Ryohsuke Yamanaka

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.

Influence of TiCl4 treatment on back contact dye-sensitized solar cells sensitized with black dye

To better understand why titanium tetrachloride (TiCl4) treatment improves short circuit current, we studied its effects on back contact dye-sensitized solar cells sensitized with black dye [tri(thiocyanato)(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)ruthenium(II), Ru(tcterpy)(NCS)3] using transient absorption spectroscopy and electrochemical impedance spectroscopy. We found that the TiCl4 treatment improved short circuit current and achieved an overall energy conversion efficiency of 8.9%. The transient absorption signals did not change as a result of the treatment, suggesting that electron injection efficiency is not affected by the treatment. The impedance related to electron transport between TiO2 particles decreased and the peak frequency of the imaginary part of the electrochemical impedance spectra assigned to electron transfer from TiO2 to the redox couple was shifted to lower frequency by the treatment. This clearly indicates that TiCl4 treatment improved electron transport in the nanocrystalline TiO2 film in back contact dye-sensitized solar cells.

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.

High Efficiency of Dye-Sensitized Solar Cell and Module

The improvement of cell performance of dye-sensitized solar cells (DSCs) was investigated by means of haze of TiO2 electrodes and series-internal resistance. It was found that the high haze of TiO 2 electrodes effectively improves the external quantum efficiency of DSCs. The series-internal resistance is successfully reduced by increasing the surface roughness of platinum counter electrodes and by decreasing the thickness of electrolyte layer. The highest single cell efficiency of 11.1% (aperture area: 0.219 cm2 ) was achieved and confirmed by a public test center (AIST). Furthermore, large-scaled cell was fabricated using current collecting metal grids, and the efficiency of 6.8% (aperture area: 101 cm2 ) was obtained. Moreover, integrated DSC module was investigated and the efficiency of 6.3% (aperture area: 26.50 cm2) was also confirmed by the public test center

Improvement of TiO2/Dye/Electrolyte Interface Conditions by Positional Change of Alkyl Chains in Modified Panchromatic Ru Complex Dyes

A series of panchromatic ruthenium sensitizers (MJ sensitizers) with attached thiophene and phenyl units bearing alkyl chains was synthesized. A new synthetic route was used to examine all possible positions for the alkyl chains. The absorption spectra showed the sum of a ruthenium complex and peripheral organic chromophore units. The hypochromic effect and blueshift of the metal-to-ligand charge-transfer band observed in the modified ruthenium sensitizers were suppressed by changing the positions of the alkyl chains on the attached thiophene ring. Changing only one alkyl chain also influenced the performance of dye-sensitized solar cells. Ruthenium sensitizer MJ-10 with bulky substituent harvests visible and near-infrared light, and solar cells sensitized by MJ-10 exhibit an efficiency of 9.1% under 1 sun irradiation.

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%.

Recent Advances of Dye-Sensitized Solar Cells and Integrated Modules at SHARP

An equivalent circuit for DSCs was studied using electrochemical impedance spectroscopy measurement, and the improvements of conversion efficiency of DSCs for not only single cells but also integrated modules were investigated. Further improvement of cell characteristics of DSCs was also investigated from the view point of modified TiO 2 films and series-internal resistance design. The series-internal resistance elements were found to correlate positively with the sheet resistance of the transparent conducting oxide and the thickness of the electrolyte layer and negatively with the roughness factor of the platinum counter-electrode. The short circuit current density (Jsc) of the DSCs was effectively improved by use of a high-haze TiO 2 film. In addition, the analysis of TiO 2 /dye interface by scanning probe microscopy and transient absorption spectroscopy were also useful for the study. As a result, the maximum single cell conversion efficiency of over 11% was obtained. Furthermore, an integrated DSC module composed of many rectangular cells connected in series was fabricated and the efficiency was increased to 8.4% (confirmed by AIST) by realizing high active area and high uniformity.

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).