A comparative study of two novel thiophene-based ancillary ligands of Ru(II) complexes for high efficiency dye-sensitized solar cells

Abstract

Two novel heteroleptic polypyridyl Ru-complexes, MMR-1 and MMR-2, containing 2-(methylthio)thiophene and 2-(4-methoxyphenyl)thiophene units on the antenna of ancillary ligands (AL), respectively, were designed, synthesized and characterized as sensitizers for dye-sensitized solar cells. The maximum absorption wavelength of MMR-1 is more red-shifted than that of MMR-2, however, MMR-2 has higher molar extinction coefficient, leading to better light harvesting. Under the same device fabrication conditions, the photovoltaic performances of these newly produced sensitizers were evaluated as anchored on mesoporous TiO2 and compared to the benchmark N719. Both MMR-1 and MMR-2 exhibited comparable or even higher solar-to-electric conversion efficiencies (η) with respect to N719 when employed as photosensitizers in DSSCs. Compared to MMR-1, MMR-2 exhibited better overall conversion efficiency, which was attributed to the electron donating effect of the 4-methoxyphenyl group and the better absorptivity by harvesting higher energetic photons. MMR-2 also displayed higher VOC than MMR-1, which is likely due to the extension of the antenna of ancillary ligand by inserting a phenyl group leading to less dye aggregation. For MMR-2, the photovoltaic performance was better with JSC of 16.76 mA∙cm-2, VOC of 0.673 V, fill factor of 73.5% and η of 8.29% with the addition of 0.5M 4-tert-butylpyridine (TBP) compared to 8.18% of N719.