Patent Application
20100200042
The present invention relates to photovoltaic devices and methods for manufacturing photovoltaic devices.
Solar cells using polycrystalline, microcrystalline, or amorphous silicon have been known. In a common process of fabricating solar cells, after a transparent conductive film of tin oxide (SnO2) or the like is formed on a glass substrate, polycrystalline, microcrystalline, or amorphous silicon constituting a photovoltaic layer is deposited by chemical vapor deposition (CVD) or the like. Then, an electrode serving as a backside electrode is formed. The electrode is formed by means of, for example, depositing a conductive material such as aluminum (Al), silver (Ag), or titanium (Ti) by vacuum deposition or sputtering.
However, when forming such an electrode layer, the metal may be provided to the backside of the glass substrate, which is opposite to the surface where the photovoltaic layer has been formed and the electrode layer is to be formed. This causes a problem of deterioration in insulation resistance between the backside electrode of the solar cell and the surface of the glass substrate, for example.
As such, in order to prevent formation of a film reaching the backside of the film forming surface of a substrate, a method for reducing a gap between the substrate and a substrate holder (tray) for mounting the substrate has been proposed (JP 2007-197745 A, and the like).
There is also a problem that when repeating the process of forming electrode layers, deposits to a substrate holder may fall off during formation of the electrode layers and be taken into the electrode layers. To prevent the deposits from falling off, measures such as keeping the substrate holder at a high temperature must be taken. As such, in order to reduce impurity intake from the substrate holder when forming the electrode layers, a holder-less method (tray-less method) has tended to be adopted.
However, in the case of adopting a holder-less method, a metal layer may reach the glass substrate side, which has been protected by the substrate holder, so that an electrode layer may be formed on the backside of the film forming surface of the photovoltaic layer. For example, as shown in
If the electrode layer is formed reaching the backside as described above, the dielectric strength feature between the electrode layer and the glass substrate may be deteriorated.
Further, even for the electrode layer formed on the photovoltaic layer side, when the photovoltaic device is modularized, an electrode portion formed near an end part of the substrate is to be positioned near the metal frame which is a structure of the module, so the electrode portion may deteriorate the dielectric strength of the module.
An aspect of the present invention is a method for manufacturing a photovoltaic device including one or a plurality of photovoltaic cells, each of the photovoltaic cells including a first electrode layer, a semiconductor layer, and a second electrode layer which are formed on a substrate. The method includes applying a voltage between a first portion of the second electrode layer in which a photovoltaic power is not obtained, and a second portion of the second electrode layer which is distant from the first portion, and in which a photovoltaic power is not obtained, so as to remove at least a part of the second electrode layer.
A method for manufacturing a photovoltaic device according to an embodiment of the present invention will be described below. In the present embodiment, description will be exemplarily given according to a tandem thin-film photovoltaic device using an amorphous silicon film (a-Si film) and a microcrystalline silicon film (μc-Si film). However, the applicable range of the present invention is not limited to this embodiment, and the present invention is applicable to various photovoltaic devices including single-layered, multilayered, thin-film type, and bulk-type devices.
First, a transparent conductive film 22 is formed as a first electrode on a substrate 20 (
Next, slits 22a are formed in the transparent conductive film 22 by a laser separation process, whereby the transparent conductive film 22 is separated into rectangles (
After the laser separation process, an a-Si film 24 and a μc-Si film 26, serving as photovoltaic layers (power generating layers), are formed on the transparent conductive film 22 in this order, each including a p-layer, an i-layer, and an n-layer (
Next, slits 26a are formed by applying a laser separation process to the photovoltaic layers 24 and 26 at positions beside the slits 22a of the transparent conductive film 22 processed in rectangles, whereby the photovoltaic layers 24 and 26 are separated into rectangles (
Then, a metal electrode 28 is formed as a second electrode on the photovoltaic layer 26 (
In this process, if sputtering is performed in a state where the substrate 20 is mounted on a substrate holder, deposits adhering to the substrate holder may be taken into the metal electrode 28. As such, as shown in
Next, slits 28a are formed by applying a laser separation process to the metal electrode 28 at positions beside the slits 26a of the photovoltaic layer 26 processed to be rectangles, whereby the metal electrode 28 is separated into rectangles (
Also, a slit 28b is formed by applying a laser separation process to a position near an end part of the substrate 20. The slit 28b is formed so as to penetrate the transparent conductive film 22, the photovoltaic layers 24 and 26, and the metal electrode 28. With the slit 28b, an ineffective portion not contributing to power generation is formed in an end region of the substrate 20.
Through these processes, the base structure of the integrated photovoltaic device is completed, in which a plurality of solar cells separated by the slits 28a are connected in series.
It should be noted that if a holder-less method (tray-less method) is adopted to form the metal electrode 28, the metal electrode 28 may reach the substrate 20 side so that the metal electrode 28 may also be formed on the side face and the surface of the substrate 20, as shown in the cross-sectional view of
As such, in the present embodiment, a process of removing the metal electrode 28 formed by reaching the surface side of the substrate 20 is performed. As shown in
While the electrode bars 30 and 32 maybe made of any conductive member, copper, for example, is preferable for their material. Further, as it is desirable to be able to arrange the electrode bars 30 and 32 over an edge of the substrate 20, the length thereof is preferably the same as or longer than the width of the substrate 20. Further, while the electrode bars 30 and 32 maybe in a columnar, cylindrical, or prismatic shape for example, it is more preferable that the electrode bars 30 and 32 are in a shape with a curved surface which linearly contacts the metal electrode 28.
Next, a voltage is applied between the electrode bars 30 and 32. The voltage to be applied is preferably at least higher than the electromotive force of the solar cells (photovoltaic cells). This means that the voltage is preferably of a level at which the metal electrode 28 evaporates by the Joule heat generated by the current flowing in the electrode bars 30 and 32. For example, the voltage is preferably not less than 100 V and not more than 5000 V.
To apply the voltage, it is preferable to use a device with a protection circuit which senses supply current and stops application of the voltage when current larger than a predetermined value flows, such as a withstand voltage test device, for example.
From this state, the electrode bar 32 is gradually moved toward the end part of the substrate 20 while contacting the surface of the substrate 20 or the surface of the metal electrode 28 formed by reaching the surface of the substrate 20, as shown in
As a voltage is applied between the electrode bars 30 and 32, it is preferable to move the electrode bar 32 to the extent that the electrode bars 30 and 32 do not contact each other. As such, as shown in the perspective view of
It should be noted that in the present embodiment, although the case of moving the electrode bar 32 has been described, it is acceptable to fix the electrode bar 32 and move the electrode bar 30. Alternatively, both electrode bars 30 and 32 maybe moved toward each other.
Further, as an alternative to the method of removing the metal electrode 28 by applying a high voltage between the electrode bars 30 and 32, the metal electrode 28 may be removed using laser light. For example, the metal electrode 28 can be removed with a laser which is used to form a thin-film solar cell module. Specifically, by emitting laser light from the photovoltaic layer 26 side under the conditions of a wavelength of 532 nm, a frequency of 10 kHz, and power of −0.7 W, and moving the substrate 20 vertically and horizontally to scan the laser light such that the irradiation areas of the laser light overlap, any desired area of the metal electrode 28 can be removed.
The metal electrode 28 may also be removed by blast processing. In blast processing, the metal electrode 28 is removed by the use of mechanical energy by spraying microparticles from a nozzle. It is preferable to use particles of tungsten, alumina, silica, oxidized zirconium, or the like. The particle size to be used is preferably similar to #1000 abrasive. For example, by spraying tungsten particles under the conditions of a spraying pressure of 0.15 MPa and 80 Hz (68 g/minute) and moving the nozzle at a relative velocity of 1.0 m/minute with respect to the substrate 20, an area of the metal electrode 28 applied with the particles can be removed.
Further, the metal electrode 28 may also be removed by etching. For example, by dipping the metal electrode 28 in a water solution prepared by mixing ammonium hydroxide (NH4OH) diluted by 28% and hydrogen peroxide water (H2O2) in the proportion of 2:1, the metal electrode 28 is etched and removed. The area other than that to be removed by etching is preferably protected by a proper resist agent or the like.
Next, a process of modularizing the photovoltaic device will be described with reference to
Pressure tests were performed on a module applied with the removing process of the metal electrode 28 according to the present embodiment and a module not applied with the removing process, to check the withstanding pressure of the respective modules. The pressure tests were performed in accordance with JIS C 8917.
In the pressure tests, no problem was found in the module to which the removing process of the metal electrode 28 had been applied. However, in the module to which the removing process of the metal electrode 28 had not been applied, overcurrent flowed during voltage application so that the withstanding pressure conditions were not cleared. As a result of examining the module after the test, the part between the extraction electrode portion and the ineffective portion was black, so it was estimated that the current flowed in this part.
It should be noted that in the present embodiment, although the process of removing the metal electrode 28 is performed after the slits 28a are formed by applying a laser separation process to the metal electrode 28, the removing process may be performed before formation of the slits 28. This means that as shown in
In general, the slits 28a are formed by allowing laser to enter from the substrate 20 side. If an unnecessary metal electrode 28 is formed on the end part of the substrate 20, there is a case where laser cannot be irradiated to the transparent conductive film 22, the photovoltaic films 24 and 26, and the like under desired conditions due to being obstructed by such metal electrode 28. In that case, it is preferable to remove the metal electrode 28 before formation of the slits 28a.
Further, in the present embodiment, although the case of applying the removing process of the metal electrode 28 to an end part on the positive electrode (+ electrode) side of the photovoltaic device has been described, the process may be applied to the metal electrode 28 of an end part on the negative electrode (− electrode) side or an end part along the slits 22a, 26a, and 28a.
Further, in the present embodiment, although the method of removing the metal electrode 28 reaching the surface side of the substrate 20 has been described, the metal removing method of the present embodiment is applicable in the case where the metal electrode 28 does not reach the surface side of the substrate 20.
For example, even in the case where the metal electrode 28 does not reach the surface side of the substrate 20, by removing the metal electrode 28 on the photovoltaic layer 26 in the ineffective area B at the end part of the substrate 20, the pressure resisting feature between the frame 48 and the photovoltaic device after modularization can be improved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-231951 | Sep 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/065340 | 9/2/2009 | WO | 00 | 3/23/2010 |
