Investigation of a copper(i) biquinoline complex for application in dye-sensitized solar cells

Abstract

The synthesis, properties and application of a Cu(2,2′-biquinoline-4,4′-dicarboxylic acid)₂ complex in dye-sensitized solar cells (DSSC) are described. The complex is electrochemically stable and strongly absorbing with a molar extinction coefficient at λ_(max) = 564 nm of 11 700 M⁻¹ cm⁻¹ (in MeOH). Experimental and computational data indicate that the HOMO, LUMO and electronic excited state energy levels are appropriate for functionality in a DSSC. From cyclic voltammetry the HOMO is estimated to be −5.27 eV, as supported by computational work, which locates the HOMO at −5.78 eV. From electrochemical, absorption and emission experiments, the MLCT energy levels are expected to be appropriate for electron injection into the TiO₂ conduction band. Our computations support this and locate the key MLCT transition at 563 nm. Despite this, the efficiency in DSSCs is extremely low (<0.1%) suggesting that the dye does not inject excited electrons into the TiO₂ conduction band.