Theoretical investigation of the donor group related electronic structure properties in push-pull organic sensitizers

Abstract

The judicious selection of donors is one common tactic to elaborately tailor metal-free chromophores, which can harness visible as well as near-infrared solar photons and modulate the charge transfer kinetics at titania/dye/electrolyte interface in dye-sensitized solar cells. In this paper, to gain insight into the effect of the donor on spectroscopic properties, electronic structures, excited state lifetimes and reorganization energies which are related to light-harvesting capacity and charge transfer reaction, we carried out a computational investigation on a variety of ordinary arylamine electron donors, by use of three cyclopentadithiophene dyes (C246, C218 and K201) with the respective N-hexyl-carbazole (HCZ), dihexyloxy-substituted triphenylamine (HTPA) and bisfluorenylaniline (HFA) electron donors. Amongst these electron donors, N-hexyl-carbazole is found to display the weakest electron-donating capacity, accounting for the corresponding C246 dye with evidently blue-shifted light absorption in comparison with the other two congeners, and endowing the hole mainly localizing on the conjugated segment, which will slow down the regeneration reaction. The HFA electron donor group with large and rigid structure not only presents longer excited state lifetime, which could be beneficial to the photoinduced electron injection, but also features smaller reorganization energy for the regeneration process.