Theoretical study of D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells

We have designed four dyes based on D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO–LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting efficiency (LHE), hole–electron distribution, charge transfer amount from HOMO to LUMO (Q(CT)), D index, H(CT) index, S(m) index and exciton binding energy (E(coul)) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D–π–A′–π–A configuration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.