Structure–property relationships: Steric effect in ancillary ligand and how it influences photocurrent and photovoltage in dye-sensitized solar cells

Abstract

Here we report structure–property relationships of naphthalene-based ancillary ligands for DSCs employing Ru (II) bipyridyl complexes containing methoxy at 4,7-positions (HL-41) and ethoxy at 2-position (HL-42) on the naphthalene moiety respectively. 2-ethoxy naphthalene stilbazole-based ligand was strategically chosen as an ancillary ligand to ascertain the influence of steric effect of alkoxy group ortho to the spacer group (CHCH) of stilbazole on the photovoltaic properties. It was found that under similar conditions photocurrent response was in the following order HL-41 > HL-42 > N719. Both HL-41 and HL-42 showed similar redox potential. The overall conversion efficiency for devices employing HL-41, HL-42 and N719 were 7.8%, 7.6% and 7.6%, respectively. DFT calculations showed that the torsion angles between the naphthyl moiety and CHCH spacer was 34.81° and 39° for HL-41 and HL-42, respectively. Thus, for HL-42 ethoxy ortho to CHCH produces more twisted naphthyl which precludes efficient charge transfer from the ancillary ligand to the metal.