Abstract
Ruthenium complexes are used as effective sensitizers for the dye-sensitized solar cells. The electrons are excited from the HOMO (metal) to LUMO (ligand), and then injected into the titania conduction band in such solar cells. Recently, titanium atom on the titania surface was coordinated to the organic ligands such as dihydroxyl and dicyanomethylene compounds in order to sensitize the titania without the Ru complexes. In such systems, the ligand to metal charge transfer process was induced by light irradiation, indicating the direct electron injection from the HOMO of the ligand to the titania conduction band. Additionally, the organic dye molecules were dispersed into the titania nanoparticles by the sol-gel method in order to enhance the interaction between the dye and titania surface. This resulted in the effective electron injection. The ligand molecules were also dispersed among the titania particles. In the 1,2-dihydroxynaphtalene-dispersing titania, a photocurrent was observed by the direct electron injection process. The electron injection efficiency can be improved by their strong interaction in the narrow spaces surrounded with the titania particles.
