高效率橘紅光熱激活化延遲螢光有機發光元件之研究

Abstract

有機發光元件已快速發展成具重要的顯示技術，近年來，由於熱激活化延遲螢光(TADF)材料具有成本低、高內部量子效率、改變分子結構可發出各式色光，以及其發光元件的外部量子效率可與磷光元件匹敵的特點，因此引起廣泛討論與研究。其中TADF OLEDs在綠光與天藍光已有超過30%及37%的外部量子效率，而在先前發表過的橘紅光TADF OLEDs最高外部量子效率僅有17.5%，明顯低於綠光與天藍光。因此在本篇論文中，針對新穎的TADF橘紅光材料做光物理與電性上的分析，並進一步製作高效率橘紅光有機發光元件。 在本篇論文的第一部分，我們探討兩種新穎的TADF橘紅光材料NAI-DMAC與NAI-DPAC的光物理特性及元件特性，兩種材料皆有水平化方向發光偶極比Θ_(//)及高內部量子效率Φ_PL；NAI-DMAC與NAI-DPAC製成的橘紅光元件其外部量子效率最高可達23.4%與29.2%，其中29.2%為目前發表過橘紅光TADF OLEDs最高的外部量子效率。並進一步探討光學微共振腔與Purcell effect在薄膜與元件結構中的增益影響。 論文的第二部分，探討新的主體材料CBPCN以及由NAI-DMAC及NAI-DPAC為基礎所延伸而出的四種新的橘紅光TADF材料:tBuFAc、2PNDMAC、2PNDPAC、2PNFAc；TADF發光材料設計理念為在分子上加上苯環，增加分子結構之線性長度，提高水平發光偶極比Θ_(//)。四種延伸而出的TADF材料其摻雜薄膜的內部量子效率Φ_PL與水平方向偶極比Θ_(//)皆有增加；在元件特性上也獲得更高外部量子效率，最高外部量子效率可達31.4%。同時研究新主體材料CBPCN的特性，其為在CBP的一側接上一氰基，使CBPCN具有較強的非等向性，有利於增加客體發光材料之水平發光偶極比Θ_(//)，以CBPCN為主體材料製作出的元件，最高外部量子效率亦可達31.1%，使得CBPCN為一具有潛力的主體材料。

Organic light-emitting diodes (OLEDs) have been rapidly developed as an important display technology. In recent years, thermally activated delayed fluorescence (TADF) materials have been studied extensively due to their lower cost, high internal quantum efficiency, the ability to emit various light by changing molecule structures, and their outstanding OLEDs performance comparable to those of phosphorescent emitters. EQEs of TADF OLEDs have been rapidly advancing in recent years, with over 30% for green and nearly 37% for sky blue. However, the highest EQEs of orange to red TADF OLEDs reported so far is only 17.5% obviously lower than those of green and blue TADF OLEDs. Therefore, in this thesis, we focused on the investigation of high performance orange-red TADF materials and device characteristics. In the first part, we investigated detailed photophysical properties and device characteristics of two novel orange-red TADF materials, NAI-DMAC and NAI-DPAC. Both NAI-DMAC and NAI-DPAC possess preferentially horizontal dipole ratio Θ_(//) and relatively high internal quantum efficiency Φ_PLs. The maximum EQEs of NAI-DMAC and NAI-DPAC OLEDs can reach 23.4% and 29.2%, respectively. 29.2% EQE represents the state-of-the-art device performance for orange-red TADF OLEDs. We also discussed the influence of optical microcavity and Purcell effect on the thin film structure and device structure. In the second part, we investigated a new host material CBPCN and four novel orange-red TADF materials derived from NAI-DMAC and NAI-DPAC, called tBuFAc, 2PNDMAC, 2PNDPAC and 2PNFAc. The design concept of those TADF materials is to add a benzene to the molecule in order to elongate the molecular structure to increase the horizontal dipole ratio Θ_(//). The internal quantum efficiency Φ_PLs and horizontal dipole ratios Θ_(//) of those four novel TADF materials are both increased. Higher EQEs of OLEDs using these TADF materials have been obtained. The maximum EQEs can reach 31.4%. Simultaneously, we studied the characteristics of the new host CBPCN. Incorporation of a CN group onto conventional CBP makes CBPCN more anisotropic in optical properties, which is beneficial for increasing emitting dopants horizontal dipole ratios. By employing CBPCN as host material, the highest device EQE achieved is up to 31.1%, making CBPCN a promising host material.