熱交聯電洞傳輸材料於溶液製程螢光與磷光有機發光二極體的應用

Abstract

本論文研究的目的在於探討熱交聯電洞傳輸材料於溶液製程的開發，以應用於製作螢光與磷光有機發光二極體。研究內容主要分為兩部分，第一部分針對熱交聯電洞傳輸材料的性質及其在螢光高分子發光二極體的應用作討論；第二部分則針對雙極性主發光體材料的開發及其使用熱交聯電洞傳輸材料於溶液製程磷光有機發光二極體的應用作討論。 第一部分研究中，三種熱交聯電洞傳輸材料DV-OMe-TPD、DV-Me-TPD與DV-F-TPD成功地被設計與合成出來，並利用推、拉電子基的觀念來調整HOMO能階，來控制層與層之間的能階差。將苯乙烯取代基運用於熱交聯反應後，此系列電洞傳輸材料其抗溶劑的能力相當的好，克服在溶液製程中層與層之間互溶的問題。導入電洞傳輸材料於元件中，成功地應用於藍光元件ITO/cross-linked HTMs/PFO/CsF/Al與黃光元件ITO/cross-linked HTMs/SY2/TPBI/LiF/Al。以PFO為主的藍光元件中，由於fluorenone defects的產生，使得元件光色產生一紅色放射峰，此放射峰座落於fluorenone與電洞傳輸層之間的介面處，即是因電洞傳輸材料其HOMO能階差所形成的exciplex而產生的放射峰。於是我們摻雜一綠光BFBT於發光層中並運用此機制，製作了三波段的高分子白光元件。在摻雜濃度為0.04 wt%時，其多層元件ITO/PEDOT:PSS/DV-Me-TPD/PFO doped with BFBT/CsF/Al效率可達到5.28 cd/A，其CIE座標座落於(0.32, 0.42)，非常接近理想的白色CIE座標(0.33, 0.33)。成功地導入交聯電洞傳導層於PFO為主的元件中，因其fluorenone defects的產生導引出exciplex電激發光行為，提供了一製作白光元件的途徑。以SY2為主的黃光元件中，DV-Me-TPD為主的雙層元件亮度可達到17060 cd/m2；效率為5.60 cd/A，多層元件效率則可達到7.19 cd/A。 第二部分研究中，我們成功合成了具電子與電洞注入與傳輸的雙極化分子。此雙極化分子有不錯的熱穩定性與玻璃轉移溫度。從電化學性質得知，雙極化性質的CzPOFA對於電子與電洞的注入而有所改善。由單一電荷元件的測試中CzPOFA具有和金屬電極形成利於電子注入的能力，因此分子可以使用於無電子傳輸以及注入材料的雙層元件，便於簡化元件的結構。摻雜一紅色Os(fptz)2(PPh2Me2)2客發光體於主發光體中，其雙層與多層元件效率皆可達到2.22與7.84 cd/A，都有出色的元件效率。此外以CzPOFA搭配一天藍色DSA-Ph與橘紅光Os(bfptz)2(PPh2Me2)2客發光體於主發光體中，所製作的雙波段白光元件效率可達到4.48 cd/A，其CIE座標為(0.30, 0.32)，非常接近於CIE標準白光座標(0.33, 0.33)，元件在不同的操作電壓下，其CIE座標幾乎沒有改變，顯示出光色的穩定性。另外將熱交聯傳輸材料導入於紅色與白色磷光元件中，因DV-Me-TPD為一電洞傳輸層與電子阻擋層材料，能將電子侷限於發光層中，增加電子與電洞再結合的機率，故其元件皆表現不錯的效率。其中紅光元件效率可達到6.75 cd/A；而白光元件效率可達到4.40 cd/A，其CIE座標為(0.33, 0.36)，非常接近於CIE標準白光座標(0.33, 0.33)，元件在不同的操作電壓下，其CIE座標幾乎沒有改變，顯示出光色的穩定性。

The objective of thesis is to examine thermally cross-linkable hole-transporting materials for their potential use in solution-processable fluorescent and phosphorescent organic light-emitting diodes (OLEDs). This thesis is divided into two parts. One is related to the applications of thermally cross-linkable hole-transporting materials in fluorescent polymeric light-emitting diodes (PLEDs). The other is related to develop a bipolar host material together with thermally cross-linkable hole-transporting materials for the applications in solution-processable phosphorescent organic light-emitting diodes. In the first part of the work, three thermally cross-linkable N,N,N’,N’-tetraphenyl-1,1’-biphenyl-4,4’-diamine (TPD)-based hole-transporting materials (HTMs), i.e., DV-OMe-TPD, DV-Me-TPD, and DV-F-TPD, were designed and synthesized. Two styryl groups in the TPD units are used for thermally cross-linking, whereas methoxy, methyl and fluoro groups are introduced to modulate the highest occupied molecular orbital (HOMO) energy levels of the HTMs. These HTMs are thermally cross-linked to overcome interfacial mixing, realizing solution-processed polyfluorene (PFO)-based devices ITO/cross-linked HTMs/PFO/CsF/Al and SY2-baesd devices ITO/cross-linked HTMs/SY2/TPBI/LiF/Al. Besides the characteristic blue emission of PFO, the devices exhibited a red emission whose energy is highly dependent on the HOMO energy of the cross-linked HTM used in the device. This result suggests that the red electroluminescence is derived from the exciplex generated by the adjacent hole and electron at the cross-linked HTM/fluorenone heterojunction interface. By doping small amount of 4,7-bis(9,9-dioctylfluoren-2-yl)-2,1,3-benzothiadiazole (BFBT) into the emissive layer (EML) to compensate green emission, the devices with the configuration of ITO/PEDOT:PSS/DV-Me-TPD/PFO doped with BFBT/CsF/Al exhibited white electroluminescence comprising three primary colors simultaneously. The 0.04 wt%-doped device achieved a maximum luminous efficiency of 5.28 cd/A which showed CIE chromaticity coordinates of (0.32, 0.42) which are close to the ideal white point (0.33, 0.33). We have demonstrated that integrating cross-linked triarylamine-based HTMs with fluorenone defects in PFO to induce exciplex electroluminescence can provide a useful way for realizing WPLED devices. In SY2-baesd devices, double-layer device achieved a maximum brightness of 17060 cd/m2, presented a maximum luminous efficiency of 5.60 cd/A, in addition to, multilayer device displayed a maximum luminous efficiency of 7.19 cd/A. In the second part of the work, a solution-processable bipolar molecule, triphenylamine-based CzPOFA comprising an electron-rich carbazole and electron-deficient diphenylphosphine oxide groups was synthesized. This molecule not only processes good thermal stability but also displayed excellent film-forming properties upon solution processing. In addition to serving as an electron-transporting host material, CzPOFA also facilitates electron injection from the Al cathode to itself in double-layer devices. Red double-layer and multilayer devices incorporating CzPOFA as the host doped with the osmium phosphor Os(fptz)2(PPh2Me2)2 all exhibited excellent device efficiencies. In addition, CzPOFA-based white light-emitting device containing blue light-emitting dye DSA-Ph and orange light-emitting osmium phosphor Os(bfptz)2(PPh2Me2)2 reached a maximum luminous efficiency of 4.48 cd/A, and the CIE coordinates of the white EL emission were (0.30, 0.32) closed to the ideal white point (0.33, 0.33). Red and white multilayer devices incorporating thermally cross-linable DV-Me-TPD HTM as the hole-transporting and electron-blocking layer material enhanced hole and electron combination presented excellent performance. Therefore, red multilayer device achieved a maximum luminous efficiency of 6.75 cd/A, and white multilayer device displayed a maximum luminous efficiency of 4.40 cd/A, displayed the CIE coordinates of the white EL emission were (0.33, 0.36) closed to the ideal white point (0.33, 0.33).