Theoretical framework for achieving high Voc in non-fused non-fullerene terthiophene-based end-capped modified derivatives for potential applications in organic photovoltaics

Non-fused ring-based OSCs are an excellent choice, which is attributed to their low cost and flexibility in applications. However, developing efficient and stable non-fused ring-based OSCs is still a big challenge. In this work, with the intent to increase Voc for enhanced performance, seven new molecules derived from a pre-existing A-D-A type A3T-5 molecule are proposed. Different important optical, electronic and efficiency-related attributes of molecules are studied using the DFT approach. It is discovered that newly devised molecules possess the optimum features required to construct proficient OSCs. They possess a small band gap ranging from 2.22-2.29 eV and planar geometries. Six of seven newly proposed molecules have less excitation energy, a higher absorption coefficient and higher dipole moment than A3T-5 in both gaseous and solvent phases. The A3T-7 molecule exhibited the maximum improvement in optoelectronic properties showing the highest λmax at 697 nm and the lowest Ex of 1.77 eV. The proposed molecules have lower ionization potential values, reorganization energies of electrons and interaction coefficients than the A3T-5 molecule. The Voc of six newly developed molecules is higher (Voc ranging from 1.46-1.72 eV) than that of A3T-5 (Voc = 1.55 eV). Similarly, almost all the proposed molecules except W6 exhibited improvement in fill factor compared to the A3T-5 reference. This remarkable improvement in efficiency-associated parameters (Voc and FF) proves that these molecules can be successfully used as an advanced version of terthiophene-based OSCs in the future.