JPH0754855B2 - How to make a solar array - Google Patents

Description

Description: FIELD OF THE INVENTION This invention relates to a method of making solar cells that generate electricity when exposed to light from silicon spheres arranged in a metal foil matrix.

PRIOR ART AND PROBLEMS Devices that generate energy by converting sunlight into other forms of useful energy are well known and because of the economics of the sun being the primary source of energy, The device is constantly being developed and improved. One such device is described in U.S. Pat. No. 4,021,323, which discloses a solar array composed of a transparent matrix, such as glass or plastic, having an N-shaped skin on one side thereof. There is described a solar array in which particles of P-type silicon or N-type silicon having a P-type skin portion on one side thereof are embedded in a matrix. It is preferable that about half of the particles are P-type having an N-type skin portion and the rest are N-type having a P-type skin portion, but this configuration can be changed. On the back side of the matrix, the particles protruding from it are interconnected by suitable conductive metallization. The skin portion of the silicon particles extends from the front side of the matrix. Such arrays are immersed in an electrolyte, preferably hydrobromic acid (HBr), which contacts the front side of the matrix. Due to the potential difference between the different conductivity type silicon particles in contact with the electrolyte, a potential difference is established therebetween under sunlight which electrolyzes HBr into bubbling hydrogen gas and bromine which remains dissolved. Hydrogen gas is collected and used as an energy source, such as a fuel cell, which is well known.

In this type of solar array, silicon particles independently participate in electrolysis. As a result, the rate at which reaction products are generated by the array is not significantly affected by shorting or shunting the P-N junction of some particles.

Another device that produces useful energy from the sun's rays is similar to the type described above, but without electrolysis,
It is configured to generate electric power. One such device is described in US Pat. No. 2,904,613. Other configurations are possible, but a useful embodiment consists of providing a transparent matrix, such as glass or plastic, with N-type silicon particles having a P-type skin. The N-shaped core of the particles projects from the backside of the matrix and is interconnected by suitable conductive metallization. A P-shaped skin projects from the front side of the matrix and is interconnected by a conductive, translucent material such as tin oxide on a thin metal grid. Under sunlight, a potential difference is set up between the back and front interconnects of this array, which can be connected appropriately to directly feed an external electrical load.

An improvement on this technique is described in US Patent Application No. 562,782. This application describes an improvement of the invention described above. However, at present, according to the above-mentioned conventional method, the cost of manufacturing a solar cell is not very economical, and this conventional method has not been economically successful so far. Therefore, in order to supply economically viable solar cells, it is an absolute requirement that such arrays can be manufactured relatively inexpensively.

Means and Actions for Solving Problems In the present invention, the conventional problems described above are significantly reduced,
It provides a method for manufacturing a solar array that allows the solar array to be manufactured economically as compared to the prior art cited above.

Briefly, in the present invention, a solar array is formed by providing a first sheet of standard type flexible aluminum foil, which is believed to have native aluminum oxide on its surface. The foil is stamped where the silicon spheres are to be placed to form the metal matrix. After that, the foil is cleaned to remove organics, the thin areas that have been stamped are removed and etched to create openings therein, creating a place for inserting silicon balls. Another etching process is used to create a matte surface on the foil. The foil forms the housing for the sphere to be applied to it and its front side contact. Deposit a silicon sphere with an N-type skin on the P-type on the front side of the foil, provide a vacuum chuck on the back side of the foil, suck the sphere into the preformed opening, and insert it halfway into it. , Blocking the passage of air through this opening. Initially we will use an excessive number of spheres compared to the number of openings, so eventually all the openings will be filled with spheres,
The unused spheres are then removed, such as by plating the rear surface of the foil.

The silicon spheres are then bonded to the aluminum foil by using an impact press. This press forces the sphere into the opening so that the equator of the sphere is above the foil and is on the front side of the foil (the side facing the sun or light). This strong pushing of the sphere into the opening tears the aluminum on the surface in contact with the silicon sphere, exposing fresh aluminum at that location. The shear caused by the movement of the silicon spheres with respect to the aluminum also scrapes off the participating aluminum on the surface, resulting in such exposed fresh aluminum. This action removes substantially all of the silicon oxide from the aluminum foil, especially the portion of the sphere that contacts the exposed aluminum. This action takes place with aluminum at a temperature in the range of about 500 ° C to less than 577 ° C, at which time aluminum is solid but prone to deformation, whereas silicon is still rigid at this temperature. is there. (If the impact duration is short enough, it can be higher than 577 ℃.) Fresh aluminum erodes silicon dioxide,
During impact, virtually remove it at the place of impact. In this way, a bond between silicon and aluminum is obtained, forming an aluminum contact to the N-skin layer of silicon. After this, the foil and sphere array is cooled to ambient temperature and allowed to set again.

Next, the back side of the foil with the exposed spheres is etched to remove the N-shaped skin portion there. This is because the aluminum foil acts as a mask for the silicon etchant. The foil itself is not very reactive, usually due to the formation of a very thin natural oxide coating on it. The array is then placed in a sulfuric acid bath (about 10% H ₂ SO
₄ ) Place in the inside for about 1/2 minute to anodize the array and place an oxide coating on the aluminum. Next, 0.5% H ₃ P was added to seal the aluminum and anodize the silicon.
Another anodizing bath containing O ₄ is used. In this way about 10
μm Al ₂ O ₃ and 0.1 μm SiO ₂ grow. Next, the back surface of the sphere is wrapped to provide a surface for contacting it. The lapping process causes this surface to be roughened so that a good ohmic texture is formed. Then apply a thin aluminum second foil to the wrapped surface, 500 ° C to 577 ° C.
After preheating to a temperature in the range of less than ° C, the foil is impact pressed into the wrapped area to form a contact to this area.

When forming the array in a reel-type embodiment, the skin is placed between two foils, at a location between adjacent arrays, prior to bonding the second foil to the sphere. In this embodiment, when the second foil is bonded to the sphere, the upper and lower foils are pressed against the skin, but not with it. Then on both sides of the array,
Scrape the foil appropriately over the skin and provide foil extensions for each foil on both sides of the array. The foil extensions can then be connected together in a series circuit to form an enlarged circuit.

Scribing an array with skins as described above, separating them from each other and chamfering them so that only one side of the rectangular array has a second foil section extending outward in the form of a contact. I can. These contacts are connected to the first foil portion of the other array in any geometric form to create a module with inputs and outputs.

The result is a solar cell in which the main portion of each silicon sphere is placed in front of the array to increase the surface area available for receiving sunlight. Further, of course, the array is flexible, has a light reflector on the aluminum foil, and is provided using a relatively small number of non-curing materials and processing steps.

Embodiments FIGS. 1 and 2 are schematic illustrations of process steps utilizing the features of the present invention to form a solar array in accordance with the present invention. First, prepare an aluminum foil 1 having a thickness of about 2 mils. The foil is flexible and normally has a very thin layer of native oxide on its surface due to its normal exposure to the environment. Although the following description refers to one member of a solar array, it should be recognized that there are multiple array members in the entire array, as can be seen from the prior art discussed above.

First, the aluminum foil 1 is cyclically 6 as shown in (a).
The embossed part 3 which is embossed in a square arrangement, for example, 16 mils between centers and has a reduced thickness, has a diameter slightly smaller than the diameter of the sphere to be arranged therein. The punching part is circular or 6
Other geometric shapes, such as prismatic, may be used. In the case of a polygonal embossing, the line through the center and across the polygon is smaller than the diameter of the sphere applied to it. Next, the foil is washed to remove organic matter, and then etched with heated sodium or potassium hydroxide as shown in (b) to remove the region of the foil where the embossed portion 3 is formed. The opening 5 is provided at that location. Since the stamped region 3 is thinner than other parts of the foil during etching, it is removed before the other parts of the foil and cold working is performed by the stamping performed there. Because of the presence, it is even faster to get etched. This is called an aluminum matrix.

In this regard, 25% HF, 60% HNO ₃ and 15% are optional.
Etching with a 50% solution of Etchant, glacial acetic acid, allows the foil to carry certain organisms and create a matrix surface that minimizes back reflections.

As shown in (c), a plurality of silicon spheres 7 having an N-shaped skin portion 9 and a P-shaped interior 11 are provided on the upper side 15 of the matrix on the foil 1.
And apply a vacuum to the backside 13 of the foil using a vacuum chuck to draw the sphere 7 into the opening 5. First, on the back side of the foil, an excess of spheres 7 is used compared to the number of openings 5, so
All the openings are filled with spheres 7, after which the excess spheres 7 are removed from the upper side of the foil 1 by brushing or the like. The spheres used here preferably have a diameter of 14.5 mils, and as mentioned previously, the cross-sectional diameter of the openings 5 is smaller than 14.5 mils and a vacuum is applied to the foil on the backside of the foil for the reason explain.

After this, the sphere 7 is bonded into the opening 5 of the aluminum foil 1 by heating the foil and then using an impact press, as shown in (d). At this time, the sphere 7 is quickly pushed into the opening 5, causing a shearing action in the opening, which scrapes away the aluminum oxide on the inner surface of the foil at the opening,
Expose fresh aluminum element. As I mentioned before,
Aluminum is 530 when the ball 7 is pushed into the opening 5.
Since it is heated to a temperature of ° C, aluminum is reactive, mechanically somewhat viscous in nature and readily deforms. Thus, the elemental aluminum reacts with and removes the highly water-free natural silicon oxide layer on top of the sphere, so that the aluminum of the foil 1 is now the N-shaped layer 9 of the sphere.
It can be joined directly to the elemental silicon inside to form a contact point thereto.

The equator of the sphere is above the aluminum foil 1 or above it
A sphere 7 is placed in the opening 5, as at 15. Such an arrangement is possible by using pressure pads arranged above and below the aluminum foil 1. The pressure pad is formed of about 8 mil thick aluminum foil coated with a release agent such as boron nitride powder which acts as a cushion.
Therefore, the hammer of the impact press does not damage the sphere when the impact is applied. In addition, the pressure pad absorbs the impact of the hammer. The upper pressure pad on the 15 side of the foil 1 is thicker than the lower pressure pad on the 13 side of the foil 1 so that the equator of the sphere is offset from the foil, as previously described. Approximately 48 feet for a 2 cm square array
It has been found that pounds of impact energy work well. Therefore, aluminum is directly bonded to silicon at this time, as described above.

Of the surface 13 on the rear side of the foil 1 and the sphere 7, the part on this side is
Thereafter, as shown in FIG. 7E, etching is performed using an etchant to remove a portion of the N-type layer 9 located on the rear surface of the array to expose the P-type region. The aluminum foil 1 with the native oxide thereon acts as a mask against this etch, so that only the part of the layer 9 on the rear side 13 of the array can be removed. After this, the array is rinsed with deionized water to remove the etchant, and then the array is anodized in 10% H ₂ SO ₄ solution for about 1/2 minute at about 20 volts as shown in (f). Oxidize to passivate the exposed silicon and foil. Then the array is anodized at about 20 volts for about 1/2 minutes 0.5% H ₃ PO ₄ solution. The time required for anodization is
It is a function when the current of the bus is cut off to zero,
It turned out to be about 1/2 minute. It has been found that the use of phosphoric acid is important, as it closes the pores in the aluminum oxide and creates an oxide layer 21 of about 1,000Å on the previously etched silicon surface.

Next, the spheres 7 of the anodized array are lapped by mechanically grinding the rear side 21 formed during the anodization by a known method. This lapping removes both the silicon dioxide 21 and some of the silicon, flattening the rear surface 17 of the sphere 7 and providing a rough surface as shown at 17, thus forming ohmic contacts thereon. You can Next, a thin foil 19 of aluminum, about 1/2 mil, is placed on the back surface 17 of each sphere 7 as shown in (h) so that it rests on the lapped flat area 17. To do. The aluminum is preferably heated to a temperature of 530 ° C, or a temperature in the range of about 500 to 577 ° C, with the conditions as previously mentioned.
The heated foil 19 is then pressure-bonded to the sphere 7 by an impact press, between the aluminum exposed by this impact and the silicon exposed on the rear face of the sphere 7 due to lapping and the impact of the aluminum element. Is formed. Bonding in the same manner as previously described for (d) forms a foil contact 19 to the silicon region 11. Due to the anodization of the aluminum foil 1, a thick aluminum oxide is deposited on the surface of this foil to prevent a short circuit between foil 1 and foil 19.
(As shown in (i), standard anti-reflective coating can be applied on the front side of the array to improve the absorption of light in the silicon.) It will be appreciated that a solar array was provided that was exposed to incident solar radiation, the array was flexible, and the processing and materials used were relatively inexpensive and few in number. .

In actual processing, arrays such as those described above are usually provided in reel-type embodiments rather than as separate arrays. Thereafter, the array is formed into a module whose dimensions are, for example, 1 m x 2 m, and is tested with this design as it is. Each array formed as described above is normally about 10 cm on each side.

To make a solar array as described above in the form of a reel and then form a module, follow the procedure shown in FIGS. 3-6. Referring first to FIG. 3, the array interconnect locations are shown in one dimension. In FIG. 3 (a), one array 30 in which a sphere 31 is fixed to the front contact foil member 33 is shown, and the rear foil member 35 is shown.
Is not yet mounted on the ball. A shim 37 is inserted between the arrays 30 as shown in FIG. As can be seen from FIG. 4 (a), the front foil 33 is the rear foil.
The dimensions are smaller than 35, but the reason will become clear later.

Next, referring to FIG. 3 (b), it can be seen that the foil 35 on the rear side is in contact with the balls 31 and 37 at this time. The upper foil 33 is also in contact with the shim. This is accomplished in step (h) of FIG. 1 when bonding the rear foil 35 to the sphere 31 as part of this processing step. The foils 33,35 do not adhere to the shim 37, they are merely in contact with it. This is then followed by scribing the foil on the shim at the V-shaped symbol in FIG. 3 (b), separating the arrays from each other and removing the shim, and then FIG. 3 (c) and FIG.
A device as shown in FIG. The array as shown in FIGS. 3 (c) and 4 (b) is then chamfered as shown in FIG. 4 (c) to create four ears that are part of the rear foil 35. These ears are on each side of the array square and are labeled A, B, C,
It is marked as D. Next, as shown in FIGS. 3 (d) and 4 (d), the ears B, C, and D are folded back under the array, and then the third
As shown in Figure (e), the ear A is then fixed to the subsequent array by ultrasonic bonding or the like, and then by coupling the ear A to one of the ears B, C or D of the array. .

The interconnection process can be performed as shown in the three-dimensional display device of FIG. In this device, one array with the extending ear A is positioned in contact with one of the ears B, C or D of another array. Continue this procedure in a straight line or other passage to create a complete module. The completed module is shown in FIG. 6 with the ear A fixed to the ear B, C or D of the adjacent array 30.
Making the passages arranged before and after forming the series circuit of the arrays. In addition, ears are provided that are inputs 41 and outputs 43 to the module.

Referring to FIG. 2 after forming the module of FIG. 6, the module is tested, and if the test is successful, the module proceeds to the step of attaching to the support material or the like, after which the ears are ultrasonically bonded at the connection part. Then, encapsulate the module and provide a suitable seal for the environment. The encapsulated module is then standardly tested and the operational module is ready for use. As described above, one feature of the solar array according to the present invention is that it includes a semiconductor member having an N-type region which is ohmic-contact bonded to the opening of the first aluminum foil by pressurization at a temperature of 500 ° C. or higher. . This feature allows for a shorter impact duration when bonding the semiconductor component to the opening in the first aluminum foil and provides a solar array suitable for higher volume production.

While this invention has been described in terms of certain preferred embodiments,
Various modifications will occur to those skilled in the art. Therefore, the scope of the claims should be interpreted as broadly as possible from the viewpoint of the prior art so as to cover all such modifications.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the process steps used to form a solar array according to the invention, FIG. 2 is a process diagram showing the process of FIG. 1, and FIG. 3 is an array in one dimension. Schematic diagram showing the interconnection procedure, FIG. 4 is a schematic diagram showing the array interconnection procedure in two dimensions, FIG. 5 is a schematic diagram showing the array interconnection in three dimensions, and FIG. 6 is a schematic diagram of the module of the invention. Is. Explanation of code 1: First aluminum foil 5: Opening 7: Silicon sphere 9: N type skin 11: P type inside 19: Second aluminum foil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ronald E. Henney, Nottingham, Litchiardson, Texas, USA 748 (56) References JP-A-58-54684 (JP, A)

Claims (1)

[Claims] 1. An aluminum foil having a plurality of openings is prepared, and a plurality of semiconductor members each having a P-type region and an N-type region are respectively ohmic-contact bonded to the respective openings of the aluminum foil. A method for manufacturing a solar array, comprising the steps of pressurizing at a temperature in the range of 500 ° C. to 577 ° C. and bonding the contact members insulated from the aluminum foil to the P-shaped regions of the plurality of semiconductor members.