Designing High-Performance Stretchable Light-Harvesting Polymers for Organic Solar Cells through Tailored Amide Units with Varied Alkyl Chain Lengths

High mechanical robustness and high photovoltaic performance are essential for the practical application of stretchable organic solar cells (SOSCs) in stretchable and wearable electronics. In this regard, we designed and synthesized a series of novel donor polymers by incorporating amide units with flexible alkyl segments of varying lengths as a third component into the conjugated backbone of the D18 polymer. Tuning the length of these alkyl segments effectively modulates the aggregation behavior and crystallinity of the donor polymers, leading to an optimal blend morphology with the polymer acceptor PY-IT and enhancing both the mechanical and photovoltaic properties of the resulting blend films. Specifically, the solar cell based on the D18-C6:PY-IT blend achieved a high power conversion efficiency of 14.67% and demonstrated excellent stretchability with a crack onset strain of 30%, marking a significant improvement over the reference D18:PY-IT blend. This study elucidates the influence of the alkyl segment length within amide units on polymer crystallinity, providing a strategic approach for the design of high-performance stretchable active layer materials.