Anchoring Modes of Ru-Based N719 Dye onto Titania Substrates

Dye anchoring plays a vital role in determining cell efficiency and extensively influences the stability of dye-sensitized solar cells (DSSCs). The investigation and characterization of the dye complex adsorption on a TiO₂ substrate are crucial for understanding the sensitization process of the TiO₂ surface and for optimizing the quantum yield of DSSCs. Many dyes used in DSSCs consist of either a carboxylic group or a cyanoacrylic acid group as dye anchors. However, with the growing interest in DSSCs, new dyes with different anchoring groups have been developed and evaluated. The present study investigates the anchoring mode of the dye-TiO₂ system with Fourier transform infrared spectroscopy (FTIR) and angle-resolved X-ray photoelectron spectroscopy (ARXPS). The FTIR results support that the carboxylic group deprotonates and that the COO^- anchors to TiO₂ via multiple modes, i.e., bidentate chelating and ester bonds. However, the changes in the features of NCS in FTIR also suggest the partial involvement of the thiocyanate ligand in the dye attachment. In addition, the depth profile obtained from ARXPS indicates that the COO^- group is found dominantly at the dye/TiO₂ interface and thus is the main anchoring group for the dye-TiO₂ system. The application of the techniques in understanding anchoring modes is not limited to the investigation of N719 and can be applied to other dye-adsorbed systems of interest.