There are few reports on photoelectric conversion efficiency using naturally-occurring dyes for dyesensitized solar cells (DSSC). This is because the matching with an excited electronic level of naturally-occurring dye to the conduction band of semiconductor is problematic; the excited electrons are easily relaxed to the steady state with fluorescence or heat emission. We examined the fluorescence inhibition effect of a self-assembled photonic crystal using Chlorine e6 dye. Chlorine e6 is derived from chlorophyll and has a long excited electron lifetime. We prepared TiO 2 inverse opals with various particle sizes by liquid phase deposition and described their effect on DSSCs with regard to structural, optical and electrochemical properties. In addition, we explored the implications of fluorescence lifetime measurements relative to the photonic band diagram and the amount of adsorbed dye. Although the main factor affecting the external photoelectric conversion efficiency was the diffusion resistance of the electrolyte and the contact resistance between TiO 2 interfaces, the possibility that the dye fluorescence lifetime, i.e. the photonic band structure, can affect the internal quantum efficiency per one dye molecule was also investigated.

The photovoltaic characteristics (short circuit current, open circuit voltage, fill factor, and photon-to-electron conversion efficiency) and electrochemical impedance measurements of normal and inverse-opal dye-sensitized electrodes were carried out in a transparent electrolyte (0.6 M triethhanolamine/0.5 M lithium perchlorate in acetonitrile) using three different methods; electrophoretic deposition, TiCl4 coating, and liquid-phase deposition (LPD). X-ray diffraction (XRD) analysis revealed that each electrode was composed of anatase TiO2. The impedance elements discussed previously were substrate resistance (R0), interface resistance at indium tin oxide (ITO)/titanium oxide (TiO2) (R1), contact resistance between TiO2 particles (R2), interface resistance at TiO2/dye/electrolyte and counter electrode/electrolyte (R3), and diffusion resistance of the electrolyte (R4). The internal resistances of inverse opal electrodes were varied with the preparation methods, especially in relation to the contact resistance between R2 and R3. The electrode prepared by LPD exhibited the smallest internal resistances and the highest photon-to-electron conversion efficiency among the three methods.