Photovoltaic device with adhesive layer

Abstract

The present invention relates to a photovoltaic device comprising a porous conductive layer 4 containing titanium particles 5 made of titanium or an alloy thereof, a conductor device in electrical contact with the porous conductive layer, and an adhesive layer 12 disposed between the porous conductive layer 4 and the conductor device 10. The adhesive layer 12 comprises an adhesive 14 and first conductive particles (16) dispersed in the adhesive. At least a portion of the porous conductive layer 4 contains second conductive particles 18 dispersed among the titanium particles 5. The second conductive particles 18 are made of a conductive material that substantially suppresses the formation of an electrically insulating oxide layer on their surface during oxidation. The titanium particles 5 and the second conductive particles 18 are sintered together so that a conductive bond 20 is formed between the titanium particles 5 and the second conductive particles 18, and the first conductive particles 16 in the adhesive layer 12 are in electrical contact with the second conductive particles 18.

Description

Technical Field

[0005]

[0001] The present invention relates to a photovoltaic device. More specifically, the present invention relates to a photovoltaic device comprising a conductive layer and a conductor attached to the conductive layer by an adhesive layer.

Background Art

[0002] Photovoltaic devices provide the conversion of light into electricity. Typical photovoltaic devices include 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 for receiving sunlight during normal operation and a back face opposite the front face.

[0003] EP2625703B1 discloses a dye-sensitized solar cell comprising a counter electrode including a porous conductive layer. This 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. This electrolyte is highly corrosive. Therefore, the material of the porous conductive layer must be resistant to corrosion.

[0004] WO2019 / 219538 discloses a photovoltaic device comprising a solar cell unit, the solar cell unit including a working electrode comprising a porous light absorption layer disposed on the top 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 a porous substrate made of an insulating material disposed on top of the upper conductive layer, where the porous upper conductive layer is formed on one side of the porous substrate, and a counter electrode comprising 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 side of the porous substrate. The photovoltaic device comprises 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 made of titanium or an alloy thereof.

[0005] A photovoltaic device includes an enclosure that encapsulates a solar cell unit to prevent the conductive medium from leaking out of the solar cell. This photovoltaic device presents a challenge in how to guide the power generated from the solar cell unit, which is encapsulated with a corrosive electrolyte, to the outside of the device. This problem is solved by applying a conductor made of a corrosion-resistant material, such as titanium or an alloy thereof, to a porous conductive layer. The conductor is positioned between the solar cell unit and the enclosure. The enclosure is provided with a perforation for accessing the power generated by the photovoltaic device. For example, wiring from outside the enclosure passes through the perforation and is electrically connected to the conductor. The perforation is tightly fitted around the wiring passing through the enclosure, thus preventing the conductive medium from passing through the perforation.

[0006] However, the problem lies in how to adhere the conductor to the porous conductive layer so that good electrical contact is achieved between the conductor and the porous conductive layer. Poor contact between the porous conductive layer and the conductor reduces the efficiency of the solar cell unit. Low electrical resistance between the conductor and the porous conductive layer is important for achieving high efficiency in solar cells. The difficulty lies in the fact that the conductive layer is porous and has a rough surface with cavities, which complicates achieving good electrical and mechanical contact between the conductor and the porous conductive layer.

[0007] WO2021209221 proposes a solution to the above-mentioned problem. WO2021209221 discloses a photovoltaic device comprising a solar cell unit, the solar cell unit having a working electrode including a light-absorbing layer, a first porous conductive layer containing titanium for extracting photogenerated electrons from the light-absorbing layer, a counter electrode including a second porous conductive layer containing titanium electrically insulated from the first porous conductive layer, a conductive medium for transferring charge between the counter electrode and the working electrode, a first conductor electrically connected to the first porous conductive layer, a second conductor electrically connected to the second porous conductive layer, a first adhesive layer disposed between the first porous conductive layer and the first conductor, and a second adhesive layer disposed between the second porous conductive layer and the second conductor. The first and second adhesive layers have an adhesive and conductive particles dispersed in the adhesive, so that a conductive network is formed in the adhesive. The conductor is in electrical contact with the conductive layer via the network of conductive particles in the adhesive layer. The adhesive makes it possible to adhere to the surface of the porous conductive layer. Furthermore, applying the adhesive does not involve applying any mechanical force to the porous conductive layer, and therefore does not cause any damage to the surface of the porous conductive layer.

[0008] For example, as mentioned in WO2020 / 015882, during the manufacture of the solar cell unit, insulating oxide layers are formed on the surface of the conductive material of the first and second porous conductive layers. The insulating oxide layers provide an electrical insulating layer on the conductive material of the conductive layers, thereby preventing at least partially the movement of electrons between the conductive material and the conductive medium, and thus improving the efficiency of the solar cell unit.

[0009] The manufacturing of a solar cell comprises a sintering step in which particles in a first porous conductive layer are sintered together, followed by an oxidation step in which the surface of the titanium particles is covered with an insulating oxide layer. The titanium particles are sintered together, and thus they are in electrical contact with one another. Since the oxidation step is performed after the sintering step, the contact surfaces between the titanium particles are not oxidized, and therefore electrical contacts exist between the titanium particles.

[0010] However, these insulating oxide layers have the problem of reducing electrical conductivity between the conductive layer and the adhesive layer. [Overview of the Initiative]

[0011] The objective of the present invention is to improve the electrical conductivity between the conductive layer and the adhesive layer of a photovoltaic device.

[0012] This objective is achieved by the photovoltaic device defined in claim 1.

[0013] Photovoltaic devices are - Light-absorbing layer, - A first porous conductive layer containing titanium particles made of titanium or an alloy thereof, for extracting photogenerated electrons from a light-absorbing layer. - A second porous conductive layer is disposed separately from the first porous conductive layer. - A conductive medium for transferring charge between the second porous conductive layer and the light-absorbing layer, - A first conductive device in electrical contact with the first porous conductive layer, and - A first adhesive layer disposed between a first porous conductive layer and a first conductive device, wherein the first adhesive layer comprises an adhesive and first conductive particles dispersed in the adhesive, so that a conductive network is formed in the adhesive, providing an electrical contact between the first porous conductive layer and the first conductive device. It is equipped with a solar cell unit having the following features.

[0014] At least a portion of the first porous conductive layer has second conductive particles dispersed between titanium particles, the second conductive particles being made of a conductive material that substantially suppresses the formation of an electrically insulating oxide layer on its surface during oxidation. The titanium particles and the second conductive particles are sintered together, so that a conductive bond is formed between the titanium particles and the second conductive particles, and the conductive network formed in the adhesive is in electrical contact with the second conductive particles.

[0015] The second conductive particles are made of a conductive material that substantially suppresses the formation of an insulating oxide layer on their surface during oxidation. The conductive material of the second conductive particles has the ability to react with titanium and its alloys, so that a conductive junction is formed between the titanium particles and the second conductive particles during the sintering process. The conductive junction forms an electrically conductive bridge between the titanium particles and the second conductive particles. The conductive junction improves the electrical contact between the titanium particles and the second conductive particles. The conductive junction is formed between the titanium particles and the second conductive particles during the sintering process of manufacturing the solar cell unit. Since the second conductive particles substantially suppress the formation of an oxide layer on their surface during the oxidation process of the manufacturing process, the second conductive particles are not covered with an electrically insulating oxide layer, just like the titanium particles. Thus, the first conductive particles in the adhesive layer are in electrical contact with the second conductive particles in the porous conductive layer, and the second conductive particles are in electrical contact with the titanium particles via the conductive junction. Thus, the conductive network in the adhesive layer is in electrical contact with the titanium particles in the first porous conductive layer via the second conductive particles. Therefore, the electrical conductivity between the porous conductive layer and the adhesive layer is essentially improved.

[0016] The characteristic that "the second conductive particles substantially suppress the formation of an insulating oxide layer on their surface during oxidation" means that the thickness of the insulating oxide layer remaining on the surface of the second conductive particles after the manufacture of the solar cell unit is less than 40 nm. Preferably, no insulating oxide layer remains on the surface of the second conductive particles after the manufacture of the solar cell unit.

[0017] The feature "at least a portion of the first porous conductive layer has second conductive particles dispersed among titanium particles" means either that the second conductive particles are dispersed among the titanium particles throughout the entire first porous conductive layer, or that the second conductive particles are dispersed among the titanium particles only in a portion of the first porous conductive layer. To achieve improved electrical conductivity between the first porous conductive layer and the first adhesive layer, the second conductive particles must be in electrical contact with the conductive network in the adhesive layer. The conductive network in the adhesive layer may be in direct or indirect electrical contact with the second conductive particles. For example, at least some of the second conductive particles are located at the interface between the first adhesive layer and the first porous conductive layer. In this case, the first conductive particles are in mechanical and electrical contact with the second conductive particles, thereby directly in electrical contact with the second conductive particles. Thus, it is ensured that the first conductive particles in the first adhesive layer are in electrical contact with the second conductive particles in the first conductive layer. However, it is also possible, for example, for the conductive network within the adhesive layer to indirectly make electrical contact with the second conductive particle via another conductive layer.

[0018] The characteristic that "the titanium particles and the second conductive particles are sintered together, and thus a conductive bond is formed between the titanium particles and the second conductive particles" means that the titanium particles and the second conductive particles are in mechanical and electrical contact with each other, and that a conductive bond exists between the titanium particles and the second conductive particles. The titanium particles and the second conductive particles are bonded to each other by sintering, and the conductive bond is formed between the titanium particles and the second conductive particles during the sintering process.

[0019] The characteristic "a second porous conductive layer disposed separately from the first porous conductive layer" means that the first and second porous conductive layers are disposed at a distance from each other. By physically separating the first and second porous conductive layers, direct electron short circuits between them are avoided.

[0020] According to one embodiment of the present invention, the first porous conductive layer comprises second conductive particles between 0.001% and 5% by weight, preferably between 0.001% and 3% by weight, where weight% is a percentage by weight relative to the total weight of the first porous conductive layer.

[0021] According to one embodiment of the present invention, the conductive material of the second conductive particles is selected from the group consisting of or including carbon, metal silicides, metal nitrides, metal carbides, doped metal oxides, doped silicon, and combinations thereof. These conductive materials have higher resistance to surface oxide formation than titanium and react with titanium during sintering to form conductive junctions between the titanium particles and the second conductive particles. For example, carbon can form conductive junctions of titanium carbides, metal silicides can form conductive junctions of titanium silicides, metal nitrides can form conductive junctions of titanium nitrides, metal carbides can form conductive junctions of titanium carbides, and doped metal oxides and doped silicon can form conductive junctions of doped titanium oxides. The material in the conductive junction improves the conductivity between the titanium particles and the conductive material of the second conductive particles.

[0022] According to one embodiment of the present invention, the conductive material of the second conductive particle is selected from the group consisting of carbon, metal silicide, metal nitride, metal carbide, and combinations thereof.

[0023] According to one embodiment of the present invention, the conductive material of the second conductive particle is selected from the group consisting of carbon, doped metal oxide, doped silicon, and combinations thereof.

[0024] According to an embodiment of the present invention, the conductive material of the second conductive particles is carbon, and the conductive junction between the titanium particles and the second conductive particles is titanium carbide. Titanium carbide improves the electrical conductivity between titanium and carbon, and thus improves the electrical conductivity between the titanium particles and the second conductive particles. Carbon is inexpensive and environmentally friendly. Furthermore, titanium carbide has an electrical conductivity approximately the same as that of titanium. Carbon forms carbon dioxide and / or carbon monoxide during oxidation, and thus no insulating oxide layer is formed on the surface of the carbon particles during the oxidation stage of manufacturing. Carbon can be any type of carbon, such as carbon black, graphene, carbon nanotubes, amorphous carbon, graphite, fullerenes, nanographite particles, or flakes.

[0025] Carbon is a catalyst material and may reduce the current generation ability in the first porous conductive layer. Preferably, the first porous conductive layer contains carbon between 0.001 wt% and 5 wt%, more preferably between 0.001 wt% and 3 wt%, and most preferably between 0.001 wt% and 1 wt%, where wt% is the weight percentage relative to the total weight of the portion of the first conductive layer containing carbon. Such a low amount of carbon does not affect the current generation ability in the first porous conductive layer.

[0026] According to an embodiment of the present invention, the second conductive particles are uniformly dispersed among the titanium particles throughout the first porous conductive layer. This is advantageous from a manufacturing perspective because it does not require an additional manufacturing process. The second conductive particles may simply be added to the ink containing the titanium particles used to form the first porous conductive layer.

[0027] When the second conductive particles are dispersed throughout the first porous conductive layer, the first porous conductive layer preferably contains carbon between 0.001 wt% and 1 wt%, and most preferably the first porous conductive layer contains carbon between 0.001 wt% and 0.8 wt%, where wt% is the weight percentage relative to the total weight of the entire first porous conductive layer. Such a low amount of carbon improves the electrical conductivity between the first porous conductive layer and the adhesive layer without affecting the current generating ability in the first porous conductive layer.

[0028] According to one embodiment of the present invention, the average size of the second conductive particles is larger than the average size of the first conductive particles. Preferably, the average size of the second conductive particles is at least 3 times the average size of the first conductive particles, and most preferably, the average size of the second conductive particles is at least 10 times the average size of the first conductive particles. The smaller the first conductive particles are compared to the second conductive particles, the greater the number of first conductive particles that can contact each of the second conductive particles at the interface between the adhesive layer and the first porous conductive layer. Thus, the interfacial surface area between the first and second conductive particles increases, and accordingly, the electrical conductivity between the first and second conductive particles increases. Thus, more contact points are achieved between the first and second conductive particles, which enhances the electrical conductivity between the two.

[0029] According to one embodiment of the present invention, the average size of the second conductive particles is between 1 μm and 5 μm, and the average size of the first conductive particles is between 1 nm and 500 nm. Thereby, sufficient contact points are achieved between the first and second conductive particles, enhancing the electrical conductivity between the two.

[0030] According to one embodiment of the present invention, at least 80 wt% of the second conductive particles have a size between 1 nm and 10 μm, preferably at least 80 wt% of the second conductive particles have a size between 0.5 μm and 5 μm, where wt% is the weight percentage relative to the total weight of the second conductive particles. Preferably, in order to achieve an appropriate conductive bond between the particles during sintering, the size of the second conductive particles is approximately the same as the size of the titanium particles.

[0031] According to one embodiment of the present invention, at least 80% by weight of the titanium particles have a size between 1 nm and 10 μm, preferably at least 80% by weight of the titanium particles have a size between 0.5 μm and 5 μm, where weight% is the weight percentage relative to the total weight of the titanium particles.

[0032] According to one embodiment of the present invention, the average size of the titanium particles and the second conductive particles is larger than the average size of the first conductive particles, preferably the average size of the titanium particles and the second conductive particles is at least three times the average size of the first conductive particles, and most preferably the average size of the titanium particles and the second conductive particles is at least ten times the average size of the first conductive particles. Since the first conductive particles are smaller than the titanium particles and the second conductive particles, the interfacial surface area between the first and second conductive particles is large. Furthermore, the first conductive particles can conform to the irregularities and cavities on the surface of the porous conductive layer, thereby achieving good electrical contact between the first and second conductive particles.

[0033] According to one embodiment of the present invention, a solar cell unit includes a porous insulating layer made of an insulating material, a light absorbing layer disposed on a first porous conductive layer, the first porous conductive layer being formed at least partially above the porous insulating layer, a second porous conductive layer being formed below the porous insulating layer, the light absorbing layer being disposed on the top surface of the solar cell unit, and the second porous conductive layer being disposed on the bottom surface of the solar cell unit parallel to the top surface of the solar cell unit.

[0034] According to one embodiment of the present invention, the first conductor device is disposed below the porous insulating layer in a direction extending normal to the top surface of the solar cell unit from the bottom surface of the solar cell unit. The first conductor device is located on the bottom surface of the solar cell unit. Therefore, in this case, the wiring is not visible above the photovoltaic device.

[0035] According to one embodiment of the present invention, the first porous conductive layer has a first portion containing second conductive particles sintered onto titanium particles, and a second portion containing titanium particles sintered together without containing any second conductive particles. Therefore, only a portion of the first porous conductive layer contains second conductive particles sintered onto titanium particles, and the remaining portion of the first porous conductive layer does not contain any second conductive particles. Preferably, the first portion containing the second conductive particles is located at or near the interface between the first porous conductive layer and the first adhesive layer. If the material of the second conductive particles is catalytic, such as carbon, the second conductive particles may reduce the current generation capacity within the first porous conductive layer; therefore, it is advantageous that only a portion of the first porous conductive layer contains the second conductive particles.

[0036] According to one embodiment of the present invention, the first portion of the first porous conductive layer is a single layer of second conductive particles and titanium particles disposed on the surface of the second portion of the first porous conductive layer. To achieve a significant improvement in electrical conductivity between the first porous conductive layer and the first adhesive layer, it is sufficient to have a single layer of second conductive particles and titanium particles disposed on the surface of the second portion of the first porous conductive layer. Therefore, the first portion containing the second conductive particles can be made very thin.

[0037] According to one embodiment of the present invention, the thickness of the first portion of the first porous conductive layer in a direction extending in the normal direction from the top surface to the bottom surface of the solar cell unit is between 0.5 μm and 20 μm, preferably between 0.5 μm and 10 μm, and most preferably between 0.5 μm and 5 μm. If the material of the second conductive particles is catalytic, the thinner the first portion, the smaller the effect on power generation.

[0038] According to one embodiment of the present invention, the second portion of the first porous conductive layer is formed on top of the porous insulating layer, and the first portion of the first porous conductive layer is formed on top of the second portion of the first porous conductive layer.

[0039] According to one embodiment of the present invention, the first porous conductive layer has a third portion containing titanium particles sintered together without any second conductive particles. The second portion of the first porous conductive layer is formed above the porous insulating layer, and the third portion of the first porous conductive layer extends through the porous insulating layer from above to below the porous insulating layer. The first portion of the first porous conductive layer is located below the porous insulating layer and is in physical and electrical contact with the third portion of the first porous conductive layer, and the first adhesive layer is located below the porous insulating layer and is in physical and electrical contact with the first portion of the first porous conductive layer. The first conductive device is disposed on the bottom surface of the solar cell unit. This makes it possible to install the first conductive device on the bottom surface of the solar cell unit, and the wiring that prevents light from reaching the light absorption layer above the photovoltaic device is not visible.

[0040] According to one embodiment of the present invention, a portion of the porous insulating layer includes one or more through holes extending in the normal direction from the top surface of the solar cell unit to the bottom surface of the solar cell unit, and a third portion of the first porous conductive layer extends through one or more through holes.

[0041] According to one embodiment of the present invention, the second porous conductive layer comprises titanium particles made of titanium or an alloy thereof, and at least a portion of the second porous conductive layer comprises second conductive particles made of a conductive material that substantially suppresses the formation of an insulating oxide layer on its surface during oxidation, the titanium particles and the second conductive particles are sintered together, and a conductive bond is formed between the titanium particles and the second conductive particles. The solar cell unit further - A second conductive device in electrical contact with the second porous conductive layer, and - A second adhesive layer disposed between a second porous conductive layer and a second conductive device, wherein the second adhesive layer comprises an adhesive and first conductive particles dispersed in the adhesive, so that a conductive network is formed in the adhesive, and the second porous conductive layer is in electrical contact with the conductive network formed in the second adhesive layer. The structure is equipped with the following features. Therefore, the electrical conductivity between the second porous conductive layer and the second adhesive layer is improved in the same way as the electrical conductivity between the first porous conductive layer and the first adhesive layer described above is improved.

[0042] According to one embodiment of the present invention, the second conductor is disposed below the second porous conductive layer in a direction extending in the normal direction from the top surface of the solar cell unit to the bottom surface of the solar cell unit. This makes it possible to install the second conductive device on the bottom surface of the solar cell unit.

[0043] According to one embodiment of the present invention, the second porous conductive layer comprises at least 0.001% by weight of second conductive particles, preferably at least 0.01% by weight of second conductive particles, where weight% is a percentage by weight of the total weight of the second porous conductive layer. Preferably, the second porous conductive layer comprises less than 40% by weight of second conductive particles, where weight% is a percentage by weight of the total weight of the second porous conductive layer. Unlike the first porous conductive layer, the second porous conductive layer is advantageous if it comprises catalyst particles. The catalyst particles function as catalysts, facilitating the transfer of electrons from titanium to the conductive medium within the pores of the second porous conductive layer. Therefore, the amount of second conductive particles can be much greater in the second porous conductive layer than in the first porous conductive layer.

[0044] According to one embodiment of the present invention, each of the first and second adhesive layers includes a non-porous conductive barrier disposed between the adhesive layer and the conductive device. If the conductive medium is an electrolyte containing ions, these ions can move through the adhesive layer. The conductive barrier prevents ions from the conductive medium from leaking out of the photovoltaic device. [Brief explanation of the drawing]

[0045] The present invention will now be described in more detail by describing various embodiments of the present invention and by referring to the accompanying drawings.

[0046] [Figure 1]An example of a photovoltaic device including a porous conductive layer and an adhesive layer is shown in a cross-sectional view. [Figure 2] The interface between the porous conductive layer and the adhesive layer is shown in a magnified view. [Figure 3] Figure 1 shows a view of the photovoltaic device from above. [Figure 4] Another example of a photovoltaic device is shown in a cross-sectional view. [Figure 5] Another example of a photovoltaic device is shown in a cross-sectional view. [Figure 6] Figure 5 shows a view of the photovoltaic device from above. [Figure 7] An example of a conductive barrier is shown. [Modes for carrying out the invention]

[0047] Aspects of this disclosure are described more fully below with reference to the accompanying drawings. However, photovoltaic devices can be realized in many different forms and should not be construed as being limited to the embodiments described herein. Similar reference numerals in the drawings refer to similar elements throughout.

[0048] The terms used herein are intended solely to describe specific aspects of this disclosure and are not intended to limit the invention. Where used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless otherwise explicitly stated in the context.

[0049] Unless otherwise defined, all terms used herein have the same meanings as those generally understood by those skilled in the art to which this disclosure belongs.

[0050] Figure 1 shows an example of a photovoltaic device 1a according to the present invention. The photovoltaic device 1a comprises a solar cell unit including a light-absorbing layer 2, a first porous conductive layer 4 containing titanium particles made of titanium or an alloy thereof for extracting photogenerated electrons from the light-absorbing layer 2, a second porous conductive layer 6 separated from the first porous conductive layer 4, and a porous insulating layer 8 disposed between the first and second porous conductive layers 4 and 6. The porous insulating layer 8 serves to physically and electrically separate the first and second porous conductive layers 4 and 6 and to prevent direct electron short circuits between them. The second porous conductive layer 6 contains titanium particles made of titanium or an alloy thereof sintered together, so that they are in electrical contact with each other. The photovoltaic device 1a further comprises a conductive medium (not shown) for transferring charge between the second porous conductive layer 6 and the light-absorbing layer 2.

[0051] The light-absorbing layer 2 is disposed on the top surface 26 of the solar cell unit so that the light-absorbing layer 2 faces the incident light. In this example, the light-absorbing layer 2 is disposed on the first porous conductive layer 4, and the second porous conductive layer 6 is disposed on the bottom surface 28 of the solar cell unit. The bottom surface 28 is parallel to the top surface 26 of the solar cell unit. In one embodiment, the light-absorbing layer 2 is porous. The light-absorbing layer may include a porous metal oxide with a light-absorbing material disposed on its top surface. For example, the light-absorbing layer 2 is a porous TiO2 nanoparticle layer on which an organic dye is adsorbed.

[0052] The conductive medium is placed within the pores of the light-absorbing layer 2, the first porous conductive layer 4, the porous insulating layer 8, and the second porous conductive layer 6. The conductive medium is, for example, an electrolyte that has permeated into the pores of the porous light-absorbing layer 2, the first and second porous conductive layers 4 and 6, and the porous insulating layer 8. The electrolyte may be a liquid electrolyte, a gel, or even a solid. The conductive medium may be, for example, an ionic electrolyte. For example, the electrolyte may be an iodide / triiodide electrolyte, a copper complex electrolyte, or a cobalt complex electrolyte, or a combination thereof. Such electrolytes may be highly corrosive. The titanium particles 5 are made of titanium or a titanium alloy, which are corrosion-resistant materials, so that the porous conductive layers 4 and 6 can withstand contact with corrosive electrolytes.

[0053] In this example, the first porous conductive layer 4 is formed on the upper side 8a of the porous insulating layer 8, and the second porous conductive layer 6 is formed on the lower side 8b of the porous insulating layer 8. In one example, the insulating layer 8 is a porous substrate made of insulating material. The porous substrate is, for example, a sheet containing woven microfibers that extend through the entire solar cell unit. For example, the woven microfibers are made of glass fibers. The first conductive layer 4 is a layer of porous conductive material located on one side of the porous substrate, and the second conductive layer 6 is a layer of porous conductive material located on the other side of the porous substrate. The first and second conductive layers 4 and 6 are, for example, printed on the porous substrate. Preferably, the titanium particles of the porous conductive layers 4 and 6 are large enough not to penetrate into the pores of the porous substrate.

[0054] The solar cell unit has a first conductor device 10 in electrical contact with a first porous conductive layer 4, and a second conductor device 11 in electrical contact with a second porous conductive layer 6. For example, the first and second conductor devices 10 and 11 include foils, wiring, conductive elements, or conductive bars. The solar cell unit further has a first adhesive layer 12 disposed between the first porous conductive layer 4 and the first conductor device 10, and a second adhesive layer 13 disposed between the second porous conductive layer 6 and the second conductor device 11. The conductor devices 10 and 11 are attached to the porous conductive layers 4 and 6 by the adhesive layers 12 and 13. The first adhesive layer 12 acts as an adhesive between the first conductor device 10 and the first porous conductive layer 4, and the second adhesive layer 13 acts as an adhesive between the second conductor device 11 and the second porous conductive layer 6.

[0055] Figure 2 shows an enlarged view of a portion C of the interface between the first porous conductive layer 4 and the first adhesive layer 12. In one embodiment of the present invention, Figure 2 may also show the interface between the second porous conductive layer 6 and the second adhesive layer 11. The first and second adhesive layers 12 and 13 comprise an adhesive 14 and first conductive particles 16 dispersed in the adhesive 14, so that a conductive network is formed in the adhesive 14, providing electrical contacts between the porous conductive layers 4 and 6 and the conductive devices 10 and 11, respectively. This means that the first conductive particles 16 are in electrical contact with each other, so that they form electrical paths through the adhesive layers 12 and 13. Preferably, the same adhesive 14 and the same first conductive particles 16 are used for the first and second adhesive layers 12 and 13.

[0056] The first conductive particles 16 are preferably well dispersed in the adhesive 14. Preferably, but not limited to, the first conductive particles 16 are made of carbon. The first conductive particles 16 are, for example, made of crystalline graphite, amorphous carbon, carbon nanotubes, or graphene. Preferably, the adhesive is made of a chemically resistant plastic material. If the conductive medium is an electrolyte, the adhesive must be made of a material that can withstand the electrolyte and does not react with ions in the electrolyte. For example, the adhesive is polyethylene, or polypropylene, or ionomer, or a mixture thereof. These materials can withstand the electrolytes used in solar cells.

[0057] The first and second porous conductive layers 4 and 6 contain sintered titanium particles 5, so that they are in electrical contact with each other. In this example, the first adhesive layer 12 is in direct mechanical and electrical contact with the first porous conductive layer 4.

[0058] The titanium particles 5 are covered with an insulating oxide layer 19. The insulating oxide layer 19 prevents the movement of electrons between the titanium particles 5 and the conductive medium 17 placed in the pores formed between the titanium particles 5 within the first and second porous conductive layers 4 and 6. As a result, more electrons reach the light absorption layer 2, thereby improving the efficiency of the solar cell unit. However, the insulating oxide layer 19 on the titanium particles 5 also reduces the electrical conductivity between the titanium particles 5 and the first conductive particles 16 in the adhesive layer. Since the oxidation process is carried out after the sintering process in the manufacture of the solar cell unit, the contact surfaces between the titanium particles 5 are not oxidized, and consequently, electrical contacts exist between the titanium particles 5.

[0059] The first porous conductive layer 4 includes second conductive particles 18 dispersed between titanium particles 5 in at least a portion of the first porous conductive layer 4. In Figure 2, titanium particles are denoted as Ti for illustrative purposes, and conductive particles 18 are denoted as C. As shown in Figure 2, the second conductive particles 18 and the titanium particles 5 are in electrical contact with each other via a conductive junction 20 formed between the titanium particles 5 and the second conductive particles 18. The conductive junction 20 is formed during the sintering process of the solar cell unit manufacturing process. The conductive material of the second conductive particles 18 reacts with the material of the titanium particles during the sintering process, thus forming the conductive junction 20 between the titanium particles 5 and the second conductive particles 18. The conductive junction 20 forms an electrically conductive bridge, thereby improving the electrical contact between the titanium particles 5 and the second conductive particles 18.

[0060] The second conductive particles 18 are made of a conductive material that substantially suppresses the formation of an electrically insulating oxide layer on their surface during oxidation. Therefore, the second conductive particles 18 are not covered with an electrically insulating oxide layer during the oxidation process of the manufacturing process, similar to the titanium particles. As shown in Figure 2, the first conductive particles 16 of the first adhesive layer 12 are in electrical contact with the second conductive particles 18 at the interface between the first porous conductive layer 4 and the first adhesive layer 12. Therefore, the conductive network formed within the adhesive 14 is in electrical contact with the second conductive particles 18. The second conductive particles 18 are in electrical contact with the titanium particles 5 via the conductive junction 20. Therefore, the electrical conductivity between the first porous conductive layer 4 and the first adhesive layer 12 is essentially improved.

[0061] The second conductive particles may have different shapes, such as fibrous, flaky, spherical, and irregular shapes. The second conductive particles may be solid or porous. For example, the conductive material of the second conductive particles 18 is selected from the group consisting of or including carbon, metal silicides, metal nitrides, metal carbides, doped metal oxides, doped silicon, and combinations thereof. These conductive materials have a higher resistance to the formation of an insulating oxide layer than titanium and can react with titanium during sintering of the particles to form conductive junctions between the titanium particles and the second conductive particles. Preferably, but not limited to, the second conductive particles 18 are made of carbon. Carbon can form titanium carbide junctions, metal silicides can form conductive junctions of titanium silicides, metal nitrides can form conductive junctions of titanium nitrides, metal carbides can form conductive junctions of titanium carbides, and doped metal oxides and doped silicon can form conductive junctions of doped titanium oxides. The material in the conductive junction improves the conductivity between the titanium and the material of the second conductive particles.

[0062] Suitablely, the first porous conductive layer 4 contains second conductive particles 18 in amounts between 0.001% and 5% by weight. Preferably, the first porous conductive layer 4 contains second conductive particles in amounts between 0.001% and 3% by weight, where weight % is a percentage by weight relative to the total weight of the first porous conductive layer. Such an amount of second conductive particles improves the electrical conductivity between the first porous conductive layer and the adhesive layer.

[0063] However, if the material of the second conductive particles 18 is catalytic, such as carbon, it may reduce the current generation capacity of the first porous conductive layer. In such cases, the amount of second conductive particles should be as low as possible. For example, the first porous conductive layer 4 may contain second conductive particles in amounts between 0.001% and 1% by weight, or between 0.001% and 0.8% by weight, where weight % is a percentage of the total weight of the first porous conductive layer. Such a low amount of second conductive particles does not affect the current generation capacity of the first porous conductive layer, but still improves the electrical conductivity between the first porous conductive layer and the adhesive layer.

[0064] In one embodiment, the conductive material of the second conductive particle 18 is carbon, and the conductive junction 20 between the titanium particle 5 and the second conductive particle 18 contains titanium carbide. The titanium carbide improves the electrical conductivity between titanium and carbon, and consequently improves the electrical conductivity between the titanium particle and the second conductive particle. The carbon forms carbon dioxide and / or carbon monoxide during oxidation, and therefore no insulating oxide layer is formed on the surface of the carbon particles during the oxidation step of the manufacturing process. The carbon may be any type of carbon, such as carbon black, graphene, carbon nanotubes, amorphous carbon, graphite, fullerene, nanographite particles, or flakes.

[0065] Carbon is a catalytic material and may reduce the current generation capacity of the first porous conductive layer. Preferably, the first porous conductive layer 4 contains carbon between 0.001% and 1% by weight, and most preferably, the first porous conductive layer contains carbon between 0.001% and 0.8% by weight, thereby improving the electrical conductivity between the first porous conductive layer and the adhesive layer without reducing the current generation capacity of the first porous conductive layer. Tests have shown that adding 0.2% carbon to the first porous conductive layer significantly improves the electrical conductivity between the first porous conductive layer and the adhesive layer without affecting the current generation capacity.

[0066] In this example, the second porous conductive layer 6 also contains titanium particles 5, and at least a portion of the second porous conductive layer 6 contains second conductive particles 18 dispersed among the titanium particles 5, similar to the first porous conductive layer 4 described. As shown in Figure 2, the titanium particles 5 and the second conductive particles 18 are sintered together, so that a conductive bond 20 is formed between the titanium particles 5 and the second conductive particles 18.

[0067] Figure 3 shows a view of the photovoltaic device 1a of Figure 1 from above. Figure 1 is a cross-sectional view AA of the photovoltaic device 1a shown in Figure 3. In this example, the first conductor device 10 is disposed on the top surface of the solar cell unit, and the second conductor device 11 is disposed on the bottom surface of the solar cell unit.

[0068] The second conductive device 11 is disposed below the second porous conductive layer 6 in a direction extending normal to the top surface of the solar cell unit from the bottom surface of the solar cell unit. The second adhesive layer 13 functions as an adhesive between the second conductive device 11 and the second porous conductive layer 6. The first conductive particles 16 in the conductive network formed in the adhesive 14 are in electrical contact with the second conductive particles 18 in the second porous conductive layer 6. The titanium particles 5 in the second porous conductive layer 6 are in electrical contact with the first conductive particles 16 in the conductive network in the second adhesive layer 13 via the second conductive particles 18. Therefore, the electrical conductivity between the second porous conductive layer 6 and the second adhesive layer 13 is improved in the same way as the electrical conductivity between the first porous conductive layer 4 and the first adhesive layer 12 described above is improved.

[0069] Unlike the first porous conductive layer 4, the second porous conductive layer 6 is advantageous when it contains catalyst particles. The catalyst particles function as catalysts, facilitating the transfer of electrons from the titanium particles 5 to the conductive medium 17 within the pores of the second porous conductive layer 6. Therefore, the amount of second conductive particles 18 can be greater in the second porous conductive layer 6 than in the first porous conductive layer 4. Preferably, the second conductive particles 18 are dispersed throughout the second porous conductive layer. This is advantageous from a manufacturing standpoint as it does not require additional manufacturing steps. Preferably, the second porous conductive layer 6 contains at least 0.001% by weight of second conductive particles, more preferably at least 0.01% by weight of second conductive particles, where weight % is a percentage by weight of the total weight of the second porous conductive layer 6. Preferably, the second porous conductive layer contains less than 40% by weight of second conductive particles, where weight % is a percentage by weight of the total weight of the entire second porous conductive layer.

[0070] Preferably, the average size of the second conductive particles 18 is larger than the average size of the first conductive particles 16. Preferably, the average size of the second conductive particles 18 is at least three times the average size of the first conductive particles 16. Most preferably, the average size of the second conductive particles 18 is at least ten times the average size of the first conductive particles 16. For example, the average size of the second conductive particles 18 is approximately 100 times the average size of the first conductive particles 16. The particle size can be measured, for example, using an SEM (Scanning Electron Microscopy). The smaller the first conductive particles 16 are compared to the second conductive particles 18, the greater the number of first conductive particles 16 that can come into contact with each of the second conductive particles 18 at the interface between the adhesive layer 12 and the first porous conductive layer 4. Thus, more contact points are achieved between the first and second conductive particles, which increases the electrical conductivity between them.

[0071] The average size of the second conductive particles 18 is, for example, between 1 μm and 5 μm. The average size of the first conductive particles 16 is, for example, between 1 nm and 500 nm. This ensures a sufficient interfacial contact area between the first and second conductive particles, thereby enhancing electrical conductivity between them.

[0072] The average size of the titanium particles and the second conductive particles is preferably larger than the average size of the first conductive particles. More preferably, the average size of the titanium particles and the second conductive particles is at least twice the average size of the first conductive particles, and most preferably, the average size of the titanium particles and the second conductive particles is at least three times the average size of the first conductive particles. Because the first conductive particles are smaller than the titanium particles and the second conductive particles, the interfacial surface area between the first and second conductive particles is large. Furthermore, the first conductive particles can conform to the irregularities and cavities on the surface of the porous conductive layer, thereby achieving good electrical contact between the first and second conductive particles.

[0073] Appropriately, at least 80% by weight of the titanium particles 5 have a size between 1 nm and 10 μm, and preferably, at least 80% by weight of the titanium particles 5 have a size between 0.5 μm and 5 μm, where weight% is the weight percentage relative to the total weight of the titanium particles.

[0074] Preferably, in order to achieve a suitable conductive bond 20 between the particles during sintering, the size of the second conductive particles 18 is approximately the same as the size of the titanium particles 5. For example, at least 80% by weight of the second conductive particles have a size between 1 nm and 10 μm, preferably at least 80% by weight of the second conductive particles have a size between 0.5 μm and 5 μm, where weight% is the weight percentage relative to the total weight of the second conductive particles. For example, the size of the second conductive particles 18 is 2 μm and the size of the first conductive particles 17 is 70 nm.

[0075] The photovoltaic device 1a includes an enclosure portion 22a-b that encloses a solar cell unit and a conductive medium. The enclosure portion may have a top sheet 22a that is at least partially transparent and covers the top surface 26 of the solar cell unit, and a bottom sheet 22b that covers the bottom surface 28 of the solar cell unit. The enclosure portion prevents the conductive medium from leaking out of the solar cell unit. At least a portion of the first conductor device 10, for example, a wire or conductive bar, extends outside the enclosure portion. The enclosure portion has a first through-hole (not shown) for connecting the first conductor device 10 to the first porous conductive layer 4, and a second through-hole (not shown) for connecting the second conductor device 11 to the second porous conductive layer 6.

[0076] The second conductive particles 18 can be dispersed among the titanium particles 5 throughout the entire first porous conductive layer 3. This is advantageous from a manufacturing standpoint because it does not require an additional manufacturing process. The second conductive particles can simply be added to the ink containing the titanium particles used to produce the first porous conductive layer. However, if the material of the second conductive particles 18 has catalytic properties such as carbon, the second conductive particles 18 will reduce the current generation capacity of the first porous conductive layer. Therefore, it may be preferable to disperse the second conductive particles 18 only among the titanium particles 5 in a portion of the first porous conductive layer 4. In such a case, the second conductive particles 18 can be dispersed among the titanium particles in a portion of the first porous conductive layer 4 that is located on the surface of the first porous conductive layer 4 and in the vicinity of the first adhesive layer 12, thereby achieving improved electrical conductivity between the first porous conductive layer and the first adhesive layer.

[0077] Figure 4 shows an example of such a photovoltaic device 1b. The first porous conductive layer 4 of the photovoltaic device 1b has a first portion 4a containing second conductive particles 18 dispersed between titanium particles 5 and sintered onto the titanium particles, and a second portion 4b containing titanium particles 5 sintered together without any second conductive particles 18. In this example, the first portion 4a of the first porous conductive layer 4 is located on the second portion 4b of the first porous conductive layer 4, and the first adhesive layer 12 is located on the first portion 4a of the first porous conductive layer. This embodiment is advantageous when the material of the second conductive particles 18 is catalytic. The first portion 4a is located between the second portion 4b of the first porous conductive layer 4 and the first adhesive layer 12. The first portion 4a is located on the surface of the second portion 4b of the first porous conductive layer 4, and this surface faces the first adhesive layer 12.

[0078] To achieve a significant improvement in electrical conductivity between the first porous conductive layer 4 and the first adhesive layer 12, it is sufficient to have a single layer of the second conductive particles 18 and titanium particles 5 on the surface of the second portion 4b of the first porous conductive layer 4. Therefore, the first portion 4a containing the second conductive particles can be made very thin. The thickness of the first portion 4a in the direction extending normal to the top surface 26 of the solar cell unit from the bottom surface 28 of the solar cell unit is, for example, between 0.5 μm and 20 μm, preferably between 0.5 μm and 10 μm, and most preferably between 0.5 μm and 5 μm. If the material of the second conductive particles 18 is catalytic, the thinner the first portion 4a containing the second conductive particles, the smaller the impact on power generation.

[0079] Preferably, the second conductive particles 18 are substantially uniformly dispersed among the titanium particles 5 in the first portion 4a of the first porous conductive layer 4. This further improves the electrical conductivity between the first porous conductive layer 4 and the first adhesive layer 12.

[0080] The second porous conductive layer 6 and the second adhesive layer 12 may be arranged in the same manner as described with reference to Figure 1, or in the same manner as the first conductive layer 4 described above with reference to Figure 4.

[0081] Figure 5 shows another example of the photovoltaic device 1c in a cross-sectional view. Figure 6 shows the photovoltaic device 1c viewed from above. In this example, the first conductor device 10 and the second conductor device 11 are positioned below the porous insulating layer 8 in a direction extending normal to the top surface of the solar cell unit from the bottom surface of the solar cell unit. Therefore, the first conductor device 10 and the second conductor device 11 are located at the bottom surface of the solar cell unit. Consequently, in this case, the wiring is not visible on the upper side of the photovoltaic device 1c. In this example, the first adhesive layer 12 is located below the porous insulating layer 8 at the bottom surface of the solar cell unit.

[0082] In this example, the first porous conductive layer 4 has a first portion 4a containing second conductive particles 18 dispersed between titanium particles 5, and a second portion 4b and a third portion 4c that neither contain sintered titanium particles 5 and neither contain any second conductive particles 18. The second portion 4b is in the form of a layer located on the upper 8a of the porous insulating layer 8. The third portion 4c extends through the porous insulating layer 8 from the upper 8a to the lower 8b. In this example, as shown in Figure 5, the first portion 4a of the first porous conductive layer 4 is located below the porous insulating layer 8 and below the third portion 4c of the first porous conductive layer. The first adhesive layer 12 is located below the first portion 4a of the first porous conductive layer 4 containing the second conductive particles 18 and is in physical and electrical contact with it. As shown in Figure 2, the first conductive particles 16 within the first adhesive layer 12 are in electrical contact with the second conductive particles 18 in the first portion 4a of the first porous conductive layer. The first adhesive layer 12 is positioned between the first portion 4a of the first porous conductive layer and the first conductive device 10, and is in electrical contact with both. The first conductive device 10 is in electrical contact with the conductive network formed in the adhesive. This makes it possible to install the first conductive device 10 on the bottom surface of the solar cell unit, and the wiring that prevents light from reaching the light absorption layer above the photovoltaic device is no longer visible.

[0083] In one embodiment, the porous insulating layer 8 includes one or more through-holes 29 extending from the upper side 8a of the porous insulating layer 8 to the lower side 8b of the porous insulating layer 8. A third portion 4c of the first porous conductive layer 4 extends through one or more through-holes 29. Preferably, the porous insulating layer 8 is a porous substrate, and a portion of this porous substrate is provided with through-holes 29 before the first porous conductive layer 4 is printed onto the substrate. The ink containing titanium particles 5 penetrates through one or more through-holes 29 during the printing process of the manufacturing process.

[0084] To avoid short circuits between the first and second porous conductive layers 4 and 6, the second porous conductive layer 6 is terminated at a distance from the first porous conductive layer 4, so that an insulating gap 40 is formed between the second porous conductive layer 6 and the first portion 4a of the first porous conductive layer 4, as shown in Figure 5. The first portion 4a of the first porous conductive layer 4 may have a different shape. For example, the first portion 4a of the first porous conductive layer 4 may have a circular shape, and the insulating gap 40 may be annular.

[0085] In one example, the second porous conductive layer 6 is made of the same material as the first portion 4a of the first porous conductive layer 4. Therefore, like the first portion 4a of the first porous conductive layer 4, the second porous conductive layer 6 also contains second conductive particles 18 dispersed among the titanium particles 5. This simplifies the manufacturing of the solar cell unit because the second porous conductive layer 6 and the first portion 4a of the first porous conductive layer 4 can be manufactured in the same process. For example, the second portion 4b of the first porous conductive layer 4 can be manufactured by printing a first ink containing titanium particles but no second conductive particles onto the surface of the upper 8a of the porous substrate. Some of the first ink remains on the surface of the upper 8a of the porous substrate, forming the second portion 4b of the first porous conductive layer 4, while some of the first ink penetrates through at least one through-hole 29 in the porous substrate, thereby forming the third portion 4c of the first porous conductive layer 4. The second porous conductive layer 6 and the first portion 4a of the first porous conductive layer 4 can be manufactured by printing a second ink containing a mixture of titanium particles 5 and second conductive particles 18 onto the underside 8b of the porous substrate. The solar cell unit is then subjected to a sintering process, where the titanium particles 5 and the second conductive particles 18 are sintered together, and conductive junctions 20 are formed between the titanium particles 5 and the second conductive particles 18 in the second porous conductive layer 6 and the first portion 4a of the first porous conductive layer 4.

[0086] The sintering process is carried out by heat-treating the solar cell unit in a non-oxidizing environment to bond the titanium particles and the second conductive particles together, thereby achieving mechanical and electrical contacts between them, and thus forming a conductive bond 20 between the titanium particles 5 and the second conductive particles 18. Preferably, the solar cell unit including the first and second conductive layers is heat-treated in a vacuum at a temperature above 550°C for at least 30 minutes. For example, the solar cell unit is vacuum-sintered at 650°C for 1 hour and then cooled to room temperature. The pressure during sintering is lower than 0.0001 mbar.

[0087] Figure 7 shows an example of a solar cell unit including conductive barriers 30 and 30b. If the conductive medium is an electrolyte containing ions, these ions may migrate through the adhesive layers 12 and 13. Non-porous conductive barriers 30a and 30b can be placed between the adhesive layers 12 and 13 and the first and second conductive devices 10 and 11, respectively, as proposed in WO2021 / 209221. For example, the non-porous conductive barriers 30a and 30b are attached to the first and second conductive devices 10 and 11 by soldering. The non-porous conductive barriers 30a and 30b prevent ions from migrating through the adhesive layers 12 and 13. The conductive barriers 30a and 30b act as barriers to ions in the conductive medium, preventing ions from penetrating through holes to the outside of the photovoltaic device. Since the conductive barriers are in contact with the conductive medium, they should preferably be made of a corrosion-resistant material, such as titanium. Preferably, the conductive barriers 30a and 30b are plate-like. For example, the conductive barrier has a circular shape. However, other shapes such as rectangles are also possible. The thickness of the conductive barrier 14 is preferably at least 10 nm.

[0088] The present invention is not limited to the disclosed embodiments and may be modified and altered within the scope of the following claims. For example, the solar cell unit may include additional layers, such as a catalyst layer, disposed between the porous insulating layer and the second porous conductive layer. There may also be other conductive materials other than those mentioned in the specification that satisfy the above requirements and are suitable for forming the second conductive particles 18. [Explanation of Symbols]

[0089] 1a; 1b, 1c Photovoltaic device 2. Light-absorbing layer 4. First porous conductive layer 4a First portion of the first conductive layer containing the second conductive particles 4b Second portion of the first conductive layer that does not contain the second conductive particles 4c Third portion of the first conductive layer that does not contain the second conductive particles 5 Titanium particles 6. Second porous conductive layer 8. Porous insulating layer 8a Upper side of the porous insulating layer 8b Lower side of the porous insulating layer 10 First Conductor Device 11. Second Conductor Device 12 First adhesive layer 13. Second adhesive layer 14 Adhesives 16. First conductive particle 17 Conductive medium 18. Second conductive particle 19. Insulating oxide layer 20 Conductive bonding 22a Top sheet of the encapsulation section 22b Bottom sheet of the enclosed section 26 Top surface of the solar cell unit 28. Bottom surface of the solar cell 29 Through holes in the porous insulating layer 30a, 30b Conductive barrier 40 Gap

Claims

1. - Light-absorbing layer (2), - A first porous conductive layer (4) containing titanium particles (5) made of titanium or an alloy thereof for extracting photogenerated electrons from the light-absorbing layer (2), - A second porous conductive layer (6) is disposed separately from the first porous conductive layer (4), - A conductive medium for transferring charge between the second porous conductive layer (6) and the light-absorbing layer (2), - The first conductive device (10) is in electrical contact with the first porous conductive layer (4), - A first adhesive layer (12) is disposed between the first porous conductive layer (4) and the first conductor device (10), wherein the first adhesive layer (12) comprises an adhesive (14) and first conductive particles (16) dispersed in the adhesive (14), so that a conductive network is formed in the adhesive, providing an electrical contact between the first porous conductive layer (4) and the first conductor device (10). In a photovoltaic device (1a; 1b; 1c) having a solar cell unit, A photovoltaic device (1a; 1b; 1c) characterized in that at least a portion of the first porous conductive layer (4) includes second conductive particles (18) dispersed between the titanium particles (5), wherein the second conductive particles (18) are made of a conductive material that substantially suppresses the formation of an electrically insulating oxide layer on their surface during oxidation, wherein the titanium particles (5) and the second conductive particles (18) are sintered together so as to form a conductive bond (20) between the titanium particles (5) and the second conductive particles (18), and the conductive network formed in the adhesive (14) is in electrical contact with the second conductive particles (18).

2. The photovoltaic device according to claim 1, wherein the conductive material of the second conductive particle (18) is selected from the group including carbon, metal silicide, metal nitride, metal carbide, doped metal oxide, doped silicon, and combinations thereof.

3. The photovoltaic device according to claim 1 or 2, wherein the conductive material of the second conductive particle (18) is carbon, and the conductive junction (20) between the titanium particle (5) and the second conductive particle (18) is titanium carbide.

4. The photovoltaic device according to claim 3, wherein at least a portion of the first porous conductive layer (4) contains carbon between 0.001% and 5% by weight, preferably between 0.001% and 3% by weight, where weight% is a percentage by weight relative to the total weight of the portion.

5. A photovoltaic device according to any one of the preceding claims, wherein the average size of the second conductive particles (18) is at least three times the average size of the first conductive particles (16), and preferably, the average size of the second conductive particles (18) is at least ten times the average size of the first conductive particles (16).

6. A photovoltaic device according to any one of the preceding claims, wherein the average size of the second conductive particles (18) is between 1 μm and 5 μm, and the average size of the first conductive particles (16) is between 1 nm and 500 nm.

7. A photovoltaic device according to any one of the preceding claims, wherein at least 80% by weight of the second conductive particles (18) have a size between 1 nm and 10 μm, preferably at least 80% by weight of the second conductive particles (18) have a size between 0.5 μm and 5 μm, where wt% is a weight percentage of the total weight of the second conductive particles (18).

8. The photovoltaic device according to any one of the preceding claims, wherein the solar cell unit has a porous insulating layer (8) made of an insulating material, the light absorbing layer (2) is disposed on the first porous conductive layer (4), the first porous conductive layer (4) is formed on the upper side (8a) of the porous insulating layer (8), the second porous conductive layer (6) is formed on the lower side (8b) of the porous insulating layer (8), the light absorbing layer (2) is disposed on the top surface (26) of the solar cell unit, and the second porous conductive layer (6) is disposed on the bottom surface (28) of the solar cell unit parallel to the top surface of the solar cell unit.

9. A photovoltaic device according to any one of the preceding claims, wherein a first portion (4a) of the first porous conductive layer (4) contains the second conductive particles (18) sintered with the titanium particles (5), and a second portion (4b) of the first porous conductive layer (4) contains titanium particles (5) sintered with each other without containing any of the second conductive particles (18).

10. The photovoltaic device according to claim 9, wherein the thickness of the first portion (4a) in a direction extending in the normal direction from the top surface (26) of the solar cell unit to the bottom surface (28) of the solar cell unit is between 0.5 μm and 20 μm, preferably between 0.5 μm and 10 μm, and most preferably between 0.5 μm and 5 μm.

11. The photovoltaic device according to claim 9, wherein the first portion (4a) of the first porous conductive layer is a single layer of second conductive particles (18) and titanium particles (5) arranged on the surface of the second portion (4b) of the first porous conductive layer.

12. The first porous conductive layer (4) includes a third portion (4c) containing titanium particles (5) sintered together without any second conductive particles (18), the second portion (4b) of the first porous conductive layer (4) is formed on the upper side (8a) of the porous insulating layer (8), the third portion (4c) of the first porous conductive layer (4) extends through the porous insulating layer (8) from the upper side (8a) to the lower side (8b) of the porous insulating layer (8), and the first porous The photovoltaic device according to claims 8 and 9, wherein the first portion (4a) of the porous conductive layer is located below the porous insulating layer (8) and is in physical and electrical contact with the third portion (4c) of the first porous conductive layer, the first adhesive layer (12) is located below the porous insulating layer (8) and is in physical and electrical contact with the first portion (4a) of the first porous conductive layer, and the first conductor device (10) is located on the lower side (28) of the solar cell unit.

13. The photovoltaic device according to claims 8 and 9, wherein the second portion (4b) of the first porous conductive layer is formed on the upper side (8a) of the porous insulating layer (8), and the first portion (4a) of the first porous conductive layer is formed on the second portion (4b) of the first porous conductive layer.

14. The second porous conductive layer (6) contains titanium particles (5) made of titanium or an alloy thereof, and at least a portion of the second porous conductive layer (6) contains the second conductive particles (18), where the titanium particles (5) and the second conductive particles (18) are sintered together, so that a conductive bond (20) is formed between the titanium particles (5) and the second conductive particles (18), and the solar cell unit (1) is, - The second conductive device (11) is in electrical contact with the second porous conductive layer (6), and - A second adhesive layer (13) disposed between the second porous conductive layer (6) and the second conductive device (11), wherein the second adhesive layer (13) comprises the adhesive (14) and the first conductive particles (16) dispersed in the adhesive (14), so that a conductive network is formed in the adhesive, and the conductive network in the second adhesive layer (13) is in electrical contact with the second conductive particles (18) in the second porous conductive layer (6). A photovoltaic device according to any one of the prior claims, having the following:

15. The photovoltaic device according to claim 14, wherein the second porous conductive layer (6) comprises at least 0.001% by weight of the second conductive particles (18), preferably at least 0.01% by weight of the second conductive particles (18), where weight% is a percentage by weight relative to the total weight of the second porous conductive layer (6).

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