SOLAR CELL HAVING MULTIPLE POROUS LAYERS AND CHARGE CONDUCTING MEDIUM PERMEATING THE POROUS LAYERS - Patent application

Abstract

The present invention relates to a solar cell (1a) comprising a stack of porous layers, a support substrate (2) for supporting the stack, and a charge conducting medium (7) permeating through the porous layers. The stack comprises a porous light absorbing layer (3), a porous first conductive layer (4) comprising a conductive material for extracting photogenerated electrons from the light absorbing layer, a porous counter electrode (6) comprising a conductive material, and a separation layer (5) made of a porous electrically insulating material and disposed between the conductive layer (4) and the counter electrode (6), where the conductive layer (4) is disposed closer to the light absorbing layer (3) than the counter electrode (6). The support substrate (2) is porous and the charge conducting medium (7) permeates through the support substrate (2).

Description

[Technical field]

[0001] The present invention relates to a solar cell for converting light energy into electrical energy comprising a plurality of porous layers and a charge conducting medium permeating the porous layers. [Background technology]

[0002] Solar cells comprising multiple porous layers for converting light into electrical energy are well known in the art.

[0003] Dye-sensitized solar cells (DSSCs) comprising a porous light absorbing layer, a porous conductive layer, and a porous isolating layer are known to have high potential for industrial-scale manufacturing using established manufacturing methods such as screen printing, inkjet printing, or slot-die coating.

[0004] Industrial scale manufacturing of dye-sensitized solar cells involves fabricating large area thin layers of solar cell components. These components undergo various processing steps during manufacture, such as printing, thermal treatment, vacuum treatment, and chemical processing. This means that to handle the processing of solar cells, the architecture of the solar cell is important, as it is possible to mechanically handle the components and perform various processes without damaging the underlying components. The architecture of the solar cell is also important for the overall performance of the solar cell.

[0005] A known process for manufacturing dye-sensitized solar cells is via a roll-to-roll process. In the June 14, 2018 Energy Trends article "Keys to Flexible Solar cell's Mass Production: Cell Encapsulation and Durability," researchers explain that flexible DSSCs produced by a roll-to-roll manufacturing process are commercially viable due to the efficiency of the manufacturing method.

[0006] In the roll-to-roll process, the solar cell is placed on a conveyor belt and is provided with a solid substrate, such as a flexible conductive foil, which can serve as a mechanically stable substrate for placing other components of the solar cell. US8658455 describes a roll-to-roll process with a flexible substrate. TiO 2 A layer of TiO 2 The layers are sintered, provided with dye and loaded with electrolyte, after which a second flexible substrate is added on top to seal the sandwich-type DSSC. The sealing step, which also involves a roll-to-roll process, is said to ameliorate the risks of leakage or evaporation of the liquid electrolyte.

[0007] For example, flexible conductive foils are known, such as foils of titanium, stainless steel, or other metals, or foils coated with conductive polymers, or thin films of conductive glass.

[0008] The problem with roll-to-roll manufacturing of dye-sensitized solar cells involves that some processes, such as heat treatment or vacuum treatment, need to be performed as the conveyor band rolls through an oven or chemical treatment box, which requires space and time for these processes.

[0009] Another means of manufacturing dye-sensitized solar cells is described in EP2834823B1, where a monolithic dye-sensitized solar cell is shown in which all layers of the components are porous. A porous insulating substrate made from woven and non-woven glass fibers serves as a support structure during manufacturing, and porous conductive metal layers are printed on both sides of the porous insulating substrate. On one side, a porous conductive layer, TiO 2 On the other side a porous conductive layer is provided with a catalyst. 2The layers are saturated with dye and electrolyte is added when the cells are cut into suitable pieces for laminating protective foils. During processing steps, including heat treatment, vacuum treatment, or various chemical treatments, the workpieces in operation are entirely porous, and multiple workpieces can be stapled onto each other, for example, without preventing evolved gases from venting. The porous insulating substrate used as a support substrate in the manufacturing becomes the insulating layer between the working and counter electrodes in the final solar cell. The thickness of the porous insulating substrate is therefore a trade-off between making the insulating layer thin enough to reduce resistive losses in the solar cell, and making the porous substrate thick enough to achieve sufficient mechanical properties to function as a support structure. During manufacturing, the support structure needs to be flipped over in order to print on both sides of the support.

[0010] EP1708301 discloses a dye-sensitized solar cell having an architecture including a stack of porous layers disposed on top of one another, an electrolyte integrally disposed within the pores of the porous layers, and a support structure for supporting the stack of porous layers made from ceramic, metal, resin or glass.

[0011] Another problem with dye-sensitized solar cells relates to possible electrolyte evaporation or depletion, or electrolyte leakage, especially during extended use of the solar cell. Summary of the Invention

[0012] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to at least partially overcome the above problems and to provide an improved solar cell.

[0013] This object is achieved by a solar cell as defined in claim 1.

[0014] The solar cell includes a stack of porous layers disposed on top of one another, a charge conducting medium permeating across the porous layers, and a support substrate for supporting the porous layers. The plurality of porous layers includes a light absorbing layer, a first conductive layer including a conductive material for extracting photogenerated electrons from the light absorbing layer, a counter electrode including a conductive material, and a separation layer made of a porous electrically insulating material and disposed between the first conductive layer and the counter electrode. The stack of porous layers is disposed on the support substrate, the support substrate being porous, and the charge conducting medium permeating across the porous support substrate.

[0015] The stack of porous layers is the active layer, meaning that they participate in the generation of electricity. It is necessary that a charge conducting medium can permeate through the stack of active porous layers to allow the transfer of charges between the light absorbing layer and the counter electrode. The supporting substrate is not an active layer in the solar cell, i.e. it does not participate in the generation of electricity. The main function of the supporting substrate is to act as a support for the stack of active layers.

[0016] The supporting substrate is porous, and the charge conducting medium permeates not only the pores of the porous layer of the solar cell but also the pores of the substrate. Due to the porosity of the supporting substrate, the pores of the supporting substrate act as reservoirs of the charge conducting medium. Thus, the total capacity of the charge conducting medium in the solar cell is enhanced. As a result, when the charge conducting medium in the solar cell decreases due to leakage or evaporation, the time until the total content of the charge conducting medium in the solar cell reaches a minimum level and the solar cell stops functioning is extended. The thicker and more porous the substrate, the larger the reservoir of the charge conducting medium. Since the supporting substrate does not participate in the power generation, the thickness of the supporting substrate is not important and does not affect the power generation.

[0017] Another advantage of a porous substrate is that it helps achieve uniform filling of the charge conducting medium within the solar cell during its manufacture, which is problematic when thin and wide solar cells are to be manufactured. For example, a solar cell having an area of ​​1 m 2and the thickness of the solar cell can be 0.2 mm. The charge conducting medium needs to infiltrate into the porous layer of the large solar cell, and preferably all the pores in the porous layer of the solar cell are filled with the charge conducting medium. Due to the porous substrate in the bottom of the solar cell, the charge conducting medium is introduced from the bottom of the solar cell, and most of the pores in the porous layer in the stack can be filled with the charge conducting medium by capillary force.

[0018] Another advantage with porous substrates is that they do not require vacuum filling of the cells with a conductive medium as described in the prior art, which is time consuming and requires additional equipment.

[0019] Another advantage of the porous substrate is that it retains the conductive medium by capillary forces, thereby preventing the conductive medium from flowing out. Thus, in the event of a solar cell breakage, the conductive medium will be retained within the porous substrate and will not flow out.

[0020] Another advantage of having the porous layers stacked on a porous support substrate instead of a solid support substrate as in the prior art is that it makes it easier to manufacture large size solar cells since it allows gases to escape through the substrate during vacuum sintering of the solar cell and also during air sintering of the solar cell. During air sintering, titanium dioxide TiO 2 If the layers comprising are air sintered, the combustion gases must be removed at a later stage and the combustion gases from the organic material must be removed by combustion, thus speeding up the production of solar cells.

[0021] The solar cell is preferably a monolithic cell, characterized in that all porous layers are deposited, directly or indirectly, on one and the same supporting substrate.

[0022] By having a porous support substrate at the bottom of the porous active layer, the manufacture of monolithic solar cell structures can benefit from the beneficial step of stapling the workpiece during the manufacturing process. Another advantage of having a support substrate at the bottom of the active layer on which the active layer is formed is that there is no need to flip the workpiece in operation during the manufacturing process.

[0023] Another advantage of the present invention is that the separation layer made from the porous electrically insulating material is not defined by the supporting substrate. The porous separation layer between the porous conductive layers can be formed by a cost-effective printing process and made from a variety of materials. The thickness of the separation layer can be designed to optimize the efficiency of the solar cell.

[0024] According to one embodiment, a solar cell includes a porous layer, a support substrate, and an encapsulation that encapsulates the conductive medium, with the porous layer disposed on one side of the support substrate and an opposite side of the support substrate facing the encapsulation.

[0025] The porous layer and the support substrate each have pores. The charge conducting medium permeates through the pores of the porous layer and the support substrate. The charge conducting medium is integrally disposed within the pores of the porous layer and within the pores of the support substrate.

[0026] According to one embodiment, the average size of the pores of the multiple porous layers is smaller than the average size of the pores of the support substrate, so that the capillary force of the pores of the porous layers is stronger than the capillary force of the support substrate. Due to the fact that the size of the pores in the porous layers above the support substrate is smaller than the size of the pores in the support substrate, the capillary force of the porous layers will preferentially pump the charge conducting medium upwards, where the capillary force is stronger than the capillary force in the support substrate. This operation is similar to that of a capillary pump. This means that in the case of leakage of the charge conducting medium in the upper active layer, the charge conducting medium will preferentially be pumped upwards from the reservoir to the active layer, and the support substrate will act as a reservoir to supply the charge conducting medium to the active layer.

[0027] The size of the pores in the substrate and the porous layer can be measured, for example, using a scanning electron microscope (SEM).

[0028] According to one embodiment, at least 80% of the pores in the support substrate are larger than 3 μm and at least 80% of the pores in the porous layer are smaller than 3 μm. Preferably, at least 90% of the pores in the support substrate are larger than 3 μm and at least 90% of the pores in the porous layer are smaller than 3 μm. Preferably, at least 80% of the pores in the support substrate are between 3 μm and 10 μm, and most preferably, at least 90% of the pores in the support substrate are between 3 μm and 10 μm. Thus, the pores in the porous layer are usually in the sub-meter range, i.e. less than 3 μm, and the pores in the support substrate are usually in the micrometer range, i.e. 3-10 μm. The difference in the size of the pores between the support substrate and the porous layer realizes that the capillary force in the porous layer is stronger than the capillary force in the support substrate, and as a result, when the content of the charge conducting medium in the active layer of the solar cell is reduced, the charge conducting medium will be pumped upwards to the active layer.

[0029] According to one embodiment, the thickness of the support substrate is at least 20 μm, preferably at least 30 μm, most preferably at least 50 μm. The thicker the substrate, the larger the reservoir of charge conducting medium.

[0030] According to one embodiment, the thickness of the support substrate is between 20 μm and 200 μm.

[0031] According to one embodiment, the porosity of the support substrate is at least 50%, preferably at least 70%, and most preferably at least 80%. The higher the porosity, the larger the reservoir of charge conducting medium.

[0032] According to one embodiment, the porosity of the support substrate is between 50% and 90%, preferably between 70% and 90%.

[0033] According to one embodiment, the support substrate comprises woven and / or non-woven microfibers, which are fibers having a diameter of less than 10 μm and greater than 1 nm.

[0034] According to one embodiment, the support substrate comprises inorganic fibers.

[0035] According to one embodiment, the support substrate comprises at least one of the following: glass fiber, ceramic fiber, and carbon fiber.

[0036] According to one embodiment, the microfibers have a diameter between 0.2 μm and 10 μm, preferably between 0.2 μm and 5 μm, more preferably between 0.2 μm and 3 μm, and most preferably between 0.2 and 1 μm.

[0037] According to one embodiment, the support substrate comprises a layer of woven microfiber, which is flexible, thus making the solar cell flexible.

[0038] According to one embodiment, the support substrate comprises a layer of non-woven microfibers arranged on a layer of woven microfibers. Woven microfibers and non-woven microfibers are flexible, thus making the solar cell flexible. The non-woven microfibers act as spring cushions, effectively absorbing and damping the incoming mechanical energy, and distributing the incoming mechanical energy over a larger area, thereby reducing local effects. The advantage of having a porous layer stacked on a substrate comprising a layer of woven microfibers and non-woven microfibers is that the support substrate becomes shock-absorbing, thus making the solar cell more mechanically robust, for example when subjected to mechanical bending or twisting or stretching or impact hammering. This is an advantage when the solar cell is integrated into consumer products, such as headphones, remote controls, and mobile phones.

[0039] According to one embodiment, the layer of nonwoven microfibers is disposed closer to the counter electrode than the layer of woven microfibers. Preferably, the layer of nonwoven microfibers is disposed adjacent to the counter electrode.

[0040] According to another aspect, the layer of woven microfibers is disposed closer to the counter electrode than the layer of non-woven microfibers. Preferably, the layer of woven microfibers is disposed adjacent to the counter electrode.

[0041] According to one embodiment, the layer of woven microfiber comprises a plurality of yarns having holes formed therebetween, and at least a portion of the non-woven microfiber is collected within the holes between the yarns.

[0042] According to one embodiment, the thickness of the separation layer is between 3 μm and 50 μm, preferably between 4 μm and 20 μm. It is desirable to make the separation layer as thin as possible to reduce resistive losses in the solar cell and thus improve the efficiency of the solar cell. However, if the separation layer becomes too thin, there is a risk of short circuits between the conductive layer and the counter electrode.

[0043] According to one embodiment, the separation layer comprises a porous electrically insulating material. Preferably, the electrically insulating material is made of electrically insulating particles. Such a separation layer can be manufactured by applying multiple layers of insulating particles on top of each other to achieve a desired thickness of the separation layer. In this way, the thickness of the separation layer can be controlled and the thickness of the separation layer can be selected as needed.

[0044] According to one embodiment, the electrically insulating particles are made of an insulating material.

[0045] According to one embodiment, the electrically insulating particles include a core of semiconducting material and an outer layer of electrically insulating material covering the core.

[0046] According to one embodiment, the insulating material of the outer layer of the insulating particles is alumina (Al 2 O 3), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), and aluminosilicates. The aluminosilicates include, for example, Al 2 SiO 5 It is.

[0047] According to one embodiment, the insulating material of the outer layer of the insulating particles is alumina (Al 2 O 3 ), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), and aluminosilicates. Aluminosilicates are, for example, Al 2 SiO 5 It is.

[0048] According to one embodiment, the semiconductor material in the core of the insulating particles is titanium dioxide (TiO 2 ) is provided.

[0049] According to one embodiment, the semiconductor material in the core of the insulating particles is titanium dioxide (TiO 2 ).

[0050] According to one embodiment, the electrically insulating material of the insulating particles is alumina (Al 2 O 3 ), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), and aluminosilicates. The aluminosilicates include, for example, Al 2 SiO 5 According to a further aspect, the insulating material may be glass.

[0051] According to one embodiment, the electrically insulating material of the insulating particles is alumina (Al 2 O 3 ), zirconium oxide (ZrO 2 ), silicon oxide (SiO 2), and aluminosilicates. Aluminosilicates are, for example, Al 2 SiO 5 According to a further aspect, the insulating material may be glass.

[0052] According to one embodiment, the charge conducting medium is a liquid electrolyte.

[0053] Certain conductive media, such as copper complex electrolytes and cobalt complex electrolytes, have very low electrical conductivity, which can result in very large electrical resistance losses. The low electrical conductivity comes from the fact that the electrolyte has large ions with low diffusion rates. When liquid electrolytes transport charges, the charges move in Brownian motion, i.e., erratically due to collisions with fast-moving atoms or molecules in the liquid. Copper and cobalt have relatively large ions that move slowly and therefore have low electrical conductivity. The efficiency of using such electrolytes is greatly improved by having a short distance between the counter electrode and the light absorbing layer. The present invention makes it possible to select the thickness of the separation layer, and therefore the suitable distance between the counter electrode and the light absorbing layer, depending on the electrolyte.

[0054] According to one embodiment, the conductive medium comprises a copper complex. The advantage of using copper complexes for charge transport is that the conductive medium is non-toxic. It has been shown that using copper as the conductive medium results in very high photovoltaic power. The solar cell according to the present invention allows the use of copper complexes due to the fact that the distance between the counter electrode and the light absorbing layer can be short.

[0055] According to a further embodiment, the charge conducting medium is iodide (I - ) and triiodide (I 3 - ) is provided.

[0056] Another object of the present invention is to provide a method for producing a solar cell, the method comprising: - providing a porous support substrate, - depositing a porous counter electrode on said porous support substrate; - depositing a porous separating layer on said counter electrode, - depositing a porous conductive layer on said separating layer, - depositing a porous light absorbing layer on said conductive layer, - introducing said charge conducting medium into said stack and said supporting substrate until said charge conducting medium permeates said supporting substrate and said stack; - encapsulating the solar cell, Equipped with.

[0057] According to one embodiment, depositing a porous counter electrode comprises depositing a porous second conductive layer and a porous catalyst layer on the second conductive layer.

[0058] According to one embodiment, the charge conducting medium is introduced to the support substrate on a surface facing away from the stack, such that the support substrate and the stack are impregnated with the charge conducting medium.

[0059] The deposition of the porous counter electrode, the porous separating layer, the porous first conductive layer and the porous light absorbing layer is done by spraying or printing techniques, such as, for example, inkjet printing or screen printing. [Brief description of the drawings]

[0060] The invention will now be explained in more detail by the description of various embodiments of the invention and with reference to the accompanying drawings.

[0061] [Figure 1] 1 shows a cross section of an example of a solar cell according to the present invention.

[0062] [Diagram 2] 3 shows a cross section of another example of a solar cell according to the present invention.

[0063] [Diagram 3] 1 shows an SEM image of a cross section of one example of one embodiment of the present invention.

[0064] [Figure 4] 1 shows an SEM image of a cross section of another example of one embodiment of the present invention.

[0065] [Diagram 5] 1 shows a block diagram of one example of a method for manufacturing a solar cell according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Aspects of the present disclosure are described more fully below with reference to the accompanying drawings. Solar cell devices may, however, be embodied in many different forms and should not be considered limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0067] FIG. 1 shows a cross-section of one example of a solar cell 1a according to the present invention. The solar cell 1a comprises a support substrate 2 and a stack 12 of porous layers 3-6 disposed on the support substrate 2. The stack 12 of porous layers comprises a light absorbing layer 3 functioning as a working electrode, a conductive layer 4 made of a porous conductive material functioning as a current collector, a separation layer 5 having a porous electrically insulating material, and a counter electrode 6 having a porous conductive material. The counter electrode 6 is formed on one side of the porous substrate 2. In this example, the counter electrode is a porous conductive layer. The separation layer 5 is disposed between the counter electrode 6 and the conductive layer 4. The separation layer 5 serves to physically and electrically separate the conductive layer 4 and the counter electrode 6 to avoid direct electronic short circuit between them. In this example, the separation layer 5 is formed on the counter electrode 6, and the conductive layer 4 is formed on the separation layer 5. The light absorbing layer 3 is disposed on the conductive layer 4. The first conductive layer 4 comprises a conductive material for extracting photogenerated electrons from the light absorbing layer 3. The light absorbing layer 3 can be made in various ways. For example, the light absorbing layer may comprise dye molecules adsorbed on the surface of semiconductor particles, or clusters of dye, or grains made from a semiconductor material such as silicon.

[0068] The porous layers 3-6 are active layers, meaning that they participate in power generation. The support substrate 2 is not an active layer in the solar cell, i.e. it does not participate in power generation. The support substrate 2 supports the stack 12 of the porous layers 3-6. Furthermore, the support substrate 2 allows a counter electrode 6 to be printed thereon during the manufacture of the solar cell. The porous layers 3-6 are disposed on one side of the support substrate 2.

[0069] Each of the porous layers formed on the support substrate has a number of pores. The solar cell further comprises a charge conducting medium 7 that permeates the pores of the porous layers 3-6 and enables the transport of charges between the light absorbing layer 3 and the counter electrode 6. The support substrate 2 is also porous and contains pores. The charge conducting medium 7 permeates the pores of the support substrate 2 as well as the pores of the porous layers 3-6 of the solar cell. Due to the porosity of the support substrate 2, the pores of the support substrate act as reservoirs for the charge conducting medium.

[0070] In one embodiment, the average size of the pores in the porous layers 3-6 in the stack 12 is smaller than the average size of the pores in the support substrate 2, so that the capillary forces of the pores in the porous layers 3-6 are stronger than the capillary forces in the support substrate 2. The difference in pore size between the support substrate 2 and the porous layers 3-6 makes the capillary forces in the porous layers stronger than the capillary forces in the support substrate 2, and as a result, when the content of the charge conducting medium in the active layers of the solar cell is reduced, the charge conducting medium 7 will be pumped upward into the active layers 3-6.

[0071] Preferably, at least 80% of the pores in the support substrate 2 are larger than 3 μm and at least 80% of the pores in the porous layers are smaller than 3 μm. More preferably, at least 90% of the pores in the support substrate 2 are larger than 3 μm and at least 90% of the pores in the porous layers 3-6 are smaller than 3 μm. For example, at least 80% of the pores in the support substrate 2 are between 3 μm and 10 μm.

[0072] The thicker the support substrate 2, the larger the reservoir of charge conducting medium within the solar cell. Typically, the thickness of the support substrate 2 is between 20 μm and 200 μm. Preferably, the thickness of the support substrate is at least 30 μm.

[0073] The higher the porosity in the support substrate, the larger the reservoir of charge conducting medium 7. Preferably, the porosity of the support substrate is at least 50%, most preferably at least 70%. If the support substrate is too porous, the mechanical strength of the substrate will be too low. Preferably, the porosity of the support substrate is between 50% and 90%.

[0074] The solar cell further comprises an encapsulation 10 that encapsulates the porous layers 3-6, the support substrate 2, and the conductive medium 7. A stack of porous layers 12 is disposed on one side of the support substrate 2, with the opposite side of the support substrate facing the encapsulation 10.

[0075] The stack of porous layers 12 may also include other porous layers disposed between the porous layers 3 to 6. For example, as shown in Fig. 2, there may be a porous catalyst layer disposed between the support substrate 2 and the counter electrode 6 or between the counter electrode 6 and the separation layer 5. In addition, there may be a porous reflective layer disposed between the conductive layer 4 and the light absorbing layer 3. The same conditions as stated above regarding the size of the pores apply to all layers in the stack of porous layers 12, regardless of the number of layers.

[0076] 2 shows a cross-section of another example of a solar cell 1b according to the present invention. The solar cell 1b comprises a support substrate 2 and a stack 12 of porous layers 3-6 disposed on the support substrate 2. The solar cell 1b differs from the solar cell 1a in that the counter electrode 6 of the solar cell 1b comprises a second porous conductive layer 6a and a porous catalyst layer 6b formed on the porous conductive layer 6a.

[0077] In this example, the support substrate 2 comprises a layer of woven microfibers 2a and a layer of nonwoven microfibers 2b arranged on the layer of woven microfibers 2a. The counter electrode 6 is arranged on the layer of nonwoven microfibers 2b. In this example, the porous conductive layer 6a of the counter electrode 6 is formed on the layer of nonwoven microfibers 2b. Alternatively, the catalyst layer 6b is arranged on the layer of nonwoven microfibers 2b. The layer 2a of woven microfibers comprises a plurality of woven threads with holes formed therebetween, and at least a portion of the nonwoven microfibers are integrated in the holes between the woven threads. Preferably, the microfibers in the layer 6b of nonwoven microfibers have a diameter between 0.2 μm and 5 μm, realizing that the pores have a size of more than 1 μm. EP2834824B1 discloses a method for manufacturing a substrate 2 comprising woven fabrics as well as nonwoven microfibers.

[0078] The solar cells 1a and 1b are of the monolithic type, which means that all the porous layers are deposited directly or indirectly on the same supporting substrate 2. The solar cells 1a and 1b may be, for example, dye-sensitized solar cells (DSC).

[0079] 3 shows an SEM image of a cross section of one example of one embodiment of the present invention showing a support substrate 2 comprising a layer of woven microfiber 2a on a layer of nonwoven microfiber 2b. A second porous conductive layer 6a is disposed on the support substrate 2, followed by a catalyst layer 6b, and a separation layer 5 on the catalyst layer. A first conductive layer 4 is disposed on the separation layer 5, and a light absorbing layer 3 is disposed on top of that.

[0080] 4 shows an SEM image of a cross section of another example of one embodiment of the present invention showing a support substrate 2 comprising a layer of nonwoven microfiber 2b on a layer of woven microfiber 2a. A second porous conductive layer 6a is disposed on the support substrate 2, followed by a catalyst layer 6b, and a separation layer 5 on the catalyst layer. A first conductive layer 4 is disposed on the separation layer 5, and a light absorbing layer 3 is disposed on top of that.

[0081] Preferably, the size of the pores in the light absorbing layer 3 is equal to or smaller than the size of the pores in the first conductive layer 4, the size of the pores in the first conductive layer 4 is equal to or smaller than the size of the pores in the separation layer 5, and the size of the pores in the separation layer 5 is equal to or smaller than the size of the pores in the layer of counter electrodes 6, 6a, 6b. The size of the pores in the counter electrodes 6, 6a, 6b is preferably smaller than the size of the pores in the supporting substrate 2, 2a, 2b.

[0082] In one embodiment of the invention, the size of the pores in the stack of porous layers 12 decreases from the counter electrode 6 to the light absorbing layer 3. For example, the size of the pores in the light absorbing layer 3 is smaller than the size of the pores in the first conductive layer 4, which is smaller than the size of the pores in the separation layer 5, which is smaller than the size of the pores in the counter electrodes 6, 6a, 6b. The size of the pores in the counter electrodes 6, 6a, 6b is smaller than the size of the pores in the support substrate 2, 2a, 2b. This embodiment will enhance the difference [0] in the capillary forces in the porous layers compared to the capillary forces in the support substrate 2.

[0083] The light absorbing layer 3 faces the incident light. The light absorbing layer 3 can be made by various means. For example, the light absorbing layer 3 can be a porous TiO 2 film deposited on the first conductive layer 4. 2 The TiO 2 The layer is a TiO layer with dye molecules adsorbed on its surface. 2 In another example, the light absorbing layer 3 comprises a plurality of grains of a doped semiconductor material, such as silicon, deposited on the conductive layer 4. The charge conducting medium is integrally disposed within pores formed between the grains. The thickness of the light absorbing layer 3 may vary and depends on the type of light absorbing layer 3.

[0084] The top surface of the solar cells 1a; 1b should face the light and allow it to hit the light absorbing layer 3. According to some embodiments, the light absorbing layer is a porous TiO2 layer with adsorbed organic or organometallic or natural dye molecules. 2However, the light absorbing layer 3 may also comprise grains of doped semiconductor material, for example Si, CdTe, CIGS, CIS, GaAs or perovskite.

[0085] The conductive layer 4 serves as a back contact to extract the photo-generated charges from the light absorbing layer 3. The porosity of the conductive layer 4 may preferably be between 30% and 85%. Depending on which material is used for the conductive layer 4 and which manufacturing method is used, the thickness of the conductive layer 4 can vary between 1 μm and 50 μm. For example, the conductive layer 4 is made of a material selected from the group consisting of titanium, titanium alloys, nickel alloys, graphite, and amorphous carbon, or mixtures thereof. Most preferably, the conductive layer is made of titanium or titanium alloys or mixtures thereof. In such a case, the thickness of the conductive layer 4 is preferably between 4 μm and 30 μm.

[0086] The separation layer 5 serves as an electrical separator between the conductive layer 4 and the counter electrode 6, avoiding short circuits between them. The distance between the counter electrode 6 and the light absorbing layer 3 depends on the thickness of the separation layer 5 and should be as small as possible so that the charge transfer between the counter electrode 6 and the light absorbing layer 3 is as fast as possible, thus reducing resistive losses in the solar cell. The thickness of the separation layer is for example between 3 μm and 50 μm, preferably between 4 μm and 20 μm. The separation layer comprises a porous electrically insulating material. For example, the separation layer comprises a porous layer of electrically insulating particles. For example, the insulating particles have a core of a semiconductor material and an outer layer of an electrically insulating material. For example, a layer of insulating oxide is formed on the surface of the semiconductor material. Preferably, the semiconductor material is titanium dioxide (TiO 2 The insulating material is, for example, alumina or silicon oxide. Alternatively, the whole particle is, for example, alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), or zirconium oxide (ZrO 2 ) may be used.

[0087] The counter electrode 6 comprises a porous conductive layer 6a. The counter electrode typically also comprises a catalyst layer 6b. The counter electrode 6 may have a separate porous catalyst layer 6b or may have catalyst particles integrated within the porous conductive layer 6a. The porosity of the counter electrode 6 may preferably be between 30% and 85%. Depending on which material is used for the counter electrode 6 and the manufacturing method, the thickness of the counter electrode 6 may vary between 1 μm and 50 μm. For example, the counter electrode 6 is made of a material selected from the group consisting of titanium, titanium alloys, nickel alloys, graphite, and amorphous carbon, or mixtures thereof. Most preferably, the counter electrode 6 is made of titanium or titanium alloys or mixtures thereof. In such a case, the thickness of the counter electrode 6 is preferably between 10 μm and 30 μm. To achieve a catalytic effect, the counter electrode 6 may comprise platinized particles of conductive metal oxides such as platinized ITO, ATO, PTO, and FTO, or platinized carbon black or graphite particles.

[0088] The support substrate 2 may be a microfibre-based substrate, such as a glass microfibre substrate or a ceramic microfibre substrate. The support substrate 2 is preferably made of microfibre. A microfibre is a fibre with a diameter of less than 10 μm and a length of more than 1 nm. Preferably, the support substrate 2 comprises woven microfibre. The microfibre may be made of glass, SiO 2 , Al 2 O 3 The support substrate 2 may be made of fire-resistant and inert materials such as cellulose, aluminosilicates, and the like. The organic microfibers are fibers made of polymers such as polycaprolactone, PET, PEO, or organic materials such as cellulose, e.g. nanocellulose (MFC) or wood pulp. The support substrate 2 may comprise woven microfibers and non-woven microfibers arranged on the woven microfibers. Preferably, the support substrate 2 comprises fiberglass. For example, the porous support substrate can be made of woven and non-woven glass fibers. The thickness of the support substrate 2 is preferably between 10 μm and 1 mm. Such a layer provides the required mechanical strength.

[0089] The charge conducting medium 7 is integrally disposed within the pores of the porous layers 3-6 and the pores of the support substrate 2, and transfers charges between the counter electrode 6 and the light absorbing layer 3. The conducting medium 7 may be any suitable conducting medium, such as a liquid, a gel, or a solid material such as a semiconductor. An example of an electrolyte is iodide (I) as a redox couple. - ) / Triiodide(I 3 - The conductive medium is a liquid electrolyte, such as one based on ionic or cobalt complexes, or a gel electrolyte, which is a conventional polymer electrolyte. Preferably, the conductive medium is a liquid electrolyte, such as an ionic liquid-based electrolyte, a copper complex-based electrolyte, or a cobalt complex-based electrolyte.

[0090] Solar cells must be properly sealed to avoid leakage of the charge conducting medium. For example, solar cells are provided with an encapsulation 10 that surrounds the solar cell unit. However, the encapsulation must be penetrated by some means to allow access to the power produced by the solar cell. Although the permeate is sealed, there is a risk of slow leakage of the charge conducting medium from the solar cell. Leakage can also occur from the sealed edges of the encapsulation. Slow leakage of the charge conducting medium will cause a slow deterioration of the efficiency of the solar cell. If the content of the charge conducting medium in the solar cell reaches a minimum level, the ability of the solar cell to convert light into electricity will be reduced. This process can take months or even years depending on the quality of the encapsulation and the seal.

[0091] The encapsulation 10 protects the solar cell against the surrounding atmosphere and acts as a barrier to prevent evaporation or leakage of the charge conducting medium from inside the cell. The encapsulation 10 may include a top sheet covering the top surface of the solar cell and a bottom sheet covering the bottom surface of the solar cell. The top sheet on the top surface of the solar cell covers the light absorbing layer and must be transparent to allow light to pass through. The bottom surface of the support substrate 2 faces the bottom sheet of the encapsulation 10. The light absorbing layer 3 faces the top sheet of the encapsulation 10. The top and bottom sheets are made, for example, from polymeric materials.

[0092] The edges of the top and bottom sheets are sealed.

[0093] According to one embodiment, the encapsulation 10 of the solar cells 1a; 1b comprises a number of through-openings (not shown in the figures) to allow access to the power produced by the solar cells. The through-openings receive wires for electrical connection to the first conductive layer 4 and to the counter electrode 6. The through-openings may be arranged in connection with the first conductive layer 4 and to the counter electrode 6. Preferably, the through-openings are arranged in a face of the encapsulation arranged below the support substrate 7.

[0094] 5 shows a block diagram of an example of a method for manufacturing a solar cell according to the invention. The method in FIG. 5 comprises the following steps:

[0095] S1: Providing a porous support substrate 2; S2: forming a porous counter electrode 6 on the porous support substrate 2; S3: forming a porous separation layer 5 on the counter electrode 6; S4: forming a first porous conductive layer 4 on the separation layer 5; S5: forming a porous light absorbing layer 3 on the first conductive layer 4; S6: Introducing the charge conducting medium 7 into the stack 12 and the supporting substrate 2 until the charge conducting medium 7 permeates the supporting substrate 2 and the stack 12; S7: Sealing the solar cell.

[0096] According to one embodiment, the charge conducting medium 7 is introduced to the support substrate on the side facing away from the stack 12 such that the support substrate and the stack are impregnated with the charge conducting medium.

[0097] The deposition steps in steps S2 to S5 are done by spraying or printing techniques, such as inkjet printing or screen printing, for example.

[0098] One example of how step S3 can be performed is now described in more detail. The separator ink is prepared by mixing a powder of insulating particles with a solvent, a dispersant, and a binder. The solvent is, for example, water or an organic solvent. The binder is, for example, hydroxypropyl cellulose. The dispersant is, for example, Byk180. The mixture is stirred until the agglomerated particles in the powder are separated into single particles, and the particles in the ink are sufficiently dispersed. The separator ink is deposited on the counter electrode 6 by spraying or printing techniques. The deposition of the separator ink can be repeated two, three, or more times until a sufficiently thick layer of insulating particles is deposited on the counter electrode. Preferably, the layer of separator ink is dried before the next layer of separator ink is deposited on the previous layer of separator ink. Repeating the deposition of the separator ink two or more times is advantageous, since the subsequent layer of ink will repair possible defects in the previous layer of insulating particles. It is important that there are no defects such as cracks or holes in the separating layer 5 as these would result in a short circuit between the counter electrode 6 and the porous first conductive layer 4 .

[0099] The solar cell 1a in FIG. 1 is infiltrated with a charge conducting medium 7 in the pores of the light absorbing layer 3, in the pores of the first conductive layer 4, in the pores of the separation layer 5, in the pores of the counter electrode 6, and in the pores of the support substrate 2. The charge conducting medium forms a continuous layer inside the pores of the conductive layer and between the conductive layers inside the pores of the separation layer, thereby allowing the transfer of charges between the counter electrode 6 and the working electrode, which includes the first conductive layer 4 and the light absorbing layer 3. The first porous conductive layer 4 extracts electrons from the light absorbing layer 3 and transfers them to an external electrical circuit (not shown in FIG. 1) connected to the counter electrode 6. The counter electrode 6 is used to transfer the electrons to the charge conducting medium 7. The conducting medium 7 transfers the electrons back to the light absorbing layer 3, thereby completing the electrical circuit.

[0100] Depending on the nature of the charge conducting medium 7, either ions or electrons and holes can be transferred between the counter and working electrodes.

[0101] Typically, electrolytes in dye-sensitized solar cells are classified as liquid electrolytes, quasi-solid-state electrolytes, or solid-state electrolytes. The electrolyte may be in the form of a liquid, a gel, or in a solid state. There are numerous electrolytes of either type known in the literature, see for example "Electrolytes in Dye-Sensitized Solar Cells" in Chemicals Reviews, January 28, 2015. The electrolyte is the expensive component of a dye-sensitized solar cell. The counter electrode is typically equipped with a catalytic material 6b that serves the purpose of facilitating the transfer of electrons to the electrolyte.

[0102] The charge conducting medium exhibits some electrical resistance when transferring charges. The electrical resistance increases with the charge transfer distance. Thus, when charges are transferred between the counter electrode and the light absorbing layer, there will always be some electrical resistance loss in the conducting medium. The resistance loss can be reduced by making the porous substrate thinner. However, as the porous substrate becomes thinner, it also becomes more mechanically fragile.

[0103] The conductive medium is, for example, a conventional I - / I 3- electrolyte or similar electrolyte, or Cu / Co complex electrolyte. Solid state transition metal based complexes or organic polymer hole conductors are known as the conductive medium.

[0104] According to some embodiments, the conductive medium comprises a copper ion complex. A conductive medium having a copper complex as a charge conductor is a non-toxic conductive medium. The use of copper complexes as the conductive medium has been shown to result in very high resulting photovoltages.

[0105] The counter electrode 6 can be deposited on the support substrate 2, for example by printing with an ink containing solid conductive particles. Conductive particles, such as metal hydride particles, can be mixed with a liquid to form an ink suitable for printing processing. The conductive particles can also be ground or otherwise processed to achieve a suitable particle size and therefore the desired pore size of the porous counter electrode 6. Preferably, the solid particles are metal-based and can be a pure metal, an alloy or a metal hydride or alloy hydride or a mixture thereof.

[0106] The conductive layer 4 can be deposited on the separating layer 5 in the same way as the counter electrode 6 is deposited on the supporting substrate 2. The deposition can also be treated by a heat treatment step. During the heat treatment, sintering of the particles also occurs, which increases the electrical conductivity and the mechanical stability of the conductive layer. The metal hydride is converted to a metal during the heat treatment. Heating in a vacuum or in an inert gas prevents contamination of the particles and improves the electrical contact between the particles.

[0107] The terms used herein are merely for the purpose of describing certain aspects of the disclosure and are not intended to be limiting of 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.

[0108] The terms photovoltaic cell and solar cell are used synonymously.

[0109] 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.

[0110] The invention is not limited to the disclosed embodiments, but can be varied and modified within the scope of the following claims, for example, the stack of porous layers can include other porous layers and the order of the porous layers within the stack can be changed.

Claims

1. 1. A solar cell comprising a stack of porous layers, a support substrate for supporting said stack, and a charge conducting medium permeating throughout said stack, wherein said stack comprises: a porous light absorbing layer, a porous first conductive layer comprising a conductive material for extracting photogenerated electrons from said porous light absorbing layer, a porous counter electrode comprising a conductive material, and a separating layer made of a porous electrically insulating material and disposed between said porous first conductive layer and said porous counter electrode; wherein the porous first conductive layer is disposed closer to the porous light absorbing layer than the porous counter electrode; A solar cell, wherein the stack of porous layers is disposed on the support substrate, the support substrate being porous, and the charge conducting medium permeating throughout the support substrate.

2. 2. The solar cell of claim 1, wherein the charge conducting medium is integrally disposed within the pores of the porous layer and within the pores of the support substrate, and the average size of the pores of the porous layer is smaller than the average size of the pores of the support substrate, such that capillary forces within the pores of the porous layer are stronger than capillary forces within the pores of the support substrate.

3. A solar cell according to any one of claims 1 to 2, wherein at least 80% of the pores in said porous layer have a size smaller than 3 μm.

4. The solar cell according to any one of claims 1 to 3, wherein at least 80% of the pores in the support substrate have a size greater than 3 μm.

5. The solar cell according to any one of claims 1 to 4, wherein the porosity of the support substrate is at least 50%.

6. The solar cell according to any one of claims 1 to 5, wherein the support substrate has a thickness of at least 20 μm.

7. The solar cell of any one of claims 1 to 6, wherein the support substrate comprises microfibers.

8. 8. The solar cell of claim 7, wherein the support substrate comprises microfibers having a diameter between 0.2 μm and 10 μm.

9. The solar cell of any one of claims 1 to 8, wherein the support substrate comprises woven and non-woven microfiber.

10. 10. The solar cell of claim 9, wherein the support substrate comprises a layer of woven microfiber and a layer of non-woven microfiber disposed on the layer of woven microfiber.

11. The solar cell of any one of claims 1 to 10, wherein the supporting substrate is flexible.

12. Solar cell according to any one of claims 1 to 11, wherein the thickness of the separating layer is between 3 μm and 50 μm.

13. The solar cell of any one of claims 1 to 12, wherein the charge conducting medium is a liquid electrolyte.

14. 13. A method for manufacturing a solar cell according to claim 1, comprising: - providing a porous support substrate, - depositing a porous counter electrode on said porous support substrate; - depositing a porous separating layer on said porous counter electrode; - depositing a porous first conductive layer on said porous separating layer, - depositing a porous light absorbing layer on said porous first conductive layer, - introducing said charge conducting medium into said stack and said supporting substrate until said charge conducting medium permeates said supporting substrate and said stack; - encapsulating the solar cell, A method for providing the above.

15. 15. The method of claim 14, wherein depositing the porous counter electrode comprises depositing a porous second conductive layer and a porous catalyst layer over the porous second conductive layer.

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