AbstractOrganic solar cells (OSCs) have demonstrated over 19% power conversion efficiency (PCE) with the help of material innovation and device optimization. Co‐working with newly designed materials, traditional solvent additives, 1‐chloronaphthalene (CN), and 1,8‐diodooctane (DIO) are still powerful in morphology modulation towards satisfying efficiencies. Here, we chose recently reported high‐performance polymer donors (PM6 & D18‐Fu) and small molecular acceptors (Y6 & L8‐BO) as active layer materials and processed them by different conditions (CN or DIO or none). Based on corresponding 12 groups of device results, and their film morphology characterizations (both ex‐situ and in‐situ ones), the property‐performance relationships are revealed case by case. It is thereby supposed to be taken as a successful attempt to demonstrate the importance and complexity of donor‐acceptor‐additive interaction, since the device performance and physics analyses are also tightly combined with morphology variation. Furthermore, ternary blend construction for PCE improvement provides an approaching 19% level and showcases the potential of understanding‐guided‐optimization (UGO) in the future of OSCs.