Insights into Working Principles of Ruthenium Polypyridyl Dye-Sensitized Solar Cells from First Principles Modeling

With the aim to better describe the phenomena taking place at the dye/semiconductor interface in dye-sensitized solar cells and to understand the interfacial electron transfer from the excited dye to the semiconductor, the cis-[Ru(4,4′-COOH-2,2′-bpy) 2 (NCS) 2 ]/TiO 2 system has been investigated using density functional theory (DFT) in conjunction with a periodic approach and a hybrid functional. At this level of theory, the interplay of the electronic and geometrical coupling between the semiconductor and the dye has been analyzed, and the feasibility of the interfacial electronic transfer has been discussed. Our results show that the electronic transfer is highly favorable from a thermodynamic point of view, the LUMO of the dye being significantly higher in energy than the conduction band of the semiconductor. In addition, the theoretical injection time, computed using the Newns−Anderson model, is in fair agreement with the observed value.