錯的元件效率。第一個系列在元件結構為ITO/ PEDOT:PSS/CBP+ (G2)3Ir (20 wt%)/TPBI/LiF/Al，有最佳元件效率為:ηext,max = 17.6 %,，ηc,max = 61.5 cd/A。相似的結果在第二個系列銥金屬化合物元件結構為ITO/PEDOT:PSS/CBP+ (G2F)3Ir (20 wt%)/TPBI/LiF/Al為結構的元件效率為: ηext,max = 13.6 %,，ηc,max = 45.8 cd/A。以Space-charge-limited current (SCLC)技術測量銥金屬混摻於CBP的薄膜，我們發現電洞的傳輸效率會因為樹枝狀分子的增加而減少。而兩個系列元件效率有些許差異，推估為電洞傳導差異所導致。 2. 磷光高分子 我們利用Suzuki coupling反應合成了以2,8取代的fluorene-dibezothiophene (PFD)，2,8取代fluorene- dibezothiophene-S,S-dioxde （PFDo）以及3,6取代fluorene- 1,4-bis(9-octyl-9H-carbarzol-3yl)-2,5-dioctyloxy-benzene （PFBCB）的高分子系列。部分高分子合成以不同比例的銥金屬於高分子主鏈。這些高分子在液態時，不論分子間與分子內的能量從高分子轉移到銥金屬效率都很差。在固態膜時，則能很明顯的觀察出能量轉移的趨勢與銥金屬含量以及各片段的組成成分有相關性，若D（Do）與BCB片段增加，則能量轉移效率增加。在PL光譜，將銥金屬標準品以摻混的形式於host，能量轉移效率皆高於以銥金屬共價連結於主鏈的高分子。因此，我們推測分子間的能量轉移較分子內能量轉移容易發生。在EL元件，以銥金屬標準品以摻混於host，效率皆高於以銥金屬共價連結於主鏈的高分子。因此我們推測，金屬共價連結於主鏈會導致三重態能量回傳（guest to host）。因此，對元件的效率有不利的影響，因此推測，影響元件效率的最大因素，三重態能量轉移與否以及三重態能量是否回傳有較大的影響性。因此，有較高三重態的高分子有較好的元件效率。另外，我們觀察出以摻混形式相較於將銥金屬共價於高分子主鏈，有較好的元件效率，我們估計是能量轉移效率以摻混系統較佳所致。以旋轉塗佈法製成PLED元件，TPBI當作電子傳輸層的條件下，可得到元件效率：ITO/PEDOT:PSS (70 nm)/10 mol% 34 + PF50D50 (60-80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm)為結構，最佳元件效率為: L = 3697 cd/m2，ηext,max = 2.32 %,，ηp□,max = 2.16 lm/W，ηc,□max = 6.20 cd/A。第二個系列的PLED：ITO/PEDOT:PSS (70 nm)/ 5 mol% 34 + PF50BCB50 (60-80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm)為結構的元件效率為: L = 4874 cd/m2，ηext,max = 4.09 %,，ηc,□max = 10.94 cd/A。在SCLC所量測到的電子、電洞傳導速度顯示，不含銥金屬的高分子在電子、電洞傳輸上皆接近高於一個order。

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□chet-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.