KR20120079590A - Solar cell module - Google Patents

Abstract

PURPOSE: A solar cell module is provided to prevent constant resistance from rising in an electrical contact with a solar cell by applying different adhesive materials on a first side and a second side of an inter-connector. CONSTITUTION: A first solar cell(10A) and a second solar cell(10B) are arranged to be adjacent each other. A first side of an inter-connector(20) is touched and connected to a direction crossing a first finger electrode. A second side of the inter-connector is electrically connected to a second back surface electrode. A first conductive adhesive material is applied to the first side. A second conductive adhesive material different from the first conductive adhesive material is applied to the second side.

Description

Solar cell module {SOLAR CELL MODULE}

The present invention relates to a solar cell module.

With the recent prediction of the depletion of existing energy resources such as oil and coal, the interest in renewable energy to replace them is increasing, and solar cell cells producing electric energy from solar energy are attracting attention.

The solar cell is used as a solar cell module of a waterproof type in the form of a panel (panel) after several are connected in series or in parallel to obtain a desired output.

In general, a solar cell module having solar cells includes a plurality of solar cells arranged at regular intervals, a shield that maintains a gap between adjacent solar cells, and electrically connecting electrodes of adjacent solar cells. An interconnector, an upper and lower protective film protecting the solar cells, a transparent member disposed on the protective film toward the light receiving surface of the solar cells, and a back sheet disposed under the lower protective film opposite the light receiving surface.

Here, the shield consists of an adhesive polyester tape, which is bonded to the ends of adjacent cells to maintain a constant gap between adjacent solar cells to maintain electrical insulation between adjacent cells. An interconnector for electrically connecting electrodes of adjacent cells is disposed on the shield.

An object of the present invention is to provide a solar cell module with improved efficiency.

One example of a solar cell module according to the present invention includes a substrate, an emitter portion positioned on an incident surface of the substrate to form a pn junction, and a finger electrode electrically connected to the emitter portion, and a substrate positioned on an opposite surface of the substrate incident surface. A first solar cell and a second solar cell including a back electrode electrically connected to and disposed adjacent to each other; An interconnector, the first surface of which is connected in contact with the first finger electrode of the first solar cell in a direction intersecting and the second surface of which is electrically connected to the second back electrode of the second solar cell; An electrically conductive first adhesive material is applied to the first surface of the second surface, and an electrically conductive second adhesive material different from the first adhesive material is applied to the second surface.

Here, the first adhesive material is applied only to a portion of the first side of the interconnector that corresponds to the incident side of the substrate, and the second adhesive material is a portion of the second side of the interconnector corresponding to the opposite side of the substrate incident side of the interconnector. Can only be applied.

Here, the first adhesive material may include silver (Ag) nanoparticles.

In addition, the second adhesive material may include at least one of Au, Ca, Ge, Cu, Fe, In, Mg, Ni, and Zn. In addition, the second adhesive material may further include at least one material of Sn, Pb, and Bi.

In addition, the width of the interconnector may be 1 mm or more and 2.5 mm or less.

Further, each of the first solar cell and the second solar cell may not include a front busbar that intersects the finger electrode and is parallel to the interconnector on the incident surface of the substrate.

In addition, each of the first solar cell and the second solar cell may not include a rear busbar parallel to the interconnector on the opposite side of the substrate incident surface.

In addition, the width of the portion of the interconnector contacting the first finger electrode may be wider than the width of the portion of the interconnector contacting the second back electrode.

The solar cell module according to an example of the present invention, as described above, by applying different adhesive materials to the first and second surfaces of the interconnector to prevent an increase in contact resistance during electrical connection with the solar cell. There is.

1 is a view for explaining an embodiment of a solar cell module according to an embodiment of the present invention.
3A and 3B are diagrams for explaining an example of the solar cell shown in FIG. 1.
4 to 6 are views for explaining the structure of the interconnector of the solar cell module according to an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In order to clearly illustrate the present invention in the drawings, portions not related to the description are omitted, and like reference numerals are given to similar portions throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. When a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case directly above another portion but also the case where there is another portion in between. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle.

Hereinafter, a solar cell module according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a view for explaining an embodiment of a solar cell module according to an embodiment of the present invention.

Referring to FIG. 1, the solar cell module 100 according to the embodiment of the present invention electrically connects a plurality of solar cells 10A, 10B, and 10C, and a plurality of solar cells 10A, 10B, and 10C to each other. Protective film (EVA) to protect interconnectors 20, solar cells 10A, 10B, and 10C (EVA) 30a and 30b, and a light shielding side toward the light receiving surface of solar cells 10A, 10B and 10C. The transparent member 40 disposed on the 30a, the back sheet 50 disposed below the protective film 30b on the opposite side of the light-receiving surface, and the frame accommodating the parts integrated by the lamination process (not shown). ) May be included.

The plurality of solar cells 10A, 10B, and 10C function to convert incident solar energy into electrical energy, and may include a first solar cell 10A and a second solar cell 10B. Here, the description of the solar cell according to the present invention will be described in more detail with reference to FIGS. 3 and 3B.

The back sheet 50 protects the solar cells 10A, 10B, 10C from the external environment by preventing moisture from penetrating at the back of the solar cells 10A, 10B, 10C. The back sheet 50 may have a multilayer structure such as a layer for preventing moisture and oxygen penetration, a layer for preventing chemical corrosion, and a layer having insulation properties.

The passivation layers 30a and 30b include an upper passivation layer 30a and a lower passivation layer 30b as shown in the drawing, and are formed by a lamination process in a state of being disposed above and below the solar cells 10A, 10B, and 10C, respectively. It is integrated with the solar cells 10A, 10B, and 10C to fill the space between the solar cells 10A, 10B, and 10C, and is cured through heat treatment. Such protective films 30a and 30b prevent corrosion due to moisture penetration and protect solar cells 10A, 10B and 10C from impact. The passivation layers 30a and 30b may be made of a material such as ethylene vinyl acetate (EVA).

The transparent member 40 is made of tempered glass having a high transmittance and an excellent damage prevention function. In this case, the tempered glass may be a low iron tempered glass having a low iron content. The transparent member 40 may be embossed with an inner surface to increase the light scattering effect.

The interconnector 20 is bonded to the front or rear of the solar cell through a tabbing process at a temperature of approximately 250 ° C to 350 ° C to electrically connect the solar cells 10A, 10B, and 10C to each other. , Formed of an electrically conductive material. The first surface of the interconnector 20 is coated with an electrically conductive first adhesive material, and the second surface is coated with an electrically conductive second adhesive material different from the first adhesive material.

As described above, the application of the metallic material to the interconnector 20 according to the present invention on the first and second surfaces is different because the materials in contact with the interconnector 20 are different from each other at the front and rear surfaces of the solar cell. By applying different metallic materials to the first side and the second side of the interconnector 20 according to the material properties of the, the adhesion between the solar cell side further improves between the interconnector 20 and the solar cell This is to minimize contact resistance.

By doing so, the interconnector in contact with the first side of the interconnector 20 in contact with the incident surface of the solar cell and the opposite side of the solar cell incident surface, while maintaining the electrical conductivity of the interconnector 20 in a good state ( The adhesion to the second side of 20) can be improved.

As described above, the plurality of solar cells 10A, 10B, and 10C are arranged in a matrix structure as shown in FIG. 1. In FIG. 1, the solar cells arranged on the lower passivation layer 30b have a 3 × 3 matrix structure, but are not limited thereto. The number of solar cells arranged in the row and column directions may be adjusted as necessary.

The plurality of solar cells 10A, 10B, 10C are electrically connected by the interconnector 20 as shown in FIG. More specifically, in a state in which the plurality of solar cells 10 are disposed adjacent to each other, the finger electrode 13 formed on the incident surface of one solar cell is electrically connected to the first surface of the interconnector 20. The back electrode 16 portion formed on the back of the solar cell is in contact with and electrically connected to the second surface of the interconnector 20.

3A and 3B are diagrams for explaining an example of the solar cell shown in FIG. 1.

As shown in FIG. 3A, the solar cell 10 according to the present invention may include a substrate 11, an emitter part 12, a finger electrode 13, an antireflection film 15, and a back electrode 16. Can be. Interconnect 20, 20 'is connected to the front or rear of the solar cell 10 as shown.

Here, the substrate 11 functions to convert light energy incident from the outside into electrical energy, and may be a semiconductor substrate made of silicon of a first conductivity type, for example, a p-type conductivity. In this case, the silicon may be monocrystalline silicon, polycrystalline silicon, or amorphous silicon. When the substrate 11 has a p-type conductivity type, it contains impurities of trivalent elements such as boron (B), gallium (Ga), indium (In), and the like.

Such a substrate 11 may be texturized to form irregularities as a texturing surface. When the surface of the substrate 11 is formed as a texturing surface, the light reflectance at the light receiving surface of the substrate 11 is reduced, and incident and reflection operations are performed on the texturing surface to trap light in the solar cell, thereby increasing light absorption. . Therefore, the reflection loss of the light incident on the substrate 11 is reduced, so that the amount of light incident on the substrate 11 may be further increased, and the efficiency of the solar cell may be further improved.

The emitter part 12 may be a second conductive type which is positioned on the light receiving surface of the substrate 11 to which light is incident and is opposite to the conductive type of the substrate 11. For example, the emitter portion 12 is a region doped with an impurity having an n-type conductivity type and forms a p-n junction with the semiconductor substrate 11. When the emitter portion 12 has an n-type conductivity type, the emitter portion 12 may be doped with impurities of a pentavalent element such as phosphorus (P), arsenic (As), antimony (Sb), and the like on the substrate 11. Can be formed.

Accordingly, when electrons in the semiconductor receive energy by light incident on the substrate 11, the electrons move toward the n-type semiconductor and the holes move toward the p-type semiconductor. Therefore, when the substrate 11 is p-type and the emitter portion 12 is n-type, the separated holes move toward the substrate 11 and the separated electrons move toward the emitter portion 12.

In contrast, the substrate 11 may be of an n-type conductivity type, and may be made of a semiconductor material other than silicon. When the substrate 11 has an n-type conductivity type, the substrate 11 may contain impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb).

Since the emitter 12 forms a p-n junction with the substrate 11, when the substrate 11 has an n-type conductivity type, the emitter 12 has a p-type conductivity type. In this case, the separated electrons move toward the substrate 11 and the separated holes move toward the emitter portion 12.

When the emitter portion 12 has a p-type conductivity type, the emitter portion 12 may dopant impurities of trivalent elements such as boron (B), gallium (Ga), indium (In), and the like onto the substrate 11. Can be formed.

The anti-reflection film 15 is positioned on the emitter portion 12 where the finger electrode 13 is not located, and functions to allow more light incident from the outside to enter the substrate 11. The anti-reflection film 15 may be formed of a silicon nitride film (SiNx), a silicon oxide film (SiO 2), or the like, and may reduce the reflectance of light incident on the solar cell 10 and increase selectivity in a specific wavelength region. Increase the efficiency of). The anti-reflection film 15 may have a thickness of about 70 nm to 80 nm, and may be omitted as necessary.

The plurality of finger electrodes 13 are formed on the emitter part 12 to be electrically connected to the emitter part 12, and are formed in one direction while being spaced apart from the adjacent finger electrodes 13. Each finger electrode 13 functions to collect charges, for example electrons, which have moved toward the emitter portion 12 and transfer them to the interconnector 20 in contact with the finger electrode 13.

The plurality of finger electrodes 13 are made of at least one conductive material, and the conductive materials include nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), and zinc (Zn). , At least one selected from the group consisting of indium (In), titanium (Ti), gold (Au), and combinations thereof, but may be formed of another conductive metal material. As an example, the solar cell according to the present invention will be described as an example that the finger electrode 13 contains silver (Ag) having good conductivity.

Each of the plurality of finger electrodes 13 may have a width in a range of 50 μm to 300 μm.

The rear electrode 16 is formed on the opposite side of the substrate 11 incident surface, that is, on the front surface of the rear surface of the substrate 11, and collects charges, for example, holes, moving toward the substrate 11.

The back electrode 16 is made of at least one conductive material. Conductive materials include nickel (Ni), copper (Cu), silver (Ag), aluminum (Al), tin (Sn), zinc (Zn), indium (In), titanium (Ti), gold (Au) and their It may be at least one selected from the group consisting of a combination, but may be made of other conductive materials.

As an example, the solar cell according to the present invention will be described as an example that the rear electrode 16 contains aluminum (Al) having good conductivity, relatively low cost, and good adhesion to a semiconductor substrate.

In addition, although not shown, the solar cell 10 may further include a back surface field (BSF) portion formed between the back electrode 16 and the substrate 11.

The backside electric field is a region in which impurities of the same conductivity type as the substrate 11 are doped at a higher concentration than the substrate 11, for example, a p + region. Such a backside electric field acts as a potential barrier for the substrate 11. Accordingly, the rear electric field reduces the electron and hole recombination and extinction at the rear side of the substrate 11 to improve the efficiency of the solar cell.

Operation of the solar cell 10 according to the present embodiment having such a structure is as follows.

When light is incident on the solar cell 10 and is incident on the substrate 11 through the antireflection film 15 and the emitter part 12, free electrons are generated by a photoelectric effect, and pn According to the principle of bonding, electrons move toward the emitter portion 12 having an n-type conductivity type, and holes move toward the substrate 11 having a p-type conductivity type. As such, the electrons moved toward the emitter part 12 move to the interconnector 20 which is collected by the finger electrode 13 and is electrically connected to the finger electrode 13, and moves to the substrate 11. Is collected by the rear electrode 16 and moves to the interconnectors 20 and 20 ', which are in contact with and are electrically connected to the rear electrode 16.

The solar cell 10 may be used alone, but for more efficient use, the solar cells 10A, 10B, and 10C having the same structure are connected in series to form a solar cell module.

Meanwhile, unlike the conventional solar cell, the solar cell 10 according to the present invention illustrated in FIG. 3A includes a front bus bar that intersects with the finger electrode 13 and is parallel to the interconnector 20 on the incident surface of the substrate. You can't.

Such front busbars typically use an electrode paste made of an expensive material such as silver (Ag). As described above, when the front busbar is omitted, the amount of the electrode paste forming the front busbar can be reduced. Since the process of forming the front busbar can be omitted, the manufacturing cost can be greatly reduced.

In addition, unlike the conventional solar cell, the solar cell 10 according to the present invention may not include a rear bus bar parallel to the interconnector 20 on the upper side of the substrate incident surface. Here, the rear busbar is disposed between the rear electrode 16 and the interconnector 20 to serve to make the interconnector 20 better contact the rear surface of the solar cell.

As such, when the rear busbar made of an expensive material such as silver (Ag) is removed from the solar cell, manufacturing cost can be reduced by reducing the amount of paste forming the rear busbar, as shown in FIG. 3B. The open voltage Voc can be further improved.

More specifically, in FIG. 3B, when A omits a rear bus bar and only the rear electrode 16 is formed, and B is a rear bus bar formed on a portion of the upper surface of the rear electrode 16, C is a portion of the rear electrode 16. In the case of removing the part and contacting the back of the substrate to form a dashed back busbar, D is a part of the rear electrode 16 is removed by a width of 2mm in the direction parallel to the interconnector 20, and contacting the back of the substrate This is the case where the rear busbar is formed to have a width of 2 mm, E is the same as D, and the rear busbar is formed to have a width of 3 mm and F is the same as D, and the rear busbar is formed to have a width of 4 mm.

According to FIG. 3B, when the rear bus bar is omitted from the rear of the substrate as shown in FIG. When the bar is formed, it can be seen that the open voltage Voc of the solar cell is smaller than that in the case of A omitting the rear bus bar.

As such, when the front busbar is omitted, when the interconnector 20 is connected in contact with the finger electrode 13 of the solar cell, the contact area may be smaller than that when the front busbar contacts the front busbar, thereby increasing the contact resistance. Therefore, in order to prevent such an increase in contact resistance, the first adhesive material which can be easily adhered to the material of the finger electrode 13 on the first surface of the interconnector 20 in contact with the finger electrode 13 is connected. By applying this, it is possible to further strengthen the adhesive force with the finger electrode 13 so that the contact resistance does not increase even though the contact area of the finger electrode 13 in contact with the first surface of the interconnector 20 is small. have.

In addition, as described above, when the interconnector 20 is directly contacted and electrically connected to the rear electrode 16 while the rear busbar is omitted, the rear busbar and the rear electrode 16 may use different materials. Even though the adhesion with the busbar is a good material, the adhesion with the rear electrode 16 may be poor. Therefore, by adhering a second adhesive material having a relatively good adhesive strength with the rear electrode 16 to the second surface, such as the interconnector 20 of the present invention, the adhesive force with the rear electrode 16 is improved to improve the interconnector. The contact resistance between the 20 and the back electrode 16 can be minimized.

In addition, the width WR of the interconnector 20 may be 1 mm or more and 2.5 mm or less. The width WR of the interconnector 20 to be 1 mm or more ensures the contact area of the interconnector 20 in contact with the finger electrode 13 or the rear electrode 16 of the solar cell to minimize the contact resistance. In order to minimize, the width WR of the interconnector 20 to be 2.5 mm or less is to minimize the area occupied by the interconnector 20 in the front of the solar cell.

Hereinafter, an electrical connection structure of the solar cell module will be described.

4 to 6 are views for explaining the structure of the interconnector 20 of the solar cell module according to an embodiment of the present invention.

As shown in FIG. 4A, the first adhesive material 20a is applied to the entire first surface of the interconnector 20 according to the present invention, and the second adhesive material ( 20b) is applied.

The interconnector 20 configured as shown in FIG. 4A has a direction in which the first surface intersects the first finger electrode 13A disposed on the front surface of the first solar cell 10A as shown in FIG. 4B. Are electrically connected in contact with each other, and the second surface thereof is electrically connected to the second back electrode 16B of the second solar cell 10B disposed on the rear surface of the second solar cell 10B.

Here, the first finger electrode 13A of the first solar cell 10A may contain silver (Ag) as described above, and the rear electrode 16 of the second solar cell 10B may be described as described above. It may contain aluminum (Al).

Here, the interconnector 20 may be formed of an electrically conductive material mainly containing copper (Cu), and the first adhesive material 20a applied to the first side of the interconnector 20 may be silver (Ag). Nanoparticles may be included in the form of a paste.

The silver (Ag) nanoparticles of the first adhesive material 20a may be easily adhered to the first finger electrode 13A when the tabbing process is performed, and the electrical conductivity is good to minimize contact resistance. It is possible to maintain the efficiency of the solar cell even if the contact area is small.

In addition, the first adhesive material 20a may also include a polymer binder in order to further improve the adhesive force of the first surface of the interconnector 20 to the first finger electrode 13A. Such a polymeric binder may be made of a material such as B 2 O 3, Bi 2 O 3, SnO, P 2 O 5, ZnO, PbO, and the like.

In addition, when the first side of the interconnector 20 is attached together to the remaining front surface of the first solar cell 10A, rather than when the first side of the interconnector 20 is bonded only to the first finger electrode 13A. The adhesion of the first surface of the interconnector 20 to the first finger electrode 13A can be further improved. Therefore, in consideration of this, the first adhesive material 20a may include glass frit. Such a glass frit has a low melting point and excellent adhesion, so that the first surface of the interconnector 20 can be easily adhered to the remaining portion of the first solar cell 10A without the first finger electrode 13A. .

Next, the second adhesive material 20b applied to the second surface of the interconnector 20 may include at least one of Au, Ca, Ge, Cu, Fe, In, Mg, Ni, and Zn. . Such electrically conductive metallic materials are metallic materials having an eutectic reaction at a relatively low temperature when bonded or mixed with an aluminum (Al) material included in the rear electrode 16 of the second solar cell 10B. Even in a tabbing process performed at a relatively low temperature, it can be easily adhered to aluminum (Al) material.

Therefore, at least one of Au, Ca, Ge, Cu, Fe, In, Mg, Ni, and Zn of the second adhesive material 20b has good adhesive strength with aluminum (Al) to minimize contact resistance. Thereby, the efficiency of the solar cell can be maintained satisfactorily.

In addition, the second adhesive material 20b may further include at least one material of Sn, Pb, and Bi. Materials such as Sn, Pb and Bi further lower the melting point of the second adhesive material 20b when used in combination with at least one of Au, Ca, Ge, Cu, Fe, In, Mg, Ni and Zn described above. There is an effect that can further improve the adhesion.

In addition, the second adhesive material 20b may also include a polymer binder or glass frit as described above in the first adhesive material 20a.

In addition, in order to further reduce the manufacturing cost of the solar cell, as shown in FIGS. 5A and 5B, the first adhesive material 20a of the interconnector 20 is the interconnector 20. Is applied only to a portion of the first side of the substrate corresponding to the incident surface of the substrate, and the second adhesive material 20b of the interconnector 20 is opposite to the substrate incident surface of the second surface of the interconnector 20. It may also be applied only to the corresponding portions.

In this way, the first adhesive material 20a is applied only to a portion of the first surface of the interconnector 20 that is substantially in contact with the first finger electrode 13A, and the second adhesive material ( 20b) may be applied only to a portion substantially contacting the second rear electrode 16B, so that the first adhesive material 20a and the second adhesive material ( By reducing the amount of use 20b) it is possible to reduce the manufacturing cost.

In addition, as shown in FIG. 6, the interconnector 20 of the solar cell according to the present invention contacts the width W1 of the portion contacting the first finger electrode 13A to the second rear electrode 16B. It may be formed wider than the width W2 of the portion.

By doing in this way, the area of the part which contacts the 1st finger electrode 13A in the interconnector 20 can be made relatively larger, and it can further prevent that a contact resistance increases.

As such, the present invention allows the first and second surfaces of the solar cell to be coated with different adhesive materials according to the material properties of the front and rear surfaces of the solar cell even when there are no bus bars on the front and rear surfaces of the solar cell. Even without the bar, the contact resistance between the interconnect and the solar cell can be minimized.

It will be apparent to those skilled in the art that various modifications, substitutions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (9)

A substrate, an emitter portion positioned on an incident surface of the substrate to form a pn junction with the substrate, a finger electrode electrically connected to the emitter portion, and positioned on an opposite surface of the substrate incident surface and electrically connected to the substrate A first solar cell and a second solar cell including a back electrode and disposed adjacent to each other;
An interconnector having a first surface in contact with and intersecting with a first finger electrode of the first solar cell and a second surface electrically connected to a second rear electrode of the second solar cell;
The first surface of the interconnector is coated with an electrically conductive first adhesive material, and the second surface is coated with an electrically conductive second adhesive material different from the first adhesive material. Battery module. The method of claim 1,
The first adhesive material is applied only to a portion of the first surface of the interconnector corresponding to the incident surface of the substrate,
And the second adhesive material is applied only to a portion of the second surface of the interconnector corresponding to the opposite surface of the substrate incident surface. The method of claim 1,
The first adhesive material is a solar cell module, characterized in that it comprises silver (Ag) nanoparticles. The method of claim 1,
The second adhesive material is a solar cell module, characterized in that it comprises at least one of Au, Ca, Ge, Cu, Fe, In, Mg, Ni, Zn. The method of claim 4, wherein
The second adhesive material further comprises at least one material of Sn, Pb, Bi. The method of claim 1,
The interconnector is a solar cell module, characterized in that 1mm or more and 2.5mm or less. The method of claim 1,
Each of the first solar cell and the second solar cell does not include a front busbar crossing the finger electrode and parallel to the interconnector on an incident surface of the substrate. The method of claim 1,
And each of the first solar cell and the second solar cell does not include a rear busbar parallel to the interconnector on an upper side of the substrate incident surface. The method of claim 1,
And a width of a portion of the interconnector in contact with the first finger electrode is wider than a width of a portion of the interconnector in contact with the second back electrode.

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