Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-11-06
2004-01-27
Tran, Minhloan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S040000, C257S043000, C257S184000, C257S111000, C257S465000, C257S449000
Reexamination Certificate
active
06683361
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor, a solar cell employing the semiconductor, a method of manufacturing the solar cell, and a solar cell unit employing the solar cell.
DESCRIPTION OF THE RELATED ART
For the approximately the past ten years, grate attention has been paid to solar cells (solar batteries) employing silicon as a power source which is harmless to the environment. As for these solar cells employing silicon, a monocrystalline silicon type solar cell is known, which is used in artificial satellites or the like. In addition, a practical application of a solar cell is also known employing polycrystalline silicon (single crystal silicon) and a solar cell employing amorphous silicon. These solar cells have already been practically used in industrial and household applications.
However, since these solar cells employing silicon are manufactured through a vacuum process, such as a CVD (chemical vapor deposition) process or the like, manufacturing cost is high. Further, since a great deal of quantity of heat and a great deal of electricity are used in the manufacturing process, the balance between the energy required for manufacturing the solar cell and the energy generated by the solar cell is very poor. Thus, these solar cells are not yet established as an energy-saving power source.
On the other hand, a new type of solar cell, which is referred to as “wet solar cell” or “fourth-generation photocell”, was proposed in 1991 by Grätzel et al. As shown in
FIG. 9
, this wet solar cell includes one electrode
901
formed of titania (titanium dioxide), which is a semiconductor, and another electrode
902
formed of platinum, ITO or the like, and these electrodes are held in an electrolyte solution
903
, such as an iodine solution.
The reaction principle of this wet solar cell is as follows. When receiving rays such as solar rays, the titania (TiO
2
), which is a semiconductor, receives electrons to deliver them to the electrodes, and holes (h
+
), which are left in the titania electrode, oxidize iodine ions to convert I
−
into I
−
3
. Then, the iodine ions, which have been oxidized, receive the electrons again to be reduced at the counter electrode. Thus, the iodine ions are cyclically moved between both of the electrodes, thereby realizing the battery.
In this wet solar cell employing such an electrode formed of titania, however, only the ultraviolet rays in the solar rays are efficiently utilized. Therefore, in order to increase sensitivity of the solar cell so as to be able to absorb light up to the visible ray region, the titania is mixed with organic dye or the like. For this reason, such a wet solar cell is called as a dye-sensitized solar cell. Since this type of wet cell can be manufactured from inexpensive materials and does not need a large scale equipment, such as an equipment for the vacuum process and the like for its manufacturing, it is greatly expected that this wet solar cell will be a low cost solar cell.
SUMMARY OF THE INVENTION
However, since this dye-sensitized solar cell is a wet cell employing an electrolyte, such as an iodine solution or the like, it is necessary to seal its solar cell containing the iodine solution as the electrolyte with a sealing material. Due to this structure, the dye-sensitized solar cell is subject to many problems in that, for example, leakage of electrolyte solution is liable to occur when the sealing is broken and the like.
Therefore, the dye-sensitized solar cell cannot have a practical life as a solar cell.
Further, current and voltage of practically required levels cannot be secured by simply employing a flat-shaped titanium electrode because of its small absorption area of solar rays.
In view of the above problems, the present invention is directed to a solar cell employing a titanium dioxide semiconductor, which includes a pair of electrodes; and a titanium dioxide semiconductor which is held between the electrodes, the surface and inside of the titanium dioxide semiconductor being formed with pores, and the titanium dioxide semiconductor being arranged so as to form a rectification barrier with respect to at least one of the electrodes.
This makes it possible to provide a solar cell which can secure current and voltage of practically required levels, that is, a solar cell which is excellent in the photoelectric conversion efficiency.
In the present invention, it is preferred that the rectification barrier is formed by contacting the titanium dioxide semiconductor with at least one of the electrodes, and the rectification barrier has a diode characteristic. According to this structure, it is possible to enhance the efficiency of power generation of the solar cell.
Further, it is preferred that the rectification barrier is the shottky barrier being formed by contacting the titanium dioxide semiconductor with at least one of said electrodes. According to this structure, it is also possible to enhance the efficiency of power generation of the solar cell.
Alternatively, it is also preferred that the rectification barrier is the PN junction being formed by contacting the titanium dioxide semiconductor with at least one of said electrodes. This also enables enhancement of the efficiency of power generation of the solar cell.
In this invention, it is also preferred that the electrode, with which said titanium dioxide semiconductor forms the rectification barrier, is formed in such a way as to penetrate into the surface of the titanium dioxide semiconductor and the inside thereof. This makes it possible to further increase the area (surface area) where the rectification barrier is formed, thereby further enhancing the efficiency of power generation of the solar cell.
Further, in the present invention, it is also preferred that the titanium dioxide semiconductor has a porosity of 5 to 90%. This increases the contacting area between the titanium dioxide semiconductor and light (that is, the irradiated area by light), thereby enhancing the efficiency of power generation of the solar cell.
Preferably, the titanium dioxide semiconductor has a porosity of 15 to 50%. This further increases the contacting area between the titanium dioxide semiconductor and light (that is, the irradiated area by light), thereby further enhancing the efficiency of power generation of the solar cell.
More preferably, said titanium dioxide semiconductor has a porosity of 20 to 40%. This further more increases the contacting area between the titanium dioxide semiconductor and light (that is, the irradiated area by light), thereby further more enhancing the efficiency of power generation of the solar cell.
In the present invention, it is also preferred that the titanium dioxide semiconductor is porous and has the fractal structure. This also enhances the efficiency of power generation of the solar cell.
Further, in the present invention, it is preferred that the electrode with which said titanium dioxide semiconductor form the rectification barrier is formed from a transparent electrode made of ITO or the like, or a metallic electrode made of a metal selected from the group consisting of Al, Ni, Cr, Pt, Ag, Au, Cu, Mo, Ti, and Ta, or a metal compound containing therein any one or more of these metals. This also enhances the efficiency of power generation of the solar cell.
Furthermore, it is also preferred that the electrode with which said titanium dioxide semiconductor forms the rectification barrier includes a solid iodide. This also enhances the efficiency of power generation of the solar cell.
Moreover, it is preferred that said titanium dioxide semiconductor forms the rectification barrier includes CuI (copper iodide). This enhances the efficiency of power generation of the solar cell.
Moreover, it is also preferred that said titanium dioxide semiconductor forms the rectification barrier includes AgI (silver iodide). This also enhances the efficiency of power generation of the solar cell.
Further, in the present invention, it is also preferred that the electrodes are formed by vacuum evaporation
Fujimori Yuji
Miyamoto Tsutomu
Oliff & Berridg,e PLC
Tran Minhloan
Tran Tan
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