Side‐Chain Asymmetry in Quinoxaline Copolymer Donors Enables Optimal Morphology and Improved Charge Dynamics for High‐Efficiency Organic Solar Cells

All-polymer solar cells (all-PSCs) have attracted increasing attention owing to their superior mechanical robustness, morphological stability, and solution-processability. However, intricate intermolecular interactions hinder the precise regulation of donor-acceptor miscibility and phase separation, thereby restricting the formation of ideal donor-acceptor interpenetrating networks and favorable charge dynamics. Herein, an asymmetric side-chain strategy is developed for a quinoxaline-based polymer donor (PBAQ6) to precisely modulate donor and acceptor miscibility. Systematic studies demonstrate that the side-chain structure could effectively modulate the film morphology features and charge dynamics of the active layer. Notably, the PBAQ6 polymer with an asymmetric side-chain configuration achieves reasonable donor-acceptor miscibility with the PYF-T-o polymer acceptor. Consequently, the PBAQ6:PYF-T-o-based binary all-PSCs deliver a power conversion efficiency (PCE) of 18.35%, and a further enhanced PCE of 19.52% is achieved for the ternary all-PSCs with a small amount of PBQ12 as a second polymer donor, which ranks among the best values reported so far. Overall, this work demonstrates that, within the investigated quinoxaline-based polymer-donor platform, asymmetric side-chain engineering can concurrently regulate donor-acceptor miscibility, active-layer morphology, and bulk charge dynamics, thereby providing a useful molecular-design principle for the development of high-performance all-polymer solar cells.