Photovoltaic solar cell

Abstract

The invention relates to a photovoltaic solar cell (1) comprising a crystalline silicon substrate (3), a first charge-collecting structure (5) comprising a first charge-extraction layer (51) being in direct contact with the substrate (3); or disposed on a first passivation layer (53) of the first charge-collecting structure (5), said first passivation layer (53) being in direct contact with 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. The invention also relates to a space-based photovoltaic device comprising such a photovoltaic solar cell (1). Figure 1

Description

Title of the invention: Photovoltaic solar cell Technical field of the invention

[0001] 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. State of the art

[0002] With a view to continuously improving photovoltaic conversion efficiencies, the latest generations of high-efficiency crystalline silicon cells are typically of the "passivated contacts" 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.

[0003] More specifically, in the field of space photovoltaics, traditionally based on multi-junction IILV 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.

[0004] In this context, silicon solar cells with passivated contacts (such as heterojunction silicon solar cells) are very good candidates to meet this need. However, it is necessary to adapt silicon solar cells with passivated contacts to obtain the best conversion efficiencies at the end of their mission. Indeed, unlike terrestrial photovoltaics, the space environment, and in particular the space radiation environment, degrades solar cells. Space photovoltaics therefore seeks to optimize the photovoltaic conversion efficiencies of cells and modules to obtain the desired power output at the end of their life.

[0005] There is therefore a need to find a photovoltaic cell structure with good conversion efficiencies, particularly at the end of its life, which is simple and inexpensive to produce.

[0006] Object of the invention

[0007] The present invention aims to provide a solution that addresses all or part of the aforementioned problems.

[0008] 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: • in direct contact with the first surface of the substrate; or • arranged on a first passivation layer of the first charge collection 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.

[0009] The arrangements described above make it possible to propose a photovoltaic solar cell in which the first passivation layer is very thin or non-existent. This allows for maintaining good charge collection performance at the end of its life, while minimizing the thickness of layers generating parasitic absorption, such as the first passivation layer. Surprisingly, it has been found that the presence of such a first charge-collecting structure exhibits end-of-life performance similar to or better than that of traditional structures with passivated contacts, due to improved optical performance.

[0010] The solar cell may also have one or more of the following characteristics, taken alone or in combination.

[0011] According to one embodiment, the first type of conductivity is the same as the second type of conductivity.

[0012] According to one embodiment, the first charge-collecting structure comprises, or is made of, silicon.

[0013] According to one embodiment, the first passivation layer comprises intrinsic amorphous silicon, a silicon oxide such as silicon dioxide, or a dielectric material.

[0014] 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 surface of the substrate.

[0015] 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.

[0016] According to one embodiment, 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.

[0017] 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 the latter 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 the latter is not in direct contact with the first surface of the substrate.

[0018] Advantageously, the use of a first load collection structure of low thickness makes it possible to improve the transparency of this first load collection structure.

[0019] According to one embodiment, the second type of conductivity is opposed to the first type of conductivity.

[0020] In this way, it is possible to form part of a heterojunction photovoltaic solar cell, in particular of silicon.

[0021] According to one embodiment, the substrate comprises monocrystalline or multicrystalline silicon.

[0022] Thus, electron / hole pair formation is facilitated. Indeed, electron / hole pair formation is a consequence of the absorption of the solar spectrum in 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 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.

[0023] According to one embodiment, the substrate comprises p-doped crystalline silicon.

[0024] In other words, the first type of conductivity is positive.

[0025] Advantageously, a p-doped crystalline silicon substrate exhibits better resistance to external irradiation, particularly when this originates from a space environment.

[0026] According to one embodiment, the first charge extraction layer comprises amorphous silicon and / or nanocrystalline silicon.

[0027] Advantageously, the presence of the first amorphous or nanocrystalline silicon charge extraction layer reduces charge carrier recombination on the surface of the crystalline silicon substrate and promotes charge carrier selectivity.

[0028] According to one embodiment, the first filler extraction layer comprises molybdenum oxide and / or lithium fluoride.

[0029] The use of molybdenum oxide or lithium fluoride reduces parasitic absorption, thereby improving optical properties. Furthermore, the use of lithium fluoride facilitates electron extraction.

[0030] According to one embodiment, the first charge extraction layer comprises oxygen and / or carbon atoms.

[0031] In this way, it is possible to improve the transparency of the first charge extraction layer, without compromising its ability to extract charges.

[0032] According to one embodiment, the first layer of charge extraction has a thickness between 0.5 nm and 10 nm and preferably between 0.5 nm and 4 nm.

[0033] Thus, the thickness of the first charge extraction layer is large enough to allow good selectivity of charge carriers, and has a thickness small enough to limit the parasitic absorption of incident light.

[0034] According to one embodiment, at least one first metallic electrode is disposed on the side of the first surface of the substrate.

[0035] According to one embodiment, at least a second metallic electrode is disposed on the side of the second surface of the substrate.

[0036] According to one embodiment, the substrate has a substrate thickness between the first surface and the second surface, said substrate thickness being less than 300pm, and in particular between 10pm and 100pm.

[0037] Thus, it is possible to propose a thin solar cell which is less subject to performance degradation when subjected to high energy irradiation, for example in a space environment.

[0038] 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.

[0039] In this way, it is possible to place the first charge collection structure on the side of the solar radiation, which makes it possible to orient towards the light radiation, a face of the solar cell having good transparency.

[0040] 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.

[0041] Thus, the presence of two charge-collecting structures having an opposite type of conductivity facilitates the separation of electron-hole pairs.

[0042] According to one embodiment, the second layer for extracting charges is: • in direct contact with the second surface of the substrate; or • arranged on a second passivation layer of the second structure charge collection, 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 that is less than or equal to 1.5 nm.

[0043] In this way, it is possible to provide a photovoltaic solar cell in which a charge collection structure favorable to the optimal operation of the photovoltaic solar cell is present on each side of the substrate. Such an architecture is compatible with solar cells capable of capturing solar radiation on their front and rear faces.

[0044] 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.

[0045] In this way, it is possible to improve the transfer of charges captured by the first charge-collecting structure to the first metallic electrode.

[0046] 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.

[0047] Brief description of the drawings

[0048] Other aspects, objectives, advantages and features of the invention will become clearer upon reading 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:

[0049] [Fig-1] Fig. 1 is a schematic view of a solar cell according to a first method of embodiment of the invention.

[0050] [Fig.2] Fig.2 is a schematic view of a solar cell according to a second method of embodiment of the invention.

[0051] [Fig. 3] Fig. 3 is a schematic view of a solar cell according to a third method of embodiment of the invention. Detailed description

[0052] 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 in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined.

[0053] 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.

[0054] The photovoltaic solar cell 1 first 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 in 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, i.e., the first type of conductivity is positive.It has been shown that a p-doped crystalline silicon substrate exhibits better resistance to external irradiation, particularly when this originates from a space environment.

[0055] 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 arranged on the side of the front face FAv of the solar cell 1, and the second surface s32 can be arranged on the side of a rear face, denoted "FAr" of the solar cell 1. Such a construction is not limiting however, 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.

[0056] The substrate 3 may have a substrate thickness e3 between the first surface s31 and the second surface s32, which is less than 300 pm, and in particular between 100 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.

[0057] 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. Figures illustrate in particular variants in which the solar cells 1 include two first metallic electrodes 2.

[0058] On the opposite side, the solar cell is generally provided with at least one second metallic electrode 4 disposed on the side of the second surface s32 of the substrate 3. The figures illustrate in particular variants in which the solar cells 1 comprise two second metallic electrodes 4.

[0059] 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 to be captured by the solar cell.

[0060] 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.

[0061] 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 of solar radiation. This is therefore particularly suitable for solar cells 1 in a space environment.

[0062] The solar cell 1 also includes a first charge-collecting structure 5, generally formed or made of silicon. "Charges" are understood to mean electrons or holes. Thus, the first charge-collecting structure can be configured to collect electrons or alternatively holes (or electron deficiency).

[0063] Although not limiting, it is possible that the first charge-collecting structure 5 be arranged on the front face FAv of the solar cell 1. In this way, it is possible to place the first charge-collecting structure 5 on the side of the solar radiation, which allows a face of the solar cell 1 with good transparency to be oriented towards the light radiation.

[0064] 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. The use of 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.

[0065] 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 envisaged that the second type of conductivity will be opposite to the first type of conductivity. In this way, it is possible to form part of a heterojunction photovoltaic solar cell 1, in particular made of silicon.

[0066] Depending on the embodiment chosen, the first charge extraction layer 51 may comprise amorphous silicon and / or nanocrystalline silicon. Advantageously, the presence of the first charge extraction layer 51 in amorphous or nanocrystalline silicon reduces charge carrier recombination and promotes charge carrier selectivity.

[0067] Alternatively, the first charge extraction layer 51 may comprise molybdenum oxide MoOx and / or lithium fluoride LiF. The use of molybdenum oxide or lithium fluoride facilitates charge extraction while providing good transparency.

[0068] It is also possible for the first charge-extracting layer 51 to include oxygen and / or carbon atoms. In this way, it is possible to improve the transparency of the first charge-extracting layer 51 without impairing its ability to extract electron or hole charges.

[0069] Regardless of the variant chosen, it is advantageous to provide that the first charge extraction 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 extraction layer 51 is sufficiently large to allow good selectivity of the charge carriers, and sufficiently small to limit the parasitic absorption of incident light.

[0070] The first charge-extraction layer 51 is in direct contact with the first surface s31 of the substrate 3, or disposed on a first passivation layer 53 of the first charge-collecting structure 5. For example, the first passivation layer 53 comprises intrinsic amorphous silicon, a silicon oxide such as silicon dioxide, or a dielectric material.

[0071] In the first case, represented in particular in [Fig.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.

[0072] 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.

[0073] 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.

[0074] The photovoltaic solar cell 1 generally comprises a second charge-collecting structure 7 arranged 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.

[0075] It is therefore understood that, with the exception of the opposing loads, the first and second load-collecting structures 5, 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-collecting structure 5 to be positioned on the front face FAv and the second load-collecting structure 7 on the rear face FAr, or vice versa.

[0076] 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.

[0077] 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 on the surface of the crystalline silicon substrate and promotes charge carrier selectivity.

[0078] Alternatively, the second charge extraction layer 71 may comprise molybdenum oxide MoOx and / or lithium fluoride LiF. The use of molybdenum oxide or lithium fluoride facilitates charge extraction while providing good transparency.

[0079] It is also possible for the second charge-extracting layer 71 to comprise oxygen and / or carbon atoms. In this way, it is possible to improve the transparency of the second charge-extracting layer 71 without impairing its ability to extract electron or hole charges.

[0080] Regardless of the variant chosen, it is advantageous to provide 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 selectivity of the charge carriers, and sufficiently small to limit the parasitic absorption of incident light.

[0081] 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.

[0082] 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.

[0083] In the second case, and as illustrated in [Fig.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.

[0084] 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 provide a photovoltaic solar cell 1 in which a charge-harvesting structure favorable 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 the front face FAv and on the rear face FAr.

[0085] All the arrangements described above make it possible to propose a photovoltaic solar cell 1 in which the first passivation layer 53 is very thin or non-existent. This makes it possible to maintain good charge collection performance at the end of life, while minimizing the thickness of layers generating 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 that is similar to or better than that of traditional structures with passivated contacts, due to improved optical performance.

Claims

Demands

1. Photovoltaic solar cell (1) comprising: • a crystalline silicon substrate (3) 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); and • a first charge-collecting structure (5) comprising a first charge-extraction layer (51), said 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-collecting 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 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.

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 amorphous silicon and / or nanocrystalline silicon.

7. Photovoltaic solar cell (1) according to any one of claims 1 to 6, wherein the first charge extraction layer (51) comprises molybdenum oxide (MoOx) and / or lithium fluoride (LiF).

8. Photovoltaic solar cell (1) according to any one of claims 1 to 7, wherein the first charge extraction layer (51) comprises oxygen and / or carbon atoms.

9. Photovoltaic solar cell (1) according to any one of claims 1 to 8, 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.

10. Photovoltaic solar cell (1) according to any one of claims 1 to 9, wherein the substrate (3) has a substrate thickness (e3) between the first surface (s31) and the second surface (s32), said substrate thickness (e3) being less than 300pm, and in particular between 10pm and 100pm.

11. Photovoltaic solar cell (1) according to any one of claims 1 to 10, 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).

12. Photovoltaic solar cell (1) according to any one of claims 1 to 11, 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).

13. Photovoltaic solar cell (1) according to claim 12, 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.

14. Photovoltaic solar cell (1) according to any one of claims 1 to 13, 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 picked up by the first charge-collecting structure (5) to the first metallic electrode (2).

15. Space photovoltaic device comprising a photovoltaic solar cell (1) according to any one of claims 1 to 14.

Images