EA046476B1 - METHOD FOR SWITCHING PHOTOVOLTAIC CONVERTERS - Google Patents

Description

Field of technology to which the invention relates

The invention relates to the field of solar energy, namely to the technology of assembling chains of photoelectric converter cells (hereinafter referred to as PV cells) based on a heterojunction, as well as for classical crystalline and polycrystalline photoelectric converters of any type.

Prior Art

The most widely used two methods of contacting switching buses are adhesive and soldering technologies. Adhesive technology uses an electrically conductive adhesive (glue). In soldering technology, a contact bus covered with solder is soldered to the elements of the contact grid, previously applied to the surface of the solar cell.

There is a known method for connecting photovoltaic cells with metal wires in contact with solder paste pads, disclosed in EP3809473, published 04/21/2021. The main object of the invention is a method for connecting photovoltaic cells with a deposited electrically conductive contact grid containing contact tracks for connection with a metal wire and a method including the step of depositing a plurality of solder paste pads; the sites are located at a distance from each other; on contact tracks, at least in part of the places intended for the formation of intersections between metal wires and contact tracks; the step of applying metal wire to the solder paste pads, laying is carried out by a wire distribution device configured to tension and press the metal wires against the photovoltaic cells and allow them to be positioned with respect to the solder paste pads in at least a specified portion of the locations.

The disadvantage of this analogue is that solder paste contact pads are applied to the surfaces of narrow contact tracks, covering them completely or covering their width. The width of the applied solder paste pad is comparable to the width of the contact track and does not exceed 200 microns. When applying solder paste, the remaining flux contained in its composition inevitably spreads. As a result, areas are formed where the paste is in contact with the surface of the solar cell, and flux residues collect at the boundaries of the contacting materials (solder paste, surface of the solar cell, contact tracks). It is known that such places are a source of accelerated corrosion destruction that occurs during the operation of solar cells. Thus, the proposed method does not consider options for preventing the corrosive effects of solder paste.

The closest analogue is a method using solder paste for the manufacture of solar cell modules, disclosed in WO 2020233839 (A1), published 11/26/2020. A method of manufacturing a solar module by connecting a plurality of photovoltaic (PV) cells, wherein at least a first photovoltaic cell is connected to a second photocell by an electrically conductive adhesive containing or consisting of solder paste. Solder paste contains solder alloy particles dispersed in solder flux. The solder alloy contains Sn-containing solder having a liquidus temperature of less than 225°C.

The disadvantage of this invention is that it does not involve the use of a connecting wire that is round in cross-section, since to form a high-quality solder connection with its surface, a significant increase in the width of the contact track will be required. This will lead to greater shading of the photoconverting surface of the plate and to increased consumption of finger metallization and soldering pastes.

The essence of the invention

The objective of the claimed invention is to develop a method for switching solar cells with a mechanically strong connection, without the use of bulk metallizing paste.

The technical result is to increase the strength of the mechanical connection when switching individual photoelectric converters into a single circuit, increasing the reliability of the connection and increasing the service life of the photoelectric converter.

The specified technical result is achieved due to the fact that the method of switching photoelectric converters, including applying solder paste to the contact pads by screen printing and subsequent soldering of the wire to the surface of the contact pads, lead or lead-free pastes containing metals from the series are used as solder paste: tin, silver, copper, bismuth, cobalt, with a metal content of at least 90 vol.% and flux up to 10 vol.%.

Soldering of the contact wire is carried out using solder paste pre-applied to individual contact pads. The proposed method involves using the same metallization paste for the manufacture of both the contact grid and the contact pads. Due to this, the number of boundaries formed in the technological process, at which processes usually develop that lead to weakening of adhesion as a result of corrosion of contacting materials or thermomechanical effects, is reduced. For switching, round wire is used, incl. without solder (or with reduced thickness), the wire is not soldered to the pseudo-basbar and pads made of bassbar paste. Soldering occurs only to the applied contact pads, so pseudo-basbars are not printed, and contact of the wire with the fingers is ensured by pressing it during subsequent lamination.

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List of figures, drawings

The invention is illustrated by a schematic drawing shown in Fig. 1, fig. 2 and fig. 3.

Wherein:

in fig. Figure 1 shows a photovoltaic plate with a contact grid applied.

In fig. Figure 2 shows the switching diagram of a solar cell using standard soldering technology.

In fig. Figure 3 shows a diagram of the photoelectric converter switching method.

In fig. 1, 2, 3 shows: 1 - contact pads, 2 - pseudo-basbars, 3 - tracks for collecting current, 4 - photoelectric converter, 5 - copper wire, 6 - solder layer, 7 - solder paste.

Information confirming the possibility of implementing the invention The solar cell (4) contains contact pads (1) mounted on it, connected to pseudo-basbars (2), between which there are tracks for collecting current (3), copper wire (5), soldered to the contact pads using layer of solder (6) and solder paste (7).

The claimed method of PV switching is characterized by a set of the following sequential operations:

The operation of preparing a solar cell (4) with a contact electrically conductive grid and contact pads (1) on the front and back sides. For metallization, finger pastes are used, including an electrically conductive silver-containing phase and an organic thermosetting binder. The application and curing mode is determined by the fluidity and curing speed parameters of the solder paste (7). For printing, a stencil is used with the required design of the contact grid and contact pads (1). After printing on the front side of the FEP (4), drying is carried out in an annealing oven at a temperature of 140-200°C (depending on the recommendations of the manufacturer of this solder paste (7)). Then, under similar conditions, printing is carried out on the back side and subsequent drying of the FEP (4) in an annealing oven.

The operation of applying solder pastes (7) to the surfaces of the contact pads (1).

Solder paste is applied by screen printing using a stencil stencil. The prints are located in the area where the contact pads are located (1) and have a height of 50 to 100 microns. The shape of the prints is close to square and has a size of 0.5x0.5 mm or more. Solder paste (7) can also be applied using inkjet printing using standard equipment. The amount of solder paste applied is determined by the requirement for reliable adhesion of the copper wire (5).

The operation of soldering copper wire (5) to the contact pads (1).

Soldering is carried out on automated equipment, which ensures the pressing of copper wire (5) to the contact pads (1) with applied solder paste (7) and the required temperature conditions, which depend on the type of solder paste (7) used. It is preferable that the soldering temperature does not exceed 200°C to reduce thermomechanical loads on the PV structure.

General conditions for implementing the PV switching method.

1. The height of the formed solder layer (6) should not lead to increased mechanical stress during lamination to eliminate the possibility of splitting the FEP (4).

2. The flux contained in the solder paste (7) should dry with a minimum of solid residue.

3. The flux contained in the solder paste (7) should not react with the surface of the solar cell (4), damaging the semiconductor structure of the solar cell (4).

4. During the application of solder paste (7), its density, quantity and viscosity of the binder, as well as the technological mode of impregnation are selected in such a way as to ensure high adhesion, absence of defects, and reliable ohmic contact. The strength of the soldered joint must be at least 0.5-1.0 N (wire pull test).

The technical result is also achieved due to the fact that the solder paste contains a flux that can activate the surface of the contact pads and the surface of the connecting wire.

Another advantage of using the technology is the reduction in the thickness of the solder on the surface of the wire. The wire in the automated soldering process may not go through the fluxing stage, which is mandatory in the existing technological process for assembling PV strings. Thus, the soldering process is reduced to mechanically pressing the wire to the surface of the contact pad covered with solder paste and supplying the required amount of heat to activate the flux, melting the paste and fixing the wire on the contact pad.

In the proposed invention, the process of applying the contact grid and contact pads to the FEP is combined into one stage, which reduces the likelihood of defects. This eliminates the need to use special basbar metallization paste, which is used in known technology and which is often responsible for increased degradation of solder joints during module operation. Eliminates the need for soldering along the entire length as in the closest invention.

Advantages of using the proposed method:

- 2 046476 reduction in the cost of the device due to the use of copper wire without a layer of solder;

improving the quality of soldering wire to contact pads;

improving the resistance of the FEP contact grid as a result of mechanical stress by eliminating the separation of pseudo-basbars, since the effect of soldering wire to pseudo-basbars is practically eliminated;

improving the stability and degradation resistance of modules by avoiding the use of silver-containing solder pastes, as well as reducing costs, since the cost of solder pastes is significantly lower.

Example No. 1.

A series of PV samples were manufactured according to the following sequence of operations:

1. A contact grid is printed on the surface of n-type silicon heterostructure solar cells using finger metallization paste.

2. Contact pads measuring 1x1 mm were printed with finger or bass metallization pastes.

3. A solder paste layer of 1x1 mm and a height of 250-300 microns was printed using pastes with compositions 99.0Sn0.3Ag0.7Cu, Sn36Pb2Ag, Sn63Pb37, Sn42Bi58. Pastes include 88-90% metal component and 10-12% flux.

4. Soldering was carried out using copper wire with a diameter of 280 microns coated with Sn43Pb43Bi14 (coating thickness 15-25 microns) and using a manual clamping device and an ST-944 infrared soldering station.

Table 1

Wire adhesion values (solder joint strength) of manufactured samples

Metallization FEP Wire, diameter 280 microns No paste applied Solder joint strength, N 99.0Sn0.3Ag0.7Cu 62Sn36Pb2Ag Sn63Pb37 Sn42Bi58 Finger mesh/basbar area With solder thickness 1520 microns (Sn60Pb40 alloy) 0.5-1.0 2.5 2.5 2.5 1.5 Finger net and pads With solder 0.0 1.0 2.0 1.5 1.0 Finter net/basbar area No solder 0.0 1.5 3.0 3.5 2.0 Finger net and pads No solder 0.0 1.0 2.0 2.5 1.0

The FEP sample, manufactured according to example 1 with contact pads printed with finger paste and applied with solder paste based on the alloy 99.0Sn0.3Ag0.7Cu, was laminated in a 3.2 mm glass/EVA laminating film (Lushan)/FEP/EVA laminating film structure (Lushan)/back protective sheet (Huitian). Also, using standard technology, a reference sample was produced that does not contain solder paste. A critical test that demonstrates the reliability of the module is the humidity heating test (under 85°C temperature and 85%RH humidity). After passing the test for 1000 hours (a requirement based on the IEC 61215-1:2021 standard), it was found that the sample manufactured using the proposed method has a 2.2% lower degree of power degradation, and there is no darkening along the soldered wire in the electroluminescence image, responsible for the development of corrosion in the solder joint (Table 2). Thus, the proposed method contributes to a significant increase in the reliability of solar modules.

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table 2

Electroluminescence images and power evolution data of solar module samples during a 1000 hour humidity heating test

Claims (2)

1. A method for switching photoelectric converters, including applying solder paste to the contact pads by screen printing and then soldering the wire to the surface of the contact pads; lead or lead-free pastes containing metals from the following are used as solder paste: tin, silver, copper, bismuth, cobalt , with a metal content of at least 90 vol.% and flux up to 10 vol.%. 2. The switching method according to claim 1, characterized in that mono-, polycrystalline silicon, and silicon using heterostructure technology are used as a photoelectric converter.