The study of nitroxide radical redox-couple and anatase surface interaction: a guide to choose the best sensitizer

Nitroxide radical redox-couple compounds have the potentials to be applied as a redox couple in dye-sensitized solar cell applications since their standard reduction potential reached almost 1 V. Unfortunately, many reports revealed the limitations of nitroxide in dye-sensitized solar cell applications. This study investigates the interaction between several nitroxide radical redox couples with anatase surface. The Ti ₁₄ O ₃₁ H ₆ cluster was built as a model of anatase surface. The calculation results show that the limitation of the nitroxide radical redox-couple compounds was laid on the high charge transfer on the TiO ₂ surface. The high charge transfer indicates that the charge recombination from the redox-couple species to the semiconductor is preferable and is not beneficial for cell efficiency. The calculation also figures that almost the observed nitroxide radical compounds shifted the TiO ₂ conduction band positively to the − 2.5 eV. This finding proved to us that it is important to choose the sensitizer which has a LUMO above − 2.5 eV to avoid the fail of charge injection.