Zinc phthalocyanine absorbance in the near-infrared with application for transparent and colorless dye-sensitized solar cells

Transparent and colorless solar cells are attractive new photovoltaic devices as they could bring new opportunities to harness sunlight energy and particularly for their integration in windows. In this work, a new zinc phthalocyanine was synthesized and investigated as sensitizer in dye-sensitized solar cell (DSSC) for this purpose. The zinc phthalocyanine features a benzoic acid anchoring group and six thio(4-tertbutylphenyl) substituents in ${\alpha }$ position of the phtalocyanine. The dye was characterized by absorption and emission spectroscopy and by electrochemistry. The physico-chemical properties show that the dye fulfills the criteria for such an application. A detailed computational study indicates that the electronic communication with $\mathrm{TiO}_{2}$ conduction is weak owing to the absence of overlapping of the wavefunctions of the dye with those of the $\mathrm{TiO}_{2}$ semiconductor. The photovoltaic performances of the zinc phthalocyanine were measured in $\mathrm{TiO}_{2}$-based DSSC that revealed inefficient electron injection, which certainly can be explained by the weak electronic coupling of the dye with $\mathrm{TiO}_{2}$ that limits electron injection efficiency. A strategy is proposed to make better-performing sensitizers.