Sensitizing and Absorption Properties of Alizarin-TiO_2 Nano-Clusters Under Varying pH Conditions

摘要

The alizarin-TiO_2 system has drawn much attention in studying the dye sensitizing mechanism for developing cost-effective dye sensitized solar cells (DSSC). In this study theoretical investigations are performed on an alizarin-anatase complex consisting of one alizarin molecule and a TiO_2 cluster which contains seven titanium atoms. The ground states were optimized for the alizarin molecule, TiO_2 cluster and alizarin-anatase complex using the first principle approach. To study the dye sensitizing process and its pH dependency, electronic-structural transitions of these neutral and anion alizarin-anatase clusters from their HOMO (highest occupied molecular orbital, denoted as H) level to the respective LUMO (lowest unoccupied molecular orbital, denoted as L) level are investigated by means of the time dependent density functional theory (TDDFT). These sensitizing processes corresponding to three different clusters are found being theoretically distinguishable under various pH conditions. The two dominant electronic transitions for the neutral cluster are found being H-2 → L + 8 and H-1 →L + 4, while the latter becomes important for larger alizarin-anatase clusters. For two anion clusters the primary electronic transitions are found being H → L-1 and H-1 → L-1.