A clear understanding of the structure–performance relationship is important for promoting the evolution of designing efficient nonfused ring electron acceptors (NFREAs). Inspired by the above intention, herein, a side‐by‐side study is carried out based on three newly developed NFREAs by regulating rigid conjugation and flexible side chains, yielding PhNT‐4Cl, PhNC‐4Cl, and PhNP‐4Cl. It is unveiled that reduced miscibility by extending rigid conjugation can help to form nanofiber features, thus allowing high crystallinity, and a hindered overaggregation tendency by increasing steric hindrance of flexible side chain can help to form suitable domain sizes, thus avoiding severe charge recombination. As a result, PhNC‐4Cl with cyclopentadithiophene building block and branched alkyl side chains achieves a good balance in the earlier two aspects, thus enabling a higher efficiency of 14.01% with both higher photocurrent and fill factor, relative to PhNT‐4Cl (6.95%) and PhNP‐4Cl (6.31%). This work points out the critical role of miscibility‐driven morphology tuning on the device performance, thus guiding the molecular design toward efficient NFREAs.