Enhancing Mechanical Durability and Long-Term Stability in Organic Solar Cells via Flexible Linker-Sequential Block Copolymerized Donors.

Multi-component copolymerized donors (MCDs) hold great promise for improving both the efficiency and mechanical robustness of flexible organic solar cells (f-OSCs) owing to their facile molecular tunability and advantageous one-pot copolymerization. However, despite the excellent crystallinity imparted by their highly conjugated polymer backbone, MCDs often struggle to retain photovoltaic performance under large external deformations, limiting their applicability in wearable devices. Herein, we developed a novel series of flexible linker-sequential block MCDs (Fs-MCDs), specifically PM6-Cl-b-D18-Cl-BTB, PM6-Cl-b-D18-Cl-BTH, and PM6-Cl-b-D18-Cl-BTD, by precisely incorporating flexible functional groups into the conjugated polymer skeleton. This design strategy introduced highly effective tensile active sites, resulting in remarkable mechanical durability, with PM6-Cl-b-D18-Cl-BTD achieving crack-onset strain (COS) values of 49.88 % in pristine films and 31.29 % in blends. The nearly 50 % COS in pristine films represents one of the highest values reported for Fs-MCD-based OSCs, marking a significant milestone in advancing f-OSC. Additionally, PM6-Cl-b-D18-Cl-BTD demonstrated excellent photovoltaic performance, with efficiencies of 18.09 % in rigid binary and 19.05 % in ternary, as well as 16.63 % in flexible OSCs. It also showed impressive device stability in invert OSC (T=9,078 h). This unique molecular design strategy provides a promising avenue for synergistically improving the photovoltaic performance, mechanical properties, and device stability of f-OSCs.