- 學位論文
新型深紅光及近紅外光熱激活化延遲螢光發光材料及元件研究
Investigations on Novel Deep-Red and Near-Infrared Thermally Activated Delayed Fluorescent Emitters and Devices
摘要
近25年來，有機發光二極體(organic light-emitting diode, OLED)在學術界和工業界迅速發展。在顯示產業，較早發展的液晶顯示器(liquid crystal display, LCD)因其高效率的背光源及成熟技術仍然在市場上佔有主要地位，但OLED讓顯示面板能有更好的發光色彩、且結構比LCD簡單，並且OLED也有比LCD更好的光利用率，因此OLEDs成為具有發展性的顯示技術。OLED目前所面臨的挑戰為發光材料及元件結構。在OLED發光材料中，其中熱激活化延遲螢光(thermally activated delayed fluorescence, TADF)材料近期被廣泛討論及研究，因其不需要在分子結構中加過渡金屬，即能使內部量子效率(internal quantum efficiency, IQE, η_int)達100%，且外部量子效率(external quantum efficiency, EQE, η_ext)也可以和有加過渡金屬的磷光(phosphorescence)材料一樣達到20~30%，甚至超過30%。然而，波長700 nm以上的近紅外光(near-infrared, NIR) TADF OLED卻仍少有EQE達15%的發表，因此本論文將研究高效率深紅光及近紅外光的有機材料與元件。 本論文的第一部分，我們探討三種新穎的深紅光及近紅外光的TADF材料：TPA-CN-N4、TPA-CN-N4-2PY及TPA-CN-N4-CH3，研究目標為：元件的電激發光(electroluminescence, EL)頻譜峰值波長在700 nm以上時仍然有高EQE。將此三種TADF材料製作成元件後，發現只有TPA-CN-N4-2PY可以達到我們NIR TADF OLED的目標，可歸因以TPA-CN-N4為主體向外接上吡啶基(pyridine, C5H5N)，使TPA-CN-N4-2PY在9 wt.%濃度下時EL峰值波長即可達700 nm，且元件EQE可高達22.8%，因此經過本論文第一部分的比較後，本論文的第二部分繼續以TPA-CN-N4外接pyridine的結構進行探討。 本論文的第二部分，我們探討分子結構與論文第一部分的TPA-CN-N4-2PY相似，但pyridine的鍵結位置不同的Py-TPA，而Py-TPA所製成的元件不管在mCPCN及CBP主體中，EL峰值波長皆比第一部分的TPA-CN-N4-2PY更大，因此證實外接不同位置的pyridine能使EL峰值波長更大的預期。另外，我們發現在Py-TPA的濃度及EQE皆相同的情況下，Py-TPA在CBP主體中元件的EL峰值波長會比在mCPCN主體中更大。
並列摘要
In the past 25 years, organic light-emitting diodes (OLEDs) have been rapidly developed in academia and industry. In the display industry, liquid crystal displays (LCDs), which have been developed for a long time, are still in demand in the market due to their high-efficiency backlight sources and maturity. On the other hand, OLEDs allow displays to have better colors and simpler structures than LCDs, and OLEDs also have better light utilization efficiency than LCDs. Thus, OLEDs have become an important display technology. Nevertheless, the challenges that OLEDs currently face are light-emitting materials and device structures. Among OLEDs’ light-emitting materials, the thermally activated delayed fluorescence (TADF) materials have been widely discussed and studied, because they require no transition metals to the molecular structures, and yet that the internal quantum efficiency (IQE) can reach 100%, and the external quantum efficiency (EQE) can also reach 20~30% like the phosphorescence materials with transition metals, or even exceed 30%. However, Near-Infrared (NIR) TADF OLEDs with wavelengths above 700 nm are rarely published in journals with EQE of 15%. Therefore, this thesis will study high-efficiency deep-red and NIR organic TADF materials and devices, and also conduct photophysical and electrical analyses In the first part of this thesis, we study three novel TADF materials for deep-red and NIR emitters: TPA-CN-N4, TPA-CN-N4-2PY and TPA-CN-N4-CH3. The research goal is to achieve OLEDs having high EQE when the peak wavelength of electroluminescence (EL) is above 700 nm. After incorporating three TADF materials into devices, it was found that only TPA-CN-N4-2PY could achieve this purpose of NIR TADF OLEDs. With TPA-CN-N4 being connected to the pyridine (C5H5N), the EL peak wavelength of TPA-CN-N4-2PY at 9 wt.% can reach 700 nm, and the EQE of the device is as high as 22.8%. In the second part of this thesis, we further explore the compound Py-TPA whose molecular structure is similar to TPA-CN-N4-2PY in the first part, but the position of pyridine is different. The EL peak wavelength of Py-TPA is larger than that of TPA-CN-N4-2PY in both mCPCN and CBP hosts, thus confirming the conjecture that appropriate positioning of pyridine can make the EL peak wavelength larger. In addition, we found that the EL peak wavelength of the Py-TPA device in the CBP host is larger than that in the mCPCN host when the Py-TPA concentration and EQE are the same.