METHOD AND SYSTEM FOR TREATING A STACK FOR THE PRODUCTION OF A HETERO-TRANSFER PHOTOVOLTAIC CELL

Description

Technical field of the invention

[0001] The present invention relates to a method for treating a stack intended for the manufacture of a heterojunction photovoltaic cell.

[0002] The invention also relates to the corresponding processing system, intended to implement said method. State of the art

[0003] Silicon heterojunction (SHJ) photovoltaic cells are known to improve their energy conversion efficiency by approximately 0.3% absolute under the combined action of illumination and temperature. Thus, it is now common to carry out a so-called enhancement treatment of stacks, particularly intended to form SHJ photovoltaic cells; in order to increase their conversion efficiency.

[0004] Document WO2013 / 001440 describes an example of a method for treating an SHJ photovoltaic cell comprising an n-doped crystalline silicon substrate. In this treatment method, the photovoltaic cell is subjected to a luminous flux with an irradiance greater than or equal to 500 W / m2 for a duration of approximately 10 hours, while being heated to a temperature between 20°C and 200°C. Such a treatment duration is however incompatible with the rate of current photovoltaic cell production lines.

[0005] Patent application FR3099294A1 describes a method for treating a so-called precursor stack of a heterojunction photovoltaic cell. This method is implemented at the end of manufacturing and consists mainly of exposing said stack to intense electromagnetic radiation (greater than 200kW / m 2 < ) for a relatively short period (around ten seconds). Thanks to this temporary and intense exposure to radiation, an improvement in the cell obtained and an increase in its operating efficiency have been observed.

[0006] When exposed to electromagnetic radiation, the temperature of the stack increases sharply and can reach a value above 200°C, up to 240°C. In order to limit the temperature of the stack to a value below 200°C and to avoid deterioration of the resulting cell, it is necessary to provide a cooling solution. The aforementioned patent application FR3099294A1 mentions the need for cooling, without proposing concrete elements for implementing it.

[0007] The referenced publication " MADUMELU CHUKWUKA ET AL: "Investigation of light induced degradation in N-type silicon heterojunction solar cells during illuminated annealing at elevated temperatures" - Solar Energy Materials and solar cells elsevier science publishers, Amsterdam NL - vol. 218, September 1, 2020 - XP086293834 "concerns a study on the degradation of heterojunction PV cells when subjected to high temperature.

[0008] The aim of the invention is therefore to propose a method for treating a precursor stack of a photovoltaic cell, which makes it possible to maintain the integrity of the stack, during its exposure to electromagnetic radiation.

[0009] The process allows, in particular, the continuous processing of photovoltaic cells, at a high rate, thus enabling industrialization of the process. Statement of the invention

[0010] This aim is achieved by a method of treating a stack which comprises at least: A crystalline silicon substrate, A first passivation layer of hydrogenated amorphous silicon, arranged on a first face of the substrate, A first layer of amorphous silicon doped according to a first conductivity type, arranged on the first passivation layer,

[0011] Said method comprising steps of: Placing said stack in a housing, Exposing said stack to electromagnetic radiation, Measuring the temperature of the stack, Measuring the ambient temperature present in said housing, Cooling said stack during exposure,

[0012] Said method being characterized in that the cooling of said stack is carried out by: Injection of a gas flow into said housing, Regulation of the injected gas flow taking into account the measured stack temperature, Evacuation of the gas flow outside the housing taking into account the ambient temperature measured in said housing.

[0013] According to a particularity, the regulation step includes steps of: Measurement of the stack temperature, Comparison of the measured temperature with a first set value, Control of a valve for injecting the gas flow into the housing as a function of the difference between the measured temperature and said set value.

[0014] According to another feature, the gas flow evacuation step includes steps of: Measurement of the ambient temperature present in said housing, Comparison of the measured ambient temperature with a second set value, Control of means for evacuating the gas flow outside the housing as a function of the difference between the measured ambient temperature and said second set value.

[0015] Another object of the invention is to propose a processing system which also makes it possible to achieve this objective.

[0016] This aim is achieved by a system for processing a stack intended for the manufacture of a photovoltaic cell, said stack comprising at least: A crystalline silicon substrate, A first passivation layer of hydrogenated amorphous silicon, arranged on a first face of the substrate, A first layer of amorphous silicon doped according to a first conductivity type, arranged on the first passivation layer,

[0017] Said system comprising: A housing intended to receive said stack, A source configured to emit electromagnetic radiation to said stack,

[0018] Said system comprising: First means for measuring the temperature of the stack, Said system being characterized in that it comprises: Second means for measuring the ambient temperature inside the housing, Means for injecting a gas flow inside the housing via a main inlet, First means for controlling said means for injecting the gas flow, taking into account the measured temperature of the stack, Means for discharging the gas flow outside the housing, Second means for controlling the discharging means, taking into account the ambient temperature measured inside the housing.

[0019] According to a particular feature, the means of emitting electromagnetic radiation comprise light-emitting diodes.

[0020] According to another feature, the means for injecting the gas flow comprise at least one valve controllable by said first control means, arranged on said main gas inlet.

[0021] According to another feature, the injection means comprise a plurality of openings provided through a wall of said housing and connected to said main gas inlet.

[0022] According to another feature, the injection means comprise a gas distribution channel arranged between said main inlet and said openings.

[0023] According to another feature, said distribution channel is of the spiral planar type.

[0024] According to another feature, the system comprises means for cooling said source of electromagnetic radiation and / or the flow of gas injected into said housing. These cooling means may comprise a coil in which a heat transfer fluid circulates.

[0025] According to another feature, the means for evacuating the gas flow comprise one or more fans arranged in a wall of the housing.

[0026] According to another feature, the system includes first means for measuring the temperature of the stack.

[0027] According to another feature, the first control means are configured to execute a first temperature regulation loop, based on the temperature measured by the first measuring means and a first setpoint value.

[0028] According to another feature, the system includes second means for measuring the ambient temperature inside the housing.

[0029] According to another feature, the second control means are configured to execute a second temperature control loop, based on the temperature measured by the second measuring means and a second setpoint value. Brief description of the figures

[0030] Other characteristics and advantages will appear in the detailed description which follows, given with reference to the attached drawings in which: There figure 1 schematically represents the processing system of the invention; The figure 2 represents, in a perspective view, the system of the invention; The figure 3 schematically represents the architecture of the system of the invention and illustrates its operating principle; The figure 4 illustrates, by means of an exploded view, the architecture of the system of the invention and illustrates its operating principle; The Figure 5 illustrates the operating principle of the gas flow evacuation means; The figure 6 represents a diagram illustrating the cooling principle employed in the system of the invention; The figure 7 shows a diagram representing an example of a temperature control loop executed to control the gas injection means; The figure 8 shows a diagram representing an example of a temperature control loop implemented to control the means of evacuating the gas flow; Detailed description of at least one embodiment

[0031] In the remainder of the description, the terms "upper", "lower", "above", "below" or equivalent are to be taken into account taking into account a vertical direction drawn in the plane of the sheet and called the main direction (A).

[0032] The method of the invention applies to a stack of layers, used to manufacture a heterojunction photovoltaic cell. Such a stack is generally called a "photovoltaic cell precursor". In a non-limiting manner, as described in patent application FR3099294A1 and shown in the figure 1 , the stack 10 can have the following architecture: A substrate 11 made of crystalline silicon, for example n-doped; A first passivation layer 14 made of hydrogenated amorphous silicon (and preferably intrinsic) arranged on the first face of the substrate 11; A first layer of amorphous silicon 12, arranged on the first passivation layer 14 and doped with a first type of conductivity; A first layer of transparent conductive oxide 15 arranged on the first doped layer of amorphous silicon 12; A second passivation layer 14 made of hydrogenated amorphous silicon (and preferably intrinsic) arranged on the second face of the substrate 11; A second layer of amorphous silicon 13, arranged on the second passivation layer 14 and doped with a second type of conductivity opposite to the first type of conductivity; and A second layer of transparent conductive oxide 15 arranged on the second doped layer of amorphous silicon 13.

[0033] Such a stack is described as asymmetric, because it has two layers of amorphous silicon 12, 13 doped with opposite conductivity types, on either side of the substrate 11.

[0034] As indicated in the aforementioned patent application FR3099294A1, the method is a so-called enhancement treatment method (also known as "Light-soaking") which consists of exposing a stack to a heat treatment under illumination; in order to improve the efficiency of the cell during its operation. The method is in particular carried out by exposure to electromagnetic radiation R using a radiation source such as, for example, light-emitting diodes. Thus, the stack is exposed to electromagnetic radiation R for a treatment duration t which is a function of the total irradiance E of the emitted radiation and its wavelength or wavelengths.

[0035] At least one face of the stack 10 is exposed to said radiation R. Of course, it is also possible to expose both faces of the stack, either one after the other or both faces at the same time. In the latter case, a second radiation source would be used to illuminate the second face.

[0036] In a non-limiting manner, the exposed face may be irradiated with radiation R having an irradiance E of less than or equal to 200kW / m2 and preferably between 25 and 100kW / m2 and for example of the order of 50kW / m2. The duration of the treatment is advantageously between 1s and 30s. The temperature of the treatment is in particular between 100 and 250°C, preferably of the order of 200°C.

[0037] On the figures 3 And 4 stack 10 is represented in the form of a rectangular parallelepiped.

[0038] The processing system for the improvement of the stack 10 is described in connection with the figure 2 , there figure 3 and the figure 4 .

[0039] The treatment system may comprise a support on which the stack 10 to be irradiated is arranged. This support 20 may be arranged on a conveyor system comprising one or more conveyor belts 21, intended to pass through the treatment system of the invention.

[0040] The treatment system of the invention comprises a housing 3, for example of parallelepiped shape. This housing 3 is made of a temperature-resistant material, for example a metallic material, for example steel, aluminum or stainless steel.

[0041] The housing 3 thus comprises a so-called upper wall 30, a so-called lower wall 31 and four side walls opposite each other in pairs and called first side walls 32, 33 and second side walls 34, 35. The housing 3 is open on two of the opposite side walls, for example the first side walls 32, 33, so as to be crossed right through by the two conveyor belts 21 of the support 20. When the stack 10 passes through the housing 3, the latter is arranged in a plane parallel to the upper wall 30 of the housing 3.

[0042] The system comprises a first radiation emission block. This first block is for example integrated into the upper wall 30 of the housing 3. It comprises the radiation source, composed for example of one or more light-emitting diodes 40, and a control and electrical power supply assembly 41 intended to power and control said radiation source. Alternatively, the source may also comprise one or more halogen or xenon type lamps. The source may also be composed of several components of a distinct nature, chosen for example from light-emitting diodes, halogen lamps, xenon lamps.

[0043] In a non-limiting manner, the light-emitting diodes 40 may be aligned in several rows and integrated into a first panel 300 forming in part the upper wall 30 of the housing 3. The light-emitting diodes 40 are oriented to emit their light signal towards the interior of the housing 3, substantially in a direction perpendicular to the plane formed by the stack 10 to be irradiated. Each row of light-emitting diodes 40 may be produced in the form of a strip of several light-emitting diodes connected in series. The strips of light-emitting diodes may be connected in parallel to the control and power supply assembly 41 or each powered and controlled independently through a separate channel of the control and power supply assembly 41.

[0044] As indicated above, the radiation R emitted by the light-emitting diodes 40 to the stack 10 causes a strong increase in temperature at the stack, as well as inside the housing 3.

[0045] The system thus comprises a cooling block, arranged and configured to maintain the temperature of the stack 10 below a threshold value and thus avoid its potential degradation. The cooling block can be activated during the radiation exposure phase and possibly after this exposure phase to lower the temperature to acceptable values.

[0046] The cooling block consists of the following main elements: Means for injecting a flow of gas F inside the housing 3, First means for controlling said means for injecting the flow of gas F, Means for discharging the flow of gas F outside the housing, Second means for controlling these discharge means.

[0047] The gas flow F is advantageously injected at a temperature sufficient to lower the temperature of the stack 10 and thus prevent its degradation. Gas cooling means may optionally be added. The gas may be injected at a temperature between 5°C and 25°C.

[0048] The first control means and the second control means may be integrated into the control and power supply assembly 41.

[0049] The injection means may comprise a gas reserve 60, the gas being able to be for example air (for example in compressed form), nitrogen or helium. The gas reserve is connected to a main inlet provided on the housing 3, arranged for example on its upper wall 30. The injection means advantageously comprise at least one controllable valve 61 to adjust the flow rate of gas injected inside the housing 3, via said main inlet. The control principle of the valve 61 is explained below. By way of example, the gas can be injected with a flow rate of between 0.5L and 10L per second.

[0050] The injection means may comprise a plurality of openings 62 made through the first panel 300 of the upper wall of the housing and each opening into the interior of the housing. These openings may be made in the form of several rows. Each row of openings 62 may be inserted between two rows of light-emitting diodes 40 ( figure 4 ). Each opening 62 has an inlet connected to the main gas inlet and an outlet opening into the interior of the housing 3.

[0051] Advantageously, the housing 3 may comprise a second panel 301 fixed to the first panel 300, above the first panel, forming with said first panel the upper wall 30 of the housing 3. This second panel 301 has the function of ensuring the distribution of the gas at the different openings. This second panel may thus integrate a planar spiral channel 302. The channel 302 is added downstream of the main gas inlet. When the gas flow F is injected, it follows the spiral shape of the channel 302. The first panel 300 is fixed under the second panel 301 so that the inlet of each opening 62 made through the first panel 300 communicates with the channel. By circulating in the channel 302, the gas thus becomes distributed uniformly through the openings 62 and diffuses inside the housing 3.

[0052] Advantageously, the system may comprise cooling means, arranged and configured to cool the radiation source and / or the injected gas. These cooling means may comprise a coil 50 in which a heat transfer fluid circulates and an external pumping system 51 intended to ensure the circulation of the heat transfer fluid in the coil 50. This coil 50 may be integrated into the first panel 300 of the upper wall 30 of the housing and be arranged above the entire set of light-emitting diodes 40 to ensure heat dissipation at the level of the radiation source. The cooling means may also be used to cool the gas injected inside the housing 3. The openings 62 may thus be arranged to pass through the coil 50, thus making it possible to cool the gas in contact with the coil.

[0053] The first control means of the injection means are configured to manage the flow rate of gas injected inside the housing 3, taking into account the temperature measured at the stack 10.

[0054] The system thus comprises means for measuring the temperature at the level of the stack 10 to be irradiated. These measuring means may comprise a pyrometer-type sensor 70 arranged under the stack 10 and for example fixed to the upper face of the lower wall 31 of the housing 3. This sensor 70 is intended to collect the temperature at the level of the stack 10 and not the ambient temperature present inside the housing 3.

[0055] In reference to the figure 7 , the first control means are configured to execute a first temperature control loop in order to apply a suitable control of the valve and to adjust the flow rate of injected gas to the temperature of the stack 10.

[0056] As an example, this first control loop B_1 can have the following structure: A comparison block C_1 receives as input a temperature setpoint value Xcons_1 and a measured temperature value Xm_1 at the stack 10 (by the pyrometer); The setpoint value Xcons_1 corresponds to the temperature that is desired to be obtained. It may be approximately 200°C, for example between 180°C and 250°C. The first comparison block B_1 is configured to determine the difference Y_1 between the two temperature values ​​received as input; The difference Y_1 between the two temperature values ​​is injected into a PID_1 (Proportional - Integral - Derivative) corrector intended to determine a command W_1 at the output, representative of the temperature difference received at the input; The transfer function F_1 of the process determines the control signal S_1 to be applied to the controllable valve 61 to regulate the measured temperature to the setpoint value;

[0057] Depending on the temperature measured at the stack 10 and its variation relative to the set value, the gas flow rate injected inside the housing 3 will thus be increased, kept constant or decreased.

[0058] The cooling block also comprises means for evacuating the flow of gas F injected into the housing 3, in order to extract the calories produced during cooling. These evacuation means may comprise one or more fans 80, 81.

[0059] Without limitation, as shown in the Figure 5 , the evacuation means are implemented in the form of several fans. The fans are for example integrated into the two second side walls 34, 35 of the housing 3.

[0060] The fans 80, 81 are advantageously all identical. In a non-limiting manner, they can be controlled separately, in groups. It is thus possible to distinguish a first group comprising one or more fans 80 integrated into a first side wall 34 of the second side walls and a second group comprising one or more fans 81 integrated into the opposite side wall 35.

[0061] For example, the evacuation means may include a total of four fans, two fans per group.

[0062] In each group of several fans, the fans 80, 81 are controlled identically to rotate at the same speed.

[0063] The second control means are configured to execute, for each group of fans, a temperature control loop, taking into account the ambient temperature measured inside the housing 3.

[0064] The system thus comprises means for measuring the temperature inside the housing 3. They may comprise one or more temperature probes 71, 72. Advantageously, the system may comprise a first probe 71 dedicated to the regulation of the first group of fans 80 and a second probe 72 dedicated to the regulation of the second group of fans 81.

[0065] In reference to the Figure 5 and to the figure 8 , for the first group of fans 80, the control loop B_2 can have the following structure: A comparison block C_2 ​​receives as input a temperature setpoint value Xcons_2 and a temperature value Xm_2 measured inside the housing 3 by a temperature probe 71; The setpoint value Xcons_2 corresponds to the temperature that is desired to be obtained. It can be approximately 200°C, for example between 180°C and 250°C. The difference Y_2 between the two temperature values ​​is injected into a PID_2 (Proportional - Integral - Derivative) corrector intended to determine a command W_2 at the output, representative of the temperature difference received at the input; The transfer function F_2 of the process determines the control signal S_2 to be applied to the evacuation means, i.e. to the fans;

[0066] The same control loop can be performed for the second group of fans 81. On the Figure 5 and the figure 8 , the index _3 is indicated to reference this loop B_3.

[0067] Depending on the temperature measured inside the housing 3 and its variation compared to the set value Xcons_2, Xcons_3, the rotation speed of the fans 80, 81 of the group will be increased, kept constant or decreased.

[0068] According to a particularity, as illustrated on the figure 8, the temperature measured by each temperature probe 71, 72 dedicated to a group of fans can be injected into the control loop intended for the control of the other group of fans. Each PID_2, PID_3 corrector of a control loop receives the measured temperature coming from the other control loop. The two control loops are thus intertwined. In other words, the second control means can be configured to act on each PID_2, PID_3 corrector in order to adjust the correction to be made. This may in particular involve correcting more significantly for one group than for the other, according to the temperature measurements obtained, for example to ensure that a uniform temperature is obtained inside the housing.

[0069] Based on the architecture described above, in conjunction with the figure 6 , the treatment process follows the following steps: E1: The stack 10 is in position inside the housing 3, ready to receive the radiation R; E2: The radiation source formed by the light-emitting diodes 40 is activated by the control and power supply assembly 41; E30, E31, E32: After activation of the radiation R, the temperature is measured respectively: By the temperature sensor 70 to measure the temperature of the stack 10 (step E30); By the first temperature probe 71 to measure the temperature in the housing 3 for the purpose of controlling the first group of fans 80 (step E31); and By the second temperature probe 72 to measure the temperature in the housing for the purpose of controlling the second group of fans 81 (step E32);E40, E41, E42: Depending on the measured temperatures, the different regulations are implemented by: Control of the valve 61 to adjust the flow of gas F injected into the housing 3 by executing the first regulation loop B_1 (step E40); Control of the first group of fans 80 to evacuate the calories by applying the second regulation loop B_2 (step E41); Control of the second group of fans 81 to evacuate the calories by executing the third regulation loop B_3 (step E42); ;

[0070] This process is applied for a determined duration, as long as the radiation R is emitted and possibly at the end of the emission to ensure a sufficient drop in temperatures in the housing 3.

[0071] Some implementation variants are possible: It is possible to provide a shape other than the spiral shape of the planar channel 302; The principle is to maintain a uniform distribution of the gas inside the housing 3; The means for evacuating the gas flow may comprise a fan integrated into the lower wall 31 of the housing 3, in addition to the fans already present or replacing them; The system may comprise a device for measuring the current flowing in each strip of light-emitting diodes 40; Depending on the measured current, the control and power supply assembly 41 may adjust the control of each strip of light-emitting diodes; It is also possible to detect a malfunction in a strip of light-emitting diodes, The system may integrate several gas inlets towards the inside of the housing 3, a separate controllable valve making it possible to adjust the flow rate of gas injected via each of these inlets;The control and electrical power supply assembly 41 of the light-emitting diodes, the first control means and the second control means can be combined into a single control block, fixed to the housing 3, for example on its upper wall 30; The regulation loops can be produced according to other variants; ;

[0072] The invention has many advantages, including: It offers a concrete cooling solution during the radiation treatment of a stack; It has a simple architecture, easily implemented on a photovoltaic cell production line;

Claims

1. Process for treating a stack (10) intended for manufacture of a photovoltaic cell, said stack comprising at least: - a crystalline silicon substrate (11), - a first passivation layer (14) made of hydrogenated amorphous silicon, placed on a first side of the substrate, - a first layer (12) made of amorphous silicon doped according to a first conductivity type, placed on the first passivation layer (14), said process comprising steps of: - placing said stack (10) in an enclosure (3), - exposing said stack (10) to electromagnetic radiation (R), - measuring the temperature of the stack (10), - measuring the ambient temperature present in said enclosure (3), - cooling said stack (10) during exposure, said process being characterized in that said stack is cooled by: - injecting a gas flow (F) into said enclosure (3), - regulating the injected gas flow (F) taking into account the measured temperature of the stack (10), - evacuating the gas flow (F) from the enclosure (3) taking into account the ambient temperature measured in said enclosure (3).

2. Process according to Claim 1, characterized in that the regulating step comprises steps of: - measuring the temperature of the stack (10), - comparing the measured temperature with a first setpoint value (Xcons_1), - controlling an injection valve (61) controlling injection of the gas flow (F) into the enclosure (3) depending on the difference between the measured temperature (Xm_1) and said setpoint value (Xcons_1).

3. Process according to Claim 1 or 2, characterized in that the step of evacuating the gas flow comprises steps of: - measuring the ambient temperature present in said enclosure (3), - comparing the measured ambient temperature (Xm_2, Xm_3) with a second setpoint value (Xcons_2, Xcons_3), - controlling means for evacuating the gas flow from the enclosure (3) depending on the difference between the measured ambient temperature and said second setpoint value.

4. System for treating a stack (10) intended for manufacture of a photovoltaic cell, said stack comprising at least: - a crystalline silicon substrate (11), - a first passivation layer (14) made of hydrogenated amorphous silicon, placed on a first side of the substrate, - a first layer (12) made of amorphous silicon doped according to a first conductivity type, placed on the first passivation layer (14), said system comprising: - an enclosure (3) intended to receive said stack (3), - a source configured to emit electromagnetic radiation (R) towards said stack (10), - first means (70) for measuring the temperature of the stack (10), - second means (71, 72) for measuring the ambient temperature inside the enclosure (3), said system being characterized in that it comprises: - means for injecting a gas flow (F) into the enclosure via a main inlet, - first control means for controlling said means for injecting the gas flow, taking into account the measured temperature of the stack, - means for evacuating the gas flow from the enclosure (3), - second control means for controlling the evacuating means, taking into account the ambient temperature measured inside the enclosure.

5. System according to Claim 4, characterized in that the means for emitting electromagnetic radiation (R) comprise light-emitting diodes (40).

6. System according to Claim 4 or 5, characterized in that the means for injecting the gas flow comprise at least one valve (61) that is controllable by said first control means, said valve being arranged on said main gas inlet.

7. System according to Claim 6, characterized in that the injecting means comprise a plurality of apertures (62) that are produced through a wall of said enclosure (3) and that are connected to said main gas inlet.

8. System according to one of Claims 4 to 6, characterized in that the injecting means comprise a channel (302) for distributing the gas, arranged between said main inlet and said apertures (62).

9. System according to Claim 8, characterized in that said distributing channel (302) is of the planar spiral type.

10. System according to one of Claims 4 to 9, characterized in that it comprises means for cooling said source of electromagnetic radiation and / or the gas flow injected into said enclosure.

11. System according to one of Claims 4 to 10, characterized in that the means for evacuating the gas flow comprise one or more fans (80, 81) arranged in a wall of the enclosure (3).

12. System according to Claim 4, characterized in that the first control means are configured to execute a first temperature-regulating loop (B_1), based on the temperature (Xm_1) measured by the first measuring means and on a first setpoint value (Xcons_1).

13. System according to Claim 4, characterized in that the second control means are configured to execute a second temperature-regulating loop (B_2, B_3) based on the temperature (Xm_2, Xm_3) measured by the second measuring means and on a second setpoint value (Xcons_2, Xcons_3).