Metallization screen for interdigitated back contact solar cells

Abstract

The invention relates to a metallization screen developed for interdigitated back contact (IBC) solar cells. The invention particularly relates to a screen developed for the production of highly efficient and inexpensive cells without the use of insulating material in the metallization process, which is the last link in the production of IBC-type solar cells.

Description

[0001] METALLIZATION SCREEN FOR INTERDIGITATED BACK CONTACT SOLAR

[0002] CELLS

[0003] Technical Field

[0004] The invention relates to a metallization screen developed for interdigitated back contact (IBC) solar cells.

[0005] The invention particularly relates to a screen developed for the production of highly efficient and inexpensive cells without the use of insulating material in the metallization process, which is the last link in the production of IBC-type solar cells.

[0006] State of the Art

[0007] Interdigitated back contact solar cells are a photovoltaic technology developed in order to optimize solar energy collection and conversion processes. Compared to conventional solar cells, these cells have a special structure and are specially designed for higher efficiency and energy obtaining. Their interdigitated layers of materials such as silicon are characterized by their ability to absorb more light from a wide solar spectrum. In addition, their back contact allows them to collect more energy by fully exposing their front surface to light. With these features, interdigitated back contact solar cells are considered an important step forward in solar technology and hold great potential for future energy efficiency and conversion.

[0008] Metallization, the final processing step in the interdigitated back contact solar cells, is an important step that provides electron conductivity and improves the electrical performance of the solar cell. This process is usually carried out by silk-screening, a specialized printing technique. Silk-screening is a method used to apply a layer of metal to the back surface of the solar cell. Highly conductive metals such as silver or aluminum are usually preferred for this purpose. These metal layers provide electrical conduction by connecting the different cell layers inside the interdigitated structure. The metallization process must be very precise in order to create a pathway through which electrons can move freely, and an electric current can be generated. It is also important that these metal layers are properly bonded in order to increase the efficiency and durability of the cell, and to ensure the resistance of the cell to mechanical stress. This metallization plays a critical role in improving the performance and overall efficiency of interdigitated back contact solar cells. In the present system, there are various patents and utility model applications related to the production methods of interdigitated back contact solar cells. One of them is the application numbered “WO 2011 / 011855 Al”. The application relates to photovoltaic cells and more particularly to high-efficiency back contact photovoltaic cells. In the prior art of the present invention, it is described that the electrical contacts on the front side surface are typically arranged in a plurality of parallel, spaced-apart strips or grid lines extending across the entire front side surface. The strips are formed by silk-screening a metal paste in a desired pattern on the front side surface, allowing it to spread over the front side surface, and leaving a portion of the solidified paste on the surface to act as a finger. The system disclosed in the invention comprises an electrically insulating film having an electrode, a surface having an adhesive layer thereon, and first and second opposed ends.

[0009] The application numbered “CN206639804U” in the state of the art, relates to the field of solar batteries, in particular to a punching PERC double-sided solar battery and a solar battery module adopting the punching PERC double-sided solar battery and a solar energy system utilizing the punching PERC double-sided solar cell. The technical problem to be solved by the utility model is to provide a punching PERC double-sided solar battery having the advantages of simple structure, low cost, easy dissemination and greatly improved photoelectric conversion efficiency. The size of the light-transmitting zone is smaller than the width of the aluminum bottom passage and larger than the width of the silver bottom passage. The width of the rear aluminum sub-grating is 150-5.5 cm, and the width of the positive silver secondary grating is 30-80 microns.

[0010] The application numbered “WO2017093527A1” in the state of the art, relates to a solar panel arrangement provided with an interconnection of a back contact solar cell to a patterned conductive backsheet. The solar cell comprises a semiconductor substrate of a base conductivity type and a base doping level, having a front surface for receiving radiation and a rear surface. Here, the solar cell is of the IBC-type with interdigitated back contacts, and the doped layer area of the first type is arranged between any of the neighboring second types on the back surface of the substrate. The intermediate conductive body is selected from the group consisting of an electrically conductive adhesive, a composite or a mixture of non-conductive filler material and conductive material, a solder. In the present system, the current-carrying metals are printed thicker to reduce the series resistance, but this reduces the series resistance while reducing the active area of the cell, thus reducing the efficiency. In cases where insulation material is not used, the problem is solved by placing distances close to 1 mm between metals of different polarity, but this distance increases the distance that the carrier charges need to move, resulting in series resistance. In addition, as an alternative to silk-screening, high yields have been achieved in cells where metallization is performed by electroplating, but compared to silk-screening, it is impractical to use this method in industrial sizes and requires extra processes, making production difficult.

[0011] As a result of the above and the inadequacy of existing solutions, there is a need for an improved screen for high efficiency and inexpensive cell production.

[0012] Brief Description and Objects of the Invention

[0013] The invention relates to a metallization screen for interdigitated back contact (IBC) solar cells. The invention particularly relates to a screen developed for highly efficient and inexpensive cell production without the use of insulating material in the metallization process, which is the last link in the production of IBC-type solar cells.

[0014] The object of the invention is to eliminate the need for insulating material used to prevent the contact areas of different polarities from coming into contact with each other. With the invention, a screen has been developed for highly efficient and inexpensive cell production without the use of insulation material in the metallization process, which is the last link in the production of IBC-type solar cells. The developed screen has also been made suitable for industrial production by silk-screening.

[0015] Another object of the invention is to shorten the distance of the current that the metals must carry and to reduce the series resistance.

[0016] Figures

[0017] Figure-1 : A view of the silk-screening design in which the aluminum metal is used for the emitter.

[0018] Figure-2: A view of silver busbar, aluminum busbar, aluminum strip and silver strip. Figure-3: A view of the silk-screening design in which the silver / aluminum metal is used for the emitter.

[0019] Figure-4: A view of the silk-screening design in which the silver or aluminum strip is used. References

[0020] In order to better explain the metallization developed with this invention, the parts and elements in the figures are numbered and the equivalent of each number is given below:

[0021] 1. Silver busbar

[0022] 2. Aluminum busbar

[0023] 3. Aluminum finger

[0024] 4. Silver finger

[0025] 5. Silver aluminum alloy finger

[0026] A. Connection zone

[0027] Detailed Description of the Invention

[0028] The invention relates to a metallization screen for interdigitated back contact (IBC) solar cells. The invention particularly relates to a screen developed for highly efficient and inexpensive cell production without the use of insulating material in the metallization process, which is the last link in the production of IBC-type solar cells. The screen is applied to the surfaces of the cell by silk-screening.

[0029] Said screen comprises at least one silver busbar (1) placed on each edge and / or corner of the cell surface area where the sun is not directly shining to transfer the electricity obtained from the solar cell to the external circuit; at least one aluminum busbar (2), by being positioned in the connection zone (A), that allows the aluminum finger (3) and the silver finger (4) to be connected to each other and thus transfer the electricity obtained from the solar cell to the external circuit; aluminum busbars (2) placed at the edges or corners of the rear surface area of the cell using silver paste, located at the connection points of the aluminum finger (3) and silver finger (4); at least one aluminum finger (3) and at least one silver finger (4) parallel to each other, placed on the surface of the semiconductor material that provides electrical conductivity in the zones where sunlight interacts to collect electrons and generate current, and that absorbs light in the cell to collect sunlight and facilitate the movement of electrons. In the solar cell, the surface where the sun does not shine directly is the back surface and the surface where it shines directly is the front surface.

[0030] The silver fingers (4) extend parallel to the surface of the solar cell and are placed on semiconductor layers. They are located where the sunlight falls on the cell and generate the electric current. Aluminum busbars (2) collect the fingers and connect the cell to the external circuit. These busbars are located on the outer edges or corners of the cell. They transfer the energy obtained from the solar cell to the external circuit thanks to the conductive structures they form by connecting the fingers together.

[0031] As shown in Figure-2, there are aluminum busbars (2) and silver busbars (1) for the thicker metal zones, 6 for the emitter and 6 for the backside area. Their thickness is 500 gm (0.5 mm), which is the approximate thickness preferred by industrial counterparts and tested in simulations. The aluminum fingers (3) are interdigitated and thinner, while the silver fingers (4) have two different thicknesses, 40 gm (0.04 mm) and 60 gm (0.06 mm), using silver paste for the back surface area. The 40 pm (0.04 mm) design targets high currents and voltages, while the 60 pm (0.06 mm) design achieves high fill factor values by reducing the series resistance and avoiding the breakage problem that can occur in thin prints during metallization.

[0032] For the transmitter region, there are two cases where both the aluminum metal and the silveraluminum alloy finger (5) are used, as shown in Figure-4. In the case where the silver and aluminum alloy finger (5) is used, the thicknesses of the silver aluminum alloy finger (5) and the silver finger (4) are 40 gm (0.04 mm) and 60 gm (0.06 mm) for the same reasons. In the case where aluminum metal is used, the thickness of the aluminum finger (3) was developed as 400 gm.

[0033] In the case where aluminum metal is used, openings in the dielectric layer must be created by laser ablation before silk-screening in order to create contact zones. Regardless of the thickness of the aluminum metal, the laser-ablated zones are important. This paves the way for efficient cell results with fewer contact zones and higher active zones compared to both silver and silver / aluminum alloys. The reason for the thicker strip thickness is that the conductivity of aluminum is lower than that of silver and for this reason, the series resistance is reduced with thicker strips.

[0034] In the metallization screen, silver and aluminum alloy fingers (5) and silver fingers (4) pass through the silicon nitride layer during the annealing process to make direct contact with the transmitter and BSF zones. The emitter zones are metalized, especially depending on the solar cell configuration. This metallization process is usually performed to provide the electrical connections of the solar cell and to collect the electric current. The screen in the transmitter zones helps to collect electrons and improve electrical conduction.

[0035] On the other hand, the silver busbar (1) and silver / aluminum busbar zones are printed separately using floating paste, so that the metal cannot pass through the silicon nitride layer in these zones and does not form si-metal interaction zones. In this way, both metal-induced recombination reduction is achieved and at the same time, it ensures high short circuit resistance by not contacting zones of opposite polarity. By removing the contact with aluminum-silver paste from the boron-doped transmitter zones, it allows the use of fingers with thinner thickness. This means that the back side of the double-sided IBC will receive more light.

[0036] For the connection points of the busbars (aluminum busbars (2) and silver busbars (1)) and fingers (aluminum finger (3) and silver finger (4)), the structure extending from the busbars to the fingers was followed. A 2 mm x 2 mm zone was left at the end of each busbar (aluminum busbars (2) and silver busbars (1)) for solder removal from the cells at the module stage. On a silicon slice, the half-cut model, which is also followed in the industry, was preferred. A 0.4 mm free space was left at the center of the silicon slice separating it into two zones.

[0037] With the screen developed with the invention, there is no need for the insulation material used to prevent the contact areas of different polarities from coming into contact with each other. At the same time, it is also suitable for industrial production by silk-screening. The distance of the current that the metals must carry is shortened and the series resistance is reduced. In the industrial screen design, aluminum paste was used instead of aluminum-silver paste for the p+ transmitter zones. Before the metallization process, local openings are made under the aluminum metal with the help of a laser and the aluminum metal is allowed to make contacts through these openings. The use of thicker metal reduces the light to be received from the back side, but thanks to the local contacts, the si-metal interaction is reduced, and efficiency is increased. Aluminum fingers (3) and aluminum busbars (2) were developed in the same way as described above, with the only difference being their thickness. In the industrial screen, the thickness of the aluminum fingers (3) is 400 pm and the thickness of the aluminum busbars (2) is 800 pm. The reason for this is that the conductivity of aluminum metal is lower than that of silver metal and is intended to facilitate the optimization of local laser openings.

[0038] With the screen, material consumption has been reduced, and the duration of silk-screening has been reduced. In addition, in interdigitated IBC cells, the ends of the cell have been joined to ensure the connection between the metallic zones and wide solder points have been developed to provide flexibility in cell measurements.

[0039] While developing the screen, various simulation programs were used, and measurements of previously designed designs were taken and analyzed. These analyses were also compared with the simulation data.

Claims

CLAIMS1. A metallization screen for interdigitated back contact solar cells, characterized in comprising;• At least one aluminum finger (3) having a thickness of 0.04 mm and at least one silver finger (4) having a thickness of 0.06 mm parallel to each other, placed on the surface of the semiconductor material that provides electrical conductivity in the zones where sunlight interacts to collect electrons and generate current, and that absorbs light in the cell to collect sunlight and facilitate the movement of electrons,• At least one silver busbar (1) placed on each edge and / or corner of the cell surface where the sun is not directly shining to transfer the electricity obtained from the solar cell to the external circuit,• At least one aluminum busbar (2), positioned in the connection zone (A), which allows the aluminum finger (3) and the silver finger (4) to be connected to each other and thus transfer the electricity obtained from the solar cell to the external circuit.

2. The metallization screen according to claim 1, wherein the thickness of silver busbar (1) is0.5 mm.

3. The metallization screen according to claim 1, wherein the thickness of aluminum busbar (2) is 0.5 mm.

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