Scalable Wide‐Bandgap Polymer Donors Enable 20.3% Efficiency and Ultra‐Stable Organic Solar Cells via Rational Halogenation Strategy

ABSTRACT The advancement of wide‐bandgap (WBG) polymer donors is crucial for enhancing the practical viability of organic solar cells (OSCs), yet balancing high efficiency, long‐term stability, and synthetic simplicity remains a significant challenge. This study presents a modular strategy involving simultaneous halogen modification and side‐chain synergy to create polymer donors (PBTQ‐F, ‐Cl, ‐2F), enabling precise adjustment of their optical and electronic properties. Notably, the monochlorinated polymer PBTQ‐Cl achieves an optimal balance: it exhibits optimal compatibility with the BTP‐eC9, promotes rapid film formation kinetics, and forms compact π–π stacking with extended crystal coherence length. PBTQ‐Cl‐based binary devices deliver a power conversion efficiency (PCE) of 18.55% with exceptional thermal stability, retaining 87% of initial PCE after 5700 h at 85°C in N 2 (T 80 > 11 000 h). When incorporated into PM6:BTP‐eC9, PBTQ‐Cl promotes crystallization, suppresses non‐radiative recombination, and optimizes morphology, raising the ternary PCE from 18.87% to 20.30% with improved stability (T 80 > 4000 h at 85°C in N 2 ; > 90% PCE retention after 600 h maximum power point (MPP) tracking). Overall, this work establishes clear structure–property–performance relationships and provides useful insights into developing scalable wide‐bandgap polymer donors with both high efficiency and exceptional long‐term stability.