Ti(IV) phthalocyanines for dye sensitized solar cells

Ti(IV) phthalocyanines axially coordinated to 2,3- and 1,8-naphthalenediols have been prepared and characterized. The naphthalene axial ligands have been endowed with none, one or two sulfonate anchoring groups in order to study the performance of the dyes as DSC photosensitizers. All studied compounds showed the same efficiency. The unexpected results suggest displacement of the axial ligand with concomitant formation of a di-μ-oxotitanium-type anchoring moiety between the hydroxylated TiO₂surface and the Ti-phthalocyanine. This is probably the reason why the type of axial ligand does not play any role on the overall device efficiency. The titanium phthalocyanine absorbed in this way shows state selective electron injection were only those photons absorbed by the Soret band are capable to inject electrons into the TiO₂, while photons absorbed by the Q-band result in negligible photocurrent. This fact could explain the low efficiency of the Ti-phthalocyanines.