Terminal Modulation of D-π-A Small Molecule for Organic Photovoltaic Materials: A Theoretical Molecular Design

A class of D-pi-A-A type small-molecule donor materials used in heterojunction solar cell has been designed and investigated by means of quantum chemical calculations. A linear D-pi-A molecule containing triphenyl-amine (TPA), ethynylbenzene (EB), and diketopyrrolopyrrole (DPP) is end-capped with various electron acceptors to further enhance its electron-accepting capability. To gain a better understanding of the effects of terminal acceptors on the modulation of electronic and optical properties of D-pi-A molecule, the geometrical structures, light-absorbing capacities, frontier orbitals, exciton binding energies, intramolecular charge transfer (ICT) properties, and exciton dissociation rates at the interface are analyzed in detail to establish the structure property relationships for D-pi-A-A type materials. The calculated results indicate that the terminal modulation is an effective strategy to enhance light-absorbing capacities, ICT properties, and exciton dissociation at the heterojunction interface. The predicted power conversion efficiency (PCE) of designed molecules by Scharber diagram could reach up to more than 8%, which sheds light on the exploration of high-performance small-molecule donors for photovoltaic applications.