One pair of isomers, centrosymmetric anti‐Py‐1 and axisymmetric syn‐Py‐2, was designed and synthesized with an acceptor–donor–acceptor (A–D–A) structure by choosing dithienocyclopentapyrene with four 4‐hexylphenyl side chains as the D unit, and 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) malononitrile as the A unit. In‐depth structure–property relationship studies revealed that the isomers have similar UV/Vis absorption, fluorescence emission, and energy levels but significant differences in molecular shape, polarity, and charge mobility. Solution‐processed bulk‐heterojunction (BHJ) small‐molecule organic solar cells with Py‐1 as the electron‐acceptor material and PTB7‐Th as the electron‐donor material exhibit a power conversion efficiency (PCE) of 6.07 %, or 60 % higher than that of Py‐2 (3.7 %), which could be mainly attributed to the higher and more balanced hole/electron mobilities and better phase separation of the Py‐1‐based active layer.