Effects of {001} Facet of Anatase TiO2 Single-crystalline Nanosheets on Photoexcited Electron Transfer from Near-infrared Dye-sensitizer

Single-crystalline anatase TiO2 nanosheets predominantly exposing the {001} facet at a surface fraction of more than 75% were constructed on transparent conductive oxide glass substrates. Application of these nanoarchitectures of TiO2 demonstrated photoelectric conversion while using near-infrared absorbing dye-sensitizer. In contrast, regular mesoporous TiO2 films with a much larger effective surface area did not exhibit a photoelectric response with the same dye-sensitizer. The results obtained here emphasize the importance of the contacted crystalline facet of TiO2 in photoinduced charge separation for minimizing the potential drop for interfacial charge-carrier transfer in dye-sensitized solar cell systems. Especially, the observed improvement of electron injection by contacted facet could contribute to the efficient photoexcited electron injection from near-infrared dye-sensitizers possessing relatively small HOMO–LUMO gap.