Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F77/00—Constructional details of devices covered by this subclass
  • H10F77/20—Electrodes
  • H10F77/206—Electrodes for devices having potential barriers
  • H10F77/211—Electrodes for devices having potential barriers for photovoltaic cells
  • H10F77/219—Arrangements for electrodes of back-contact photovoltaic cells
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
  • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
  • H10F10/16—Photovoltaic cells having only PN heterojunction potential barriers
  • H10F10/164—Photovoltaic cells having only PN heterojunction potential barriers comprising heterojunctions with Group IV materials, e.g. ITO/Si or GaAs/SiGe photovoltaic cells
  • H10F10/165—Photovoltaic cells having only PN heterojunction potential barriers comprising heterojunctions with Group IV materials, e.g. ITO/Si or GaAs/SiGe photovoltaic cells the heterojunctions being Group IV-IV heterojunctions, e.g. Si/Ge, SiGe/Si or Si/SiC photovoltaic cells
  • H10F10/166—Photovoltaic cells having only PN heterojunction potential barriers comprising heterojunctions with Group IV materials, e.g. ITO/Si or GaAs/SiGe photovoltaic cells the heterojunctions being Group IV-IV heterojunctions, e.g. Si/Ge, SiGe/Si or Si/SiC photovoltaic cells the Group IV-IV heterojunctions being heterojunctions of crystalline and amorphous materials, e.g. silicon heterojunction [SHJ] photovoltaic 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

Definitions

• the invention relates to the production of photovoltaic cells, or solar cells, and more particularly photovoltaic cells with heterojunctions and discontinuous interdigitated structure.
• a conventional photovoltaic cell based on crystalline silicon, comprises a homojunction structure as well as contacts on the front and rear faces of the cell.
• the conversion efficiency of such a cell is generally between about 14% and 18%.
• Two other types of photovoltaic cell structure, more complex, make it possible to obtain conversion efficiencies greater than 20%: they are photovoltaic cells with rear-panel contacts (RCC) and heterojunction photovoltaic cells (HJ). .
• N and P doped zones, as well as metallizations associated with these zones, forming an electrode called emitter and a rear field electrode, are placed on the same face of a substrate (the rear face of the cell, that is to say the opposite side to that receiving the light rays) of this cell, in the form of interdigitated combs.
• comb here and throughout the rest of the document, a pattern comprising several fingers, or portions of elongated shape (for example rectangles), substantially parallel to each other and interconnected at one of their side by a finger disposed perpendicularly to the other fingers.
• interdigitated combs here and throughout the rest of the document, are understood to mean two combs as described above, arranged opposite each other and whose fingers are arranged between the fingers. the other.
• the doped zone forming the emitter is continuous over the entire length of a cell (for example greater than 100 mm) and its width is generally between 1 mm and a few hundred microns.
• the widths of the N and P doped zones are different.
• the technologies implemented for producing such a cell are similar to those used for producing a conventional photovoltaic cell. Additional steps of masking and lithography are however necessary to perform the localized doping (N and P areas on the same side).
• HJ photovoltaic cells use completely different technologies: thin layers of undoped and doped amorphous silicon must first be deposited by CVD (Chemical Vapor Deposition), and for example by PECVD (assisted chemical vapor deposition) by plasma) on the crystalline substrate of such a cell, then thin conductive layers must then be deposited by PVD (Physical Vapor Deposition). These deposits are made on the entire surface of the solar cell.
• CVD Chemical Vapor Deposition
• PECVD sisted chemical vapor deposition
• PVD Physical Vapor Deposition
• HJ + RCC back contacts and heterojunctions
• FIG. 1 is a view of a rear face of a photovoltaic cell HJ + RCC 1.
• This cell 1 comprises a substrate on which is deposited, at a rear face of this substrate, a thin layer of non-amorphous silicon. doped 2, a thin layer of amorphous silicon forming N + 4 doped zones and a thin layer of amorphous silicon forming P + doped zones 6, these doped zones 4 and 6 being arranged in the form of interdigitated combs. These doped zones 4 and 6 are covered with ITO (indium tin oxide). Finally, this structure comprises metallizations 8 and 10 made on the ITO, to contact the doped zones 4 and 6.
• An object of the present invention is to provide a new semiconductor device for obtaining photovoltaic cells with back contacts and low cost heterojunctions.
• the present invention proposes a photovoltaic device, which can comprise:
• a substrate based on a crystalline semiconductor material at least two heterojunctions made on a face, referred to as the back face, of the substrate and possibly comprising a first layer based on an amorphous semiconductor material doped with a first type of conductivity, and a second layer based on an amorphous semiconductor material doped with a second type of conductivity, the first and the second layer being able to be arranged on the rear face of the substrate in a pattern of interdigital combs at least one of the first and second layers may comprise a plurality of portions, or pads, of the doped amorphous semiconductor material of the first or the second conductivity type, separate or disjoint, and spaced from each other .
• the present invention also relates to a photovoltaic device comprising:
• a first electrode comprising at least one heterojunction made on a face, called the rear face, of the substrate, this heterojunction having a layer based on a doped amorphous semiconductor material,
• the device according to the invention makes it possible to obtain a photovoltaic cell with heterojunctions and rear contacts whose production costs are reduced compared with the photovoltaic cells of the prior art, while avoiding costly masking steps. photolithography.
• the first electrode can form an emitter of the photovoltaic device.
• the device may further comprise at least one intrinsic amorphous semiconductor layer disposed between the substrate and the doped amorphous semiconductor layer, the second electrode possibly comprising at least one metallization carried out on the intrinsic amorphous semiconductor base.
• the layer of the first electrode called the first layer, may be based on a doped amorphous semiconductor material of a first conductivity type, the second electrode may comprise at least one heterojunction comprising a second layer based on a material. amorphous semiconductor doped with a second type of conductivity.
• the device may further comprise at least one intrinsic amorphous semiconductor layer disposed between the substrate and the first and second doped amorphous semiconductor layers.
• the second layer may comprise a plurality of portions of the doped semiconductor material of the second distinct conductivity type, or disjoint, and spaced apart from each other.
• the portions of doped amorphous semiconductor material may be of substantially rectangular shape, the length and width dimensions of the doped semiconductor material portions of the first conductivity type may be different from those of the doped semiconductor material portions of the second type of conductivity.
• the portions of amorphous semiconductor material doped with the same type of conductivity may be isolated from each other by portions of insulating material disposed at least between said portions of doped amorphous semiconductor material and possibly partially arranged on the portions of amorphous semiconductor material doped, and / or be electrically connected to each other by metallizations made on said portions of doped amorphous semiconductor material.
• the metallizations made on the portions of amorphous semiconductor material doped with the same type of conductivity may be formed by a continuous portion based on a conductive material or comprise portions of a conductive material distinct, or disjointed, and spaced apart from each other.
• the device may further comprise at least one layer based on at least one conductive material, for example a transparent conductive oxide such as ITO, and / or a metal, disposed between the portions of doped amorphous semiconductor material. and the metallizations, and which may comprise distinct, or disjointed, and spaced apart portions of the conductive material of substantially similar shape to that of the portions of doped amorphous semiconductor material, and arranged substantially at the level of the portions of semiconductor material doped amorphous.
• the device may further comprise at least one intrinsic amorphous semiconductor layer disposed between the substrate and the first and second doped amorphous semiconductor layers.
• the device may be a photovoltaic cell with heterojunctions and rear contacts.
• An object of the present invention is also to provide a method for reducing the cost of producing a solar cell with back contacts and heterojunctions.
• the present invention also proposes a process for producing a structure with heterojunctions and with rear contacts which is not made up of long continuous doped zones but of discontinuous short doped zones, the electrical continuity of these aligned zones of the same polarity being only performed at the end of the process during the deposition of a conductive material forming the metallizations of the structure.
• the present invention also relates to a method for producing a photovoltaic device, which may comprise at least the steps of:
• the present invention also relates to a method for producing a photovoltaic device, comprising at least the steps of:
• - Realization of a first electrode comprising at least one step of depositing, on a face called rear face of a substrate based on a crystalline semiconductor material, a layer based on a semiconductor material amorphous doped through a mask whose pattern has openings discontinuous, forming a plurality of separate doped amorphous semiconductor material portions, or disjointed, and spaced apart from each other,
• first and second electrodes being disposed on the rear face of the substrate in a pattern of interdigitated combs.
• the method may further comprise, prior to the production of the first electrode, a step of depositing an intrinsic amorphous semiconductor layer on the rear face of the substrate, the layer based on the doped amorphous semiconductor material being able to to be deposited on the intrinsic amorphous semiconductor layer, the production of the second electrode comprising a step of depositing at least one metallization on the intrinsic amorphous semiconductor layer.
• the layer may be based on an amorphous semiconductor material doped with a first type of conductivity
• the production of the second electrode may comprise a step of depositing a second layer based on a amorphous semiconductor material doped with a second conductivity type on the back side of the substrate.
• the method may further comprise, prior to the production of the first electrode, a step of depositing an intrinsic amorphous semiconductor layer on the rear face of the substrate.
• the deposition of the second layer based on the doped amorphous semiconductor material of the second conductivity type can be obtained by depositing the doped amorphous semiconductor material of the second conductivity type through a second mask whose pattern comprises discontinuous openings. , capable of forming a plurality of portions of the doped amorphous semiconductor material of the second conductivity type which are distinct, or disjoint, and spaced from one another.
• the method may further comprise, after the production of the first and / or the second electrode, a deposition step, at least between the portions of amorphous semiconductor material doped with the same type of conductivity, through a mask whose pattern comprises discontinuous openings, an insulating material and / or partially on the portions of doped semiconductor material.
• the method may further comprise, before the first electrode is made, a step of depositing an insulating material through a mask whose pattern comprises discontinuous openings, intended to form portions of at least one insulating material. between said portions of amorphous semiconductor material doped with the same type of conductivity.
• the method may further comprise, after the realization of the first and / or second electrode, a deposition step on the portions of amorphous semiconductor material doped with the same type of conductivity, through a mask whose pattern comprises discontinuous openings, portions of at least one conductive material, for example metal and / or transparent conductive oxide such as ITO.
• portions of conductive material may be deposited on the portions of amorphous semiconductor material doped through the mask used for the deposition of the doped amorphous semiconductor material layer of the first electrode and, when the second electrode comprises a second layer. of doped amorphous semiconductor material of the second conductivity type deposited through the second mask, the portions of conductive material may be deposited on the portions of doped amorphous semiconductor material of the second conductivity type through the second mask.
• the portions of conductive material have a shape and dimensions substantially similar to the portions of doped amorphous semiconductor material.
• the method may further comprise, before the deposition of the first layer of doped amorphous semiconductor material of the first conductivity type, a step of depositing an intrinsic amorphous semiconductor layer on the rear face of the substrate.
• the method may also comprise a step of producing metallizations on the portions of doped amorphous semiconductor material that can electrically connect the semiconductor material portions.
• This embodiment of metallizations can be obtained by the deposition of a conductive material through a mask having discontinuous openings, forming separate portions of conductive material, or disjoint, and spaced from each other.
• FIG. 1 previously described, shows a view from below of a photovoltaic cell with heterojunctions and rear-panel contacts according to the prior art
• FIG. 2 represents a view from below of a photovoltaic cell with heterojunctions and rear-panel contacts, object of the present invention, according to a first embodiment
• FIGS. 3 to 8B show the steps of a method for producing a photovoltaic cell with heterojunctions and rear-face contacts, also the subject of the present invention
• FIG. 9 represents a view from below of a photovoltaic cell with heterojunctions and rear-panel contacts, object of the present invention, according to a second embodiment.
• Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the passage from one figure to another.
• the different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.
• FIG. 2 shows a photovoltaic cell 100 with heterojunctions and rear-panel contacts according to a first embodiment.
• the photovoltaic cell 100 comprises a substrate, not visible in FIG. 2, based on a crystalline semiconductor, for example silicon.
• a thin layer 102 of undoped amorphous semiconductor, such as silicon, is disposed on a rear face of the substrate.
• Thin film here and throughout the rest of the document, means a layer of thickness for example less than or equal to about 10 microns. In this first embodiment, this thin layer 102 has for example a thickness equal to about 15 nm.
• the amorphous materials used in the invention may be purely amorphous materials, but also polymorphic, microcrystalline or polycrystalline materials.
• the photovoltaic cell 100 comprises two layers, 104 and 106, of doped amorphous semiconductor, here silicon, according to two different types of conductivity, respectively N + and P +, in a pattern of interdigitated combs, forming two heterojunctions.
• the layer 104 forms the emitting electrodes, the layer 106 forming the rear field electrodes.
• the pattern of interdigitated combs formed by these two layers is not continuous, but discontinuous. Indeed, each of these layers is formed of portions, or pads, distinct or disjoint, from each other.
• the portions of the N + doped amorphous silicon layer 104 have a substantially rectangular shape, for example of width equal to approximately 1 mm, of length equal to approximately 3.5 mm and are spaced from each other by a distance equal to about 150 microns.
• the portions of the P + doped amorphous silicon layer 106 also have a substantially rectangular shape, of width equal to about 0.3 mm, of length equal to about 3.5 mm, and are spaced apart from each other. a distance equal to about 150 microns.
• the spaces, here 150 ⁇ m, separating the portions of doped amorphous semiconductor material are here filled by an insulating material 108, for example based on silicon dioxide.
• the insulating material 108 overflows on the portions of the doped amorphous silicon layers 104 and 106, thus partially covering these portions.
• a conductive layer is disposed on the portions of doped amorphous silicon formed by the layers 104 and 106.
• the patterns formed by this conductive layer substantially correspond to the patterns formed by the doped layers. 104 and 106, but slightly smaller dimensions (eg less than about 0.1 mm).
• This layer may be based on a conductive material such as a transparent conductive oxide, for example ITO, ZnO, SnO 2 , TiO 2 , or a metal, for example silver or silver. 'aluminum.
• the photovoltaic cell 100 comprises metallizations 110 and 112 arranged on the preceding conductive layer, not represented, thus connecting the portions of doped amorphous silicon of the same type of conductivity, via this previous conductive layer.
• the metallizations 110 connect the portions of the N + layer 104, the metallizations 112 connecting the portions of the P + layer 106.
• the metallizations 110 and 112 are represented as having a width less than that of the doped amorphous silicon portions 104 and 106.
• the metallizations 110 and 112 and the conductive layer are not in short circuit with the crystalline silicon substrate covered by the thin layer 102.
• FIG. 3 a rear surface 202 of a substrate 204, for example similar to the substrate of the photovoltaic cell 100, is deposited first, a thin layer of amorphous silicon 206, for example similar to the thin layer. 102 of the photovoltaic cell 100.
• the pattern of the mask is therefore transferred to the layer 208, forming separate doped amorphous silicon portions, or disjoint, and spaced from each other.
• the openings of the first mask, and thus also the portions of doped amorphous silicon produced have a substantially rectangular shape, for example of width equal to about 1 mm, of length equal to about 3.5 mm, these openings being spaced from each other by a distance of about 150 microns. As shown in FIGS.
• the apertures of the second mask have a width of about 0.3 mm, a length of about 3.5 mm, and an aperture spacing of about 150 ⁇ m.
• the thin layers 208 and 210 form a pattern of interdigitated combs. These two layers 208 and 210 form the two heterojunctions of the photovoltaic cell 200. It is possible that the thin layer of P + doped amorphous silicon 210 is deposited before the thin layer of amorphous silicon N + doped 208.
• an insulating thin layer 212 may advantageously be provided: it is deposited at the spaces separating the portions of the doped amorphous silicon layers 208 and 210, by the intermediate of a third mask having discontinuous openings.
• This insulating layer 212 is formed of a plurality of portions superimposed on the spaces separating the portions of the doped layers 208 and 210.
• the spacing between the portions of the doped layers 208 and 210 is subject to a double tolerance of the previous dimension, for example about +/- 100 ⁇ m.
• the portions of the insulating layer 212 may be widened to integrate the tolerances mentioned above. They may for example be of a width equal to about 350 microns.
• the ends of the portions of the doped layers 208 and 210 are covered by the material of the insulating layer 212, even in the case of a possible mask shift during the production of these doped layers 208 and 210.
• the insulating layer 212 may be deposited before the deposition of one of the doped amorphous silicon layers 208 or 210, or before the deposition of the two doped amorphous silicon layers 208 and 210.
• conductive thin film 214 for example based on conductive transparent oxide (TCO) such as ITO and / or ZnO and / or SnO 2 and / or TiO 2, and / or metal such as silver and / or aluminum (FIGS. 7A and 7B).
• This deposit is made through a fourth mask whose openings correspond to those of the first and the second mask, but of slightly smaller dimensions to prevent overflowing of the conductive material relative to the doped amorphous silicon layers 208 and 210.
• the conductive material 214 deposited on the portions of the doped layer 208 can form portions of substantially rectangular shape, for example of width equal to about 0.9 mm and length of about 3.4 mm, the conductive material 214 deposited on the portions of the doped layer 210 can also form portions of substantially rectangular shape for example with a width of about 0.2 mm and a length of about 3.4 mm.
• This layer forms metallizations 216 connecting the amorphous silicon portions N + 208 between them and metallizations 218 connecting the portions of amorphous silicon P + 210 between them.
• these metallizations 216 and 218 have a width that is substantially similar to that of the conductive material portions 214 on which these metallizations are located: for example, the metallizations 216 here have a width equal to about 0.9 mm and the metallizations 218 here have a width equal to about 0.2 mm.
• These metallizations 216, 218 are here made by screen printing a low-temperature polymer-based paste loaded with silver and / or any other suitable metal to form metallizations.
• the given dimensions have been defined to guarantee the critical overlaps and this, in taking into account possible offsets of about 50 microns with respect to the dimensions of the deposited patterns (offset at masks and alignment, burrs at the deposit, ).
• the masks used for its realization allow the deposition of rectangles of dimensions equal to 170 x 50 microns in the 200 x 70 micron step without burrs, with a dynamic alignment realized by a system of vision.
• CVD deposits for example PECVD or HW-CVD (hot wire chemical vapor deposition).
• the conductive transparent oxide and metal deposits are PVD deposits, for example sputtering or evaporation.
• the deposits of insulating materials are CVD deposits, for example PECVD.
• FIG. 9 shows a photovoltaic cell 300 with heterojunctions and rear-panel contacts according to a second embodiment.
• the photovoltaic cell 300 comprises metallizations 302 and 304 which are not continuous, that is to say comprising conductive portions, each of these conductive portions connecting two portions of amorphous silicon of a same type of conductivity.
• These metallizations 302 and 304 are thus not produced by screen printing but by through a mask whose pattern corresponds to the pattern of these metallizations 302 and 304.
• a conductive layer 214 is advantageously provided with a lower resistivity.
• metal having a lower resistivity than the ITO or an ITO / metal bilayer for example 40 nm of ITO and 150 nm aluminum.
• the photovoltaic cell 300 comprises portions of amorphous silicon doped N + 306 and P + 308 of different lengths.
• the portions of amorphous silicon N + 306 have a length greater than that of the portions of amorphous silicon P + 308.
• the openings of the mask used for producing the conductive layer, for example of ITO, deposited on the portions of N + 306 doped amorphous silicon and those for the realization of the ITO layer on the P + 308 doped amorphous silicon portions are not aligned next to each other, which eliminates the constraint on the minimum width of the bridge of material lying between the openings of the mask.
• the insulating portions separating the portions of amorphous silicon P + 308 are here made as long as possible in order to optimize the passivation at the rear field electrode.
• the mask openings used for the deposition of the insulating layer may be elongated to take advantage also of a lateral overflow, forming for example insulating portions whose width is for example equal to about 1.1 mm (deposited on portions of amorphous silicon whose width is for example equal to about 1 mm ) or 0.4 mm (deposited on portions of amorphous silicon whose width is for example equal to about 0.3 mm).
• the portions of ITO may be deposited in two steps: a first step carrying portions of ITO on the portions of N + doped amorphous silicon, and then a second step carrying portions of ITO on the portions of doped amorphous silicon. P +.
• the same mask it is also possible for the same mask to be used for the deposition of the doped amorphous silicon layers and the deposition of the conductive portions on the portions of the doped amorphous silicon layers.
• the deposition of the N + doped amorphous silicon layer is first performed, then the deposition of the conductive portions intended to be on the portions of the N + doped amorphous silicon layer, the deposition of the silicon layer.
• doped amorphous P + the deposition of the conductive portions intended to be on the P + doped amorphous silicon layer portions, the deposition of the insulating layer and finally the realization of the metallizations.
• the masks used during the production of a photovoltaic cell are suitably pressed against the cell, using a flat mask very tight on a frame, in order to avoid any overflow of the material applied to the cell. through the mask, to avoid short circuits between areas of different polarity.
• the masks used may be metal masks.
• the masks are preferably made by electrodeposition, offering excellent geometry, or chemical or laser cutting.
• the mask openings have a certain conicity (slightly larger dimensions of one side of the mask than the other), this size difference is taken into account for the choice of the side of the mask in contact with the substrate.
• a reduced thickness of the mask (for example equal to about 50 microns) makes it possible to reduce the shading phenomena.
• Masks of varying thickness can also be envisaged, with reduced thicknesses in the vicinity of the openings relative to the remainder of the mask.
• Another of these conditions is to have a good alignment between the different levels of layers made on the substrate.
• the masks are indexed with respect to the substrate via patterns included in the mask. These patterns, or indexing holes, are used either to perform a mechanical positioning substrate / mask (or frame), or to preference for dynamic alignment via a vision system.
• the differential expansion phenomena caused by the PECVD and PVD deposits produced in the range 150 to 200 ° C. are also taken into account, in particular by making sure to make the masks with the same materials.
• the masks are designed so that the width of the material bridges, that is to say the size of the portions of material of the mask between two openings, is at least equal to the thickness of the mask at the level of the mask. from this area.
• the two electrodes of the photovoltaic cell are made from disjoint portions of doped amorphous semiconductor material.
• the other electrode can then be formed of a simple conductive track, for example based on metal such as aluminum, deposited directly on the intrinsic amorphous silicon layer.
• the electrode made from disjoint portions of doped amorphous semiconductor is the electrode forming the emitter of the photovoltaic cell.

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