AbstractThree novel copolymers based on zigzag naphthodithiophene (zNDT) with different aromatic rings as π bridges and different core side substitutions are designed and synthesized (PzNDT‐T‐1,3‐bis(4‐(2‐ethylhexyl)‐thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c′]‐dithiophene‐4,8‐dione (BDD), PzNDT‐TT‐BDD, and PzNDTP‐T‐BDD, respectively). The 2D conjugation structure and molecular planarity of the polymers can be effectively altered through the modification of conjugated side chains and π‐bridges. These alterations contribute to the variation in energy levels, light absorption capacity, and morphology compatibility of the polymers. When blended with the nonfullerene acceptor (2,2′‐[(4,4,9,9‐tetrahexyl‐4,9‐dihydro‐sindaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis‐propanedinitrile) (IDIC), PzNDT‐T‐BDD exhibits the highest power conversion efficiency (PCE) of 9.72% among the three polymers. This result can be attributed to its superior crystallinity and more obvious face‐on orientation in blending film. PzNDT‐TT‐BDD and PzNDTP‐T‐BDD present PCE values of 8.20% and 4.62%, respectively. The alteration of polymer structure, particularly the modification of conjugated side chains and π‐bridges, is an effective strategy for designing NDT‐based polymers with high photovoltaic performance and potential applications in fullerene‐free solar cells.