Theoretical Expedition for Enhancing Photovoltaic Performance: DFT Investigation of Benzo[c][1,2,5] thiadiazole-Based Scaffolds for Organic Solar Cells

Currently, the development of efficient photovoltaic materials is accelerated by the use of fullerene-free small molecular acceptors. Therefore, we designed and studied the optoelectronic characteristics of eight new A(1)-D-A(2)-D-A(1) configured benzothiazole-based molecules (BDIDZ2-BDIDZ9), obtained by the structural modification of the reference molecule (BDIDR1) with various acceptors. The M06/6-31G(d,p) functional was selected through a benchmarked study using DFT and the experimental UV-vis values of BDIDR1. Various parameters, like transition density matrix (TDM), frontier molecular orbitals (FMOs), binding energy (Eb), open-circuit voltage (V-oc), reorganization energies (RE) for holes and electrons, and density of states (DOS), were used to understand the optoelectronic properties of the designed compounds. Structural tailoring via the modification of terminal acceptors minimized the energy gap and shifted the absorption spectra toward redshift (752.37-778.89 nm), resulting in an enhanced charge transfer toward the LUMO from the HOMO. Moreover, the open-circuit voltage was calculated by HOMOPBDB-T-LUMOacceptor and compared with the parent chromophore. All of the derivatives showed a relatively higher open-circuit value. The lower reorganization energies in the holes and electrons suggested a higher rate of charge mobility. Interestingly, all of the modified chromophores displayed a better optoelectronic response than the reference molecule. The above-mentioned results indicate that molecular engineering with benzothiophene acceptors improves the photovoltaic response of nonfullerene chromophores and encourages experimentalists to develop high-efficacy photovoltaic devices.