高迁移率窄带隙聚合物材料的侧链调控及其光电性能研究

Polymer Solar cells (PSCs) is one of the important devices which can directly convert solar energy into electricity. So far, power conversion efficiency (PCE) up to 11% has been achieved in a single junction device, which significantly encourages the community to commercialize the photovoltaic product by the roll-to-roll processing technique. However, how to maintain high power conversion efficiency within a wide range of the active layer thickness is still an issue during roll-to-roll process. This project utilizes the promising quarterthiophene-fluorobenzothiadiazole repeating unit as main chain to synthesize new high-performance polymer donors through side chain control so as to realize highly efficient PSCs with active layer thickness in range of 100-800 nm. Designing and synthesizing new monomers with alkylester, alkylthio, alkylsulfonyl and their corresponding siloxane-terminated side chains, which can construct new polymers to achieve low-lying HOMO level and good planarity, and further high mobility and high power conversion efficiency. Furthermore, mixed type side chain from two of the above new side chains could be incorporated for polymer backbone with different ratios to obtain new random polymers with high mobility and high power conversion efficiency in thick-film devices. In this project, the comparative study based on the side chain controlling approach will develop many new polymer donors with PCEs of 10-12% for thick-film device applications, which may largely accelerate the commercialization of PSCs.

聚合物太阳能电池是将太阳能直接转换成电能的重要器件之一。如今，单结聚合物光伏器件的最高效率已达到11%，鼓舞了采用卷对卷工艺来商业化聚合物太阳能电池。然而在厚度有较大变化时如何仍能维持高器件效率是个难题。本项目基于具有重要研究价值的联四噻吩和氟代苯并噻二唑的重复单元为主链，通过侧链调控来提高聚合物的迁移率及其对应的光伏器件效率，实现膜厚在100纳米-800纳米变化范围下仍可获得高效率光伏器件。设计合成采用含烷酯基、烷砜基、烷硫基的新型侧链以及含端基为硅氧烷修饰的烷酯基、烷砜基、烷硫基的新型侧链构筑聚合物，保证其深HOMO能级和良好平面性，从而获得高迁移率和厚膜器件的高效率。再者，研究混合型侧链对所构筑的聚合物影响，可望获得具有高迁移率和高效率的无规型聚合物。总之，通过比较性研究，深入挖掘FBT-4T的最优侧链，实现厚膜光伏器件最高效率达到10-12%，加速聚合物太阳电池商业化进程。

获得活性层厚度不敏感的聚合物太阳电池是实现器件印刷的有效途径之一。针对厚膜（厚度>200nm）的关键科学问题，本项目提出高迁移率聚合物给体材料的设计和合成，主要采用有效的侧链工程，改善聚合物的分子量、聚集行为以及与给体相容性等问题，从而制备高性能厚膜聚合物太阳电池。基于氟代苯并噻二唑单元的聚合物给体，通过含硅氧烷封端的侧链无规共聚调控，与非富勒烯受体IDTBR所制备的器件，活性层厚度从210纳米到560纳米，器件效率均超过10%，在400纳米下，获得11.54%的最高效率。GIWAXS等测试表明，高迁移率聚合物在厚膜器件中能保证较好的形貌和载流子传输通道，特别是随着共混膜厚度增加，非富勒烯受体的电子迁移率逐渐增加，从而随厚度增加填充因子下降不明显。通过长支化侧链的引入，增加了含二噻吩并苯并氧二唑单元的聚合物的溶解性，仍保持很好的结晶性，从而提高富勒烯厚膜器件，并且与非富勒烯ITIC和IDIC都表现较高器件效率，而且用非卤溶剂三甲苯所制备的器件效率也不低。接着通过三元共混策略，进一步提高厚膜器件效率。我们还设计合成了含硅氧烷封端的烷硫侧链和烷氧侧链，分别构筑了聚合物给体CY1和PQSi05,获得了与非富勒烯更加匹配的聚合物给体，并且通过给受体的合成复杂度和器件效率的综合考虑计算了器件的平均品质因子。我们工作表明基于功能化的侧链调控策略具有很好的应用前景。