有機小分子材料應用於有機發光二極體元件之合成、鑑定及元件製作與測試

Abstract

本論文主要分為兩個部分，第一部分為設計合成一系列可濕式製程磷光有機發光二極體(PHOLED)主體材料。研究合成一系列1,3-di(9H-carbazol-9-yl)benzene (mCP)衍生物主體材料，開發暖白色或藍色有機發光二極體主體材料為目標，改變不同的中心架橋(矽、氮、磷)或接上不同拉電子基團組成雙極性主體材料CzPAMe、CzPAPm、CzPPO、CzPATPE。主體材料進行詳細之熱性質、光物理性質鑑定，並製作成暖白光或藍色PHOLED。藍光PHOLED中以CzPPO為主體材料製成單層濕式藍光元件之電流效率最大可以達到9.32 cd/A，最大功率效率為5.0 lm/W。CzPATPE為具AIE (aggregation-induced emission)性質的藍綠色發光材料，在其中摻入橘色磷光材料(Ir(2-phq)3)製作成混合型白光OLED，CRI達到72。 第二部分為設計並合成熱活化型延遲螢光(thermally activated delayed fluorescence, TADF)材料，自從日本安達千波矢教授提出了第三代OLED—熱活化延遲螢光的概念後，我們積極尋找這個成本低且具有高效率的材料。本篇論文合成FN2D、DPP2D、4PhOXD、OXD和OXD2D系列TADF材料，搭配不同的推拉電子基，探討對TADF性質、螢光量子效率(PLQY)、放光波長(PL)、單重態和三重態能差(EST)、分子取向性等影響，並製作成元件量測其外部量子效率(EQE)。我們提出一簡單的分子修飾結構擁有協同可變構形(synergetic variable conformation)可以在o-DiCbzBz主體材料中擁有高分子水平排列取向性進而增加元件出光率，使得元件擁有高的外部量子效率，其中4PhOXD-PXZ元件最大外部量子效率為29.2 %。

My doctoral dissertation can be divided into three parts. The first and the second parts were focused on designing and synthesizing host materials for the application of blue or hybrid white phosphorescence organic-emitting diodes (OLEDs). The third part was focused on developing of thermally activated delayed fluorescent (TADF) emitters contain high horizontally emitting dipole orientation. In the first part, three new solution processable small molecular host materials based on bis-[3,5-di(9H-carbazol-9-yl)phenyl] structural moiety have been developed for blue phosphorescence (FIrpic dopant) OLEDs. All three host materials have been characterized for high glass transition temperatures (Tgs), 155~175 oC, indicative of good morphological stability of their amorphous thin films prepared from solution process. Whereas N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]methylamine (CzPAMe) has the highest solid state triplet energy gap (ET) of 2.73 eV, tetrakis-[3,3',5,5'-(9H-carbazol-9-yl)]triphenylphosphine oxide (CzPPO) and N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]pyrimidin-2-amine (CzPAPm) are two host materials potentially being bipolar for charge transport due to the electron deficient unit of triphenylphosphine oxide and pyrimidine, respectively. Having no OXD-7 co-host and no vacuum-thermal-deposited extra electron transporting layer, single-layer CzPPO devices reach current efficiency as high as 9.32 cd/A (or power efficiency of 4.97 lm/W), one of the highest efficiency among devices with the same fabrication process and same device configuration. In the second part, a judicious structure hybrid of bis(3,5-di(9H-carbazol-9-yl)phenyl)amine (CzPA) and 1,1,2,2-tetraphenylethene (TPE) generates the first aggregation-induced emission (AIE) fluorophore, CzPATPE, as a solution processed host material in hybrid white OLED. Small molecule CzPATPE has been verified for the amorphous characteristics by a featureless halo in powder X-ray diffraction spectra and a glass transition temperature as high as 180 oC. Solution (THF/water) fluorescence spectroscopy study clearly demonstrate that CzPATPE is a typical AIE fluorophore. Whereas CzPATPE is virtually non-emissive in common organic solvents, thin film photoluminescence (PL) spectroscopy shows that CzPATPE has a strong sky blue emission around 495 nm with a relatively wide full width at half maximum (FWHM) about 95 nm and a reasonable PL quantum yield of 40%. Low temperature time-gated PL spectroscopy identifies CzPATPE’s triplet optical gap energy ET ~2.05-2.12 eV, which is barely enough for phosphorescence dopant, tris(2-phenylquinoline) iridium (III) (Ir(2-phq)3) (ET~2.13 eV). This AIE hybrid white OLED displays white electroluminescence (EL) with colour chromaticity of CIEx,y(0.36, 0.43). Although the maximum EL efficiency is modest 3.4 cd/A or 1.8 lm/W, the white OLED has a colour rendering index (CRI) of 72, which is unusually high considering the orange dopant and two-colour white feature. We attribute such CRI to the relatively large FWHM of CzPATPE, which is common for most AIE materials. In the final part, I designed and synthesized four series of TADF materials include FN2D, DPP2D, OXD2D, OXD, and 4PhOXD series. 4PhOXD-based emitters are demonstrated as a novel strategy for greatly enhancing the horizontally oriented alignment of the emitters without shifting the emission spectrum to shorter wavelengths. Doping of blue-emitting 4PhOXDDMAC or greenish-blue-emitting 4PhOXDPXZ into host films yielded much higher degrees of horizontally oriented alignment for the emitter (up to 92%) compared to when the 4Ph unit was excluded (69% and 75%, respectively). The enhanced alignment results in high out-coupling efficiencies of 24% and 35% in organic light-emitting diodes based on 4PhOXDDMAC and 4PhOXDPXZ, respectively, and boosts the external quantum efficiencies to values (8.8% and 29.2%, respectively) that are higher than would be expected for randomly oriented emitters (out-coupling efficiency of 20%). These enhancements are achieved while avoiding the red-shift that often occurs using the common strategy of increasing molecular length, and, thereby, conjugation, to increase orientation.