NEW SOLID MEDIUM FOR ELECTROCHEMISTRY AND ITS APPLICATION TO DYE-SENSITIZED SOLAR CELLS - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 128

the cell medium. Although optimum conditions were not investigated, the solid-state cell
showed even better performance than the corresponding conventional (reference) liquid type
cell. In the recent investigation it was elucidated that the difference between the solid-type
and liquid-type cell is ascribable to the delicate difference of the liquid phase thickness for
both cells. A careful comparison between the two type cells showed that both the type cells
exhibit very similar performance [12].
The diffusion coefficient of holes via the I - /I 3 - redox couple in the solid involving 2.5
wt% carrageenan, 0.3 M KI and 0.03 M I 2 and excess water was investigated by an
impedance spectroscopy: it was ca. 1.7 x 10 -5 cm 2 s -1 , almost the same as in a liquid water
showing that the hole transport in the solid is not problem in comparison with the liquid
medium system. A similar results have been obtained also for a solid involving redox
electrolyte and organic liquid [38]. In the present solid transport of small ions and molecules
takes place the same as in a liquid showing that the liquid phase in this solid behaves as in a
pure liquid.

Conclusive Remarks

A solid-type dye-sensitized solar cell was thus easily fabricated by using an inexpensive
and commercially available polysaccharide solid involving organic medium and I - /I 2 redox
electrolyte. Polymer gels are usually soft and fragile. However, the present solid is tight and
elastic. Although a long-term performance was not tested yet, the photocurrent did not
decrease in a 3 h irradiation without any sealing of the solid-type cell showing that it is stable
against evaporation of the organic liquid.

Conclusion and Future Scopes

It has been shown that in a tight and elastic polysaccharide solid involving excess water
molecular and ionic diffusion takes place the same as in liquid water. This allows its use as a
solid electrolyte in place of liquid water for conventional electrochemical measurements and
other electrochemical devices. Application of the solid to solidify a dye-sensitized solar cell
was successfully achieved. Another interesting behavior in this polysaccharide solid with
excess water is the entire prohibition of bulk convection in contrast to the free diffusion of
molecules, which would allow its application to fundamental investigations to discriminate
diffusion and convection in chemical processes that has been impossible on the earth because
of the gravity. The concept of chemical reactions including electrochemistry, photochemistry,
chemical dynamics and other applications to devices and sensors could be changed in the near
future by using this interesting solid.

References

[1] Y.Osada and K.Kajiwara eds, Gel Handbook , NTS, Tokyo, 1997.

[2] M.Kaneko, N.Mochizuki, K.Suzuki, H.Shiroishi, K.Ishikawa, Chem.Lett ., 2002, 530

(2002).