Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2000-03-27
2001-10-09
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S252000, C136S256000, C429S111000, C257S043000, C257S040000, C438S104000, C438S085000, C438S082000, C438S099000
Reexamination Certificate
active
06300559
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a dyo-sensitization-type photoelectric conversion element, which is used for a solar cell and other photoelectric conversion elements, an optical sensor, and a photo-revolving element.
(2) Description of the Related Art
Solar cells such as a silicon solar cell, a gallium arsenide (GaAs) solar cell, and an indlum phosphide (InP) solar cell have so far been put into practice. However, these cells are disadvantageously high-cost products.
A solar cell comprising an oxide semiconductor such as titanium dioxide (TiO
2
) is already known. However, titanium oxide exhibits poor photoelectric conversion since it absorbs exclusively light having a short wavelength. Thus, a dye-sensitization-type photoelectric conversion element has been proposed to improve photoelectric conversion.
A typical dye-sensitizatlon-type photoelectric conversion element has a laminate structure, illustrated in
FIG. 1
, which comprises a thin film
3
formed of titanium oxide particles, a transparent electrode
2
disposed on one side of the film
1
, and a dye
4
, an electrolyte
5
, and an electrode
6
which are disposed in this order on the other side of the film
1
. The dye absorbs sunlight to thereby generate electrons (e
−
) and holes (h
+
). The thus-released electrons (e
−
) are injected into the thin titanium oxide film
3
, while the holes (h
+
) react With the electrolyte
5
. When the employed electrolyte
5
includes, for example, iodide ions (I
−
) which react with the holes (h
+
) to thereby form I
3
−
ions.
3/2I
−
+h
+
→1/2I
3
−
On the electrode
6
disposed in the side of electrolyte
5
, electrons (e
−
) react with I
3
−
contained in the electrolyte, to thereby form I
−
. Thus, a circuit is formed to thereby generate an electromotive force.
1/2I
3
−
+e
−
→3/2I
−
As specific examples of semiconductors which are used in such a photoelectric conversion element, there can be mentioned titanium oxide, zinc oxide, and zinc sulfide. Of these, titanium oxide is most popularly used. As specific examples of the dye, there can be mentioned ruthenium complexes and porphyrin derivatives.
Titanium oxide (titanium dioxide) includes three known crystal structures, i.e., anatase, brookite, and rutile. When titanium oxide is produced by a vapor phase method wherein titanium tetrachloride is subjected to premixed combustion by incorporation with oxygen or oxygen-containing gas, an anatase crystal structure is formed at a low temperature and remains stable. When the anatase crystal structure is heated for firing, a brookite crystal structure is formed at a temperature of 816 to 1.040° C, and a rutile crystal structure is formed at a temperature higher than 1,040° C. (
Rikagaku jiten
, 3rd edition, p. 514-515).
Although titanium oxide is most popularly used as a semiconductor employed for a dye-sensitization-type photoelectric conversion element, almost no investigation has been conducted on the influence of the particular types of crystal structure. Typically, rutile-type titanium oxide or anatase-type titanium oxide is employed, as described in Japanese Unexamined Patent Publication (kokai) No. H10-255863.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a dye-sensitization-type photoelectric conversion element comprising titanium oxide as a semiconductor, which exhibits an enhanced photoelectric conversion.
The present inventor has studied photoelectric effect of a dye-sensitization-type photoelectric conversion element comprising titanium oxide as a semiconductor, and found that, when electron and holes are generated in a dye upon absorption of light, the excited electrons are deactivated within a very short time, i.e., 10
−5
to 10
−12
seac, and further found that it is important to inject the excited electrons into titanium oxide at a very high rate, more specifically, at a rate more than 100 times of the rate of deactivation to attain a high photoelectric conversion efficiency. The present inventor further studied the relationship between the crystal structure of titanium oxide and photoelectric conversion efficiency of photoelectric conversion elements, and have found that when brookite-type titanium oxide, which has not been paid any attention so far, is employed, excellent photoelectric conversion efficiency is attained as compared with a photoelectric conversion element comprising rutile- or anatase-type titanium oxide. The present invention has been accomplished on the basis of this finding.
In accordance with the present invention, there is provided a dye-sensitization-type photoelectric conversion element comprising a semiconductor and a dye adhering onto a surface of the semiconductor, which semiconductor is predominantly comprised of brookite-type titanium oxide.
Preferably, the semiconductor comprises at least about 70% by weight, based on the weight of the semiconductor, of brookite-type titanium oxide.
In accordance with the present invention, there is further provided a process for producing the above-mentioned dye-sensitization-type photoelectric conversion element, which comprises a step of immersing a substrate having a titanium oxide surface layer predominantly comprised of brookite-type titanium oxide in a solution containing a dye to allow the dye to adhere onto the titanium oxide surface layer.
REFERENCES:
patent: 5885368 (1999-03-01), Lupo et al.
patent: 826633 (1998-03-01), None
Diamond Alan
Showa Denko Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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