Department of Materials Science and Engineering and The Shenzhen Key Laboratory for Printed Organic Electronics , Southern University of Science and Technology (SUSTech) , No. 1088, Xueyuan Road , Shenzhen , Guangdong 518055 , China.
ACS Appl Mater Interfaces. 2018 Jun 27;10(25):21481-21491. doi: 10.1021/acsami.8b05231. Epub 2018 Jun 13.
High-performance polymer solar cells (PSCs) with thick active layers are essential for large-scale production. Polymer semiconductors exhibiting a temperature-dependent aggregation property offer great advantages toward this purpose. In this study, three difluorobenzoxadiazole (ffBX)-based donor polymers, PffBX-T, PffBX-TT, and PffBX-DTT, were synthesized, which contain thiophene (T), thieno[3,2- b]thiophene (TT), and dithieno[3,2- b:2',3'- d]thiophene (DTT) as the π-spacers, respectively. Temperature-dependent absorption spectra reveal that the aggregation strength increases in the order of PffBX-T, PffBX-TT, and PffBX-DTT as the π-spacer becomes larger. PffBX-TT with the intermediate aggregation strength enables well-controlled disorder-order transition in the casting process of blend film, thus leading to the best film morphology and the highest performance in PSCs. Thick-film PSCs with an average power conversion efficiency (PCE) of 8.91% and the maximum value of 9.10% are achieved using PffBX-TT:PCBM active layer with a thickness of 250 nm. The neat film of PffBX-TT also shows a high hole mobility of 1.09 cm V s in organic thin-film transistors. When PffBX-DTT and PffBX-T are incorporated into PSCs utilizing PCBM acceptor, the average PCE decreases to 6.54 and 1.33%, respectively. The performance drop mainly comes from reduced short-circuit current, as a result of nonoptimal blend film morphology caused by a less well-controlled film formation process. A similar trend was also observed in nonfullerene type thick-film PSCs using IT-4F as the electron acceptor. These results show the significance of polymer aggregation strength tuning toward optimal bulk heterojunction film morphology using ffBX-based polymer model system. The study demonstrates that adjusting π-spacer is an effective method, in combination with other important approaches such as alkyl chain optimization, to generate high-performance thick-film PSCs which are critical for practical applications.
具有厚活性层的高性能聚合物太阳能电池 (PSC) 对于大规模生产至关重要。表现出温度依赖性聚集性质的聚合物半导体在这方面具有很大的优势。在这项研究中，合成了三种基于二氟苯并二恶唑 (ffBX) 的给体聚合物 PffBX-T、PffBX-TT 和 PffBX-DTT，它们分别含有噻吩 (T)、噻吩并[3,2-b]噻吩 (TT) 和二噻吩并[3,2-b:2',3'-d]噻吩 (DTT) 作为π-间隔基。温度依赖性吸收光谱表明，随着π-间隔基的增大，聚集强度按 PffBX-T、PffBX-TT 和 PffBX-DTT 的顺序增加。具有中等聚集强度的 PffBX-TT 可在共混膜的浇铸过程中实现良好控制的无序-有序转变，从而导致最佳的薄膜形态和 PSCs 的最高性能。使用 PffBX-TT:PCBM 活性层厚度为 250nm 的厚膜 PSCs 获得了平均功率转换效率 (PCE) 为 8.91% 和最大值为 9.10%。PffBX-TT 的纯膜在有机薄膜晶体管中也表现出 1.09cmV s 的高空穴迁移率。当 PffBX-DTT 和 PffBX-T 分别与 PCBM 受体一起用于 PSCs 时，平均 PCE 分别降低至 6.54%和 1.33%。性能下降主要归因于短路电流的减少，这是由于薄膜形成过程中控制不佳导致的非最优共混膜形态所致。在使用 IT-4F 作为电子受体的非富勒烯型厚膜 PSCs 中也观察到了类似的趋势。这些结果表明，在基于 ffBX 的聚合物模型系统中，调节聚合物聚集强度对于获得最佳体异质结薄膜形态以实现高性能厚膜 PSCs 非常重要。该研究表明，调整π-间隔基是一种有效的方法，与烷基链优化等其他重要方法相结合，可生成对于实际应用至关重要的高性能厚膜 PSCs。
