Star-branched polymer donors enabling high-performance organic solar cells with superior flexibility and intrinsic stretchability

Emerging wearable electronics are anticipated to leverage the flexibility and stretchability of organic solar cells (OSCs). However, achieving a balance between power conversion efficiency (PCE) and mechanical robustness remains challenging, as the molecular structural modifications required for enhanced flexibility of photovoltaic materials typically compromise charge transport and extraction. Herein, we design and synthesize three star-branched polymer donors (SPDs: S1, S2, and S3) by introducing different contents of 1,3,5-tris(bromomethyl)benzene, which boost fracture strain compared to the linear PM6 (12.70%, 15.33% and 19.16% to 10.46%), improving devices’ stress resistance/fatigue endurance. More importantly, these SPDs are able to self-assemble into refined fibrous architectures to retain perfect optoelectronic properties: S2:L8-BO OSCs reach 19.51% (rigid), 18.39% (flexible), 15.40% (stretchable); ternary ones hit 20.48%. This molecular engineering strategy successfully overcomes the unfavorable competition between efficiency and mechanical compliance, paving the way for the commercialization of high-performance OSCs as reliable power sources for wearable electronics.