FR2853993A1 - Production of a photovoltaic module with photovoltaic cells arranged between glass substrates and incorporating a sealing joint enclosing the volume containing the cells - Google Patents

Abstract

Production of a photovoltaic module incorporating photovoltaic cells (1) with positive and negative poles arranged on the same side, the cells being arranged side by side between two glass substrates (2, 3) and connected in series, comprises: (a) assembling the cells; (b) depositing, on an internal surface of only one of the glass substrates (3), of strips of silver paste (5) constituting the interconnection conductors; (c) the putting in place of a sealing joint (4) of a mineral material between the two glass substrates to delimit a sealed inner volume inside which all the cells are contained. An independent claim is also included for a photovoltaic module produced by this method.

Description

i

  Technical field of the invention The invention relates to a method of making a photovoltaic module comprising photovoltaic cells each having positive and negative poles arranged with the same side of the cell, the cells being placed side by side between internal faces of two front and rear glass substrates and connected in series by interconnection conductors connecting a positive pole of a cell to a negative pole of the cell adjacent.

  STATE OF THE ART A photovoltaic cell is conventionally formed on a solid silicon substrate cut in the form of slices a few hundred microns thick. The substrate may consist of monocrystalline silicon, polycrystalline silicon or semiconductor layers deposited on a glass or ceramic substrate. It has on its surface a network of narrow electrodes, generally in silver or aluminum, intended to drain the current towards one or more main electrodes from 1 to a few millimeters in width, also in silver or aluminum. Each cell supplies a light-dependent current at an electric voltage which depends on the nature of the semiconductor and which is usually of the order of 0.45 V to 0.65 V for crystalline silicon. Voltages of 6V to several tens of volts are usually necessary to operate electrical devices, a photovoltaic module is generally constituted by an assembly of several cells in series. A 40-cell module supplies, for example, almost 24 volts. Depending on the currents requested, several cells can also be placed in parallel. A generator can then be produced by optionally adding accumulators, a voltage regulator, etc. To manufacture a photovoltaic module, the cells are prepared, that is to say covered with a network of electrodes and connected together by 10 metallic conductors. The assembly thus formed is then placed between two sheets of polymer, themselves sandwiched between two glass substrates.

  The assembly is then heated to around 1200C to strongly soften the polymer, make it transparent and ensure the mechanical cohesion of the module.

  In a known photovoltaic module, rear connection conductors associated with a first cell are connected to the front connection conductors associated with a second, adjacent cell. If the module has more than two cells, the rear connection conductors of the second cell are then connected to the front connection conductors of the next cell, all the cells thus being connected in series. In practice, a rear connection conductor of a cell and the associated front connection conductor of the neighboring cell can be formed by the same interconnection conductor. The connecting conductors of the end cells serve as connectors to the outside.

  An array of photovoltaic cells in matrix form may include conductors of transverse links connecting the cells in parallel. Typically the transverse connection conductors, constituted by a copper core and a surface deposit of a tin-lead alloy, are soldered with a tin-lead alloy on connection areas of the cell. The connecting conductors can also be produced by depositing a silver paste according to the desired pattern, then baking at high temperature.

  In document DE-A-4128766, the front and rear connection conductors are formed on the internal face of the front and rear glass substrates opposite the location of each of the cells. The connecting conductors are then soldered onto the cells and onto interconnection elements intended to connect the cells in series. The space remaining between the glass substrates is then filled with an organic resin.

  Furthermore, in certain known cells (US Pat. No. 6,383,317), the positive and negative poles of the cell are brought back on one of the faces of the latter, in particular on its rear face.

  The soldering of the connection conductors and the assembly of the cells constitutes a handicap since these are long operations which can break the cells and entail a high production cost.

  OBJECT OF THE INVENTION The object of the invention is to remedy these drawbacks and, in particular, a method for producing a photovoltaic module minimizing the number of welding operations and the manufacturing cost, more particularly for cells. whose positive and negative poles are arranged on the same side of the cell.

  According to the invention, this object is achieved by the fact that, before the placement of the cells, the deposition, on an internal face of only one of the glass substrates, of strips of silver paste constituting the interconnection conductors, and that it includes the installation of a sealing joint made of mineral material, disposed between the two glass substrates and delimiting a sealed interior volume inside which all the cells are arranged.

  The object of the invention is also to provide a photovoltaic module comprising a sealing joint made of mineral material, disposed between the two glass substrates and delimiting a sealed interior volume inside which all the cells are arranged, the interconnection conductors being formed by strips of silver paste placed on an internal face of only one of the glass substrates.

Brief description of the drawings

  Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples and represented in the appended drawings, in which: FIGS. 1 and 2 represent a mode particular embodiment of a photovoltaic module according to the invention respectively in section along the axis AA and in view from below.

  FIG. 3 represents another particular embodiment of a photovoltaic module comprising protective layers.

  Description of particular embodiments.

  The photovoltaic module according to FIG. 1 comprises photovoltaic cells 1 placed side by side between the internal faces of two 5 glass substrates, front 2 and rear 3. Only three cells 1a, 1b and 1c are shown in FIG. 1 for reasons of clarity. The positive and negative poles of each cell are brought to the back of the cell.

  The connection of a positive pole of a cell and a negative pole of the adjacent cell 10 is carried out very simply by means of at least one interconnection conductor constituted by a strip of silver paste deposited on the face internal of the rear glass substrate 3 before placing the cells.

  In FIGS. 1 and 2, a strip of silver paste 5a, deposited on the back glass substrate 15 3, is positioned on an area connecting the locations of the two adjacent cells 1 a and 1 b, so as to come into contact on the rear face of cells la and 1b, respectively with the positive pole of cell la and with the negative pole of cell lb. The area has the shape of a staircase. A strip of silver paste 5b, connecting the positive pole of cell 1b to the negative pole of cell 1c, is similarly arranged on the rear glass substrate 3. A network of interconnection conductors (5) is thus formed on the glass substrate 3, before placing the cells. When the rear face is not optically active, there is no constraint on the optical transmission of the rear glass substrate 3 and the pattern of the network of 25 strips of silver paste 5 is chosen so that conduction is maximum. According to a first alternative embodiment, the width of the strips of silver paste 5 is large, each strip of silver paste 5 can, for example, have a width of between 3mm and 10 mm, more typically between 3mm and 5 mm.

  In the particular embodiment of FIG. 2, the seal 4 is located at the periphery of the surface common to the two glass substrates 2 and 3. It is thus arranged on the periphery of the rear glass substrate 3 except on the left side 5 for the rear glass substrate 3, in order to allow access from the outside to conductors 6 for connection with the outside. For example, a conductor 6 for connection to the outside of the end cells (la and 1c) can project outwards beyond the joint 4.

  The glass substrates 2 and 3 are preferably constituted by a soda-lime glass 1.6 to 6mm thick, a typical value being 3 to 4mm for the front glass substrate 2 and 2 to 4mm for the substrate rear glass 3.

  The glass is advantageously a clear or extra white glass, that is to say containing little iron, since the optical transmission of such a glass is optimal. The glass may also have been thermally toughened in order to increase its mechanical strength.

  The strips of silver paste 5 can be produced in silver or in a silver-rich alloy according to a conventional method in the industry of display screens, plasma panels in particular. This classic process includes depositing the desired pattern from a silver paste, then baking between 4000C and 6000C. The thickness of the strips of silver paste 5 is between 2.5 µm and 15.5 µm, more typically between 4 µm and 7 µm.

  According to an alternative embodiment, the known conventional method, described above, is modified and the firing following the deposition of a silver paste 5 is carried out at a temperature between 6200C and 6600C. Such baking, followed by rapid cooling as is the practice for thermal tempering, makes it possible to reduce the duration of the thermal cycle, to very greatly reduce the resistivity of the electrode material as well as to obtain the hardening of the glass by tempering. thermal. Consequently, it is then possible not to soak the glass of the substrates 2 and 3 before the deposition of the strips of silver paste 5.

  In a particular variant embodiment, the cooking is completed by an operation of recharging the strips of silver paste 5 by chemical or electrochemical means. The recharging operation is particularly known in the field of printed circuits. It conventionally consists of depositing one or more layers of a metal or a metal alloy on existing conductors 10 in silver or in a silver alloy. This method makes it possible to deposit strips of thin silver paste 5, therefore reducing the cost of the silver material. This variant also makes it possible to bake the silver paste strips 5 at low temperature in order to degrade the organic binders initially contained in the silver paste. It does not require high temperature cooking of the silver paste, although it is compatible with such cooking. Finally, it makes it possible, by chemical or electrochemical recharging, to greatly increase the conductivity of the strips of silver paste 5 and possibly to cover them with a protective layer. The advantage derived from this method is therefore a great reduction in cost and an improvement in the performance of the strips of silver paste 5.

  One can, for example, deposit and bake strips of silver paste 5 with a baked thickness of 2, pm to 3, um, then deposit a layer of copper by chemical means as it is conventional to do for circuits printed, and finally 25 deposit, still chemically, a thin protective layer of nickel or silver. The thickness of deposited copper can vary from 2 µm to more than 100 µm, a typical value being 50 µm. The thickness of nickel or silver deposited may vary from 0.1 μm to more than 2 μm, a typical value being 1 μm.

  As shown in FIGS. 1 and 2, a seal 4 made of mineral material is disposed between the front 2 and rear 3 glass substrates, at the periphery of the module, so as to delimit a sealed interior volume inside which 5 are all arranged. cells 1. The softening in temperature of the mineral material constituting the seal 4 makes it possible to seal the front glass substrates 2 and rear 3. The seal seal 4 has a thickness of several hundred microns, which depends above all on the thickness silicon substrates constituting the cells 1, to which is added the thickness of the strips of silver paste 5 constituting interconnection conductors, formed on the front face of the rear glass substrate, connecting the cells 1 in series by connecting a positive pole of a cell la to a negative pole of the adjacent cell lb.

  The sealing joint 4 preferably has a width of between 2mm and 1 mm, more typically between 3mm and 5mm. It is preferably made up of a sealing glass whose softening temperature is as low as possible and whose softening in temperature allows the front substrate 2 to be welded to the rear substrate 3. This type of product is conventional in 20 l industry of plasma display screens or cathode ray tubes. It is, for example, a lead silicate or a lead borosilicate possibly containing some addition elements. The sealing glass is preferably of the non-crystallizable type, although this is not absolutely necessary. The particle size of the frit of the sealing glass 25 is such that the average diameter is between 2 μm and 100 μm, more typically between 6 μm and 40 μm.

  The seal 4 is deposited on one of the glass substrates or on the two glass substrates 2 and 3, along a path described below, that is to say either along the four sides or, generally, along three sides of the module and recessed on a fourth side.

  During the sealing operation, which takes place between 3800C and 4800C for a period of less than 30 minutes, the material of the sealing joint 4 softens considerably and makes the interior volume of the sealing joint vis-à-vis, outside. Any diffusion of water towards the interior of the module will be prohibited during the entire lifetime of the module. The pressure of the interior volume is of the order of one atmosphere at the sealing temperature. The final pressure, after cooling to room temperature, is lower, for example of the order of about 400 millibars. A vacuum vis-à-vis the outside therefore forms automatically inside the module and causes the application of a force by the glass substrates 2 and 3 on the cells 1. This force ensures excellent contact between the cells 1 and the strips of silver paste 5 deposited on one of the glass substrates without it being necessary to have a solder between the cells 1 and connecting conductors. Thus, this manufacturing process eliminates all the elements necessary for welding while ensuring a high degree of cell protection.

  According to a development of the invention, the sealed interior volume comprised between the two glass substrates 2 and 3 is filled, during the assembly operation, with a mixture of one or more neutral gases, chosen from nitrogen. , helium, neon or argon. The mixture can also include hydrogen or methane. The presence of such a neutral or reducing atmosphere makes it possible to keep the silicon cells 1 an excellent conversion efficiency. Typically, and to avoid the risks due to the presence of hydrogen or methane, the mixture comprises less than 8% of hydrogen or methane.

  The manufacture of a module will be described in more detail below, for the production of a photovoltaic module of 12.5 cm x 12.5 cm and 200 pum.

thick.

  We have two glass substrates of 550mm x 275mm, for example in soda-lime glass. One of them, intended to constitute the front glass substrate 2, is preferably made of clear soda-lime glass, that is to say containing little iron. The thickness of the glass substrates is preferably between 2mm and 4mm (for example 3mm). Above these values, the weight becomes too great, while below, the substrates are too fragile.

  To make the strips of silver paste 5 on the rear glass substrate 3, a mixture of a glass powder and 80% to 97% of a silver powder, of a silver alloy, is prepared. , nickel-plated copper or silver-plated copper. The glass powder 15 is preferably constituted by lead silicate with an average particle size of between 0.3 μm and 3 μm (preferably 0.5 μm), at 12% to 20% (preferably 15%) of silica . The silver powder has an average particle size between 0.5 pim and 2 pim (preferably lpm). This mixture of powders is suspended in a solution consisting of propylene glycol or butylene glycol, supplemented with ethyl cellulose. The dough has a viscosity of 5000 centipoises to 200,000 centipoises (preferably of the order of 20,000 centipoises).

  The strips of silver paste 5 can be deposited on the rear glass substrate 2 by screen printing. They are deposited in a pattern made up of bands of length close to or slightly greater than twice the width of a cell 1, for example 250 mm long, on the rear glass substrate 3. The number of bands associated with each cell 1 is between 2 and 10, the width of a strip being a function of the density of the chosen pattern. The width of a strip can thus be of the order of 2mm for a 2-stripe pattern and of the order of 0.2mm for a 10-stripe pattern. On the rear glass substrate 3, it is possible to produce a full surface of 120 x 120 mm per cell, 2 strips of approximately 5mm wide, 10 strips of approximately 1mm wide or a denser thin network 5 with strips of 0.2mm to 0.3mm wide. After drying at 1400C for minutes in a hot air oven, the dry thickness of the strips of silver paste 5 is between 5 μm and 15 μm (preferably 12 μm).

  The rear glass substrate 3 is then baked in order to adhere the strips of silver paste 5 to the substrate and to burn the organic components contained in the deposit. This cooking is carried out at a temperature of 4500C to 6800C, for 10 minutes, and is optionally followed by a thermal toughening (at more than 6000C) which gives the glass substrate great mechanical resistance. In the case where a refill operation is planned, the dry thickness is preferably smaller, for example of the order of 3 μm.

  The strips of silver paste 5 are then recharged by chemical deposition, for example of 50 μm of copper and 1 μm of silver. A reflective layer may possibly be produced on the internal face of the rear glass substrate 3, on the areas not covered by the strips of silver paste 5.

  The frit is then deposited on the sealing glass intended to form the seal 4.

  For this, use is made of a powder of a sealing frit of the non-crystallizable type based on a composition of lead borosilicate, with an average particle size of between 5 μm and 100 μm (12 μm for example) and of which the softening temperature is 3800C. This frit is suspended in a solution consisting of propylene glycol supplemented with ethylcellulose. The dough has a viscosity of around 40,000 centipoise. A bead of dough is deposited using a syringe at the periphery of the rear glass substrate 3, except on one side where the bead is deposited 5 mm from the edge, as shown in FIG. 2.

  The cells 1 are then placed on the rear glass substrate 3. This assembly is preferably introduced into a volume, the atmosphere of which is a mixture of nitrogen and hydrogen comprising from 0% to 8% hydrogen. and in which the front glass substrate is positioned 2. Pliers are placed on the periphery of the module so as to apply a crushing force on the sealing bead. The assembly is then brought to a temperature between 41 ° C. 10 and 4600 ° C. for 10 minutes so as to seal the two substrates. In an alternative embodiment, the assembly is assembled in air before being introduced into an oven in which a vacuum is created at 10 millibars and which is then filled with a mixture of nitrogen and hydrogen before heating. After cooling, the clamps are removed. The module is then ready to be integrated into a generator.

  In the variant embodiment illustrated in FIG. 3, the thickness of the glass substrates is reduced, which makes it possible to reduce the weight of the module. Each glass substrate has a thickness of between 0.5 and 2mm, typically between 0.8 and 1.6mm and preferably 1.2mm. The front 2 and rear 3 glass substrates preferably have the same thickness. Heat treatment operations, and in particular sealing, are more efficient and less costly because the mass of glass to be heated is lower. In the previous embodiments, the front glass substrate was toughened to resist impact, for example, hail. In the variant of FIG. 3, the front 2 and rear 3 glass substrates are not tempered. The mechanical resistance of the module, in particular, its impact resistance is nevertheless ensured by front 7 and rear 8 protective layers produced after the sealing operation, respectively on the external faces of the front 2 and rear 3 glass substrates. front protective layer 7 is transparent and can be formed by laminating a transparent polymer film, by spraying a transparent plasticizing primer or by fixing, for example by gluing or pinching, a sheet of tempered glass or a polymer sheet (polycarbonate, PMMA, etc .... The 5 rear protective layer 8 can be formed by laminating a polymer film, by spraying a plasticizer primer or by fixing, for example by gluing or pinching, d 'a sheet of polymer (polyethylene, PVC, etc ...). The final weight of the module is reduced thanks to the reduction of the thickness of the glass substrates. For example, glass substrates of 4mm d thickness can be replaced by glass substrates 2 and 3 of 1 mm thickness, a front protective layer 7 of 3 mm thick tempered glass and a rear protective layer 8 formed by a polymer film, reducing at 5mm the thickness of the glass layers of the module, while ensuring good protection.

  An essential advantage of a module according to the invention is a perfect seal which gives it a lifespan of several tens of years in humid environments. The method according to the invention also makes it possible to produce modules with a very low production cost.

  Another advantage of the module according to the invention lies in its high thermal conductivity, which makes it possible to dissipate the heat and to maintain a relatively low temperature, which in turn makes it possible to maintain a good conversion efficiency of the photovoltaic cells.

  The method according to the invention can be applied to the production of photovoltaic modules, then of solar generators, from square, rectangular or round photovoltaic cells and whose characteristic dimensions can range from a few centimeters to several tens of centimeters. The cells are preferably square cells whose side is between 8cm and 30cm.

  The invention is not limited to the particular embodiments described and 5 shown above. In particular, the strips of silver paste can be deposited on the internal face of the front glass substrate. The invention applies to all types of photovoltaic cells, not only to silicon, monocrystalline or polycrisalline photovoltaic cells, but also to gallium arsenide cells, to cells formed by silicon ribbons, to cells with silicon balls formed by an array of silicon balls inserted in conductive sheets, or with photovoltaic cells formed by depositing and etching a thin layer of silicon, copper / indium / selenium or cadmium / tellurium on a substrate glass or ceramic.

Claims (13)

claims   1. Method for producing a photovoltaic module comprising photovoltaic cells 5 (1) each having positive and negative poles arranged on the same side of the cell, the cells being arranged side by side between internal faces of two substrates of front (2) and rear (3) glass and connected in series by interconnection conductors connecting a positive pole of a cell (la) to a negative pole of the adjacent cell (lb), process characterized in that before the installation of the cells (1), it comprises, on an internal face of only one of the glass substrates (3), strips of silver paste (5) constituting the interconnection conductors, and that it comprises the installation of a sealing joint (4) made of mineral material, disposed between the two glass substrates (2, 3) and delimiting a sealed interior volume inside which all of the cells (1).   2. Method according to claim 1, characterized in that a strip of silver paste (5a, 5b) is deposited on an area connecting locations of two adjacent cells (la, lb).   3. Method according to claim 2, characterized in that said zone has the form of a stair step.   4. Method according to any one of claims 1 to 3, characterized in that a sealing operation of the module is carried out between 3800C and 4800C, for a duration of less than 30 minutes.   5. Method according to any one of claims l to 4, characterized in that it comprises, after the deposition of the strips of silver paste (5a, 5b), baking carried out at a temperature between 6200C and 6600C and followed by an operation of recharging the strips of silver paste (5a, 5b), by chemical or electrochemical means.   6. photovoltaic module produced by a method according to any one of claims 1 to 5 and comprising photovoltaic cells (1) each having positive and negative poles arranged on the same side of the cell, the cells being arranged side by side between the internal faces of two front (2) and rear (3) glass substrates and connected in series by interconnection conductors 10 connecting a positive pole of a cell (la) to a negative pole of the cell (1b) adjacent, module characterized in that it comprises a sealing joint (4) made of mineral material, disposed between the two glass substrates (2, 3) and delimiting a sealed interior volume inside which all the cells are arranged ( 1), the interconnection conductors being constituted by strips of silver paste (5a, 5b) arranged on an internal face of only one of the glass substrates (3).   7. Module according to claim 6, characterized in that a strip of silver paste (5a, 5b) is arranged on an area connecting locations of two adjacent cells (la, lb).   8. Module according to claim 7, characterized in that the zone, connecting locations of two adjacent cells (1a, 1b), has the shape of a staircase.   9. Module according to any one of claims 6 to 8, characterized in that the sealing joint (4) is a mineral glass with low softening point.   10. Module according to any one of claims 6 to 9, characterized in that the sealing joint (4) comprises lead silicate or lead borosilicate.   11. Module according to any one of claims 6 to 10, characterized in that the sealing joint (4) has a width between 2mm and 1 Omm.   12. Module according to any one of claims 6 to 11, characterized in that the sealing joint (4) is disposed at the periphery of the opposite surfaces 10 of the glass substrates (2, 3).   13. Module according to any one of claims 6 to 12, characterized in that the glass substrates (2, 3) having a thickness of between 0.5mm and 2mm, the module comprises front protective layers (7) and rear (8) 15 formed respectively on the glass substrates before (2) and rear (3) after sealing.