Manufacturing process for photovoltaic subcells

Abstract

A method for manufacturing photovoltaic subcells of various shapes, starting from a back-contact interdigitated photovoltaic cell (C0) comprising a crystalline silicon substrate (1), the method combining laser (L) ablation (A1) of a first part of the substrate (1) with selective chemical etching of a second part (S2) of the substrate (1). Figure 4

Description

Title of the invention: Method for manufacturing photovoltaic sub-cells Technical field

[0001] The invention relates to the technical field of photovoltaic cells. More specifically, the invention relates to the manufacture of photovoltaic sub-cells having a wide variety of shapes, for example square, rectangular, triangular, circular shapes, etc.

[0002] The invention finds its application in the manufacture of photovoltaic cells based on crystalline silicon whose front face, intended to be exposed to solar radiation, is devoid of electrical contacts. In other words, the invention finds its application in the manufacture of photovoltaic cells with rear contact, in particular with: - an interdigitated back contact (IBC) architecture; - a TOPCon (“Tunnel Oxide Passivated Contact”) type architecture with interdigitated rear contact, where the passivated rear contact comprises a tunnel oxide film covered with alternating n-type and p-type doped polycrystalline silicon layers; - an amorphous silicon / crystalline silicon heterojunction type architecture with interdigital rear contact; - an emitter wrap-through architecture (EWT for “Emitter Wrap Through” in English). State of the art

[0003] A first method of manufacturing photovoltaic sub-cells, known from the state of the art, uses a laser cleaving technique.

[0004] More specifically, for an interdigitated rear contact architecture, a first variant (laser-induced cleavage, LIC) of the first method comprises the steps: Aoi) use a photovoltaic cell comprising: - a substrate, based on crystalline silicon, having first and second opposite surfaces, the first surface being intended to be exposed to solar radiation; - a stack of active layers, formed on the first surface of the substrate; - an alternation of n-type and p-type doped zones (forming electron and hole collection zones), extending in a direction transverse to the normal to the second surface of the substrate; - first and second sets of metal pads, respectively in contact with the n-type doped zones and with the p-type doped zones; Boi) apply laser irradiation to the photovoltaic cell so as to: - locally obtain ablations of a first part of the substrate; - draw an outline delimiting photovoltaic sub-cells; - keep a second part of the substrate, extending in the extension of the ablations; Coi) separate the photovoltaic sub-cells delimited at the end of step BOi) by mechanical stress.

[0005] The first part of the substrate ablated during step BOi) makes it possible to weaken the photovoltaic sub-cells delimited at the end of step BOi), so that it is possible to separate them by mechanical stress during step COi).

[0006] Such a first variant of the first method, involving non-through grooves, is not very suitable for obtaining shapes other than square or rectangular for the photovoltaic sub-cells. In other words, such a first variant of the first method is only suitable when the contour delimits rectilinear portions. Indeed, during the step Coi) of separating the photovoltaic sub-cells by mechanical stress, a crack will be created and propagate along the preferential cleavage directions, which will induce breakage of the photovoltaic sub-cells.

[0007] A second variant (laser direct cleavage, LDC) of the first method comprises the steps: A'oi) use a photovoltaic cell comprising: - a substrate, based on crystalline silicon, having first and second opposite surfaces, the first surface being intended to be exposed to solar radiation; - a stack of active layers, formed on the first surface of the substrate; - an alternation of n-type and p-type doped zones (forming electron and hole collection zones), extending in a direction transverse to the normal to the second surface of the substrate; - first and second sets of metal pads, respectively in contact with the n-type doped zones and with the p-type doped zones; B'oi) apply laser cleavage to the photovoltaic cell so as to: - locally obtain ablations of the entire substrate; - draw an outline delimiting photovoltaic sub-cells.

[0008] The photovoltaic sub-cells delimited at the end of step B'oi) are spontaneously separated.

[0009] Such a second variant of the first method, involving through grooves, is suitable for obtaining various shapes for the photovoltaic sub-cells, unlike the first variant.

[0010] However, the first and second variants of such a first method of the state of the art are not entirely satisfactory insofar as the laser irradiation applied during steps BOi) and B'Oi) creates defects, in particular amorphization of the silicon on the edges of the photovoltaic sub-cells which makes the subsequent passivation of these edges difficult, or even impossible. Passivation of the substrate surfaces is a major challenge in the photovoltaic sector, making it possible to limit recombinations between carriers, which results in a significant improvement in efficiency. By "passivation" is meant the reduction of recombinations of carriers at the surfaces of the substrate. Indeed, a surface of a crystalline silicon substrate has a density of defects (e.g. dangling bonds, impurities, discontinuity of the crystal, etc.) which can lead to significant losses linked to the surface recombination of carriers in the case of a photovoltaic application.

[0011] A second method of manufacturing photovoltaic sub-cells, known from the state of the art, uses a thermal laser separation technique (TLS for “Thermal Laser Separation” in English).

[0012] More precisely, for an interdigitated rear contact architecture, the second method comprises the steps: A02) use a photovoltaic cell comprising: - a substrate, based on crystalline silicon, having first and second opposite surfaces, the first surface being intended to be exposed to solar radiation; - a stack of active layers, formed on the first surface of the substrate; - an alternation of n-type and p-type doped zones (forming electron and hole collection zones), extending in a direction transverse to the normal to the second surface of the substrate; - first and second sets of metal pads, respectively in contact with the n-type doped zones and with the p-type doped zones; B02) apply a laser thermal separation technique to the photovoltaic cell so as to: - locally obtaining crack propagations across the entire substrate, the cracks preferentially defining an axis passing between adjacent pairs of metal studs, each pair of metal studs comprising a metal stud from the first set and a metal stud from the second set; - draw an outline delimiting photovoltaic sub-cells.

[0013] The photovoltaic sub-cells delimited at the end of step B02) are spontaneously separated.

[0014] Such a second method of the state of the art makes it possible, at the end of step B02), to obtain edges of photovoltaic sub-cells which can be passivated. However, such a second method of the state of the art is not entirely satisfactory insofar as it is poorly suited to obtaining various shapes for the photovoltaic sub-cells, in particular when the outline does not delimit rectilinear portions.

[0015] The person skilled in the art is therefore looking for a solution making it possible to obtain various shapes (i.e. not only involving rectilinear portions) for the photovoltaic sub-cells, with edges that can be easily passivated. Statement of the invention

[0016] The invention aims to remedy all or part of the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing at least one photovoltaic sub-cell, comprising the steps: a) use a photovoltaic cell comprising: - a substrate, based on crystalline silicon, having first and second opposite surfaces, the first surface being intended to be exposed to solar radiation; - a stack of active layers, formed on the first surface of the substrate; - at least one alternation of electron and hole collection zones, formed on the second surface of the substrate; - first and second sets of metal pads, respectively in contact with the electron collection zones and with the hole collection zones; b) forming a dielectric layer extending over the first and second sets of metal pads; c) applying laser radiation to the photovoltaic cell obtained at the end of step b) so as to: - locally obtain ablations of a first part of the substrate; - draw an outline delimiting at least one photovoltaic sub-cell; - retaining a second part of the substrate, extending in the extension of the ablations, and adapted to retain mechanical strength of said at least one photovoltaic sub-cell delimited by the traced outline; d) chemically etching, with an etching agent, at least partially the second part of the substrate extending in the extension of the ablations obtained at the end of step c), so as to weaken said at least one photovoltaic sub-cell delimited at the end of step c), and so as to retain for the or each photovoltaic sub-cell at least one pair of adjacent metal pads comprising a metal pad from the first set and a metal pad from the second set; the etching agent being chosen so as to allow selective etching of the silicon relative to the dielectric layer; e) separating said at least one weakened photovoltaic sub-cell at the end of step d).

[0017] Thus, such a method according to the invention makes it possible to obtain at least one photovoltaic sub-cell of various shapes (not necessarily involving only rectilinear portions) with edges that can be easily passivated, thanks to the combination of steps c) and d). Indeed, the laser ablation of step c) makes it possible to trace a contour of varied shape, which can be for example rectilinear or curvilinear. Step d), for its part, makes it possible to: (i) weakening the photovoltaic sub-cell(s) delimited at the end of step c), and (ii) remove a large part of the defects linked to silicon amorphization (caused by laser irradiation) on the edges of the photovoltaic sub-cell(s), using chemical etching.

[0018] Such a step d), considerably reducing the amorphization defects of the silicon, thus facilitates subsequent passivation of the edges of the photovoltaic sub-cell(s) compared to the state of the art. The dielectric layer formed during step b) acts as an etching mask.

[0019] The invention also relates to a method for manufacturing a photovoltaic sub-cell, comprising the steps: a) use a photovoltaic cell comprising: - a substrate, based on crystalline silicon, having first and second opposite surfaces, the first surface being intended to be exposed to solar radiation; - a stack of active layers, formed on the first surface of the substrate; - an electron collection area and a hole collection area, formed on the second surface of the substrate; - first and second metal pads, respectively in contact with the electron collection zone and with the hole collection zone; b) forming a dielectric layer extending over the first and second metal pads; c) applying laser radiation to the photovoltaic cell obtained at the end of step b) so as to: - locally obtain ablations of a first part of the substrate; - draw an outline delimiting a photovoltaic sub-cell; - retain a second part of the substrate, extending in line with the ablations, and adapted to maintain mechanical strength of the photovoltaic sub-cell delimited by the traced outline; d) chemically etching, with an etching agent, at least partially the second part of the substrate extending in the extension of the ablations obtained at the end of step c), so as to weaken the photovoltaic sub-cell delimited at the end of step c), and so as to retain the first and second metal pads for the photovoltaic sub-cell; the etching agent being chosen so as to allow selective etching of the silicon relative to the dielectric layer; e) separating the weakened photovoltaic sub-cell at the end of step d).

[0020] Thus, such a method according to the invention makes it possible to obtain a single photovoltaic sub-cell of various shapes (not necessarily involving only rectilinear portions) with edges that can be easily passivated, thanks to the combination of steps c) and d). Indeed, the laser ablation of step c) makes it possible to trace a contour of varied shape, which can be, for example, rectilinear or curvilinear. Step d), for its part, makes it possible to: (i) weaken the single photovoltaic sub-cell delimited at the end of step c), and (ii) remove a large part of the defects linked to the amorphization of the silicon (caused by laser irradiation) on the edges of the single photovoltaic sub-cell, using chemical etching.

[0021] Such a step d), considerably reducing the amorphization defects of the silicon, thus facilitates a subsequent passivation of the edges of the single photovoltaic sub-cell compared to the state of the art. The dielectric layer formed during step b) acts as an etching mask.

[0022] The method according to the invention may comprise one or more of the following characteristics.

[0023] According to a characteristic of the invention, the laser radiation is applied during step c) so as to locally obtain longitudinal ablations defining an axis passing between adjacent pairs of metal pads, each pair comprising a metal pad from the first set and a metal pad from the second set.

[0024] The longitudinal ablations of the first part of the substrate define an axis physically passing between adjacent pairs of metal pads when the laser radiation is applied on the side of the second surface of the substrate.

[0025] The longitudinal ablations of the first part of the substrate define an axis passing virtually between adjacent pairs of metal pads when the laser radiation is applied on the side of the first surface of the substrate. It should be noted that, for laser radiation applied on the side of the first surface of the substrate, it is not necessary for the longitudinal ablations to define a virtual axis passing between adjacent pairs of metal pads. In other words, the virtual axis can point towards a metal pad. The application of the laser radiation on the side of the first surface of the substrate is therefore less restrictive in terms of alignment and presents less risk of altering the quality of the electron and hole collection zones.

[0026] According to a characteristic of the invention, the longitudinal ablations are longitudinal ablations of the dielectric layer and of the first part of the substrate.

[0027] Thus, it may be advantageous to apply the laser radiation on the side of the second surface of the substrate according to the photovoltaic cell architecture used during step a). Obtaining longitudinal ablations, defining an axis passing preferentially between adjacent pairs of metal pads, is facilitated to the extent that the alignment procedure is easier to implement compared to the case where the laser radiation is applied on the side of the first surface of the substrate.

[0028] According to a characteristic of the invention: - step d) is performed so that the second part of the substrate is completely chemically etched; - step e) consists of a spontaneous separation of the photovoltaic sub-cell(s) weakened at the end of step d).

[0029] Thus, an advantage provided is to avoid operations dedicated to the separation of the photovoltaic sub-cell(s).

[0030] According to a characteristic of the invention: - step d) is performed so that the second part of the substrate is partially chemically etched; - step e) is carried out by a separation technique chosen from thermal shock, mechanical stress, ultrasonic treatment.

[0031] Thus, an advantage provided is to reduce the operating time linked to the chemical etching of the second part of the substrate.

[0032] According to a characteristic of the invention, step d) consists of immersing the photovoltaic cell obtained at the end of step c) in an etching bath.

[0033] Thus, an advantage provided is the simplicity of implementation of the method.

[0034] According to a characteristic of the invention: - the dielectric layer formed during step b) is made of silicon oxide; - step d) is carried out so that the etching agent is chosen from a potassium hydroxide KOH solution, a tetramethylammonium hydroxide TMAH solution, a sodium hydroxide NaOH solution.

[0035] Thus, an advantage provided by such etching agents is to allow selective etching of silicon relative to a silicon oxide.

[0036] According to a characteristic of the invention, the laser radiation is applied during step c) in a direction parallel to the normal to the first and second surfaces of the substrate.

[0037] Thus, an advantage provided is to optimize the useful volume of the photovoltaic cell used during step a) to manufacture one or more photovoltaic sub-cells. voltaic.

[0038] According to a characteristic of the invention, the laser radiation applied during step c) is pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation of the first part of the substrate.

[0039] According to a characteristic of the invention, the photovoltaic sub-cell(s) separated at the end of step e) have exposed lateral edges; the method comprising a step f) consisting of passivating the exposed lateral edges.

[0040] Thus, one advantage provided is to limit recombinations between the carriers, which results in a significant improvement in efficiency.

[0041] According to a characteristic of the invention, step f) comprises a step consisting of forming an aluminum oxide on the exposed lateral edges, by atomic layer deposition (ALD).

[0042] Thus, an advantage provided is to be able to form a good quality passivation layer, after activation of the passivation (for example by annealing or by a treatment of the light exposure type “Light Soaking”), despite a potential high surface roughness of the exposed lateral edges.

[0043] According to a characteristic of the invention: - step b) comprises a step consisting of forming an additional dielectric layer extending over the stack of active layers; - the etching agent with which step d) is carried out is chosen so as to allow selective etching of the silicon with respect to the dielectric layer and the additional dielectric layer.

[0044] Thus, an advantage provided is to protect the stack of active layers from chemical etching during step d) when the surface active layer of the stack can be attacked by the etching agent used during step d). The additional dielectric layer then acts as an etching mask.

[0045] According to a characteristic of the invention, the laser radiation is applied during step c) so as to locally obtain longitudinal ablations of the stack of active layers and of the first part of the substrate.

[0046] Thus, it may be advantageous to apply the laser radiation on the side of the first surface of the substrate according to the photovoltaic cell architecture used during step a). It is also possible to apply the laser radiation both on the side of the first surface of the substrate and on the side of the second surface of the substrate.

[0047] According to a characteristic of the invention, the laser radiation is applied during step c) so as to locally obtain longitudinal ablations of the additional dielectric layer, of the stack of active layers, and of the first part of the substrate.

[0048] According to a characteristic of the invention, step a) is executed so that: - the alternation of electron and hole collection zones extends under the second surface of the substrate; - the electron collection zone and the hole collection zone extend under the second surface of the substrate; - the first and second sets of metal pads are formed on the second surface of the substrate; - the first and second metal pads are formed on the second surface of the substrate.

[0049] Thus, the photovoltaic cell used during step a) has a homojunction interdigitated back contact (IBC) architecture.

[0050] According to a characteristic of the invention, step a) is executed so that: - the second surface of the substrate is at least partially covered with a tunnel oxide film; - the alternation of electron and hole collection zones extends over the tunnel oxide film; - the electron collection zone and the hole collection zone extend over the tunnel oxide film; - the first and second sets of metal pads are formed respectively on the electron collection areas and on the hole collection areas; - the first and second metal pads are formed respectively on the electron collection area and on the hole collection area.

[0051] Thus, the photovoltaic cell used during step a) has a TOPCon (“Tunnel Oxide Passivated Contact”) type architecture with interdigitated rear contact.

[0052] According to a characteristic of the invention, step d) is followed by partial etching of the dielectric layer, preferably using a hydrofluoric acid solution.

[0053] Thus, this partial etching step makes it possible in particular to adjust the thicknesses of the dielectric layer in order to obtain optimal optical properties (e.g. anti-reflection property).

[0054] Definitions

[0055] - By “substrate” is meant a physical, self-supporting support intended for manufacturing of a photovoltaic cell. The substrate can be a wafer cut from a crystalline silicon ingot.

[0056] - By "crystalline silicon" is meant the multicrystalline form or the monocrystalline form crystalline silicon, therefore excluding amorphous silicon.

[0057] - By "based on" we mean that crystalline silicon is the main material and ma majority composing the substrate.

[0058] - By "active layer" we mean a layer (or zone) having a role in the operation of the photovoltaic cell, for example a role of separation of charges, a role of electrical passivation of the substrate surfaces, an optical role of anti-reflection, a role of sub-cell (other than crystalline silicon) in the case of a multi-junction etc.

[0059] - By “plot” we mean an electrical contact pad.

[0060] - By "electron collection zone" is meant an area designed to extract electrons from the photovoltaic cell. As non-limiting examples, the electron collection zone can be: (i) a region of the substrate, made of crystalline silicon, comprising n-type dopants; (ii) a layer of n-type doped polycrystalline silicon formed on a tunnel oxide layer, the tunnel oxide layer having a passivation role; (iii) a thin layer of n-type doped amorphous silicon; (iv) a thin layer introducing a band curvature favorable to the extraction of electrons.

[0061] - By "hole collection area" is meant an area designed to extract holes of the photovoltaic cell. As non-limiting examples, the hole collection area can be: (i) a region of the substrate, made of crystalline silicon, comprising p-type dopants; (ii) a p-type doped polycrystalline silicon layer formed on a tunnel oxide layer, the tunnel oxide layer having a passivation role; (iii) a thin layer of p-type doped amorphous silicon; (iv) a thin layer introducing a band curvature favorable to hole extraction.

[0062] - By "n-type doped zone" is meant an area made of a semi- conductor (e.g. crystalline silicon of the substrate, polycrystalline silicon of a layer formed on a tunnel oxide film) comprising n-type dopants, i.e. introduced species which donate an electron to the conduction band of the semiconductor material.

[0063] - By "p-type doped zone" is meant an area made of a semi- conductor (e.g. crystalline silicon of the substrate, polycrystalline silicon of a layer formed on a tunnel oxide film) comprising p-type dopants, i.e. introduced species which accept an electron from the conduction band of the semiconductor material.

[0064] - By "alternation" we mean that the electron collection zones (eg zones n-type doped) and the hole collection zones (e.g. p-type doped zones) are spaced so that they follow one another in turn in a repeated manner. This allows for n / p / n / p etc. or p / n / p / n etc. alternations. The photovoltaic cell can have several alternations that do not start with the same type of doping. For example, a first alternation can be n / p / n / p while a second alternation can be p / n / p / n.

[0065] - By "formed on the first surface of the substrate" is meant that the stack of active layers is formed on the first surface of the substrate, and may include areas extending under the first surface of the substrate, for example heavily doped areas providing an electrical passivation role for the first surface of the substrate.

[0066] - By "formed on the second surface of the substrate", we mean that the alternation(s) electron and hole collection zones are formed either: (i) under the second surface of the substrate; or (ii) on the second surface of the substrate, a tunneling oxide film preferably being interposed between the second surface of the substrate and the electron and hole collection areas.

[0067] - By "tunnel oxide film" is meant an oxide film thin enough to allow the transport of electrical charges (i.e. electrons, holes) within it by tunnel effect or by the presence of localized conduction paths (commonly called “pinholes” in English).

[0068] - By "semiconductor" is meant a material having a conductivity electric at 300 K between 106 S / cm and 103 S / cm.

[0069] - By "dielectric" is meant a layer made of a material having a electrical conductivity at 300 K less than or equal to 106 S / cm.

[0070] - By "ablation" is meant an ejection of material from a material passed through by laser radiation at a given fluence.

[0071] - By “axis passing between adjacent pairs of metal studs” we mean: (i) an axis passing virtually (in the extension of the longitudinal ablation) between adjacent pairs of metal pads when the ablation crosses the first surface of the substrate; (ii) an axis physically passing between adjacent pairs of metal pads as the ablation passes through the second surface of the substrate.

[0072] - By "adjacent pair of metal studs" we mean that each pair has distinct metal pads from an adjacent pair. In other words, the same metal pad cannot belong to two adjacent pairs.

[0073] - By "contour" is meant all or part of all the surfaces delimiting the photovoltaic sub-cells. A partial contour is a part of the set of surfaces delimiting the photovoltaic sub-cells. A total contour is the set of surfaces delimiting the photovoltaic sub-cells.

[0074] - By "photovoltaic sub-cell" is meant a photovoltaic cell obtained from from a division of the initial photovoltaic cell, used in step a). Not all photovoltaic sub-cells obtained from the initial photovoltaic cell used in step a) are necessarily functional.

[0075] - By "mechanical strength", we mean that the photovoltaic sub-cells, limited at the end of step c), resist rupture in response to mechanical stress.

[0076] - By "at least partially" is meant that the second part of the substrate is by partially or completely chemically etched during step d).

[0077] - By "selective etching" is meant that the silicon of the substrate can be etched without significantly attack the material of the dielectric layer (and where appropriate the additional dielectric layer). In practice, the etching agent is chosen so that the etching speed of the silicon is at least 3 times higher (preferably 5 times higher, more preferably 10 times higher) than that of the material of the dielectric layer (and where appropriate the additional dielectric layer).

[0078] - By "spontaneous separation" we mean a rupture of the photo sub-cells voltaic without external stress.

[0079] - By “silicon oxide” is meant an oxide of the empirical formula SixOy.

[0080] - By "passivate" we mean the reduction of carrier recombinations to substrate surfaces. Indeed, the edges of a crystalline silicon substrate have a density of defects (e.g. dangling bonds, impurities, crystal discontinuity, etc.) which can lead to significant losses linked to the surface recombination of carriers in the case of a photovoltaic application.

[0081] - By “aluminum oxide” is meant an oxide of the empirical formula AlxOy. Brief description of the drawings

[0082] Other characteristics and advantages will appear in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the attached drawings.

[0083] [Fig.l] is a schematic sectional view, illustrating a step a) of a method according to the invention, for an interdigitated rear contact architecture.

[0084] [Fig.2] is a schematic sectional view, illustrating a step b) of a method according to the invention, for an interdigital rear contact architecture.

[0085] [Fig.3] is a schematic sectional view, virtually illustrating (in dotted lines) the first part of the substrate which will be ablated during step c) on the side of the first surface of the substrate, and the second part of the substrate, in the extension of the ablations, which will be preserved at the end of step c).

[0086] [Fig.4] is a schematic sectional view, illustrating a step c) of a method according to the invention, when the first part of the substrate is ablated from the side of the first surface of the substrate.

[0087] [Fig.5] is a schematic sectional view, illustrating a step d) of a method according to the invention, the chemical etching of the second part of the substrate being partial.

[0088] [Fig.6] is a schematic sectional view, virtually illustrating (in dotted lines) the first part of the substrate which will be ablated during step c) on the side of the second surface of the substrate, and the second part of the substrate, in the extension of the ablations, which will be preserved at the end of step c).

[0089] [Fig.7] is a schematic sectional view, illustrating a step c) of a method according to the invention, when the first part of the substrate is ablated from the side of the second surface of the substrate.

[0090] [Fig.8] is a schematic sectional view, illustrating a step d) of a method according to the invention, the chemical etching of the second part of the substrate being partial.

[0091] [Fig.9] is a schematic sectional view, illustrating a step d) of a method according to the invention, the chemical etching of the second part of the substrate being complete.

[0092] [Fig. 10] is a schematic sectional view, illustrating a step e) of a method according to the invention after partial chemical etching of the second part of the substrate.

[0093] [Fig. 11] is a schematic sectional view illustrating a photovoltaic sub-cell obtained at the end of step e).

[0094] [Fig.12] is a schematic sectional view, similar to [Fig.11], illustrating a step f) of a method according to the invention, in which the exposed lateral edges of the photovoltaic sub-cell are passivated.

[0095] [Fig. 13] is a schematic sectional view, illustrating a step b) of a method according to the invention, comprising a step consisting of forming an additional dielectric layer extending over the stack of active layers.

[0096] [Fig. 14] is a schematic sectional view, illustrating a step b) of a method according to the invention, for a TOPCon (“Tunnel Oxide Passivated Contact”) type architecture with interdigitated rear contact.

[0097] It should be noted that the drawings described above are schematic, and are not necessarily to scale for the sake of readability and to simplify their understanding. The sections are made along the normal to the first and second surfaces of the substrate. Detailed description of the implementation methods

[0098] Elements that are identical or provide the same function will bear the same references for the different embodiments, for the sake of simplification.

[0099] An object of the invention is a method of manufacturing at least one photovoltaic sub-cell Cl, comprising the steps: a) use a photovoltaic C0 cell comprising: - a substrate 1, based on crystalline silicon, having first and second opposite surfaces 10, 11, the first surface 10 being intended to be exposed to solar radiation; - a stack 2 of active layers, formed on the first surface 10 of the substrate 1; - at least one alternation 3 of collection zones 30, 31 of electrons and holes, formed on the second surface 11 of the substrate 1; - first and second sets PI, P2 of metal pads, respectively in contact with the electron collection zones 30 and with the hole collection zones 31; b) forming a dielectric layer 4 extending over the first and second sets PI, P2 of metal pads; c) applying laser radiation L to the CO photovoltaic cell obtained at the end of step b) so as to: - locally obtain Al ablations of a first part SI of the substrate 1; - draw an outline delimiting at least one photovoltaic Cl sub-cell; - retain a second part S2 of the substrate 1, extending in the extension of the ablations Al, and adapted to retain mechanical strength of said at least one photovoltaic sub-cell Cl delimited by the traced contour; d) chemically etching, with an etching agent, at least partially the second part S2 of the substrate 1 extending in the extension of the ablations Al obtained at the end of step c), so as to weaken said at least one photovoltaic sub-cell Cl delimited at the end of step c), and so as to preserve for the or each photovoltaic sub-cell Cl at least one pair PI, P2 of adjacent metal pads comprising a metal pad of the first set PI and a metal pad of the second set P2; the etching agent being chosen so as to allow selective etching of the silicon with respect to the dielectric layer 4; e) separating said at least one weakened photovoltaic sub-cell Cl at the end of step d).

[0100] The invention also relates to a method for manufacturing a photovoltaic sub-cell Cl, comprising the steps: a) use a photovoltaic C0 cell comprising: - a substrate 1, based on crystalline silicon, having first and second opposite surfaces 10, 11, the first surface 10 being intended to be exposed to solar radiation; - a stack 2 of active layers, formed on the first surface 10 of the substrate 1; - an electron collection zone 30 and a hole collection zone 31, formed on the second surface 11 of the substrate 1; - first and second metallic pads PI, P2, respectively in contact with the electron collection zone 30 and with the hole collection zone 31; b) forming a dielectric layer 4 extending over the first and second metal pads PI, P2; c) apply laser radiation L to the photovoltaic cell C0 obtained at the end from step b) so as to: - locally obtain Al ablations of a first part SI of the substrate 1; - draw an outline delimiting a photovoltaic Cl sub-cell; - retain a second part S2 of the substrate 1, extending in the extension of the ablations Al, and adapted to retain mechanical strength of the photovoltaic sub-cell Cl delimited by the traced contour; d) chemically etching, with an etching agent, at least partially the second part S2 of the substrate 1 extending in the extension of the ablations Al obtained at the end of step c), so as to weaken the photovoltaic sub-cell Cl delimited at the end of step c), and so as to preserve for the photovoltaic sub-cell Cl the first and second metal pads PI, P2; the etching agent being chosen so as to allow selective etching of the silicon with respect to the dielectric layer 4; e) separating the weakened photovoltaic Cl sub-cell at the end of step d).

[0101] Step a)

[0102] The photovoltaic CO cell used during step a) may comprise: - a substrate 1, based on crystalline silicon, having first and second opposite surfaces 10, 11, the first surface 10 being intended to be exposed to solar radiation; - a stack 2 of active layers, formed on the first surface 10 of the substrate 1; - at least one alternation 3 of collection zones 30, 31 of electrons and holes, formed on the second surface 11 of the substrate 1; - first and second sets PI, P2 of metal pads, respectively in contact with the electron collection zones 30 and with the hole collection zones 31.

[0103] The photovoltaic C0 cell used during step a) may comprise: - a substrate 1, based on crystalline silicon, having first and second opposite surfaces 10, 11, the first surface 10 being intended to be exposed to solar radiation; - a stack 2 of active layers, formed on the first surface 10 of the substrate 1; - a single electron collection zone 30 and a single hole collection zone 31, formed on the second surface 11 of the substrate 1; - first and second metallic pads PI, P2, respectively in contact with the single electron collection zone 30 and with the single hole collection zone 31.

[0104] The substrate 1 is based on crystalline silicon. The substrate 1 is advantageously made from monocrystalline silicon. The substrate 1 may be n-type doped or p-type doped, depending on the architecture of the photovoltaic C0 cell. The substrate 1 may also be intrinsic. The first surface 10 of the substrate 1 and / or the second surface 11 of the substrate 1 can be textured. The first surface 10 of the substrate 1 is intended to form the front face of the photovoltaic CO cell. The second surface 11 of the substrate 1 is intended to form the rear face of the photovoltaic CO cell.

[0105] The stack 2 of active layers advantageously comprises a passivation layer, designed to passivate the first surface 10 of the substrate 1. By way of non-limiting example, the passivation layer may be made of an aluminum oxide. The stack 2 of active layers advantageously comprises at least one anti-reflection layer, formed on the passivation layer. By way of non-limiting example, the anti-reflection layer may be made of a silicon nitride, preferably hydrogenated. The active layers are advantageously thin layers, the thickness of which is preferably less than 1 μm. The stack 2 of active layers may comprise at least one heavily doped zone formed under the first surface 10 of the substrate 1, and ensuring a role of electrical passivation of the first surface 10 of the substrate 1.In the case of an interdigital back contact architecture, when substrate 1 is doped, the heavily doped area is doped with the same conductivity type as that of substrate 1. In other words, when substrate 1 is n-type doped, the heavily doped area is n++ doped. When substrate 1 is p-type doped, the heavily doped area is p++ doped.

[0106] The alternation 3 of electron and hole collection zones 30, 31 forms a charge separation region. The electron collection zones 30 are advantageously n-type doped zones. The hole collection zones 31 are advantageously p-type doped zones.

[0107] According to a first photovoltaic cell architecture, step a) is executed so that: - the alternation 3 of collection zones 30, 31 of electrons and holes extends under the second surface 11 of the substrate 1; - the first and second sets PI, P2 of metal pads are formed on the second surface 11 of the substrate 1.

[0108] According to a variant, the single electron collection zone 30 and the single hole collection zone 31 extend under the second surface 11 of the substrate 1. The first and second metal pads PI, P2 are formed on the second surface 11 of the substrate 1.

[0109] The electron and hole collection zones 30, 31 are advantageously n-type and p-type doped zones respectively. The electron and hole collection zones 30, 31 may form wells extending under the second surface 11 of the substrate 1. The electron and hole collection zones 30, 31 extend under the second surface 11 of the substrate 1, preferably in a direction transverse to the normal to the second surface 11 of the substrate 1.

[0110] The first architecture is a homo-interdigitated back contact architecture junction.

[0111] According to a second photovoltaic cell architecture, step a) is executed so that: - the second surface 11 of the substrate 1 is at least partially covered with a tunnel oxide film 5; - the alternation 3 of collection zones 30, 31 of electrons and holes extends over the tunnel oxide film 5; - the first and second sets PI, P2 of metal pads are formed respectively on the electron collection zones 30 and on the hole collection zones 31.

[0112] According to a variant, the single electron collection zone 30 and the single hole collection zone 31 extend over the tunnel oxide film 5. The first and second metal pads PI, P2 are formed respectively on the single electron collection zone 30 and on the single hole collection zone 31.

[0113] The second surface 11 of the substrate 1 is at least partially covered with a tunnel oxide film 5. In other words, the second surface 11 of the substrate 11 is totally or partially covered with a tunnel oxide film 5.

[0114] The electron and hole collection zones 30, 31 are advantageously n-type and p-type doped polycrystalline silicon layers respectively. The electron and hole collection zones 30, 31 extend over the tunnel oxide film 5 in a direction transverse to the normal to the second surface 11 of the substrate 1.

[0115] The second architecture is a TOPCon type architecture with interdigital rear contact. In the second architecture, the electron and hole collection zones 30, 31 are advantageously separated from each other by a separation material 7, such as a layer of intrinsic polycrystalline silicon. The polycrystalline silicon layers (n-type doped, p-type doped, intrinsic) are preferentially covered by a dielectric material (not shown in [Fig. 14] for the sake of simplicity) open at the metal pads.

[0116] It should be noted that other architectures are conceivable, in particular an emitter wrap-through architecture (EWT) known to those skilled in the art.

[0117] The first and second sets PI, P2 of metal pads are made of a metallic material, which may be, for example, silver Ag, copper Cu, or aluminum Al. The first and second sets PI, P2 of metal pads may be formed by screen printing. Other metallization techniques are conceivable for forming the first and second sets PI, P2 of metal pads. Examples include physical vapor deposition, inkjet deposition, vacuum evaporation deposition, and electrodeposition.

[0118] The photovoltaic CO cell used during step a) may include alignment marks, formed for example by printing, in order to subsequently facilitate the alignment of the laser radiation L during step c) with respect to the adjacent pairs PI, P2 of metal pads.

[0119] Step b)

[0120] The dielectric layer 4 formed during step b) extends over the first and second sets PI, P2 of metal pads so as to completely cover the first and second sets PI, P2 of metal pads. The dielectric layer 4 formed during step b) may be made of a silicon oxide. However, other dielectric materials are conceivable. Examples include a silicon oxynitride SixOyNz, a silicon nitride SixNy, an aluminum oxide AlxOy.

[0121] The dielectric layer 4 may be formed during step b) by a deposition technique known to those skilled in the art. Examples include physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-enhanced chemical vapor deposition (PECVD), subatmospheric pressure chemical vapor deposition (LPCVD), etc.

[0122] More precisely, the deposition technique is advantageously chosen to have a compliance rate (ratio between the width of the sides of the deposited dielectric layer 4 and the surface thickness of the deposited dielectric layer 4) sufficient to allow the surface topology of the first and second sets PI, P2 of metal pads to be followed. In this respect, preference will be given to deposition by ALD or deposition by LPCVD which have compliance rates close to 1. In other words, the deposition technique is advantageously chosen to have a dielectric layer 4 with the greatest possible coverage.

[0123] It is possible to combine several deposition techniques to form the dielectric layer 4 during step b). For example, the formation of the dielectric layer 4 can begin with an ALD deposition, for excellent conformity, and continue with a PECVD deposition, for the high deposition speed. The dielectric layer 4 formed during step b) can have a thickness of between 10 nm and 1 μm, preferably between 10 nm and 200 nm.

[0124] Step b) may include a step consisting of forming an additional dielectric layer 4' extending over the stack 2 of active layers. The additional dielectric layer 4' may be made of a silicon oxide. However, other dielectric materials are conceivable. For example, an oxynitride of silicon SixOyNz, silicon nitride SixNy, aluminum oxide AlxOy.

[0125] The dielectric layer 4 and the additional dielectric layer 4' formed during step b) may respectively be made of first and second dielectric materials. The first and second dielectric materials may be identical. However, the first and second dielectric materials may be different. Furthermore, it is also possible to combine several dielectric materials to form the dielectric layer 4 or the additional dielectric layer 4'.

[0126] The main role of the dielectric layer 4 and the additional dielectric layer 4' is to form a protective barrier layer against the chemical attack of step d). In other words, the dielectric layer 4 and the additional dielectric layer 4' act as an etching mask. However, the dielectric layer 4 and the additional dielectric layer 4' may have additional functions. Examples include a function of protection against UV radiation, a buffer layer function to protect the surface active layers, etc.

[0127] Step c)

[0128] The laser radiation L is advantageously applied to the photovoltaic cell CO during step c) so as to: - locally obtaining longitudinal Al ablations of a first part SI of the substrate 1, the longitudinal Al ablations defining a Z axis passing between adjacent pairs PI, P2 of metal pads, each pair PI, P2 of metal pads comprising a metal pad of the first set PI and a metal pad of the second set P2; - draw an outline delimiting the photovoltaic Cl sub-cell(s); - retain a second part S2 of the substrate 1, extending in the extension of the longitudinal ablations Al, and adapted to retain mechanical strength of the photovoltaic sub-cell(s) Cl delimited by the traced outline.

[0129] According to a variant, the laser radiation L is applied to the photovoltaic cell C0 during step c) so as to: - locally obtain Al ablations of a first part SI of the substrate 1; - draw an outline delimiting a single photovoltaic Cl sub-cell; - retain a second part S2 of the substrate 1, extending in the extension of the ablations Al, and adapted to maintain mechanical strength of the single photovoltaic sub-cell Cl delimited by the traced outline.

[0130] The laser radiation L is advantageously applied during step c) in a direction parallel to the normal to the first and second surfaces 10, 11 of the substrate 1.

[0131] The laser radiation L applied during step c) is advantageously a pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation of the first part SI of the substrate 1. In other words, the laser radiation L applied during step c) must reach the substrate 1 in order to expose the crystalline silicon. The pulse duration can be of the order of a nanosecond or a picosecond. The scanning speed of the laser radiation L applied during step c) is also adjusted to obtain the desired ablation depth, which may be, for example, of the order of 25 microns. Several successive irradiations can also be envisaged. The width of the amorphized zone of the silicon by the laser irradiation can be of the order of 5 microns. The laser radiation L applied during step c) can have a wavelength belonging to the infrared, or to the visible spectrum (e.g. green, blue). As a non-limiting example, the wavelength can be 1024 nm. The laser radiation L applied during step c) can form an irradiated zone having a diameter of the order of 30 microns.

[0132] According to a first embodiment, the laser radiation L is applied during step c) so as to locally obtain longitudinal Al ablations of the dielectric layer 4 and of the first part SI of the substrate 1, the longitudinal Al ablations defining an axis Z passing between adjacent pairs PI, P2 of metal pads, each pair PI, P2 of metal pads comprising a metal pad of the first set PI and a metal pad of the second set P2.

[0133] According to a second embodiment, the laser radiation L is applied during step c) so as to locally obtain longitudinal ablations Al of the stack 2 of active layers and of the first part SI of the substrate 1. The longitudinal ablations Al of the stack 2 of active layers and of the first part SI of the substrate can define a Z axis passing virtually between adjacent pairs PI, P2 of metal pads. However, the virtual Z axis can point to a metal pad. The application of the laser radiation L on the side of the first surface 10 of the substrate 1 is therefore less restrictive in terms of alignment and presents less risk of altering the quality of the collection zones 30, 31 of electrons and holes.

[0134] According to a third embodiment, the laser radiation L is applied during step c) so as to locally obtain longitudinal Al ablations of the dielectric layer 4, of the stack 2 of active layers, and of the first part SI of the substrate 1.

[0135] When an additional dielectric layer 4', extending over the stack 2 of active layers, is formed during step b), then the laser radiation L is applied during step c) so as to locally obtain longitudinal ablations Al of the additional dielectric layer 4', of the stack 2 of active layers, and of the first part SI of the substrate 1.

[0136] Step d)

[0137] The second part S2 of the substrate 1, extending in the extension of the ablations Al, is at least partially chemically etched with an etching agent of so as to weaken the photovoltaic sub-cell(s) Cl delimited at the end of step c), and so as to retain at least one pair PI, P2 of adjacent metal pads comprising a metal pad from the first set PI and a metal pad from the second set P2.

[0138] According to a variant, the second part S2 of the substrate 1, extending in the extension of the ablations Al, is at least partially etched so as to weaken the single photovoltaic sub-cell Cl delimited at the end of step c), and so as to preserve for the single photovoltaic sub-cell Cl the first and second metal pads PI, P2.

[0139] The etching agent is chosen so as to allow selective etching of the silicon relative to the dielectric layer 4.

[0140] When an additional dielectric layer 4', extending over the stack 2 of active layers, is formed during step b), then the etching agent with which step d) is carried out is advantageously chosen so as to allow selective etching of the silicon with respect to the dielectric layer 4 and to the additional dielectric layer 4'.

[0141] According to a first embodiment, step d) is executed so that the second part S2 of the substrate 1 is completely chemically etched.

[0142] According to a second embodiment, step d) is executed so that the second part S2 of the substrate 1 is partially chemically etched.

[0143] Step d) advantageously consists of immersing the photovoltaic C0 cell obtained at the end of step c) in an etching bath.

[0144] When the dielectric layer 4 formed during step b) is made of a silicon oxide, step d) is advantageously carried out so that the etching agent is chosen from a potassium hydroxide KOH solution, a tetramethylammonium hydroxide TMAH solution, a sodium hydroxide NaOH solution.

[0145] By way of non-limiting example, step d) can be carried out at a temperature of 80°C with a potassium hydroxide KOH solution as etching agent, having a mass percentage of 2.5%.

[0146] Step d) may be followed by a step of partial etching of the dielectric layer 4 and, where appropriate, of the additional dielectric layer 4', for example using a hydrofluoric acid HF solution. The partial etching step may be carried out before or after step e). This partial etching step makes it possible in particular to adjust the thicknesses of the dielectric layer 4, and, where appropriate, of the additional dielectric layer 4', in order to obtain optimal optical properties (e.g., anti-reflection property).

[0147] Step e)

[0148] The photovoltaic sub-cell(s) Cl weakened at the end of step d) are separated during step e).

[0149] When step d) is carried out so that the second part S2 of the substrate 1 is completely chemically etched, step e) consists of a spontaneous separation of the photovoltaic sub-cell(s) Cl weakened at the end of step d).

[0150] When step d) is carried out so that the second part S2 of the substrate 1 is partially chemically etched, step e) is advantageously carried out by a separation technique chosen from thermal shock, mechanical stress, and ultrasonic treatment. Those skilled in the art know how to adjust the parameters of the thermal shock, the mechanical stress, and the ultrasonic treatment in order to obtain physical separation.

[0151] The photovoltaic sub-cell(s) Cl separated at the end of step e) have exposed lateral edges BL. The photovoltaic sub-cell(s) Cl advantageously have a P / S ratio greater than or equal to 8.9 102 mm ', where "P" is the perimeter of the photovoltaic sub-cell Cl, and "S" is the surface area of ​​the photovoltaic sub-cell Cl.

[0152] Step f)

[0153] The method advantageously comprises a step f) consisting of passivating the exposed lateral edges BL. In other words, step f) consists of forming a passivation layer 6 on each of the exposed lateral edges BL.

[0154] Step f) advantageously comprises a step consisting of forming an aluminum oxide 6 on the exposed lateral edges BL, by deposition of atomic layers, prior to a step of activating the passivation by annealing or by a treatment of the light exposure type “Light Soaking”. However, other passivation layers 6 (different passivation materials) can be formed on the exposed lateral edges BL, including by other deposition techniques.

[0155] The invention is not limited to the embodiments disclosed. Those skilled in the art are able to consider their technically effective combinations and to substitute equivalents for them.

Claims

Claims

1. Method for manufacturing at least one photovoltaic sub-cell (Cl), comprising the steps: a) use a photovoltaic cell (CO) comprising: - a substrate (1), based on crystalline silicon, having first and second opposite surfaces (10, 11), the first surface (10) being intended to be exposed to solar radiation; - a stack (2) of active layers, formed on the first surface (10) of the substrate (1); - at least one alternation (3) of collection zones (30, 31) of electrons and holes, formed on the second surface (11) of the substrate (1); - first and second sets (PI, P2) of metal pads, respectively in contact with the electron collection zones (30) and with the hole collection zones (31); b) forming a dielectric layer (4) extending over the first and second sets (PI, P2) of metal pads; c) applying laser radiation (L) to the photovoltaic cell (C0) obtained at the end of step b) so as to: - locally obtain ablations (Al) of a first part (SI) of the substrate (1); - draw an outline delimiting at least one photovoltaic sub-cell (Cl); - retaining a second part (S2) of the substrate (1), extending in the extension of the ablations (Al), and adapted to retain mechanical strength of said at least one photovoltaic sub-cell (Cl) delimited by the traced outline; d) chemically etching, with an etching agent, at least partially the second part (S2) of the substrate (1) extending in the extension of the ablations (Al) obtained at the end of step c), so as to weaken said at least one photovoltaic sub-cell (Cl) delimited at the end of step c), and so as to retain for the or each photovoltaic sub-cell (Cl) at least one pair (PI, P2) of adjacent metal pads comprising a metal pad of the first set (PI) and a metal pad of the second set (P2); the etching agent being chosen so as to allow selective etching of the silicon with respect to the dielectric layer (4); e) separating said at least one photovoltaic sub-cell (Cl) weakened at the end of step d).

2. Method of manufacturing a photovoltaic sub-cell (Cl), including the steps: a) use a photovoltaic cell (CO) comprising: - a substrate (1), based on crystalline silicon, having first and second opposite surfaces (10, 11), the first surface (10) being intended to be exposed to solar radiation; - a stack (2) of active layers, formed on the first surface (10) of the substrate (1); - an electron collection zone (30) and a hole collection zone (31), formed on the second surface (11) of the substrate (1); - first and second metal pads (PI, P2), respectively in contact with the electron collection zone (30) and with the hole collection zone (31); b) forming a dielectric layer (4) extending over the first and second metal pads (PI, P2); c) applying laser radiation (L) to the photovoltaic cell (C0) obtained at the end of step b) so as to: - locally obtain ablations (Al) of a first part (SI) of the substrate (1); - draw an outline delimiting a photovoltaic sub-cell (Cl); - retain a second part (S2) of the substrate (1), extending in the extension of the ablations (Al), and adapted to retain mechanical strength of the photovoltaic sub-cell (Cl) delimited by the traced outline; d) chemically etching, with an etching agent, at least partially the second part (S2) of the substrate (1) extending in the extension of the ablations (Al) obtained at the end of step c), so as to weaken the photovoltaic sub-cell (Cl) delimited at the end of step c), and so as to preserve for the photovoltaic sub-cell (Cl) the first and second metal pads (PI, P2); the etching agent being chosen so as to allow selective etching of the silicon relative to the dielectric layer (4); e) separating the weakened photovoltaic sub-cell (Cl) at the end of step d).

3. Method according to claim 1, in which the laser radiation (L) is applied during step c) so as to locally obtain longitudinal ablations (Al) defining an axis (Z) passing between adjacent pairs (PI, P2) of metal pads, each pair (PI, P2) comprising a metal pad from the first set (PI) and a metal pad from the second set (P2).

4. Method according to claim 3, wherein the longitudinal ablations (Al) are longitudinal ablations (Al) of the dielectric layer (4) and of the first part (SI) of the substrate (1).

5. Method according to one of claims 1 to 4, in which: - step d) is carried out so that the second part (S2) of the substrate (1) is completely chemically etched; - step e) consists of a spontaneous separation of the photovoltaic sub-cell(s) (Cl) weakened at the end of step d).

6. Method according to one of claims 1 to 4, in which: - step d) is carried out so that the second part (S2) of the substrate (1) is partially chemically etched; - step e) is carried out by a separation technique chosen from thermal shock, mechanical stress, ultrasonic treatment.

7. Method according to one of claims 1 to 6, in which step d) consists of immersing the photovoltaic cell (CO) obtained at the end of step c) in an etching bath.

8. Method according to one of claims 1 to 7, in which: - the dielectric layer (4) formed during step b) is made of a silicon oxide; - step d) is carried out so that the etching agent is chosen from a potassium hydroxide KOH solution, a tetramethylammonium hydroxide TMAH solution, a sodium hydroxide NaOH solution.

9. Method according to one of claims 1 to 8, in which the laser radiation (L) is applied during step c) in a direction parallel to the normal to the first and second surfaces (10, 11) of the substrate (1).

10. Method according to one of claims 1 to 9, in which the laser radiation (L) applied during step c) is pulsed radiation having a fluence and a pulse duration adapted to obtain an ablation of the first part (SI) of the substrate (1).

11. Method according to one of claims 1 to 10, in which the photovoltaic sub-cell(s) (Cl) separated at the end of step e) have exposed lateral edges (BL); the method comprising a step f) consisting of passivating the exposed side edges (BL).

12. A method according to claim 11, wherein step f) comprises a step of forming an aluminum oxide (6) on the exposed side edges (BL), by atomic layer deposition.

13. Method according to one of claims 1 to 12, in which: - step b) comprises a step consisting of forming an additional dielectric layer (4') extending over the stack (2) of active layers; - the etching agent with which step d) is carried out is chosen so as to allow selective etching of the silicon with respect to the dielectric layer (4) and to the additional dielectric layer (4').

14. Method according to one of claims 1 to 13, in which the laser radiation (L) is applied during step c) so as to locally obtain longitudinal ablations (Al) of the stack (2) of active layers and of the first part (SI) of the substrate (1).

15. Method according to claim 14 in combination with claim 13, in which the laser radiation (L) is applied during step c) so as to locally obtain longitudinal ablations (Al) of the additional dielectric layer (4'), of the stack (2) of active layers, and of the first part (SI) of the substrate (1).

16. Method according to one of claims 1 to 15, wherein step a) is carried out so that: - the alternation (3) of electron and hole collection zones (30, 31) extends under the second surface (11) of the substrate (1) when claim 16 depends on claim 1; - the electron collection zone (30) and the hole collection zone (31) extend under the second surface (11) of the substrate (1) when claim 16 depends on claim 2; - the first and second sets (PI, P2) of metal pads are formed on the second surface (11) of the substrate (1) when claim 16 depends on claim 1; - the first and second metal pads (PI, P2) are formed on the second surface (11) of the substrate (1) when claim 16 depends on claim 2.

17. Method according to one of claims 1 to 15, in which step a) is carried out so that: - the second surface (11) of the substrate (1) is covered at least partially with a film (5) of tunnel oxide; - the alternation (3) of electron and hole collection zones (30, 31) extends over the tunnel oxide film (5) when claim 17 depends on claim 1; - the electron collection zone (30) and the hole collection zone (31) extend over the tunnel oxide film (5) when claim 17 depends on claim 2; - the first and second sets (PI, P2) of metal pads are formed respectively on the electron collection zones (30) and on the hole collection zones (31) when claim 17 depends on claim 1; - the first and second metal pads (PI, P2) are formed respectively on the electron collection zone (30) and on the hole collection zone (31) when claim 17 depends on claim 2.

18. Method according to one of claims 1 to 17, in which step d) is followed by partial etching of the dielectric layer (4), preferably using a hydrofluoric acid solution.

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