Ryoichi Komiya

Dye-Sensitized Solar Cells with Conversion Efficiency of 11.1%

Dye-sensitized solar cells (DSCs) using titanium dioxide (TiO2) electrodes with different haze were investigated. It was found that the incident photon to current efficiency (IPCE) of DSCs increases with increase in the haze of the TiO2 electrodes, especially in the near infrared wavelength region. Conversion efficiency of 11.1%, measured by a public test center, was achieved using high haze TiO2 electrodes. This indicates that raising the haze of TiO2 electrodes is an effective technique for improvement of conversion efficiency.

Conversion efficiency of 10.8% by a dye-sensitized solar cell using a TiO2 electrode with high haze

We have investigated the effects of titanium dioxide (TiO2) electrodes with high haze on dye-sensitized solar cells (DSCs). The incident photon to current conversion efficiency of the DSCs was greatly improved using TiO2 electrodes with high haze. It was found that haze of the TiO2 electrodes in the infrared region is important for advancing the conversion efficiency of DSCs. A DSC using a high haze TiO2 electrode showed a conversion efficiency of 10.8%, as measured by a public testing center in Japan.

Integrated dye-sensitized solar cell module with conversion efficiency of 8.2%

We investigated an integrated dye-sensitized solar cell (DSC) module composed of a number of rectangular cells connected in series. Because neighboring cells are processed in reverse, the module is known as the W-contact module. It achieves a high active area of 85% by eliminating the interconnection between neighboring cells. By adjusting the transmittance of the Pt-coated counterelectrode, the TiO2 thickness, and the composition of the electrolyte, we achieved an overall energy conversion efficiency of 8.2% (aperture area of 25.45 cm2) as measured by a public test center under AM 1.5 irradiation. This sets a record for the confirmed efficiency of a DSC submodule.

Back Contact Dye-Sensitized Solar Cells

A new structure for dye-sensitized solar cells (DSCs) was proposed in which the transparent conducting oxide (TCO) is omitted and the cathode is located on the opposite side of the titanium dioxide (TiO2) film surface to the side of light irradiation. DSCs with this structure are called back contact DSCs (BCDSCs). The structure and fabrication of the cathode of BCDSCs was investigated in comparison with silicon solar cells. BCDSCs with conversion efficiency of 7.1% were achieved by vacuum deposition of the cathode directly onto the TiO2 film, suggesting that BCDSCs can function as effective solar cells with potentially increased efficiency due to the omission of the TCO.

Dye-Sensitized Photovoltaic Module with Conversion Efficiency of 8.4%

In this paper we investigate a dye-sensitized photovoltaic module (DSM) composed of many rectangular cells connected in series, known as a W-connected type module, where neighboring cells are processed in reverse. The characteristics of the serial connection of silicon solar cells have been investigated extensively, while, with dye-sensitized photovoltaic modules, the influence of each rectangular cell performance on the serially connected module has not been investigated as thoroughly. Here we investigate the performance of the rectangular cell in dye-sensitized photovoltaic modules, and we clarify the correlation between the conversion efficiency of the module and the uniformity of the TiO2 layer thicknesses. With these improvements, we achieved an overall energy conversion efficiency of 8.4% (aperture area: 26.47 cm2) as measured by a public test center under AM-1.5 irradiation. This sets a record for the confirmed efficiency of the DSM.

Electron transport in back contact dye-sensitized solar cells

The electron transport properties of a back contact dye-sensitized solar cell (BCDSC) were investigated in comparison with a conventional DSC. It was found that the BCDSC had a lower short circuit current density (JSC) at the same thickness of TiO2 film and that JSC was not proportional to the thickness of the TiO2 film. Calculation of electron transport length in the TiO2 film suggested that the injected electron travels a longer distance to the electrode in the BCDSC than in the DSC. TiCl4 treatment of the TiO2 film produced a marked improvement of the JSC value in the BCDSC due to an increase in the electron diffusion coefficient of the TiO2 film, whereas the JSC of the DSC remained almost unchanged. It is clear that the value of JSC in the BCDSC is more dependent on the electron transport properties of the TiO2 film than in the DSC. Under standard AM 1.5 irradiation (100 mW cm−2), a BCDSC with N719 dye yielded an overall conversion efficiency of 8.0%.

Improvement of efficiency of dye-sensitized solar cells by reduction of internal resistance

In order to elevate conversion efficiency, the series-internal resistance of dye-sensitized solar cells (DSCs) was investigated with electrochemical impedance spectroscopy measurement based on an equivalent circuit of DSCs. It was found that series-internal resistance correlates negatively with the roughness factor of the platinum counter electrode and positively with the thickness of the electrolyte layer. A cell sensitized with a black dye with series-internal resistance of 1.8 /spl Omega/cm/sup 2/ was fabricated and showed conversion efficiency of 10.2%, which was confirmed at the National Institute of Advanced Industrial Science and Technology (AIST, Japan).