含卡唑及噻吩衍生物之合成及其在有機太陽能電池應用之光電特性

Abstract

本研究運用烏曼偶合(Ullmann coupling)及鈴木偶合(Suzuki coupling)合成出以卡唑(carbazole)為主體，並由卡唑9號位置引入噻吩(thiophene)及苯並噻二唑(benzothiadiazole)的施體-受體(donor-acceptor)分子結構O1及O2，並在合成過程中得到卡唑對稱分子CBC、CTC及C2TC。進而以Yamamoto反應聚合成卡唑為主鏈，噻吩及苯並噻二唑為側鏈之聚合物P1。聚合物以凝膠滲透層析儀(GPC)測試，分析結果P1之重量平均分子量(Mw)為4333 g/mol，PDI為1.28。在熱性質上，各組化合物皆展現了良好的熱穩定性，熱裂解溫度(Td 5%)都在350℃以上。在光學性質方面，證實了在分子結構內引入噻吩確實能達到使吸收光譜紅移的效果，其中O2薄膜的最大吸收波長紅移至493 nm、吸收起始波長為604 nm，光學能隙為2.05 eV，O1和P1的能隙則分別為2.20 eV及2.18 eV。電化學分析顯示，隨著噻吩的增加，最高填滿分子軌域(highest occupied molecular orbital, HOMO)有向上提升的趨勢，不過各組材料大多落在-5.4 eV的位置，而結構內酯基的引入有助於最低未填分子軌域能階(lowest unoccupied molecular orbital, LUMO)的下降，這點在此材料的能階設計上有正面的影響。此外，三組卡唑對稱分子的HOMO及LUMO能階介於ITO (4.80 eV)和Alq3 (5.80 eV)之間，有機會作為發光二極體之電洞傳遞層材料。體異質接面太陽能電池元件的初步測試以O1和O2為主。O1與PCBM以1: 2的重量比例混摻，在以氯仿作為溶劑、900 rpm旋轉塗佈的條件下，得到最佳效率值為0.056%，其中開路電壓為0.53 V、短路電流0.32 mA/cm2、填充因子為0.33； 而O2以相同溶劑和旋轉塗佈轉速下，與PCBM 1:4重量比混摻，效率值為0.045%，其中開路電壓為0.44 V、短路電流0.38 mA/cm2、填充因子為0.27。

In this study, two carbazole derivatives (O1 and O2) with thiophene and benzothiadiazole-containing donor-acceptor structure were synthesized via Ullmann coupling and Suzuki coupling reactions. During the synthesizing process, three extra N-carbazole endcapped derivatives (CBC, CTC, and C2TC) were obtained. We also tried polymerizing the carbazole derivative monomers with thiophene and benzothiadiazole-containing side chain via Yamamoto coupling reaction, and Homopolymer P1 were synthesized with weight-average molecular weight of 4333 g/ mol, PDI 1.28. All derivatives were found with good thermal stability, and 5% thermal degradation temperature over 350 oC. The optical properties indicated that the absoption and emission maxma were red-shifted with increasing number of thiophene unit. The optical band gap of O1, O2 and P1 are 2.20 eV, 2.05 eV, 2.18 eV respectively. We also observed that the HOMO of these derivatives increased with increasing number of thiophene unit. The energy level of the three N-carbazole endcapped derivatives were found suitable for application of hole transporting layer of OLED. The preliminary bulk heterojunction solar cell device were fabricated with compound O1 and O2. The power conversion efficiency of the device based on O1: PCBM = 1 : 2 and O2: PCBM = 1 : 4 are 0.056% and 0.045% under AM 1.5G solar simulator.