Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2002-08-01
2003-12-09
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S265000, C136S252000, C257S043000, C257S431000, C257S432000, C438S085000, C438S098000, C438S069000, C438S072000, C428S701000, C427S074000, C204S192290, C205S199000, C205S333000
Reexamination Certificate
active
06660931
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for a solar cell with a metal surface having formed thereon a zinc oxide film containing water in a prescribed amount or lower, a solar cell, and a production process of a solar cell.
2. Related Background Art
As a method for forming an oxide thin film by a vacuum process, well-known are an evaporation method, a sputtering method, a CVD method and the like. In the case of forming an oxide thin film by these methods, water adhering to the walls of a vacuum furnace is possibly taken into the film. However, any prior technique has not been described ever regarding the water content in a film in such a case.
Regarding the method for forming an oxide by intentionally introducing water molecules in the vacuum process, a relevant description is described in Japanese Patent Application Laid-Open No. 61-64874 document. According to the document, there is description that an oxide is deposited using argon gas mixed with water vapor as a sputtering gas, however the document has no particular description referring to the water content in the oxide film after deposition.
In place of the vacuum process, some methods (electrodeposition methods) for depositing oxide utilizing electrochemical reactions of aqueous solutions have been disclosed. For example, Japanese Patent Application Laid-Open No.
11-302896,
titled, “production method of an oxide thin film” discloses a method of producing an objective oxide by depositing a hydrate, a hydroxide, or a water-containing substance containing metal species a support and then changing the duty ratio of pulses of applied voltage to dehydrate while suppressing the dissolution. Here, existence of water in any form in the oxide deposited by the electrodeposition method is disclosed as a conventional technique. Further, there is also a description that dehydration is needed since the existence of water or the like deteriorates the reliability of the film. However, there is no description at all regarding the amount of the water contained in the objective oxide.
Further, Japanese Patent Application Laid-Open No. 10-140373 document discloses a method (an electro-deposition method) of forming a zinc oxide thin film on a support by applying an electric current in an aqueous solution produced by adding a carbohydrate to an aqueous solution containing nitrate ions and zinc ions. However, no description is given regarding the amount of water contained in the zinc oxide thin film.
Presuming that the usability of a substrate for solar cells depends on the amount of water contained in an oxide thin film, the present inventors have made an investigation of a zinc oxide film formed by a sputtering method, an investigation of a zinc oxide thin film involving water vapor introduction by a sputtering method, and an investigation of a zinc oxide film by deposition from an aqueous solution by an electrodeposition method.
As a result, in the case of a zinc oxide film produced by deposition from an aqueous solution by an electrodeposition method, it has been found that the electric resistance value of the film is not constant. Although the reason for that is not clear, when the resistance is changed by two or more orders of magnitude and becomes high, the initial characteristics of solar cells are deteriorated.
Also, in the case of making the surface area large in terms of industrial productivity, the uniformity, the adhesion and the like are sometimes insufficient.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the above mentioned situation, and it is, therefore, an object of the present invention to provide a substrate for a solar cell having a zinc oxide film with optimal overall characteristic and a solar cell using the substrate.
According to a first aspect of the present invention, there is provided a substrate for a solar cell comprising a support having a metal surface and a zinc oxide film formed on the metal surface and having a water content of 7.5×10
−3
mol/cm
3
or less.
In the present invention, it is preferable that the zinc oxide film has a water content of 4.0×10
−4
mol/cm
3
or more and more preferable that the film has a water content of not less than 1.0×10
−3
mol/cm
3
and not more than 5.0×10
−3
mol/cm
3
.
Further, it is preferable that the zinc oxide film is formed by electrodeposition utilizing an electrochemical reaction in an aqueous solution.
Moreover, it is preferable that the zinc oxide film is formed by sputtering in an atmosphere comprising water.
Also, it is preferable that the zinc oxide film is comprised of a plurality of layers.
In addition, it is preferable that the metal surface of the support comprises a metal selected from the group consisting of silver, aluminum, copper, silver alloy, aluminum alloy, and copper alloy.
According to a second aspect of the present invention, there is provided a process of producing a solar cell comprising the steps of:
forming a zinc oxide film on a support using an aqueous solution;
drying the zinc oxide film at a first temperature; and
forming a semiconductor layer on the zinc oxide film at a second temperature that is not higher than a temperature which is higher by 100° C. than the first temperature. Incidentally, when a layer such as another semiconductor layer is further formed on the above-mentioned semiconductor layer, there is no restriction as to the formation temperature of the further formed layer (i.e., the layer which is not in contact with the zinc oxide film).
In the present invention, it is preferable that the second temperature is not higher than the first temperature.
Further, it is preferable that the first temperature is not lower than 200° C. and not higher than 400° C.
Presuming that problems in the above-described substrate for solar cells having a zinc oxide thin film significantly depends on the water content in the zinc oxide thin film, the inventors have carried out the following experiments.
Measurement of Water Content and Correlation of Water Content with Resistance and Reflectivity
A silver film with a thickness of 800 nm and successively a zinc oxide thin film with a thickness of 1 &mgr;m were formed on a SUS 430 (2D surface) support at a set temperature of 200° C. in argon atmosphere by a commercially available sputtering apparatus (manufactured by ULVAC, Inc.) (sample A).
Next, after a silver film was formed in the same conditions, the partial pressure of water was changed to be 5, 10, 15, and 30% and a zinc oxide thin film with a thickness of 1 &mgr;m was formed (samples B to E). Further, the partial pressure of water was changed to be 0.1% and a zinc oxide thin film with a thickness of 1 &mgr;m was formed (sample L).
Further, using a support on which a silver film was formed in the above-described conditions as a cathode and a zinc plate as an anode, a zinc oxide film with a thickness of 1 &mgr;m was formed on the silver by an electrodeposition method in an aqueous zinc nitrate solution (sample F). Moreover, same samples F were dried under some different drying conditions to obtain samples (sample G to K).
In such a manner, several sheets of each samples were produced and their water contents were measured by Karl Fisher Moisture Titrator (MKC-510, manufactured by Kyoto Electronics).
Further, metals of Cr and successively Au, were evaporated on the zinc oxide thin film of each sample by a vacuum evaporation apparatus using a 0.25 cm
2
mask and used as an upper electrode to measure the electric resistance value between the upper electrode and the SUS support. Since the measurement system including the measurement probe itself has the circuit resistance of about 0.1 &OHgr;cm
2
, the electric resistance measurement was supposed to include measurement error to the extent of such a level.
Further, the total reflectivity and the irregular reflectivity of each sample were measured by a spectrometer (V-570, manufactured by JASCO Corporation Ltd.) in a range of 400 nm to 1,200 nm.
The measure
Miyamoto Yusuke
Sonoda Yuichi
Toyama Noboru
LandOfFree
Substrate for solar cell, solar cell having the same, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Substrate for solar cell, solar cell having the same, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Substrate for solar cell, solar cell having the same, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3097133