TW201725749A - Method for manufacturing a heterojunction for photovoltaic cell - Google Patents

Abstract

The invention relates to a method for manufacturing a heterojunction for photovoltaic cell, the heterojunction comprising a crystalline silicon substrate (1) and a doped hydrogenated amorphous silicon layer (2, 2'), the method comprising the following steps: - depositing a hydrogenated amorphous silicon layer on a crystalline silicon substrate so as to form a stack, the hydrogenated amorphous silicon layer having a thickness comprised between 5 and 30 nm, and preferably between 15 and 25 nm; - doping at least one part of the hydrogenated amorphous silicon layer by ion implantation, the ion implantation being carried out an energy less than 2000 V, and preferably comprised between 1000 and 1500 V, from a precursor gas comprising a dose of doping ions comprised between 10<SP>14</SP> and 10<SP>17</SP> cm<SP>-2</SP>, and preferably between 10<SP>15</SP> and 10<SP>16</SP> cm<SP>-2</SP>; - then annealing at a temperature comprised between 150 DEG C and 350 DEG C, and preferably between 200 and 300 DEG C, for a duration comprised between 5 minutes and 3 hours.

Description

Method for manufacturing a heterojunction for a photovoltaic cell

The field of the invention is a photovoltaic cell having a heterojunction junction and a method for fabricating such a photovoltaic cell. More precisely, the present invention relates to a method for making a heterojunction for a photovoltaic cell and a method for fabricating a photovoltaic cell comprising such a heterojunction.

Figure 1 is a schematic representation of a photovoltaic cell having a heterojunction of the prior art. During the fabrication of such a photovoltaic cell having a heterojunction, a hydrogenated amorphous germanium layer (i) a-Si-H is deposited on each surface of a germanium substrate (n) c-Si. Next, a (n) or (p) doped hydrogenated amorphous germanium layer "(n)a-Si-H is formed on the surface of each of the hydrogenated amorphous germanium layers (i) a-Si-H. Or "(p)a-Si-H". Then, a transparent conductive oxidation is deposited on each of the (n) or (p) doped hydrogenated amorphous germanium layers "(n)a-Si-H" or "(p)a-Si-H" Layer TCO. Finally, a metal contact MC is formed on each of the transparent conductive oxide layers TCO.

In a method of the prior art, (n) or (p) doping is formed during a step of introducing a doping gas into a plasma enhanced chemical vapor deposition (PECVD) doping the hydrogenated amorphous germanium layer. Hydrogenated amorphous ruthenium layer. When it is desired to obtain an (n)-doped hydrogenated amorphous germanium layer, the introduced dopant gas The system is based on phosphorus like phosphine. When it is desired to obtain a (p) doped hydrogenated amorphous germanium layer, the introduced dopant gas system is based on boron like diborane.

However, these methods are not capable of doping certain portions of each hydrogenated amorphous germanium layer in a selective and targeted manner. In fact, the doping of a doping gas introduced during the PECVD deposition step can only dope all of the hydrogenated amorphous germanium layer and the selected portion of the layer that cannot be doped.

Other methods, such as the prior art of document US 2012/0279562, teach the doping of the hydrogenated amorphous germanium layer by ion implantation. However, the photovoltaic solar cells thus produced have degraded performance. In fact, as document Defresne, A.; Plantevin, O.; Sobkowicz, I.; Bourcois, J. & i Cabarrocas, PR, "Interface defects in a-Si: H/c-Si heterojunction solar cells", Nuclear Instruments And Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015, implanting atoms into a thin amorphous germanium layer greatly damages the junction between the amorphous germanium layer and the germanium germanium substrate. The solar cell thus obtained thus has a lower open circuit voltage and a lower output.

The present invention is directed to overcoming the disadvantages of the prior art by proposing a method in which a portion of a hydrogenated amorphous germanium layer on a layer of germanium can be doped selectively and in a targeted manner, while at the same time obtaining suitable A heterojunction of the characteristics of the use of solar cells.

In order to do so, the first aspect of the invention relates to a method for producing a heterojunction for a photovoltaic cell, the method comprising the steps of: - depositing a hydrogenated amorphous germanium layer on a germanium substrate to form a stack, the hydrogenated amorphous germanium layer having a thickness between 5 and 30 nm and preferably between 15 and 25 nm; - doping at least a portion of the hydrogenated amorphous germanium layer by ion implantation from a precursor gas, the ion implant system Performing at an energy of less than 2000 V and preferably between 1000 and 1500 V, the precursor gas comprising a dose of doping ions between 10 ¹⁴ and 10 ¹⁷ cm ^-2 and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 ; Annealing is carried out at a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C for a duration of 5 minutes to 3 hours.

In this document, the term "heterogeneous junction for photovoltaic cells" means a heterojunction junction, that is, a stack of amorphous germanium layers on a germanium layer, regardless of the blend of these layers. miscellaneous.

The method according to the invention is particularly advantageous in that it can be doped with ion implantation using ion implantation without damaging the junction between the hydrogenated amorphous germanium layer and the germanium layer. In order to do so, the thickness of the hydrogenated amorphous germanium layer is selected such that the layer: - is thick enough to limit the amount of dopant ions that penetrate the junction during ion implantation, - but thin enough to be used In solar cells.

Ion implantation at low temperatures limits the damage to the joint. Despite all this, the junction is partially damaged after the ion implantation step of the dopant atoms, so that the passivation of the hydrogenated amorphous layer is also impaired. Annealing the stack for 5 minutes to 3 hours at a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C The duration of time can be restored without damaging the conductivity of the hydrogenated amorphous germanium layer. The method thus provides a heterojunction that can be used in a photovoltaic cell because the thickness of the hydrogenated amorphous germanium layer, its open circuit voltage, and its conductivity are suitable for such use. Furthermore, by performing the doping by ion implantation, the region of the hydrogenated amorphous germanium layer that is desired to be doped can be selected. Moreover, the method has the advantage of low cost.

The method according to the first aspect of the invention may also have one or more of the features obtained hereinafter individually or in accordance with any of its possible combinations of techniques.

Advantageously, the step of doping by ion implantation comprises the following sub-steps: - converting the precursor gas into a plasma; - immersing the stack in the plasma; - applying a potential to the stack for ion implantation Into the stack.

Therefore, preferably, by immersing the stack in the plasma formed by the precursor gas, a step of doping with ion implantation is performed, which can plant the substance formed during the generation of the plasma. In. In fact, unlike standard ion implantation methods, in which a plasma is generated in a closed enclosure, and then the species to be implanted is selected and transferred to a reaction chamber containing the substrate, according to the method of this embodiment. Plasma is generated directly in the reaction chamber containing the layer to be implanted, which allows all species formed during the generation of the plasma to be implanted without selection. Thus, chemical species larger than conventional techniques are implanted in particular such that they do not penetrate deep through the hydrogenated amorphous layer and less damage to the junction between the hydrogenated amorphous layer and the wafer substrate. In addition, plants containing hydrogen can also be planted. In, this increases the open circuit voltage of the stack. In order to do so, the ion implantation can be carried out by a PIII (plasma immersion ion implantation) method or by a PLAD (plasma doping) method. Finally, the method has the advantage of being faster than standard methods of ion implantation and is therefore more suitable for industrial manufacturing of batteries.

Advantageously, the annealing treatment step is carried out under ambient atmosphere, which may not impose any restrictions on the annealing environment.

According to an embodiment, the precursor gas comprises B ₂ H ₆ . A p-doped hydrogenated amorphous germanium layer can be obtained by driving the gas.

When the precursor gas comprises B ₂ H ₆ , the duration of the annealing treatment is preferably from 30 minutes to 1.5 hours, which is the most effective between the open circuit of the p-doped hydrogenated amorphous germanium layer and its conductivity. Good compromise.

According to another embodiment, the precursor gas comprises PH _3, this can be obtained a hydrogenated n-doped amorphous silicon layer.

When the precursor gas comprises PH ₃ , the duration of the annealing treatment is preferably between 15 minutes and 30 minutes, which can achieve the best compromise between the open circuit of the n-doped hydrogenated amorphous germanium layer and its conductivity. .

A second aspect of the invention relates to a method for fabricating a photovoltaic cell having a heterojunction, the method for fabricating a photovoltaic cell comprising generating a heterojunction by a fabrication method in accordance with the first aspect of the invention Steps to face.

According to various embodiments, a heterojunction of the photovoltaic cell comprising a p-doped layer and a heterojunction of the photovoltaic cell comprising an n-doped layer may be produced in accordance with one of the methods of the present invention; or One of the two heterojunctions can be produced in a method in accordance with the invention.

The method for fabricating a photovoltaic cell preferably comprises the steps of: - (a) depositing a first hydrogenated amorphous germanium layer on a first surface of a crystalline germanium substrate, the first hydrogenated amorphous germanium layer having between 5 and 30 nm Preferably, the thickness is between 15 and 25 nm; - (b) doping at least a portion of the first hydrogenated amorphous germanium layer by ion implantation from the first precursor gas, the ion implant system being less than 2000V and preferably 1000 Performing at an energy between 1500V, the first precursor gas comprises a dose of doping ions between 10 ¹⁴ and 10 ¹⁷ cm ^-2 and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 , and the first precursor gas comprises B ₂ H ₆ ;- (a') depositing a second hydrogenated amorphous germanium layer on the second surface of the germanium substrate, the second hydrogenated amorphous germanium layer having a distance between 5 and 30 nm and preferably between 15 and 25 nm a thickness; - (b') doping at least a portion of the second hydrogenated amorphous germanium layer by ion implantation from a second precursor gas, the ion implant being at an energy of less than 2000V and preferably between 1000 and 1500V embodiment, the second precursor gas comprises and preferably ¹⁰¹⁵ to 10 ¹⁶ cm ^-2 dose of dopant ions between between ¹⁰¹⁴ to 10 ¹⁷ cm ^-2, and the second precursor gas Includes PH _3; - (c ') at between 150 deg.] C to 350 deg.] C and preferably a temperature of between 300 to 200 ℃ annealing deg.] C for 5 minutes to 3 hours duration of time.

According to an embodiment, the manufacturing method may further comprise an annealing step (c) between steps (b) and (a'). During this annealing step, The heterojunction is preferably annealed at a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C for a duration of 5 minutes to 3 hours.

In fact, the manufacturing method includes at least one annealing step, but it may also include two annealing steps thereof. More precisely, according to different embodiments: - The method may comprise a single annealing step, which is carried out once the doping steps of the first and second hydrogenated amorphous germanium layers have been carried out. In this case, the two hydrogenated amorphous germanium layers are simultaneously annealed. This embodiment may reduce the cost of the method for fabricating a photovoltaic cell; or - the method may include two annealing steps: after the step of doping the first hydrogenated amorphous germanium layer, performing a first annealing step, and After the step of doping the second hydrogenated amorphous germanium layer, a second annealing step is performed. This embodiment provides a higher performance photovoltaic cell. In fact, the annealing step is particularly suitable for the doping just performed, which gives better results. In fact, when performing two annealing steps, the first annealing step preferably lasts from 30 minutes to 1.5 hours; and the second annealing step preferably lasts between 15 minutes and 30 minutes.

Furthermore, according to various embodiments, the step of doping with the first precursor gas comprising B ₂ H _{6 may} be carried out before the step (b′) of doping with the second precursor gas comprising PH ₃ (b) And, conversely, the step (b') of doping with a second precursor gas comprising PH _{3 may} be carried out prior to step (b) of doping with a first precursor gas comprising B ₂ H ₆ .

Preferably, the generation of a layer requiring the highest annealing temperature is performed first. In this way, the lower annealing temperature of the other layer only slightly modifies the characteristics of the previously produced layer.

Advantageously, the method for fabricating a photovoltaic cell further comprises the steps of: - depositing a transparent conductive oxide layer on each doped hydrogenated amorphous germanium layer; - forming at least one metal contact on each transparent conductive oxide The steps on the layer.

Preferably, these steps are carried out prior to the (equal) annealing step. This avoids surface oxidation of the hydrogenated amorphous germanium during the (equal) annealing.

1‧‧‧ wafer substrate

2‧‧‧ Hydrogenated amorphous layer

2'‧‧‧ Hydrogenated amorphous layer

4‧‧‧Precursor gas

5‧‧‧Stacking

6‧‧‧ Hydrogenated amorphous layer

7‧‧‧ first surface

8‧‧‧ second surface

9‧‧‧Stacking

10‧‧‧Transparent conductive oxide layer

11‧‧‧Metal contacts

Other features and advantages of the present invention will become apparent from the following detailed description of the appended claims. FIG. 1 FIG. 1 is a schematic diagram of a photovoltaic cell having a heterojunction in one of the prior art; Figure 2c shows a step of a method for fabricating a heterojunction comprising a p-doped layer in accordance with an embodiment of the present invention; and Figure 3 is a method similar to the method of Figures 2a through 2c. Schematic diagram of the obtained heterojunction; Figures 4a to 4c show the steps of a method for fabricating a heterojunction comprising an n-doped layer in accordance with an embodiment of the present invention; A schematic diagram of a heterojunction obtained by a method similar to the method of Figures 4a to 4c; Figures 6a through 6f show the steps of a method for fabricating a solar cell having a heterojunction in accordance with a method of practicing the invention.

Manufacture of heterojunction including p-doped hydrogenated amorphous germanium layer

A method for fabricating a heterojunction comprising a p-doped hydrogenated amorphous germanium layer in accordance with an embodiment of the present invention will now be described with reference to Figures 2a through 2c.

Referring to Figure 2a, the method includes a first step 101 of depositing a hydrogenated amorphous germanium layer 2 on a germanium substrate 1. In this embodiment, the wafer substrate is deoxygenated just prior to depositing the amorphous germanium. Deoxidation allows the amorphous germanium to have good direct contact with the germanium and thus its passivation characteristics.

In this embodiment, the hydrogenated amorphous germanium layer 2 is an essentially hydrogenated amorphous germanium layer, that is, undoped. In another option, the hydrogenated amorphous germanium layer 2 may have been partially doped in accordance with another embodiment of the present invention. On the other hand, in this case, the doping may have the same type as implanted ions. In the opposite case, the required dose for implanting ions will be different. The hydrogenated amorphous germanium layer 2 has a thickness of between 5 and 30 nm and preferably between 15 and 25 nm. At the end of step 101, a stack 5 is obtained comprising: - a germanium substrate 1; - a hydrogenated amorphous germanium layer 2 deposited on the substrate.

Referring to Figure 2b, the method then includes the step of doping the hydrogenated amorphous germanium layer to produce a hydrogenated amorphous germanium layer having a p-doped surface. In order to do so, the doping of the hydrogenated amorphous germanium layer 2 is carried out by a precursor gas by means of an ion cloth value. The precursor gas 4 may be, for example, B ₂ H ₆ . The precursor gas comprises a dose of doping ions between 10 ¹⁵ and 10 ¹⁶ cm ^-2 and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 .

The precursor gas is converted to a plasma. Preferably, the ion implantation is carried out by immersing the layer to be implanted in the formed plasma. To do so, preferably, the plasma is formed in a reaction chamber containing the stack 5. To do so, a plasma immersion ion implantation technique or a plasma doping technique can be used.

Then, a negative potential is applied to the hydrogenated amorphous germanium layer 2 to effect implantation so that the chemical species of the plasma pass through the surface of the hydrogenated amorphous germanium layer 2. The ion implantation is carried out at an energy of less than 2000 V and preferably between 1000 and 1500 V.

Referring to Figure 2c, the method then includes an annealing step 103 during which the stack is heated to a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C, preferably between 30 minutes and 1.5 hours. The duration of time is such that the passivation of the p-doped hydrogenated amorphous germanium layer is restored while maintaining good electrical conductivity of the layer.

This method provides a heterojunction that can be used to produce a photovoltaic cell with a heterojunction, since the resulting heterojunction has the following characteristics: - The hydrogenated amorphous germanium layer has a thickness suitable for photovoltaic cells because It is between 5 and 30 nm; the heterojunction mask has a sufficient passivation level for a photovoltaic cell with a heterojunction because it has an open circuit voltage iV _OC greater than 700 mV; - the hydrogenated amorphous The tantalum layer has sufficient conductivity for the photovoltaic cell because it has a conductivity greater than 10 ^-4 Ω ^-1 cm ^-1 .

Experimental results:

Figure 3 shows a substrate obtained by a method similar to that described in Figures 2a to 2c.

This method is carried out in the special case of grinding the 280 μm of the wafer substrate 1 into a low surface roughness. It has a low surface roughness and can have better passivation. In this case, this roughness is also not affected by surface texturing before the battery is produced.

A first hydrogenated amorphous germanium layer 2 is deposited on the first surface 7 of the wafer substrate 1. The first hydrogenated amorphous germanium layer 2 has a thickness of 25 nm. A second hydrogenated amorphous germanium layer 6 is deposited on the second surface of the germanium substrate. The second hydrogenated amorphous germanium layer 6 has a thickness of 25 nm.

Boron is implanted into the first hydrogenated amorphous germanium layer 2 from a precursor gas at 1500 V by plasma immersion ion implantation. The precursor gas system comprises a dose of B ₂ H ₆ equal to a dopant ion of 5 × 10 ¹⁵ cm ^-2 .

The second hydrogenated amorphous germanium layer 6 is undoped.

Then, a stack 9 is obtained comprising: - a first p-doped hydrogenated amorphous germanium layer 2; - a germanium substrate 1; - a second undoped hydrogenated amorphous germanium layer 6.

At the end of the doping step: - the p-doped hydrogenated amorphous germanium layer 2 has a conductivity of 10 ^-8 Ω ^-1 cm ^-1 ; - the stack 9 has an open circuit voltage iV _OC equal to 560 mV.

After the doping step, the stack 9 was annealed at 300 ° C for 1.5 hours.

At the end of the annealing step: - the p-doped hydrogenated amorphous germanium layer 2 has a conductivity of 10 ^-5 Ω ^-1 cm ^-1 ; - the stack 9 has an open circuit voltage iV _OC equal to 705 mV.

The method thus actually provides a heterojunction having properties suitable for photovoltaic cells.

Manufacture of heterojunction comprising n-doped hydrogenated amorphous germanium layer

A method for fabricating a heterojunction comprising an n-doped hydrogenated amorphous germanium layer in accordance with an embodiment of the present invention will now be described with reference to Figures 4a through 4c.

Referring to Fig. 4a, the method includes a first step 101' of depositing a hydrogenated amorphous germanium layer 2' on a germanium substrate 1. In this embodiment, the wafer substrate is deoxygenated prior to depositing the hydrogenated amorphous germanium.

In this embodiment, the hydrogenated amorphous germanium layer 2' is an essentially hydrogenated amorphous germanium layer, i.e., undoped. The hydrogenated amorphous germanium layer 2 has a thickness of between 5 and 30 nm and preferably between 15 and 25 nm. At the end of step 101', a stack 5 is obtained comprising: - a germanium substrate 1; - a hydrogenated amorphous germanium layer 2' deposited on the substrate.

Referring to Figure 4b, the method then includes the step of implanting the hydrogenated amorphous germanium layer to produce a hydrogenated amorphous germanium layer having an n-doped surface. In order to do this, the doping of the hydrogenated amorphous germanium layer 2' is carried out by a precursor gas by means of an ion cloth value. The precursor gas lines 4 PH _3. The precursor gas comprises a dose of doping ions between 10 ¹⁵ and 10 ¹⁶ cm ^-2 and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 .

The precursor gas is converted to a plasma. The stack 5 is immersed in this plasma. To do so, preferably, the plasma is formed in a reaction chamber containing the stack 5. Then, a negative potential is applied to the stack to effect implantation so that dopant ions of the plasma penetrate into the hydrogenated amorphous germanium layer 2'. The ion implantation is carried out at an energy of less than 2000 V and preferably between 1000 and 1500 V.

Referring to Figure 4c, the method then includes an annealing step 103' during which the stack is heated to a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C for preferably 15 minutes. The duration of 30 minutes is required to restore passivation of the n-doped hydrogenated amorphous germanium layer while maintaining good electrical conductivity of the layer.

This method provides a heterojunction that can be used in the production of a photovoltaic cell having a heterojunction, since the resulting heterojunction has the following characteristics: - The hydrogenated amorphous germanium layer has a thickness suitable for photovoltaic cells Because it is between 5 and 30 nm; - the heterojunction mask has a sufficient passivation level for a photovoltaic cell with a heterojunction because it has an open circuit voltage iV _OC greater than 700 mV; - the hydrogenation The amorphous germanium layer has sufficient conductivity for photovoltaic cells because it has a conductivity greater than 10 ^-4 Ω ^-1 cm ^-1 .

Experimental results:

Figure 5 shows a substrate obtained by a method similar to that described in Figures 4a to 4c.

This method is carried out in the special case of grinding the 280 μm of the wafer substrate 1 into a low surface roughness.

A first hydrogenated amorphous germanium layer 2' is deposited on the first surface 7 of the wafer substrate 1. The first hydrogenated amorphous germanium layer 2' has a thickness of 25 nm. A second hydrogenated amorphous germanium layer 6 is deposited on the second surface of the wafer substrate 8. The second hydrogenated amorphous germanium layer 2 has a thickness of 25 nm.

Boron is implanted into the first hydrogenated amorphous germanium layer 2' from a precursor gas at 1500 V by plasma immersion ion implantation. The precursor gas system comprises a pH _{3 of} a dose equal to 10 ¹⁶ cm ^-2 of dopant ions.

The second hydrogenated amorphous germanium layer 6 is undoped.

Then, a stack 9 is obtained which comprises: - a first n-doped hydrogenated amorphous germanium layer 2'; - a germanium substrate 1; - a second undoped hydrogenated amorphous germanium layer 6.

At the end of the doping step: - the n-doped hydrogenated amorphous germanium layer 2' has a conductivity of 2 x 10 ^-4 Ω ^-1 cm ^-1 ; - the stack 9 has an open circuit voltage iV _OC equal to 570 mV.

After the doping step, the stack 9 was annealed at 250 ° C for 30 minutes.

At the end of the annealing step: - the n-doped hydrogenated amorphous germanium layer "doped a-Si-H"2' has a conductivity of 4 x 10 ^-4 Ω ^-1 cm ^-1 ; - the stack 9 has Equal to the open circuit voltage iV _{OC of} 700mV.

The method thus actually provides a heterojunction having properties suitable for photovoltaic cells.

Method for manufacturing photovoltaic cells

A method for fabricating a photovoltaic cell will now be described with reference to Figures 6a through 6b.

The photovoltaic cell is produced starting from a wafer substrate 1.

The method includes a first step 201 of producing a p-doped hydrogenated amorphous germanium layer 2 on the first surface 7 of the substrate 1. This p-doped hydrogenated amorphous germanium layer is produced by the method described in Figures 2a to 2c.

The method then includes the step 202 of producing an n-doped hydrogenated amorphous germanium layer 2' on the second surface 8 of the substrate 1. This n-doped hydrogenated amorphous germanium layer 2' is produced by the method described in Figures 4a to 4c.

Then, the stack shown in Fig. 6d is obtained. The stack comprises: - a first hydrogenated amorphous germanium layer 2 having at least one p-doped portion; - a germanium substrate 1; - a second hydrogenated amorphous germanium layer 2' having at least one n-doped portion.

The method then includes the step 203 of depositing a transparent conductive oxide layer (TCO) on each of the doped hydrogenated amorphous germanium layers 2, 2'.

The method then includes the step 204 of creating a metal contact 11 on each of the transparent conductive oxide layers (TCO).

Of course, the invention is not limited to the embodiments described with reference to the drawings, and various modifications may be devised without departing from the scope of the invention. Therefore, the n-doping can be produced before the p-doped hydrogenated amorphous germanium layer A hetero-hydrogenated amorphous layer. Furthermore, instead of performing two annealing steps during the method of fabricating a photovoltaic cell, a single annealing step can be performed only after the second doping step.

Finally, the invention can also be applied to the manufacture of hybrid tandem photovoltaic cells incorporating a germanium-based heterojunction and a perovskite based battery.

1‧‧‧ wafer substrate

2'‧‧‧ Hydrogenated amorphous layer

4‧‧‧Precursor gas

Claims (11)

A method for manufacturing a heterojunction for a photovoltaic cell, the method comprising the steps of: - (101, 101') depositing a hydrogenated amorphous germanium layer (2, 2') on a germanium substrate to form a stack The hydrogenated amorphous germanium layer (2, 2') has a thickness between 5 and 30 nm and preferably between 15 and 25 nm; - (102, 102') is doped with a hydrogenated amorphous germanium by ion implantation from a precursor gas At least a portion of the layer (2, 2'), the ion implant is carried out at an energy of less than 2000 V and preferably between 1000 and 1500 V, the precursor gas comprising between 10 ¹⁴ and 10 ¹⁷ cm ^-2 and preferably 10 ¹⁵ a dose of doping ions to 10 ¹⁶ cm ^-2 ; - (103, 103'), then annealing at a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C for 5 minutes to 3 hours Duration of time. The method of claim 1, wherein the doping step (102, 102') by ion implantation comprises the following sub-steps: - converting the precursor gas into a plasma; - immersing the stack (5) in the plasma Medium; - Apply a potential to the stack to implant ions into the stack. The method of claim 1 or 2, wherein the annealing step is performed under ambient air. The method of any one of claims 1 to 3, wherein the precursor gas comprises B ₂ H ₆ . The method of any one of claims 1 to 4, wherein the duration of the annealing is between 30 minutes and 1.5 hours. The method of any one of claims 1 to 3, wherein the precursor gas comprises PH ₃ . The method of any one of claims 1 to 6, wherein the duration of the annealing is between 15 and 30 minutes A method for producing a photovoltaic cell having a heterojunction, the method for producing a photovoltaic cell comprising the step of producing a heterojunction by the manufacturing method according to any one of claims 1 to 7. The method for manufacturing a photovoltaic cell according to any one of claims 1 to 8, the method comprising the steps of: - (a) depositing a first hydrogenated amorphous germanium layer (2) on a germanium substrate (1) On the first surface (7), the first hydrogenated amorphous germanium layer (2) has a thickness between 5 and 30 nm and preferably between 15 and 25 nm; - (b) is doped by the first precursor gas by ion implantation At least a portion of the first hydrogenated amorphous germanium layer (2), the ion implant system is carried out at an energy of less than 2000 V and preferably between 1000 and 1500 V, the first precursor gas comprising 10 ¹⁴ to 10 ¹⁷ cm ^-2 And preferably a dose of doping ions between 10 ¹⁵ and 10 ¹⁶ cm ^-2 , and the first precursor gas comprises B ₂ H ₆ ; - (a') depositing a second hydrogenated amorphous germanium layer (2') On the second surface (8) of the wafer substrate (1), the second hydrogenated amorphous germanium layer (2') has a thickness between 5 and 30 nm and preferably between 15 and 25 nm; - (b') Doping at least a portion of the second hydrogenated amorphous germanium layer (2') from the second precursor gas by ion implantation, the ion implant system being carried out at an energy of less than 2000 V and preferably between 1000 and 1500 V, the first The second precursor gas contains 10 ¹⁴ to 10 ¹⁷ cm ^-2 and is relatively a dose of doping ions between 10 ¹⁵ and 10 ¹⁶ cm ^-2 , and the second precursor gas comprises PH ₃ ; - (c') at a temperature between 150 ° C and 350 ° C and preferably between 200 ° C and 300 ° C The annealing treatment is carried out for a duration of 5 minutes to 3 hours. The method of any one of clauses 1 to 9, further comprising an annealing step (c) between steps (b) and (a'). The method of any one of claims 8 to 10, further comprising the step of: - (203) depositing a transparent conductive oxide layer (10) on each doped hydrogenated amorphous germanium layer (2, 2') Step; - (204) forming at least one metal contact (11) on each of the transparent conductive oxide layers (10).