Influence of end-capped group on structural and electronic properties of the At-π-Ac-π-At small molecule donor for high-performance organic solar cells

Abstract

To achieve high efficient donors for organic solar cells, structural, electronic, and optical properties of the At-π-Ac-π-At small molecules were systematically evaluated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The At-π-Ac-π-At structure consists of a benzo[1,2-b:4,5-c′]dithiophene-4,8-dione (BDD) unit acting as the central core acceptor (Ac) incorporated with 8 different end-capped groups (At) via trithiophene linkages. The results revealed that the coplanar structures were elucidated from A3 to A7 due to intramolecular hydrogen bonds and strong non-covalent S⋯O interactions along the molecular backbone. The HOMO-LUMO gap of a referenced DR3TBDD (A3) structure calculated from the B3LYP/6-31G(d,p) method is in very good agreement with the experimental evaluation. The end-capped units pronounced a significant influence on the modulation of molecular energy level. The HOMO-LUMO gaps obtained from A1, A4, A5, A6, and A8 are narrower than that determined from DR3TBDD (A3), implying the enchantment of the short circuit density (Jsc). For electron mobility, A1, A4, A6, and A7 structures were an easier hole transport character compared with A3, while a higher deformation energy for oxidation process was demanded for A2, A5, and A8. The dicyano terminals exhibited a larger red-shifted peak with broader absorption spectra compared with other end-capped functionals. Our results supplied theoretical descriptions of the At-π-Ac-π-At donor material for further enhancing the performance of organic solar cells.