Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2000-05-18
2003-08-05
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S336000, C428S702000, C136S243000, C136S252000
Reexamination Certificate
active
06602606
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a glass sheet with a conductive film, a method of manufacturing the same, and a photoelectric conversion device, such as a solar cell or the like, using the same.
BACKGROUND OF THE INVENTION
Generally, a thin film photoelectric conversion device includes a transparent conductive film containing tin oxide as a main component, a thin film silicon layer as a photovoltaic layer, and a back electrode of aluminum or the like, which are formed on a glass substrate in this order. In such a configuration, the transparent conductive film positioned on a window side from which light is introduced into the photovoltaic layer is required to have high light transmittance. It also is required to have high conductivity (low resistance) in view of its function as an electrode. Furthermore, it has been known that when the transparent conductive film is formed to have a surface with roughness, the introduced light can be used efficiently due to a so-called “light trapping effect”. The degree of the roughness formed at the surface of the transparent conductive film can be indicated by a haze ratio.
As the transparent conductive film, a fluorine doped tin oxide (hereinafter referred to as “SnO
2
:F”) film has been used in many cases. This film is more excellent in chemical stability such as plasma resistance or the like compared to a tin doped indium oxide (ITO) film. Therefore, the SnO
2
:F film does not deteriorate greatly in forming a photovoltaic layer (a thin film silicon layer) by using a plasma CVD method. The SnO
2
:F film is formed to have a certain thickness in order to decrease its sheet resistance to a value that is desirable for an electrode, although its sheet resistance is intended to be decreased by doping with fluorine. Therefore, in order to improve the conversion efficiency of the photoelectric conversion device, it is necessary to improve the light transmittance in view of the thickness of the SnO
2
:F film.
For instance, JP 1-259572 A describes that the light absorption of a transparent conductive film is suppressed by setting the concentration of chlorine introduced into a SnO
2
:F film from raw materials in forming the film to be 0.40 wt. % or lower. The specific chlorine concentration described therein is 0.12 to 0.36 wt. %. A glass sheet used therein is a soda-lime glass sheet precut to have a predetermined size.
JP 2-181473 A describes that the plasma resistance of a SnO
2
:F film is improved by adjusting levels of trace components in the SnO
2
:F film. JP 2-181473 A discloses that fluorine in the film deteriorates the plasma resistance of the SnO
2
:F film more than the chlorine in the film does. JP 2-181473 A also describes a SnO
2
:F film in which the fluorine concentration is 0.04 to 0.2 wt. % and the chlorine concentration is 0.4 wt. % or lower. In a film with a low chlorine concentration, the fluorine concentration is adjusted to be further lower than the chlorine concentration. Further, as a heating temperature of a glass sheet, a temperature of 550° C. is described as an example. The glass sheet used therein also is a soda-lime glass sheet precut to have a predetermined size.
However, the influences of film formation conditions and trace components other than chlorine on the light transmittance of a conductive film such as a SnO
2
:F film have not been clarified.
Further, the following problem has been pointed out. In a thin film photoelectric conversion device, defect levels are formed in an amorphous silicon-based photovoltaic layer due to light irradiation, thus decreasing a photoelectromotive force. Recently, therefore, an amorphous silicon-based photovoltaic layer tends to be formed to be thin. However, in the above-mentioned conventional SnO
2
:F film, components other than chlorine and characteristics of the film have not been adjusted to satisfy the characteristics required for the silicon-based photovoltaic layer with a reduced thickness.
Further, the light trapping effect by a transparent conductive film becomes more important in a thinner photovoltaic layer. Therefore, the transparent conductive film is required to have a high haze ratio in addition to a low absorptance for achieving a high light transmittance. In order to increase the haze ratio, the thickness of the film may be increased.
However, the simple increase in film thickness results in the increase in absorption of the film.
The absorptance and the haze ratio of the SnO
2
:F film are affected by manufacturing conditions and raw materials. One of the typical raw materials used for forming a tin oxide film by a CVD method is tetramethyltin. For instance, JP 55-56041 A discloses a method of forming a tin oxide film by pyrolysis of a mixed gas containing tetramethyltin and oxygen. This mixed gas contains about 1% tetramethyltin and about 20% oxygen. Since tetramethyltin has a high reactivity, the control of film formation is not easy.
JP 2-175631 A and JP 8-508006 A disclose a method of forming a tin oxide film with a mixed gas containing tin tetrachloride and dry air. Since tin tetrachloride has a high reactivity with respect to water, the dry air is used as a gas for oxidizing the tin tetrachloride. Further, JP56-24708 A describes that hydrogen is added as a reductant for suppressing the reaction between tin tetrachloride and water.
Materials that can be handled more easily than those tin materials include organic tin chlorides such as dimethyltin dichloride, monobutyltin trichloride, and the like. For instance, JP 4-502305 A discloses a method of forming a film using dimethyltin dichloride and describes a mixed gas containing dimethyltin dichloride, oxygen, water, and nitrogen. This mixed gas is indicated to have a volume ratio of dimethyltin dichloride:oxygen:water:nitrogen=50:50:23:250.
JP 63-242947 A describes an example in which the haze ratio of a tin oxide film is varied by adjusting the mole ratio of dimethyltin dichloride and water. Oxygen is not added simultaneously.
U.S. Pat. No. 5,698,262 describes a method of doping a tin oxide film with fluorine using not trifluoroacetic acid or the like but hydrogen fluoride in order to obtain low and uniform sheet resistance. The mixed gas disclosed therein contains dimethyltin dichloride, oxygen, water, hydrogen fluoride, and helium. The concentrations of oxygen and water vapor are 10 to 60 mol % and 2 to 50 mol %, respectively. In the examples and comparative examples, the concentration of dimethyltin dichloride (vapor) is described as about 2.5 mol %. However, the thickness (320 nm) of the SnO
2
:F film disclosed therein limits the size of crystal grains, thus preventing the film surface from having great irregularities. Therefore, a high haze ratio cannot be obtained.
SUMMARY OF THE INVENTION
The present invention is intended to provide a glass sheet with a conductive film having a higher light transmittance than that in a conventional one and a method of manufacturing the same, by directing attention not only to chlorine but also to trace components other than that.
Another object of the present invention is to provide a glass sheet with a conductive film that can be used suitably even when a photoelectric conversion layer is thin. Particularly, the present invention is intended to provide a glass sheet with a conductive film having both a low light absorptance and a high haze ratio and a method of manufacturing the same.
Furthermore, still another object of the present invention is to provide a photoelectric conversion device such as a photovoltaic device using any one of the above-mentioned glass sheets.
The present inventors found that especially the concentrations of fluorine and carbon in a conductive film containing tin oxide as a main component affected the light transmittance of the conductive film. The present inventors also found that an oxygen concentration in the atmosphere in forming the conductive film affected the light transmittance. By controlling these conditions suitably, the absorption coefficient of the conductive film containing tin oxide as the main comp
Fujisawa Akira
Hirata Masahiro
Kiyohara Koichiro
Otani Tsuyoshi
Seto Yasunori
Jones Deborah
Nippon Sheet Glass Co. Ltd.
Stein Stephen
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