小分子和高分子發光體與其在有機電致發

Abstract

本論文主要著重在具備熱穩定性之小分子與高分子主發光體材料的化學部分與元件應用的探討。首先，第一章針對有機電激發光的發展史與元件工作原理作簡短的敘述。第二章則對於本文中的材料合成與鑑定方法進行說明。 由於DPVBi具有優異的螢光效率，使它成為藍色主發光體的主力。但是它成膜後易結晶的缺點，一直是它朝向OLED應用的主要障礙。有鑑於此，在第三章中我們提出一DPVBi相似化合物，DPVSBF。DPVSBF是以旋環雙茀（spirobifluorene）中心結構取代DPVBi的中心聯苯基（biphenyl），並將兩側的2,2-diphenylvinyl基團鍵結在spirobifluorene中心的2,7位置上。此化合物具備高玻璃轉移溫度（Tg = 115 ℃）且擁有優於DPVBi的薄膜形貌穩定度。DPVSBF元件壽命也比DPVBi元件增加了近16倍。第四章中，我們進一步設計合成具有咔唑（carbazole）中心基團的DPVBi相似化合物，意圖實現具有電洞傳輸性之藍光distyrylcarbazole化合物。於簡單的雙層元件下，相較於DPVBi元件，distyrylcarbazole化合物為主的元件，具有較低的起始電壓與較高的電激發藍光效率。 客磷光體/高分子主發光體共混系統中，藉由能量轉移（energy transfer）及電荷捕捉（charge trapping）的機制，能導致客磷光體發光。第五章中，我們利用本實驗室已開發之具有電荷傳輸側鏈的聚茀衍生物（polyfluorene derivatives），PF-OXD 以及PF-TPA-OXD，摻雜入少量含有Ir金屬或 Os金屬之紅色磷光體，能得到高效率（最大元件外部量子效率，EQEmax ~ 8.5 %）、高亮度（> 104 cd/m2）的紅光元件，在這些高效率的紅光元件中，電荷捕獲機制被視為磷光產生的主要來源機制。而以POF（缺少電荷傳輸側鏈）為主發光體的元件，其效率及亮度（5.8%，2144 cd/m2）明顯不佳。 第六章係關於合成出雙偶極傳輸性之共聚高分子，PFA-OXD。雖然此高分子具有很高的玻璃轉移溫度 （306 ℃ ），但並未喪失溶液加工性。元件實驗結多證明PFA-OXD除了是高效能高分子藍光體外（EQEmax = 1.53%），亦是優異的紅色磷光體主發光體材料（EQEmax = 9.30%）。

The work presented here describes the chemistry and the device applications of small molecule-based and polymer-based emitters with improved thermal stability. Chapter one briefly introduces the history of organic electroluminescence and how these devices work; chapter two summaries the experiement section of synthetic routes and the characterization methods of these emitters. 4,4´-bis(2,2-diphenylvinyl)-1,1´-biphenyl (DPVBi) has been proved to be one of the most promising blue emitter because of its high photoluminescence (PL) efficiency in solid-state. However, the deposited films of DPVBi have a strong tendency to crystallize, which hinders its applications in OLEDs (organic light-emitting diodes). Chapter three describes the synthesis and characterization of the spirobifluorene-based DPVBi analogue, DPVSBF, in which the bis(2,2-diphenylvinyl) groups are connected through the 2 and 7 positions of the spirobifluorene framework. DPVSBF possess a high glass transition temperature (Tg) of 115 ℃ and enhanced morphological stability in comparison with DPVBi. The DPVSBF-based device exhibits a 16-fold enhancement in the operation lifetime relative to that of a similar device based on DPVBi. In chapter four, we further prepared a serial of DPVBi analogues based on carbazole-core in attempt to realize distyrylcarbazole compounds served as blue light-emitting and hole-transporting materials for OLED applications. In a simple double-layer device configuration, the distyrylcarbazole materials exhibited lower turn-on voltages and more efficient blue light than those obtained from the DPVBi-based device. In a phosphorescent dye-doped polymeric light emitting diodes, two different operating mechanisms, energy transfer and direct charge trapping, can lead to the phosphorescence of dopants. In chapter five, we have realized the preparation of highly efficient red-electrophosphorescent devices (maximum external quantum efficiency, EQEmax ~ 8.5%) incorporating Ir or Os complexes at low doping contents by using blue polyfluorene copolymers with built-in charge-transporting side chains (PF-OXD and PF-TPA-OXD), in which the direct charge trapping on dopant sites is the main operating mechanism. The absence of charge-transporting pendent units—i.e., the device fabricated from poly[9,9-dioctylfluorene-2,7-diyl] (POF)—led, however, to relatively poor electroluminescence characteristics (5.81% and 2144 cd/m2) In chapter six, we report a bipolar charge-transporting copolymer, PFA-OXD, which possesses electron-rich fluorene-triphenylamine backbones and electron-deficient oxadiazole pendent groups. This polymer exhibited a very high glass transition temperature (306 °C) and good thermal stability, without sacrificing its good solution processability. According to the performances of the electroluminescent devices, PFA-OXD is not only an efficient blue emitter (EQEmax = 1.59 %) but also a good polymeric host for red phosphor (EQEmax = 9.30 %).