Precise Structure Regulation Induced Morphological Ordering Enables All‐Polymer Solar Cells With 20.29% Efficiency and Extreme Mechanical Robustness

All polymer organic solar cells (APSCs) demonstrate distinctive advantages in balancing device efficiency while enhancing operational stability, particularly regarding mechanical robustness. However, their power conversion efficiency (PCE) has long been behind that of the corresponding devices with small molecular acceptors. This is due to the precise chemical structure modulation of polymer acceptors (PAs), enabling relatively coplanar conformation and ordered molecular stacking and thus achieving ideal morphology, which remains critically challenging. Herein, in this work, we have designed two biaxial conjugate extension PAs, with various side chain/terminal substituents to control their intermolecular non-covalent interactions, thereby optimizing aggregation behavior and microstructural orientation of polymer assemblies. It was found that the alkoxy-functionalized PQxO-IT facilitates stronger intermolecular interactions and tighter π-π stacking. Furthermore, the PQx-FT:PQxO-IT composite promoted charge carrier mobility and charge transport, while effectively suppressing non-radiative decay pathways. Consequently, the corresponding ternary device achieved the highest PCE of 20.29% (certified as 20.03%) for the APSC systems so far. Furthermore, the tight and ordered molecular packing endowed the flexible device with a PCE of 18.93% and remarkable durability during continuous bending tests. This study demonstrates a precise structure modulation strategy that offers a viable materials design pathway for high-performance flexible photovoltaics.