Controlling the aggregation and crystallization kinetics of donors and acceptors is crucial for forming the desired morphology of the active layer, which heavily determines the power conversion efficiency (PCE) of organic solar cells (OSCs). In particular, modulating the crystallisation kinetics of ternary blend films, which are more complex than classic binary systems, is a great challenge. Here, we designed and synthesized two guest acceptors, Qx-8Cl and Qx-5Cl, based on a quinoxaline core with symmetric and asymmetric terminal groups, respectively. The crystallization kinetics of the ternary films, by blending Qx-8Cl and Qx-5Cl into the host system of PM6:BTP-eC9, were monitored using in situ optical spectroscopy. Compared with the symmetric Qx-8Cl, the asymmetric Qx-5Cl effectively balanced the aggregation of donor and acceptor and avoided the limitation of the preformed polymetric donor aggregation framework, resulting in more desired intermixed domain and favored vertical phase separation in the ternary film, thereby creating an ideal morphology of the active layer. As a result, the ternary OSCs based on PM6:BTP-eC9:Qx-5Cl exhibited an outstanding PCE of 19.83% (one of the highest PCE), while that of the PM6:BTP-eC9:Qx-8Cl-based device was only 18.81%. Moreover, a 17.3 cm2 OSC module based on PM6:BTP-eC9:Qx-5Cl has been fabricated with a remarkable PCE of 14.1%. Our work provides the detailed and deeper analysis of the morphology modulation by asymetric structure in the ternary strategy which contribute to favorable morpology by modulating crystallization kinetics of molecules.