Depicting the role of end-capped acceptors to amplify the photovoltaic properties of benzothiadiazole core-based molecules for high-performance organic solar cell applications

In this study, the intention to improve the efficiency of OSCs, five molecules of A2-D-A1-D-A2 have been designed. Optoelectronic properties of all the investigated molecules are analyzed computationally by employing the DFT method with CAM-B3LYP functional at a 6-31G (d, p) basis set. By introducing acceptor groups to the terminal ends, it has been noticed that all the optoelectronic parameters of designed molecules have improved to a considerable extent when compared with the reference molecule, e.g., absorption properties, exciton mobility, molecular electrostatic potential (MEP), HOMO-LUMO band gap, light-harvesting efficiency (LHE), etc. Amongst all the designed molecules, T3 possesses the maximum absorption (λmax = 541 nm) with the smallest bandgap (4.21 eV), least excitation and binding energy i.e., (Ex = 2.29 eV) and (1.92 eV) respectively, as well as the smallest interaction coefficient (0.5877). While, T2 molecule has the maximum oscillator strength f = (3.51) with the most efficient light-harvesting efficiency (LHE = 0.9996). T1 with the least hole (λh = 0.01594) and electron (λe = 0.01723) reorganization energy values possesses better hole as well as electron mobility when compared with all other designed molecules. VOC is calculated by making a complex of investigated acceptor molecules with PTB7-Th donor molecules and the values obtained range from 2.27 to 3.22 eV. Additionally, the T4 molecule has a maximum open-circuit voltage (VOC) of 2.69 eV, VOC is directly related to the normalized VOC and FF so, T4 also possesses proficient results for both (normalized VOC = 104.0538 eV and FF = 0.9462). These results illustrate that the introduction of new acceptor groups to small molecules is worthwhile for organic solar cells (OSCs).