Photovoltaic solar cell
A thin charge-collecting structure for silicon solar cells addresses space-based degradation, maintaining efficiency and reducing unwanted absorption, thus enhancing performance in space environments.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
- Filing Date
- 2025-12-08
- Publication Date
- 2026-06-18
AI Technical Summary
Existing silicon solar cells with passivated contacts face degradation in the space environment, necessitating a solution that maintains high conversion efficiency and is cost-effective, while minimizing unwanted absorption and thickness of layers.
A photovoltaic solar cell design featuring a crystalline silicon substrate with thin or nonexistent passivation layers and charge-collecting structures, each less than 1.5 nm thick, optimized for space environments.
The design maintains good charge collection performance at the end of its life, achieving efficiency comparable to traditional structures with improved optical performance.
Smart Images
Figure EP2025085935_18062026_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Photovoltaic Solar Cell
[0003] Technical field of the invention
[0004] The present invention relates to a photovoltaic solar cell, for example, used in a space-based photovoltaic device. The invention also relates to such a space-based photovoltaic device.
[0005] State of the art
[0006] With a view to continuously improving photovoltaic conversion efficiencies, the latest generations of high-efficiency crystalline silicon cells are typically of the "passivated contact" type. Passivated contacts incorporate thin films into the device surfaces, within the contact structure, which simultaneously suppress carrier recombination and promote charge carrier selectivity, thus allowing the crystalline silicon cell to approach its maximum theoretical efficiency.
[0007] More specifically, in the field of space photovoltaics, traditionally based on III-V multi-junction technologies, the massive deployment of satellite constellations calls for a paradigm shift in cell technologies: it is now necessary to find radically cheaper solutions with high production volumes.
[0008] In this context, silicon solar cells with passivated contacts (such as heterojunction silicon solar cells) are excellent candidates for meeting this need. However, it is necessary to adapt these silicon solar cells to achieve optimal conversion efficiencies at the end of their mission. Unlike terrestrial photovoltaics, the space environment, and particularly the radiation environment, degrades solar cells. Space-based photovoltaics therefore aims to optimize the photovoltaic conversion efficiencies of cells and modules to achieve the desired power output at the end of their lifespan.
[0009] There is therefore a need to find a photovoltaic cell structure with good conversion efficiencies, especially at the end of its life, which is simple and inexpensive to produce.
[0010] Object of the invention
[0011] The present invention aims to provide a solution that addresses all or part of the aforementioned problems.
[0012] This goal can be achieved through the implementation of a photovoltaic solar cell comprising: a crystalline silicon substrate doped according to a first type of conductivity, said substrate having a first surface and a second surface opposite to the first surface; and a first charge-collecting structure comprising a first charge-extraction layer, said first charge-extraction layer being doped according to a second type of conductivity and being: o in direct contact with the first surface of the substrate; or o disposed on a first passivation layer of the first charge-collecting structure, said first passivation layer being in direct contact with the first surface of the substrate and having a first passivation thickness measured between the first surface of the substrate and the first charge-extraction layer which is less than or equal to 1.5 nm.
[0013] The previously described features allow for the design of a photovoltaic solar cell in which the first passivation layer is very thin or nonexistent. This maintains good charge collection performance at the end of its life while minimizing the thickness of layers that generate unwanted absorption, such as the first passivation layer. Surprisingly, it has been found that the presence of such a first charge-collecting structure results in end-of-life performance similar to or better than that of traditional structures with passivated contacts, due to improved optical performance.
[0014] The solar cell may also exhibit one or more of the following characteristics, taken alone or in combination.
[0015] According to one embodiment, the first type of conductivity is the same as the second type of conductivity.
[0016] According to one embodiment, the first charge-collecting structure comprises, or is made of, silicon.
[0017] According to one embodiment, the first passivation layer comprises intrinsic amorphous silicon, a silicon oxide such as silicon dioxide, or a dielectric material.
[0018] According to one embodiment, the first charge collection structure comprises only the first charge extraction layer when the latter is in direct contact with the first substrate surface.
[0019] According to one embodiment, the first charge collection structure includes the first charge extraction layer and the first passivation layer when the first charge extraction layer is not in direct contact with the first substrate surface.
[0020] The thickness of the first charge-collecting structure, measured substantially perpendicular to the first surface of the substrate, is less than 10 nm, and preferably between 0.5 nm and 4 nm.
[0021] It is therefore well understood that the thickness of the first charge collection structure is equal to the thickness of the first charge extraction layer when it is in direct contact with the first surface of the substrate, and that the thickness of the first charge collection structure is equal to the sum of the thickness of the first passivation layer and the thickness of the first charge extraction layer when it is not in direct contact with the first surface of the substrate.
[0022] Advantageously, using a first load collection structure of low thickness improves the transparency of this first load collection structure.
[0023] According to one embodiment, the second type of conductivity is opposed to the first type of conductivity.
[0024] In this way, it is possible to form part of a heterojunction photovoltaic solar cell, in particular of silicon.
[0025] According to one embodiment, the substrate comprises monocrystalline or multicrystalline silicon.
[0026] Thus, electron / hole pair formation is facilitated. Indeed, electron / hole pair formation is a consequence of the absorption of the solar spectrum within the semiconductor. This collection of electron / hole pairs is facilitated by the presence of a p / n junction in the passivated contact cell. Preferably, this p / n junction is located on the front face (the side exposed to the solar spectrum), formed by the n-doped amorphous silicon layer and the p-doped monocrystalline silicon.
[0027] According to one embodiment, the substrate comprises p-doped crystalline silicon.
[0028] In other words, the first type of conductivity is positive.
[0029] Advantageously, a p-doped crystalline silicon substrate exhibits better resistance to external irradiation, particularly when this originates from a space environment.
[0030] According to one embodiment, the substrate comprises n-doped crystalline silicon. In other words, the first type of conductivity is negative.
[0031] The first charge extraction layer comprises amorphous silicon and / or nanocrystalline silicon. Advantageously, the presence of amorphous or nanocrystalline silicon in the first charge extraction layer reduces charge carrier recombination on the surface of the crystalline silicon substrate and promotes charge carrier selectivity.
[0032] According to one embodiment, the first filler extraction layer comprises molybdenum oxide and / or lithium fluoride.
[0033] The use of molybdenum oxide or lithium fluoride reduces unwanted absorption, thereby improving optical properties. Furthermore, the use of lithium fluoride facilitates electron extraction.
[0034] According to one embodiment, the first charge extraction layer comprises oxygen and / or carbon atoms.
[0035] In this way, it is possible to improve the transparency of the first charge extraction layer, without compromising its ability to extract charges.
[0036] According to one embodiment, the first layer of filler extraction has a thickness between 0.5 nm and 10 nm and preferably between 0.5 nm and 4 nm.
[0037] Thus, the thickness of the first charge extraction layer is large enough to allow good selectivity of charge carriers, and is thin enough to limit the parasitic absorption of incident light.
[0038] According to one embodiment, at least one first metallic electrode is disposed on the side of the first surface of the substrate.
[0039] According to one embodiment, at least a second metallic electrode is disposed on the side of the second surface of the substrate.
[0040] The substrate has a substrate thickness between the first surface and the second surface, said substrate thickness being between 10pm and 100pm.
[0041] Thus, it is possible to offer a thin solar cell that is less prone to performance degradation when subjected to high-energy irradiation, for example in a space environment.
[0042] According to one embodiment, the first charge collection structure is arranged on a front face of the solar cell, said front face being intended to be turned towards the solar radiation captured by the solar cell.
[0043] In this way, it is possible to place the first charge collection structure on the side of the solar radiation, which allows a face of the solar cell with good transparency to be oriented towards the light radiation.
[0044] According to one embodiment, the photovoltaic solar cell further comprises a second charge-collecting structure comprising a second charge-extraction layer, said second charge-extraction layer being of a third type of conductivity opposite to the second type of conductivity, said second charge-collecting structure being disposed on the opposite side to the first charge-collecting structure with respect to the substrate.
[0045] Thus, the presence of two charge-collecting structures having an opposite type of conductivity facilitates the separation of electron-hole pairs.
[0046] According to one embodiment, the second charge extraction layer is: o in direct contact with the second substrate surface; or o disposed on a second passivation layer of the second charge collection structure, said second passivation layer being in direct contact with the second substrate surface and having a second passivation thickness measured between the second substrate surface and the second charge extraction layer which is less than or equal to 1.5 nm.
[0047] In this way, it is possible to design a photovoltaic solar cell in which a charge collection structure, conducive to optimal cell performance, is present on each side of the substrate. Such an architecture is compatible with solar cells capable of capturing solar radiation on both the front and rear surfaces.
[0048] According to one embodiment, the photovoltaic solar cell comprises a first metallic electrode disposed on the side of the first surface of the substrate and a transparent conductive electrode interposed between the first charge-collecting structure and the first metallic electrode, said transparent conductive electrode being configured to transfer charges captured by the first charge-collecting structure to the first metallic electrode.
[0049] In this way, it is possible to improve the transfer of charges captured by the first charge-collecting structure to the first metallic electrode.
[0050] The objective of the invention can also be achieved through the implementation of a space-based photovoltaic device comprising a photovoltaic solar cell as described above. Such a photovoltaic device exhibits improved end-of-life performance.
[0051] Brief description of the drawings
[0052] Other aspects, purposes, advantages and features of the invention will become more apparent from the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: Figure 1 is a schematic view of a solar cell according to a first embodiment of the invention.
[0053] Figure 2 is a schematic view of a solar cell according to a second embodiment of the invention.
[0054] Figure 3 is a schematic view of a solar cell according to a third embodiment of the invention.
[0055] Detailed description
[0056] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and can be combined.
[0057] As can be seen in Figures 1 to 3, the invention relates to a photovoltaic solar cell 1, for example intended to be included in a space-based photovoltaic device. The invention also relates to a space-based photovoltaic device comprising such a photovoltaic solar cell 1.
[0058] The photovoltaic solar cell 1 initially comprises a crystalline silicon substrate 3, for example, monocrystalline or multicrystalline silicon. This facilitates the formation of electron / hole pairs. Indeed, electron / hole pair formation results from the absorption of the solar spectrum within the semiconductor. This collection of electron / hole pairs is facilitated by the presence of a p / n junction in the solar cell 1 with passivated contacts. Preferably, this p / n junction is located on the front face, denoted "FAv," of the solar cell 1 (the side exposed to the solar spectrum), formed by a layer of n-doped amorphous silicon and p-doped monocrystalline silicon. The substrate 3 is doped according to a first type of conductivity. Advantageously, the substrate 3 comprises p-doped crystalline silicon, meaning that the first type of conductivity is positive.It has been shown that a p-doped crystalline silicon substrate 3 exhibits better resistance to external irradiation, particularly when this originates from a space environment.
[0059] The substrate 3 has a first surface s31 and a second surface s32 opposite the first surface s31. For example, the first surface s31 can be positioned on the front face FAv of the solar cell 1, and the second surface s32 can be positioned on the rear face, denoted "FAr", of the solar cell 1. Such a construction is not, however, limiting, and it is quite possible to interchange the position of the constituent elements of the solar cell 1 between the front face FAv and the rear face FAr.
[0060] The substrate 3 can have a substrate thickness e3 between the first surface s31 and the second surface s32 that is less than 300 pm, and specifically between 10 pm and 100 pm. Thus, it is possible to propose a thin solar cell 1 that is less prone to performance degradation when subjected to high-energy irradiation, for example in a space environment.
[0061] The solar cell 1 is generally provided with at least one first metallic electrode 2 disposed on the side of the first surface s31 of the substrate 3. The figures illustrate in particular variants in which the solar cells 1 include two first metallic electrodes 2.
[0062] On the opposite side, the solar cell is generally provided with at least one second metallic electrode 4 arranged on the side of the second surface s32 of the substrate 3. The figures illustrate in particular variants in which the solar cells 1 include two second metallic electrodes 4.
[0063] Furthermore, although not limiting, the photovoltaic solar cell 1 may include a transparent conductive electrode 6 interposed between the first surface s31 and the first metallic electrode 2. This transparent conductive electrode 6 is configured to transfer charges captured by a first charge-collecting structure 5 (which will be described later) to the first metallic electrode 2. In this way, it is possible to improve the transfer of charges captured by the first charge-collecting structure 5 to the first metallic electrode 2. Moreover, the transparency of the transparent conductive electrode 6 allows solar radiation to pass through for capture by the solar cell.
[0064] Similarly, the photovoltaic solar cell 1 may include a transparent conductive electrode 6 interposed between the second surface s32 and the second metallic electrode 4. This transparent conductive electrode 6 is configured to transfer charges captured by a second charge-collecting structure 7 (which will be described later) to the second metallic electrode 4. In this way, it is possible to improve the transfer of charges captured by the second charge-collecting structure 7 to the second metallic electrode 4.
[0065] Advantageously, the presence of a transparent conductive electrode 6 on both sides of the solar cell 1 allows solar radiation to pass through to the front face FAv and the rear face FAr of the solar cell 1, thus enabling the capture of a maximum amount of solar radiation. This is therefore particularly suitable for solar cells 1 in a space environment.
[0066] The solar cell 1 also includes a first charge-collecting structure 5, generally formed or made of silicon. "Charges" refers to electrons or holes. Thus, the first charge-collecting structure can be configured to collect electrons or, alternatively, holes (or electron deficiency). Although not a limitation, it is possible for the first charge-collecting structure 5 to be located on the front face FAv of the solar cell 1. In this way, it is possible to position the first charge-collecting structure 5 on the side facing the sunlight, thereby orienting a face of the solar cell 1 with good transparency towards the light.
[0067] Advantageously, a thickness e5 of the first charge-collecting structure 5, measured substantially perpendicular to the first surface s31 of the substrate 3, is less than 10 nm, and preferably between 0.5 nm and 4 nm. Using a first charge-collecting structure 5 with a small thickness (i.e., less than 10 nm) improves the transparency of this first charge-collecting structure 5.
[0068] The first collection structure comprises a first charge-extraction layer 51, said first charge-extraction layer 51 being doped according to a second type of conductivity. Although it is possible for the first type of conductivity to be the same as the second type of conductivity, it is generally assumed that the second type of conductivity is opposite to the first type of conductivity. In this way, it is possible to form part of a heterojunction photovoltaic solar cell 1, particularly one made of silicon.
[0069] Depending on the chosen embodiment, the first charge extraction layer 51 may comprise amorphous silicon and / or nanocrystalline silicon. Advantageously, the presence of amorphous or nanocrystalline silicon in the first charge extraction layer 51 reduces charge carrier recombination and promotes charge carrier selectivity.
[0070] Alternatively, the first filler extraction layer 51 may consist of molybdenum oxide (MoOx) and / or lithium fluoride (LiF). The use of molybdenum oxide or lithium fluoride facilitates filler extraction while providing good transparency.
[0071] It is also possible for the first charge extraction layer 51 to include oxygen and / or carbon atoms. In this way, it is possible to improve the transparency of the first charge extraction layer 51 without compromising its ability to extract electron or hole charges.
[0072] Regardless of the variant chosen, it is advantageous to ensure that the first charge-harvesting layer 51 has a thickness e51 between 0.5 nm and 10 nm, and preferably between 0.5 nm and 4 nm. Thus, the thickness e51 of the first charge-harvesting layer 51 is sufficient to allow good charge carrier selectivity, yet thin enough to limit unwanted absorption of incident light. The first charge-harvesting layer 51 is in direct contact with the first surface s31 of the substrate 3, or is placed on a first passivation layer 53 of the first charge-harvesting structure 5. For example, the first passivation layer 53 comprises intrinsic amorphous silicon, a silicon oxide such as silicon dioxide, or a dielectric material.
[0073] In the first case, represented in particular in Figure 1, the first charge collection structure 5 comprises only the first charge extraction layer 51. Thus, the thickness e5 of the first charge collection structure 5 is equal to a thickness e51 of the first charge extraction layer 51.
[0074] In the second case, and as illustrated in Figures 2 and 3, the first charge collection structure 5 comprises the first charge extraction layer 51 and the first passivation layer 53. The first passivation layer 53 is thus in direct contact with the first surface s31 of the substrate 3.
[0075] The first passivation layer 53 has a first passivation thickness e53, measured between the first surface s31 of the substrate 3 and the first charge extraction layer 51, which is less than or equal to 1.5 nm. The thickness e5 of the first charge-collecting structure 5 is therefore generally equal to the sum of the thickness e53 of the first passivation layer 53 and the thickness e51 of the first charge extraction layer 51.
[0076] The photovoltaic solar cell 1 typically includes a second charge-collecting structure 7 positioned on the opposite side of the substrate 3 from the first charge-collecting structure 5. This second charge-collecting structure 7 is configured to collect charges of opposite polarity to those collected by the first charge-collecting structure 5. For example, if the first charge-collecting structure 5 is configured to collect electrons, then the second charge-collecting structure 7 is configured to collect holes. The reverse is also possible. The presence of two charge-collecting structures 5 and 7 facilitates the separation of electron-hole pairs.
[0077] It is therefore understood that, with the exception of the opposing loads, the first and second load-bearing structures 5 and 7 can have similar designs, particularly with regard to their thicknesses and the types of materials used. Furthermore, it is possible for the first load-bearing structure 5 to be positioned on the front face FAv and the second load-bearing structure 7 on the rear face FAr, or vice versa.
[0078] The second charge-collecting structure 7 may include a second charge-extraction layer 71 of a third type of conductivity opposite to the second type of conductivity. Depending on the embodiment chosen, the second charge-extraction layer 71 may comprise amorphous silicon and / or nanocrystalline silicon. Advantageously, the presence of the second charge-extraction layer 71 in amorphous or nanocrystalline silicon reduces charge carrier recombination at the surface of the crystalline silicon substrate and promotes charge carrier selectivity.
[0079] Alternatively, the second filler extraction layer 71 may consist of molybdenum oxide (MoOx) and / or lithium fluoride (LiF). The use of molybdenum oxide or lithium fluoride facilitates filler extraction while providing good transparency.
[0080] It is also possible that the second charge extraction layer 71 comprises oxygen and / or carbon atoms. In this way, it is possible to improve the transparency of the second charge extraction layer 71 without compromising its ability to extract electron or hole charges.
[0081] Regardless of the variant chosen, it is advantageous to ensure that the second charge extraction layer 71 has a thickness e71 between 0.5 nm and 10 nm, and preferably between 0.5 nm and 4 nm. Thus, the thickness e71 of the second charge extraction layer 71 is sufficiently large to allow good charge carrier selectivity, and sufficiently small to limit unwanted absorption of incident light.
[0082] The second charge-harvesting layer 71 can be in direct contact with the second surface s32 of the substrate 3, or disposed on a second passivation layer 73 of the second charge-harvesting structure 7. For example, the second passivation layer 73 comprises intrinsic amorphous silicon, a silicon oxide such as silicon dioxide, or a dielectric material.
[0083] In the first case, represented in particular in Figures 1 and 3, the second charge collection structure 7 comprises only the second charge extraction layer 71. Thus, the thickness e7 of the second charge collection structure 7 is equal to a thickness e71 of the second charge extraction layer 71.
[0084] In the second case, and as illustrated in Figure 2, the second charge-collecting structure 7 comprises the second charge-extraction layer 71 and the second passivation layer 73. The second passivation layer 73 is thus in direct contact with the second surface s32 of the substrate 3.
[0085] The second passivation layer 73 may have a second passivation thickness e73, measured between the second surface s32 of the substrate 3 and the second charge-harvesting layer 71, which is less than or equal to 1.5 nm. The thickness e7 of the second charge-harvesting structure 7 is therefore generally equal to the sum of the thickness e73 of the second passivation layer 73 and the thickness e71 of the second charge-harvesting layer 71. In this way, it is possible to design a photovoltaic solar cell 1 in which a charge-harvesting structure conducive to the optimal operation of the photovoltaic solar cell 1 is present on each side of the substrate 3. Such an architecture is compatible with solar cells capable of capturing solar radiation on their front face FAv and rear face FAr.
[0086] The aforementioned provisions allow for the design of a photovoltaic solar cell 1 in which the first passivation layer 53 is very thin or nonexistent. This maintains good charge collection performance at the end of its life, while minimizing the thickness of layers that generate parasitic absorption, such as the first passivation layer 53. Surprisingly, it has been found that the presence of such a first charge collection structure 5 exhibits end-of-life performance similar to or superior to that of traditional structures with passivated contacts, due to improved optical performance.
Claims
DEMANDS 1. Photovoltaic solar cell (1) comprising: a substrate (3) of crystalline silicon doped according to a first type of conductivity, said substrate (3) having a first surface (s31) and a second surface (s32) opposite the first surface (s31), the substrate (3) having a substrate thickness (e3) between the first surface (s31) and the second surface (s32), said substrate thickness (e3) being between 10 pm and 100 pm; and a first charge-collecting structure (5) comprising a first charge-extraction layer (51) comprising amorphous silicon and / or nanocrystalline silicon, a thickness (e5) of the first charge-collecting structure (5) measured substantially perpendicular to the first surface (s31) of the substrate (3) being less than 10 nm, the first charge-extraction layer (51) being doped according to a second type of conductivity and being: • in direct contact with the first surface (s31) of the substrate (3); or • disposed on a first passivation layer (53) of the first charge collection structure (5), said first passivation layer (53) being in direct contact with the first surface (s31) of the substrate (3) and having a first passivation thickness (e53) measured between the first surface (s31) of the substrate (3) and the first charge extraction layer (51) which is less than or equal to 1.5 nm.
2. Photovoltaic solar cell (1) according to claim 1, wherein the thickness (e5) of the first charge-collecting structure (5) is between 0.5 nm and 4 nm.
3. Photovoltaic solar cell (1) according to any one of claims 1 or 2, wherein the second type of conductivity is opposed to the first type of conductivity.
4. Photovoltaic solar cell (1) according to any one of claims 1 to 3, wherein the substrate (3) comprises monocrystalline or multicrystalline silicon.
5. Photovoltaic solar cell (1) according to any one of claims 1 to 4, wherein the substrate (3) comprises p-doped crystalline silicon.
6. Photovoltaic solar cell (1) according to any one of claims 1 to 5, wherein the first charge extraction layer (51) comprises molybdenum oxide (MoOx) and / or lithium fluoride (Li F).
7. Photovoltaic solar cell (1) according to any one of claims 1 to 6, wherein the first charge extraction layer (51) comprises oxygen and / or carbon atoms.
8. Photovoltaic solar cell (1) according to any one of claims 1 to 7, wherein the first charge extraction layer (51) has a thickness (e51) of between 0.5 nm and 10 nm and preferably of between 0.5 nm and 4 nm.
9. Photovoltaic solar cell (1) according to any one of claims 1 to 8, wherein the first charge-collecting structure (5) is disposed on a front face (FAv) of the solar cell (1), said front face (FAv) being intended to be turned towards the solar radiation captured by the solar cell (1).
10. Photovoltaic solar cell (1) according to any one of claims 1 to 9, further comprising a second charge-collecting structure (7) comprising a second charge-extraction layer (71), said second charge-extraction layer (71) being of a third type of conductivity opposite to the second type of conductivity, said second charge-collecting structure (7) being disposed on the opposite side to the first charge-collecting structure (5) with respect to the substrate (3).
11. Photovoltaic solar cell (1) according to claim 10, wherein the second charge extraction layer (71) is: • in direct contact with the second surface (s32) of the substrate (3); or • disposed on a second passivation layer (73) of the second charge-collecting structure (7), said second passivation layer (73) being in direct contact with the second surface (s32) of the substrate (3) and having a second passivation thickness (e73) measured between the second surface (s32) of the substrate (3) and the second charge extraction layer (71) which is less than or equal to 1.5 nm.
12. Photovoltaic solar cell (1) according to any one of claims 1 to 11, comprising a first metallic electrode (2) disposed on the side of the first surface (s31) of the substrate (3) and a transparent conductive electrode (6) interposed between the first charge-collecting structure (5) and the first metallic electrode (2), said transparent conductive electrode (6) being configured to transfer charges captured by the first charge-collecting structure (5) to the first metallic electrode (2).
13. Space photovoltaic device comprising a photovoltaic solar cell (1) according to any one of claims 1 to 12.