JP6044503B2 - Conductive adhesive film and multi-junction solar cell using the same - Google Patents

Description

  The present invention relates to a conductive adhesive film suitably used for a multi-junction solar cell that can effectively use sunlight in the near-infrared region, and a multi-junction solar cell using the same.

  A solar cell that converts sunlight energy into electric energy can improve conversion efficiency by forming a multi-junction solar cell having a tandem structure by stacking power generation layers having different spectral sensitivities. In this multi-junction solar cell, power generation layers having a large band gap (absorbing short wavelengths) as viewed from the sunlight incident side are sequentially stacked from a power generation layer having a small band gap (absorbing long wavelengths).

  There are a monolithic type and a mechanical stack type as an electrical connection method between the stacked power generation layers. The monolithic solar cell has a two-terminal structure having metal electrodes at both ends, and is a method in which an n + / p + tunnel diode is sandwiched between a power generation layer having a pn junction and a power generation layer having a pn junction. Generally, it is formed using a thin film growth technique.

  On the other hand, a mechanical stack type solar cell has a multi-terminal structure having metal electrodes between both ends and a power generation layer, and is formed by mechanically bonding two separately formed solar cells. A cell in which a pn junction and a (minus) metal electrode are sequentially stacked on a positive electrode is a cell with a large band gap (absorbs short wavelengths) to a power generation cell with a small band gap (long). Are sequentially laminated (see Patent Documents 1 to 4).

  In the monolithic solar cell, the subsequent layers must be stacked in consideration of the physical properties of the previously stacked layers. For example, if the upper limit of the stable temperature of the semiconductor layer laminated earlier is lower than the optimum lamination temperature of the semiconductor layer laminated later, the semiconductor layer laminated later is laminated first at the optimum temperature. There is a problem that the semiconductor layer deteriorates. On the other hand, in a mechanical stack type solar cell, since two solar cells are formed separately, each solar cell can be formed under different conditions.

  However, in the mechanical stack type solar cells described in Patent Document 1 and Patent Document 2, each solar battery cell is mechanically joined with an insulating transparent epoxy resin or the like, and the electrical connection between the solar battery cells is Absent. Therefore, the electrode of each photovoltaic cell must be taken out from the junction, resulting in a multi-terminal structure. In a solar battery having such a multi-terminal structure, when the area of the solar battery cell is large, the distance from the center of the solar battery cell to the outside of the electrode is increased, so that the electrical resistance increases and the power loss increases. The problem of becoming larger arises. In addition, since an extra space for taking out and connecting the electrodes to the outside is necessary, there is a problem that the size of the element increases.

  The mechanical stack type photoelectric conversion device of Patent Document 3 enables optical and electrical bonding by bringing transparent conductive films into close contact with each other. However, in order to improve the mechanical bonding strength, there is a problem that the degree of structural freedom such as the type of transparent conductive film that can be bonded and the flatness of the transparent conductive film is very small.

  In Patent Document 4, a multijunction solar cell has a structure in which two or more solar cells having different spectral sensitivities are optically and electrically connected in series via an anisotropic conductive adhesive layer. Proposed. The conductive fine particles include solder balls, copper, nickel, graphite, silver, aluminum, tin, gold, and platinum fine particles, alloy fine particles made of a plurality of different metals, fine particles such as polystyrene and acrylic, such as gold and nickel. There have been proposed ones covered with a metal thin film, fine particles of conductive oxide, fine particles of conductive semiconductor, and the like.

  However, although metal particles are excellent in electrical conductivity, there is a problem in sunlight transmittance. Conductive oxide particles represented by ITO (tin-added indium oxide) and ATO (antimony-added tin oxide) generally have high transmittance in the visible light region, but they absorb in the near infrared region due to free electron plasmon absorption. In addition, there is a problem that a solar cell (absorbing a long wavelength) far from the light-receiving surface has a problem that the long-wavelength light is absorbed by the conductive oxide particles in the middle and the amount of power generation is reduced.

  On the other hand, in Patent Documents 5 and 6, as an oxide transparent electrode film having excellent transmittance in the infrared region as well as the visible light region and having a low resistance value, indium oxide containing titanium is used as a main component, Indium oxide is crystalline, and the indium oxide indium oxide is replaced with titanium at a titanium / indium atomic ratio of 0.003 to 0.120, and the oxide transparent electrode film of Ti-added indium oxide, An oxide transparent electrode film of W-added indium oxide containing tungsten W having an atomic ratio of tungsten / indium of 0.001 to 0.17 is disclosed.

JP-A-6-283737 JP-A-7-122762 JP-A-64-41278 WO2011 / 024534 International Publication Pamphlet JP 2004-207221 A JP 2004-091265 A

  The present invention has been made to solve the above-described problem, and is a conductive adhesive film suitably used for a multi-junction solar cell that can effectively use sunlight in the near infrared region, and a multiplicity using the same. It aims at providing a junction type solar cell.

  In view of the above situation, the present inventor has conducted extensive research on a conductive adhesive film that can effectively use sunlight in the near-infrared region, and as a result, has been oxidized by adding tungsten (W) and / or titanium (Ti). It has been found that by using indium fine particles, absorption in the infrared light region can be suppressed in the conductive adhesive film, and further the conversion efficiency of the solar cell can be improved, and the present invention has been completed.

That is, the first invention of the present invention is a conductive adhesive film for connecting between solar cells of a mechanical stack type solar cell,
Containing an insulating adhesive and conductive particles;
The conductive particles are particles having at least a Ti-added indium oxide containing Ti of 0.003 to 0.120 in Ti / In atomic ratio and / or 0.001 in W / In atomic ratio. The conductive adhesive film is a particle having at least a surface layer of W-added indium oxide containing 0.17 W.

The second invention of the present invention is a mechanical stack type multi-junction solar cell formed by laminating a plurality of solar cells having different spectral sensitivities,
The multi-junction solar cell according to claim 1, wherein the conductive adhesive film according to claim 1 is disposed in at least one place between the adjacent solar cells.

  According to the present invention, by using Ti-added indium oxide particles containing Ti or W-added indium oxide particles containing W as the conductive particles of the conductive adhesive film, sunlight in the near infrared region is effectively used. A conductive adhesive film suitably used for a multi-junction solar cell that can be produced and a multi-junction solar cell using the same are obtained.

  The conductive adhesive film according to the present invention is for optically and electrically connecting between solar cells of a mechanical stack type solar cell. And this electroconductive adhesive film contains an insulating adhesive agent and electroconductive particle at least.

<Insulating adhesive>
Although there is no restriction | limiting in particular as a component of an insulating adhesive agent, From a viewpoint of connection reliability, it is preferable to use a thermosetting resin.

  Known thermosetting resins can be used, for example, epoxy resins, phenoxy resins, acrylic resins, polyimide resins, polyamide resins, polycarbonate resins, etc. Among them, the viewpoint of obtaining more sufficient connection reliability Therefore, it is preferable to include at least one of an epoxy resin, a phenoxy resin, and an acrylic resin.

  From the viewpoint of resin fluidity and film physical property control, the conductive adhesive film preferably contains a rubber component as a component of the insulating adhesive. As the rubber component, known materials can be used. Examples thereof include acrylic rubber, butyl rubber, silicone rubber, urethane rubber, and fluororubber, and are miscible with thermosetting resin and adherence to an adherend. In view of the above, acrylic rubber is preferable.

The compounding amount of the rubber component is preferably 9 to 34% by mass based on the total amount of the insulating adhesive. The amount of the rubber component is 9 to 34 based on the total amount of the insulating adhesive.
If it is% by mass, the adhesion between the conductive adhesive film and the adherend is excellent, and the physical fluctuation of the adherend due to environmental changes is also good, so that poor connection between the adherends is sufficient. Can be suppressed.

<Conductive particles>
As the conductive particles, it is desirable that the visible light and near-infrared region have high transmittance and high electrical conductivity. Metal particles such as solder balls, copper, nickel, graphite, silver, aluminum, tin, gold, and platinum fine particles are excellent in electrical conductivity, but have a problem in sunlight transmittance.

  Conductive oxide particles represented by ITO (tin-added indium oxide) and ATO (antimony-added tin oxide) generally have high transmittance in the visible light region, but they absorb in the near infrared region due to free electron plasmon absorption. In addition, in the solar battery cell (absorbing the long wavelength) far from the light receiving surface, the light having a long wavelength is absorbed by the conductive oxide particles, and the amount of power generation is reduced.

  The electrical conductivity σ is expressed by σ = e × n × μ (e: elementary electric quantity, n: carrier concentration, μ: mobility). In order to suppress near-infrared absorption, the carrier concentration n is lowered. Although it is necessary, decreasing the carrier concentration n decreases the electrical conductivity σ. In order to solve this, it is effective to use a material having a high mobility μ.

  Here, as described above, according to Patent Documents 5 and 6, it is known that when W or Ti is added to an indium oxide thin film, the mobility is improved. This time, the present inventors succeeded in achieving the knowledge obtained in the conductive thin film also in the conductive “particles”, and further dispersing the particles in a binder to form a film, The present invention is characterized in that it is applied as a conductive adhesive film between battery cells.

  Specifically, particles having at least a surface layer of Ti-added indium oxide containing Ti of 0.003 to 0.120 in Ti / In atomic ratio, and / or 0.001 to 0 in W / In atomic ratio. It was found that a conductive adhesive film having high transmittance in the visible light and near-infrared region and high electrical conductivity can be produced if the particles have at least a surface layer containing W-added indium oxide containing W of .1. is there.

  Here, the particles having at least the surface layer of Ti-added indium oxide or the particles having at least the surface layer of W-added indium oxide may be composed of Ti-added indium oxide or W-added indium oxide, such as polystyrene. The surface of inorganic particles such as resin particles and barium sulfate may be coated with the above-described layer of Ti-added indium oxide or W-added indium oxide.

  Specifically, for example, a method of obtaining conductive oxide particles by coating the surface of inorganic oxide particles described in JP-A-8-175815 with a conductive inorganic oxide, or described in JP-A-6-329415. Electrolysis using an alloy of indium and tin as an anode, and calcining the obtained mixed precipitate of indium hydroxide and metastannic acid to obtain indium oxide-tin oxide particles, and JP2009-123458A In the method of obtaining indium oxide-tin oxide particles by mixing a mixed aqueous solution of an aqueous solution of indium salt and an aqueous solution of tin salt and an alkaline aqueous solution and calcining a hydroxide obtained by coprecipitation reaction, It can be obtained by replacing with a Ti source or a W source.

  The average particle size of the conductive particles is preferably 1 μm or more and 40 μm or less. When the average particle diameter of the conductive particles is small, the conductive particles are buried in the concave portions of the uneven electrode surface, and therefore it is preferably 1 μm or more. When the average particle diameter of the conductive particles is large, the thickness of the conductive adhesive film increases and the amount of light absorption increases, so that the thickness is preferably 40 μm or less.

<Conductive adhesive film>
The conductive particles of the present invention are obtained by dispersing the conductive particles in the insulating adhesive by a conventionally known method to obtain a conductive adhesive composition, and forming a film by a conventionally known method. An adhesive film can be obtained.

  The content of the conductive particles in the conductive adhesive composition is preferably 1% by volume or more based on the total solid content of the conductive adhesive composition in order to extrude the resin and make electrical contact, and the amount of the resin When there is little, since adhesiveness falls, 12 volume% or less is preferable.

  The thickness of the conductive adhesive film is preferably 5 μm or more, and preferably 100 μm or less in terms of the surface roughness of the adherend and the conductive particle diameter.

  The transmittance of visible light and near infrared region of the conductive adhesive film of the present invention is as high as 86% or higher at a wavelength of 1000 μm, and at the same time, high conductivity of 1 S / cm is obtained as electrical conductivity. A conductive adhesive film having both high light transmittance and high conductivity can be obtained.

<Multi-junction solar cell>
The multi-junction solar cell according to the present invention is a multi-junction solar cell in which a plurality of solar cells having different spectral sensitivities are stacked and optically and electrically connected, and between adjacent solar cells. The conductive adhesive film according to claim 1 is disposed in at least one place.

  More specifically, at least the solar cell at the end opposite to the light incident side has a conductive adhesive film on the uppermost layer on the connecting side, and the other solar cells are on the connecting side. The structure which has a conductive adhesive film in the uppermost layer and the lowermost layer, respectively, and joined the uppermost layer and the lowermost layer with the conductive adhesive film can be illustrated.

  The solar cell constituting the multi-junction solar cell may be any cell as long as the band gap is larger on the side closer to the light receiving surface and the band gap becomes smaller as the distance increases.

  As the solar cell, a crystalline Si solar cell, a thin-film Si solar cell, a III-V group compound solar cell, a CdTe solar cell, a chalcopyrite solar cell (CIGS, CZTS, etc.) and the like are used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example at all.

[Example 1]
<Preparation of conductive adhesive film>
First, an acrylic rubber obtained by copolymerizing 40 parts by mass of butyl acrylate, 30 parts by mass of ethyl acrylate, 30 parts by mass of acrylonitrile, and 3 parts by mass of glycidyl methacrylate was prepared. 125 g of this acrylic rubber and 50 g of phenoxy resin were dissolved in 400 g of ethyl acetate to obtain a 30% solution. Next, 325 g of liquid epoxy containing a microcapsule-type latent curing agent was added to the above solution and stirred to obtain an adhesive composition.

To this adhesive composition, conductive particles having an average particle diameter of 2 μm (Ti-added indium oxide containing Ti of 0.003 in Ti / In atomic ratio) were dispersed to obtain a conductive adhesive composition. . At this time, the content of the conductive particles is 5 based on the total solid content of the conductive adhesive composition.
It mix | blended so that it might become volume%.

  The obtained conductive adhesive composition was applied onto a polyethylene terephthalate film using an applicator and dried on a hot plate at 70 ° C. for 3 minutes to prepare a 25 μm conductive adhesive film. The film thickness was adjusted by changing the gap of the applicator. At this time, the gap was adjusted from the relational expression between the gap and the film thickness after drying so that a desired film thickness was obtained.

<Production of multi-junction solar cell>
Amorphous Si thin film solar cell (AR coat layer / glass / TCO / a-Si: H (pi-in) / TCO) and heterojunction solar cell (TCO / a-Si: H (pi)) / C-Si (n-type) / Al), a conductive adhesive film is placed, and then crimped at 170 ° C. and 2 MP for 20 seconds to optically and electrically connect the solar cells and solar cells. A multi-junction solar cell was obtained.

[Measurement of transmittance of conductive adhesive film]
The transmittance of the conductive adhesive film was measured using a spectrophotometer (U-4000 manufactured by Hitachi, Ltd.). The results are shown in Table 1.

[Measurement of conversion efficiency of multi-junction solar cells]
The conversion efficiency of the multi-junction solar cell was measured by irradiating light of 100 mW / cm 2 with a solar simulator and obtaining the conversion efficiency from current-voltage measurement at that time. The results are shown in Table 1.

[Example 2]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were Ti-added indium oxide containing Ti having an atomic ratio of Ti / In of 0.01. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 3]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were Ti-doped indium oxide containing 0.05 Ti in an atomic ratio of Ti / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 4]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were Ti-added indium oxide containing Ti having an atomic ratio of Ti / In of 0.1. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 5]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were Ti-added indium oxide containing 0.12 Ti in Ti / In atomic ratio. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 6]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were changed to W-doped indium oxide containing 0.001 W in atomic ratio of W / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 7]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were changed to W-added indium oxide containing 0.01 W in the atomic ratio of W / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 8]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were changed to W-added indium oxide containing 0.05 W in atomic ratio of W / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 9]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were changed to W-doped indium oxide containing 0.1 W in atomic ratio of W / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Example 10]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner as in Example 1 except that the conductive particles were changed to W-doped indium oxide containing 0.17 W in atomic ratio of W / In. . The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. Table 1 shows the measurement results of the transmittance of the conductive adhesive film and the conversion efficiency of the multi-junction solar cell.

[Comparative Example 1]
A conductive adhesive film and a multi-junction solar cell were produced in the same manner except that the conductive particles were changed to ITO in Example 1. The transmittance of the produced conductive adhesive film and the conversion efficiency of the multi-junction solar cell were measured in the same manner as in Example 1. The transmittance measurement results of the conductive adhesive film are shown in Table 1. Table 1 shows the measurement results of the conversion efficiency of the multijunction solar cell.

  From the results in Table 1, it can be understood that in the conductive film of the present invention, a solar cell having a high transmittance at a wavelength of 1000 nm and a high conversion efficiency of 14% or more is obtained.

Claims (3)

A conductive adhesive film for connecting between solar cells of a mechanical stack type solar cell,
Containing an insulating adhesive and conductive particles;
The conductive particles are particles having at least a Ti-added indium oxide containing Ti of 0.003 to 0.120 in Ti / In atomic ratio and / or 0.001 in W / In atomic ratio. A conductive adhesive film, wherein the conductive adhesive film is a particle having at least a surface layer of W-added indium oxide containing 0.17 W. The conductive adhesive film according to claim 1, wherein the insulating adhesive contains acrylic rubber. A mechanical stack type multi-junction solar cell in which a plurality of solar cells having different spectral sensitivities are stacked,
The multi-junction solar cell, wherein the conductive adhesive film according to claim 1 or 2 is disposed at least at one or more locations between the adjacent solar cells.