Howard Jenna B, Noh Sangtaik, Beier Alejandra E, Thompson Barry C
Department of Chemistry, Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, California 90089-1661, United States.
ACS Macro Lett. 2015 Jul 21;4(7):725-730. doi: 10.1021/acsmacrolett.5b00328. Epub 2015 Jun 23.
Recent work has pointed to polymer miscibility and surface energy as key figures of merit in the formation of organic alloys and synergistic behavior between components in ternary blend solar cells. Here, we present a simple model system and first report of poly(3-hexylthiophene)-based random copolymers featuring either a semifluoroalkyl (P3HTFHT) or oligoether (P3HTMET) side chain, prepared via Stille polycondensation. Water drop contact angle measurements demonstrated that P3HTFHT polymers reached a minimum surface energy of 14.2 mN/m at 50% composition of comonomers, while in contrast, P3HTMET polymers increased as high as 27.0 mN/m at 50% composition, compared to P3HT at 19.9 mN/m. Importantly, the surface energy of the copolymers was found to vary regularly with comonomer composition and exhibited fine-tuning. Optical and electronic properties of the polymers are found to be composition independent as determined by UV-vis and CV measurements; HOMO energy levels ranged from 5.25 to 5.30 eV; and optical band gaps all measured 1.9 eV. Following this model, surface energy modification of state-of-the-art polymers, without altering desirable electronic and optical properties, is proposed as a useful tool in identifying and exploiting more alloying polymer pairs for ternary blend solar cells.
近期的研究指出，聚合物的混溶性和表面能是有机合金形成以及三元共混太阳能电池中各组分间协同行为的关键性能指标。在此，我们展示了一个简单的模型体系，并首次报道了通过Stille缩聚反应制备的、带有半氟烷基（P3HTFHT）或低聚醚（P3HTMET）侧链的聚（3-己基噻吩）基无规共聚物。水滴接触角测量表明，P3HTFHT聚合物在共聚单体组成为50%时表面能达到最小值14.2 mN/m，而相比之下，P3HTMET聚合物在组成为50%时表面能高达27.0 mN/m，P3HT的表面能为19.9 mN/m。重要的是，发现共聚物的表面能随共聚单体组成呈规律性变化，并表现出微调特性。通过紫外可见光谱和循环伏安法测量确定，聚合物的光学和电子性质与组成无关；最高占据分子轨道（HOMO）能级范围为5.25至5.30 eV；光学带隙均为1.9 eV。按照此模型，在不改变现有聚合物理想的电子和光学性质情况下对其表面能进行改性，被认为是一种用于识别和开发更多用于三元共混太阳能电池的合金化聚合物对的有用工具。
