Side‐Chain Substituents on Benzotriazole‐Based Polymer Acceptors Affecting the Performance of All‐Polymer Solar Cells

• Published in: Macromolecular rapid communications. 2022-08, Vol.43 (16), p.e2200062-n/a
• Main Authors: Fu, Huiting, Li, Yuxiang, Wu, Ziang, Lin, Francis R., Woo, Han Young, Jen, Alex K.‐Y.
• Format: Article
• Language: English
• Subjects: alkyl chains; all‐polymer solar cells; Benzotriazole; Chain branching; Comparative studies; crystallinity; Electromagnetic absorption; Energy conversion efficiency; Photovoltaic cells; Photovoltaics; polymer acceptors; Polymers; power conversion efficiencies; Solar cells
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202200062

Recently, the strategy of polymerized small‐molecule acceptors (PSMAs) has attracted extensive attention for applications in all‐polymer solar cells (all‐PSCs). Although side‐chain engineering is considered as a simple and effective strategy for manipulating polymer properties, the corresponding effect on photovoltaic performance of PSMAs in all‐PSCs has not been systemically investigated. Herein, a series of PSMAs based on the benzotriazole (BTz)‐core fused SMAs with different N‐alkyl chains including branched 2‐butyloctyl, linear n‐octyl, and methyl on the BTz unit, namely PZT‐C12, PZT‐C8, and PZT‐C1, respectively, is presented. Comparative studies show that the size of alkyl chains has a significant impact on the solid‐state behavior of PZT polymers, which in turn affects their light absorption and charge transporting capacities, and subsequently the all‐PSC performances. When combining with the polymer donor PBDB‐T, PZT‐C1 affords a champion power conversion efficiency of 14.9%, compared to 13.1% of PZT‐C12, and 13.8% of PZT‐C8 in the resultant all‐PSCs, mainly benefiting from its better crystallinity and the more favorable blend morphology. This work emphasizes the importance of optimizing side‐chain substituents on PSMAs for improving the device efficiency of all‐PSCs. A series of benzotriazole (BTz)‐containing polymer acceptors are synthesized with varied N‐alkyl chains to systematically investigate the influence of side chains on photovoltaic performance of their derived all‐polymer solar cells (all‐PSCs). It is found that the reduction of alkyl chain size can significantly optimize the optical absorption, charge‐transporting properties, and crystallinity of the corresponding polymers, leading to enhanced all‐PSC efficiencies.