Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array
Reexamination Certificate
2000-03-02
2001-09-11
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Panel or array
C136S256000, C136S293000, C136S255000, C438S066000, C438S067000, C438S074000, C438S080000, C438S088000, C257S443000, C257S448000, C257S431000
Reexamination Certificate
active
06288323
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-238708, filed Aug. 25, 1999; No. 11-238709, filed Aug. 25, 1999; No. 11-262214, filed Sep. 16, 1999; and No. 11-262215, filed Sep. 16, 1999; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a thin film photoelectric conversion module and a method of manufacturing the same, particularly, to a thin film photoelectric conversion module having a plurality of thin film photoelectric conversion cells connected in series and a method of manufacturing the same.
In general, a thin film photoelectric conversion module comprises a plurality of band-like thin film photoelectric conversion cells arranged in the direction of the short axis of the cell and connected to each other in series. In general, such a module is not used singly and is used generally in the form of a module array consisting of a plurality of modules connected in series or in parallel.
Where a leaf or bird droppings are attached to the light-receiving surface of a certain thin film photoelectric conversion cell included in such a thin film photoelectric conversion module, the light to the particular cell is partially or entirely intercepted so as to decrease the photoelectromotive force, leading to a marked reduction in the output of the entire module. It should be noted that the cell with the decreased photoelectromotive force acts as a diode connected in series in the reverse direction to the direction of the power generation, i.e., in the reverse direction to the direction in which the current generated by the photoelectric conversion flows. As a result, the light-intercepted cell exhibits a very high resistance, leading to the marked reduction in the output of the entire module as pointed out above.
The decreased photoelectromotive force of the cell affects not only the particular module but also the module array. More specifically, the module including a cell whose photoelectromotive force is decreased causes the output of the module array to be lowered markedly.
A measure for overcoming the problem is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 57-53986. Specifically, it is disclosed that a plurality of thin film photoelectric conversion cells connected in series are divided into a plurality of series arrays, and that these series arrays are connected in parallel. The particular technique makes it possible to prevent the output of the module array from being lowered markedly even if the photoelectromotive force of any of the cells has become zero. Also, in order to prevent the output of the module array from being lowered markedly, another measure such as mounting a single bypass diode to every module is known.
However, an additional problem is produced by the attachment of, for example, a leaf to the thin film photoelectric conversion cell, as follows. Specifically, if voltage higher than the withstand voltage is applied to the cell having the light thereto intercepted by the attached leaf or the like, an insulation breakdown is generated. Current does not flow uniformly through the cell of the particular state so as to bring about a local heating called a hot spot phenomenon. The local heating does not produce a serious problem where the current flowing through the cell is small. However, a module having a large area generally produces a large output current, with the result that, in the conventional module having a large area, the light-intercepted cell is heated to a very high temperature.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a thin film photoelectric conversion module in which, even if the light to one of the thin film photoelectric conversion cells is intercepted, the particular cell is not heated to an excessively high temperature, and a method of manufacturing the particular module.
Another object is to suppress the heating of a thin film photoelectric conversion cell where the light to one of the cells is intercepted so as to prevent the particular cell from being broken.
Still another object of the present invention is to provide a thin film photoelectric conversion module having a high reliability and a method of manufacturing the same.
As a result of an extensive research conducted in an attempt to achieve the objects given above, the present inventors have found that a thin film photoelectric conversion module of a high reliability comprising a plurality of thin film photoelectric conversion cells can be achieved by suppressing the behavior of the cell as a diode, by preventing a large current from flowing through the light-intercepted cell, or by facilitating the formation of a short-circuit in the light-intercepted cell. By employing any of these measures, the cell having the light thereto intercepted can be prevented from being heated to an excessively high temperature.
For example, where the behavior as a diode of the light-intercepted cell is suppressed, the light-intercepted cell is capable of easily permitting a current to flow in the direction equal to the power generating direction. As a result, it is possible to suppress the heat generation within the particular cell or to prevent the cell from being broken. Where a large current is not allowed to flow through the light-intercepted cell, the heat generation in the cell can be suppressed so as to prevent the cell from being broken. Further, where a short-circuit is easily formed within the light-intercepted cell, the short-circuiting can be generated at a relatively low temperature, making it possible to prevent the cell from being heated to an excessively high temperature.
The present inventors have conducted an extensive research in suppressing the behavior of the light-intercepted cell as a diode. As a result, a special phenomenon has been found that, where a reversed bias, i.e., voltage in the forward direction relative to the power generation direction, is applied repeatedly to the thin film photoelectric conversion cell, it is possible to increase the current flowing through the cell on applying a reversed bias voltage while scarcely affecting the fill factor (F.F.). The present inventors considered that, even if light to a certain cell was intercepted, it would be possible to prevent the light-intercepted cell from being heated to an excessively high temperature, to prevent the output of the entire module from being markedly lowered, and to prevent the cell from being broken by utilizing the particular phenomenon pointed out above. These effects have been actually confirmed.
According to a first aspect of the present invention, there is provided a thin film photoelectric conversion module, comprising a substrate; and a series-connected array including a plurality of thin film photoelectric conversion cells formed on the substrate and connected to each other in series, the number of cells being represented by N, an open-circuit voltage of each the cells being represented by E, and N being an integer of at least
10
, wherein a current equal to a short-circuit current of each of the cells under conditions that a xenon lamp is used as a light source, an irradiance is 100 mW/cm
2
, air mass is 1.5, and temperature is 25° C., is allowed to flow through each of the cells by application of a reversed bias voltage not higher than (N−1)×E.
According to a second aspect of the present invention, there is provided a method of manufacturing a thin film photoelectric conversion module including a substrate and a plurality of thin film photoelectric conversion cells formed on the substrate and connected to each other in forward direction, comprising the step of repeatedly applying a reversed bias voltage to each of the cells so as to increase the magnitude of the current flowing through the cells on applying the reversed bias voltage.
In the first aspect of the present invention, the reversed bias voltage is, for example, not higher than 8V.
Hayashi Katsuhiko
Yamagishi Hideo
Diamond Alan
Hogan & Hartson L.L.P.
Kaneka Corporation
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