有機電化學發光元件之高能隙離子性材料及載子平衡研究

Abstract

在本論文中，我們研究有機電化學發光元件之高能隙離子性材料及載子平衡，在第一章中，我們簡介電化學發光元件原理及發展現況。接下來研究內容主要分為下列幾個部分: 一、在第二及第三章中，利用與台大化學系汪根欉教授合作並由其合成之新穎三芴及二芴離子性衍生物製造出第一個深藍光及紫外光電化學發光元件，並利用載子平衡理論進行元件效率優化，有效提昇元件效能。 二、在第四章中，我們利用電化學發光元件之主客體系統進行元件效率優化工程，並使用深藍色三芴離子性衍生物為載子傳輸主體及紅色離子性銥錯合物為載子捕捉客體，此主客體系統擁有高效率能量傳輸機制，可使用極低濃度之客體搭配主體，有效調整元件載子平衡，並大幅抑制自我猝熄效應，使整體元件效能達到理想元件之特性。 三、在第五章中，我們藉由載子平衡理論基礎，利用藍色離子性銥錯合物為主要材料，並由相關文獻的回顧中，了解其元件效率並未達到理想元件之標準，且其載子傳輸特性偏向以電洞為主，因此我們利用紅外光染料其最高佔有軌域能階之能階差，進行電洞載子捕捉，將其元件載子平衡調整至最佳狀態，使元件效率得到大幅提昇。 四、在第六章中探討載子注入效率對於元件特性之影響，我們使用兩種離子性銥錯合物為主要研究材料，分別為藍色離子性銥錯合物及橘色離子性銥錯合物，上述材料分別擁有相異之載子傳輸特性，並利用額外加入的電洞及電子注入層去研究其對元件特性的影響，研究發現，根據本體材料的載子傳輸特性，添加適當的載子注入層，可有效改善元件效率。 最後在第七章作一個總結。

In this thesis, we study the carrier balance in light-emitting electrochemical cells (LECs). First, the theory and development of LECs are discussed in chapter 1. In chapter 2, we obtained saturated deep-blue electroluminescence (EL) from solid state LECs incorporating the ionic terfluorene derivative 1. The peak external quantum efficiency and peak power efficiency of 1 in the presence of the ionic liquid reached 1.14% and 1.24 lm W–1, respectively. These CIE coordinates are the most saturated blue emissions ever reported from LECs. In chapter 3, UV LECs were, for the first time, achieved by the ionic 2,2’-bifluorene derivative. LEC devices incorporating bifluorene 1 exhibited UV EL emissions at 386 and 388 nm with maximum EQE and power efficiencies of 0.66 % and 0.23 lm W-1. The EL emissions in the UV region are successfully achieved by LECs based on 1, which are so far the shortest emission wavelength achieved in LECs. In chapter 4, we report efficient host-guest solid-state LECs utilizing a cationic terfluorene derivative as the host and a red-emitting cationic transition metal complex as the guest. Experimental results confirm that in addition to reducing self-quenching of guest molecules, the strategy of utilizing a carrier transporting host doped with a proper carrier trapping guest would improve balance of carrier mobilities in the host-guest emissive layer, offering an effective approach for optimizing device efficiencies of LECs. In chapter 5, we demonstrate improving balance of carrier mobilities in neat-film LECs utilizing a cationic transition metal complex (CTMC) as the emissive material and a cationic near-infrared laser dye as the carrier trapper. Experimental results confirm that balance of carrier mobilities in the CTMC neat films would be improved by doping a proper carrier trapper and such technique offers a general approach for optimizing device efficiencies of CTMC-based neat-film LECs. In chapter 6, we study the influence of carrier injection efficiency on the performance of LECs based on a hole-preferred transporting CTMC [Ir(dfppz)2(dtb-bpy)]+(PF6─) (complex 1) and an electron-preferred transporting CTMC [Ir(ppy)2(dasb)]+(PF6─) (complex 2). Experimental results show that even with electrochemically doped layers, ohmic contacts for carrier injection could be formed only when carrier injection barriers are relatively lower. Thus, adding carrier injection layers in LECs with relatively higher carrier injection barriers would affect carrier balance and thus would result in altered device efficiency. Finally, the thesis is concluded in chapter 7.