EP0000715B1 - Method for manufacturing cadmium sulfide-copper sulfide solar cells and solar cells manufactured by this method - Google Patents

Description

The invention relates to a method for producing solar cells with a pn thin-film heterojunction from an electrically conductive base applied to a carrier, a cadmium sulfide layer vapor-deposited thereon and a copper sulfide layer chemically produced thereon, onto which an electrically conductive grid is placed, which is covered, heat-sealed and pressed with a cover glass which is provided with a heat-sealing adhesive on the side facing the grating, the carrier with the base, with the cadmium sulfide layer and with the copper sulfide layer being produced as a prefabricated component.

Cadmium sulfide solar cells have a lower efficiency than the known silicon single-crystal solar cells, but they have the considerable advantage that they can be manufactured much more cheaply. It is known to produce a semiconductor photo element from a thin silicon single crystal with p- and n-type zones, which is then or the like by enveloping with a casting resin. is encapsulated. Cadmium sulfide solar cells, which belong to the so-called thin-film solar cells, have a polycrystalline semiconductor layer which is evaporated onto an electrically conductive base, usually a metallic support, so that their production is considerably cheaper.

It is known (magazine: THIN SOLID FILMS, vol. 45, no. 1, August 1977, Lausanne) to apply an electrically conductive base on which a cadmium sulfide, Layer is evaporated, on which a copper sulfide layer is then chemically generated. A grid is then placed on the copper sulfide layer of the prefabricated lower part, after which the solar cell is covered with a cover glass which is provided on the side facing the grid with a heat seal adhesive with which the solar cell is sealed. The grid used here is a separate component that must be handled in this form. This means a considerable practical difficulty, since minor deformations or damage can hardly be avoided on the very fine grid. This damage or deformation leads to poorer contact and thus to a reduction in the possible efficiency, in particular because then the grid often only abuts the copper sulfide layer in pump form, so that the number of contact points has been restricted.

It is also known (US Pat. No. 3,472,690) to produce a grid for a solar cell serving as a contact element by etching it out of a metal foil. Such a thing. Grid produced as an independent component cannot eliminate the difficulties described above in the production of a solar cell.

The invention is based on the object of further improving the method for producing cadmium sulfide solar cells of the type mentioned at the outset in order to obtain a favorable efficiency and at the same time to produce a self-contained, encapsulated cell. This object is achieved in that the prefabricated lower part is heat-sealed and pressed with a prefabricated upper part which consists of the cover glass, the heat-sealing adhesive and the grid, which is sealed onto the cover glass in the form of a film with the aid of the heat-sealing adhesive, after which the heat sealing is carried out and pressing the upper part and the lower part out of the foil, the grid is etched out.

The heat seal adhesive used in this training has several functions. First, it has the function of holding the copper foil on the upper part and then establishing the connection to the lower part, at the same time obtaining an encapsulated cell. This has the advantage that the grid is etched out of the film while it is held by the upper part, so that the risk of deformation or damage is further reduced, so that the possible efficiency is obtained with greater certainty.

In a further embodiment of the invention, it is provided that the lower part contains a glass plate, on which, preferably using an adhesion promoter, a base made of silver or zinc is applied, onto which the cadmium sulfide layer is evaporated. The use of a glass plate in the lower part has the advantage that not only the mechanical strength is increased, but also that uniform thermal expansions of the entire cell are ensured, so that destruction or damage by thermal stresses is not to be expected, even if this is particularly true for terrestrial application certain solar cell is set up in areas where, for example, very large differences between the day and night temperatures occur.

In a further advantageous embodiment it is provided that the heat seal adhesive is applied in liquid form and then dried in vacuo and, if appropriate, thereafter in the atmosphere. As a result of the first drying under vacuum, all gases and vapors that may interfere with the electrical properties of the solar cell are removed, an adhesive layer is created, which then enables heat sealing and whose thickness is somewhat thicker than the thickness of the grid. The subsequent drying to be carried out under atmospheric conditions leads to an appropriate oxidation of the heat seal adhesive layer in some cases.

In an expedient embodiment, it is further provided that a thin gold layer is applied galvanically before the upper part and lower part are joined onto the grid in order to achieve a barrier-free contact.

In a further embodiment of the invention, a solar cell is produced according to the method according to the invention, in which the cover glass with the grid and the base plate with the base are laterally offset from one another in such a way that on one side one of the base and on the other side one of the Contact formed by the grid is exposed. Such a solar cell is very easy to connect to other solar cells, since the necessary contacts are created and freely accessible.

In a further advantageous embodiment of the invention, a large cover glass is provided as the upper part with a plurality of electrically conductive grids arranged in a row, each of which is assigned a lower part, which are arranged so offset to the grids that the documents are on one side with the grating assigned to the adjacent lower part are in contact and that on one side of the cover glass an edge of the outer grid is exposed as a contact, while on the other side an edge of the base of the outer lower part is exposed as a contact. This makes it easy to create a fully connected solar battery, in which a one-piece cover glass serves as a supporting element for several solar cells. In a further embodiment of the invention it can be provided that a large cover glass is provided with several rows of grids and accordingly with several rows of lower parts. This results in a very efficient production, the somewhat simple upper part taking up a larger area, while the lower parts are designed as individually manufactured elements which are of a size which is favorable for the application of the cadmium sulfide layer.

• Fig. 1 zeigt eine schematische Darstellung einer nach dem erfindungsgemäßen Verfahren hergestellten erfindungsgemäßen Solarzelle, bei welcher Unterteil und Oberteil noch gegetrennt sind,
• Fig 2 eine Seitenansicht einer aus mehreren Zellen und einem einteiligen Deckglas gebildeten Solarbatterie,
• Fig. 3 eine Ansicht der Solarbatterie der Fig. 2 in Richtung des Pfeiles 111 und
• Fig. 4 eine schematische Darstellung einer Einrichtung zum Aufdampfen einer Cadmiumsulfid-Schicht.

Further features and advantages of the invention result from the following description of the embodiments shown in the drawing.

• 1 shows a schematic illustration of a solar cell according to the invention produced by the method according to the invention, in which the lower part and the upper part are still separated,
• 2 shows a side view of a solar battery formed from a plurality of cells and a one-piece cover glass,
• Fig. 3 is a view of the solar battery of Fig. 2 in the direction of arrow 111 and
• Fig. 4 is a schematic representation of a device for evaporating a cadmium sulfide layer.

The solar cell shown in Fig. 1 has a prefabricated lower part 1 and a prefabricated upper part 2, which are assembled into a self-contained cell in a subsequent operation.

The lower part 1 has a base plate 3, which preferably consists of a substrate glass. This glass is ultrasonically cleaned in a solvent before an adhesion-promoting layer 4 is applied on one side, for which vapor-deposited chromium (Cr) is preferably used. A layer 5 of silver (Ag) is also applied to this adhesion promoter by vapor deposition. This vapor deposition of both the adhesion promoter and the silver takes place at approximately 400 ° C., which on the one hand leads to water vapor being released and on the other hand to good crystallization of the silver layer 5, which is advantageous for the subsequent operations.

A layer of cadmium sulfide (CdS) of approximately 3011 is evaporated onto the layer 5 made of silver. This vapor deposition takes place in the device shown in FIG. 4, which will be explained later. The previously prefabricated lower part 1 is kept at a temperature of 200 °.

Next, the cadmium sulfide layer 6 is roughened using an aqueous hydrochloric acid (HCl) to reduce reflection and to etch out grain boundaries. A copper sulfide (Cu 2S) layer 7 is then produced on the cadmium sulfide layer 6, which is done by a chemical reaction by briefly immersing the lower part in a monovalent copper ion solution for about 5 to 10 seconds. This copper sulfide layer should have an order of magnitude of 0.2 μ thickness.

A copper (Cu) layer 8, which has a thickness of 30 to 100 Å, is also evaporated onto the copper sulfide layer 7. Subsequently, the lower part is heated at about 180 ° under atmosphere, which makes it possible to fill in vacancies due to copper diffusing into the copper sulfide layer and to form a copper oxide layer (Cu _z O). With this operation, the manufacture of the lower part 1 is finished. As can be seen from FIG. 1, the layers 6, 7 and 8 are applied in such a way that an edge strip 9 of the base 5 made of silver remains free in FIG. 1 on the right, which can later be used as a contact.

The upper part 2 is also manufactured separately. It contains a cover glass 10, which is also cleaned with ultrasound in a solvent before further processing. On this cover glass 10, a liquid heat seal adhesive 11 with a layer thickness of 120 to 150 .mu.m is applied on one side by means of a doctor or the like. applied. In practice, an adhesive from Kömmerling, Zweibrücker Landstrasse, 6780 Pirmasens, which has the company identification AK 543, is suitable. The cover slip 10 and the initially applied liquid heat seal adhesive 11 are in one Vacuum oven then subjected to drying at about 100 ° C for 4 to 5 hours, so that vapors and chamfers can escape from the initially liquid heat seal adhesive. It has been shown that subsequent drying at a likewise elevated temperature in the atmosphere can lead to advantages, with an oxidation of the heat seal adhesive 11 probably taking place. During this drying process, the heat seal adhesive reduces its thickness to approximately 25% of the original application thickness of 120 to 15µ µ. With the help of the heat seal adhesive 11, a copper foil with a thickness of approximately 35 p is then sealed onto the cover glass 10 at approximately 170 ° to 180 °. The grid 12 shown in FIG. 1 is then etched out of this copper foil, using the technique known in the production of printed circuit boards. First, a lacquer grid is applied using the screen printing process, which corresponds to the grid 12 that remains afterwards. After the grid 12 has been created and the lacquer has been removed again, a layer 13 of gold is applied galvanically to the grid in order to enable a barrier-free contact. The layer thickness is approximately 100 to 1000 A, preferably 250 A.

The now finished upper part 2 is connected to the lower part 1 in a vacuum press at approx. 170 ° to 180 °, the connection being obtained by the layer 11 of the heat seal adhesive, which has a layer thickness which is somewhat larger than the thickness of the grid 12 . The grid 12 lies with its gold layer 13 on the layer 8 made of copper and establishes a secure contact, while subsequently the grid 12 penetrates into the layer 11 during heating, which also has an adhesive connection between the cover glass 10 and the layer 8 manufactures. The upper part 2 is applied so offset on the lower part 1 that on the left in the drawing, i.e. A strip 14 of the grid 12, which also serves as a contact, is exposed opposite the contact strip 9. After the upper part and lower part have been joined together, there is a solid, self-contained cell that does not require any further treatment or reinforcement. If appropriate, it is expedient to seal the edges running transversely to the contact strips 9 and 14, which can be done, for example, by gluing, welding or soldering the cover plate 10 and the base plate 3.

A solar battery can be assembled from several of the solar cells shown in FIG. 1, the contacts of the adjacent solar cells formed by the edge strips 9 and 14 then being connected to one another.

In order to save additional support elements when creating a solar battery, a common cover glass 15 can be provided for several solar cells, as shown in FIGS. 2 and 3. In this case, lower parts 1 are used which have been produced in accordance with the preceding description. These bases are appropriately manufactured in a certain size in which they can be manufactured economically. On the other hand, there is no major difficulty in producing the common cover glass 15 over a large area and providing it with a large number of gratings 12 in the manner described above. The contacts between the individual solar cells are produced in the manner described for FIG. 1, which are only indicated schematically in FIG. 2. In this case, contact is made between the grid 12 and the layer 5 of silver serving as an electrically conductive base for those solar cells lying in a row. As can be seen in Fig. 3, several rows of such cells can of course be attached to the common cover slip. The attachment is then carried out by the layer 11 of the heat seal adhesive in a single operation. In practice, it is advisable to seal the end faces between the contacts 14 and 9 and the joints between the individual cells, which can be achieved by casting with an adhesive or the like. can be done appropriately. It is also possible to solder or weld the glass plates.

4 schematically shows a device with which a homogeneous layer of cadmium sulfide can be evaporated onto a lower part 1 of a solar cell. For this purpose, a graphite furnace 16 is provided, which is surrounded by a graphite heating coil 17 to which a power supply 18 is connected. The outside of the graphite heating coil 17 is surrounded by a radiation reflector 19. A thermocouple 20 measuring the temperature for temperature control projects into the graphite furnace 16. The graphite furnace is seated on an insulating ceramic ring 21. The graphite furnace 16 has the shape of a cylinder, in which an upwardly open chamber 23 is divided by an annular collar 22, into which cadmium sulfide in powder form is filled. The chamber 23 is closed at the top by a porous quartz frit 24 which is closely fitted into the cylindrical part adjoining the collar 22 to the outside. For this purpose, the quartz frit 24 and the inner surface of the graphite furnace 16 are expediently ground. In order to enable perfect processing, it is advisable to melt the quartz frit 24 into a quartz glass tube, which is then ground on the outside. The quartz frit 24 is secured in its position in a manner not shown by one or more pins. The quartz frit 24 is arranged at a sufficient distance from the end of the graphite furnace 16, that is to say approximately one third of the height, so that a temperature high enough to be maintained in the region of the quartz frit is that vaporization and so that the quartz frit can be prevented from becoming impermeable. A cylindrical extension 25 adjoins the graphite furnace, which sits on the ceramic ring. This approach envelops the thermocouple 20 over a sufficient length so that it is ensured that the temperature measured by the thermocouple 20 corresponds as closely as possible to the temperature of the chamber 23.

Arranged above the outlet of the graphite furnace 16 is a displaceable diaphragm 26, with which the evaporating gas from the lower part 1 of the solar cell can initially be maintained. This lower part 1 rests on a support 27, which leaves a section of the size to be vaporized on the lower part 1 with cadmium sulfide. On the opposite side, a heating part 28 designed as a graphite meander is provided, which is covered by a radiation reflector 29. This heating part 28 ensures that the lower part of the solar cell maintains a temperature of approximately 200 ° C. when the cadmium sulfide is evaporated.

Claims (9)

1. A method for producing solar cells with a thin film PN heterojunction using an electrically conductive support applied upon a base, a cadmium sulfide layer vapor deposited thereon and a cuprous sulfide layer chemically produced on the said cadmium sulfide layer, upon said cuprous sulfide layer an electrically conductive grid being superimposed, said grid being covered heat-sealed and pressed with a cover glass member provided on the side facing the grid with a heat-sealing adhesive, whereby the base with the support, the cadmium sulfide layer and the cuprous sulfide layer being initially produced to form a prefabricated lower part, characterized in that said pre-fabricated lower part being heat-sealed and compressed with a pre-fabricated upper part consisting of the cover glass member, the heat-sealing adhesive and the grid, said grid being heat-sealed as a film to the cover glass member by means of the heat-sealing adhesive and then etched out of said film before the upper part and the lower part are heat-sealed and compressed.

2. A method in accordance with claim 1, characterized in that the lower part (1) comprises a glass plate (3) upon the said glass plate (3), a support (5) consisting of silver or zinc is vapor deposited at about 400°C, using preferably an adhesion promoter (4), upon said support (5) the cadmium sulfide layer (6) is vapor deposited.

3. A method in accordance with claim 1, characterized in that the heat-sealing adhesive (11) is applied in the liquid state and subsequently dried in a vacuum, which drying process may be followed by drying in air.

4. A method in accordance with claim 1 or 3, characterized in that a thin gold layer (13) is formed on the grid (12) by electrodeposition, prior to joining the upper part (2) and lower part (1), to produce a contact which is free of insulation.

5. A solar cell produced by the process according to any of claims 1 to 4, characterized in that the cover glass member (10) with the grid (12) and the base plate (3) with the support (5) are shifted laterally relative to each other so as to expose contacts (9, 14) formed on the one side by the support (5) and on the other side by the grid (12).

6. A solar cell in accordance with claim 5, characterized in that the upper part consists of a large-area cover glass member (15) with a plurality of electrically conductive grids provided thereon in one row, each of said grids is associated with one lower part (1) shifted relative to the grid in such a way that the supports (5) have one side in contact with the grid associated with the neighbouring lower part and that on one side of the cover glass an edge strip of the outer grid is exposed to serve as a contact while on the opposite side an edge strip of the support (5) of the outer lower part (1) is exposed to serve as a contact.

7. A solar cell in accordance with claim 6, characterized in that a large-area cover glass (15) is provided with several rows of grids and a corresponding number of rows of lower parts (1 ).

8. A solar cell in accordance with at least one of claims 5 to 7, characterized in that the edges of the cover glass (10, 15) and of the base plate (3) outside the area of the exposed contacts are sealed together.

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