以咔唑及芴為核心之雙極性磷光主體材料之合成、性質與元件應用

Abstract

本論文於同一分子上加入予體、受體基團，開發具有雙極性或雙偶極性之磷光主體材料，在具有高電洞傳輸特性的咔唑核心之 3、6 位置上，引入具有電子傳輸特性之基團，包括苯並咪唑或噁二唑 (o-Cz2B, m-Cz2B, o-Cz2O)；於芴環核心之9號位上引入兩個相同之高電洞傳輸特性之基團，包含咔唑或三苯胺，2號位則加入一具有電子傳輸特性之基團，為苯並咪唑或噁二唑(F2Cz1B, F2Cz1O, F2TPA1O)。 分子設計將予體與受體基團之間以芴環或苯環為阻隔，利用鄰、間位的連接方式產生扭曲的結構：(1)以理論計算證實能有效增加 HOMO、LUMO 上予體與受體之電子分布差異；(2)增加立障提高材料之熱穩定性；(3)減少分子內予體與受體間之電荷轉移以維持高三重態能量。元件應用上，咔唑為核心的分子中，以m-Cz2B之電洞電子傳輸最為平衡，為一雙偶極性之主體材料，搭配綠色磷光材料Ir(pbi)2(acac)之三層元件的效率最高(ηext=21.7%,ηp= 72lm/W,Lmax=195000 cd/m 2)；而以芴為核心的分子中，F2Cz1B 可搭配黃綠紅三色的磷光材料，元件表現搶眼 (ηext > 16 %)，其中以紅色磷光材料 Ir(NTHU)元件效率最佳 (ηext=19.6%,ηp=14.4 lm/W)，為一深紅色 (CIE =0.66,0.33)磷光元件。

We have designed and synthesized a series of twisted bipolar molecules, o-Cz2B, m-Cz2B, o-Cz2O, F2Cz1B, F2Cz1O, and F2TPA1O, which incorporate hole-transporting unit (D) such as carbazole or triphenylamine and benzimidazole/oxa- diazole as electron-transporting unit (A). The ortho/meta linkages between donor and acceptor and the existence of saturated carbon on fluorene obstruct the conjugation between D and A. DFT calculations show that spatial distributions of the HOMO and LUMO are nearly fully localized at the D and A units, respectively. The result indicates the bipolar hosts possess less intramolecular charge-transfer and improved charge transporting properties. Efficient performance (ηext=19.6%) of a deep-red (CIE=0.66, 0.33) PhOLED is obtained by using F2Cz1B doped with Ir(NTHU). In addition, m-Cz2B exhibits great balance in charge mobility, the green device with Ir(pbi)2acac as dopant shows an extremely high maximum external quantum efficiency, power efficiency and maximum luminance of 21.7%, 72 lm/W, and 195000 cd/m2, respectively.