Tandem solar cells

Abstract

The present invention provides a tandem solar cell that suppresses losses caused by uneven power generation in the silicon element positioned beneath the perovskite element, and can efficiently extract the generated current. [Solution] The tandem solar cell 1 is a tandem solar cell 1 in which multiple perovskite elements 41 are arranged on the surface side of multiple silicon elements 51, and a portion of the multiple silicon elements 51 are arranged on the back side of the gap between the perovskite elements 41, or light passing from the surface side to the back side through the gap between the perovskite elements 41 reaches a portion of the multiple silicon elements 51, wherein the silicon elements 51 that are in contact with the gap between the perovskite elements 41 and the silicon elements 51 that are not in contact with the gap between the perovskite elements 41 are each connected separately in series.

Description

Technical Field

[0001] The present invention relates to a tandem solar cell.

Background Art

[0002] Patent Document 1 discloses a tandem solar cell in which a perovskite solar cell is laminated and joined on a silicon solar cell. This tandem solar cell has a perovskite solar cell including an absorption layer having a relatively large bandgap and a silicon solar cell including an absorption layer having a relatively small bandgap joined through a joining layer, and the perovskite solar cell disposed on the upper part absorbs light in the short wavelength region to generate electricity, and the silicon solar cell disposed on the lower part absorbs light in the long wavelength region to generate electricity, so that the threshold wavelength can be shifted to the longer wavelength side, and as a result, the wavelength band absorbed by the entire solar cell can be widened (the region of the total absorption wavelength can be widely used), and thus light energy in a wide spectral region can be efficiently utilized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Silicon solar cells have standardized cell sizes, offering little flexibility in terms of size (area). Perovskite solar cells, on the other hand, can be manufactured to have large-area cells according to the manufacturer's intentions. Larger-area cells have better area efficiency in receiving light such as sunlight, so it is desirable to use large-area cells whenever possible. This results in a difference in cell size between silicon solar cells and perovskite solar cells. When silicon solar cells and perovskite solar cells with different cell sizes are used in tandem, the number and position of cells that can be placed in the upper and lower solar cells (specifically, the silicon elements that make up the bottom cell and the perovskite elements that make up the top cell) will change, and some or all of the silicon elements may be placed below the gap between the perovskite elements.

[0005] When silicon solar cells and perovskite solar cells are used in tandem, the silicon element constituting the bottom cell receives afterglow from the perovskite solar cell, which absorbs some of the light energy, and generates electricity using this afterglow. On the other hand, there is no absorption of light energy by the perovskite solar cell in the gaps between the perovskite elements, and the light energy reaches the silicon element directly. If strong light that has passed through the gaps and not transmitted through the perovskite elements reaches the silicon element located below the gaps between the perovskite elements, power generation becomes uneven within the silicon element (uneven power generation occurs). When silicon cells that are in the gaps between the perovskite elements and silicon cells that are not in the gaps are connected in series, the silicon cells in the gaps can generate a high current, but the low current of the silicon cells not in the gaps becomes the rate-limiting factor, preventing the extraction of a high current and resulting in losses.

[0006] The present invention has been made in view of the above problems, and aims to provide a tandem solar cell that can suppress losses caused by uneven power generation of the silicon element placed below the perovskite element and efficiently extract the generated current. [Means for solving the problem]

[0007] To solve the above problems, the tandem solar cell according to the present invention is a tandem solar cell in which a plurality of perovskite elements are arranged on the surface side of a plurality of silicon elements, a portion of the plurality of silicon elements is arranged on the back side of the gap between the perovskite elements, or light passing from the surface side to the back side of the gap between the perovskite elements reaches a portion of the plurality of silicon elements, characterized in that the silicon elements that are connected to the gap between the perovskite elements and the silicon elements that are not connected to the gap between the perovskite elements are each connected separately in series. [Effects of the Invention]

[0008] According to the present invention, since silicon elements that receive light in different ways, such as sunlight, are not connected in series, losses caused by uneven power generation in the silicon elements placed below the perovskite element can be suppressed, and the generated current can be extracted efficiently. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic plan view showing an example of mounting a tandem solar cell according to one embodiment of the present invention. [Figure 2] This is an enlarged cross-sectional view schematically showing a tandem solar cell according to one embodiment of the present invention. [Figure 3] This is a schematic plan view showing an example of silicon element connection (Part 1: Parallel) of a silicon solar cell according to one embodiment of the present invention. [Figure 4] This is a schematic plan view showing an example of connecting silicon elements in a silicon solar cell according to one embodiment of the present invention (Part 2: Parallel). [Figure 5] This is a schematic plan view showing an example of connecting silicon elements in a silicon solar cell according to one embodiment of the present invention (Part 3: System division). [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described in detail below with reference to Figures 1 to 5. Note that the embodiments described below are only one aspect of the present invention and do not limit the technical scope of the present invention.

[0011] Figure 1 is a schematic plan view showing an example of mounting a tandem-type solar cell 1 (hereinafter sometimes simply referred to as solar cell 1) according to this embodiment. Specifically, it is a schematic plan view showing the solar cell 1 according to this embodiment mounted on an existing roof substrate of a vehicle 10. By mounting the solar cell 1 according to this embodiment on the roof substrate, it constitutes the roof 11 of the vehicle 10. The solar cell 1 has a curved plate-like shape. Therefore, it can be mounted on the roof substrate according to the similarly curved shape of the roof substrate of the vehicle 10.

[0012] The solar cell 1 has a tandem structure and has a translucent glass surface layer 2 on the uppermost layer of the roof 11 (i.e., the layer closest to the viewer in the orientation of Figure 1). When sunlight or other light is shone on the solar cell 1, the shone light passes through the surface layer 2 and reaches the inside of the solar cell 1. This generates an electromotive force between the positive and negative electrodes of the solar cell 1, and the generated electricity can be supplied to the vehicle 10 or the like.

[0013] Furthermore, the solar cell 1 is thin and lightweight. Taking advantage of these characteristics, the solar cell 1 can be mounted on various things, such as building roofs, in addition to the roof substrate of the vehicle 10 exemplified in Figure 1.

[0014] Figure 2 is a schematic enlarged cross-sectional view showing a tandem-type solar cell 1 according to this embodiment. Note that the solar cell 1 is for vehicle mounting and is curved to correspond to the shape of the roof substrate of the vehicle 10, but for the sake of explanation, it is shown as a flat plate in the cross-sectional view.

[0015] Solar cell 1 comprises a surface layer 2, a back layer 3, perovskite solar cell units 4 and silicon solar cell units 5 arranged sequentially from the surface layer 2 side between the surface layer 2 and the back layer 3, and a sealing material (also called an intermediate layer, etc.) 6 that seals the perovskite solar cell 4 and silicon solar cell 5. The back layer 3 is also made of glass, just like the surface layer 2. In other words, in solar cell 1, the perovskite solar cell 4 is stacked on the surface layer 2 side (upper side) of the silicon solar cell 5 between the surface layer 2 and the back layer 3, and these are sealed and joined together by the sealing material 6.

[0016] The perovskite solar cell 4 has a plurality of roughly rectangular perovskite cells 40 (3 left-right x 3 front-back = 9 in the example of Figure 1), and the plurality of perovskite cells 40 are slightly spaced apart from each other and arranged in a matrix in a plan view. Each perovskite cell 40 has a perovskite element 41, electrodes, etc., and is curved according to the curved shape of the solar cell 1. The perovskite element 41 is a power generation element made from titanite and is flexible.

[0017] The silicon solar cell 5 has a plurality of silicon cells 50 (6 left-right x 8 front-back = 48 in the example of Figure 1) which are roughly rectangular in shape. The plurality of silicon cells 50 are arranged in a matrix, slightly spaced apart from each other in a plan view, so as to face the plurality of perovskite cells 40 from above and below. Each silicon cell 50 has a silicon element 51, electrodes, etc., and is curved according to the curved shape of the solar cell 1. The silicon element 51 is also a type of power generation element, and the silicon element 51 may be a single crystal or a polycrystalline material.

[0018] As described above, after the irradiation light passes through the surface layer 2, it reaches the inside of the solar cell 1. When this irradiation light first reaches the perovskite element 41, depending on the wavelength range of the irradiation light, the irradiation light is absorbed by the perovskite element 41 or passes through the perovskite element 41 and is absorbed by the silicon element 51. Specifically, light in a wavelength range shorter than a predetermined value such as visible light is absorbed by the perovskite element 41, and light in a wavelength range longer than a predetermined value such as infrared light passes through the perovskite element 41 and is absorbed by the silicon element 51. That is, by laminating power generation elements with different absorption wavelength lengths, light with wavelengths in a wide spectral range can be absorbed and power generation can be performed, and the energy of the irradiation light can be converted into electrical energy with high conversion efficiency.

[0019] Each perovskite element 41 and each silicon element 51 are electrically connected by an interconnector (not shown), and current flows through the perovskite solar cell 4 and the silicon solar cell 5 via the interconnector. Specifically, each perovskite element 41 and each silicon element 51 are electrically connected by an interconnector separately or independently, and the perovskite element 41 (perovskite solar cell 4) and the silicon element 51 (silicon solar cell 5) are not electrically connected. The solar cell 1 that separately extracts power generation from the perovskite solar cell 4, which is such a top cell, and the silicon solar cell 5, which is a bottom cell, is called a four-terminal tandem solar cell.

[0020] The perovskite elements 41 that make up the top cell and the silicon elements 51 that make up the bottom cell have different cell sizes (area in a plan view). Specifically, the perovskite elements 41 have a larger cell size (area in a plan view) than the silicon elements 51. Therefore, fewer cells can be arranged using the perovskite elements 41 than using the silicon elements 51. In the example in Figure 1, a total of 9 perovskite elements 41 are arranged at predetermined intervals from each other: 3 in the left-right direction (vehicle width direction) and 3 in the front-rear direction (vehicle length direction). In addition, a total of 48 silicon elements 51 are arranged at predetermined intervals from each other: 6 in the left-right direction (vehicle width direction) and 8 in the front-rear direction (vehicle length direction). When silicon solar cells 5 and perovskite solar cells 4 with different cell sizes are used in tandem, the number and position of cells that can be placed in the upper and lower solar cells (specifically, the silicon elements 51 that make up the bottom cell and the perovskite elements 41 that make up the top cell) change, and some or all of the silicon elements 51 may be placed on the back layer 3 side (lower side) of the gap between the perovskite elements 41. In the example in Figure 1, for the 24 silicon elements 51 in total, six from each of the 2nd, 4th, 5th, and 7th rows from the front (left side of Figure 1), the entire silicon element 51 is placed below the perovskite element 41. However, for the 24 silicon elements 51 in total, six from each of the 1st, 3rd, 6th, and 8th rows from the front (left side of Figure 1), some (or all) of the silicon elements 51 are placed below the gap between the perovskite elements 41.

[0021] When a silicon solar cell 5 (silicon element 51 thereof) and a perovskite solar cell 4 (perovskite element 41 thereof) are used tandemly (stacked), in the silicon element 51 that constitutes the bottom cell, the remaining light after a part of the light energy is absorbed by the perovskite solar cell 4 reaches, and power generation is carried out with the remaining light. On the other hand, in the gap between the perovskite elements 41, there is no absorption of light energy by the perovskite solar cell 4, and the light energy directly reaches the silicon element 51. When strong light that has passed through the gap between the perovskite elements 41 (from the upper side to the lower side) and has not passed through the perovskite elements 41 reaches the silicon element 51 disposed below the gap between the perovskite elements 41, power generation in the silicon element 51 becomes non-uniform (power generation unevenness occurs) (see particularly FIG. 2). When the silicon cells 50 related to the gap portion between the perovskite elements 41 and the silicon cells 50 not related to the gap portion are connected in series, the silicon cells 50 related to the gap portion can generate a high current, but the current of the silicon cells 50 not related to the gap portion is rate-limitingly low, and a high current cannot be extracted and is lost.

[0022] Therefore, the solar cell 1 according to the present embodiment has a configuration in which there are a plurality of ways in which light reaches the silicon element 51 due to the arrangement of the perovskite elements 41 above the silicon element 51, and when the silicon element 51 can be layer-separated according to the way light reaches, it is a connection configuration in which different types are not connected in series with the layer-separated silicon elements 51, in other words, a configuration in which only the same type of silicon elements 51 are connected in series. Specifically, the solar cell 1 according to the present embodiment has the silicon elements 51 related to the gap portion between the perovskite elements 41 (below) connected in series separately from each other, and the silicon elements 51 not related to the gap portion between the perovskite elements 41 connected in series separately from each other.

[0023] FIG. 3, FIG. 4, and FIG. 5 schematically show connection examples of the silicon element 51 (silicon cell 50) of the silicon solar cell 5, respectively.

[0024] As mentioned above, in the example in Figure 1, the 24 silicon elements 51, consisting of 6 elements in each of the 2nd, 4th, 5th, and 7th rows from the front (left side of Figure 1), do not overlap the gaps between the perovskite elements 41. On the other hand, the 24 silicon elements 51, consisting of 6 elements in each of the 1st, 3rd, 6th, and 8th rows from the front (left side of Figure 1), overlap the gaps between the perovskite elements 41. Furthermore, in the example in Figure 1, the amount of light reaching the 24 silicon elements 51 that overlap the gaps between the perovskite elements 41 is approximately the same, and the power generation in these 24 silicon elements 51 is approximately the same.

[0025] Therefore, in this embodiment, as an example of connecting the silicon elements 51 (silicon cells 50) of the silicon solar cell 5, the solar cell 1 is configured in a parallel circuit as shown in Figure 3, such that silicon elements 51 that overlap the gaps between the perovskite elements 41 and silicon elements 51 that do not overlap the gaps between the perovskite elements 41 are not connected in series. Specifically, in this embodiment, the solar cell 1 has a group of silicon elements (four groups of silicon elements) in which silicon elements 51 overlapping the gaps between the perovskite elements 41 are connected in series in row units (each row), and a group of silicon elements (four groups of silicon elements) in which silicon elements 51 that do not overlap the gaps between the perovskite elements 41 are connected in series in row units (each row), connected in parallel. By connecting the silicon elements 51 (silicon cells 50) as shown in Figure 3, a high current can be extracted.

[0026] Furthermore, in this embodiment, as an example of connecting the silicon elements 51 (silicon cells 50) of the silicon solar cell 5, as shown in Figure 4, groups of silicon elements (1st and 3rd rows, and 6th and 8th rows) where silicon elements 51 that overlap the gaps between perovskite elements 41 are connected in series in units of two rows (every two rows), and groups of silicon elements (2nd and 4th rows, and 5th and 7th rows) where silicon elements 51 that do not overlap the gaps between perovskite elements 41 are connected in series in units of two rows (every two rows), and these groups of silicon elements are connected in parallel. By connecting the silicon elements 51 (silicon cells 50) as shown in Figure 4, the voltage can be increased and the current can be decreased.

[0027] Furthermore, in this embodiment, as an example of connecting the silicon elements 51 (silicon cells 50) of the silicon solar cell 5, as shown in Figure 5, silicon elements 51 that overlap the gaps between the perovskite elements 41 and silicon elements 51 that do not overlap the gaps between the perovskite elements 41 are connected in series, and the silicon elements 51 that do not overlap the gaps between the perovskite elements 41 are connected in series, and the power is extracted from the power converter 7 by separating the power grid according to voltage into a group of silicon elements where silicon elements 51 overlapping the gaps between the perovskite elements 41 are connected in series and a group of silicon elements where silicon elements 51 not overlapping the gaps between the perovskite elements 41 are connected in series.

[0028] As described above, the tandem solar cell 1 according to this embodiment has multiple perovskite elements 41 arranged on the surface side (surface layer 2 side) of multiple silicon elements 51, and a portion of the multiple silicon elements 51 is arranged on the back side (back layer 3 side) of the gap between the perovskite elements 41, or light passing through the gap between the perovskite elements 41 from the surface side (surface layer 2 side) to the back side (back layer 3 side) reaches a portion of the multiple silicon elements 51, wherein the silicon elements 51 that are in contact with the gap between the perovskite elements 41 and the silicon elements 51 that are not in contact with the gap between the perovskite elements 41 are each connected separately in series.

[0029] According to this embodiment, since the silicon elements 51 that receive light in different ways, such as sunlight, are not connected in series, losses caused by uneven power generation (non-uniform power generation) in the silicon elements 51 positioned below the perovskite element 41 can be suppressed, and the generated current can be extracted efficiently (without waste). This makes it possible to suppress a decrease in the power generation efficiency of the tandem solar cell 1.

[0030] In the above embodiment, the silicon elements 51 are shown as being connected in series in the left-right direction or the vehicle width direction, depending on how light reaches the silicon elements 51, that is, how the gaps between the perovskite elements 41 overlap. However, the connection configuration of the silicon elements 51 can be arbitrarily set depending on the arrangement of the perovskite elements 41 (perovskite cells 40) and the silicon elements 51 (silicon cells 50). For example, the arrangement of the perovskite elements 41 (perovskite cells 40) and the silicon elements 51 (silicon cells 50) can be changed so that the power generation of the silicon elements 51 is equivalent in the front-rear direction or the vehicle length direction, and the silicon elements 51 can be connected in series in the front-rear direction or the vehicle length direction.

[0031] Furthermore, as mentioned above, in a tandem solar cell 1, it is desirable that the entire silicon element 51 is positioned below the perovskite element 41. However, if part or all of each silicon element 51 is positioned below the gap between the perovskite elements 41, it is desirable that the silicon elements 51 connected in series have the same degree of overlap with the perovskite elements 41 in a plan view (when viewed from top to bottom) (more specifically, the ratio of the area of ​​the overlapping portion with the perovskite elements 41 to the total area of ​​the silicon element 51, or the ratio of the area of ​​the portion exposed from the perovskite elements 41 to the total area of ​​the silicon element 51) (corresponding to the amount of power generated). Therefore, it is preferable to set the connection configuration of the silicon elements 51 (i.e., the silicon elements 51 connected in series) so that the degree of overlap of each silicon element 51 with the perovskite elements 41 is the same for the silicon elements 51 connected in series. Furthermore, for example, in order to simplify the connection configuration of the silicon elements 51, the arrangement of the perovskite elements 41 (perovskite cells 40) and the silicon elements 51 (silicon cells 50), that is, their relative (up and down) positional relationship, may be set in advance so that the degree of overlap between the silicon elements 51 connected in series and the perovskite elements 41 is the same, or so that the number of types of overlap between the silicon elements 51 connected in series and the perovskite elements 41 is reduced.

[0032] Furthermore, the present invention is not limited to the embodiments described above, and can be appropriately modified and altered without departing from the objectives of the present invention. [Explanation of Symbols]

[0033] 1: Tandem solar cell, 2: Front layer, 3: Back layer, 4: Perovskite solar cell, 40: Perovskite cell, 41: Perovskite element, 5: Silicon solar cell, 50: Silicon cell, 51: Silicon element, 6: Encapsulation material, 7: Power converter, 10: Vehicle, 11: Roof

Claims

1. Multiple perovskite elements are arranged on the surface side of multiple silicon elements. A tandem solar cell in which a portion of the plurality of silicon elements is arranged on the back side of the gap between the perovskite elements, or in which light passing through the gap between the perovskite elements from the front side to the back side reaches a portion of the plurality of silicon elements, A tandem solar cell characterized in that silicon elements that overlap the gaps between the perovskite elements and silicon elements that do not overlap the gaps between the perovskite elements are connected in series separately.

2. A tandem solar cell according to claim 1, characterized in that a group of silicon elements, where silicon elements overlapping the gaps between the perovskite elements are connected in series, and a group of silicon elements, where silicon elements not overlapping the gaps between the perovskite elements are connected in series, are connected in parallel.

3. The tandem solar cell according to claim 1, characterized in that the generated current is extracted by dividing the power converter into separate systems for each voltage, using a group of silicon elements connected in series that are located in the gaps between the perovskite elements and a group of silicon elements connected in series that are not located in the gaps between the perovskite elements.

4. The tandem solar cell according to claim 1, characterized in that the silicon elements connected in series are set based on the degree of overlap with the perovskite elements when viewed from the front side to the back side of the silicon elements, or the relative positional relationship between the perovskite elements and the silicon elements is set.

5. The tandem solar cell according to claim 1, characterized in that the perovskite element has a larger area than the silicon element.

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