Low temperature fabrication of electron-nano-path and the performance of the solar cell consisting of the bi-continuous nano-path.

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The improvement of the photovoltaic performance for dye sensitized solar cells prepared at low temperatures was discussed from the view point of the fabrication of nano-paths for electrons and ions in the TiO_2 electrodes.The effect of ionic diffusions in the TiO_2 nano-porous electrodes on the solar cell performance was simulated by using a new model. It was concluded that the retardation of the ionic diffusions in the TiO_2 electrode causes the deterioration of the solar cell performance. The results suggested that the nano-pores have to be designed well. In order to improve the ionic diffusions in the TiO_2 nano-porous electrode, TiO_2 electrodes consisting of fractal like structures were fabricated by the electro-spray deposition of TiO_2 nano-particles on the conductive substrate. The short circuit current (Jsc) increased due to the increase in ionic diffusion coefficients in the nano-pores, which was consistent with the simulation results. In addition, we found that the addition of needle like TiO_2 help increase the ionic diffusions in the TiO_2 nano-porous electrodes. The addition of the needle increased the Jsc.Another approach for the improvement is to make electron paths at low temperature. We focused on TiO_2 grain boundary. Low V acceleration electron beam exposure (LVEB) which does not damage the substrate because of the low voltage was tried at room temperature. After the LVEB exposure, the increases in the electron diffusion coefficient and Jsc were observed, suggesting that the LVEB is useful for linking the boundary at low temperatures. The dye-staining of TiO2 surface under CO_2 super critical conditions increased Jsc because of the increase in the surface coverage of the nano-porous TiO_2 electrode. However, the surface trap passivation with dye molecules did not increase the electron diffusion coefficient because on the traps remaining at the interface of the grain boundary. This contrasted the results of DSCs prepared at 450℃.