Thiophene–benzothiadiazole–thiophene (D–A–D) based polymers: effect of donor/acceptor moieties adjacent to D–A–D segment on photophysical and photovoltaic properties
作者:Prashant Sonar、Evan L. Williams、Samarendra P. Singh、Ananth Dodabalapur
DOI:10.1039/c1jm10649j
日期:——
New pushâpull copolymers based on thiophene (donor) and benzothiadiazole (acceptor) units, poly[4,7-bis(3-dodecylthiophene-2-yl) benzothiadiazole-co-thiophene] (PT3B1) and poly[4,7-bis(3-dodecylthiophene-2-yl) benzothiadiazole-co-benzothiadiazole] (PT2B2), are designed and synthesized via Stille and Suzuki coupling routes respectively. Gel permeation chromatography shows the number average molecular weights are 31â100 and 8400 g molâ1 for the two polymers, respectively. Both polymers have shown absorption throughout a wide range of the UV-vis region, from 300 to 650 nm. A significant red shift of the absorption edge is observed in thin films compared to solution of the copolymers; the optical band gap is in the range of 1.7 to 1.8 eV. Cyclic voltammetry indicates reversible oxidation and reduction processes with HOMO energy levels calculated to be in the range of 5.2 to 5.4 eV. Upon testing both materials for organic field-effect transistors (OFETs), PT3B1 showed a hole mobility of 6.1 Ã 10â4 cm2 Vâ1 sâ1, while PT2B2 did not show any field effect transport. Both copolymers displayed a photovoltaic response when combined with a methanofullerene as an electron acceptor. The best performance was achieved when the copolymer PT3B1 was blended with [70]PCBM in a 1â:â4 ratio, exhibiting a short-circuit current of 7.27 mA cmâ2, an open circuit voltage of 0.85 V, and a fill factor of 41% yielding a power conversion efficiency of 2.54% under simulated air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cmâ2). Similar devices utilizing PT2B2 in place of PT3B1 demonstrated reduced performance with a short-circuit current of 4.8 mA cmâ2, an open circuit voltage of 0.73 V, and a fill factor of 30% resulting in a power conversion efficiency of roughly 1.06%.
基于噻吩(供体)和苯并噻二唑(受体)单元的新型推拉共聚物--聚[4,7-双(3-十二烷基噻吩-2-基)苯并噻二唑-共噻吩](PT3B1)和聚[4、7-双(3-十二烷基噻吩-2-基)苯并噻二唑-共噻吩](PT2B2)。凝胶渗透色谱法显示,这两种聚合物的平均分子量分别为 31â100 和 8400 g molâ1 。这两种聚合物在 300 至 650 纳米的紫外可见光范围内均有吸收。与这两种共聚物的溶液相比,薄膜的吸收边缘出现了明显的红移;光带隙在 1.7 至 1.8 eV 之间。循环伏安法显示了可逆的氧化和还原过程,计算得出的 HOMO 能级在 5.2 至 5.4 eV 之间。在对这两种材料进行有机场效应晶体管(OFET)测试时,PT3B1 显示出 6.1 Ã 10â4 cm2 Vâ1 sâ1 的空穴迁移率,而 PT2B2 则没有显示出任何场效应传输。这两种共聚物与作为电子受体的甲烷富勒烯结合后,都显示出光电效应。当共聚物PT3B1与[70]PCBM以1â:â4的比例混合时,性能最佳,在模拟空气质量(AM)1.5全球(1.5 G)照明条件(100 mW cmâ2)下,短路电流为7.27 mA cmâ2,开路电压为0.85 V,填充因子为41%,功率转换效率为2.54%。利用 PT2B2 代替 PT3B1 的类似器件性能有所下降,短路电流为 4.8 mA cmâ2,开路电压为 0.73 V,填充因子为 30%,功率转换效率约为 1.06%。