# The BCL Method for DSSC: Basis and Applications +
## 8 Improvement of the Performance of N3 with a Mono Carboxylate Ligand
### Results  
The results for the four complexes are summarized in Table 9. The last column of this table displays the final value for the Global Efficiency Index (GEI), obtained as the product of F1, F2, and F3, divided by \(\mathrm{E_{SUN}}\), which is the total energy received from the Sun. Column two and three display the different components involved in the calculation of light-harvesting capacity (see Section 4): absorbed energy (EA), delivered energy, (ED) and composition of the triplet state (\(\Phi_{\mathrm{t}}\)). A first result of the GEI analysis indicates that, in the case of the bisubstituted bipyridine ligand, the method can differentiate between two binding modes: the bridging mode  
Figure 37: DoLAc structure for the N3 mono a di carboxyl complex showing three binding modes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**COMPLEX** & **EA** & **ED** & \(\Phi_{\mathrm{t}}\) & **F1** & **F2** & **F3** & **\%GEI \({}^{*}\)** \\ \hline N3 bcp1 & 0.91 & 0.59 & 0.12 & **0.069** & **0.124** & **3.059** & **0.64** \\ N3 bcp2 & 0.81 & 0.76 & 0.10 & **0.074** & **0.124** & **3.034** & **0.68** \\ N3 mcp2 & 0.61 & 0.56 & 0.15 & **0.084** & **0.134** & **2.915** & **0.80** \\ N3 mcp1 & 0.73 & 0.29 & 0.05 & **0.015** & **0.140** & **2.633** & **0.13** \\ \hline \end{tabular} \({}^{(*)}\)\%GEI = 100F1F2F3/Esum (Esum = 4.13 eV).  
\end{table} 
Table 9: Calculated values for the Global Efficiency Index, F1, F2, and F3. of N3 bcp1, where the two binding positions come from the same bpy ligand; and the bidentate mode of N3 bcp2, where the carboxi anchors come from different bpy ligands. The increase in overall efficiency is from 0.64% in the first to 0.68% in the latter. This increase of 0.4% in efficiency occurring in the bidentate mode can be attributed to an increase in the ability to transmit and deliver light energy: the N3 bcp1 absorb more sunlight energy, (0.91 eV), but the fraction of it that reaches the anchor ligand, is greater in the bidentate mode (0.76 eV). When comparing the Global Efficiency Index of complexes with the same bonding mode as N3 bcp2 and the monocarboxylate equivalent ligand, N3 mcp2, an increase from 0.68% to 0.80% is observed for the latter. This greater efficiency is located in the light-harvesting energy because the greater participation of the anchor group in the triplet state. The monocarboylate complex absorbs less energy from the sunlight spectra than the di carboxylate counterpart; its capacity to deliver energy to the anchor ligand is lesser, but these effects are completely compensated by a 50% increase in the participation of the anchor group on the triplet state and the F1 parameter raises from 0.074 to 0.084. In this sense, it can be concluded that the second carboxylic group on the bipyridine ligands has no effect on the energy delivery capacity of the corresponding ruthenium complex. It is interesting to examine the increase in the electron injection efficiency which can be understood in collaboration with Figure 38a. The SOMO of the monocarboxylated complex is destabilized according to this scheme resulting in a higher electron gradient (\(\delta\epsilon\)) potential and higher F2 value. The GEI dramatical drops on going from the bidentate mode of N3 mcp2 to the monocotentate N3 mcp1 with respect to N3 mcp2 has its origin in the two factors F1 and F3. For the first index, the light-harvesting energy is strongly reduced because the participation of the anchor group in the triplet state is poor because there is only one point of contact with the semiconductor acceptor group. The second index, F2, however, slightly increases, driven by the destabilization of the SOMO that enhances the electron injection gap (\(\delta\epsilon\)) respect to the LUMO of Ti(OH)\({}_{3}\). The HOMO is also destabilized but, in this case, its lower values reduce the energy gradient (\(\Delta\)E) with respect to the HOMO of Iodide and the regeneration index (F3) is lowered as shown in Figure 38a. The transition density analysis (TDA), Section 3.2, for the four LUMOs is displayed in Figure 38b.