Effect of “push–pull” sensitizers with modified conjugation bridges on the performance of p-type dye-sensitized solar cells

Abstract

A series of “push–pull” sensitizers with modified conjugation bridges are designed and investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT), with the purpose of revealing the effect of different linker moieties on the performance of p-type dye-sensitized solar cells (DSSCs). Creatively, the electron-rich unit (thiophene) and the electron-deficient unit (pyrimidine) are studied as the linking groups in p-type sensitizers from a comparative perspective, two special bridge-sites and the lengths of conjugation bridges are also taken into account. Calculations of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) indicate that there is efficient hole injection and dye regeneration for all the sensitizers. Importantly, the influence of the number of thiophene and pyrimidine moieties is seen mainly on the long-wavelength region and the short-wavelength region, respectively. According to the charge transfer properties and the driving forces of hole injection, dye regeneration and charge recombination (ΔG_inj, ΔG_reg and ΔG_CR, respectively), the increased length of the thiophene-based bridge close to the carboxyl group has a positive impact on the device performance. Likewise, for the pyrimidine-based bridges, it is probably the increased conjugation length between the donor and acceptor that significantly improves the device efficiency. Our intensive analysis on the π-bridges provides assistance for designing more efficient p-type photosensitizers, which contributes to the rational design for tandem DSSCs.