Resolving the Efficiency–Mechanical Trade‐off in Organic Solar Cells: 20.4% Enabled by Hydrogen‐Bonding Engineering

ABSTRACT Organic solar cells (OSCs) face a trade‐off between power conversion efficiency (PCE) and mechanical robustness: high toughness requires low‐crystallinity amorphous polymers, which impair photovoltaic performance. Herein, we propose a strategy combining random copolymerization and hydrogen‐bonding modulation to resolve this conflict. First, the incorporation of an ester‐substituted thiophene yields PM6‐H, exhibiting improved toughness (high crack‐onset strain, COS ) but lower PCE. Subsequently, introducing ─OH and ─OOCNHC 6 H 13 groups at the terminals of alkyl chains forms PM6‐OH and PM6‐UR. The hydrogen bonding serves dual functions: acting as dynamic cross‐linking sites to further enhance mechanical properties while restoring optimal lamellar stacking for efficient charge transport. As a result, these copolymers simultaneously achieve a COS exceeding 46%, a high PCE of up to 20.4%, and superior storage, thermal, and light stability (with T 80 being twice that of the PM6 benchmark). Flexible OSCs fabricated using these donor polymers deliver a PCE of 18.22% while maintaining outstanding flexibility, with ∼90% PCE retention after 2200 bending cycles (vs. 78% for controls). This work demonstrates that copolymerization with controlled hydrogen‐bonding interactions overcomes the efficiency‐robustness trade‐off in OSCs through precise structural modulation, paving the way for high‐performance, mechanically durable, and stable OSCs suitable for practical applications.