Development of a functionally separated D–π-A fluorescent dye with a pyrazyl group as an electron-accepting group for dye-sensitized solar cells

Abstract

A functionally separated D–π-A dye OUK-3 with a pyrazyl group as an electron-withdrawing anchoring group and a carboxyl group as an additional anchoring group has been newly developed as a photosensitizer for dye-sensitized solar cells. The optical and electrochemical properties, adsorption states on TiO₂ nanoparticles, and photovoltaic performances in dye-sensitized solar cells (DSSCs) were investigated. It was found that the maximum adsorption amount of dye adsorbed on the TiO₂ electrode for OUK-3 is 3 times as much as that of the D–π-A dye sensitizer OUK-1 with a pyrazyl group as an electron-withdrawing anchoring group. Moreover, this work revealed that the DSSC based on the dye OUK-3 exhibits a higher photovoltage (V_oc) value than the DSSC based on the dye OUK-1. On the basis of the FTIR spectra of the dyes adsorbed on TiO₂ nanoparticles and the electrochemical impedance spectroscopy (EIS) analysis of DSSCs based on the two dyes OUK-1 and OUK-3, the differences of photovoltaic performances between the two dyes are discussed by taking into account the adsorption states of the dyes adsorbed on the TiO₂ surface. This work demonstrates that functionally separated D–π-A dye sensitizers can achieve effective surface coverage of the TiO₂ electrode due to their high adsorption ability onto the TiO₂ electrode, leading to not only the improvement of light-harvesting efficiency (LHE), but also an increase in the number of injected electrons in the CB of TiO₂, which is responsible for the higher V_oc value of functionally separated D–π-A dye sensitizers.