JP2006100652A - Photovoltaic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric converter with high reliability and excellent anti-environmental performance by preventing the adhesion strength between a photoelectric conversion element (cell) and a sealing resin from being decreased. <P>SOLUTION: The photovoltaic device is module-designed by sealing the photoelectric conversion element employing a single crystal silicon substrate 1 subjected to charge electron control, and having an irregular surface in the microne order between a front glass and a backside member by means of a hot melt type filling member. The device has an SiOx layer 20 wherein the unevenness pitch of the irregularities of the outermost surface on at least the light incident side is controlled to be 0.8 h or below, in which h is the unevenness pitch of the irregularities of the single crystal silicon substrate 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photovoltaic device, and in particular, to a photovoltaic device that is sealed with a hot-melt filler between a front glass and a back material and modularized.

  In recent years, as photovoltaic devices, research and practical application of solar cells using crystalline semiconductors such as single crystal silicon and polycrystalline silicon have been actively conducted. Among them, a solar cell having a hetero semiconductor junction constituted by combining amorphous silicon and crystalline silicon can form the junction by a low temperature process such as a plasma CVD method at 200 ° C. or less, and Because of its high conversion efficiency, it has attracted attention. In such a photovoltaic device, in order to improve the photoelectric conversion efficiency, it is necessary to improve the fill factor (FF) while maintaining a high short circuit current (Isc) and an open circuit voltage (Voc).

  Therefore, a substantially intrinsic amorphous silicon layer containing hydrogen (i-type amorphous silicon layer) is inserted between the n-type single crystal silicon substrate and the p-type amorphous silicon layer containing hydrogen. A solar cell having a so-called HIT structure has been developed (see, for example, Patent Document 1).

  In the solar cell having the above-described HIT structure, micron-sized pyramidal irregularities are formed on the surface of the single crystal silicon substrate in order to obtain a light confinement effect. Then, an i-type amorphous silicon layer, a p-type or n-type amorphous silicon layer, and an oxide transparent conductive film are sequentially provided on the single crystal silicon substrate, and an electrode paste is formed on the oxide transparent conductive film. An electrode is provided.

In a photovoltaic power generation system installed on a roof or the like, a photoelectric conversion element having the above-mentioned HIT structure is sealed with a hot-melt filler such as EVA (ethylene vinyl acetate) between the front glass and the back material. It is modularized and used.
JP-A-11-224954

  When an excessive environmental resistance test is performed on the above-described modularized photovoltaic device, the adhesion strength between the photoelectric conversion element (cell) and the EVA in the uneven valley may be relatively lowered. there were. A solar power generation system installed on a roof or the like requires higher environmental reliability than a conventional consumer solar cell device.

  The present invention has been made in view of the above circumstances, and prevents a decrease in adhesion strength between the photoelectric conversion element (cell) and the sealing resin, and is excellent in high reliability and high environmental resistance. It is an issue to provide.

  In the present invention, a photovoltaic element using crystalline silicon that is controlled by valence electrons and has an uneven surface on the order of microns is sealed with a hot-melt filler between a surface glass and a back surface material to be modularized. In the photovoltaic device, an inorganic thin film protective layer controlled so that the height of the ridges and valleys on the outermost surface is 0.8 h or less is provided at least on the light incident side, where h is the height of the ridges and valleys of crystalline silicon. It is provided.

  Further, it is preferable to control the inorganic thin film protective layer at least on the light incident side so that the peak height of the concave and convex portions on the outermost surface is 0.4 h or less with respect to the peak height h of the concave and convex portions of the crystalline silicon.

  The inorganic thin film protective layer may be one containing at least silicon.

  The hot-melt type fillers are ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), ethylene-methyl acrylate copolymer (EMA), and ethylene-ethyl acrylate copolymer (EEA). You may choose from either.

  The present invention relates to a photovoltaic device in which a photovoltaic element using crystalline silicon having a concavo-convex surface of micron order is sealed with a hot-melt filler between a front glass and a back material to form a module. By forming the inorganic thin film protective layer at least on the light incident side so as to control the uneven surface valley height of the outermost surface to be 0.4 h or less with respect to the uneven surface valley height h of the crystalline silicon, The adhesion strength between the photoelectric conversion element (cell) / filler after the environmental test is significantly improved, and a photoelectric conversion device having high reliability and high environmental resistance can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram of a cross-sectional structure of a solar cell module using a photoelectric conversion element having a HIT structure to which the present invention is applied. FIG. 1B is a partially enlarged sectional view of a portion b of FIG. 1A, and FIG. 1C is a partially enlarged sectional view of a portion c. The film thickness of the amorphous silicon layer formed on the substrate is very thin compared to the film thickness of the substrate, and the amorphous silicon layer or the like cannot be described with the same ratio. The amorphous silicon layer and the like are described by ignoring the ratio.

  In this photoelectric conversion element (cell) having the HIT structure, micron-sized pyramidal irregularities are formed on the surface of the single crystal silicon substrate 1 in order to obtain a light confinement effect. The single crystal silicon substrate 1 is formed with pyramidal irregularities by the following anisotropic etching process.

First, an n-type (100) single crystal silicon substrate 1 having a thickness of about 1 Ω · cm and a thickness of 300 μm is prepared, and this substrate is immersed in a solution of NaOH (2.5 mol / l, 85 ° C.), followed by NaOH. / IPA (0.5 mol / l NaOH, 2 mol / l IPA, 85 ° C.) is dipped and etched. Thereafter, the substrate is washed with H ₂ O rinse (room temperature), and further washed with HF / H ₂ O (2 mol / l HF room temperature).

Then, after H ₂ O rinsing (room temperature) treatment, the substrate is immersed in a HF / HNO ₃ (1:10, room temperature) solution for 30 seconds to perform H ₂ O rinsing (room temperature) treatment. Thereafter, O ₃ / H ₂ O (15 ppm, room temperature) is treated for 5 minutes, H ₂ O rinse (room temperature), HF / H ₂ O (2 mol / l HF room temperature), H ₂ O rinse (room temperature) treatment The process is performed. By this treatment, cleaning and uneven formation were performed.

  The unevenness formed by this method had an average mountain valley height (h) of about 10 μm and an average pitch (W) of about 17 μm. In the anisotropic etching of the normal (100) single crystal silicon substrate 1, the average pitch (W) is larger than the average peak / valley height (h).

  Next, the amorphous semiconductor layer 2 in which the i-type amorphous silicon layer and the p-type amorphous silicon layer are stacked on the surface side of the single crystal silicon substrate 1 and the single crystal silicon substrate 1 are formed by a known plasma CVD method. An amorphous semiconductor layer 4 in which an i-type amorphous silicon layer and an n-type amorphous silicon layer are stacked is formed on the back side. Thereafter, oxide transparent conductive films 3 and 5 were formed on both surfaces of the amorphous semiconductor layers 2 and 4 by sputtering. And the collector electrodes 6 and 7 are formed by the electrode paste of front and back, and the photoelectric conversion element (cell) of a HIT structure is formed.

  The amorphous semiconductor layer described above is formed using a known RF plasma CVD (13.56 MHz) at a forming temperature of 100 ° C. to 250 ° C., a reaction pressure of 26.6 to 80.0 Pa, and an RF power of 10 to 100 W. did. The thickness of the p-type amorphous silicon layer and the n-type amorphous silicon layer was 5 nm, and the thickness of the i-type amorphous silicon layer was 5 nm.

As the oxide transparent conductive films 3 and 5, an oxide indium tin (ITO) film was used. The ITO (SnO ₂ doped) film is formed using a known magnetron sputtering at a forming temperature of 50 to 250 ° C., a gas flow rate of Ar to 200 sccm, an O _{2 to} 50 sccm, a power of 0.5 to 3 kw, and a magnetic field strength of 500 to 3000 Gauss. The film was formed with a thickness of 100 nm.

  Next, the collector electrodes 6 and 7 made of paste were formed using an Ag electrode paste made of epoxy as a main binder resin using a known screen printing method.

  By the way, the solar cell module is a photoelectric conversion element in which an EVA (ethylene vinyl acetate) sheet 11 and a tab electrode 12 made of copper foil are soldered onto the collector electrodes (bus bar electrodes) 6 and 7 of Ag paste on the surface glass 10. (Cell), EVA sheet 11, and PVF (polyvinyl fluoride) sheet (back material) 13 are laminated in order, and are heated and vacuum laminated.

  In this embodiment, a simple module structure using one photoelectric conversion element (cell) of this HIT structure is used, and the surface of the photoelectric conversion element (cell) opposite to the surface glass 10 has a large moisture permeability compared to a commercially available product. It is an accelerated structure that performs reliability tests under stricter conditions.

  A simple module shown in FIG. 1 was prepared using a photoelectric conversion element (cell) having a conventional HIT structure, and an excessive moisture resistance test (temperature 85 ° C., humidity 85%, 3000 hours) was performed. In the peeling test between the photovoltaic element and EVA of the sample after the test, it was confirmed that there was a region where the adhesion strength of the concave and convex valley portions was relatively weak. This may be due to the fact that internal stress is generated in the process of EVA cross-linking, and stress is particularly concentrated in the valleys of the unevenness.

  The present inventors have found that the height of the uneven valleys affects the adhesion strength, and provided a transparent metal oxide thin film or the like on the photoelectric conversion element (cell), and controlled the unevenness of this thin film, thereby improving the adhesion strength. Tried to improve.

  First, a first embodiment in which a transparent metal oxide thin film or the like is provided on a photoelectric conversion element (cell) and blasting is performed to control the size of the unevenness will be described with reference to FIGS.

  In order to control the height of the unevenness according to the embodiment of the present invention, as shown in FIG. 2, ion plating is performed on the light incident side and the back side on the photovoltaic element on which the paste electrodes 6 and 7 are formed. The SiOx film 20 (X: 1.5-2) was formed to 20 μm under the conditions of an Ar flow rate of 150 sccm and a gun current of 150 A. This film thickness was controlled by the conveyance speed.

Next, as a blasting device, MB1ML-011 manufactured by Shinto Blator is used to uniformly irradiate the substrate surface with alumina (Al ₂ O ₃ ) fine particles by compressed air, and the light incident side and back surface side are irradiated under the same conditions. Surface irregularities were controlled by treatment time. As the abrasive, Al ₂ O ₃ having an average particle diameter of 5 μm was used.

  FIG. 2 is a cross-sectional SEM image view of the light incident side surface immediately after the formation of the SiOx film 20, and FIG. 2B is a partially enlarged view of a portion b of FIG. The single crystal silicon substrate 1 used this time has an average ridge / valley height (h) of about 10 μm and an average pitch (W) of about 17 μm, and a 20 μm SiOx layer 20 is formed thereon.

  When a film is formed on the concavo-convex substrate 1 by a PVD-like method, it is known that the concavo-convex becomes dull at each of the peaks and troughs, but in this embodiment, a change of about 0.05 μm is seen in the height of the ridges and valleys. The surface irregularity height h was 9.95 μm. It is considered that the unevenness of the unevenness depends on the manufacturing method and the film thickness of the thin film, but it was confirmed that the change can be almost ignored in sputtering and ion plating (1% or less of the height of the valley).

  Next, FIG. 3 is a cross-sectional SEM image of the light incident side surface after blasting. As a result of the blast treatment, the film thickness of the 20 μm thick SiOx layer 20 was reduced to 10.6 μm, and the surface unevenness height h2 was about 4 μm. Thus, a photovoltaic element sample was prepared by utilizing the fact that the film thickness of the SiOx layer 20 decreased and the surface unevenness height became smaller as the blast treatment time increased. Further, the back surface side of the same sample was also made a sample with uniform surface unevenness height by the same method.

  Using this sample, a simple module was prepared by the method described above, and a moisture resistance test (temperature 85 ° C., humidity 85%, 3000 hours) was performed. The adhesion between the EVA after the test and the surface roughness control photovoltaic device was evaluated. The evaluation was performed using a peel strength measuring device 40 shown in FIG. For measurement, the end of the solder-coated copper foil tab 12 on the light incident side is sandwiched between the clips 41, and a handle (not shown) is rotated to pull the clip 41 until the copper foil tab 12 is peeled off, and to pull the maximum strength. By measuring, the strength is measured.

  The adhesion strength was normalized by the adhesion strength between the photoelectric conversion element (cell) / EVA having a height of 10 μm without any coating and evaluated as normalized strength.

  The result is shown in FIG. From FIG. 5, the normalized strength was improved by about 13 to 18% even when the SiOx film 20 was formed and blasting was not performed. This indicates that the SiOx film surface can achieve better adhesion with EVA than the ITO film surface, and is considered to be related to the amount of —OH groups on the surface. Furthermore, the normalized strength was improved as the height of the valleys was controlled and decreased, and very good adhesiveness with a height of 4 μm or less and a normalized strength of 2 or more was confirmed. The state of the surface of the SiOx film is considered to be independent of the film thickness change if the film thickness is 1 μm or more. The improvement of the adhesion strength is achieved by reducing the height of the valleys on the uneven surface, thereby reducing the EVA film stress. This is thought to be due to the suppression of concentration.

  Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, polysilazane is applied to control the height of peaks and valleys on the uneven surface.

A compound having a Si—N (silicon-nitrogen) bond is called silazane. Polysilazane is an inorganic polymer soluble in an organic solvent having — (SiH ₂ NH) — as a basic unit. PHPS = polysilazane whose entire side chain is hydrogen) is an accurate substance name. As shown in FIG. 6, a photovoltaic element having an average mountain valley height of about 10 μm and an average pitch W of about 17 μm was prepared by the above-described method. FIG. 6 is a cross-sectional SEM image of the light incident side surface, and FIG. 6B is a partially enlarged view of a portion b of FIG.

  A solution in which polysilazane was dissolved in a xylene solvent at a volume concentration of 1 to 20% was prepared on the ITO film 3 shown in FIG. 6, and a photovoltaic device was dipped in this solution, and uniformly applied to the substrate surface with an air knife. Then, the sample of this invention was created by drying at 200 degreeC for 1 hour in air | atmosphere. FIG. 7 is an example of a cross-sectional SEM image diagram of the light incident side surface after drying of polysilazane (Yamatani height to 4 μm).

  FIG. 8 shows the relationship between the concentration of polysilazane and the height of the surface peaks and valleys of the SiOx film 25 after drying. Since the polysilazane solution is liquid, deposition on the valleys of the surface irregularities is relatively large. Also in this embodiment, the higher the polysilazane concentration is, the thicker the SiOx film is deposited on the uneven valleys. As a result, for example, the height of the surface valleys is reduced as shown in FIG.

  Using a photovoltaic element (cell) with controlled surface unevenness height created under the conditions of FIG. 8, a simple module is created by the procedure described above, and a moisture resistance test (temperature 85 ° C., as in the first embodiment). (Humidity 85%, 3000 hours). The adhesion between the EVA / surface roughness control photovoltaic element after the test was evaluated. For evaluation, the end of the solder-coated copper foil tab on the light incident side was sandwiched with clips, and the strength was similarly evaluated with a peel strength measuring instrument shown in FIG.

  The result is shown in FIG. The normalized adhesion strength was normalized by the adhesion strength of EVA / photovoltaic element (cell) without polysilazane coating.

  From FIG. 9, the normalized strength was improved by about 13 to 15% at the height of the valley and valleys of 9.7 μm. This indicates that in addition to the unevenness reducing effect, the SiOx surface can achieve better adhesion with EVA than the ITO surface, and the amount of —OH groups on the surface as in the first embodiment. It seems to be related. Furthermore, the normalized strength was improved as the height of the valleys was controlled and decreased, and very good adhesiveness with a height of 4 μm or less and a normalized strength of 2 or more was confirmed.

  Furthermore, using a substrate having an average unevenness and valley height of about 8 μm and an average pitch of about 13 μm before polysilazane coating, a simple sample in which the surface average unevenness and valley height after formation of the SiOx film 25 is controlled by the polysilazane concentration as described above. The module was subjected to a moisture resistance test (temperature 85 ° C., humidity 85%, 3000 hours). FIG. 10 shows the results of evaluating the adhesion between the EVA and the surface unevenness control photovoltaic element after the test. The normalized adhesion strength was normalized by the adhesion strength of the EVA / photovoltaic element when the average unevenness and valley height before application of polysilazane was about 8 μm and the average pitch was about 13 μm. As shown in FIG. 10, a normalized adhesion strength of 1.5 or more was already obtained at an average irregularity mountain valley height of 6.4 μm, and a normalized adhesion strength of 2 or more was obtained at an average irregularity mountain valley height of 3.2 μm.

  As described above, in both the first and second embodiments, the average unevenness and valley height is set to 4 μm in the case of FIGS. 5 and 9, and in the case of FIG. 10, the normalized strength is 2 or more at 3.2 μm, that is, 0.4 h. Is realized. 5 and 9, a normalized strength of 1.5 or more was confirmed at 8 μm and in the case of FIG. 10 at 6.4 μm, that is, 0.8 h. In both the embodiments, the SiOx film thickness is greatly different, so that it is considered that the stress distribution between the EVA / photovoltaic element by controlling the height of the irregularities on the surface contributes to the improvement of the adhesion.

  Moreover, in the said embodiment, although the adhesive strength between photovoltaic elements / EVA by the side of light incidence was evaluated, the same tendency was confirmed also in the adhesive strength between photovoltaic elements (cell) / EVA by the side of a back surface.

  Needless to say, this effect is effective not only when ITO is used as the transparent conductive film but also when another conductive metal oxide film such as ZnO is used.

  In the above-described embodiment, EVA is used as the hot-melt filler, but in addition to EVA, polyvinyl butyral (PVB), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer It can be easily imagined that a material having high sunlight transmittance and good environmental resistance such as coalescence (EEA) may be used.

  Furthermore, in the above-described embodiment, the case of using a solar cell photoelectric conversion element (cell) having a HIT structure has been described. However, other crystalline solar cell photoelectric conversion elements (cells), for example, a single crystal junction type solar cell The present invention can be applied to a solar cell photoelectric conversion element (cell) having an uneven shape on a substrate, such as a battery photoelectric conversion element (cell) or a polycrystalline solar cell photoelectric conversion element (cell).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram of a cross-sectional structure of a solar cell module using a photoelectric conversion element having a HIT structure to which the present invention is applied, and FIG. (C) is the elements on larger scale of c section of the figure (a). 1 is a cross-sectional SEM image of a light incident side surface immediately after formation of a SiOx film, showing a first embodiment of the present invention, and FIG. 2B is a partially enlarged view of a portion b in FIG. The 1st Embodiment of this invention is shown and the cross-sectional SEM image figure of the light-incidence side surface after a blast process is shown. It is a schematic block diagram which shows the measuring machine of peeling strength. In a simple module using a photovoltaic device whose surface unevenness and valley height is controlled by SiOx coating and blast treatment, it is a characteristic diagram showing unevenness and valley height and normalized adhesion strength of EVA / photovoltaic element after moisture resistance test is there. The cross-sectional SEM image figure of the incident side surface before polysilazane application | coating is shown, The figure (b) is the elements on larger scale of b part of the figure (a). It is a figure which shows an example of the cross-sectional SEM image figure of the light-incidence side surface after drying of polysilazane. It is a characteristic view which shows the relationship between polysilazane density | concentration and average uneven | corrugated mountain valley height. It is a characteristic view which shows the uneven | corrugated mountain valley height and normalized adhesion strength of the EVA / photovoltaic element after a moisture resistance test in a simple module using a photovoltaic element in which the surface uneven mountain valley height is controlled by polysilazane coating. After a moisture resistance test with a simple module of a sample in which the surface average unevenness and valley height after SiOx formation was controlled by polysilazane concentration using a substrate having an average unevenness and valley height of about 8 μm and an average pitch of about 13 μm before polysilazane coating. It is a characteristic view which shows the result of having evaluated the adhesiveness between EVA / photovoltaic element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal silicon substrate 2, 4 Amorphous semiconductor layer 3, 5 Oxide transparent conductive film 6, 7 Collector electrode 10 Surface glass 11 EVA
12 Copper foil tab 13 PVF (polyvinyl fluoride) sheet 20 SiOx layer

Claims (4)

Photovoltaic device in which a photovoltaic element using crystalline silicon having an uneven surface of micron order is controlled by a charged electron and sealed with a hot-melt type filler between the surface glass and the back surface material. In this case, an inorganic thin-film protective layer that is controlled so that the height of the ridges and valleys on the outermost surface is 0.8 h or less is provided at least on the light incident side, where h is the height of the ridges and valleys of the crystalline silicon. A featured photovoltaic device. The inorganic thin-film protective layer is controlled at least on the light incident side so that the height of the ridges and valleys on the outermost surface is 0.4 h or less with respect to the height h of the ridges and valleys of crystalline silicon. 2. The photovoltaic device according to 1. The photovoltaic device according to claim 1 or 2, wherein the inorganic thin film protective layer contains at least silicon. The hot melt type filler is any of ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), ethylene-methyl acrylate copolymer (EMA), and ethylene-ethyl acrylate copolymer (EEA). The photovoltaic device according to claim 1, wherein the photovoltaic device is selected from the above.

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