功能性三聚芴衍生物應用於濕式製程有機發光材料之開發探究、光電應用及其電聚合性質探討

Development of Solution-Processable Terfluorene Derivatives and Study of Their Optoelectronic Applications and Electropolymerization Properties

王鐘鋒(Chung-Feng Wang)

指導教授 ： 梁文傑

共同指導教授 ： 汪根欉(Ken-Tsung Wong)

國立臺灣大學/工學院/高分子科學與工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.00652

摘要

經由正確的分子設計及合理的合成策略，我們開發了新穎的多功能性藍光材料TFDPA及TFDPABT。本論文鉅細靡遺地從分子設計、合成策略與步驟、應用於小分子濕式製程有機發光二極體（organic light-emitting diodes, OLEDs）深藍元件等的優異表現、利用能量轉移製作多色磷光放光元件等應用逐一探討。且由於此系列分子可透過施加電壓誘發聚合反應，我們也一併對電聚合的過程與條件進行探究，並嘗試製作此系列分子電聚薄膜的元件並開發其光電應用。
TFDPA的分子結構包含高螢光性的三聚芴主幹、提供良好溶解度及濕式製程能力的長碳鏈，以及具電洞傳導性質及電聚合能力的三苯胺基團，並具有良好熱穩定性及以濕式製程方式製作電致放光元件的能力。在元件的製作上可以完全省略電洞傳導層（hole-transport layer, HTL）的使用仍維持高效率表現，達成簡化元件製程的目的（simple fabrication）。做為發光材料方面，我們以TFDPA製作效率極高的無摻雜（nondoped）螢光飽和深藍（deep-blue）發光元件，完成了無使用電洞傳導層的濕式製程高效率深藍發光元件，元件放光之CIE座標位於深藍區的（0.17, 0.07），且元件外部量子效率（exerternal quantum efficiency, EQE）高達2.7 %。此外我們也以TFDPA作為主體材料（host material），分別摻雜橘光[Ir(2–phq)3]及紅光[(Mpq)2Ir(acac)]磷光染料，成功地利用能量轉移（energy transfer）的方式，製作出高效率的橘光及紅光磷光放光元件。另更藉由控制適當微量比例黃光磷光材料[(Bt)2Ir(acac)]的摻雜，巧妙利用不完全的能量轉移，以主體材料之深藍光螢光放光，搭配客體之黃光磷光材料放光，以簡易之雙色調控，達成螢光-磷光混成之純白放光元件製作，大舉簡化了一般以多色調控以達成白光元件之複雜製程，且該白光元件放光之CIE座標位於接近純白光區域中心之（0.38, 0.33）。
由於TFDPA的成功，我們在其基礎之上，再加入電子傳導基團，以期達到更多功能性而設計了TFDPABT分子。除了高螢光性的三聚芴主幹外，同時兼納了具電洞傳導性質及電聚合能力的三苯胺基團和具電子傳導性質的PBI（Phenylbenzimidazole）基團。我們以濕式製程方式製作無摻雜的純螢光藍光元件及摻雜磷光染料的紅光元件，發光強度及效率等各項表現均佳。並嘗試用以製作單層結構藍光元件，因高效率可濕式製程的非聚合物OLED單層結構藍光元件至今仍相當少見，這部分研究非常具有潛力，是未來展望的重點。
除了直接以「小分子」的型態應用於有機電致放光元件之外，我們所發明的TFDPA及TFDPABT分子，由於所引入的三苯胺基團具有氧化聚合的特性，透過電化學裝置施加電壓後，將發生聚合反應而形成高分子薄膜於電極之上。經由訂製的電聚合裝置，直接以ITO（indium tin oxide，氧化銦錫）玻璃做為電化學工作電極，並對各項電聚合條件進行最適化後，成功地將高分子發光層沈積於ITO之上，生成有機分子薄膜。另也嘗試將帶有電聚基團的高分子polyvinylcarbazole（PVK）加入進行共電聚合，續以電子顯微鏡及原子力顯微鏡進行不同聚合條件下生成之有機薄膜的鑑定。此外，我們也嘗試直接以電聚合（in situ electropolymerization）發光層後的ITO玻璃進行有機電致放光元件之製做，試圖開發一套以電聚合方式直接製做高分子發光層並應用於電致放光元件的一貫化製程。
除了將電沉積薄膜應用於電致放光元件外，我們另開發其光致放光方面的應用，將圖形化（patterned）後的ITO電極直接以電聚合方式覆蓋上高螢光性的藍光發光材料薄膜，在紫外光源激發下發出高亮度藍光，以提供更多層面的應用。

關鍵字

深藍螢光 ； 有機發光二極體 ； 濕式製程 ； 白光有機發光二極體 ； 電沈積 ； 電聚合

並列摘要

Organic light-emitting diodes (OLEDs) have been recognized as a promising alternative display or lighting technology and have been studied for decades. And because of the intrinsic wide-band-gap nature of deep-blue emitters, it will be a great challenge to develop an efficient and stable blue-emitting material with a Commission Internationale de L’Eclairage (CIE) y coordinate value < 0.10. Although many academic and industrial research endeavors already focused on this topic, saturated deep-blue fluorescent small molecule-based emitters suitable for solution-process to give high efficiency and thermal stability remain relatively rare so far. Solution processability usually requires material with a large molecule size, while the molecular p-conjugation system should not be too extended to ensure the deep-blue emission of the material. In this regard, we designed a new multifunctional blue-emitting terfluorene derivative (TFDPA), which is featured with triphenylamine groups for hole-transportation and long alkyl chains for solution processability on the conjugation inert bridge centers.
TFDPA can give homogeneous thin film by soultion process and exhibits high hole mobility (mh ≈10–3 cm2 V–1s–1) and suitable HOMO for hole injection. Particularly, TFDPA performs efficient deep-blue emission with high quantum yield (~100% in solution, 43% in thin film) and suitable triplet energy (ET = 2.28 eV), making solution-processed OLED devices of using TFDPA as blue emitter and as host for iridium-containing phosphorescent dopants feasible. The solution-processed nondoped blue OLED device gives saturated deep-blue electroluminescence [CIE = (0.17, 0.07)] with EQE of 2.7 %. TFDPA-hosted electrophosphorescent devices performed with EQE of 6.5% for yellow [(Bt)2Ir(acac)], 9.3% of orange [Ir(2–phq)3], and 6.9% of red [(Mpq)2Ir(acac)], respectively. In addition, with careful control on the doping concentration of [(Bt)2Ir(acac)], a solution-processed fluorescece-phosphorecence hybrided two-color–based WOLED with EQE of 3.6% and CIE coordinate of (0.38, 0.33) was successfully achieved.
Based on the success of TFDPA, we designed and synthesized another new three-in-one material TFDPABT, which is both a highly luminescent deep-blue emitter and hole-transporting material, and featured with electron-transporting ability. TFDPABT is also a terfluorene derivative and therefore guarantees highly deep-blue luminescence. In addition, it carries triphenylamine groups for hole-transportation and phenylbenzoimidazole groups for electron-transportation. Due to sort of ambipolar property, TFDPABT has suitable HOMO and LUMO for hole and electron injections, which are -5.34 eV and -2.31 eV respectively. We used TFDPABT to fabricate nondoped deep-blue electroluminescence device and it showed efficient emission at saturated deep-blue corner [CIE = (0.18, 0.10)]. TFDPABT-hosted red [(Mpq)2Ir(acac)] electrophosphorescent device also performed well and left no residue luminescence from host, which indicates successful energy transfer.
Besides the development of solution-processed, simple fabricated OLEDs which based on monomer TFDPA or TFDPABT, we also tried to study the properties of electrodeposited films. Due to the electropolymeriable triphenylamine moieties carried by TFDPA and TFDPABT, these two emitters could become polymers if electric potential is applied to trigger the polymerization reaction. After some trial-and-error process, we successfully deposited emissive thin films of TFDPA and TFDPABT on electrode through cyclic voltammetry (CV) oxidation and characterized the films by SEM and AFM. Then we used the in-situ electropolymerized thin films directly to fabricate the electroluminescent devices, or deposited the emitters on the patterned ITO glass substrates to develop applications of our novel materials. All the details will be discussed in this dissertation.

並列關鍵字

OLED ； deep-blue ； non-doped ； solution-processable ； white light OLED ； electrodeposited ； electropolymerization

參考文獻

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