# The BCL Method for DSSC: Basis and Applications +
## 5 The \(\mathbf{I_{T}}\) Parameter: A Measure of the Electronic Density on the Anchor Group
### Results
#### 5.1.2 Analisys of Complexes
The low efficiency values presented by these complexes can be attributed to two causes: (1) the different fragment composition of the ppl(COOH)\({}_{2}\) respect the dcbpy ligand, reduces the amount of delivered energy to the anchor group, and (2) the participation of the anchor group on the thexi state is greater in the dcbpy than in the ppl ligand. If we compare these results with those obtained by the hot injection mechanism where no intersystem crossing occurs, and therefore all the available energy for injection (\(I_{S}\)) is the delivered energy (\(E_{D}\)), complex 3 displays the higher value followed by the ester substituted and the cyanide group. This tendency is different to that predicted from the thexi state were the cyanide group exhibit a higher value that the ester substituent. In conclusion, although the types of ligands chosen for this part of the study are not very promising for dye use in solar cells, the method developed in this chapter allowed us to calculate a theoretical index that measures the amount of energy available to be injected. This index can be related to light harvesting efficiency, one of the three parameters composing the experimental PCE. The other two factors, electronic injection and regeneration, cannot be calculated by means of this model since it is established that the load reaches only the anchor group. To include and calculate the other two factors, it is necessary to build a new system of the type donor-linker-acceptor (DoAlc), where the complex is attached to some acceptor that simulates the behavior of titanium dioxide. This will be worked out in the next chapters. Reproducing the Photo Conversion Efficiency of a series of Ruthenium Dyes with a Three-Parameter Model  
The BCL approach [18] merged as a theoretical tool to help to understand the results obtained for the efficiency of five ruthenium dyes measured in the same experimental conditions. The set of ruthenium complexes was chosen according to a predefined strategy, that consisted in modifying physical properties of the [Ru(dcbpy)\({}_{2}\)]\({}^{+2}\) core by incorporating different types of ligands, and then observing how these changes influenced the overall performance of the solar cell. Figure 21 displays the different types of ligands that were employed: bipirydine, thiocianate, phenylipydine and 4,4' distyril,2,2' dipyridine (LH). The general design follows according to the following sequence: starting with the unsubstituted complex, C1, a thiocyanate ligand was introduced giving the N3 complex labeled as C2. When SCN is replaced with the cyclometalated ligand the C3 complex is obtained. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Complexes** & **E\({}_{\mathbf{A}}\)** & **E\({}_{\mathbf{D}}\)** & **\(\mathbf{\varphi_{T}}\)** & **I\({}_{\mathbf{T}}\)** \\ \hline [Ru(dmbpy)\({}_{2}\) ppl(OH)\({}_{2}\)]\({}^{2+}\) & **(1)** & 1.31 & 0.39 & 0 & 0 \\ \hline [Ru(dmbpy)\({}_{2}\) ppl(COOEt)\({}_{2}\)]\({}^{2+}\) & **(2)** & 1.12 & 0.33 & 0.30 & 0.1 \\ \hline [Ru(dmbpy)\({}_{2}\) ppl(COOH)\({}_{2}\)]\({}^{2+}\) & **(3)** & 1.89 & 0.44 & 0.31 & 0.14 \\ \hline [Ru(dmbpy)\({}_{2}\) ppl(CN)\({}_{2}\)]\({}^{2+}\) & **(4)** & 1.10 & 0.23 & 0.52 & 0.12 \\ \hline [Ru(bpy)\({}_{2}\) dcbpy]\({}^{2+}\) & **(5)** & 1.87 & 0.77 & 0.83 & 0.64 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Calculated values of I\({}_{\mathrm{T}}\) for R2 ppl complexes. Changing one bpy of C1 with one LH chromophoric ligand gives C4 and introduces a second chromophore result in complex C6. Figure 22 shows the induced photocurrent efficiency measured for the five complexes. Some general conclusions can be obtained. For example, C2 displays a far better response than the other dyes, until 600 nm, where it begins to decay. A detailed comparison between the other dyes seems difficult since their relative response varies along wavelength. A complementary analysis can be done by looking for wavelength independency in the 400-600 nm range.