Dye Sensitized Solar Cells Consisting of Metallophthalocyanine Axially Anchored on Metal Oxide Nanoparticles through Metal-O-Metal Linkages-Difference in Photovoltaic Performances between TiO2 and SnO2 Electrode

Abstract

High performance SnO2-based bottom electrodes are necessary for tandem dye-sensitized solar cells (DSSCs) harvesting infrared (IR) lights. Sensitizing dyes based on macrocyclic ligands are one of the candidates among the IR dyes. However, it is difficult to introduce anchoring groups such as carboxylic acid at the right position of macrocyclic rings where electron injection occurs. It was proved that axially anchored phthalocyanines (model compounds) bonded to SnO2 nanoparticle surfaces with short metal-O-metal linkage inject electrons from dyes to SnO2 layers spatially, because the macrocyclic rings are very close to SnO2 surfaces. TiO2 based DSSCs did not show photovoltaic properties because of very fast charge recombination between injected electrons and oxidized dyes which were measured by a transient absorption spectroscopy technique. In the case of SnO2-based DSSC, the charge recombination was slower than that of the TiO2-based DSSCs, which enabled the collection of electrons. Since this anchoring system can be prepared easily, it is a good strategy for use in the design of near-IR absorbing dye.