Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
  • H01L31/184—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP
  • H01L31/1844—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIIBV compounds, e.g. GaAs, InP comprising ternary or quaternary compounds, e.g. Ga Al As, In Ga As P
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/042—PV modules or arrays of single PV cells
  • H01L31/043—Mechanically stacked PV cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/544—Solar cells from Group III-V materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates, in general, to the conversion of light energy, in particular of solar energy, into electrical energy by means of components implementing the photovoltaic effect produced in semiconductors.
• solar cells use only one species of semiconductor material (mainly silicon or gallium arsenide), they cannot transform the light energy of the sun's rays as well as possible, due to the spread of the spectrum of the latter.
• a given semiconductor material has a determined forbidden bandwidth, so that the photons of energy less than this bandwidth are never absorbed and therefore cannot generate the electron-hole pairs necessary for the photocurrent production.
• photons of energy greater than that of the forbidden band will, in turn, create electron-hole pairs, but with a excess of energy compared to that of the forbidden band, excess which will be converted into heat and not into electrical energy.
• multispectral solar cells To improve the conversion of solar energy, it has been proposed to combine, according to various configurations, several different semiconductors having different bandwidths. These components are called “multispectral solar cells”.
• One of the proposed configurations, to which the invention relates, is said to be "stacked" and consists in making beforehand, each on its own substrate, two (or more) different cells which are then superimposed by fixing with transparent glue.
• This adhesive can either be conductive, which makes it possible to connect the two cells in series (but in this case, the photocurrent produced by the device is limited by the weakest photocurrent generated), or insulating, each cell then being provided clean electrodes connected separately to circuits separate from the electronics of the load block (which must therefore have been designed accordingly).
• This configuration has a certain number of drawbacks, in particular the fact that, as two cells have to be produced separately, the final component comprises two thicknesses of substrate, thereby increasing the weight and the cost of the structure, all particu ⁇
• the GaAs substrate which is the heaviest and most expensive, does not serve as a mechanical support and does not play any active role.
• One of the aims of the invention is to remedy the drawbacks of multispectral cells of this type, by reducing the cost and the weight thereof by elimination and recovery of one or both of the substrates, with all the correlative advantages which could result.
• the substrate being eliminated, it is no longer necessary to make vias to cross it and ensure contact with the lower layer of the component; the manufacturing cost of the latter is reduced especially ; the weight of the component is considerably reduced, which is advantageous in the space domain; finally, thermal dissipation is significantly improved due to the elimination of the thermal resistance formed, in current components, by the substrate (GaAs and InP being poor conductors of heat).
• the invention proposes to produce the component by a process consisting in: (a) producing a first cell comprising a first substrate, a first optically active layer and, between this substrate and this active layer, a thin soluble layer; (b) producing a second cell comprising a second substrate and a second optically active layer, of a different nature from the first; (c) arranging opposite these two cells so that the active layers are turned towards one another; (d) joining the two elementary cells by their active layers by means of a transparent adhesive; and (e) dissolving the material of the soluble layer leaving the other materials intact, so as to separate, without dissolving it, the first substrate from the rest of the structure.
• step (b) the second cell is produced with, between its substrate and its active layer, a thin soluble layer, so as to also separate, in step (e), the second substrate d 'with the rest of the structure.
• the material of the first substrate and / or of the second substrate may in particular be a binary or ternary III-V semiconductor, in which case the corresponding soluble thin layer may be an epitaxial layer of a ternary III-V semiconductor material having a molar fraction of aluminum of at least 40% and an atomic mesh compatible with that of the substrate on which it is epitaxied, the dissolution of step (e) being effected by chemical means.
• This material can also be a semi-insulating or n-type semiconductor, in which case the corresponding soluble thin layer can be a layer of p + doped semiconductor material, the corresponding active layer comprising at least one infe ⁇ higher doped n and the dissolution of step (e) being effected anodically and without illumination.
• the corresponding soluble thin layer can be a layer of p + doped semiconductor material, the corresponding active layer comprising at least one infe ⁇ higher doped n and the dissolution of step (e) being effected anodically and without illumination.
• We can also, in either case, fix the structure obtained in step (e) on a reflective support.
• the subject of the invention is also, as a new product, a multispectral photovoltaic component comprising a stack of at least two elementary cells associated with different spectral response characteristics and comprising a first cell comprising a first layer optically active, a second cell comprising a second optically active layer, of a different nature from the first, and a layer of transparent adhesive joining these two cells.
• the first cell is essentially devoid of a layer forming a substrate, and the active layers of the two cells are turned towards one another and joined by said layer of transparent adhesive.
• the second cell can also be, if desired, essentially devoid of a substrate layer.
• the component may advantageously further comprise a reflective support.
• FIG. 1 shows the structure of a multispectral cell of the prior art, the two elementary cells of which are connected in series.
• FIG. 2 shows the structure of a multispectral cell of the prior art, the two elementary cells of which are provided with independent independent electrodes.
• Figures 3a to 3d illustrate the successive steps of a first method of implementing the invention.
• FIGS. 1 and 2 illustrate the successive steps of a second method of implementing the invention.
• FIGS. 1 and 2 the conventional structure of a multispectral cell of the stacking type is shown, according to two alternative embodiments.
• the component is essentially constituted from two elementary cells 1 and 2 of different band gap widths, most often chosen from cells on amorphous silicon, on gallium arside and on indium phosphide.
• the first elementary cell 1 comprises a substrate 4 on which an active layer 5 is formed, the thickness and the composition of which are chosen as a function of the component to be produced.
• This active layer 5 can consist of a stack of successive layers each having a different composition, doping and thickness, the term “active layer” here collectively designating this stack.
• Metallizations 6 and 7 ensure contact and constitute the electrodes of this first elementary cell.
• the second elementary cell 2 has a similar structure (but with a different choice of material): a substrate 8 carries an active layer 9, and metallizations 10, 11 constitute the electrodes of the cell.
• This cell 2 can be a cell of a common commercial type, used as it is without any particular structural modification, for example an amorphous silicon solar cell such as those described by A. Takeoka, Technology Brightens Prospects for Solar Power, Journal of Electronic Engineering, July 1991, p. 100.
• the adhesive 3 is conductive (FIG. 1), it electrically connects the electrodes 7 and 10, thus putting the two cells 1 and 2 in series; the electrodes 6 and 11 then constitute the terminals A and B of the component.
• each group of metallizations is connected to respective terminals A 1? A 2 and B l5 B 2 of the component, which will supply separate circuits to the electronic load block.
• This configuration is more complex, but it makes it possible to take account of the different electrical parameters of the two cells, in particular avoiding the disadvantage, specific to the coupling in series of two cells, that the photocurrent produced and necessarily limited by most weak photocurrent generated by one of the cells.
• the two cells are always turned with their active face upwards, that is to say that, during bonding, it is the back (sub ⁇ strat 4) of cell 1 which is just glued against the face (active layer 9) of cell 2.
• the basic idea of the invention consists in recovering the substrate of at least one of the two cells, for example by chemical or electxochemical dissolution of an intermediate layer provided between sub ⁇ stratum and active layer, this dissolution being done after the two cells are already glued together.
• Figures 3a to 3d schematically illustrate the successive steps of such a method.
• First Figure 3a
• the soluble thin layer 12 is an epitaxial layer of a ternary III-V semiconductor material rich in aluminum and atomic mesh compatible with that of the substrate 4.
• This material of layer 12 can in particular be Al ⁇ Ga 1. ⁇ As (on GaAs substrate) or Al ⁇ In 1 _ x As (on InP substrate) with a molar fraction (content) of aluminum ⁇ j > 0.50 approximately.
• the substrate 4 may for example have a thickness of 500 ⁇ m and the soluble thin layer a thickness of the order of a few tens of nanometers.
• the active layer 5 itself comprises layers rich in aluminum, it will be necessary to protect its sides with an inert material, because otherwise these layers rich in aluminum would also be damaged. during the dissolution.
• French patent application 91-15139 in the name of the Applicant, which describes in detail such a technique.
• a photosensitive resin or a passivation layer of the component (oxide or nitride) deposited by a conventional route is chosen as inert protective material, and this material is selectively removed so as to expose the intermediate layer 12 in a region iso ⁇ lée such as that referenced at 13 in Figure 3a.
• This selective removal can be carried out by conventional techniques of electronic photolithography (in the case of a photosensitive resin layer) or of etching (in the case of a passivation layer).
• the material constituting the face of the active layer 5 which is in contact with the intermediate layer 12 has a low aluminum content, otherwise the component would be attacked from below when the intermediate layer 12 is dissolved.
• This material is generally a layer of GaAs, InP or Ga ⁇ ⁇ As, the layers of ⁇ Ga ⁇ As rich in aluminum being located deeper in the stack of layers of the active layer 5.
• the two components are then bonded together (FIG. 3b) with an adhesive, conductive or insulating as the case may be, in the same way as in the prior art, but with the essential difference that, in the case of the invention, the substrate of cell 1 is turned upwards, i.e. it is by the active layer 5 that cell 1 is bonded to cell 2, and not by its substrate 4 (as was the case with the configuration of the prior art, illustrated in FIGS. 1 and 2).
• the process continues (FIG. 3d) by depositing metallizations on the free face of cell 1; it will be noted that, due to the absence of a substrate, the deposition of the metallization allows direct contact, without interposition of the substrate, on the rear face of the active layer 5 and therefore without the need to form vias .
• the component can advantageously be bonded to a reflecting support 14, which makes it possible to double the absorption path of the photons by reflection from them and therefore improve the overall yield of the component.
• Another technique implementing an electrochemical dissolution (anodic dissolution) can also be used. yée, especially for components which are not realized on a GaAs or InP substrate and to which the above technique is not applicable.
• This other technique which is set out in French patent application 91-15138 in the name of the Applicant, consists essentially of epitaxing on the substrate 4, which may be made of silicon, GaAs, InP, etc., a thin interlayer 12 which is a p + doped.
• the active layer 5 is then formed on this intermediate layer 12.
• the intermediate layer 12 can also be obtained by implantation through the active layer 5.
• the material constituting the face of the active layer 5 in contact with the intermediate layer 12 is not doped p, ver ⁇ ment the component would be attacked from below during the electrochemical dissolu ⁇ tion of the intermediate layer 12 ; this material is generally an n + doped layer.
• the active layer has one or more p layers, special precautions must be taken by protecting the sides of the layer with an inert material, in the same way as for layers rich in aluminum in the case of dissolution by chemical means.
• the anodic dissolution step consists in dissolving the semiconductor material of the p + doped interlayer 12 by contacting with an electrolyte (for example KOH), this material constituting the anode with respect to a reference electrode.
• this electrode gradually disappears, that is to say that the material of the intermediate layer - and of this single layer - is gradually eliminated.
• the electrolyte attacks this layer at the exposed place 13, then by the edge of this layer.
• the rest of the structure, in particular the substrate and regions possibly protected by an inert layer, which are neutral from the electrochemical point of view, are however left intact.
• cell 2 has an inexpensive substrate, for example silicon, and especially amorphous silicon.
• the two substrates are expensive or of high weight, such as GaAs and InP, it is preferred to eliminate the substrates from each of the two elementary cells.
• FIGS. 4a to 4d are homologous to FIGS. 3a to 3d, for such a method: in this case, in addition to the thin soluble layer 12 for the component 1, a soluble thin layer 15 for the component 2 is inserted, inserted between the substrate 8 and the active layer 9, this layer being exposed at 16.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Photovoltaic Devices (AREA)

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• 1992
  • 1992-04-15 FR FR9204633A patent/FR2690278A1/fr active Pending
• 1993
  • 1993-04-15 JP JP5518059A patent/JPH06511357A/ja active Pending
  • 1993-04-15 WO PCT/FR1993/000375 patent/WO1993021662A1/fr not_active Application Discontinuation
  • 1993-04-15 EP EP93909024A patent/EP0591500A1/de not_active Ceased
  • 1993-04-15 US US08/162,174 patent/US5458694A/en not_active Expired - Fee Related

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