Chemical modifications of ruthenium- TiO2 sensitizers: implications for electron transfer and light harvesting in DSSCs via computational approach

Chemical modifications in dye-sensitized solar cells (DSSCs), including the use of various anchoring groups, can enhance the absorption of the dye sensitizer on the semiconductor substrate. This facilitates efficient electron transfer from the sensitizer to the semiconductor, activating the solar cell. This study aims to investigate the structural, electronic and optical properties of four designed ruthenium sensitizers with and without binding to (TiO₂)₈ clusters in the gas phase and acetonitrile solvent to evaluate their potential in DSSCs. The Ru(II) sensitizers, obtained from the modification of anchoring groups including oxime (D1), carboxylic acid (D2), phendione (D3) and phosphonic acid (D4) on the bipyridine (bpy) ligand of the reference dye D0, showed variations in properties. Among them, D3 exhibited superior reactivity and stability due to a smaller energy gap. Time-dependent density functional theory (TD-DFT) simulations were used to evaluate key parameters. In particular, D2 showed enhanced light harvesting in the UV/Vis region, indicating improved carrier generation. Furthermore, changing the anchoring group had a positive effect on intramolecular charge transfer, light absorption, and energy levels, potentially enhancing the photovoltaic performance of DSSCs. Investigation of dye adsorption on the (TiO₂)₈ surface revealed strong chemical bonding, which has promising practical implications for future development of efficient Ru(II) dyes for DSSCs.