Two new building blocks of perylene-embedded benzoazoles containing both rigid 2D-conjugated aromatic rings and flexible branched alkyl chains were designed and facilely synthesized in high yields for organic solar cells (OSCs). With a typical acceptor of diketopyrrolopyrrole, small molecular OSC donors constructed in an acceptor-fused donor-acceptor motif exhibit excellent solubility, stability, and light absorption with tunable frontier orbitals, leading to a power conversion efficiency of up to 2.88% in preliminary OSCs.