Inner side-chain engineering of non-fullerene acceptors enables efficient thick-film all-polymer solar cells

Morphology control remains a formidable challenge in all-polymer solar cells (all-PSCs). To finely tune the molecular packing and blend morphology, we propose an isobaric spacer modulation strategy focusing on the inner side chains of Y-series polymer acceptors. Three polymers (PY-EH, PY-BO, and PY-HD) were synthesized by solely varying the inner alkyl spacer length (C12, C8, and C4). We reveal that this spacer length strictly dictates the aggregation modes. The optimal C12 spacer in PY-EH introduces proper conformational flexibility to prevent excessive crystallization, inducing a disorder-limited weak H-aggregation. This ensures a highly compatible blend morphology with the PM6 donor, yielding a champion power conversion efficiency (PCE) of 16.38%. Furthermore, this robust continuous phase network endows the PM6:PY-EH blend with exceptional thickness tolerance, retaining an outstanding PCE of 14.24% even at an extended active layer thickness of 410 nm. This work provides a fundamental molecular design route for highly efficient and scalable all-PSCs.