Theoretically designing and evaluation of highly efficient small donor molecules for organic solar cells

Abstract The development of High-efficiency photovoltaic devices are the need of time with increasing demand for energy. Herein, we designed seven small molecule donors (SMDs) with A-π-D-π-A backbones containing various acceptor groups for high-efficiency organic solar cells (OSCs). The molecular engineering was performed through substituting the acceptor group in the synthesized compound ( BPR ) with another highly efficient acceptor group to improve the photoelectric performance of the molecule. The photovoltaic, optoelectronic, and photophysical properties of the proposed compounds ( BP1–BP7 ) were investigated in comparison to BPR using theoretical approaches (DFT and TD-DFT). The key element for effective OSCs is SMDs' red-shifted absorption. All molecules we designed have red-shifted absorption spectra. The modification of the acceptor fragment of the BPR resulted in a reduced HOMO-LUMO energy gap; thus, the designed compounds ( BP1–BP7 ) had improved optoelectronic responses as compared with the BPR molecule. The various key factors are crucial for efficient SMDs such as exciton binding energy, frontier molecular orbitals (FMOs), absorption maximum ( λ max ), open circuit voltage ( V OC ), dipole moment ( µ ), excitation charge nobilities, and transition density matrix of ( BPR, BP1 ‒ BP7 ) have also been studied. High charge mobility is provided by low reorganizational energy (holes and electrons) values, and all the designed compounds were enhanced in this regard. Low excitation energies, large dipole moment, and high open-circuit voltage suggest that our proposed SMDs are appropriate for high-efficiency OSCs. The superiority of the envisioned molecules is also superior, to experimenters to anticipate future developments in extremely effective OSC devices.