Liyuan Han

Modeling of an equivalent circuit for dye-sensitized solar cells

Internal resistance in a dye-sensitized solar cell (DSC) was investigated using electrochemical impedance spectroscopy measurements. Four resistance elements were observed in the impedance spectra, and their dependencies on the applied bias voltage were characterized. It is found that the resistance element related to charge transport at the TiO2/dye/electrolyte interface displays behavior like that of a diode, and the series resistance elements largely correspond to the sum of the other resistance elements. An equivalent circuit for DSCs is proposed based on these results.

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

With the aim of increasing 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 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. A cell sensitized with a black dye with series-internal resistance of 1.8Ωcm2 was fabricated and showed conversion efficiency of 10.2% when measured with a metal mask under an air mass of 1.5 sunlight.

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.

Measuring methods of cell performance of dye-sensitized solar cells

Cell performance measuring methods for dye-sensitized solar cells (DSCs) were investigated in comparison with those of crystalline silicon solar cells. It was found that cell performances of DSCs varied according to voltage sweep direction and sampling delay time. On the other hand, this dependence was not observed in silicon solar cells. Measurement of the transient photocurrent revealed that the dependence on sweep direction and sampling delay time may be explained by the longer time constant of DSCs. To improve accuracy, measurement should be carried out with a sampling delay time exceeding several seconds. However, it is also found that the average value of the efficiency measured by two sweeping directions is constant when the sampling delay time is longer than 40u2002ms. These measurement conditions will be useful to measuring cell performance more accurately and rapidly. Additionally, determining cell area using a shading mask with an area smaller than that of TiO2 electrodes will improve accuracy when...

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 25.45u2002cm2) as measured by a public test center under AM 1.5 irradiation. This sets a record for the confirmed efficiency of a DSC submodule.

Scanning Tunneling Microscopy Study of Black Dye and Deoxycholic Acid Adsorbed on a Rutile TiO2(110)

Trithiocyanato(4,4,4-tricarboxy-2,2:6,2-terpyridine)ruthenium(II), black dye, was adsorbed on a rutile TiO(2)(110) surface and imaged by an ultrahigh vacuum scanning tunneling microscope. The TiO(2)(110)-(1 x 1) surface was prepared in a vacuum, covered with pivalate monolayer, and immersed in acetonitrile containing black dye. Black dyes exchanging preadsorbed pivalates were observed on the surface as protrusions with lateral dimensions from 2 to 10 nm. Protrusions with a minimum lateral dimension of 2 nm were assigned to single, isolated black dyes, and larger protrusions were attributed to aggregated dyes. When deoxycholic acid was added to the dye solution, the number ratio of the single dyes to the aggregated dyes increased, while adsorbed deoxycholic acid was not observed.

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

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 (100u2002mWu2009cm−2), a BCDSC with N719 dye yielded an overall conversion efficiency of 8.0%.

Improvement of Efficiency of Polymer Solar Cells with Soluble Fullerene Derivatives

Soluble fullerene derivatives, [6,6]-phenyl C₆₁ butyric acid hexyl ester (PCBH) and [6,6]-phenyl C₆₁ butyric acid dodecyl ester (PCBD), were synthesized, and current-voltage (I-V) characteristics of polymer solar cells using these fullerene derivatives were investigated. It is found that PCBH cells show higher short circuit current density (J_sc) than conventional [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) cells. J_sc further increases with using high haze TCO substrates and thermal annealing. The efficiency of 3.3%, 3.8% (aperture illumination area were 1.00 cm₂ and 0.25 cm₂, respectively) were obtained. Finally the efficiency of 2.96% (aperture area was 1.001 cm₂) was confirmed by a public test center (AIST, JAPAN)