Structure-function relationships in unsymmetrical zinc phthalocyanines for dye-sensitized solar cells

The impact of the anchoring group on photovoltaic performance by a series of phthalocyanine sensitisers (see figure) has been demonstrated. A series of unsymmetrical zinc phthalocyanines bearing an anchoring carboxylic function linked to the phthalocyanine ring through different spacers were designed for dye-sensitised solar cells (DSSC). The modification of the spacer group allows not only a variable distance between the dye and the nanocrystalline TiO₂, but also a distinct orientation of the phthalocyanine on the semiconductor surface. The photovoltaic data show that the nature of the spacer group plays a significant role in the electron injection from the photo-excited dye into the nanocrystalline TiO₂ semiconductor, the recombination rates and the efficiency of the cells. The incident monochromatic photon-to-current conversion efficiency (IPCE) for phthalocyanines bearing an insulating spacer is as low as 9 %, whereas for those with a conducting spacer an outstanding IPCE 80 % was obtained.
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