Role of acceptor guests in tuning optoelectronic properties of benzothiadiazole core based non-fullerene acceptors for high-performance bulk-heterojunction organic solar cells

Recently, end-capped acceptors tailoring approach has attracted many researchers because of unceasing higher power conversion efficiencies (PCEs) of resulted compounds. By keeping in view, the crucial role of NFAs in bulk-heterojunction OSCs, herein, we molecularly engineered five new non-fullerene acceptor materials (Y6A1-Y6A5) by modifying a recently synthesized Y6 molecule (R), having 18% power conversion efficiency when combined with D18 donor polymer. The structural-elemental connection, physical-chemical, optoelectronic, and photovoltaic characteristics of novel deigned and reference material (R) are studied with advanced quantum-chemical modulations. Density functional theory and time dependent-density functional theory has been employed through various basis sets to investigate the designed molecules theoretically. Interestingly, all of the newly modeled materials displayed lower excitation energies with lower HOMO-LUMO energy-gaps in-contrast with R molecule. Moreover, a red-shifted absorption and lower reorganizational energies of electron and hole are also a novel feature of these designed materials. The lower binding energy values of modeled materials offers better charge separation and high photo-current density (J_sc) as compared to R. Transition density analysis, open circuit voltage, and molecular electrostatic potential analysis suggested that end-capped acceptors alteration of R molecule is an efficient approach for tuning the optoelectronic properties of non-fullerene-based acceptor molecules (Y6A1-Y6A5). In last, composite study of donor: acceptor (D18:Y6A2) complex has also been carried-out to realize the charge transfer process at the donor-acceptor interface. After all investigations, we hope that our theoretical modeled materials are superior than Y6 molecule, therefore, we endorse these materials for the synthesis to prepare highly-efficient BHJ-OSCs devices.