Electrical and photophysical analyses on the impacts of arylamine electron donors in cyclopentadithiophene dye-sensitized solar cells

The electron donor of a D-pi-A dye is known for its capability to tune both the electronic trait and packing mode of dye molecules chemisorbed on titania nanocrystals of dye-sensitized solar cells (DSCs), bringing on the opportunity to impact cell performance by modulating the physicochemical characteristics at the titania/dye/electrolyte interface. In this paper, we scrutinize the influences of arylamine electron donors on the optoelectronic features of thin-film DSCs employing a tris(1,10-phenanthroline) cobalt(II/III) redox electrolyte, by use of four cyclopentadithiophene dyes (C218, C244, C245 and C246) with the respective dihexyloxy-, diphenothiazinyl- or di-tert-butylphenyl-substituted triphenylamine and N-hexyl-carbazole electron donors. Amongst these electron donors, dihexyloxy-substituted triphenylamine is found to present the strongest electron-donating capacity, endowing the corresponding C218 dye with evidently red-shifted light absorption in comparison with the other three congeners. Transient absorption measurements show that all DSCs exhibit expeditious dye regeneration, guaranteeing efficient long-distance charge separation at the titania/dye/redox couple interface. Furthermore, it is worthwhile noting that the C218 dye prompts the highest open-circuit photovoltage amongst these chromophores, which is primarily attributed to the positive effect of slow cobalt(III) interception of titania electrons, highlighting the superiority of applying dihexyloxy-substituted triphenylamine as the electron donor for a cyclopentadithiophene dye.