含多環咪唑團基聚噻吩衍生物之合成、性質分析及其有機光電應用

Abstract

本研究之目的在於合成含多環咪唑團基之聚噻吩衍生物，並探討不同多環咪唑團基在熱性質、光學及電化學性質之影響。這些材料可作為主動層材料以製作高分子太陽能元件。本研究同時製備聚(3-己基噻吩) (P3HT)以作為對照之用。

利用GRIM途徑合成之高分子其立體規則度皆達95 %以上。所有高分子之數量平均分子量經測定為0.63-1.16×104 g/mol，重量平均分子量則為1.07-2.06×104 g/mol，PDI在1.53-1.84之間。引入咪唑團基之聚噻吩分子量較P3HT為小，乃因聚合時加入巨大的剛硬團基所致。所有高分子的熱裂解溫度皆達300 oC以上，引入剛硬咪唑團基之高分子經高溫加熱後，相較於P3HT有更多的殘留重量，確實可增強材料的熱穩定性。

含有咪唑團基之高分子薄膜態的最大吸收峰相較於P3HT產生藍位移。吸光範圍變大，且出現類似於P3HT之肩峰，顯示引入較巨大的咪唑團基仍具有主鏈間的堆疊及較強的吸收。所有高分子之螢光放射波長差異不大，但衰減的放射強度顯示這些材料中激子不易經由再結合而放光，暗示載子有更多機會傳遞至兩端電極。電化學分析顯示主鏈引入拉電子咪唑團基致使HOMO能階下降，且其還原起始電位均低於P3HT，顯示其注入電子的能力較佳。

本研究意外得到寡聚物O4與O5且其具有螢光特性，故製作三層式OLED元件以探討其光電應用。O4元件可發出綠光，最高亮度與效率達到238 cd/m2與0.12 cd/A，而O5元件則發出橘紅光，最高亮度與效率達到260 cd/m2與0.13 cd/A，說明這兩種寡聚物材料具有應用於發光元件之潛力。

The goal of this research is to synthesize polythiophene derivatives containing polycyclic aromatic imidazolyl substituents and to study the influence of different imidazolyl substituents on thermal, optical, and electrochemical properties. Those materials can be used as active layer for fabrication of organic solar cells. Poly(3-hexylthiophene) (P3HT) were also synthesized for comparison in this study.

Polymers with high regioregularity > 95% were synthesized via the Grignard metathesis. The number-average molecular weights of polymers are in the range of 0.63-1.16×104 g/mol, while their weight-average molecular weights are in the range of 1.07-2.06×104 g/mol, with PDI in between 1.53 and 1.84. The molecular weights of polythiophene derivatives containing imidazolyl substitutes are lower than P3HT because of introducing bulky and rigid groups. The decomposition temperatures of all polymers exceed 300 oC. Polythiophene derivatives containing imidazolyl substituents possess more weight residues than P3HT after heating, indicative of enhanced thermal stabilities.

The maximum UV-vis absorption of polythiophene derivatives containing imidazolyl substitutes show blue-shifted compared to P3HT in film state. Broader absorption range and shoulder bands of polythiophene derivatives analogous to P3HT indicate preserved stacking between backbones and enhanced absorption after introducing imidazolyl groups. All polymers show insignificant difference in PL emission wavelength; however, attenuation of fluorescent intensity demonstrates that excitons are not easy to recombine to emit light in those materials, implying more opportunity for carrier to transport to both electrodes. Electrochemical analysis shows that introducing imidazolyl groups onto main chains results in decreasing HOMO level, and the onset of reduction potentials of those derivatives are lower than P3HT, revealing the ease of electron injection.

In this research, oligomers O4 and O5 were unexpectedly obtained and found to be fluorescent, thus triple-layer OLED devices were fabricated to evaluate their optoelectronic applications. O4 device emitted green light, and its highest brightness and current efficiency reached 238 cd/m2 and 0.12 cd/A, respectively. O5 device emitted red light, and its highest brightness and current efficiency reached 260 cd/m2 and 0.13 cd/A, respectively. The above results indicate that these two materials are potential candidates for the application in light-emitting devices.