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

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.