Method for improving contact resistance of multi-junction solar cells

Abstract

The invention relates to a method for improving the contact resistance of a multi-junction solar cell having a front side, a back side and a plurality of sub-cells, the method comprising: a) the multi-junction solar cell is provided with a front side contact and a back side contact, b) one region of the back side contact is in electrical contact with a contact device, the contact device being electrically connected to one pole of a voltage source, one region of the front side contact or another region of the back side contact is in electrical contact with another contact device, the other contact device being electrically connected to another pole of the voltage source, c) a voltage is applied to the front side contact and the back side contact by the voltage source in a direction opposite to the multi-junction solar cell, d) during the application of the voltage, at least one point light source is directed to the front side and / or the back side of the multi-junction solar cell to illuminate one or more segments of a local region of the front side or the back side, thereby inducing a current in the respective local region and acting on the respective local region, the one or more segments of the local region being illuminated by the point light source with a plurality of different wavelengths of light beams.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for improving the contact resistance of a multi-junction solar cell. Multi-junction solar cells have at least two sub-cells, so-called p / n junctions, which are stacked from different materials. Each sub-cell has an absorber, which is usually designed to absorb light of a different wavelength range than the corresponding sub-cell. The upper sub-cell facing the sun is usually designed to absorb short-wavelength light and to allow longer-wavelength light to pass through, while the sub-cell arranged thereunder is designed to absorb the part of the spectrum below the critical wavelength, which is determined by the so-called bandgap energy in the semiconductor. In this way, in principle any number of sub-cells can be stacked together to increase the efficiency of the conversion of sunlight into electrical energy (compared to a simple solar cell). Therefore, a multi-junction solar cell has an upper sub-cell facing the sun, a lower sub-cell and one or more intermediate sub-cells between the upper sub-cell and the lower sub-cell. BACKGROUND

[0002] Multi-junction solar cells can be divided into mechanically stacked multi-junction solar cells and monolithic multi-junction solar cells, which are distinguished in that the sub-cells of the former are manufactured separately and then connected to each other in a hybrid construction, while all sub-cells of the latter are constructed on the same substrate. Furthermore, the front side and the back side of the multi-junction solar cell are each provided with at least one contact body, respectively.

[0003] Depending on the manufacturing process of the multi-junction solar cell, there can be a problem of locally high contact resistance of these contact bodies. This excessively high contact resistance can lead to a reduction in the efficiency of the multi-junction solar cell.

[0004] DE 102 16 009 560 A1 and DE 102 18 00 105 7 A1 disclose a method for improving the ohmic contact between a front side contact grid and a doped layer designed as an emitter layer, mainly providing a single solar cell in the form of a silicon-wafer solar cell, which includes a doped layer as an emitter, a front side contact grid and a back side contact grid. The front side contact grid is in electrical contact with a contact means electrically connected to one pole of a voltage source, and the back side contact grid is in electrical contact with a contact means electrically connected to the other pole of the voltage source. The voltage source is used to apply a voltage in the reverse direction to the silicon-wafer solar cell, which is lower than the breakdown voltage of the silicon-wafer solar cell. When the voltage is applied, a point light source is directed to the side of the silicon-wafer solar cell facing the sun. A partial area of the side facing the sun is illuminated, and an electrical current is generated in the partial area. The current density is 200 A / cm 2 to 20 000 A / cm 2 , and the time of action on the partial area is 10 ns to 10 ms. However, this method fails in the case of a multi-junction solar cell, because as soon as one sub-cell is still in the off direction, no current is generated.

[0005] Furthermore, WO 2017 / 175491 A1 describes a method of manufacturing a stacked cell of a first solar cell and a second solar cell with a first electrode, wherein a reverse voltage is applied between a certain area of the first electrode and the second solar cell and a reverse voltage is applied to the second solar cell while it is illuminated. SUMMARY

[0006] Therefore, the present invention aims to provide a method for improving the contact resistance of a multi-junction solar cell in order to increase the efficiency of the multi-junction solar cell.

[0007] The present invention is achieved by a method having the technical features of claim 1. Advantageous embodiments and refinements of the invention are subject matter of the sub-claims.

[0008] The present invention relates to a method for improving the contact resistance of a multi-junction solar cell having a front side, a back side and a plurality of sub-cells, the method comprising:

[0009] a) configuring the multi-junction solar cell with a front side contact and a back side contact, wherein the front side contact and / or the back side contact is / are grid-like, strip-like or transparent-like,

[0010] b) electrically contacting one area of the back side contact with a contact means, which is electrically connected to one pole of a voltage source, and electrically contacting one area of the front side contact and / or another area of the back side contact with another contact means, which is electrically connected to another pole of the voltage source, wherein the one area of the back side contact and the other area of the back side contact are electrically insulated from each other,

[0011] c) applying a voltage to the front side contact and the back side contact by means of the voltage source, which voltage is applied in a reverse direction to the multi-junction solar cell and has a magnitude below the breakdown voltage of the multi-junction solar cell,

[0012] d) during the application of the voltage, directing at least one point light source to the front side and / or the back side of the multi-junction solar cell, so that it illuminates one or more segments of a certain local area of the front side or the back side, thereby inducing an electrical current in the respective local area and acting on one or more portions of the respective local area, wherein the one or more segments of the local area are illuminated by the point light source with a plurality of light beams of different wavelengths.

[0013] In order to improve the contact resistance of the contact, very large current must flow locally through the contact of the multi-junction solar cell. For this purpose, a reverse voltage is applied to the multi-junction solar cell in step c) and, in step d), the multi-junction solar cell is locally irradiated while the voltage is applied, so that current can flow. The different wavelengths of the light beams can be adapted to the respective absorption coefficient of the absorber of the sub-cells, so that they fall within the respective absorption range of the absorber of the sub-cell. This ensures that even at a depth of more than 2-5 μm of the solar cell surface irradiated by the multi-junction solar cell, charge carriers are generated by the photoelectric effect, so that current can flow. For a multi-junction solar cell having a plurality of sub-cells, depending on the different wavelengths of the light used, current flows only through one sub-cell. The other sub-cell or sub-cells are prevented from current flow to the opposite contact because they are still in the off direction. By using a plurality of light beams of different wavelengths adapted to the respective sub-cell, current can flow. Preferably, each of the plurality of light beams of different wavelengths is adapted to one of the sub-cells and, more preferably, to the band gap of the absorber of the respective sub-cell and can be applied to the surface or to the same point locally as for the other sub-cells. The basic idea of the present application is that all sub-cells are irradiated with the respective wavelength so that current can flow. The present application is based on the recognition that if only one of the sub-cells is irradiated with the wavelength adapted thereto, the other sub-cells are in a state in which current cannot flow. Only by irradiation with light beams of different wavelengths can current flow through all sub-cells. In order to protect the upper sub-cells, the local current density can be adjusted by the size of the irradiated area. Thus, sufficient charge carriers can be generated in all sub-cells so that current flows through the entire multi-junction solar cell. By the method according to the present application, it is thus possible to achieve a good controllability of the contact resistance and to achieve a local and subsequent improvement of the contact resistance.

[0014] The at least one point light source can be directed to the front side or the back side. The front side contact and / or the back side contact of the multi-junction solar cell can be grid-like, strip-like or transparent, so that the different wavelengths of the light beams emitted by the at least one point light source are each absorbed by the absorber of one of the sub-cells. If the front side contact and / or the back side contact is transparent, it is preferably made of TCO (transparent conductive oxide), such as ITO (indium tin oxide). The front side contact and / or the back side contact can also or simultaneously be made of metal, such as silver or aluminum.

[0015] Preferably, the point light source is directed to the front side and / or the back side of the multi-junction solar cell in step d) so that several local areas and several sections of the local areas are irradiated successively. Preferably, the at least one point light source is directed to the front side and / or the back side so that it scans the respective surface. In this way, the contact can be irradiated over the entire surface or substantially over the entire surface.

[0016] In a preferred embodiment, a plurality of light beams of different wavelengths is used to simultaneously illuminate a portion of a sub-cell, the plurality of light beams of different wavelengths illuminating the portion in an overlapping manner. For example, suitable optics can be used to cause all light beams to simultaneously scan the surface of the underlying sub-cell, or preferably of the uppermost sub-cell, so that the focal points of all light beams overlap each other or at least partially overlap.

[0017] Preferably, at least one point light source is directed to the front side or the back side of the multi-junction solar cell. This ensures that the plurality of light beams can overlap.

[0018] In a preferred embodiment, the at least one point light source has a plurality of flash lamps with different spectral filters. Thus, only one point light source is required for performing step d). This reduces the costs and the space required for performing the method.

[0019] Another preferred way is that the one or more point light sources have a laser device with a plurality of lasers that can emit laser light of different wavelengths. Laser light can be precisely directed to a point. The lasers can be diode lasers, Nd:YAG lasers or fiber lasers.

[0020] Alternatively, the at least one point light source has a laser device consisting of a laser and a frequency doubler. Such a laser device is relatively inexpensive. The laser can be a diode laser, an Nd:YAG laser or a fiber laser.

[0021] In a preferred embodiment, each sub-cell has an absorber, and the different wavelengths of the plurality of light beams are adapted to the absorption coefficient of the corresponding absorber. Thus, in step d) sufficient charge carriers can be generated to generate a sufficiently large current for performing the method.

[0022] Preferably, one of the plurality of sub-cells is a perovskite sub-cell, i.e. has a perovskite as an absorber. For the illumination of a perovskite absorber, wavelengths in the range of 500 to 650 nm are preferred, for example 532 nm or 630 nm. The thickness of the perovskite absorber is preferably in the range of 0.1 to 0.8 pm, further preferably 0.1 to 0.3 pm.

[0023] In a preferred embodiment, one of the plurality of sub-cells has a silicon-based absorber, i.e. this sub-cell is designed as a silicon sub-cell. For example, the lower sub-cell is a p-type PERC (passivated emitter and rear cell) sub-cell, a heterojunction sub-cell, an n-type TOPCon (tunnel oxide passivated contact) sub-cell or an IBC (interdigitated back contact) sub-cell. Preferably, the silicon sub-cell is irradiated with an infrared wavelength, such as 1064 nm. The thickness of the silicon absorber is preferably between 100 and 200 pm. At a wavelength of 1064 nm, a silicon sub-cell with a thickness of about 150 ± 50 pm has a high transmittance of more than 20% and also a certain absorption at a depth of more than 2-5 pm below the surface of the solar cell, so that sufficient charge carriers are generated over the entire thickness of the silicon absorber or silicon sub-cell, resulting in the desired high current density.

[0024] Preferably, the multi-junction solar cell has an upper perovskite sub-cell and a lower silicon sub-cell. The manufacturing costs of such a multi-junction solar cell are substantially lower than those of a multi-junction solar cell based on InGaP, for example, and the efficiency is relatively high. Preferably, the multi-junction solar cell provided has one upper perovskite sub-cell and one lower silicon sub-cell and uses an infrared wavelength laser, for example a laser with a wavelength of about 1064 nm, for irradiating the lower silicon sub-cell, while a frequency doubler or another laser provides a shorter wavelength of 532 nm or 630 nm for the upper perovskite sub-cell. Due to the high transmittance, the light beam with a wavelength of 1064 nm will pass through the perovskite sub-cell. This means that, if only one wavelength, for example 1064 nm, of the light beam is used, the number of charge carriers generated locally in the perovskite sub-cell will not be sufficient to generate the desired high current density between the contact fingers. Only the use of two different wavelengths of the light beam, for example 1064 nm and 532 nm, ensures that this requirement is met.

[0025] Preferably, the multi-junction solar cell consists of an upper sub-cell and a lower sub-cell and is designed as a 2T or 3T multi-junction solar cell, where T stands for terminal or connection. If the lower sub-cell is designed as an IBC sub-cell, it is preferred that, in step b), one area of the back contact is electrically contacted with a contact means and another area of the back contact, which is insulated from the aforementioned area, is electrically contacted with another contact means, and that, in step d), the at least one point light source is directed to the front side of the multi-junction solar cell. Thus, in step d), the area of the front side is not covered by the other contact means, so that the front side is not obscured by the other contact means when the at least one point light source is directed to the front side.

[0026] Preferably, the multi-junction solar cell consists of an upper sub-cell and a lower sub-cell, and is designed as a 4T multi-junction solar cell, where T represents a terminal or connection. Preferably, the upper sub-cell is a perovskite sub-cell. Preferably, the lower sub-cell is a silicon sub-cell, such as a p-type PERC sub-cell or an n-type TOPCon sub-cell.

[0027] In a preferred embodiment, the multi-junction solar cell has an upper sub-cell, a lower sub-cell, and at least one intermediate sub-cell. Preferably, the multi-junction solar cell is configured as a triple-junction solar cell, i.e., a multi-junction solar cell with three sub-cells. Preferably, in step d), the multi-junction solar cell is irradiated with multiple light beams of different wavelengths, the number of light beams corresponding to the number of sub-cells or the number of absorbers in the sub-cells, wherein each wavelength is preferably adapted to one of the absorbers, particularly to the absorption coefficient.

[0028] For example, a multi-junction solar cell can be a triple-junction cell, such as an InGaP / InGaAs / Ge cell. Such triple-junction cells have very high efficiency, greater than 30%. To perform step d), three different wavelengths of light are required, such as 1064 nm, 830 nm, and 488 nm, which can be provided by diode lasers or fiber lasers. The upper InGaP sub-cell is relatively transparent to wavelengths of 1064 nm and 830 nm, and the middle InGaAs sub-cell is relatively transparent to wavelength 1064 nm. Therefore, a 488 nm laser can be used to generate charge carriers in the upper sub-cell, an 830 nm laser in the middle sub-cell, and a 1064 nm laser in the lower sub-cell. Preferably, all three wavelengths of laser light are irradiated onto the surface of the upper sub-cell, so that the three focal points overlap or at least partially overlap.

[0029] Preferably, after step d, the power of the multi-junction solar cell is measured, particularly the IV characteristic measurement using a cell tester. Attached Figure Description

[0030] Other advantages and features of this method will be illustrated by the preferred embodiments described below. The accompanying drawings are not to scale and are for illustrative purposes only.

[0031] Figure 1 This is a flowchart of the method of the present invention;

[0032] Figure 2 yes Figure 1 Perspective view of the steps of the method shown;

[0033] Figure 3 yes Figure 2 A sectional view of the steps shown;

[0034] Figure 4 is Figure 1 and Figure 2 detailed partial sectional view of a multi-junction solar cell according to the method shown in

[0035] Figure 5 is Figure 1 cross-sectional view of another multi-junction solar cell in the method shown in

[0036] Figure 6 is Figure 1 cross-sectional view of yet another multi-junction solar cell in the method shown in

[0037] List of reference signs

[0038] 1 multi-junction solar cell

[0039] 2 sub-cell

[0040] 3 sub-cell

[0041] 4 contact means

[0042] 5 light source

[0043] 6 section

[0044] 7 light beam

[0045] 8 another light beam

[0046] 9 voltage source

[0047] 10 sub-cell

[0048] 11 front contact

[0049] 11a MgF2 layer

[0050] 12 conductive layer

[0051] 13 electron conductor layer

[0052] 14 passivation and hole-blocking layer

[0053] 15 absorber

[0054] 16 PFN layer

[0055] 17 PTAA layer

[0056] 18 conductive layer

[0057] 19 n-type amorphous silicon layer

[0058] 20 intrinsic amorphous silicon layer

[0059] 21 absorber

[0060] 22 intrinsic amorphous silicon layer

[0061] 23 p-type amorphous silicon layer

[0062] 24 conductive layer

[0063] 25 backside contact

[0064] 26 intermediate layer

[0065] 27 terminal connection

[0066] 28 reflective layer

[0067] 29 p-emitter region

[0068] 30 n-emitter region

[0069] 31 configuring

[0070] 32 contacting

[0071] 33 applying a voltage

[0072] 34 directing

[0073] 35 testing

[0074] 100 front side

[0075] 101 back side DETAILED DESCRIPTION

[0076] Figure 1 is a flow chart of a method according to the present application. The method is for improving the contact resistance of a multi-junction solar cell having a front side, a back side and a plurality of sub-cells. The method has a step 31 in which the multi-junction solar cell is configured with a front side contact and a back side contact, wherein the front side contact and / or the back side contact is / are provided in a grid, strip or transparent form.

[0077] Step 31 is followed by step 32 in which one area of the back side contact is electrically contacted with a contact means which is electrically connected to one pole of a voltage source, one area of the front side contact and / or another area of the back side contact is electrically contacted with another contact means which is electrically connected to another pole of the voltage source, the one area of the back side contact and the other area of the back side contact being insulated from each other.

[0078] Subsequently, step 33 is performed in which a voltage is applied by the voltage source to the front side contact and the back side contact, the voltage being applied in a direction opposite to the multi-junction solar cell, the voltage being applied at a magnitude below the breakdown voltage of the multi-junction solar cell.

[0079] Subsequently, step 34 is performed, in which at least one point light source is directed to the front side and / or the back side of the multi-junction solar cell during the application of the voltage, wherein one or more segments of the local area of the front side or the back side are illuminated, so that an electrical current is induced in the respective local area and acts on the respective local area, wherein the one or more segments of the local area are illuminated by the point light source with several light beams of different wavelengths.

[0080] Optionally, step 35 is performed after step 34, in which a power measurement of the multi-junction solar cell is performed, in particular an IV characteristic measurement using a solar cell tester.

[0081] Figure 2 is a perspective view of one step of the method shown in Figure 1 Figure 2 A multi-junction solar cell 1 is shown, which has a front side 100, a back side (not shown) and a plurality of sub-cells (not shown), which multi-junction solar cell 1 employs step 34 shown in Figure 1 The multi-junction solar cell 1 has a front side contact 11 and a back side contact (not shown), wherein the front side contact 11 is in the form of a grid, which consists of a plurality of fingers and two busbars. The front side contact 11 is electrically contacted with a contact device 4, which is electrically connected to one pole of a voltage source (not shown), and the back side contact is electrically contacted with another contact device (not shown), which is electrically connected to another pole of the voltage source. A voltage is applied to the front side contact 11 and the back side contact of the multi-junction solar cell 1 by the voltage source, which voltage is applied in the opposite direction to the multi-junction solar cell and has a magnitude which is below the breakdown voltage of the multi-junction solar cell 1. In step 34 shown in Figure 1 During the application of the voltage, a point light source 5 is directed to the front side 100 of the multi-junction solar cell 1 in step 34 shown in. One or more segments 6 of the local area of the front side are illuminated, so that an electrical current is induced in the respective local area and acts on the respective local area. The point light source 5 illuminates the one or more segments 6 of the local area with several light beams 7, 8 of different wavelengths. The focal points of the light beams 7, 8 at least mostly overlap.

[0082] Figure 3 is a cross-sectional view of the step shown in Figure 2 For the sake of clarity, the point light source and the front side contact in Figure 2 are omitted. The front side contact (not shown) is electrically contacted with a contact device 4, which is electrically connected to one pole of a voltage source 9, and the back side contact (not shown) is electrically contacted with another contact device 4, which is electrically connected to another pole of the voltage source 9. The multi-junction solar cell 1 is embodied as a tandem solar cell, which has an upper sub-cell 2 and a lower sub-cell 3, wherein the upper sub-cell 2 forms the front side 100 of the multi-junction solar cell 1 and the lower sub-cell forms the back side 101.

[0083] Figure 4 is a cross-sectional view of the step shown in Figure 1 and​Figure 2 A partial cross-sectional detail of a multi-junction solar cell is shown. The multi-junction solar cell 1 consists of an upper sub-cell 2 with an absorber 15 and a lower sub-cell 3 with another absorber 21. The lower sub-cell 3 is designed as a hetero-junction sub-cell just as an example. The lower sub-cell can also be designed as a PERC or TOPCon sub-cell, not shown here. The multi-junction solar cell 1 has the following structure in the order shown in the figure:

[0084] - a front side contact 11, for example consisting of a silver and MgF2 layer 11a,

[0085] - a conductive layer 12, like an ITO layer,

[0086] - a buffer and electron conductor layer 13, like a Sn02 layer,

[0087] - a passivation and hole blocker layer 14, like a LiF / C60 layer,

[0088] - an absorber 15 with a layer thickness of about 500 nm,

[0089] - a PFN layer 16

[0090] - a PTAA layer 17

[0091] - a conductive layer 18, like an ITO layer,

[0092] - an n-type amorphous silicon layer 19,

[0093] - an intrinsic amorphous silicon layer 20,

[0094] - another absorber 21, like a p-type or n-type Cz-Si silicon substrate,

[0095] - an intrinsic amorphous silicon layer 22,

[0096] - a p-type amorphous silicon layer 23,

[0097] - a conductive layer 24, for example an ITO layer, and

[0098] - a back side contact 25, for example made of Ag.

[0099] Figure 5 is Figure 1 A cross-sectional view of another multi-junction solar cell provided by the method shown can be used as an alternative to the multi-junction solar cell shown in Figure 4 An alternative to the multi-junction solar cell shown in Figure 4 An alternative to the solar cell shown in Figures 1 to 3 The multi-junction solar cell 1 shown can also be a 3T multi-junction solar cell. This multi-junction solar cell 1 has an upper sub-cell with an absorber 15 and a lower sub-cell with an absorber 21. The lower sub-cell is designed as an IBC cell.

[0100] Figure 5 The illustrated stacked multi-junction solar cell has a front side 100, a back side 101 and the following layer structure:

[0101] - a front side contact 11,

[0102] - a reflective layer 28,

[0103] - an absorber 15, for example a perovskite absorber,

[0104] - a reflective layer 28,

[0105] - an intermediate layer 26,

[0106] - a reflective layer 28,

[0107] - a further absorber 21, for example a silicon absorber,

[0108] - a p-type emitter region 29 and an n-type emitter region 30, and

[0109] - a back side contact 25, arranged in strips on the p-type emitter region 29 and the n-type emitter region 30.

[0110] wherein the above-mentioned stacked multi-junction solar cell is provided as a three-terminal solar cell, having three electrical connection points 27.

[0111] Figure 6 is Figure 1 The illustrated method provides for a further multi-junction solar cell, which can be used as Figure 4 and Figure 5 The illustrated multi-junction solar cell is provided as a 4T multi-junction solar cell. This multi-junction solar cell 1 consists of an upper sub-cell containing an absorber 15 and a lower sub-cell containing a silicon absorber 21. Its layer structure is as follows:

[0112] - a front side contact 11 of the upper sub-cell,

[0113] - a reflective layer 28,

[0114] - an absorber 15, for example a perovskite absorber,

[0115] - a reflective layer 28,

[0116] - a back side contact 25 of the upper sub-cell,

[0117] - an intermediate layer 26,

[0118] - a front side contact 11 of the lower sub-cell,

[0119] - a reflective layer 28,

[0120] - another absorber 21, for example a silicon absorber,

[0121] - a reflective layer 28, and

[0122] - a back contact 25 of the lower sub-cell.

[0123] wherein each of the upper and lower sub-cells has one front contact 11 and one back contact 25, each set of contacts being electrically connected by two of the four electrical connection points 27.

Claims

1. A method for improving the contact resistance of a multi-junction solar cell (1) having a front side (100), a back side (101), and multiple sub-cells (2, 3), the method comprising: a) A multi-junction solar cell (1) is configured with a front contact (11) and a back contact (25), wherein the front contact (11) and / or the back contact (25) are grid-shaped, strip-shaped, or transparent. b) One area of ​​the back contact (25) is electrically in contact with a contact device (4) electrically connected to one pole of a voltage source (9), and one area of ​​the front contact (11) or another area of ​​the back contact (25) is electrically in contact with another contact device (4), wherein one area of ​​the back contact (25) and another area of ​​the back contact (25) are insulated from each other, and the other contact device (4) is electrically connected to the other pole of the voltage source (9). c) A voltage source (9) applies a voltage opposite to that of the multijunction solar cell (1) to one and another contact device (4), the magnitude of which is lower than the breakdown voltage of the multijunction solar cell (1). d) During the application of voltage, at least one point light source (5) is directed to illuminate one or more segments (6) of a local area of ​​the front (100) and / or back (101) of the multijunction solar cell (1), thereby inducing current in the corresponding local area and acting on the corresponding local area, wherein one or more segments of the local area are illuminated by the point light source (5) with multiple beams (7, 8) of different wavelengths; The at least one point light source (5) includes multiple flash lamps with different spectral filters. Alternatively, the at least one point light source (5) may include a laser device having multiple lasers designed to emit lasers of different wavelengths. Alternatively, the at least one point light source (5) may include a laser device with a laser and a frequency multiplier.

2. The method of claim 1, wherein, Multiple light beams (7, 8) of different wavelengths simultaneously irradiate a segment (6) of a local area, and the areas irradiated by the multiple light beams (7, 8) of different wavelengths at least partially overlap.

3. The method of claim 1, wherein, Guide the at least one point light source (5) to the front (100) or back (101) of the multijunction solar cell (1).

4. The method according to one of the preceding claims, characterized in that, Each sub-cell (2, 3) has an absorber, and each wavelength of the selected plurality of beams (7, 8) is adapted to the absorption coefficient of each absorber.

5. The method according to any one of claims 1 to 3, characterized in that, One of the multiple sub-cells (2, 3) is a perovskite sub-cell.

6. The method according to any one of claims 1 to 3, characterized in that, One of the multiple sub-cells (2, 3) has a silicon-based absorber.

7. The method according to any one of claims 1 to 3, characterized in that, The multijunction solar cell (1) consists of an upper sub-cell (2) and a lower sub-cell (3), forming a 2T, 3T or 4T multijunction solar cell.

8. The method according to any one of claims 1 to 3, characterized in that, The multijunction solar cell (1) has an upper subcell (2), a lower subcell (3) and at least one intermediate subcell.

9. The method according to any one of claims 1 to 3, characterized in that, In step d), the number of wavelengths of the multiple light beams corresponds to the number of sub-cells or absorbers of the sub-cells, and each wavelength is matched with the absorption coefficient of the absorber.

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