In organic photovoltaics (OPVs), the π-orbital coherent stack of π-conjugated polymers in the active layer exerts a profound influence on exciton dissociation and charge transport. Nevertheless, the structural flexibility intrinsic of π-conjugated polymers fundamentally restricts ordered π-orbital coherent stack, thereby establishing persistent performance limitations in OPVs. Here, we demonstrate a universal crystal-induced polymeric π-orbital coherent stack reinforcement strategy by incorporating nano-monolayer nickel phosphorus trisulfide (NiPS₃) crystal as a multifunctional additive, to modulates tighter π–π stacking and extended crystallite coherence length. These structural improvements synergistically extend exciton lifetime, suppress carrier recombination, and optimize charge transport. Consequently, OPVs based on D18-Cl:L8-BO system achieves an impressive power conversion efficiency (PCE) of 20.83% with concurrent improvements in short-circuit current density and fill factor. The universality of this approach is further confirmed in PM6:L8-BO (PCE boosts from 17.41% ± 0.21% to 18.08% ± 0.11%) and D18:L8-BO (PCE improves from 19.20% ± 0.27% to 20.19% ± 0.20%) systems, where nano-monolayer NiPS₃ crystal universally mediates the formation of tightly π-orbital coherent stack of π-conjugated polymers with enhanced crystallite coherence length. This work establishes nano-monolayer NiPS₃ crystal as powerful tools for modulates π-orbital coherent stack of conjugated polymers, offering a materials-agnostic pathway toward high-efficiency OPVs.