Evaporation Kinetics Engineering Suppressed Bimolecular Recombination in All‐Polymer Solar Cells

All-polymer solar cells (all-PSCs) combine the synthetic tunability of non-fullerene acceptor systems with intrinsic mechanical and thermal robustness of polymer active layers, yet their performance remains limited by pronounced bimolecular recombination, leading to insufficient fill factors (FFs) compared to polymer:small-molecule counterparts. Here, we introduce Phenanthrene (Ph) as a donor-selective morphology regulator in the benchmark all-PSC system. Capacitance spectroscopy reveals that bimolecular recombination dominates the recombination landscape and that Ph nearly halves the Langevin reduction factor, resulting in substantial improvement in FFs. Multiscale characterization, together with in situ optical spectroscopy and all-atom molecular-dynamics simulations, collectively show that, in contrast to 1-chloronaphthalene (1-CN, which remains in the film) and 2-methylnaphthalene (2-MN, which evaporates rapidly), Ph exhibits moderate evaporation kinetics during annealing. This enables enhanced donor crystallinity together with sufficient time and space for acceptor crystallization into fractal networks with increased fractal dimension, thereby reducing donor-acceptor interfacial area. As a result, Ph-assisted binary and ternary all-PSCs achieve power conversion efficiencies of 18.74% and 19.35%, respectively. By explicitly correlating additive molecular structure and evaporation kinetics with multiscale morphology and recombination pathways, this work establishes rational selection rules for volatile solid additives and provides a general strategy to suppress bimolecular recombination in high-performance all‑PSCs.