新型藍光和紅光熱激活化延遲螢光發光材料之光物理特性及有機發光元件研究

Abstract

有機發光二極體(organic light-emitting diode, OLED)已成為顯示和照明上的主要技術，我們的日常生活中已有越來越多採用OLED的電子產品。而為了提升OLED的性能於各種應用，持續提高元件的效率以降低功耗相當重要。在本論文中，我們主要研究基於熱激活延遲螢光(thermally activated delayed fluorescence, TADF)的新型有機發光材料和其高性能元件結構。 在本論文的第一部分，我們研究一系列藍光TADF發光材料(DPA-MeTRZ、c-NN-TRZ和c-NN-MeTRZ)的光物理特性，以探討引入甲基取代基和大環施體的效應。透過上述分子結構調控，其中c-NN-MeTRZ同時具有接近100% 的光致發光量子效率(photoluminescence quantum yield, PLQY)和高水平偶極矩方向性 (horizontal dipole ratio)。因此，基於c-NN-MeTRZ製成的藍光 TADF OLED，其外部量子效率(external quantum efficiency, EQE)可高達超過32%。 在第二部分中，接續第一部分的研究工作，我們研究一系列基於大環施體的深藍光發光材料(c-ON-MeTRZ、c-NS-MeTRZ 和c-NN-MePym)。我們對其光物理特性進行了完整的分析，對結構-特性關係進行了探討。與對照材料相比，這些材料成功地展現了顯著的藍移，驗證了所提出的施體-受體修飾策略。而採用c-ON-MeTRZ作為發光體所製作的深藍光TADF OLED其外部量子效率可達到30.2%，而CIE1931坐標可達(0.14, 0.13)；進一步透過適當的主體優化工程其可以實現超過34%的高外部量子效率。 在第三部分中，我們研究了兩個新型TADF 發光材料 BTDMAc-NAI 和 BFDMAc-NAI，其分子結構上為分別將benzothiophene和benzofuran兩雜環結合到 acridine施體上。這兩個發光材料展現了從橘紅光到純紅光不同的發光波段，其中BTDMAc-NAI的發光波峰紅移達到650 nm。當摻雜在主體材料中，這兩個材料都展現出明顯的 TADF 特性。應用 BFDMAc-NAI 作為發光體所製作的橘紅光 TADF OLED 其可達到超過 20% 的外部量子效率。 在本論文的第四部分，根據第三部分的研究，我們進一步研究了兩個新型紅光TADF發光材料ANQDC-MSTA和ANQDC -PSTA。其分子結構為剛性、具有強給電子特性的benzothiophene複合spiroacridine作為施體，並結合剛性、線性、平面的受體。這兩種材料都展現了明顯的 TADF 特性、高光致發光量子效率和約 85%的高水平偶極矩比例。以ANQDC-PSTA做為發光體製作的紅光TADF OLED實現了近25%的高外部量子效率，發光波峰為622 nm，CIE1931坐標為(0.61, 0.38)。此外，透過調控元件結構的微共振腔效應，此些元件可以涵蓋從淺紅光到深紅光的發光範圍。

Nowadays, organic light-emitting diodes (OLEDs) have penetrated into our daily lives by their display and lighting applications. To further enhance OLED performances for various applications, continuously improving efficiencies of the devices for low power consumption is desired. In this dissertation, we focus on the investigation of novel organic light-emitting materials and high-performance device architectures based on thermally activated delayed fluorescence (TADF) emitters. In the first part of this dissertation, we study detailed photophysical properties of a series of blue TADF emitters (DPA-MeTRZ, c-NN-TRZ, and c-NN-MeTRZ) with introducing methyl substituents and macrocyclic donor. In virtue of the combined advantages of the above structural features, c-NN-MeTRZ exhibits unitary photoluminescence quantum yield (PLQY) and preferentially horizontally oriented emitting dipoles simultaneously. Highly efficient blue TADF OLED based on c-NN-MeTRZ delivers an excellent external quantum efficiency (EQE) of over 32%. In the second part, following the work in the first part, we report a new series of deep-blue emitters (c-ON-MeTRZ, c-NS-MeTRZ, and c-NN-MePym) based on macrocyclic donors. Through studies of photophysical properties, the clear structure-property relationships were well discussed. Significant hypsochromic shift in emission of these emitters as compared to the reference compound is successfully demonstrated, and the modification strategies on donor-acceptor features were verified. Deep-blue TADF OLED employing c-ON-MeTRZ as the emitter presents a high EQE of 30.2% together with CIE1931 coordinates of (0.14, 0.13). An outstanding EQE exceeding 34% can be further achieved by rational host engineering. In the third part, we investigate two novel TADF emitters, BTDMAc-NAI and BFDMAc-NAI, with benzothiophene and benzofuran fused to the acridine donor, respectively. The two emitters reveal different emissions from orange-red to pure red, with the emission peak of BTDMAc-NAI red-shifting to 650 nm. As doped into the host matrix, both emitters show distinct TADF nature. Orange-red TADF OLED using BFDMAc-NAI as the emitter gives an EQE beyond 20%. In the fourth part of this dissertation, based on the work in the third part, we further study two new red TADF emitters, ANQDC-MSTA and ANQDC-PSTA, based on the rigid and strong electron-rich benzothiophene-fused spiroacridine donor and a rigid, linear, and planar acceptor. Both emitters display distinct TADF nature, high PLQY, and high horizontal dipole ratio of ~ 85%. Red TADF OLED incorporating ANQDC-PSTA realizes a high EQE of nearly 25% and emission peak at 622 nm, together with CIE1931 coordinates of (0.61, 0.38). Furthermore, with the modulation of the microcavity effect on the device architecture, the devices can cover an emission range from light-red to deep-red.