有機π-共軛高分子之設計與合成及其於有機光電元件之應用

Design and Synthesis of π-Conjugated Polymers for Organic Optoelectronics

陳宏揚(Hung-Yang Chen)

指導教授 ： 陳昭岑

共同指導教授 ： 陳錦地(Chin-Ti Chen)

國立臺灣大學/理學院/化學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.00581

摘要

以高分子為主的有機發光二極體(OLEDs)和有機光伏電池(OPVs)為高分子光電元件中最被廣泛研究的領域。本論文旨在設計與合成有機π-共軛共聚物 (Copolymer)於有機發光二極體和有機光伏電池之應用，尤其針對共聚物化學結構與有機光電元件表現之間的關係加以研究和討論。
在有機發光二極體的應用中，本論文合成了一系列由9,10-二苯蔥(9,10-Diphenylanthracene)的2,6-位置延伸，並具有電洞、電子傳輸功能以及高立體障礙取代基的藍色螢光共聚物。在此一系列共聚物的光物理、熱、電化學以及電激發光(Electroluminescence)性質的特性表徵與研究中，高立體障礙官能基取代的共聚物在固態中具有較高的螢光量子效率，而具電洞和電子傳輸功能的取代基皆明顯提升有機發光二極體元件的電激發光表現。其中，電子傳輸功能取代的共聚物在連續操作電壓下的發光效率衰退較緩和，可歸因於其較佳的電子/電洞價荷平衡。
在有機光伏電池的應用中，本論文設計與合成了兩系列低能隙(Low-Band-Gap)共聚物。首先，本論文做了一系列以噻吩(Thiophene)和硒吩(Selenophene)為π-共軛橋樑之予體-受體共聚物的比較研究。共聚物骨架中的噻吩以硒吩取代導致共聚物能隙明顯減小；主要是因為最低未填充分子軌域(LUMO)能階的下降，次要則是最高填充分子軌域(HOMO)能階的上升。密度泛函理論(Density Functional Theory)計算的研究被使用來協助解釋在HOMO/LUMO能階上不同變化程度的差異。此系列共聚物也藉由其有機場效電晶體(OFETs)的表現來探討硒吩取代噻吩對電洞移動率的影響。在有機光伏電池的表現上，以硒吩為主的共聚物相對於以噻吩為主的共聚物具有明顯增加的短路電流密度(JSC)及僅些微減小的開路電壓(VOC)。
另一低能隙共聚物則是以多電子的苯并二噻吩(Benzo[1,2-b:4,5-b’]dithiophene)為予體和缺電子的腈乙烯(Cyanovinylene)或丁烯二腈(Fumaronitrile)為受體來設計與合成一系列具不同烷基鏈取代之予體-受體交替共聚物。共聚物骨架上的腈基(Cyano-group)不僅明顯減小能隙也拉深共聚物的HOMO能階，如此有利於增加有機光伏電池的開路電壓。以含腈乙烯共聚物或其PC61BM混成物為主的有機場效電晶體具有和文獻發表未退火(Non-Annealed)的立體規則聚(3-己烷基噻吩)(Regioregular Poly(3-hexylthiophene)或其PC61BM混成物相似的電洞移動率；此結果說明了含腈乙烯共聚物與立體規則聚(3-己烷基噻吩)在以富勒烯(Fullerene)為主的有機光伏電池中具有類似的電荷傳輸特性。此共聚物也被發現可使用溶劑退火(Solvent Annealing)的方式來提升有機光伏電池的能量轉換效率(Power Conversion Efficiency)；此現象在以苯并二噻吩為主的低能隙予體-受體共聚物中非常少見。以此類共聚物為電子予體材料及PC71BM為電子受體材料的異質界面(Bulk-Heterojunction)有機光伏電池可達到大於0.8伏特的開路電壓及接近5%的能量轉換效率。

關鍵字

π-共軛共聚物 ； 有機發光二極體 ； 有機光伏電池 ； 硒吩 ； 苯并二噻吩 ； 腈乙烯 ； 丁烯二腈溶劑退火

並列摘要

Polymer-based organic light-emitting diode (OLED) and organic photovoltaic (OPV) are two most extensively studied fields in polymer-based optoelectronics. In this thesis, three different series of π-conjugated copolymers have been designed and synthesized for OLED and OPV applications, respectively. The correlations between chemical structures and device performances have been studied and discussed in the context.
For OLED application, a series of new 9,10-diphenylanthracene-based, 2,6-linked blue-light-emitting copolymers bearing hole- or electron-transporter as well as bulky substituent have been successfully synthesized. Photophysical, thermal, electrochemical, and electroluminescent properties of these copolymers have studied and characterized. Bright and efficient blue fluorescence in the solid state have achieved by incorporating bulky substituent into the copolymer backbone. Both hole- and electron-transport-substituted copolymers apparently enhance the electroluminescent performance of their OLEDs. A better-balanced hole/electron charge carrier has ascribed to electron transporter-bearing copolymer OLED with a very mild luminous efficiency rolls off under a continuous operating voltages.
For OPV application, two series of low-band-gap copolymers have been designed and synthesized, first for a comparison study of thiophene- or selenophene-bridged donor-acceptor copolymers. The replacement of thiophene with selenophene in the backbone of these copolymers has found a significant reduction of energy band gaps, principally due to the lowering energy level of LUMO than the raising energy level of HOMO in these copolymers. Density functional theory (DFT) calculations are performed on these copolymers to assist explaining the heteroatom substitution on the variation of HOMO/LUMO energy levels. Organic field-effect-transistors (OFETs) have also been fabricated to study the heteroatom effect on the hole mobility of these copolymers. Largely increased short-circuit current density (JSC) and slightly decreased open-circuit voltage (VOC) in OPVs using [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the electron acceptor have been demonstrated for selenophene-bridged donor-acceptor copolymers when compared with those of thiophene-bridged copolymers.
Second, a series of donor-acceptor π-conjugated copolymers based on electron-rich benzo[1,2-b:4,5-b’]dithiophene (BDT) and electron-deficient cyanovinylene (CNV) or fumaronitrile (FN) moieties have been newly designed and synthesized. These copolymers are structurally tailored by anchoring alkyl chains on the backbone of the copolymer main chain to increase the solubility and molecular weights of copolymers. Having cyano- (CN) substituent on the copolymer chain, a considerable reduction of energy band-gap (Eg) has been found. It also deepens the HOMO energy level of copolymers, which increases VOC of OPVs. OFETs based on the CNV-containing copolymers and its composites with PC61BM have demonstrated hole mobilities close to those of non-annealed regioregular poly(3-hexylthiophene) (rrP3HT) and rrP3HT/PC61BM OFETs reported in literature, indicating similar charge transporting characteristics of the CNV-containing copolymer in fullerene-based OPVs. The CNV-containing copolymers are found solvent annealing effective in OPV fabrication for enhancing power conversion efficiency (PCE). This is rarely seen among BDT-based low band-gap donor-acceptor copolymers. High VOC (> 0.80 V) and PCE (~5.0 %) bulk-heterojunction [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based OPVs have achieved by using the copolymers as the electron-donor material.

並列關鍵字

π-Conjugated Polymers ； Organic Light-Emitting Diodes ； Organic Photovoltaics ； Selenophene ； Benzo[1,2-b:4,5-b’]dithiophene ； Cyanovinylene ； Fumaronitrile ； Solvent Annealing

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