Patent Application
20230197307
This application claims priority to European Patent Application No. 21306854.7, filed Dec. 20, 2021, the entire content of which is incorporated herein by reference in its entirety.
The present invention relates to an electromagnetic radiation source that may be used to perform a light-soaking treatment of a photovoltaic cell. The present invention also relates to a light soaking system comprising such an electromagnetic radiation source.
The heterojunction is formed by the n-doped crystalline silicon substrate 11 and the p-doped amorphous silicon layer, this layer forming the emitter of the photovoltaic cell. The emitter may be located on the front face or the back face of the photovoltaic cell.
The SHJ photovoltaic cell is particularly sensitive to defects located at the interface between the crystalline silicon substrate 11 and the amorphous silicon layers 12-13. These defects can be dangling bonds or impurities such as metal ions. They introduce energy levels into the silicon bandgap and increase the number of electron-hole recombinations at the interfaces, which degrades the output parameters of the photovoltaic cell, such as the open circuit voltage VOC.
To achieve a high performance photovoltaic cell, it is therefore necessary to minimize the number of recombinations at the surface of the substrate 11. This is generally accomplished by depositing a passivation layer 14 made of intrinsic hydrogenated amorphous silicon on each side of the substrate 11, prior to the amorphous silicon layer 12, 13. Hydrogen atoms contained in the passivation layers 14 diffuse to the surface of the substrate 11 and neutralize defects.
A transparent conductive oxide (TCO) layer 15 is then deposited on each of the amorphous silicon layers 12-13.
It is known that the energy conversion efficiency of SHJ photovoltaic cells may be improved and stabilize under the combined action of illumination and temperature. This cell “enhancement” phenomenon results from the improvement of at least one of the hydrogenated amorphous silicon passivation layers 14, as well as from the improvement of the interfaces between the amorphous silicon layers 12-13 and the TCO layers 15.
The observation of the enhancement phenomenon of SHJ photovoltaic cells has led to the development of treatment methods comprising a step of exposing the photovoltaic cells to a light radiation. These treatment methods are referred to as light soaking methods.
Document WO2021/018757 discloses a light soaking method comprising a step of exposing a SHJ photovoltaic cell (or a SHJ photovoltaic cell precursor) to an electromagnetic radiation having an irradiance greater than or equal to 200 kW/m2 and at least one wavelength comprised between 400 nm and 1100 nm. This exposing step is accomplished by arranging the photovoltaic cell on a support and under an electromagnetic radiation source. The electromagnetic radiation source may be a laser system comprising one or more laser arrays, an assembly of light emitting diodes or any other illuminating device capable of emitting electromagnetic radiation with an irradiance greater than 200 kW/m2.
An aspect of the invention is to provide an electromagnetic radiation source that allows to accomplish a light soaking treatment in an efficient way.
According to a first aspect of the invention, there is provided an electromagnetic radiation source designed for a light-soaking treatment of a photovoltaic cell or a photovoltaic cell precursor, the source comprising a plurality of first radiation emitters and a plurality of second radiation emitters, the first and second radiation emitters being arranged in a plurality of rows, each first radiation emitter being configured to emit a first electromagnetic radiation having a spectrum comprised between 300 nm and 550 nm and each second radiation emitter being configured to emit a second electromagnetic radiation having a spectrum comprised between 800 nm and 1100 nm.
In an embodiment, the plurality of rows comprise rows of a first type and rows of a second type alternating with the rows of the first type.
According to a first development of the embodiment, each row of the first type comprises several first radiation emitters and several second radiation emitters alternating with the first radiation emitters and each row of the second type comprises several first radiation emitters and several second radiation emitters alternating with the first radiation emitters.
For example, the first and second radiation emitters are arranged according to a checkerboard pattern.
According to a second development of the embodiment, each row of the first type is composed of the first radiation emitters and each row of the second type is composed of the second radiation emitters.
According to a third development of the embodiment, each row of the first type comprises several first radiation emitters and several second radiation emitters alternating with the first radiation emitters and each row of the second type is composed of the first radiation emitters.
According to a fourth development of the embodiment, each row of the first type comprises several first radiation emitters and several second radiation emitters alternating with the first radiation emitters and each row of the second type is composed of the second radiation emitters.
The electromagnetic radiation source according to the first aspect of the invention may also have one or more of the following characteristics, considered individually or according to any technically possible combinations thereof:
A second aspect of the invention relates to a light soaking system comprising:
In an embodiment of the light soaking system, the support is mobile in translation with respect to the source and configured to transport simultaneously a plurality of photovoltaic cells or a plurality of photovoltaic cell precursors.
According to a development of this embodiment, the light soaking system further comprises a controller configured to adjust the displacement speed of the support as a function of a treatment time of the photovoltaic cells or photovoltaic cell precursors.
According to another development, the controller is further configured to adjust the light power of the first radiation emitters and/or the light power of the second radiation emitters as a function of a temperature of the photovoltaic cells or photovoltaic cell precursors.
The light soaking system comprises a temperature regulation device configured to maintain a temperature of the at least one photovoltaic cell or the at least one photovoltaic cell precursor below a temperature threshold.
The temperature regulation device may comprise an air blowing system and the controller may be further configured to adjust the air speed as a function of the temperature of the at least one photovoltaic cell or the at least one photovoltaic cell precursor.
The light soaking system beneficially comprises a photoluminescence or electroluminescence device configured to capture a photoluminescence or electroluminescence image of the at least one photovoltaic cell or the at least one photovoltaic cell precursor.
A third aspect of the invention relates to a treatment method by light soaking of a photovoltaic cell or of a photovoltaic cell precursor, comprising exposing the photovoltaic cell or photovoltaic cell precursor to the first and second electromagnetic radiations emitted by an electromagnetic radiation source according to the first aspect of the invention.
Other characteristics and benefits of the invention will become clear from the description that is given thereof below, by way of indication and in no way limiting, with reference to the appended figures, among which:
For greater clarity, identical or similar elements are marked by identical reference signs in all of the figures.
The photovoltaic cell may be a silicon heterojunction (SHJ) photovoltaic cell like the photovoltaic cell 10 shown in
The first and second amorphous silicon layers 12-13 are doped of opposite conductivity type. The amorphous silicon of the first and second doped layers 12-13 may be hydrogenated.
With reference to
The first electromagnetic radiation may be monochromatic or polychromatic. A radiation is considered to be monochromatic when it has only one line (or component) having a full width at half maximum (FWHM) lower than or equal to 10 nm. Conversely, a radiation is considered to be polychromatic when it has several lines (or components) or when the full width at half maximum (FWHM) of the single line is greater than 10 nm.
In an embodiment, the first radiation emitters 21 have substantially the same size and substantially the same light power density (also called irradiance, in W/m2). “Substantially” means that the size/density difference between the first radiation emitters 21 does not exceed 5%.
Each of the second radiation emitters 22 is configured to emit a second electromagnetic radiation having a spectrum comprised between 800 nm and 1200 nm (limits included), and in an embodiment between 900 nm and 1100 nm (limits included). The second electromagnetic radiation may be monochromatic or polychromatic. It has a spectrum limited to the 800-1200 nm range, in an embodiment to the 900-1100 nm range. Given their emission spectrum, the second radiation emitters 22 are referred to as near infrared light sources.
In an embodiment, the second radiation emitters 22 have substantially the same size and substantially the same light power density (or irradiance). “Substantially” means that the size/density difference between the second radiation emitters 22 does not exceed 5%.
Exposing a photovoltaic cell (such as that shown in
The first radiation (between 300-550 nm) is absorbed at least partially in the first few hundred nanometers of the photovoltaic cell, which significantly improves the quality of the layers arranged on the exposed side of the photovoltaic cell (in the example above, one of the doped amorphous silicon layers 12-13, the passivation layer 14 and the transparent conductive oxide layer 15), as well as the quality of their interfaces.
The exposed side of the photovoltaic cell is for example the n-side, i.e. the side where is arranged the n-doped amorphous silicon layer.
The very short wavelengths, below 400 nm, are very energetic and may degrade the passivation layer. Restricting the wavelength range between 400 nm and 550 nm limits the risk of degradation of the passivation layer. However, the longer the wavelength of the first radiation, the less efficiently the first radiation is absorbed. The wavelength range between 400 nm and 450 nm represents a good compromise between the absorption of the first radiation (and thus the treatment efficiency) and the risk of degradation of the amorphous silicon.
Mixing the first radiation with the second radiation (between 800-1200 nm) limits the heating of the photovoltaic cell which could degrade the amorphous silicon. Indeed, the second radiation is less energetic than the first radiation but contributes to the conversion efficiency gain. The second radiation is absorbed at least in part into the crystalline substrate 11, resulting in a decrease in the number of interface states between the crystalline substrate 11 and the passivation layers 14 arranged on both sides of the crystalline substrate 11. In other words, the number of neutralized interface defects increases and the quality of the passivation improves. The wavelength range between 900 and 1100 nm represents a good compromise between the absorption of the second radiation and the heating of the cell.
The first radiation emitted by the first radiation emitters 21 has a first light power density E1 and the second radiation emitted by the second radiation emitters 22 has a second light power density E2. A ratio R between the first light power density E1 and the second light power density E1 may be comprised between 10/90 and 90/10, and in an embodiment between 30/70 and 70/30. The ratio R is chosen in function of the technology of the photovoltaic cell to be treated. It is defined as follows:
where ET is the total light power density of the overall radiation emitted by the source 20, f1 is the fraction (or percentage) of the first radiation in the overall radiation and f2 is the fraction of the second radiation in the overall radiation.
The total light power density ET may be greater than or equal to 10 kW/m2. It is in an embodiment equal to the sum of the first light power density E1 and the second light power density E2 (i.e. f1+f2=1). In other words, the source 20 comprises no more radiation emitters than the first radiation emitters 21 and the second radiation emitters 22. In particular, the source 20 may be devoid of radiation emitter emitting at a wavelength strictly greater than 550 nm and strictly lower than 800 nm, such that the light power density in the 550-800 nm range (excluding the limits) is zero.
The first and second radiation emitters 21-22 may be light-emitting diodes (LED) or lasers. LED are cheaper than lasers, especially for high light power densities (>10 kW/m2).
For the sake of simplicity, the first and second radiation emitters 21-22 will be considered hereafter to be LED. Consequently, the first radiation emitters 21 will be designated “first LED” and the second radiation emitters 22 will be designated “second LED”.
The first and second LED 21-22 of the source 20 are arranged so as to form a plurality of row Ri (the index i being a natural integer comprised between 1 and N, N being the total number of rows). The different rows Ri comprise, in an embodiment, the same number of LED. In the embodiments of
The row Ri of LED are, in an embodiment, parallel to each other. The distance between two consecutive rows Ri may be comprised between 0 mm (i.e. the rows are adjacent) and 20 mm. Beneficially, the rows Ri are regularly spaced apart from each other. The distance between two consecutive LED in a row Ri may be comprised between 0 mm (i.e. the LED are adjacent) and 20 mm. It is also beneficial that, in each row Ri, the LED are regularly spaced apart from each other. A constant distance between the rows Ri or between the LED in each row Ri improves the homogeneity of the radiation emitted by the source 20.
The first and second LED 21-22 are in an embodiment mounted on a printed circuit board (PCB). They may have a square-shape packaging, as shown in the figures.
Alternatively, the packaging may be rectangular, circular or hexagonal.
In the embodiments of
More particularly, in the embodiment of
In the embodiments of
These two embodiments offer the best radiation homogeneity (for a given size of LED) since the alternation between the first LED 21 and the second LED 22 is more frequent (from one row to the other, like in
The number of first LED may be equal to the number of second LED, as shown in
The number N1 of first LED 21 and the number N2 of second LED 22 may be calculated as follows:
where PT1 is the total light power of the first LED 21, PLED1 is the light power of one first LED 21, E1 is the first light power density and S is the emission surface of the source 20 (i.e. the surface available to accommodate the first and second LED 21-22); and
where PT2 is the total light power of the second LED 22, PLED2 is the light power of one second LED 22 and E2 is the second light power density.
In the embodiments of
In the embodiment of
From a radiation homogeneity point of view, it is desirable that the source 20 comprises high numbers N1, N2 of LED having a low surface than low numbers N1, N2 of LED having a high surface. In an embodiment, the first and second LED 21-22 occupy at least 30% of the emission surface S.
In summary, the arrangement in rows composed of the same LED (
In the embodiment of
In the embodiment of
The irradiance is simulated at 20 mm from the PCB of the LED. As expected, the irradiance E2 of the second radiation is higher than the irradiance E1 of the first radiation. One can also notice that the irradiance E1 of the first radiation and the irradiance E2 of the second radiation are substantially constant (variation of less than 20%) over a distanced of about 160 mm, this distanced being centered on the center of the LED array. The distance d corresponds to the width of a standard cell (square or pseudo-square of 156 mm side). It follows that a standard cell can receive a substantially homogenous radiation from the source 20. The radiation homogeneity can be further improved by increasing the size of the LED array, in order to limit the edge effects (LEDs are in practice components with very divergent lighting).
The greater the distance between the source and the photovoltaic cell, or the greater the emission angle of the LED, the greater the homogeneity of the radiation received by the photovoltaic cell.
In the embodiments of
It is however possible to use LED of different sizes and/or light powers. In the embodiment of
In an alternative embodiment, not shown in the figures, the first LED 21 have a surface (and a light power) greater than the surface (light power) of the second LED 22, and in an embodiment of at least twice the surface (light power) of the second LED 22.
In the embodiment of
The different rows of the source 20 may be aligned in the direction of the columns Cj, as shown in
In addition to the first LED 21 and the second LED 22, the source 20 may further comprise a power supply and a (LED) driver. The power supply is connected to the first and second LED 21-22 through the driver. The driver distributes the electric power of the power supply between the group of first LED 21 and the group of second LED 22. The driver is beneficially configured to control the electric power of the first LED 21 independently of the electric power of the second LED 22, thus making the power distribution variable. This enables the light power of the LED to be adjusted, for example to compensate a more pronounced ageing of one of the LED groups.
The LED array may be composed of modules, each module comprising at least one row Ri of LED. The modules are electrically connected in parallel. In each module, the LED are electrically connected in series. The modules are removably connected to a socket. Such a configuration simplifies the maintenance of the electromagnetic radiation source 20 (and reduces its cost), since a defective LED can be easily replaced by changing the module to which it belongs.
As described previously, the source 20 may be used for the light soaking treatment of SHJ photovoltaic cell, such as the photovoltaic cell 10 of
A light soaking treatment by means of the source 20 may also be interesting for an SHJ-based tandem photovoltaic cell. A SHJ-based tandem photovoltaic cell comprises a SHJ sub-cell (referred as the bottom cell) and a perovskite sub-cell arranged on the SHJ sub-cell (and referred as the top cell). The first electromagnetic radiation (blue/near UV radiation) emitted by the first LED 21 is mainly absorbed by the perovskite sub-cell, whereas the second electromagnetic radiation (near IR radiation) emitted by the second LED 22 is mainly absorbed by the SHJ sub-cell. The treatment makes it possible to heal defects in both the sub-cells.
Finally, the source 20 may also be used for the light soaking treatment of silicon homojunction photovoltaic cell.
The light soaking treatment may be performed at the end of the method of manufacturing the photovoltaic cells (i.e. on finished photovoltaic cells) or during the method of manufacturing the photovoltaic cells, with a stack of layers commonly called a photovoltaic cell precursor. For example, a precursor of a SHJ photovoltaic cell comprises the crystalline silicon substrate 11 (n-type or p-type) and at least one passivation layer made of hydrogenated amorphous silicon and arranged on a face of the substrate 11. The photovoltaic cell precursor is, in an embodiment, exposed with the passivation layer oriented towards the source 20 (for the blue/UV absorption in the passivation layer).
The light soaking treatment of the photovoltaic cells may also be performed when the photovoltaic cells are electrically connected in a string or into a photovoltaic panel.
In this embodiment, the support 30 is mobile in translation with respect to the source 20 and configured to transport simultaneously a plurality of photovoltaic cells (or a plurality of photovoltaic cell precursors). The photovoltaic cells 10 are successively moved in front of the source 20 by the support 30. The LED array of the source 20 may be dimensioned to expose simultaneously several photovoltaic cells. The mobile support 30 is in an embodiment a conveyor (for example a belt conveyor or a chain conveyor).
A source 20 according to the embodiment of
In an embodiment, the light soaking system 100 further comprises a controller 40 (or control circuit) configured (or programmed) to adjust the displacement speed Vsupp of the support 30 as a function of the treatment time of the photovoltaic cells 10. The displacement speed Vsupp of the support 30 (and thus of the photovoltaic cells 10) is indeed calculated as a function of the desired treatment time (for example comprised between 5 s and 60 s), given the length of the LED array in the movement direction. The controller 40 may be a microcontroller (or MCU, for microcontroller unit).
In alternative embodiments (not shown), the support 30 is stationary with respect to the source 20 or is mobile in rotation with respect to the source 20.
The light soaking system 100 may further comprise a temperature regulation device 50 configured to maintain the temperature of the photovoltaic cell(s) 10 below a temperature threshold. The temperature threshold is for example equal to the temperature above which the amorphous silicon of the photovoltaic cell 10 is degraded. This threshold may be comprised between 200° C. and 320° C. (depending on the technique used to deposit the material).
The temperature regulation device 50 may comprise an air blowing system to cool the photovoltaic cell 10. The air blowing system is in an embodiment servo-controlled by the controller 40 and a sensor measuring the temperature of the photovoltaic cell 10. The sensor, for example a pyrometer, is connected to the controller 40. In other words, the controller 40 is further configured to adjust the air speed Vair as a function of the temperature of the photovoltaic cell 10.
Another way to regulate the temperature is to contact the photovoltaic cell 10 (for instance using air sucking) to a temperature-regulated part (typically a metallic part).
Instead or in addition, the controller 40 may be further configured to adjust the light power PLED1 of the first LED 21 and/or the light power PLED2 of the second LED 22 as a function of the temperature of the photovoltaic cell 10.
Finally, the light soaking system 100 may also comprise a photoluminescence or electroluminescence device 60 configured to capture a photoluminescence/electroluminescence image of the photovoltaic cell 10 after it has been exposed to the electromagnetic radiation emitted by the source 20. In an embodiment of the light soaking system 100, the imaging device 60 is then located downstream of the source 20 (in the direction of movement of the cells).
Measuring the photoluminescence or electroluminescence intensity is a simple method to evaluate the benefits of the light soaking method. Indeed, the photoluminescence (respectively electroluminescence) intensity is representative of the open circuit voltage VOC (respectively of the series resistance Rs) of the photovoltaic cell.
An additional photoluminescence (electroluminescence) device (not shown in the figure) may be located upstream of the source 20 to determine the variation of the open circuit voltage VOC (of the series resistance Rs) during the exposition.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21306854.7 | Dec 2021 | EP | regional |
