WO2017064383A1

WO2017064383A1 - Method for producing a heterojunction for a photovoltaic cell

Info

Publication number: WO2017064383A1
Application number: PCT/FR2016/052471
Authority: WO
Inventors: Tristan CARRERE; Maria-Delfina MUNOZ
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2015-10-16
Filing date: 2016-09-29
Publication date: 2017-04-20
Also published as: FR3042646A1; TW201725749A; FR3042646B1; EP3363053A1

Abstract

The invention concerns a method for producing a heterojunction for a photovoltaic cell, the heterojunction comprising a substrate (1) made from crystalline silicon and a layer (2, 2') made from doped hydrogenated amorphous silicon, the method comprising the following steps: - depositing a layer of hydrogenated amorphous silicon on a crystalline silicon substrate in such a way as to form a stack, the layer of hydrogenated amorphous silicon having a thickness of between 5 and 30 nm, and preferably of between 15 and 25 nm; - doping at least a part of the layer of hydrogenated amorphous silicon by ion implantation, the ion implantation being carried out at an energy of less than 2000 V, and preferably of between 1000 and 1500 V, from a precursor gas comprising a dose of dopant ions of between 10¹⁴ and 10¹⁷ cm^-2", and preferably of between 10¹⁵ and 10¹⁶ cm^-2; - followed by annealing at a temperature of between 150 °C and 350 °C, and preferably of between 200 and 300 °C, for a period of between 5 minutes and 3 hours.

Description

PROCESS FOR PRODUCING A HETEROJONTION FOR CELL

PHOTOVOLTAIC

TECHNICAL AREA

The field of the invention is that of silicon heterojunction photovoltaic cells and methods of manufacturing such photovoltaic cells. More specifically, the invention relates to a method of manufacturing a heterojunction for a photovoltaic cell and a method of manufacturing a photovoltaic cell comprising such a heterojunction.

STATE OF THE PRIOR ART

FIG. 1 schematically represents a photovoltaic cell with heterojunction of the prior art. During the manufacture of such a heterojunction photovoltaic cell, a hydrogenated amorphous silicon layer (i) a-Si-H is deposited on each of the faces of a crystalline silicon substrate (n) c-Si. A doped hydrogenated (n) or (p) "(n) a Si-H" or "(p) a Si-H" amorphous silicon layer is then formed on the surface of each of the hydrogenated amorphous silicon layers (i). a-Si-H. A layer of conductive transparent oxide TCO is then deposited on each of the doped hydrogenated amorphous silicon (n) or (p) "(n) a Si-H" or "(p) a Si-H" layers. Finally, metal contacts MC are formed on each of the conductive transparent oxide TCO layers.

In the processes of the prior art, the doped (n) or (p) hydrogenated amorphous silicon layers are formed during a plasma-assisted chemical vapor deposition (PECVD) step in which a doping gas is introduced to boost the layers of hydrogenated amorphous silicon. When it is desired to obtain a layer of doped hydrogenated amorphous silicon (n), the doping gas introduced is based on phosphorus such as phosphine. When it is desired to obtain a layer of doped hydrogenated amorphous silicon (p), the doping gas introduced is based on boron, such as diborane.

However, these methods do not allow selective and targeted doping of certain parts of each hydrogenated amorphous silicon layer. Indeed, the doping by introduction of a doping gas during the deposition step by PECVD only serves to dope all of the hydrogenated amorphous silicon layer and not selected portions of this layer. Other methods of the prior art, such as that of US2012 / 0279562, propose to perform the doping of the hydrogenated amorphous silicon layer by ion implantation. However, the photovoltaic solar cell thus produced has degraded performance. Indeed, as explained in the document Defresne, A .; Plantevin, O .; Sobkowicz, I .; Bourçois, 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, the fact implanting atoms in a thin amorphous silicon layer, strongly degrades the interface between the amorphous silicon layer and the crystalline silicon substrate. The solar cell thus obtained then has a lower open circuit voltage, as well as lower yields.

SUMMARY OF THE INVENTION

The aim of the invention is to overcome the drawbacks of the state of the art by proposing a method which makes it possible to selectively and specifically target certain parts of a hydrogenated amorphous silicon layer on a crystalline silicon layer, while allowing the obtaining a heterojunction which has properties compatible with use in a solar cell.

To do this, a first aspect of the invention relates to a method for manufacturing a heterojunction for a photovoltaic cell, 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 of between 5 and 30 nm, and preferably between 15 and 25 nm;

doping at least a portion of the hydrogenated amorphous silicon layer by ion implantation, the ion implantation being carried out at an energy of less than 2000 V, and preferably between 1000 and 1500 V, from a precursor gas comprising a dose of doping ions of between 10 ¹⁴ and ¹⁷ cm ^-2 , and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 ;

- Annealing at a temperature between 150 ° C and 350 ° C, and preferably between 200 and 300 ° C for a period of between 5 minutes and 3 hours.

In this document, the term "silicon heterojunction for photovoltaic cells" designates a silicon heterojunction, namely a stack comprising an amorphous silicon layer on a crystalline silicon layer, whatever the doping of these layers.

The method according to the invention is particularly advantageous because it makes it possible to use ion implantation to dope the hydrogenated amorphous silicon layer without degrading the interface between the hydrogenated amorphous silicon layer and the crystalline silicon layer. To do this, the thickness of the hydrogenated amorphous silicon layer is chosen so that this layer is:

- thick enough to limit the amount of doping ions that penetrate to the interface during ion implantation,

- but thin enough to be used in a solar cell.

Achieving ion implantation at low energy limits the degradation of the interface. Despite everything, after the step of ion implantation of the doping atoms, the interface is partially degraded so that the passivation of the hydrogenated amorphous silicon layer is also degraded. The fact of annealing the stack at a temperature of between 150 ° C. and 350 ° C., and preferably between 200 and 300 ° C., for a time of between 5 minutes and 3 hours, makes it possible to recover the passivation without degrading the conductivity. of the hydrogenated amorphous silicon layer. The method thus makes it possible to obtain a heterojunction that can be used in a photovoltaic cell since the thickness of the hydrogenated amorphous silicon layer, its open circuit voltage and its conductivity are compatible with such use. In addition, the fact of performing doping by ion implantation allows to choose the zones of the hydrogenated amorphous silicon layer that is to be doped. The method also has the advantage of being inexpensive.

The method according to the first aspect of the invention may also have one or more of the following features taken individually or in any technically possible combination. Advantageously, the doping step by ion implantation comprises the following sub-steps:

- transformation of the precursor gas into plasma;

immersion of the stack in the plasma;

- Application of a potential to the stack so as to implant ions in the stack.

Thus, the doping step by ion implantation is preferably carried out by immersing the stack in the plasma formed from the precursor gas, which allows to implant all the species formed during the creation of the plasma. Indeed, unlike standard ion implantation methods, in which the plasma is generated in a chamber, then a species to be implanted is selected and sent to the chamber containing the substrate, the method according to this embodiment proposes to generate the Plasma directly into the chamber that contains the layer to be implanted, which allows to implant all the species formed during the generation of the plasma without selection. Thus, in particular, larger chemical species are implanted than in the prior art, so that they penetrate less deeply through the hydrogenated amorphous silicon layer and less degrade the interface between the hydrogenated amorphous silicon layer and the silicon substrate. lens. In addition, it also makes it possible to implant species containing hydrogen, which makes it possible to increase the open circuit voltage of the stack. To do this, the ion implantation can be carried out by a plasma immersion ion implantation method (also known as "plasma immersion ion implantation") or by a plasma doping method (also known as plasma doping PLAD). . Finally, this process has the advantage of being faster than the standard ion implantation process and therefore better suited to the industrial manufacture of cells.

Advantageously, the annealing step is carried out under ambient atmosphere, which makes it possible to have no constraint on the annealing atmosphere.

According to one embodiment, the precursor gas comprises B ₂ H ₆ . This precursor gas makes it possible to obtain a p-doped hydrogenated amorphous silicon layer. When the precursor gas comprises B ₂ H _6, the annealing time is preferably between 30 minutes and 1 h 30, which makes it possible to obtain the best compromise between the open circuit voltage of the p-hydrogenated amorphous silicon layer. and its conductivity.

According to another embodiment, the precursor gas comprises PH ₃ , which makes it possible to obtain a n-doped hydrogenated amorphous silicon layer.

When the precursor gas comprises PH ₃ , the annealing time is preferably between 15 and 30 minutes, which makes it possible to obtain the best compromise between the open circuit voltage of the n-doped hydrogenated amorphous silicon layer and its conductivity. .

A second aspect of the invention relates to a method of manufacturing a cell heterojunction photovoltaic system, the method of manufacturing the photovoltaic cell comprising a step of producing a heterojunction by a manufacturing method according to the first aspect of the invention. According to different embodiments:

the heterojunction of the photovoltaic cell comprising a p-doped layer and the heterojunction comprising the photovoltaic cell comprising an n-doped layer can be both carried out with a method according to the invention; or

- Only one of these two heterojunctions can be achieved with a method according to the invention.

The method of manufacturing the photovoltaic cell preferably comprises the following steps:

(a) depositing a first hydrogenated amorphous silicon layer on a first face of a crystalline silicon substrate, the first hydrogenated amorphous silicon layer having a thickness of between 5 and 30 nm, and preferably between 15 and 25 μm; nm;

(b) doping at least a portion of the first hydrogenated amorphous silicon layer by ion implantation, the ion implantation being carried out at an energy of less than 2000 V, and preferably between 1000 and 1500 V, from a first precursor gas having a doping ion dose of 10 ^{14 to} ¹⁷ cm ^-2 , and preferably 10 ^{15 to} 10 ¹⁶ cm ^-2 , the first precursor gas comprising B ₂ H ₆ ;

- (a ') depositing a second hydrogenated amorphous silicon layer on a second face of the crystalline silicon substrate, the second hydrogenated amorphous silicon layer having a thickness of between 5 and 30 nm, and preferably between 15 and 25 nm ;

- (b ') doping at least a portion of the second hydrogenated amorphous silicon layer by ion implantation, the ion implantation being performed at an energy of less than 2000 V, and preferably between 1000 and 1500 V, from a second precursor gas comprising a dose of doping ions of between 10 ¹⁴ and ¹⁷ cm ^-2 , and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 , the second precursor gas comprising PH ₃ .

- (c ') annealing at a temperature between 150 ° C and 350 ° C, and preferably between 200 and 300 ° C for a period of between 5 mhutes and 3 hours. According to one embodiment, the manufacturing method may further comprise a step (c) of annealing 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 and 300 ° C, for a period of time between 5 minutes and 3 hours.

Indeed, the manufacturing method comprises at least one annealing step, but it can also include two. More precisely, according to various embodiments:

the process may comprise a single annealing step, which takes place once the doping steps of the first and second hydrogenated amorphous silicon layers have been carried out. In this case, the two layers of hydrogenated amorphous silicon are annealed at the same time. This embodiment makes it possible to reduce the cost of the manufacturing process of the photovoltaic cell; or

the process may comprise two annealing steps: a first annealing step is then performed following the doping step of the first hydrogenated amorphous silicon layer, whereas a second annealing step is carried out following the step of annealing; doping of the second layer of hydrogenated amorphous silicon. This embodiment makes it possible to obtain a more efficient photovoltaic cell. Indeed, it is then possible to specifically adapt the annealing step to the doping that has just been performed, which makes it possible to obtain better results. Indeed, when two annealing steps are performed, the first annealing step preferably lasts between 30 minutes and 1 hour 30 minutes; while the second annealing step preferably lasts between 15 and 30 minutes.

Furthermore, according to various embodiments, the doping step (b) from a first precursor gas containing B ₂ H ₆ can be carried out before the doping step (b ') from a second a precursor gas containing PH ₃ , or conversely the doping step (b ') from a second precursor gas containing PH ₃ can be carried out before the doping step (b) from a first precursor gas containing B ₂ H _6. Preferably, the production of the layer requiring the highest annealing temperature is carried out first. In this way, the lower annealing temperature of the other layer will not change much the properties of the former.

Advantageously, the method of manufacturing a photovoltaic cell further comprises the following steps:

a step of depositing a transparent conductive oxide layer on each layer doped hydrogenated amorphous silicon;

a step of forming at least one metal contact on each transparent conductive oxide layer. These steps are preferably performed before the annealing step (s). This makes it possible to avoid surface oxidation of the hydrogenated amorphous silicon during the annealing (s).

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will emerge on reading the detailed description which follows, with reference to the appended figures, which represent:

FIG. 1, a schematic representation of a heterojunction photovoltaic cell of the prior art;

FIGS. 2a to 2c, the steps of a process for manufacturing a heterojunction comprising a p-doped layer, according to one embodiment of the invention;

FIG. 3 is a schematic representation of a heterojunction obtained by a process similar to the method of FIGS. 2a to 2c;

FIGS. 4a to 4c, the steps of a process for manufacturing a heterojunction comprising an n-doped layer, according to one embodiment of the invention;

FIG. 5, a schematic representation of a heterojunction obtained by a process similar to the method of FIGS. 4a to 4c;

FIGS. 6a to 6f, the steps of a method for manufacturing a heterojunction solar cell according to a method of embodiment of the invention. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

Fabrication of a heterojunction comprising a p-doped hydrogenated amorphous silicon layer: A process for manufacturing a heterojunction comprising a p-doped hydrogenated amorphous silicon layer according to one embodiment of the invention will now be described with reference to FIGS. at 2c.

With reference to FIG. 2a, the method comprises a first step 101 for depositing a hydrogenated amorphous silicon layer 2 on a crystalline silicon substrate 1. In this embodiment, the crystalline silicon substrate is deoxidized just before the deposition of the amorphous silicon. Deoxidation allows the amorphous silicon to be in direct contact with the lens and thus to have its passivating properties.

In this embodiment, the hydrogenated amorphous silicon layer 2 is an intrinsic hydrogenated amorphous silicon layer, that is to say undoped. Alternatively, according to another embodiment of the invention, the hydrogenated amorphous silicon layer 2 could already be partially doped. On the other hand, in this case, the doping will be of the same type as the implanted ions. Otherwise, the implanted ion doses required would be different. The hydrogenated amorphous silicon 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 crystalline silicon substrate 1;

A layer of hydrogenated amorphous silicon deposited on the substrate.

With reference to FIG. 2b, the method then comprises a step 102 for doping the hydrogenated amorphous silicon layer so as to produce a hydrogenated amorphous silicon layer whose surface is p-doped. For this, the doping of the hydrogenated amorphous silicon layer 2 is carried out by ion implantation from a precursor gas. The precursor gas 4 may for example be B ₂ H ₆ . The precursor gas comprises a dopant ion dose of between 10 ¹⁵ and 10 ¹⁶ cm ^"2, and preferably between 10 ¹⁵ and 10 ¹⁶ ^{cm" 2.}

The precursor gas is transformed into plasma. Ion implantation is preferably performed by immersing the layer to be implanted in the formed plasma. For this purpose, the plasma is preferably formed in a chamber containing the stack 5. For this purpose, it is possible to use a plasma immersion ion implantation technique or a plasma doping technique.

A negative potential is then applied to the hydrogenated amorphous silicon layer 2 to be implanted so that chemical species of the plasma penetrate the surface of the hydrogenated amorphous silicon layer 2. The ion implantation is carried out at a lower energy than 2000V and preferably between 1000 and 1500 V.

With reference to FIG. 2c, the method then comprises a step 103 of annealing during which the stack is heated to a temperature of between 150 and 350 ° C., and preferably between 200 and 300 ° C. for a duration of preference. between 30 minutes and 1 h 30 in order to recover the passivation of the doped hydrogenated amorphous silicon layer p while maintaining good conductivity for this layer.

This method makes it possible to obtain a heterojunction which can be used for producing a heterojunction photovoltaic cell since the heterojunction thus obtained has the following properties:

- The hydrogenated amorphous silicon layer has a thickness compatible with use in a photovoltaic cell since it is between 5 and 30 nm;

The heterojunction has a passivation level sufficient for use in a heterojunction photovoltaic cell since it has an open circuit voltage i-Voc greater than 700 mV;

- The hydrogenated amorphous silicon layer has a sufficient conductivity for use in a photovoltaic cell since it has a conductivity greater than 10 ^"4 Ω ^{" 1} cm ^"1 .

Experimental results :

FIG. 3 represents a substrate obtained by a method analogous to the method described with reference to FIGS. 2a to 2c.

The method has been implemented in the particular case where the crystalline silicon substrate 1 of 280 μηι is polished so as to have a low surface roughness. The fact of having a low surface roughness makes it possible to have a better passivation. In this case, this roughness also makes it possible to overcome the effects of texturing prior to the realization of the cell.

A first hydrogenated amorphous silicon layer 2 is deposited on a first face 7 of the crystalline silicon substrate 1. The first layer of hydrogenated amorphous silicon 2 has a thickness of 25 nm. A second layer of hydrogenated amorphous silicon 6 is deposited on a second face of the crystalline silicon substrate. The second hydrogenated amorphous silicon layer 6 has a thickness of 25 nm.

Boron is implanted in the first hydrogenated amorphous silicon layer 2 from a precursor gas by a 1500 V plasma immersion ion implantation process. The precursor gas is B ₂ H ₆ containing an equal dopant ion dose. at 5.10 ¹⁵ cm ^"2 .

The second hydrogenated amorphous silicon layer 6 is not doped. We then obtain a stack 9 comprising:

A first p 2 doped hydrogenated amorphous silicon layer;

A crystalline silicon substrate 1;

A second undoped hydrogenated amorphous silicon layer 6.

At the end of the doping step:

- doped hydrogenated amorphous silicon p-layer 2 has a conductivity of 10 ^{^"8} ^{Ω" 1} cm ^"1;

- The stack 9 has an open circuit voltage iV _0C equal to 560 mV.

Following the doping step, the stack 9 is annealed at 300 ° C. for 1 h 30 min.

At the end of the annealing step:

- doped hydrogenated amorphous silicon p-layer 2 has a conductivity of 10 ^{^"5} ^{Ω" 1} cm ^"1;

- The stack 9 has an open circuit voltage iV _0C equal to 705 mV.

The method therefore makes it possible to obtain a heterojunction whose properties are compatible with use in a photovoltaic cell.

Fabrication of a heteroionction comprising a layer of hydrogenated amorphous silicon doped n:

A method for manufacturing a heterojunction comprising an n-doped hydrogenated amorphous silicon layer according to one embodiment of the invention will now be described with reference to FIGS. 4a to 4c.

With reference to FIG. 4a, the method comprises a first step 101 'for depositing a hydrogenated amorphous silicon layer 2' on a crystalline silicon substrate 1. In this embodiment, the crystalline silicon substrate is deoxidized before the deposition of the hydrogenated amorphous silicon.

In this embodiment, the hydrogenated amorphous silicon layer 2 'is an intrinsically hydrogenated, that is undoped, hydrogenated amorphous silicon layer. The hydrogenated amorphous silicon 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 crystalline silicon substrate 1; A layer of hydrogenated amorphous silicon 2 'deposited on the substrate.

With reference to FIG. 4b, the method then comprises a step 102 'for doping the hydrogenated amorphous silicon layer so as to produce a layer of hydrogenated amorphous silicon whose surface is n-doped. For this, the doping of the hydrogenated amorphous silicon layer 2 'is carried out by ion implantation from a precursor gas. The precursor gas 4 is PH ₃ . The precursor gas comprises a dopant ion dose of between 10 ¹⁵ and 10 ¹⁶ cm ^"2, and preferably between 10 ¹⁵ and 10 ¹⁶ ^{cm" 2.} The precursor gas is transformed into plasma. The stack 5 is immersed in this plasma. For this, the plasma is preferably formed in a chamber containing the stack 5. A negative potential is then applied to the stack so that plasma dopant ions enter the hydrogenated amorphous silicon layer 2 '. Ion implantation is performed at an energy of less than 2000V and preferably between 1000 and 1500 V.

With reference to FIG. 4c, the process then comprises an annealing step 103 'during which the stack is heated to a temperature of between 150 and 350 ° C., and preferably between 200 and 300 ° C. for a reference period. between 15 minutes and 30 minutes, in order to recover the passivation of the n-doped hydrogenated amorphous silicon layer while maintaining a good conductivity for this layer.

Experimental results FIG. 5 represents a substrate obtained by a method analogous to the method described with reference to FIGS. 4a to 4c.

The method has been implemented in the particular case where the crystalline silicon substrate 1 of 280 μηι is polished so as to have a low surface roughness.

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

Phosphorus is implanted in the first hydrogenated amorphous silicon layer 2 'from a precursor gas by a plasma immersion ion implantation process at 1500 V. The precursor gas is PH ₃ containing a dose of doping ions equal to 10 ¹⁶ cm ^"2 .

The second hydrogenated amorphous silicon layer 6 is not doped.

We then obtain a stack 9 comprising:

- A first layer of hydrogenated amorphous silicon doped n 2 ';

A crystalline silicon substrate 1;

A second undoped hydrogenated amorphous silicon layer 6.

At the end of the doping step:

the doped hydrogenated amorphous silicon n 2 'layer has a conductivity of 2.10 ^"4 Ω ^{" 1} cm ^"1 ;

the stack 9 has an open circuit voltage iV _0C equal to 570 mV. Following the doping step, the stack 9 is annealed at 250 ° C for 30 minutes.

At the end of the annealing step:

the n-doped α-Si-H 2 'doped hydrogenated amorphous silicon layer has a conductivity of 4.10 ^"4 Ω ^{" 1} cm ^"1 ;

the stack 9 has an open circuit voltage iV _0C equal to 700 mV.

The method therefore makes it possible to obtain a heterojunction whose properties are compatible with use in a photovoltaic cell. Method of manufacturing a photovoltaic cell:

A method of manufacturing a photovoltaic cell will now be described with reference to Figures 6a to 6b.

The photovoltaic cell is made from a crystalline silicon substrate 1.

The method comprises a first step 201 for producing a p-doped hydrogenated amorphous silicon layer 2 on a first face 7 of the substrate 1. This p-doped hydrogenated amorphous silicon layer is produced by the method described with reference to FIGS. 2a to 2c.

The method then comprises a step 202 for producing a n-doped hydrogenated amorphous silicon layer 2 on a second face 8 of the substrate 1. This layer of hydrogenated amorphous silicon doped n '2' is carried out by the method described with reference to Figures 4a to 4c.

The stack shown in FIG. 6d is then obtained. This stack comprises:

a first layer 2 of hydrogenated amorphous silicon, at least a portion of which is p-doped;

a crystalline silicon substrate 1;

a first hydrogenated amorphous silicon layer 2, at least a portion of which is n-doped. The method then comprises a step 203 for depositing a transparent conductive oxide layer TCO on each of the doped hydrogenated amorphous silicon layers 2, 2 '.

The method then comprises a step 204 for producing metal contacts 1 1 on each TCO transparent conductive oxide layer.

Naturally, the invention is not limited to the embodiments described with reference to the figures and variants could be envisaged without departing from the scope of the invention. Thus, the n-doped hydrogenated amorphous silicon layer could be produced before the p-doped hydrogenated amorphous silicon layer. Moreover, instead of carrying out two annealing steps during the manufacturing process of the photovoltaic cell, only one annealing step could be performed following the second doping step.

Finally, the invention can also be applied to the manufacture of a photovoltaic cell hybrid tandem, combining a silicon-based heterojunction with a perovskite-based cell.

Claims

1. A method of manufacturing a heterojunction for a photovoltaic cell, the method comprising the following steps:

- (101, 101 ') depositing a hydrogenated amorphous silicon layer (2, 2') on a crystalline silicon substrate so as to form a stack, the hydrogenated amorphous silicon layer (2, 2 ') having a thickness between 5 and 30 nm, and preferably between 15 and 25 nm;

- (102, 102 ') doping at least a portion of the hydrogenated amorphous silicon layer (2, 2') by ion implantation, the ion implantation being carried out at an energy of less than 2000 V, and preferably between 1000 and 1500 V, from a precursor gas comprising a dose of doping ions of between 10 ¹⁴ and ¹⁷ cm ^-2 , and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 ;

- (103, 103 ') and then annealing at a temperature between 150 ° C and 350 ° C, and preferably between 200 and 300 ° C for a period of between 5 minutes and 3 hours.

2. Method according to the preceding claim, wherein the doping step (102, 102 ') by ion implantation comprises the following substeps:

- transformation of the precursor gas into plasma;

- Immersion of the stack (5) in the plasma;

- Application of a potential to the stack so as to implant ions in the stack.

3. Method according to one of the preceding claims, wherein the annealing step is carried out under ambient atmosphere.

4. Method according to one of claims 1 to 3, wherein the precursor gas comprises B ₂ H ₆ .

5. Method according to the preceding claim, wherein the annealing time is between 30 minutes and 1 hour 30 minutes.

6. Method according to one of claims 1 to 3, wherein the precursor gas comprises PH ₃ .

7. Method according to the preceding claim, wherein the annealing time is between 15 and 30 minutes.

8. A method of manufacturing a heterojunction photovoltaic cell, the method of manufacturing the photovoltaic cell comprising a step of producing a heterojunction by a manufacturing method according to one of the preceding claims.

9. A method of manufacturing a photovoltaic cell according to the preceding claim, the method comprising the following steps:

- (a) depositing a first hydrogenated amorphous silicon layer (2) on a first face (7) of a crystalline silicon substrate (1), the first hydrogenated amorphous silicon layer (2) having a thickness of between 5 and 30 nm, and preferably between 15 and 25 nm;

(b) doping at least a portion of the first hydrogenated amorphous silicon layer (2) by ion implantation, the ion implantation being carried out at an energy of less than 2000 V, and preferably between 1000 and 1500 V, starting from a first precursor gas comprising a doping ion dose of between 10 ¹⁴ and ¹⁷ cm ^-2 , and preferably between 10 ¹⁵ and 10 ¹⁶ cm ^-2 , the first precursor gas comprising B ₂ H ₆ ;

- (a ') depositing a second layer of hydrogenated amorphous silicon (2') on a second face (8) of a crystalline silicon substrate (1), the second layer of hydrogenated amorphous silicon (2 ') having a thickness between 5 and 30 nm, and preferably between 15 and 25 nm;

- (b ') doping at least a portion of the second layer of hydrogenated amorphous silicon (2') by ion implantation, the ion implantation being performed at an energy of less than 2000 V, and preferably between 1000 and 1500 V, from a second precursor gas comprising a dose of doping ions of between 10 ¹⁴ and 10 ¹⁷ cm ^"2, and preferably between 10 ¹⁵ and 10 ¹⁶ ^{cm" 2,} the second precursor gas containing PH _3;

- (c ') annealing at a temperature between Ι δΟ' Ό and 350 ° C, and preferably between 200 and 300 ° C for a period of between 5 mhutes and 3 hours.

10. Method according to the preceding claim, further comprising a step (c) of annealing between steps (b) and (a '). Method according to one of claims 8 to 10, further comprising the following steps

- (203) a step of depositing a conductive transparent oxide layer (10) on each doped hydrogenated amorphous silicon layer (2, 2 ');

- (204) a step of forming at least one metal contact (1 1) on each transparent conductive oxide layer (10).