# The BCL Method for DSSC: Basis and Applications +
## 8 Improvement of the Performance of N3 with a Mono Carboxylate Ligand
### Results
The population of the set of LUMOs with the energy captured from the absorption process generates a transient density that is distributed along the different fragments composing the molecular orbital. In this figure, it is clearly demonstrated how complexes in the bidentate binding mode, the transition density is equally distributed for all the anchor ligand. In the other two modes, unidentate and bridging, part of the absorbed energy is directed towards the ancillary ligand and not towards the anchor and a lost in the overall yield is caused. As a whole, the present study confirms the result of previous [31] calculations that indicate the increase in the photo conversion efficiency in homoleptic ruthenium complexes with thiocyanate when the monocarboxybipyridine anchor ligand is used instead of the dicarboxylated. The results show that ruthenium complexes with a monocarboxylated ligand could present two binding modes: unidentate and bidentate. The unidentate mode occurs when the homoleptic complex binds to the surface by means of one anchor ligand. The other ligand, which is not bound to the semiconductor, acts as an ancillary ligand. In the bidentate mode, the complex binds to the surface with two contact points, coming from the two anchor ligands. According to our calculations, the bidentate mode displays a higher value of photoconversion efficiency (0.80) than the monodentate (0.13) and the bridging (0.64). Comparing complexes in the bidentate binding, in the monocarboxylate complex (N3 mcp2) the GEI value shows an increment in regard to the latter (N3 bcp2), from 0.68 to 0.80, could result in the increment of the PCE of N3 from 7.1 to 7.6%. This increase of 0.5% in the overall yield is of a similar magnitude to that registered in the complex with carboxy pyridyl quinoline, whose yield increases by 0.3% [32]. In summary, the BCL method was employed to gain more insight in the role of the anchor ligand, and the number of anchoring groups, in the overall yield of ruthenium-thiocyanate-based dyes. The method predicts that a ruthenium complex with monocar-boxylated ligands is more efficient than a similar complex with dicarboxylic ligands. Figure 38: (**a**) Molecular orbital energies scheme. (**b**) Transition density analysis (yellow: ancillary ligand, blue: anchor ligand, pink: ruthenium, white: acceptor). **Author Contributions:** Conceptualization, M.B. ; methodology, M.B., I.C. and B.L. ; formal analysis, M.B., I.C. and B.L. ; writing--original draft preparation, M.B., I.C. and B.L. ; writing--review and editing, M.B., I.C. and B.L. ; supervision, M.B. ; funding acquisition, M.B., I.C. and B.L. All authors have read and agreed to the published version of the manuscript. **Funding:** The initial part of this work was funded through the Chilean research agency Fondecyt, through Projects No. 1020517, 7070181 and 1070799. The second part received no external funding. **Acknowledgments:** The authors acknowledge former graduate and undergraduate students for their unvaluable contribution to this work. Collaborations with Faculty members of national and international universities, cited in the different references, were crucial to make this review possible. One of us ([PERSON]) acknowledges the scientific inspiration received by [PERSON] (RIP) at the first stages of his career. **Conflicts of Interest:** The authors declare no conflict of interest.