JPH0613633A - Formation of solar array - Google Patents

Abstract

PURPOSE: To economically manufacture a solar array. CONSTITUTION: A semiconductor grain 7, having a 1st conductive epidermal part 9 and a 2nd conductive inner part 11, is arranged on an aperture 5 of an aluminum foil 1, so as to be projected from both the sides of a foil 1, and the epidermal part 9 on one side is removed to form an insulating layer 21. Then a part of the inner part 11 and the insulating layer 21 formed on the part are removed, and a 2nd aluminum foil 19 is connected to the removed region 17. The planar region 17 provides a fine ohmic contact with the 2nd aluminum foil 19 as a conductive part.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of forming a solar cell from a sphere of silicon placed in a metal foil matrix that produces power when exposed to light.

[0002]

BACKGROUND OF THE INVENTION 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, such devices. Is constantly being developed and improved. One such device is U.S. Pat. No. 4,021,32
No. 3, which describes a solar array made of a transparent matrix such as glass or plastic, with P-type silicon having an N-type skin on one side, or P on one side. A solar array is described in which particles of N-type silicon having a shaped skin portion 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 these types of solar arrays, 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 solar radiation is similar to the type described above, but is configured to produce electrical power without electrolysis. 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 was found in US Patent Application No. 562.
No. 782. This application describes an improvement of the invention described above.

[0006]

However, at present, according to the conventional method described above, the cost of manufacturing a solar cell is not very economical, and this conventional method has hitherto been economically very successful. I haven't. Therefore, in order to supply economically viable solar cells, it is an absolute requirement that such arrays be economically producible and relatively inexpensive.

[0007]

SUMMARY OF THE INVENTION The present invention significantly reduces the above-noted conventional problems and allows the solar array to be economically manufactured as compared to the prior art cited above. A method of forming a solar array is provided.

Briefly, the invention provides a solar array by providing a first sheet of standard type flexible aluminum foil, such as 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 punched thin area is removed and etched to create an opening there, and a place to insert a silicon ball is made. The matte surface is applied to the foil using another etching process.
ace). The foil forms the housing for the sphere to be applied to it and its front side contact. P
Deposit a silicon sphere with an N-shaped skin on the front side of the foil, place a vacuum chuck on the back side of the foil, suck the sphere into the preformed opening, and insert it halfway , Blocking the passage of air through this opening. Initially, an excess number of spheres is used compared to the number of openings, so eventually all openings are filled with spheres, and unused spheres are removed by brushing the back surface of the foil. .

The spheres of silicon are then bonded to 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 relative to the aluminum also scrapes off the surface aluminum oxide, resulting in such exposed fresh aluminum. This action removes substantially the front 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 duration of the impact is sufficiently short, the temperature can be higher than 577 ° C.) Fresh aluminum erodes silicon dioxide, and at the time of impact, virtually removes it at the place of impact. To do. In this way, a bond between silicon and aluminum is obtained, forming an aluminum contact to the N-type skin layer of silicon. After this, cool the array of foils and spheres to ambient temperature,
Let the foil cure 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 because it usually has a very thin native oxide coating formed on it. Next, the array is placed in a sulfuric acid bath (b
the anodization of the array by placing it in a) (about 10% H ₂ SO ₄ ) for about 1/2 minute to provide an oxide coating on aluminum. Then another anodizing bath containing 0.5% H ₃ PO ₄ is used to seal the aluminum and anodize the silicon. In this way, A of about 10 μm
l 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 contact is formed. Then apply a thin foil of aluminum to the wrapped surface and apply 5
After preheating to a temperature in the range of 00 ° C to less than 577 ° C, the foil is impact pressed into the wrapped area to form a contact to this area.

When forming an array in a reel type embodiment,
Prior to bonding the second foil to the sphere, the skin is placed between the two foils, at a location between adjacent arrays. 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. The foil is then scribed appropriately on the skin on both sides of the array, and foil extensions for each foil are provided on both sides of the array. The foil extensions can then be connected together in a series circuit to form an enlarged circuit.

An array having skins as described above is scribed, separated from each other and chamfered so that only one side of the rectangular array has a second foil portion extending outward in the form of a contact. You can do it. These contacts are the first of the other arrays
Make a module with inputs and outputs by connecting it to the foil part of any geometry.

The result is a solar cell in which the main portion of each silicon sphere is located 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 inexpensive materials and processing steps.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 are schematic illustrations of process steps utilizing the features of this invention to form solar arrays in accordance with this invention. First, prepare an aluminum foil 1 having a thickness of about 2 mils. Because the foil is flexible and normally exposed to the environment, it typically has a very thin layer of native oxide on its surface. The following description relates to one element of the solar array, but as can be seen from the prior art described above,
It should be noted that there are multiple array members throughout the array.

First, the aluminum foil 1 is arranged in a periodic hexagonal arrangement as shown in (a), for example, a punching section 3 having a thickness of 16 mils and having a reduced thickness is arranged therein. The diameter should be slightly smaller than the diameter of the sphere to be tried. The embossments may be circular or other geometric shapes such as hexagons. 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 the organic matter, and then etched using 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 the other parts of the foil during etching, it is removed before the other parts of the foil and cold worked by the stamping performed there. Because it is there, it is even faster to be etched. This is called an aluminum matrix.

In this respect, 25% HF, optionally
Etching with a 50% solution of an etchant that is 60% HNO ₃ and 15% glacial acetic acid can give the foil some texture and create a matrix surface that minimizes back reflection.

As shown in (c), a plurality of silicon spheres 7 having an N-type skin portion 9 and a P-type interior 11 are deposited on the upper side 15 of the matrix on the foil 1 and the foil is deposited using a vacuum chuck. A vacuum is applied to the back side 13 to draw the sphere 7 into the opening 5. First, on the back side of the foil, excess spheres 7 are used compared to the number of openings 5, so all the openings are filled with spheres 7 and then excess spheres 7 are removed from the upper side of 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 1
A vacuum of less than 4.5 mils is applied to the foil on the back side of the foil, the reason for which will be explained later.

Thereafter, as shown in (d), the foil is heated,
The sphere 7 is then bonded into the opening 5 of the aluminum foil 1 by using an impact press. At this time, the sphere 7 is quickly embedded in 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, exposing fresh aluminum element. As mentioned previously, when the sphere 7 is embedded in the opening 5, the aluminum is heated to a temperature of 530 ° C., which makes it reactive and its mechanical properties somewhat viscous. Holds and transforms easily. Thus, the elemental aluminum reacts with and removes the very thin native silicon oxide layer on top of the sphere, so that the aluminum of the foil 1 is now replaced by the silicon element present in the N-type layer 9 of the sphere. It can be directly coupled to form a contact point thereto.

A sphere 7 is arranged in the opening 5 such that the equator of the sphere is above or 15 above the aluminum foil 1. Such an arrangement is possible by using pressure pads arranged above and below the aluminum foil 1. The pressure pad is made of about 8 mil thick aluminum foil coated with a release agent, such as boron nitride powder, which acts as a cushion, which allows the hammer of the impact press to squeeze the sphere when it is impacted. No damage. In addition, the pressure pad absorbs the impact of the hammer. Foil 1 of 1
The upper pressure pad on the 5 side 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. It has been found that for a 2 cm square array, an impact energy of about 48 ft-lbs works well. Therefore, aluminum is directly bonded to silicon at this time, as described above.

The surface 13 on the rear side of the foil 1 and the portion on this side of the sphere 7 are etched using an etchant as shown in (e), and the rear surface of the array in the N-type layer 9 is etched. The portion overlying is removed to expose the P-shaped region. The aluminum foil 1 with the native oxide on it acts as a mask for this etchant, the layer 9 on the rear side 13 of the array.
Make it possible to remove only the part. After this,
The array is washed with deionized water to remove the etchant and then anodized in a 10% H ₂ SO ₄ solution for about 1/2 minute at about 20 volts as shown in (f). ,
Passivate the exposed silicon and aluminum foil 1. Next, 0.5% H ₃ PO for about 1/2 minute at about 20 volts
₄ Anodize the array in solution. It has been found that the time required for anodization is a function of when the bus current is zero and is cut off, which is about 1/2 minute. It has been found that it is important to use phosphoric acid, which blocks the pores in the aluminum oxide and creates an oxide layer 21 of approximately 1,000Å on the previously etched silicon surface.

Next, the rear side 21 formed during anodization
The spheres 7 of the anodized array are lapped by mechanically abrading them in a known manner. 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 an ohmic contact 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 is over the flat area 17 that is wrapped. To do. This aluminum is preferably 530 ° C
Or at a temperature in the range of about 500 to 577 ° C., with the conditions as previously described. Heated foil 1
9 is then pressure-bonded to the ball 7 by an impact press, and aluminum exposed by this impact,
A bond is formed between the exposed silicon on the rear surface of the sphere 7 due to lapping and impact by the aluminum element. Bonding in the same manner as previously described for (d) forms a foil contact 19 to the silicon region 11. Due to the anodic oxidation of the aluminum foil 1, there is thick aluminum oxide on the surface of this foil, which prevents a short circuit between foil 1 and foil 19. ((I)
A standard anti-reflective coating can be applied on the front side of the array to improve the light absorption of the silicon, as shown in. ) Therefore, most of the silicon spheres are exposed to the incident sun rays, the array is flexible, the processing used and the materials used are relatively inexpensive and few, It will be appreciated that the array was provided.

In actual processing, the array as described above is typically provided in a reel-type embodiment rather than as a separate array. After that, the array is formed into a module whose dimensions are, for example, 1 m × 2 m, and is tested as it is. Each of the arrays formed as described above is normally about 10 cm on each side.

To make a solar array such as that described above in the form of a reel and then to form a module, the process shown in FIG.
Through the procedure as shown in FIG. Referring first to FIG. 3, an array interconnect device is shown in one dimension. FIG. 3 (a) shows one array 30 in which the sphere 31 is fixed to the front contact foil member 33, and the rear foil member 35 is not yet attached to the sphere. Figure 4
A shim 37 is inserted between the arrays 30, as clearly shown in (a). As can be seen from FIG. 4 (a), the front foil 33 has a smaller size than the rear foil 35, but the reason for this will become clear later.

Next, referring to FIG. 3B, it can be seen that the foil 35 on the rear side is in contact with the sphere 31 and the shim 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.
After this, the foil is then scribed on the shim at the location of the V-shaped symbol in FIG. 3 (b), the arrays are separated from each other and the shim is removed, and then FIG. 3 (c) and FIG. 4 (c). Make a device as shown in. 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 square of the array and are labeled A, B, C, D. Next in FIG.
As shown in (d) and FIG. 4 (d), the ears B, C, and D are folded back under the array, and thereafter, as shown in FIG. Array ears B, C or D
This array is secured to the subsequent array by bonding to one of the two.

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 so that the ear A is 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 make a complete module. The completed module is shown in FIG. 6, with ears A, B, C or D of adjacent array 30.
Fixed in place to form the front and rear passages forming a series circuit of 60 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 it to a support material or the like, after which the ear is ultrasonically ultrasonically coupled. After bonding, the module is then encapsulated to provide the appropriate environmental seal. The encapsulated module is then standardly tested and the working module is ready for use.

While this invention has been described in terms of a particular preferred embodiment, various modifications will occur to those skilled in the art. Therefore, the scope of the claims should be construed as broadly as possible in view 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 in accordance with the present invention.

FIG. 2 is a process diagram showing the process of FIG.

FIG. 3 is a schematic diagram showing a one-dimensional array interconnection procedure.

FIG. 4 is a schematic diagram showing an array interconnection procedure shown in two dimensions.

FIG. 5 is a schematic diagram showing an array interconnect in three dimensions.

FIG. 6 is a schematic diagram of the module of the present invention.

[Explanation of symbols]

 1 First Aluminum Foil 5 Opening 7 Sphere of Silicon 9 N-Type Skin 11 P-Type Inside 19 Second Aluminum Foil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ronald E. Hennei 748 Nottingham, Richardson, Texas, United States 748

Claims (1)

[Claims] 1. A method for forming a solar array comprising: (a) preparing a first aluminum foil; (b) forming an opening at a predetermined position of the first aluminum foil; and (c) a skin portion. Is arranged in each of the openings so that the semiconductor particles protrude from both sides of the first aluminum foil, and (d) the first aluminum is used. Removing the first conductivity type skin on one side of the foil, (e) the one side of the first aluminum foil, and the first
An insulating layer is formed on the surface of the semiconductor particle from which the conductivity type skin is removed, and (f) a part of the surface of the semiconductor particle from which the first conductivity type skin is removed, and the insulating layer covering the part. And (g) bonding a second aluminum foil to a region of the semiconductor grain surface where a portion of the semiconductor grain surface has been removed, thereby forming a solar array.