Molecular Engineering of Unidirectional Non-Fused π-Bridge Containing Asymmetric Non-Fullerene Acceptors for High-Performance Organic Solar Cells

Developing small molecule-based asymmetric non-fullerene (SM-NFAs) acceptors is highly desirable because they possess a great structural diversity, higher dipole moment, and strong intermolecular interactions. Herein, eight new A-D-π-A type SM-NFAs PS-1 to PS-8, having an indacenodithiophene central core, are designed. These designed materials and a synthetic reference molecule (PS) are characterized using various advanced quantum chemical approaches. The theoretical analysis investigated the structure-property relationship, optical, optoelectronics, and photovoltaic characteristics of synthetic PS and modeled PS-1 to PS-8 molecules. Moreover, the electron-hole overlapping, frontier molecular orbitals, excitation energy, dipole moment, binding energy, molecular electrostatic potential, density of states, heat map, transition density of states, and reorganization energies of the hole and electrons are specifically investigated. These modeled PS-1 to PS-8 series showed narrower energy gaps, decreased binding energies, and improved absorption characteristics. Among these, the modeled PS-2 molecule shows a narrow energy gap (E_g) of 1.79 eV and enhanced absorbance of 877.45 nm compared to the synthetic reference PS molecule (E_g 2.02 eV and absorption 741.58 nm). Moreover, a thorough analysis of the PS-2/PTB7-Th complex demonstrates efficient charge transfer at the donor-acceptor interface. Therefore, it is believed that the proposed molecules PS-1 to PS-8 could be efficiently employed in preparing highly efficient organic solar cells (OSCs).