METHOD OF MANUFACTURING A SOLAR CELL WITH INTEGRAL COVER GLASS, AND CELL OBTAINED

Abstract

Method of manufacturing a solar cell, comprising: providing a solar cell (100) having an active surface (105a) intended, in use, to be exposed to sunlight; forming, in correspondence of said active surface, a protection against low-energy protons and other radiations harmful to the solar cell. Forming a protection comprises forming a layer of resin (110; 210) and forming by deposition of material on the resin layer a layer of protective material (115; 215b) on top of the resin layer.

Claims

1. Method of fabrication of a solar cell, comprising: providing a solar cell having an active surface which, in use, is intended to be exposed to sunlight for performing photovoltaic conversion; forming, in correspondence of said active surface, a protection against low-energy protons and other radiations harmful to the solar cell, characterized in that said forming a protection comprises: forming a layer of resin and forming by means of deposition of material on the layer of resin a layer of a non-conductive protective material, transparent in an electromagnetic radiation frequency range in which the solar cell is intended to perform the photovoltaic conversion, over the layer of resin, wherein said forming by means of deposition of material comprise a process or processes of physical vapour deposition—“PVD”, particularly thermal evaporation, electron beam, pulsed-laser deposition—“PLD”, sputtering.

2. Method according to claim 1, wherein said layer of resin is formed directly on the active surface of the solar cell.

3. Method according to claim 1, further comprising: forming by means of deposition of material a further layer of protective material interposed between the layer of resin and the active surface of the solar cell.

4. Method according to claim 3, wherein said forming by means of deposition of material a further layer of protective material interposed between the layer of resin and the active surface of the solar cell comprise a process or processes of physical vapour deposition—“PVD”, for example thermal evaporation, electron beam, pulsed-laser deposition—“PLD”, sputtering.

5. Method according to claim 1, wherein said layer or layers of protective material comprise or consist of layers of oxide, in particular one or more layers of SiO2 and/or Al2O3 and/or Ta2O5 and/or Nb2O5and/or Y2O3and/or TiO2and/or Sc2O3 and/or CeO2and/or HfO2and/or SnO2 and/or LaTiO3 and/or other materials transparent in the range of frequencies exploited by the solar cell for performing the photovoltaic conversion, comprising MgF2 and/or CeF3 and/or ZnS and/or Si3N4.

6. Method according to claim 1, wherein said phase of forming a layer of resin comprises a process of deposition.

7. Method according to claim 1, further comprising: forming alternated layers of resin and protective material repeated more times.

8. Method according to claim 1, further comprising: forming anti-reflecting layers on the topmost layer of protective material.

9. Method according to claim 1, wherein said layer of protective material, or at least one of the layers of protective material, has a thickness greater than 2 μm.

10. Solar cell comprising an active surface which, in use, is intended to be exposed to sunlight for performing photovoltaic conversion, in correspondence of which active surface there is provided a protection against low-energy protons and other radiations harmful to the solar cell, characterized in that said protection comprises at least one layer of resin and, above the layer of resin, at least one layer of a protective material, protecting the solar cell against low-energy protons and other harmful radiations, transparent to the solar radiation in a range of frequencies exploited by the solar cell for performing the photovoltaic conversion, said at least one layer of protective material being a layer of deposited material having a thickness greater than 2 μm and being non-conductive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] These and other features, as well as these and other advantages, of the present invention will be made more apparent by reading the following detailed description of some of its possible embodiments, exemplary and by no means limitative; in the following description reference will be made, for a better intelligibility, to the attached figures, in which:

[0053] FIGS. 1A to 1C show three stages of a method of manufacturing a solar cell according to an embodiment of the present invention;

[0054] FIGS. 2A to 2D show four steps of a method of manufacturing a solar cell according to another embodiment of the present invention, and

[0055] FIG. 3 is a diagram showing the “cut-off” energy as a function of the thickness and the type of protective material used, for certain types of exemplary protective materials.

[0056] It should be noted that the drawings shown in the figures are schematic and not necessarily executed to scale. In particular, some details of the drawings can be very exaggerated (compared to their real size) for purely explanatory purposes.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

[0057] With reference to the drawings, in FIGS. 1A to 1C three phases of a method of manufacturing a solar cell according to an embodiment of the present invention are shown.

[0058] Reference 100 denotes a solar cell, such as a space solar cell. The solar cell 100 can for example be a cell in compounds of groups III and V of the periodic table of the elements (“III-V solar cell”), for example in gallium arsenide (GaAs) or in Indium and Gallium phosphide (InGaP). The solar cell 100 can be a single-junction solar cell, i.e. with a single pn junction, or a multi-junction solar cell, with two or more pn junctions, for example a triple junction solar cell (comprising three pn junctions). The steps of the manufacturing process of the solar cell 100 are neither shown nor described as they are known to those skilled in the art.

[0059] The solar cell 100 has an active surface 105a (the surface of the solar cell which, in use, is intended to be exposed to sunlight for allowing the solar cell performing the photovoltaic conversion) and an opposite, non-active surface 105b (which in use is not exposed to sunlight) in correspondence of which the solar cell 100 is applied to a support panel (not shown in the drawings).

[0060] As shown in FIG. 1B, on the active surface 105 of the solar cell 100 (the surface of the solar cell which, in use, is intended to be exposed to sunlight) a layer of resin 110 transparent to sunlight is formed. The resin may for example be of the same type as the resins which in the art are used to glue the protective coverglass to the solar cell. For example, the resin used may be a transparent silicone adhesive material, for example the material commercially known as Elastosil® S 695 or S 690, or the elastomeric silicone material commercially known as DC93-500 manufactured by Dow Corning®. The resin layer 110 can for example be formed by means of any deposition technique used for the integration of space solar cells (with the usual steps which will not be described as they are known to those skilled in the art). In FIG. 1B it is also shown (in a very exaggerated way compared to the actual dimensions) how, as a consequence of the formation process of the resin layer 110 by deposition, the material of the resin layer 110 protrudes from the edges of the active surface 105a of the solar cell 100 and descends along the lateral walls of the solar cell 100 itself, covering them (in a gradually decreasing way as one moves away from the active surface 105). The resin layer 110 can for example have a thickness ranging from some tens of microns to about 100 μm.

[0061] Turning to FIG. 1C, on the resin layer 110 a layer of protective material 115 is formed which is transparent to sunlight (in the range of wavelengths for which the solar cell is intended to perform the photoelectric conversion) but capable of blocking low-energy protons and other radiations harmful to the solar cell 100. The protective material layer 115 is a layer in a non-conductive material. The protective material layer 115 may comprise or consist of a layer of a non-conductive oxide, e.g. Silicon oxide (SiO.sub.2) or oxides of other elements, or other non-conductive materials, transparent in the frequency range used by the solar cell to perform the photovoltaic conversion. For example, in addition to Silicon oxide (SiO.sub.2), the protective material layer 115 may comprise or consist of Aluminum oxide (Al.sub.2O.sub.3), Tantalum oxide (Ta.sub.2O.sub.5), Niobium oxide (Nb.sub.2O.sub.5), Yttrium oxide (Y.sub.2O.sub.3), Titanium oxide (TiO.sub.2), Scandium oxide (Sc.sub.2O.sub.3), Cerium oxide (CeO.sub.2), Hafnium dioxide (HfO.sub.2), Tin dioxide (SnO.sub.2), LaTiO.sub.3, Indium Tin oxide (also known as Indium-doped Tin Oxide or ITO), or other transparent materials in the frequency range used by the solar cell to carry out the photovoltaic conversion, such as for example Magnesium fluoride (MgF.sub.2), Cerium fluoride (CeF.sub.3), Zinc sulphide (ZnS), Silicon nitride (Si3N4). The layer of protection material 115 has a suitable thickness, chosen so as to provide, in use, the desired protection of the solar cell 100.

[0062] The shielding power (so-called “Stopping Power”) that the layer of protective material 115 has on low-energy protons depends, in addition to the thickness of this layer, on the density and on the atomic composition of the protective material used. The cut-off energy (maximum energy of the protons that the material is able to completely shield), as a function of the thickness of the layer of protective material 115 used, can be obtained using models and calculation codes known in the literature (for example, SRIM, www.srim.org). FIG. 3 shows the cut-off energy performance as a function of the thickness of the protective material layer for three types of exemplary protective materials: SiO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5.

[0063] For example, if the layer of protective material 115 has a thickness of at least 2 μm, the protons with energy less than or equal to 0.2 MeV are shielded.

[0064] The layer of protective material 115 can for example be formed by means of deposition techniques, using for example any known technique of Physical Vapor Deposition (PVD), such as thermal evaporation, electronic beam, Pulsed Laser Deposition (PLD), cathodic sputtering (or cathodic vaporization, simply “sputtering”) etc. Similarly to FIG. 1B, FIG. 1C also shows (in a very exaggerated way compared to the actual dimensions) how, as a consequence of the process of forming the layer of protective material 115 by deposition, the material of the layer of protective material 115 protrudes from the edges of the active surface 105a of the solar cell 100 and descends along the side walls of the solar cell 100 itself, covering (in a decreasing way as one moves away from the active surface 105) the same side walls (which had already been covered by the material of the resin layer 110).

[0065] The manufacture of the solar cell takes place with the usual steps, which will not be described as they are known to those skilled in the art.

[0066] The adhesive resin layer 110 has essentially no protection function of the solar cell against low energy protons. The presence of the adhesive resin layer 110 interposed between the layer of protective material 115 and the active surface 105a of the solar cell 100 helps to reduce the mechanical stresses between the layer of protective material 115 and the solar cell 100.

[0067] The layer of protective material 115 present above the resin layer 110, in addition to carrying out the function of protection against low-energy protons and other radiations harmful to the solar cell 100, avoids the phenomenon of yellowing (“darkening”) of the resin layer 110 which on the contrary could affect the latter as a result of the exposure to ultraviolet radiation in the use of the solar cell. The layer of protective material 115 also protects the resin layer 110 against low energy protons, avoiding the degradation of the resin layer 110 consequent to exposure to low energy proton radiation.

[0068] In FIGS. 2A to 2D four phases of a method of manufacturing a solar cell according to another embodiment of the present invention are shown.

[0069] Starting from the solar cell 100 shown in FIG. 2A (as in the embodiment described above, the solar cell 100 can for example be a III-V solar cell, for example in GaAs or InGaP, single junction or multi-junction), on the active surface 105a of the solar cell 100 a first layer of protective material 215a is formed, as shown in FIG. 2B. The layer of protective material 215a is transparent to sunlight (in the range of wavelengths for which the solar cell is intended to perform the photoelectric conversion). The protective material layer 115 is a layer in a non-conductive material. The layer of protective material 215a can, for example, include or consist of a layer of SiO.sub.2 or oxides of other elements, or other non-conductive materials transparent in the range of frequencies used by the solar cell to make the photovoltaic conversion. In addition to Silicon oxide (SiO.sub.2), the protective material layer 215a may comprise or consist of Aluminum oxide (Al.sub.2O.sub.3), Tantalum oxide (Ta.sub.2O.sub.5), Niobium oxide (Nb.sub.2O.sub.5), Yttrium oxide (Y.sub.2O.sub.3), Titanium oxide (TiO.sub.2), Scandium oxide (Sc.sub.2O.sub.3), Cerium oxide (CeO.sub.2), Hafnium dioxide (HfO.sub.2), Tin dioxide (SnO.sub.2), LaTiO.sub.3, or other transparent materials in the frequency range used by the solar cell to perform the photovoltaic conversion, such as for example Magnesium fluoride (MgF.sub.2), Cerium fluoride (CeF.sub.3), Zinc sulphide (ZnS), Silicon nitride (Si3N4).

[0070] The thickness of the layer of protective material 215a can be sized as a function of the energy of the protons that the oxide layer must be able to shield. The layer of protective material 215a can for example be formed by deposition techniques, such as those mentioned in the description of the previous embodiment. In FIG. 2B it is also shown (much exaggerated compared to the actual size) as, in consequence of the forming process of the protective material layer 215a by deposition, the material of the protective material layer 215a overlaps the edge of the active surface 105a of the solar cell 100 and descends along the side walls of the solar cell 100 itself, covering them (in a gradually decreasing way as one moves away from the active surface 105).

[0071] A sunlight transparent resin layer 210 is formed on the first layer of protective material 215a, as shown in FIG. 2C. The resin layer 210 can for example be made as described in relation to the resin layer 110 of the previous embodiment. Also in this case, FIG. 2C also shows (in a very exaggerated way compared to the actual dimensions) how, as a consequence of the formation process of the resin layer 210 by deposition, the material of the resin layer 210 protrudes from the edges of the surface activates 105a of the solar cell 100 and descends along the side walls of the solar cell 100 itself, covering (in a gradually decreasing extent as one moves away from the active surface 105) the side walls themselves (which had already been covered by the material of the material layer protection 215a).

[0072] A second layer of sunlight-transparent protective material 215b is formed over the resin layer 210, as shown in FIG. 2D. The second layer of protective material 215b is a layer in a non-conductive material. The second layer of protective material 215b can for example comprise or consist of a layer of SiO.sub.2 or oxides of other elements, or other non-conductive materials transparent in the range of frequencies used by the solar cell to carry out the photovoltaic conversion. Also in this case, in addition to SiO.sub.2, the layer of protective material 215b can comprise or consist of Aluminum oxide (Al.sub.2O.sub.3), Tantalum oxide (Ta.sub.2O.sub.5), Niobium oxide (Nb.sub.2O.sub.5), Yttrium oxide (Y.sub.2O.sub.3), Titanium oxide (TiO.sub.2), Scandium oxide (Sc.sub.2O.sub.3), Cerium oxide (CeO.sub.2), Hafnium dioxide (HfO.sub.2), Tin dioxide (SnO.sub.2), LaTiO.sub.3, or other transparent materials in the frequency range used by the solar cell to perform the photovoltaic conversion, such as for example Magnesium fluoride (MgF.sub.2), Cerium fluoride (CeF.sub.3), Zinc sulphide (ZnS), Silicon nitride (Si3N4). The layer of protective material 215b can for example be formed by the same deposition techniques used to form the first layer of protective material 215a. In FIG. 2D it is also shown (much exaggerated compared to the actual size) as, in consequence of the protective material layer formation process 215b by deposition, the material of the protective material layer 215b overlaps the edge of the active surface 105a of the solar cell 100 and descends along the side walls of the solar cell 100 itself, covering (in a gradually decreasing extent as one moves away from the active surface 105) the side walls themselves (which had already been covered by the material of the first layer of protective material 215a and the material of the resin layer 210).

[0073] The presence of the resin layer 210 helps to reduce the mechanical stress between the layers of protective material 215a and 215b and the solar cell 100.

[0074] The layers of protective material 215a and 215b perform the function of protection against low-energy protons and other harmful radiations to the solar cell 100.

[0075] The second layer of protective material 215b which covers the resin layer 210 avoids the phenomenon of yellowing (darkening) resulting from exposure to ultraviolet radiation.

[0076] The layers of protective material 215a and 215b also protects the resin layer 210 against low energy protons, avoiding the degradation of the resin layer 110 consequent to exposure to low energy proton radiation.

[0077] Other embodiments of the present invention are possible, for example by iterating the structure shown in FIG. 2D by forming one or more further pairs of resin layer 210 and protective material layer 215b above the protective material layer 215b.

[0078] The materials used to form the resin layers 110, 210, and the materials used to form the layers of protective material(s) 115, 215a, 215b may be different from the materials previously indicated by way of example, and the thicknesses of these layers may vary from the indicated thicknesses.

[0079] Over the last layer of protective material (at the top of the solar cell) it is possible to deposit a layer or a multilayer with an anti-reflective function.