A comparative investigation of the role of anchoring group on perylene monoimide dyes in NiO based dye-sensitized solar cells.

The anchoring group of a sensitizer may strongly affect the overall properties and stability of the resulting dye sensitized solar cells (DSSCs) and dye sensitized photoelectrosynthetic solar cells (DSPECs). This article describes a comprehensive study of the properties of seven perylene monoimide dyes (PMI) for their immobilization on nanocrystalline NiO film. The PMI dyes differ only by the nature of the anchoring group, which are: carboxylic acid (PMI-CO 2 H), phosphonic acid (PMI-PO 3 H 2 ), acetyl acetone (PMI-acac), pyridine (PMI-Py), aniline (PMI-NH 2 ), hydroxyquinoline (PMI-HQ), and dipicolic acid (PMI-DPA). The dyes were investigated by cyclic voltammetry, spectroelectrochemistry, modeled by DT-DFT quantum chemical calculations. The mode of binding of these anchoring groups was investigated by infrared spectroscopy and the stability of the binding to NiO surface was studied by desorption experiments in acidic and basic media. Overall, we found that phosphonic acid group offers the strongest binding to NiO surface in terms of stability and dye loading. Finally, a photophysical study by ultrafast transient absorption spectroscopy shows that all dyes inject a hole in NiO with rate constants on a subpicosecond timescale and display similar charge recombination kinetics. The photovoltaic properties of the dyes show that PMI-HQ and PMI-acac gave the highest photovoltaic performances due to lower degree of aggregation on the surface.