Photovoltaic device

Abstract

The present invention relates to a photovoltaic device (1a) comprising a solar cell unit (2a) including a working electrode with a light-absorbing layer (3), a counter electrode including a porous conductive layer (6), and a conductive medium for transferring charges between the counter electrode and the working electrode, and a conductor (7) electrically connected to the porous conductive layer (6). The solar cell unit (2a) also comprises at least one adhesive layer (8) disposed between the conductor (7) and the porous conductive layer (6) for attaching the conductor to the porous conductive layer. The adhesive layer (8) comprises an adhesive and conductive particles distributed in the adhesive to form a conductive network.

Description

Technical Field

[0001] Technical Field The present invention relates to a photovoltaic device. More specifically, the present invention relates to a photovoltaic device including a conductive layer and a conductor attached to the conductive layer.

[0002] Background A photovoltaic device provides a function of converting light into electricity. A typical photovoltaic device includes one or more solar cells. A solar cell is a well-known device for converting solar radiation into electrical energy. A solar cell has a front face facing the sun during normal operation for collecting solar radiation and a back face opposite to the front face.

[0003] EP2625703B1 discloses a dye-sensitized solar cell including a counter electrode including a porous conductive layer. The porous conductive layer is in contact with an electrolyte containing ions for moving electrons from the counter electrode to the working electrode. The electrolyte penetrates through the porous conductive layer. The electrolyte is highly corrosive. Therefore, the material of the porous conductive layer must be corrosion-resistant. The porous conductive layer may be composed of titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or mixtures thereof.

[0004] WO2019 / 219538 discloses a photovoltaic device including a solar cell unit. The solar cell includes a working electrode having a porous light absorption layer disposed on the upper surface of the solar cell unit, a porous upper conductive layer for extracting photo-generated electrons from the light absorption layer, where the light absorption layer is disposed above the upper conductive layer, a porous substrate made of an insulating material, with the porous upper conductive layer formed on one surface of the porous substrate, and a counter electrode including a porous lower conductive layer disposed on the bottom surface of the solar cell unit, where the porous lower conductive layer is formed on the opposite surface of the porous substrate. The photovoltaic device includes a conductive medium such as a liquid electrolyte for moving charges between the counter electrode and the working electrode. The porous conductive layer may be composed of titanium or its alloy.

[0005] The photovoltaic device includes a sealing body for sealing the solar cell unit so that the electrolyte does not leak from the solar cell. The problem of this photovoltaic device is how to lead the generated power from the photovoltaic device out of the photovoltaic device while being sealed with a corrosive electrolyte. This problem is solved by applying a conductor made of a corrosion-resistant material such as titanium or its alloy to the porous conductive layer. The conductor is disposed between the solar cell unit and the sealing body. The sealing body is provided with a through-hole for accessing the power generated by the photovoltaic device. For example, wiring from outside the sealing body passes through the through-hole and is electrically connected to the conductor. The through-hole is in close contact with the periphery of the wiring passing through the sealing body so that the liquid can permeate through the through-hole.

[0006] However, how to attach the conductor to the porous conductive layer is a problem so that good electrical contact can be obtained between the conductor and the porous conductive layer. If the contact between the porous conductive layer and the conductor is poor, the efficiency of the solar cell unit will decrease. In order to obtain a highly efficient solar cell, it is important that the electrical resistance between the conductor and the porous conductive layer is low. Since corrosion-resistant materials such as titanium have a high melting temperature, welding or soldering cannot be used for joining the conductor and the conductive layer. Also, since the conductive layer is porous and has a rough surface with cavities, there is also the difficulty that it is more difficult to obtain good electrical and mechanical contact between the conductor and the porous conductive layer. Furthermore, since the conductive layer is porous, it is fragile and vulnerable to mechanical forces. Also, the high corrosivity and chemical reactivity of the electrolyte sealed in the solar cell unit are also problems. It is important to properly seal the solar cell unit so that the electrolyte does not leak to the surroundings.

[0007] Summary An object of the present invention is to overcome at least partially the above problems. This object is achieved by the photovoltaic device defined in claim 1. The photovoltaic device includes a working electrode having a light absorption layer, a counter electrode including a porous conductive layer, a conductive medium for moving charges between the counter electrode and the working electrode, and a conductor electrically connected to the porous conductive layer. The solar cell unit includes at least one adhesive layer disposed between the conductor and the porous conductive layer for attaching the conductor to the porous conductive layer, and the adhesive layer includes an adhesive and conductive particles distributed in the adhesive so that a conductive network is formed in the adhesive.

[0008] The conductor is in electrical contact with the conductive layer through a network of conductive particles in at least one adhesive layer. The adhesive enables it to adhere to the surface of the porous conductive layer. Furthermore, by applying the adhesive, no mechanical force is applied to the porous conductive layer, and thus the surface of the porous conductive layer is not damaged.

[0009] The temperature required to dissolve the adhesive is lower compared to the temperature required for welding or soldering. This facilitates the manufacture of the solar cell unit.

[0010] Preferably, the porous conductive layer is made of a corrosion-resistant material such as any one of titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or a mixture thereof. Therefore, the porous conductive layer can withstand contact with the electrolyte as a medium for moving charges.

[0011] According to one embodiment, the photovoltaic device includes a sealing body surrounding the solar cell unit. The sealing body is provided with a through-hole including at least a part of the adhesive layer. The conductor is attached to the adhesive layer and extends outside the sealing body. The adhesive layer seals the through-hole and prevents the conductive medium from leaking from the solar cell through the through-hole. Due to the network of conductive particles in the adhesive layer, the conductor does not need to enter through the through-hole to provide electrical contact with the porous conductive layer. Therefore, the risk of leakage of the conductive medium is further reduced. Also, the conductor is disposed outside the sealing body and is in electrical contact with the porous conductive layer through the adhesive layer. As a result, since the conductor does not contact the conductive medium, it does not need to be made of a corrosion-resistant material. Therefore, the conductor can be made of a commonly used conductive material such as copper or silver.

[0012] The adhesive layer has three functions: providing electrical connection between the conductor and the porous conductive layer, attaching the conductor to the porous conductive layer, sealing the through-hole to prevent leakage of the conductive medium to the outside of the solar cell, and preventing contact between the conductor and the conductive medium within the solar cell unit.

[0013] According to one embodiment, the encapsulant includes a gluing layer for attaching the encapsulant to the solar cell unit, and the gluing layer is made of the same material as the adhesive of the adhesive layer. This is advantageous because the gluing layer of the encapsulant and the adhesive are required to have the same ability to withstand the electrolyte. Also, since the adhesive and the gluing layer of the encapsulant have the same melting temperature, the manufacture of the photovoltaic device is also facilitated.

[0014] According to one embodiment, the solar cell unit includes a non-porous conductive barrier disposed between a conductor and a porous conductive layer, and at least one adhesive layer includes a first adhesive layer disposed between the porous conductive layer and the conductive barrier for attaching the conductive barrier to the porous conductive layer, and a second adhesive layer disposed between the conductive barrier and the conductor for attaching the conductor to the conductive barrier. When the conductive medium is an electrolyte containing ions, the ions may pass through the adhesive layer. To prevent this, a conductive barrier is disposed between the first adhesive layer and the second adhesive layer.

[0015] According to one embodiment, the encapsulant surrounds the first adhesive layer, the second adhesive layer, and the conductive barrier. The encapsulant prevents ions in the electrolyte from entering the second adhesive layer and thereby leaking outside the solar cell unit.

[0016] Preferably, the conductive barrier is a solid flat plate made of a conductive material capable of withstanding the conductive medium of the solar cell.

[0017] According to one embodiment, the thickness of the conductive barrier is at least 10 nm.

[0018] According to one embodiment, the conductive barrier includes any one of titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or a mixture thereof.

[0019] According to one embodiment, the conductive barrier is made of titanium or its alloy. Thereby, since titanium can withstand the electrolyte, corrosion of the conductive barrier can be prevented.

[0020] According to one embodiment, the thickness of the adhesive layer is at least 3 μm, preferably at least 5 μm, and most preferably at least 10 μm. Thereby, good mechanical contact between the adhesive layer and the porous conductive layer is ensured.

[0021] According to one embodiment, the adhesive layer contains conductive particles of up to 40 vol-%, where vol-% is the ratio with respect to the total volume of the adhesive layer. That is, the adhesive layer contains at least 60 vol% of an adhesive. Therefore, sufficient adhesion ability of the adhesive layer is obtained.

[0022] According to one embodiment, the adhesive layer contains at least 20 vol-% of conductive particles. Thereby, good electrical conductivity of the adhesive layer is ensured.

[0023] Preferably, the adhesive layer contains 20 to 40 vol-% of conductive particles.

[0024] According to one embodiment, at least 80 wt-% of the conductive particles have a size of 5 μm or less, where wt-% is the ratio with respect to the total weight of the conductive particles. Preferably, at least 80 wt-% of the conductive particles have a size of 3 μm or less. Thereby, the electrical contact with the porous conductive layer is improved. Since the conductive particles are small, they can fit into the irregularities and cavities on the surface of the porous conductive layer, and good electrical contact between the conductive particles and the porous conductive layer can be obtained.

[0025] According to one embodiment, the adhesive layer contains a mixture of conductive particles having a size smaller than 200 nm and conductive particles having a size larger than 1 μm. The mixture of large particles and small particles can improve the conductive network formed in the adhesive because the small particles fill the spaces between the large particles and electrically connect the large particles.

[0026] According to one embodiment, the mass ratio of the conductive particles larger than 1 μm to the conductive particles smaller than 200 nm is between 1.5 and 3. The mass ratio means the value obtained by dividing the mass of the large particles in the adhesive layer by the mass of the small particles in the adhesive layer. Thereby, the conductive network formed in the adhesive can be further improved.

[0027] Preferably, the adhesive is made of a chemically resistant plastic material. When the conductive medium is an electrolyte, the adhesive must be made of a material that can withstand the electrolyte and does not react with the ions in the electrolyte. Most of the known plastic materials cannot withstand contact with the electrolyte. Also, known adhesive plastic materials such as epoxy react immediately with the electrolyte solution and cannot be used.

[0028] According to one embodiment, the adhesive is polyethylene, or polypropylene, or ionomer, or a mixture thereof. These materials can withstand the electrolytes used in solar cells.

[0029] According to one embodiment, the adhesive contains polyethylene. Polyethylene has a high adhesion ability to non-corrosive materials such as titanium, I - ,I3 - It has been tested that it can withstand electrolytes used in solar cells such as electrolytes containing ion pairs. Furthermore, polyethylene is an inexpensive material.

[0030] According to one embodiment, the adhesive layer contains polyethylene, or polypropylene, or ionomer, or a mixture thereof.

[0031] According to one embodiment, the melting temperature of the adhesive and the adhesive layer is substantially equal, or the melting temperature of the adhesive is lower than the melting temperature of the encapsulant. Thereby, the adhesive melts during the lamination of the encapsulant, facilitating the manufacture of the photovoltaic device. Therefore, an extra heating process is not required during the manufacture of the photovoltaic device.

[0032] According to one embodiment, the adhesive contains polyethylene, and the adhesive layer of the encapsulant contains polyethylene. Since polyethylene can withstand the electrolyte, tests have shown that it is a suitable material.

[0033] In one aspect, the conductive medium is an electrolyte. In one aspect, the conductive medium is an ionic electrolyte. The electrolyte may be a liquid electrolyte, a gel, or a solid.

[0034] In one aspect, the electrolyte is any one of an iodide / triiodide electrolyte, a copper complex-based electrolyte, a cobalt complex-based electrolyte, or a combination thereof.

[0035] According to one embodiment, the conductive particles contain carbon. Since carbon has good electrical contact with titanium, it is advantageous to use carbon in the conductive particles when the porous conductive layer is made of titanium. Furthermore, carbon is an inexpensive material.

[0036] In one aspect, the conductive particles are made of battery-grade carbon. Ordinary carbon contains impurities such as iron, for example, and may impair the performance of the solar cell. Battery-grade carbon is developed for use in carbon for batteries and fuel cells and is more pure than ordinary carbon, so it is suitable for use in solar cells.

[0037] According to one embodiment, the conductive particles are made of battery-grade graphite and battery-grade carbon black. Battery-grade graphite is larger carbon particles, and battery-grade carbon black is smaller carbon particles. Using a mixture of battery-grade graphite and battery-grade carbon black allows the small particles to fill the spaces between the large particles and electrically connect the large particles, so a good conductive network can be obtained in the adhesive.

[0038] According to one embodiment, the conductive particles are composed of one or more from the group consisting of crystalline graphite, amorphous carbon, carbon nanotubes, and graphene.

[0039] According to one embodiment, the conductive particles are composed of a metal or a metal alloy containing one or more of titanium, nickel, molybdenum, cobalt, and niobium. The metal alloy may be any nitride, hydride, silicide, or carbide of a metal, such as titanium hydride, boron nitride, or titanium silicide.

[0040] According to one embodiment, the conductive particles are composed of titanium or an alloy thereof. According to one embodiment, the porous conductive layer is composed of any one of titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or a mixture thereof.

[0041] According to one embodiment, the porous conductive layer contains titanium or an alloy thereof. In one aspect, the porous conductive layer is composed of titanium or an alloy thereof.

[0042] According to one embodiment, the photovoltaic unit includes a porous substrate made of an insulating material, an upper conductive layer formed on one surface of the porous substrate for extracting photo-generated electrons from the light absorption layer, and a second conductor in electrical contact with the second conductive layer. A part of the porous substrate includes a conductive material disposed between the second conductor and the upper conductive layer. The photovoltaic device includes at least one adhesive layer disposed between the second conductor and a part of the porous substrate for adhering the second conductor to the porous substrate, the adhesive layer containing the conductive particles.

[0043] Brief Description of the Drawings Next, with reference to the accompanying drawings, the present invention will be described in more detail by explaining various embodiments of the present invention.

[0044] FIG. 1 shows a first example of a photovoltaic device according to the present invention. FIG. 2 shows a first embodiment of an adhesive layer disposed between a conductor and a porous conductive layer. FIG. 3 shows a second embodiment of an adhesive layer disposed between a conductor and a porous conductive layer. FIG. 4 shows a second embodiment of a photovoltaic device according to the present invention. FIG. 5 shows an enlarged view of a part of the photovoltaic device shown in FIG. 4. FIG. 6 shows a second embodiment of an adhesive layer disposed between the conductor and the porous conductive layer in FIG. 4. FIG. 7 shows a third embodiment of a photovoltaic device according to the present invention. FIG. 8 shows a fourth embodiment of a photovoltaic device according to the present invention.

[0045] Detailed Description Hereinafter, aspects of the present disclosure will be described more fully with reference to the accompanying drawings. However, the photovoltaic device can be realized in many different forms and should not be construed as limited to the aspects described herein. Like numbers in the drawings refer to like elements throughout.

[0046] The terms used herein are for the purpose of describing particular aspects of the present disclosure only and are not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0047] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0048] FIG. 1 shows a first embodiment of a photovoltaic device 1a according to the present invention. The photovoltaic device 1a includes a solar cell unit 2a including a working electrode having a light absorption layer 3, a counter electrode having a porous conductive layer 6, and a conductive medium (not shown) for moving charges between the counter electrode and the working electrode. The solar cell unit 2a includes a conductor 7 and an adhesive layer 8 disposed between the conductor 7 and the porous conductive layer 6. The adhesive layer 8 is in mechanical and electrical direct contact with the porous conductive layer 6. The adhesive layer 8 adheres to the porous conductive layer 6. The conductor 7 is attached to the porous conductive layer 6 by the adhesive layer 8. The adhesive layer 8 functions as an adhesive between the conductor 7 and the porous conductive layer 6.

[0049] The conductor 7 is, for example, an electric wire or a conductive bar. The photovoltaic device 1a includes a sealing body 9 that seals the solar cell unit 2a including the conductive medium. The sealing body 9 prevents the conductive medium from leaking from the solar cell unit. The conductor 7 is attached to the adhesive layer 8 and extends outside the sealing body 9.

[0050] In one aspect, the light absorption layer 3 is porous and is disposed on the upper surface of the solar cell unit 2a. The light absorption layer 3 faces the sun to receive light. The solar cell unit 2a further includes an upper porous conductive layer 4 for extracting photo-generated electrons from the light absorption layer 3. In this embodiment, the light absorption layer 3 is disposed above the upper conductive layer 4. In this embodiment, the solar cell unit 2a includes a porous substrate 5 made of an insulating material, and the upper conductive layer 4 is formed on one surface of the porous substrate 5. The conductive layer 6 (hereinafter referred to as the lower conductive layer 6) is disposed on the bottom surface of the solar cell unit. In this embodiment, the lower conductive layer 6 is formed on the opposite surface of the porous substrate 5. A conductive medium, such as an electrolyte, penetrates into the pores of the porous light absorption layer 3, the upper and lower porous conductive layers, and the porous substrate 5. The conductive medium moves charges between the lower conductive layer 6 and the light absorption layer 3. In one aspect, the conductive medium is an electrolyte. The conductive medium can be an ionic electrolyte. For example, the electrolyte can be any of an iodide / triiodide electrolyte, a copper complex electrolyte, or a cobalt complex electrolyte, or a combination thereof. Such electrolytes can be highly corrosive.

[0051] Preferably, but not limited to the following, the upper and lower porous conductive layers are made of a corrosion-resistant material such as titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or mixtures thereof. Therefore, the porous conductive layer can withstand contact with the electrolyte as a medium for moving charges. Preferably, the upper and lower porous conductive layers contain titanium or its alloy.

[0052] The subsequent layer 8 includes an adhesive and conductive particles dispersed in the adhesive, and forms a conductive network in the adhesive to obtain electrical contact between the conductor 7 and the lower porous conductive layer 6. FIGS. 2 and 3 show two examples of the adhesive layers 8a and 8b disposed between the conductor 7 and the lower porous conductive layer 6. The adhesive layer 8 can be either of the adhesive layers 8a and 8b. Each of the adhesive layers 8a and 8b includes an adhesive 20 and conductive particles 22, 22a-b distributed in the adhesive 20 such that a conductive network is formed therein. That is, the conductive particles are in electrical contact with each other so as to form a conductive path through the adhesive. The conductive particles are preferably well dispersed in the adhesive.

[0053] The thickness of the adhesive layers 8, 8a-b is at least 3 μm, preferably at least 5 μm, and most preferably at least 10 μm in order to obtain sufficient mechanical contact between the conductor 7 and the lower porous conductive layer 6. Preferably, at least 80 wt-% of the conductive particles 22, 22a, 22b have a size of 5 μm or less, and most preferably, the conductive particles 22, 22a, 22b have a size of 3 μm or less. Wt% is the ratio with respect to the total weight of the conductive particles in the adhesive layer. This improves the electrical contact with the porous conductive layer 6. Further, since the conductive particles are small, they can fit into the unevenness and cavities on the surface of the porous conductive layer, and good electrical contact between the conductive particles and the porous conductive layer 6 can be obtained.

[0054] Preferably, although not limited to the following, the conductive particles 22, 22a-b are made of carbon. Since carbon has good electrical contact with titanium, when the porous conductive layer 6 is made of titanium, it is advantageous to use carbon for the conductive particles. Preferably, the conductive particles are made of battery-grade carbon. Ordinary carbon may contain impurities, which may impair the performance of the solar cell. Battery-grade carbon has been developed as carbon for batteries and fuel cells and has a higher purity than ordinary carbon, so it is suitable for use in solar cells. The conductive particles 22, 22a-b are made of, for example, crystalline graphite, amorphous carbon, carbon nanotubes, or graphene.

[0055] When the conductive medium is an ionic electrolyte, the adhesive 20 must be made of a material that can withstand the electrolyte and does not react with the ions in the electrolyte. Appropriately, the adhesive 20 is made of a chemically resistant plastic material. For example, the adhesive is made of polyethylene, or polypropylene, or an ionomer or a mixture thereof. These materials are suitable because they can withstand the electrolytes generally used in solar cells. For example, the adhesive 20 is made of polyethylene. Polyethylene has a high adhesion ability to non-corrosive materials such as titanium and has been tested to withstand electrolytes used in solar cells, such as electrolytes containing iodide I - and / or triiodide I3 - ions.

[0056] The encapsulant 9 may include an upper sheet at least partially transparent that covers the upper surface of the solar cell unit 2a and a lower sheet that covers the bottom surface of the solar cell unit. The encapsulant 9 may include a plurality of layers having different functions. The encapsulant 9 may include a barrier layer 10 that prevents the conductive medium from leaking from the solar cell. The encapsulant 9 may further include an adhesive layer 11 for attaching the encapsulant 9 to the solar cell. The adhesive layer 11 is disposed between the barrier layer 10 and the solar cell 2a. The adhesive layer 11 also functions as a barrier to prevent the conductive medium from leaking from the solar cell. When the conductive medium is a corrosive electrolyte, the adhesive layer 11 of the encapsulant needs to be made of a material that can withstand the electrolyte. Since the encapsulant and the adhesive are required to have the same ability to withstand the electrolyte solution, it is advantageous for the adhesive 20 and the encapsulant 9 to be made of the same material. Also, since the adhesive and the encapsulant have the same melting temperature, the manufacture of the photovoltaic device is also facilitated. Appropriately, the adhesive and the encapsulant are made of polyethylene. For example, the adhesive layer 11 is made of polyethylene, or polypropylene, or an ionomer or a mixture thereof. For example, the encapsulant 9 is made of polyethylene. Polyethylene is a suitable material because it can withstand the electrolyte solution and is transparent.

[0057] In one aspect, the encapsulant 9 includes a through-hole 12 that is arranged to connect the photovoltaic device 1a to an external device, thereby enabling the use of the electric power generated by the photovoltaic device. The through-hole 12 is a through-hole in the encapsulant. The through-hole includes at least a part of the adhesive layer 8 so that the through-hole 12 is sealed and gas and liquid cannot pass through the through-hole. The adhesive layer 8 seals the through-hole 12 by filling the through-hole 12, preventing the conductive medium from leaking out of the photovoltaic device through the through-hole. Due to the network of conductive particles in the adhesive layer 8, the conductor 7 can be in electrical contact with the lower porous conductive layer 6 even without entering from the through-hole 12. Therefore, the risk of leakage of the conductive medium is further reduced. Also, the conductor 7 is arranged outside the encapsulant and is in electrical contact with the porous conductive layer 6 through the adhesive layer 8. As a result, since the conductor 7 is not in contact with the conductive medium, it does not need to be made of a corrosion-resistant material. Therefore, the conductor 7 can be made of a commonly used conductive material such as copper or silver.

[0058] FIG. 2 shows an example of an adhesive layer 8a that includes an adhesive 20 and conductive particles 22 dispersed in the adhesive. The adhesive layer 8a is arranged between the conductor 7 and the lower porous conductive layer 6. In this example, the sizes of the conductive particles 22 are substantially the same.

[0059] FIG. 3 shows another example of an adhesive layer 8b arranged between the conductor 7 and the lower porous conductive layer 6. In this example, the adhesive layer 8b includes a mixture of conductive particles 22a having a size larger than 1 μm and conductive particles 22b having a size smaller than 200 nm distributed in the adhesive 20. The mixture of large particles and small particles can improve the conductive network formed in the adhesive 20 because the small particles fill the spaces between the large particles and electrically connect the large particles to each other. Preferably, the mass ratio of the conductive particles 22a larger than 1 μm to the conductive particles 22b smaller than 200 nm is between 1.5 and 3. Thereby, the conductive network formed in the adhesive 20 can be further improved. The mass ratio means the value obtained by dividing the total mass M1 of the large particles 22a by the total mass M2 of the small particles 22b in the adhesive layer.

[0060] 1.5 < M1 / M2 < 3

[0061] FIG. 4 shows a second embodiment of the photovoltaic device 1b according to the present invention including the solar cell unit 2a. FIG. 5 shows an enlarged part of the photovoltaic device 1b. When the conductive medium is an electrolyte containing ions, the conductive particles may reduce the sealing property of the adhesive 20, so that the ions may move through the adhesive layer. To prevent this, a conductive barrier 14 is disposed between the first and second adhesive layers 16 and 17. The solar cell unit 2b is different from the solar cell unit 2a in that it includes a non-porous conductive barrier 14 disposed between the conductor 7 and the lower porous conductive layer 6, and at least one adhesive layer is disposed between the lower porous conductive layer 6 and the conductive barrier 14 to attach the conductive barrier 14 to the lower porous conductive layer 6 and a second adhesive layer 17 disposed between the conductive barrier 14 and the conductor 7 to attach the conductor 7 to the conductive barrier 14. Thus, the first adhesive layer 16 functions as an adhesive between the lower porous conductive layer 6 and the conductive barrier 14, and the second adhesive layer 17 functions as an adhesive between the conductive barrier 14 and the conductor 7. The first adhesive layer 16 is in direct mechanical and electrical contact with the lower porous conductive layer 6. The conductive barrier 14 has two surfaces on opposite sides of the barrier 14. The first adhesive layer 16 is also in direct mechanical and electrical contact with one surface of the conductive barrier 14, and the second adhesive layer 17 is in direct mechanical and electrical contact with the other surface of the conductive barrier 14. The conductor 7 is disposed outside the seal 9.

[0062] The second adhesive layer 17 is disposed in the through-hole 12 so that the through-hole 12 is sealed and gas or liquid cannot pass through the through-hole.

[0063] The first and second adhesive layers 16, 17 contain conductive particles distributed in the adhesive so that a conductive network is formed in the adhesive. Suitably, the first and second adhesive layers 16, 17 are composed of the same type of adhesive 20 and conductive particles 22, 22a-b as the adhesive layer 8. The adhesive layers 16, 17 can be of the same type as either of the adhesive layers 8a, 8b. The conductor 7 is in electrical contact with the underlying porous conductive layer 6 through the first and second adhesive layers 16, 17 and the conductive barrier 14.

[0064] Preferably, the conductive barrier 14 is a solid piece made of a conductive material capable of withstanding the conductive medium of the solar cell. For example, the conductive barrier 14 includes any one of titanium, nickel, molybdenum, tungsten, cobalt, niobium, zirconium, and their alloys, or a mixture thereof. Preferably, the conductive barrier is made of titanium or its alloy. Thereby, since titanium can withstand the electrolytic solution, corrosion of the conductive barrier can be prevented. For example, the conductive barrier 14 is made of the same material as the underlying porous conductive layer 6.

[0065] To further improve the sealing property, the width of the conductive barrier 14 is made wider than the width of the second adhesive layer 17, and the peripheral portion of the second adhesive layer 17 is arranged at a distance from the peripheral portion of the conductive barrier 14. Thereby, as shown in FIG. 5, the path for ions to move between the first and second adhesive layers 16, 17 increases. Preferably, the distance between the peripheral portion of the second adhesive layer 17 and the peripheral portion of the conductive barrier 14 is longer than 1 mm.

[0066] Suitably, the conductive barrier 14 is plate-shaped. For example, the conductive barrier 14 has a circular shape such as the shape of a coin. However, other shapes such as a rectangle are also possible. The thickness of the conductive barrier 14 is preferably at least 10 nm.

[0067] To further improve the sealing property of the solar cell, the adhesive layer 11 of the sealing body 9 surrounds the first and second adhesive layers 16, 17 and the conductive barrier 14. The adhesive layer 11 can prevent ions in the electrolytic solution from entering the second adhesive layer 17, thereby preventing the ions from leaking out of the solar cell unit.

[0068] FIG. 5 shows an enlarged view of a part of the photovoltaic device shown in FIG. 4. In this embodiment, the first and second adhesive layers 16, 17 include conductive particles 22 distributed in the adhesive 20. In this embodiment, the sizes of the conductive particles 22 are substantially the same.

[0069] FIG. 6 shows an enlarged view of another embodiment of the first and second adhesive layers 16, 17 shown in FIG. 4. In this embodiment, the adhesive layers 16, 17 include a mixture of conductive particles 22a having a size larger than 1 μm and conductive particles 22b having a size smaller than 200 nm distributed in the adhesive 20.

[0070] FIG. 7 shows a third embodiment of the photovoltaic device 1c according to the present invention. The solar cell unit 1c includes a second conductor 7b through which the solar cell unit 1c is in electrical contact with the upper conductive layer 4, and is different from the photovoltaic devices 1a and 1b in that the conductive portion 23 of the porous substrate 5 contains a conductive material 24. Further, the photovoltaic device 1c includes an adhesive layer 25 disposed between the second conductor 7b and the conductive portion 23 of the porous substrate 5 to attach the second conductor 7b to the porous substrate 5 and provide electrical contact between the upper conductive layer 4 and the second conductor 7b. The conductive portion 23 is disposed between the adhesive layer 25 and the upper conductive layer 4. The adhesive layer 25 is in mechanical and electrical contact with the conductive portion 23.

[0071] The second conductor 7b is disposed outside the sealing body 9 and is in electrical contact with the upper porous conductive layer 4 through the adhesive layer 25 and the conductive material 24 in the porous substrate 5. As a result, since the conductor 7b is not in contact with the conductive medium, it does not need to be made of a corrosion-resistant material. The second conductor 7b can be made of a commonly used conductive material such as copper or silver. The second conductor 7b is, for example, an electric wire or a conductive bar.

[0072] The subsequent layer 25 includes conductive particles 22 distributed in the adhesive 20 such that a conductive network is formed in the adhesive 20 to obtain electrical contact between the second conductor 7b in the porous substrate 5 and the conductive material 24. Accordingly, electrical contact between the second conductor 7b and the upper porous conductive layer 4 can be obtained. Appropriately, the adhesive layer 25 is composed of the same type of adhesive 20 and the same type of conductive particles 22 as the adhesive layer 8. The sealing body 9 includes a first through-hole 12a for connecting the first conductor 7 to the lower porous conductive layer 6 and a second through-hole 12b for connecting the second conductor 7b to the upper porous conductive layer 4.

[0073] In this embodiment, since the lower porous conductive layer 6 ends at a position away from the adhesive layer 25, an insulating gap 27 can be formed between the adhesive layer 25 and the lower porous conductive layer 6 so that the adhesive layer 25 and the lower conductive layer 6 are electrically insulated from each other.

[0074] FIG. 8 shows a fourth embodiment of the photovoltaic device 1d according to the present invention. The solar cell unit 1d is different from the photovoltaic device 1c in that, similar to that shown in FIG. 4, the solar cell unit 1d includes a non-porous conductive barrier 14 disposed between the first conductor 7 and the lower porous conductive layer 6. The solar cell unit 1d includes a first adhesive layer 16 disposed between the lower porous conductive layer 6 and the conductive barrier 14 for attaching the conductive barrier 14 to the lower porous conductive layer 6, and a second adhesive layer 17 disposed between the conductive barrier 14 and the first conductor 7a for attaching the first conductor 7a to the conductive barrier 14.

[0075] The solar cell unit 1d further includes a second non-porous conductive barrier 14b disposed between the second conductor 7b and the porous substrate 5, a third adhesive layer 26 disposed between the conductive portion 23 of the porous substrate 5 and the second conductive barrier 14b for attaching the conductive barrier 14b to the porous substrate 5, and a fourth adhesive layer 28 disposed between the second conductive barrier 14b and the second conductor 7b for attaching the second conductor 7b to the conductive barrier 14b. The first and second conductive barriers 14, 14b both function as barriers to ions in the conductive medium and prevent ions from penetrating outside the photovoltaic device through the through holes 12a-b. Preferably, the conductive barriers 14 and 14b are made of the same material. Since the conductive barriers 14 and 14b are in contact with the conductive medium, they preferably need to be made of a corrosion-resistant material, such as titanium.

[0076] The third and fourth adhesive layers 26, 28 contain conductive particles distributed in the adhesive 20 in order to form a conductive network in the adhesive and obtain electrical contact between the second conductor 7b and the conductive material 24 in the porous substrate 5. Appropriately, the adhesive layers 26, 28 are made of the same type of adhesive 20 and the same type of conductive particles 22 as the adhesive layers 16, 17. The adhesive layers 26, 28 can be of any of the types of adhesive layers 8a-b described above with reference to FIGS. 2-3.

[0077] Since the adhesive layer 28 is disposed in the through hole 12b, the through hole 12b is sealed and gas and liquid cannot pass through the through hole. For example, the conductive barriers 14, 14b have a circular shape. However, other shapes such as rectangular are also possible.

[0078] The present invention is not limited to the disclosed embodiments and may be modified and corrected within the scope described in the following claims. For example, each of the adhesive layers 16, 17, 25, 26, and 28 can be of any of the types described with reference to FIGS. 2-3. Reference Numerals

Explanation of Reference Numerals

[0079] 1a-d: Photovoltaic device 2a, 2b: Solar cell unit 3: Light absorption layer 4: Upper porous conductive layer 5: Porous substrate 6: Lower porous conductive layer 7: Conductor 7b: Second conductor 8, 8a - b: Adhesive layer 9: Encapsulant 10: Barrier layer of the encapsulant 11: Adhesive layer of the encapsulant 12, 12a - b: Through - hole 14, 14a - b: Non - porous conductive barrier 16: First adhesive layer 17: Second adhesive layer 20: Adhesive 22, 22a, 22b: Conductive particles 23: Conductive part of the porous substrate 24: Conductive material 25: Adhesive layer 26: Third adhesive layer 27: Insulating gap 28: Fourth adhesive layer

Claims

1. A working electrode including a light absorption layer (3), A counter electrode including a porous conductive layer (6), and A conductive medium for moving charges between the counter electrode and the working electrode - including a solar cell unit (2a; 2b); - A sealing body (9) surrounding the solar cell unit (2a; 2b); - A conductor (7) electrically connected to the porous conductive layer (6); - A non-porous conductive barrier (14) disposed between the conductor (7) and the porous conductive layer (6); - A first adhesive layer (16) disposed between the porous conductive layer (6) and the conductive barrier (14) for attaching the conductive barrier (14) to the porous conductive layer (6); - A second adhesive layer (17) disposed between the conductive barrier (14) and the conductor (7) for attaching the conductor (7) to the conductive barrier (14), The conductor (7) extends outside the sealing body (9), the first adhesive layer (16) and the second adhesive layer (17) include an adhesive (20) and conductive particles (22; 22a-b) distributed in the adhesive (20) so as to form a conductive network in the adhesive (20), and the sealing body (9) surrounds the first adhesive layer (16), the second adhesive layer (17) and the conductive barrier (14), characterized in that the photovoltaic device (1a-d).

2. The sealing body (9) is provided with a through hole (12) including at least a part of the second adhesive layer (17), and the conductor (7) is adhered to the second adhesive layer (17) and extends outside the sealing body (9). The photovoltaic device according to claim 1.

3. The sealing body (9) includes an adhesive layer (11) for attaching the sealing body (9) to the solar cell unit (2a; 2b), and the adhesive layer (11) is made of the same material as the adhesive (20). The photovoltaic device according to claim 1.

4. The conductive barrier (14) includes titanium or an alloy thereof. The photovoltaic device according to claim 1.

5. The thickness of the first adhesive layer (16) and the second adhesive layer (17) is at least 3 μm. The photovoltaic device according to claim 1.

6. The first adhesive layer (16) and the second adhesive layer (17) include 20 to 40 vol% of the conductive particles (22; 22a-b). The photovoltaic device according to claim 1.

7. The photovoltaic device according to claim 1, wherein at least 80 wt% of the conductive particles (22; 22a-b) have a size of 5 μm or less.

8. The photovoltaic device according to claim 1, wherein the first adhesive layer (16) and the second adhesive layer (17) contain a mixture of conductive particles (22a) having a size smaller than 200 nm and conductive particles (22b) having a size larger than 1 μm.

9. The photovoltaic device according to claim 1, wherein the adhesive (20) is polyethylene, or polypropylene, or ionomer, or a mixture thereof.

10. The photovoltaic device according to claim 3, wherein the adhesive (20) and the adhesive layer (11) contain polyethylene.

11. The photovoltaic device according to claim 1, wherein the conductive particles (22; 22a-b) contain carbon.

12. The photovoltaic device according to claim 1, wherein the conductive particles (22; 22a-b) contain titanium or an alloy thereof.

13. The solar cell unit (2a; 2b) is - a porous substrate (5) made of an insulating material, - an upper conductive layer (4) formed on one surface of the porous substrate (5) for extracting photo-generated electrons from the light absorption layer (3), and - a second conductor (7b) in electrical contact with the upper conductive layer (4), wherein the conductive portion (23) of the porous substrate (5) contains a conductive material (24), the photovoltaic device includes the adhesive (20) containing the conductive particles (22; 22a, 22b), and is disposed between the second conductor (7b) and the conductive portion (23) of the porous substrate, and comprises at least one adhesive layer (25; 26, 28) for attaching the second conductor (7b) to the porous substrate (5). The photovoltaic device according to claim 1.

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