Zhong-Sheng Wang

Substituted carbazole dyes for efficient molecular photovoltaics: long electron lifetime and high open circuit voltage performance

We designed and synthesized new substituted carbazole dyes, MK-14 and -16, for dye-sensitized solar cells (DSSCs) employing the I−/I3−redox couple. By the addition of a hexyloxyphenyl substituent to previously reported carbazole dyes MK-1 and -2, the electron lifetime and open circuit voltage of the DSSCs employing these dyes were increased, showing comparable values with those using a conventional Ru complex dye. This result was achieved by the retardation of the charge recombination, caused by more effective blocking of the I3− ion in the electrolyte than that in the cases of MK-1 and -2. The result shows the importance of the position of alkyl chains attached to the main framework of dye molecules.

Long-term stability of organic–dye-sensitized solar cells based on an alkyl-functionalized carbazole dye

We investigated the long-term stability of performance for dye-sensitized solar cells (DSSCs) based on an alkyl-functionalized carbazole dye (MK-2) and used in conjunction with ionic liquid-based electrolytes. We observed good long-term stability of the performance of the DSSCs during 60 days under visible-light irradiation at ca. 50 °C. The performance of the DSSC decreased gradually under white-light irradiation including UV light or at 80 °C under dark conditions. However, no decomposition or detachment of the dye molecule from the TiO2electrode was observed after these measurements. These results indicate that the MK-2dye molecule in the cell was stable even under white-light irradiation and at 80 °C under dark conditions.

Femtosecond diffuse reflectance transient absorption for dye-sensitized solar cells under operational conditions: effect of electrolyte on electron injection.

By applying diffuse reflectance transient absorption spectroscopy to dye-sensitized solar cells under operational conditions, we were able to directly correlate interfacial electron injection kinetics from a Ru complex sensitizer to a TiO(2) nanocrystalline electrode with the incident photon to current efficiency values. It was revealed that ionic liquid electrolytes reduced the initial electron injection efficiency by suppression of the approximately 100 ps process.

Efficient Organic-Dye-Sensitized Nanocrystalline TiO2 Solar Cells

We have developed dye-sensitized nanocrystalline TiO2 solar cells (DSSCs) based on organic-dye photosensitizers. DSSCs based on the organic dyes gave good performance of incident-photon-to-current conversion efficiencies in the range of 400 to 800 nm. Solar energy-to-electricity conversion efficiencies of up to 7.6% were obtained with DSSCs based on coumarin dyes (NKX-2677 and NKX-2883) under AM 1.5 G irradiation (100 mW cm-2). Our results strongly suggest that organic-dye photosensitizers can be successfully designed for use in DSSCs and demonstrate the promising performance of DSSCs based on organic dyes