Rational Design of Bay-Annulated Indigo (BAI)-Based Oligomers for Bulk Heterojunction Organic Solar Cells: A Density Functional Theory (DFT) Study

[Image: see text] In this paper, we have designed a series of oligomers based on the donor–acceptor concept. Here, acceptor bay-annulated indigo (BAI) dye and donor N-methyl-4,5-diazacarbazole (DAC) are joined by a thiophene linkage. We have substituted the 5th and 5′th positions of the acceptor unit and the 2nd position of the donor unit with various electron-withdrawing and electron-donating groups to study various structural and electronic properties of the compounds. In this regard, we have calculated the dihedral angle, distortion energy, bond length alteration (BLA) parameters, bang gap (Δ(H – L)) values, partial density of states (PDOS), electrostatic potential (ESP) surface analysis, reorganization energy, charge transfer rates, hopping mobility values, and absorption spectra of the compounds. The ESP plots of the compounds indicate significant charge separation in the studied compounds. Our study manifests that the designed compounds are prone to facile charge transport.