包含吡啶結構之新型近紅外光熱激活化延遲螢光材料之光物理特性及元件研究

Investigations on photophysical properties and devices of novel pyridine-incorporated near-infrared thermally activated delayed fluorescent emitters

施雨葳(Yu-Wei Shih)

指導教授 ： 吳忠幟

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202203688

摘要

近年有機發光二極體(organic light-emitting diode, OLED)隨著製程的成熟與新材料的開發，且本身具廣色域、高對比度、可製程於可撓基板上等特色，逐漸成為市場上重要的顯示與照明技術。然而，尚有一些技術瓶頸有待討論，如藍光OLED的可靠度以及目前紅光OLED的波長限制。本篇論文將聚焦紅光OLED之熱激活化延遲螢光(thermally activated delayed fluorescence, TADF)材料，研究具高外部量子效率之深紅光到近紅外光(near-infrared, NIR)元件。
在第一部分討論具吡啶結構且外加吸電子氰基(-CN)之長形分子Py-CN-TPA，與系列材料Py-TPA之薄膜特性與元件效率。在薄膜之光物理特性中，Py-CN-TPA的磷光螢光光譜較Py-TPA紅移，然而在元件製備與量測得到的發光頻譜與元件外部量子效率的表現皆略遜於Py-TPA。可得初步結論，除了薄膜的光物理特性與元件表現相關外，也要考慮元件導通時內部結構是否產生電磁場以及帶電載子注入，產生的交互作用也會影響元件特性，有待進一步驗證。雖然在元件頻譜與效率的表現上略遜Py-TPA，Py-CN-TPA的元件在近紅外光波段(744 nm)仍保有11.1%之外部量子效率。
第二部分討論同樣以TPA做為D-A結構中施體的TADF材料TPA-CN-N4-2MD，相較前章的元件採蒸鍍製程，TPA-CN-N4-2MD的元件採溶液製程，涉及旋塗薄膜的製程方式。本章主要聚焦固定摻雜濃度下(12 wt.%)，搭配不同的發光層主體材料—PVK混mCP、CBP、mCPCN，可證實主客體材料吸收與放光波段的匹配度確實會影響元件效率，同時可觀察到調變電子傳輸層厚度的元件趨勢。

關鍵字

有機發光二極體 ； 熱激活化延遲螢光 ； 磷光螢光光譜 ； 光物理特性 ； 水平發光偶極比 ； 外部量子效率 ； 蒸鍍製程 ； 溶液製程(solution process)

並列摘要

Recently, OLED had become one of the mainstream display and illumination technologies due to their various merits, such as the wide color gamut, the true-black characteristics, and the “foldable” and “rollable” features. However, there are still bottlenecks to be solved, such as the reliability of blue OLEDs. This thesis work mainly focuses on the development of materials and devices to reach the long wavelength red-emitting OLED with high EQE.
In the first part of this thesis we studied the TADF material, Py-CN-TPA, which has a cyano(-CN) in the end of the Y-shape molecules. The existence of an additional electron-withdrawing cyano group provided a smaller bandgap and also restrict the rotation and vibration of TPA to a certain degree. Compared with the same series material, Py-TPA, Py-CN-TPA owns a longer emission spectrum in solution and doped film in CBP. However, in OLED devices, the emission wavelength of Py-CN-TPA is not as long as that of Py-TPA. We suppose that there might have electronic field or carrier interactions happening in the emission layer of the OLED.
In the second part we studied the TADF material, TPA-CN-N4-MD, which is designed based on the D-A1-A2-A3 structure, by the solution process. We doped 12 wt.% TPA-CN-N4-MD in three kinds of host materials, (PVK:mCP), CBP, mCPCN. Partly restricted by the quality of the film fabrication, EQE of the devices were not extraordinary. However, results still indicate effectiveness of the functional group in causing red shift of emission wavelengths.

並列關鍵字

organic light-emitting diode(OLED) ； thermally activated delayed fluorescence(TADF) ； horizontally oriented dipole ratio ； PLQY ； external quantum efficiency(EQE) ； vacuum-deposition ； solution process

參考文獻

第一章參考資料

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