“Steric‐Locking” Polymer Acceptor Enabled 20.53% Efficiency With Suppressed Energetic Disorder and Enhanced Mechanical Robustness in Green‐Solvent Processed All‐Polymer Solar Cells

The realization of high-performance organic photovoltaics via environmentally benign manufacturing is pivotal for sustainable energy. While all-polymer solar cells (all-PSCs) offer superior stability and mechanical resilience, achieving high efficiencies in nonhalogenated green solvents remains a formidable challenge. Here, we report a "steric-locking" strategy for polymer acceptor design that enables a record-breaking power conversion efficiency of 20.53% (certified 19.79%) in o-xylene-processed all-PSCs. The introduction of a steric-locking guest polymer acceptor (PY-IDT) into the PM6:PYF-T-o host matrix profoundly regulates the crystallization kinetics and suppresses the excessive self-aggregation of the host acceptor. This molecular-level structural refinement significantly reduces energetic disorder and minimizes non-radiative voltage loss. Consequently, the suppressed energetic disorder and refined nanostructured domains yielded a concurrent leap in open-circuit voltage (0.942 V) and fill factor (82.11%). Furthermore, the steric-locked morphology demonstrates exceptional mechanical robustness, maintaining 92.6% of its initial efficiency after 1000 bending cycles. This work establishes a new efficiency benchmark and provides a universal chemical framework for developing high-performance, sustainable, and flexible optoelectronics.