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

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 ─OOCNHC₆H₁₃ 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 T₈₀ 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.