Method for improving the conversion efficiency of a photovoltaic cell, and equipment therefor

Abstract

The invention relates to a method (1) for improving the conversion efficiency of a photovoltaic cell, comprising the steps of: - treating (12) the cell by exposing it to electromagnetic radiation having a treatment irradiance (IT); and - cooling (13) the cell until its temperature (T) reaches a threshold temperature (TS), the exposure of the cell to the electromagnetic radiation being maintained and the cooling irradiance of the electromagnetic radiation (IR) being greater than or equal to the treatment irradiance (IT).

Description

DESCRIPTION TITLE: METHOD FOR IMPROVING THE CONVERSION EFFICIENCY OF A PHOTOVOLTAIC CELL AND ASSOCIATED EQUIPMENT TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of improving the conversion efficiency of a photovoltaic cell, whether isolated or grouped in a photovoltaic module (or a photovoltaic string).

[0002] The present invention relates more particularly to a method for improving the conversion efficiency of a photovoltaic cell and associated equipment. It also relates to a method for improving the conversion efficiency of a plurality of interconnected photovoltaic cells. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] High-efficiency photovoltaic cells are known to see their energy conversion efficiency improve under the combined effects of illumination and exposure to high temperatures. These treatments are collectively referred to as "enhancement treatments." These effects can be highly diverse and may originate from improvements in the photovoltaic cell substrate and / or the interfaces between the cell's component layers.

[0004] Despite the diversity of the physical mechanisms underlying these effects, it is noteworthy that recent developments in enhancement processes now make it possible to consider treatments lasting on the order of tens of seconds, enabling industrial-scale processing. However, the enhancement gain offered by these short enhancement processes is generally incomplete, meaning it falls short of the maximum gain achievable with longer enhancement processes.

[0005] In this context, there is a need to improve the bonus gain while maintaining an industrial pace.

[0006] One reason for this reduction in bonus gain is the creation of defects in the substrate and / or the layers of a cell when it is maintained at a high temperature "in the dark," that is, without any processing illumination. This is particularly the case at the end of the enhancement process, when the illumination is stopped but the treated cell remains hot.

[0007] Among the proposed solutions, one known method is to reduce the time required to cool the cell in the absence of illumination. Document WO 2020 / 082131, for example, discloses a method for improving a silicon substrate in which cooling is carried out actively at a rate between 10 °C / s and 20 °C / s, while simultaneously reducing substrate illumination. Cooling is maintained until the substrate reaches a temperature below 150 °C.

[0008] However, this solution does not provide the expected results. Indeed, even a short stay at a high temperature (between 150°C and 200°C), without illumination or with insufficient illumination, can impact the gain achieved.

[0009] Therefore, there is a need to effectively fix the effect of the bonus at the end of the process. SUMMARY OF THE INVENTION

[0010] To this end, the invention relates to a method for improving the conversion efficiency of a photovoltaic cell, said method comprising the following steps: heating the photovoltaic cell so that its temperature reaches a temperature range [Tm, TM] called the "processing temperature range", said processing temperature range extending between a minimum processing temperature Tm and a maximum processing temperature TM, the difference between the maximum processing temperature TM and the minimum processing temperature Tm being less than 30 °C; treating the photovoltaic cell so as to increase its conversion efficiency by exposing it to electromagnetic radiation, the temperature of the photovoltaic cell being maintained within the processing temperature range [Tm, TM], the irradiance of the electromagnetic radiation having a first substantially constant value, called the "processing irradiance"; to cool the photovoltaic cell by means of an active cooling device until the temperature of the photovoltaic cell reaches a temperature, called the "threshold temperature", at which the absence of exposure no longer has an effect on the conversion efficiency of the photovoltaic cell; the process being notable in that the exposure of the photovoltaic cell to electromagnetic radiation is maintained until the end of the cooling stage and in that the irradiance of the electromagnetic radiation during the cooling stage has a second value called the "cooling irradiance" and in that the cooling irradiance is greater than or equal to the processing irradiance.

[0011] Conversion efficiency refers to the ratio between the electrical power delivered by a photovoltaic cell subjected to radiation and the power of that radiation. Radiation, for example, is solar radiation, which has a certain irradiance.

[0012] Irradiance refers to the surface power density of light. It represents the power of electromagnetic radiation received by a unit area. Electromagnetic radiation is preferably directed perpendicularly to the surface of the photovoltaic cell.

[0013] Irradiance refers to the total irradiance of the radiation. This is, for example, the integral of the spectral irradiance of electromagnetic radiation over a spectral range, extending, for example, between 300 nm and 1200 nm.

[0014] By value of irradiance substantially constant, we mean that the irradiance in question varies by less than 10% over time and advantageously by less than 5% over time.

[0015] Increasing or improving conversion efficiency means increasing the electrical power delivered by the photovoltaic cell for a given received irradiance and temperature (the received irradiance depends on the spectral irradiance). Increasing or improving conversion efficiency means increasing the output parameters of the photovoltaic cell, such as the open circuit voltage and / or short circuit current of the photovoltaic cell and / or the form factor of the photovoltaic cell.

[0016] The effect on conversion efficiency means that the exposure or non-exposure of the photovoltaic cell to electromagnetic radiation does not influence its conversion efficiency, either positively or negatively. In other words, ceasing the exposure of the photovoltaic cell to electromagnetic radiation does not alter its output parameters, such as its open-circuit voltage and / or short-circuit current.

[0017] Photovoltaic cell temperature refers to its average temperature.

[0018] Maintaining exposure to electromagnetic radiation during cooling, with an irradiance at least equal to the processing irradiance, preserves the increased conversion efficiency, known as the "bonus gain," provided by the cell treatment. Once the photovoltaic cell reaches the threshold temperature, exposure to electromagnetic radiation can be stopped, thus preserving the bonus gain. Indeed, below the threshold temperature, the bonus gain is fixed. The active cooling system allows the photovoltaic cell temperature to be reduced despite the increased electromagnetic radiation irradiance.

[0019] In addition to the characteristics mentioned in the preceding paragraph, the method for improving the conversion efficiency of a photovoltaic cell according to the invention may have one or more of the following complementary characteristics, considered individually or in all technically possible combinations: the threshold temperature is strictly lower than the processing temperature range [Tm, TM] and preferably at least 10°C away from this range, or even at least 20°C away from this range, or even more preferably, at least 30°C away from this range; in other words, the threshold temperature is strictly lower than the minimum processing temperature Tm and at least 10°C lower. this minimum treatment temperature Tm (that is to say the threshold temperature T s check T s< Tm - 10 °C), or even at least 20 °C lower than this minimum treatment temperature Tm, or preferably at least 30 °C lower than this minimum treatment temperature Tmi; the range of treatment temperatures [Tm, TM] extends over less than 20 °C, or even less than 10 °C; in other words, the difference between the maximum treatment temperature TM and the minimum treatment temperature Tm is less than 20 °C, or even less than 10 °C; the cooling irradiance is greater than 1 kW / m² 2 , preferably greater than 3 kW / m 2 , and preferably greater than 5 kW / m² 2; the cooling irradiance is strictly greater than the processing irradiance; the cooling irradiance is constant; the electromagnetic radiation has, during the cooling step, at least one component within [300 nm; 1200 nm] and advantageously at least a first component within [300 nm; 550 nm] and at least a second component within [800 nm; 1200 nm]; the process includes a threshold temperature estimation step, determined by means of conversion efficiency measurements obtained on at least one photovoltaic cell, referred to as the "control cell", having undergone a processing step and a cooling step during which exposure to electromagnetic radiation is interrupted when said photovoltaic cell reaches an arbitrary temperature;the process includes a threshold temperature estimation step, determined by means of conversion efficiency measurements obtained on at least one photovoltaic cell, referred to as a "control cell", as a function of a cooling rate without illumination; the total duration of the treatment and cooling steps is less than 60 s, or even less than 15 s; The active cooling device is based on heat transfer by convection and / or conduction; the active cooling device is based on the convection of an airflow; maintaining the photovoltaic cell temperature within the processing temperature range [Tm, TM], for example during the processing stage, is achieved by means of electromagnetic radiation and the active cooling device; in the absence of the active cooling device during the processing stage, the processing irradiance is less than 100 kW / m²2 and preferably less than 50 kW / m² 2 , preferably within [3 kW / m 2 ; 5 kW / m 2 when the photovoltaic cell is a "perovskite-based tandem" type photovoltaic cell, preferably within [7 kW / m²] 2 ; 10 kW / m 2 when the photovoltaic cell is a silicon heterojunction photovoltaic cell, and less than 100 kW / m² 2 , and preferably less than 50 kW / m² 2, when the photovoltaic cell is a "TOPCon" type photovoltaic cell; the electromagnetic radiation has, during the processing step, at least one component within [300 nm; 1200 nm] and advantageously at least a first component within [300 nm; 550 nm] and at least a second component within [800 nm; 1200 nm]; the heating step is advantageously configured to minimize the following quantity: 1 - where Tf is the final temperature of the photovoltaic cell at the end of the heating stage, within the processing temperature range [Tm, TM], T tis the initial temperature of the photovoltaic cell during the heating step and T is the duration of the heating step; when the photovoltaic cell is a perovskite-based tandem photovoltaic cell, the processing temperature range [Tm, TM] is greater than 100 °C (i.e., Tm > 100 °C) and less than 200 °C (i.e., TM < 200 °C) and preferably less than 150 °C (i.e., TM < 150 °C); when the photovoltaic cell is a silicon heterojunction photovoltaic cell, the processing temperature range is greater than 170 °C (i.e., Tm > 170 °C) and less than 300 °C (i.e., TM < 300 °C) and preferably less than 250 °C (i.e., TM < 250 °C); when the photovoltaic cell is a TOPCon type photovoltaic cell, the processing temperature range is greater than 400 °C (i.e., Tm > 400 °C) and less than 600 °C (i.e., TM < 600 °C); minimize the quantity 1 - includes minimizing the quantity (r f- T^ / R OÙ R is the heating rate in °C / s; during the heating stage, the photovoltaic cell is exposed to electromagnetic radiation, the irradiance of the electromagnetic radiation having a third value, called "heating irradiance", advantageously strictly greater than the cooling irradiance and preferably greater than 10 kW / m² 2 advantageously greater than 30 kW / m 2 and even more advantageously greater than 50 kW / m 2The electromagnetic radiation during the heating stage has at least one component within the range [300 nm; 1200 nm], and advantageously a first component within the range [300 nm; 550 nm] and a second component within the range [800 nm; 1200 nm]. The temperature of the photovoltaic cell during the heating stage is controlled so that it remains above the processing temperature range [Tm; TM] for less than a limit; the limit satisfying max • (T ~ T M ) < 100 °C • s where d max is the time limit, T is the temperature of the photovoltaic cell and T M is the maximum processing temperature.

[0020] The invention further relates to equipment for improving the conversion efficiency of a photovoltaic cell, comprising at least a light source, an active cooling device and means configured to carry out the process of improving the conversion efficiency of a photovoltaic cell according to the invention.

[0021] Advantageously, the equipment also includes a controller that allows each light source and the cooling device to be controlled according to a predetermined profile.

[0022] Advantageously, the radiation source is sized to fully irradiate the photovoltaic module.

[0023] Even more advantageously, the equipment includes a mobile support that translates relative to the light source and is configured to carry a group of photovoltaic cells simultaneously.

[0024] The invention also relates to a method for improving the conversion efficiency of a group of interconnected photovoltaic cells, said method comprising the step of improving the conversion efficiency of each photovoltaic cell of the group of photovoltaic cells by means of the method for improving the conversion efficiency of a photovoltaic cell according to the invention.

[0025] Advantageously, the step of improving the conversion efficiency of each photovoltaic cell is carried out simultaneously on all photovoltaic cells in the group of photovoltaic cells.

[0026] Advantageously, the group of photovoltaic cells is encapsulated in a transparent matrix.

[0027] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0028] The figures are shown for illustrative purposes only and are not intended to limit the invention. Unless otherwise specified, the same element appearing in different figures has a unique reference numeral.

[0029] Figure 1 schematically represents an example of a photovoltaic cell such as can be implemented by the invention.

[0030] Figure 2 represents an implementation of a method of the invention, enabling the improvement of the conversion efficiency of a photovoltaic cell as represented by Figure 1.

[0031] Figure 3 schematically represents equipment configured to implement the process of Figure 2.

[0032] Figure 4 shows two examples of the implementation of a heating step in the process of Figure 2.

[0033] Figure 5 schematically represents an example of the implementation of another method according to the invention, allowing the improvement of the conversion efficiency of a group of photovoltaic cells. DETAILED DESCRIPTION

[0034] A method 1 for improving the conversion efficiency of a photovoltaic cell 2 will now be described. This method 1 is applicable to various types of photovoltaic cells. It is particularly well suited to a silicon heterojunction (SHJ) cell 2, such as that represented in [Fig. 1]. The cell 2 comprises, for example, a doped crystalline silicon substrate 21 and two layers of amorphous silicon 22, 23 arranged on either side of the substrate 21. One of the amorphous silicon layers 22, 23 is doped with the same type of conductivity as the substrate 21, for example, type n, and the other layer is doped with the opposite type of conductivity, i.e., type p.

[0035] The heterojunction is formed by the n-doped crystalline silicon substrate 21 and the p-doped amorphous silicon layer, this layer forming the emitter of cell 2. The emitter can be located on the front or rear face of cell 2.

[0036] The silicon heterojunction cell 2 is particularly sensitive to defects located at the interface between the crystalline silicon substrate 21 and the amorphous silicon layers 22-23. These defects can be dangling bonds or impurities such as metal ions. They introduce energy levels into the silicon band gap and increase the number of electron-hole recombinations at the interfaces, which deteriorates the cell's conversion efficiency, including the output parameters of the photovoltaic cell, such as the open-circuit voltage.

[0037] The cell 2 may also include a passivation layer 24 of intrinsic hydrogenated amorphous silicon, disposed between the substrate 21 and each layer of amorphous silicon 22, 23. It may also be covered with a layer of transparent conductive oxide 25 (or TCO, for "Transparent Conductive Oxide" in English).

[0038] Alternatively, photovoltaic cell 2 can be a so-called "tandem" perovskite-based photovoltaic cell. It includes, for example, a silicon heterojunction coupled to a perovskite-based junction.

[0039] According to another alternative, photovoltaic cell 2 could be a so-called "TOPCon" photovoltaic cell, short for "Tunneling Oxide Passivated Contact." This is a silicon heterojunction cell in which the substrate is separated from a doped layer (including the emitter) by a tunnel barrier.

[0040] Figure 2 illustrates an example of implementing process 1 for improving the conversion efficiency of a silicon heterojunction cell 2. Figure 2 specifically illustrates a measurement of the temperature T (shown on the left-hand axis) of cell 2 during the execution of process 1. The temperature T of cell 2 is preferably understood to be the average temperature of said cell 2. In practice, this temperature T is, for example, measured at a point in cell 2 using a thermocouple and may not accurately represent the average temperature of cell 2. However, to simplify the description of process 1, it will be assumed that the temperature varies little within cell 2 itself.

[0041] The method 1 is, for example, implemented using equipment 3 as illustrated in [Fig. 3]. This equipment may be conventional, such as cell interconnection equipment, known as a "stringer." However, said equipment 3 is advantageously configured to perform the method 1 according to the invention. It includes, for example, at least one light source 32, an active cooling device 34, and a controller 36. The equipment 3 also includes a movable support 35 that translates relative to to the light source. This mobile support 35 is referred to as "conveyor 35" in the following.

[0042] The controller 36 is configured to control the light source 32 and the active cooling device 34 in order to implement the method 1 for improving the conversion efficiency of a photovoltaic cell 2 as described below.

[0043] More specifically, the controller 36 is configured, for example, to control the aforementioned elements according to a predetermined profile. This predetermined profile includes, for example, as a function of time, the irradiance of each light source 32, the cooling power of the active cooling device 34, and the conveyor speed under each light source 32. A cell 2 can be placed on the conveyor 35 of the equipment 3 for processing. The conveyor 35 is sized to support a group of cells 2, interconnected or not, so that they can be processed simultaneously.

[0044] Initially (before t = 0.0 s), the measured temperature T of cell 2 is 12 °C. In the implementation of [Fig. 2], process 1 initially includes a heating step 11 of cell 2 so that its temperature T reaches a temperature range [Tm; TM] referred to as the "treatment temperature range" or "enhancement temperature range".

[0045] The processing temperature range is unique in that it extends below 30°C. It defines a temperature range within which cell 2 will be maintained during a processing step. Advantageously, this temperature range extends below 20°C, or even below 10°C.

[0046] Heating step 11 is carried out so that the net heat flux of cell 2 is positive (from the perspective of cell 2). Net heat flux is understood to be the sum of the heat fluxes leaving cell 2 and the heat fluxes entering cell 2. The outgoing heat fluxes include, for example, heat fluxes removed by conductive transfer (with elements in contact with the cell) and / or convective transfer (e.g., with the ambient air) and / or radiative transfer (according, for example, to the Stefan-Boltzmann law). The incoming heat fluxes include, for example, heat fluxes added by conductive transfer (e.g., with a hot element in contact with the cell) and / or radiative transfer (e.g., to the ambient air). by means of electromagnetic radiation E). A net positive heat flux allows the temperature of cell 2 to increase.

[0047] The heating of cell 2 is preferentially achieved by exposing it to electromagnetic radiation E (radiative heat transfer). This can be supplemented by a heating plate (conductive heat transfer). The irradiance of the radiation in this stage has a value le, called the heating irradiance. In the current example, the heating irradiance le is constant and equal to 50 kW / m². 2 (Irradiance values ​​are plotted on the right-hand axis in [Fig. 2]). The objective of heating step 11 is to increase, if possible rapidly, the temperature T of cell 2 so that it reaches the treatment temperature range [Tm; TM]. The heating irradiance is therefore relatively high, so that the temperature rise time is short. Heating step 11 ends as soon as the temperature T of cell 2 reaches the treatment temperature range [Tm; TM].

[0048] In the example in [Fig. 2], the processing temperature range extends, in this example, between Tm = 210 °C and TM = 220 °C. The temperature T of cell 2 at the end of heating step 11 is T = 210 °C.

[0049] The temperature rise during heating step 11 can be very rapid and may induce a brief overshoot of the treatment temperature range. This overshoot should preferably be limited as it can significantly impact the thermal budget of cell 2. Therefore, the overshoot is preferably minimal, or even absent. The presence of an overshoot may be acceptable if it allows for a short heating step 11, thus reducing the overall treatment time. To this end, a criterion can be used to determine whether the cell temperature during heating step 11 is controlled. This criterion indicates that the temperature of cell 2 must not exceed the maximum treatment temperature for more than a specified duration.Beyond this time limit, the heating step 11 can be considered insufficiently controlled and has too significant an impact on the thermal budget of cell 2. The greater the temperature overshoot relative to the maximum processing temperature TM, the shorter this time limit must be. The time limit d is advantageously described by... d • (T - T M < 100 °C • s where T M is the upper limit of the processing temperature range.

[0050] Thus, an overshoot of 50 °C, during which the temperature of cell 2 reaches 270 °C for a treatment temperature range of [210 °C; 220 °C], should preferably last less than two seconds. An overshoot of 320 °C, considering the same treatment temperature range (i.e., an overshoot of 100 °C), should preferably last less than one second. Advantageously, the limiting time d is preferably described by d • T - T M < 50 °C • s

[0051] In this case, an overshoot of 50 °C should preferably last less than one second and an overshoot of 100 °C should preferably last less than 0.5 s. Note that the time limit is advantageously considered over the entire heating step 11. It therefore corresponds to the sum of the durations of several overshoots.

[0052] In all cases, the temperature of cell 2 should preferably not exceed a critical temperature beyond which the cell suffers rapid and irreversible damage. The critical temperature of a silicon heterojunction cell is, for example, 300 °C. The critical temperature of a tandem cell is, for example, 200 °C (tandem cells are not designed to withstand overshoot). The critical temperature of a TOPCon cell is, for example, 600 °C.

[0053] To avoid a potential overshoot, the heating step 11 can end briefly before the temperature T of cell 2 reaches the treatment temperature range [Tm; TM]. However, it ends prematurely, still taking into account the thermal inertia of cell 2 (and advantageously also the thermal inertia of the cell 2 environment) and the radiation irradiance E during the subsequent treatment step. In this way, the temperature T of cell 2 reaches the treatment temperature range while minimizing the chance of an overshoot.

[0054] The electromagnetic radiation E used during the heating step 11 is emitted by the light source 32. The cell 2 is advantageously oriented so that one of its faces is directed towards the light source 31 and preferably so that the electromagnetic radiation E is perpendicular to this face.

[0055] Process 1 comprises, consecutively, a treatment step 12 of cell 2. The treatment 12 of cell 2 is carried out by exposing it to electromagnetic radiation E. However, this radiation has an irradiance IT, called the "treatment irradiance" or "enhancement irradiance," which is preferably lower than the heating irradiance. The electromagnetic radiation E used in this step is advantageously obtained from the same light source 32 as that used in the heating step. However, it may be obtained from a different light source. The treatment irradiance IT is chosen to increase the conversion efficiency of cell 2. In the example given, the treatment irradiance IT is substantially constant and equal to 9.5 kW / m². 2

[0056] Silicon heterojunction cells 2 are known to exhibit an improvement in energy conversion efficiency of approximately 0.3% absolute under the combined influence of illumination and temperature. This phenomenon, known as "enhancement," results, for example, from the improvement of at least one of the hydrogenated amorphous silicon passivation layers 24 and / or the improvement of the interfaces between the amorphous silicon layers 22, 23 and the TCO layers 25. Enhancement can also improve the TCO layer 25 itself.

[0057] The same principle applies to other types of cells, such as a tandem cell or a TOPCon cell. However, the processing temperature range may differ.

[0058] The IT treatment irradiance is also chosen so that the temperature of cell 2 is maintained within the temperature range [Tm; TM] during this step. For example, the treatment temperature range for a silicon heterojunction cell is advantageously above 170 °C. It is advantageously below 300 °C when the treatment time is short (e.g., well below 15 s). Except for short treatment times, the temperature range is preferably below 250 °C.

[0059] The processing temperature range for a tandem cell is advantageously above 100 °C and advantageously below 160 °C. For a TOPCon cell, it is advantageously above 400 °C and advantageously below 600 °C.

[0060] Within these extended temperature ranges, the range of processing temperatures considered is advantageously reduced to less than or equal to 30 °C (or even lower). In this way, the temperature of cell 2 remains approximately constant, and process 1 is carried out in a controlled and reproducible manner.

[0061] To keep the temperature of cell 2 within the temperature range [Tm; TM], the treatment irradiance IT is chosen, for example, so that the net heat flux of cell 2 is low or zero during the duration of the treatment step 12. The incoming heat flux depends at least on the heat supplied by the electromagnetic radiation E of irradiance IT.

[0062] A net heat flux of zero maintains the thermal equilibrium of cell 2 throughout the treatment. Achieving perfect equilibrium (i.e., a perfectly zero heat flux) can be challenging. The net heat flux is then advantageously low enough to keep the temperature of cell 2 within the treatment range [Tm; TM] for the duration of treatment step 12.

[0063] It is also advantageous to actively cool cell 2 during processing step 12 to increase the heat flux exiting cell 2. This allows the processing irradiance (IT) to be increased to compensate for the outgoing heat flux. Higher processing irradiance (IT) increases the processing kinetics and further improves the energy conversion efficiency. Active cooling of cell 2 during processing step 12 can be achieved using the active cooling device 34.

[0064] Process 1 then includes a cooling step 13 of cell 2. The cooling 13 of cell 2 is carried out in such a way as to freeze the increase in the conversion efficiency of cell 2 obtained during the treatment step 12. In particular, it is carried out until the temperature of cell 2 is less than or equal to a temperature Ts, called the "threshold temperature". At a temperature below the threshold temperature Ts, the absence of exposure to electromagnetic radiation no longer has any effect on the conversion efficiency of the cell 2. The threshold temperature Ts is, in this example of a silicon heterojunction cell, equal to 150 °C (i.e., 60 °C away from the treatment range).

[0065] During the cooling stage 13, the exposure of cell 2 to electromagnetic radiation E is maintained. The electromagnetic radiation E then exhibits an IR irradiance during this stage, known as "cooling irradiance".

[0066] At the start of cooling stage 13 (when the irradiance drops from 9.5 kW / m²) 2 at 20 kW / m 2A period of thermal inertia can be observed, during which cell 2 maintains a virtually constant temperature T within the processing temperature range. This observable thermal inertia may include the thermal inertia inherent to cell 2 and / or the thermal inertia of the cooling device 34 (which may have a significant start-up time). The end of the processing step 12 and the beginning of the cooling step 13 then conveniently coincide with the moment when the control commands are sent to the various instruments (such as the light source 32 or the cooling device 34). In practice, the start-up inertia of the light source 32 is generally zero, and the abrupt change in irradiance can then indicate the change of step.

[0067] The E radiation can be emitted by a different light source provided that the cooling irradiance meets the aforementioned conditions (particularly irradiance and orientation). However, it is more advantageous for the E radiation to come from the same source as that used during treatment 12. Indeed, it is preferable to maintain exposure to this E radiation without a decrease in exposure (which can be observed when switching from one source to another), otherwise a reduction in conversion efficiency may occur.

[0068] The IR cooling irradiance is chosen so that it does not compensate for the heat flux exiting cell 2 during the cooling stage. The net heat flux is therefore negative (from the perspective of cell 2, in other words, the outgoing heat fluxes exceed the incoming heat fluxes). Thus, even in the presence of electromagnetic radiation E, the temperature of cell 2 decreases. Cooling 13 (i.e., the negative net heat flux) is made possible, for example, by the implementation of the active cooling device 34, which allows, Despite the heat provided by the IR cooling irradiance, the temperature of cell 2 is lowered to the threshold temperature Ts. The active cooling device 34 can implement heat transfer by conduction and / or convection. In the first case, it can be a temperature-controlled plate (called a "chuck"). In the second case, it can be a blower configured to create an airflow 340 sweeping over one face of cell 2 (preferably the face exposed to the E radiation). The airflow rate is then adjusted (for example, by means of the controller 36) to remove the heat required for cooling.

[0069] Another way to define the end of treatment step 12 and the beginning of cooling step 13 is to observe the change in sign of the net heat flux. The beginning of cooling step 13 corresponds to the moment when the net heat flux becomes negative.

[0070] Counterintuitively, the IR cooling irradiance is greater than or equal to the IT treatment irradiance. In the example in [Fig. 2], the IR cooling irradiance is constant and strictly greater than the IT treatment irradiance, equal to 20 kW / m². 2 The IR cooling irradiance could, according to one implementation method, exhibit a non-constant irradiance, for example increasing or decreasing, while being greater than or equal to the IT treatment irradiance.

[0071] When the temperature of cell 2 reaches the threshold temperature Ts, the exposure of cell 2 to electromagnetic radiation E is advantageously stopped. The cooling device 34 can then also be switched off. However, it is preferable for the active cooling device 34 to continue operating until the temperature of cell 2 reaches a temperature well below the threshold temperature Ts, for example, ambient temperature.

[0072] In the example illustrated in [Fig. 2], maintaining the exposure of cell 2 to electromagnetic radiation E during the cooling step 13 allows the cell 2 to continue its improvement effect until the temperature T of cell 2 is sufficiently low to fix the arrangement of the layers and the interfaces between these layers. The threshold temperature Ts thus corresponds to a temperature at which the arrangement of these layers and / or interfaces It no longer changes over time. Exposure to electromagnetic radiation E can therefore be stopped without risk of degradation of these structures and thus without risk of degradation of conversion efficiency.

[0073] The threshold temperature Ts varies depending on the cell type. For example, the threshold temperature Ts of a tandem cell is less than or equal to 70 °C. In the case of a TOPCon cell, the threshold temperature Ts is less than or equal to 400 °C. In the case of a silicon heterojunction cell (as in [Fig. 2]), the threshold temperature Ts is less than or equal to 160 °C.

[0074] In the example of [Fig. 2], the duration of the process (heating steps 11, treatment steps 12, and cooling steps 13) is 7.5 s. The process therefore improves the conversion efficiency of cell 2 and achieves this improvement in a time well under 60 s, or even under 15 s. The improvement process itself is thus compatible with an industrial production rate (a duration of less than 60 s being an upper limit and a duration between 15 s and 20 s being a common upper limit).

[0075] While process 1 allows for the rapid improvement of cell 2, the cooling rate is not a constraint of process 1. Indeed, prior art processes offer solutions for rapidly cooling the cell to be improved, thus minimizing the loss of gain. Conversely, process 1 according to the invention proposes continuing the heat treatment of cell 2 until the temperature of cell 2 stabilizes its state (and therefore the improvement in conversion efficiency). The cooling step 13 can therefore be carried out slowly, as long as it maintains the exposure of cell 2 to electromagnetic radiation when its temperature is above its threshold temperature Ts. Slow cooling may prove necessary when the thermal stresses in cell 2 during rapid cooling are too great. This is, for example, the case for a cell in a photovoltaic module or a photovoltaic string.

[0076] For the IR cooling irradiance to have a sufficient impact on conversion efficiency, it is advantageously chosen to be greater than 1 kW / m². 2 The higher the IR cooling irradiance, the better the preservation (or even improvement) of conversion efficiency during cooling. The irradiance of IR cooling is therefore preferably greater than 3 kW / m 2 and preferably, greater than 5 kW / m² 2 .

[0077] The active cooling device 34 is sized according to the IR cooling irradiance so that the net heat flux for cell 2 is outward. The active cooling device is all the more important when the IR cooling irradiance is high, when the difference between the treatment temperature range and the threshold temperature is large, and when the target cooling time is short.

[0078] However, thanks to the active cooling device 34, the IR cooling irradiance can be chosen to be strictly higher than the IT treatment irradiance without negatively impacting cell 2 (since its temperature decreases and moves away from the critical temperatures at which it can be damaged). In this way, the IR cooling irradiance can be high, allowing the conversion efficiency to be maintained or even further improved.

[0079] Table 1 illustrates an example of the improvement (referred to as "gain" in the table) in conversion efficiency obtained with five silicon heterojunction cells, after implementation of method 1 according to the invention and after implementation of a prior art method. The considered processing temperature range is between Tm = 210 °C and TM = 220 °C. The considered threshold temperature is Ts = 160 °C. The considered IT processing irradiance is 9.5 kW / m². 2 The heating irradiance considered is 50 kW / m². 2 In both processes, the cells are heated for 1.5 s and then treated for 1 s. The two processes differ in that the process according to the invention includes a cooling step 13 as described above (cooling irradiance of 20 kW / m²). 2until the cell temperature reaches 160 °C after approximately 5 s) and in that the prior art process includes a cooling step without illumination and at a cooling rate of 10 °C / s (i.e., rapid cooling in the dark as suggested by document WO 2020 / 082131). Each process is implemented on a group of five silicon heterojunction cells. Each group of five cells shows an almost identical initial conversion efficiency (within 0.1%). The first group, having undergone the prior art process, sees an absolute gain in its conversion efficiency of less than 0.3%. In contrast, the second group, having undergone the process according to the invention, sees a gain in its conversion efficiency greater than 0.4% absolute.

[0080] [Table 1]

[0081] During cooling step 13, the electromagnetic radiation E must have at least one component within the [300 nm; 1200 nm] range. This spectral window offers the best enhancement efficiency. Below 300 nm, the radiation E is too energetic and can damage cell 2. Furthermore, absorption occurs mainly at the surface and therefore does not allow for effective treatment throughout the thickness of cell 2. Above 1200 nm, the absorption of electromagnetic radiation E is weak and considerably increases the minimum cooling time. It is therefore advantageous for the electromagnetic radiation E to include at least one component between [300 nm; 1200 nm], or even to extend substantially over this spectral range.

[0082] Even more advantageously, electromagnetic radiation E comprises at least two components. At least one component falls within the range [300 nm; 550 nm], known as the "blue" range, and at least one component falls within the range [800 nm; 1200 nm], known as the "infrared" or "IR" range. Combining these two ranges allows us to take advantage of the strengths of each. Each component in the blue range is efficiently absorbed at the surface, thus effectively improving the conversion efficiency (particularly through improved layer stacking on the surface of cell 2). Each component in the IR range is absorbed throughout the entire thickness of cell 2, thus ensuring a more consistent efficiency improvement across the entire cell.

[0083] In the example in [Fig. 2], the electromagnetic radiation E used comprises a first component at 455 nm and a second component at 940 nm. The irradiance of the second component represents 70% of the total irradiance of the electromagnetic radiation. The irradiance of the first component represents 30% of this total irradiance.

[0084] The threshold temperature Ts plays a crucial role in the successful execution of process 1. Indeed, an incorrect assessment of this temperature can lead to a premature shutdown of the electromagnetic radiation E and thus a reduction in the conversion efficiency improvement. Therefore, process 1 can advantageously include a preliminary step to estimate the threshold temperature Ts of cell 2. By "estimate," we mean that the threshold temperature Ts is not measured directly on cell 2 but determined using measurements obtained from cells with equivalent characteristics.

[0085] One approach is to measure the conversion efficiency on a number of cells, called "control cells," with properties similar to the cell 2 that needs improvement (which we will call the "improvement cell"). The properties that can influence the threshold temperature Ts of a cell are generally the state of the layers composing that cell, as well as the state of the interfaces between these layers. It is therefore advisable that the control cells be obtained using the same process as that used to obtain the cell 2 to be improved. For example, the deposition or growth processes of the different layers are carried out under the same conditions and using the same materials.

[0086] Each control cell in the plurality of control cells undergoes a treatment process similar to the heating 11, treatment 12, and cooling 13 steps described previously. However, the treatment process differs from the process according to the invention in that exposure to electromagnetic radiation is arbitrarily stopped during cooling at different temperatures, referred to as cutoff temperatures. The conversion efficiency of each control cell is then determined, for example, by measuring the open-circuit voltage of each control cell. The conversion efficiencies obtained before and after treatment are compared as a function of the cutoff temperatures. A first group of control cells may show a substantially equal (for example, within 20%) and maximum improvement in conversion efficiency. In contrast, Another group of control cells may show a smaller, or even zero, improvement in efficiency. Control cells whose exposure to electromagnetic radiation was stopped while their temperatures were still above the threshold temperature Ts (which is yet to be determined) show the least significant gains in conversion efficiency. Control cells whose exposure to electromagnetic radiation was stopped while their temperatures were below the threshold temperature Ts (which is yet to be determined) show the greatest gains in conversion efficiency. A cutoff temperature associated with a high efficiency gain can be considered the estimated threshold temperature Ts for improving cell 2. The threshold temperature Ts can also be estimated by interpolating between the measured conversion efficiency gains and the associated cutoff temperatures.

[0087] In another approach, each control cell in the plurality of control cells is exposed to high irradiance, for example 10 kW / m². 2 The cells are exposed to radiation for approximately one minute, while maintaining the temperature of each cell at 200 °C. Once the radiation exposure is stopped, the control cells are stored at different constant temperatures, for example, between 100 °C and 300 °C. This can be achieved, for instance, by placing the cells on supports heated to the desired temperatures for at least 30 seconds. Measuring the conversion efficiency of each cell allows the determination of the cell(s) for which the efficiency gain is acceptable, as well as the desired storage temperatures. The threshold temperature is then the lowest storage temperature.

[0088]

[0089] The active cooling device 34 can also be implemented during processing step 12 (provided the net heat flux is low or even zero). This device 34 thus contributes to regulating the temperature of cell 2 during its exposure to electromagnetic radiation E. In this way, the temperature T of cell 2 can be maintained more reliably within the processing temperature range. The advantage is the ability to use a higher processing irradiance IT than without thermal regulation, thereby accelerating or increasing the improvement in conversion efficiency.

[0090] In the absence of the active cooling device 34 during treatment step 12, the IT treatment irradiance is advantageously chosen so that the temperature T of cell 2 remains within the treatment temperature range [Tm; TM]. The IT treatment irradiance is advantageously less than 100 kW / m². 2 and even more advantageously less than 50 kW / m² 2 The irradiance of IT treatment can depend strongly on the type of cell 2 to be enhanced.

[0091] For example, when the latter is a silicon heterojunction photovoltaic cell, as shown in [Fig. 2], then the IT processing irradiance is preferentially within [7 kW / m²]. 2 ; 10 kW / m 2 Indeed, a silicon heterojunction cell 2 should preferably maintain a temperature below 300 °C or even below 250 °C.

[0092] According to another example, when cell 2 is a tandem photovoltaic cell, the IT processing irradiance is preferentially within [3 kW / m²]. 2 ; 5 kW / m 2 ].

[0093] The processing temperature range for a TOPCon cell must be below 600 °C. Therefore, the IT processing irradiance can be less than 100 kW / m² in this case. 2 and for example close to 50 kW / m 2

[0094] The electromagnetic radiation E may also have, during processing step 12, at least one component in the range [300 nm; 1200 nm] and advantageously at least one component in the blue range and at least one component in the IR range. This may also be the case during heating step 11.

[0095] To reduce the overall duration of process 1, it is advantageous to perform the heating step quickly. Therefore, it is beneficial to heat cell 2 rapidly so that its temperature T quickly reaches the processing temperature range. Figure 4 illustrates, for example, a measurement of the temperature T of a silicon heterojunction cell 2 as a function of time t, during two implementations of the heating step 11. The two implementations differ from each other in the heating irradiance le used. In the first case (squares in Figure 4), the heating irradiance le is 48 kW / m². 2 In a second case (circles in [Fig. 4]), the heating irradiance is reduced by half and is equal to 24 kW / m² 2 .

[0096] In the first case, the temperature rise of cell 2 to a final temperature Tf of 180 °C is achieved in T = 2 s. The heating step 11 then advantageously ends after this duration T. In the second case, the temperature rise of cell 2 to the final temperature Tf of 180 °C is achieved in 7 s.

[0097] Reducing the duration of heating step 11 is equivalent to minimizing the area between the ordinate on [Fig. 4] and the temperature curve T. In other words, reducing the duration is equivalent to minimizing the following quantity where Tf is the final temperature of cell 2 at the end of heating step 11; 7 is the initial temperature of cell 2 and T is the duration of heating step 11 (in [Fig. 4], T is shown for an associated irradiance of 48 kW / m² 2Minimizing this quantity is approximately equivalent to minimizing the area of ​​the triangle formed by the ordinate of [Fig. 4] and the rising edge of the temperature curve. In other words, the quantity to be minimized can be approximated by where R is the heating rate in °C / s. The area of ​​the triangle associated with the first heating (the = 48 kW / m²) 2 ) is doubly hatched. The area of ​​the triangle associated with the second heating (the = 24 kW / m²) 2 ) is equal to the area of ​​the doubly shaded triangle and the area of ​​the single-shaded triangle. In order to reduce the duration of the heating stage 11, the heating irradiance is then advantageously greater than 10 kW / m² 2 A heating irradiance greater than 30 kW / m² 2 This allows a silicon heterojunction cell to reach operating temperature in less than 4 seconds. A heating irradiance greater than 50 kW / m² is required. 2allows the temperature of the same cell to rise in less than 2 seconds.

[0098] The heating irradiance is advantageously kept substantially constant in order to provide the maximum energy in a minimum amount of time.

[0099] The invention also relates to a method 4 for improving the conversion efficiency of a group of cells 2. The group is particular in that the cells Two cells are interconnected in pairs. For example, these are the two cells within a photovoltaic string or within a photovoltaic module. In the latter case, the two cells may be encapsulated in a transparent matrix, designed to protect the cells from the external environment (such as air or humidity), and / or arranged between two protective plates, for example made of glass, designed to ensure the mechanical strength of the assembly. The group of two cells may also include a backsheet.

[0100] The transparent matrix and / or protective plates can increase the thermal inertia of cells 2, as they can also contribute to their thermal insulation. This can result in a reduction in conversion efficiency when these cells are processed using a prior art method. Indeed, the cells are likely to remain at a high temperature for longer periods without being exposed to electromagnetic radiation (or not sufficiently exposed) at the end of the illumination cycle.

[0101] Process 4 offers a solution to this problem by including a step 40 for improving the conversion efficiency of each cell 1 in the cell group. This improvement step involves performing process 1 for improving the conversion efficiency of a cell 2, as described previously, on each cell 2 in the cell group. Thanks to the active cooling device 34, exposure to electromagnetic radiation can be maintained until the cells 2 reach the threshold temperature Ts. This implementation method is similar to the slow cooling discussed earlier.

[0102] Improvement process 1 is advantageously applied simultaneously to all cells 2 of the group. In this way, even if the cooling is slow (for example, due to the thermal inertia caused by the transparent matrix and / or the protective plates and / or the base sheet), the number of cells processed in parallel makes process 4 compatible with an industrial production rate.

[0103] The equipment 3 illustrated in [Fig. 3] can advantageously be configured to carry out the improvement process on the cell group 2. It is sufficient, for example, that the entire group can be placed under the light source 32 and under the blower 34.

Claims

DEMANDS

1. A method (1) for improving the conversion efficiency of a photovoltaic cell (2), said method (1) comprising the following steps: - heat (11) the photovoltaic cell (2) so that its temperature (T) reaches a temperature range [Tm, TM] called the "processing temperature range", said processing temperature range extending between a minimum processing temperature Tm and a maximum processing temperature TM, the difference between the maximum processing temperature TM and the minimum processing temperature Tm being less than 30 °C; - treat (12) the photovoltaic cell (2) in such a way as to increase its conversion efficiency by exposing it to electromagnetic radiation (E), the temperature (T) of the photovoltaic cell (2) being maintained in the range of treatment temperatures [Tm, TM], the irradiance of the electromagnetic radiation (E) having a first value (IT) substantially constant, called "treatment irradiance"; - cooling (13) the photovoltaic cell (2) by means of an active cooling device (34) until the temperature (T) of the photovoltaic cell (2) reaches a temperature (Ts), called the "threshold temperature", at which the absence of exposure to electromagnetic radiation (E) no longer has any effect on the conversion efficiency of the photovoltaic cell (2); the process (1) being characterized in that the exposure of the photovoltaic cell (2) to electromagnetic radiation (E) is maintained until the end of the cooling step (13) and in that the irradiance (IR) of the electromagnetic radiation (E) during the cooling step (13) has a second value called the "cooling irradiance" and in that the cooling irradiance is greater than or equal to the processing irradiance (IT).

2. A method (1) according to the preceding claim, characterized in that the threshold temperature (Ts) is strictly less than the minimum processing temperature Tm. [Claims] A method (1) according to any one of the preceding claims, characterized in that the cooling irradiance (IR) is strictly greater than the treatment irradiance (IT).

4. A method (1) according to any one of the preceding claims, characterized in that the electromagnetic radiation (E) has, during the cooling step (13), at least a first component within [300 nm; 550 nm] and at least a second component within [800 nm; 1200 nm], [Claims] A process (1) according to any one of the preceding claims, characterized in that the total duration of the process (1) is less than 60 s. [Claims] A method (1) according to any one of the preceding claims, characterized in that the active cooling device (34) is based on heat transfer by convection and / or conduction.

7. A method (1) according to any one of the preceding claims, characterized in that maintaining the temperature (T) of the photovoltaic cell (2) within the processing temperature range [Tm, TM] is achieved by means of electromagnetic radiation (E) and the active cooling device (34). [Claims] A method (1) according to any one of the preceding claims, characterized in that, in the absence of the active cooling device (34) during the treatment step (12), the treatment irradiance (IT) is less than 100 kW / m² 2

9. A method (1) according to any one of the preceding claims, characterized in that, during the heating step (11), the photovoltaic cell (2) is exposed to electromagnetic radiation (E), the irradiance of the electromagnetic radiation having a third value (the), called "heating irradiance", strictly greater than the cooling irradiance (IR).

10. Equipment (3) for improving the conversion efficiency of a photovoltaic cell, comprising at least one light source (32), an active cooling device (34) and means (35, 36) configured to carry out the method (1) for improving the conversion efficiency of a photovoltaic cell (2) according to any one of the preceding claims.

11. Equipment (3) according to the preceding claim, also comprising a controller (36) enabling each light source (32) and the cooling device (34) to be controlled according to a predetermined profile.

12. A method (4) for improving the conversion efficiency of a group of interconnected photovoltaic cells (2), said method (4) being characterized in that it comprises the step of improving (40) the conversion efficiency of each photovoltaic cell (2) of the group of photovoltaic cells (2) by means of the method (1) for improving the conversion efficiency of a photovoltaic cell (2) according to any one of claims 1 to 9.

13. A method (4) according to the preceding claim, characterized in that the step of improving (40) the conversion efficiency of each photovoltaic cell (2) of the group of photovoltaic cells (2) is carried out simultaneously on all the photovoltaic cells (2) of the group of photovoltaic cells (2).

14. Method (4) according to the preceding claim, characterized in that the group of photovoltaic cells (2) is encapsulated in a transparent matrix and / or arranged between two protective plates.

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