Theoretical Understanding and Role of Guest π-Bridges in Triphenylamine-Based Donor Materials for High-Performance Solar Cells

In recent years, significant attention has been devoted to developing small-molecule-based donor materials to prepare efficient and highly stable solar cell devices. For this purpose, development of several kinds of donor materials has received much attention from the scientific community. Herein, a new strategy to design photovoltaic materials using various bridged-core modifications to tune the optoelectronic properties of the materials has been reported. Therefore, eight newly designed donor materials (DP1–DP8) have been studied by modifying a formerly reported and scientifically verified reference molecule R. These newly designed materials (DP1–DP8) were theoretically optimized with different functionals used in density functional theory (DFT) and time-dependent-DFT (TD-DFT). Precise but advanced quantum chemical techniques, such as the configuration of the frontier molecular orbitals (FMOs), absorption maxima, density of states (DOS), excitation and binding energies, reorganization energy, transition density matrix (TDMs), and open-circuit voltages (Voc), on these designed (DP1–DP8) molecules were used to explore these materials theoretically. Furthermore, a study of the donor–acceptor (DP4–PC61BM) complex was also performed to address the possible charge-shifting phenomenon. Further characterization of these molecules (DP1–DP8) suggests that all of the systems are red shifted in the absorption spectrum and have lower binding and excitation energy values. In addition, all of the newly designed materials/molecules (DP1–DP8) showed narrow band gaps and higher charge transformation capability compared with the reference molecule R. The improvement in the photovoltaic and optoelectronic properties in all of the newly designed materials (DP1–DP8) showed that this is an effective strategy to build an efficient molecule for solar cell applications. Hence, DP1–DP8 were used to synthesize highly efficient and stable solar cell devices.