A filter layer for testing sub-cell current of a solar cell, a test piece and a preparation method of the test piece

Abstract

The application discloses a filter layer for testing the sub-cell current of a solar cell, a test piece and a preparation method of the test piece. The filter layer is designed with reference to a solar cell, and the solar cell is composed of a stacked substrate, a to-be-tested sub-cell and an upper sub-cell. The upper sub-cell comprises a back field, a base region, an emission region and a window layer which are stacked. The doping type of the filter layer is the same as that of the emission region. The filter layer comprises a first filter layer, a second filter layer and a third filter layer which are stacked. The material of the first filter layer is the same as that of the back field. The material of the second filter layer is the same as that of the emission region. The doping concentration of the second filter layer is greater than or equal to 8*10 18 . The material of the third filter layer is the same as that of the cap layer. The doping concentration of the third filter layer is 5*10 16 -1*10 18 . The filter layer can accurately obtain the current of the to-be-tested sub-cell. The application further provides a test piece comprising the filter layer and a preparation method of the test piece.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a filter layer, a test piece, and a method for preparing the test piece for testing the sub-cell current of a solar cell. Background Technology

[0002] Among various solar cell technologies, III-V compound multi-junction solar cells boast the highest conversion efficiency. Furthermore, due to their high power-to-weight ratio, they are widely used in power systems for aerospace applications. However, the harsh operating environment of spacecraft, exposed to high-energy charged particles, high vacuum, extreme temperature shocks, and atomic oxygen, causes varying degrees of degradation in the individual sub-cells of multi-junction solar cells. As is well known, the sub-cells of a multi-junction cell are connected in series, and the overall output current depends on the minimum current of each sub-cell. For example, in a lattice-matched GaInP / Ga(In)As / Ge triple-junction cell, experimental data shows that after irradiation, GaInAs sub-cells degrade significantly more than GaInP sub-cells, easily becoming current-limiting junctions. Conversely, if the current design of the InGaAs sub-cell before irradiation is too high, leading to current limitation in the top GaInP sub-cell, the optimal conversion efficiency will also be compromised. Therefore, combining the space solar spectrum and the irradiation degradation patterns of each sub-cell, and rationally designing the current of each junction sub-cell, is crucial for improving the final photoelectric conversion efficiency of space solar cells.

[0003] Currently, most methods for testing sub-cell current employ the method of saturating the non-sub-cell under test with a bandpass filter, testing the EQE curve (external quantum efficiency) of the multi-junction cell, and then calculating the integrated current of the sub-cell under test. This method has extremely high requirements for the quality of the multi-junction solar cell, and the test results often show varying degrees of leakage in the short-wave band (400~700nm for neutron cells matched with triple junction cells), resulting in inaccurate integrated current of the sub-cell under test.

[0004] The test piece for the intermediate sub-cell is usually prepared by adding a filter layer on top of the sub-cell. However, due to the photoelectric coupling effect, specifically the absorption of fluorescent photons emitted by the filter layer material under illumination by the sub-cell under test, a photocurrent is generated, resulting in a high integrated current. Therefore, the accurate value of the integrated current of the sub-cell under test cannot be obtained.

[0005] In summary, existing test specimens cannot obtain accurate integrated current values, and therefore cannot provide effective data references for the design of multi-junction cells. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a filter layer for testing the sub-cell current of a solar cell. This filter layer can effectively simulate the light exposure of the sub-cell under test in a multi-junction solar cell, thereby achieving the purpose of accurately calculating the current of the sub-cell under test and providing reliable data support for the design of high-efficiency multi-junction tandem solar cells.

[0007] The present invention also provides a test piece including the above-described filter layer.

[0008] The present invention also provides a method for preparing the above-mentioned test specimen.

[0009] According to an embodiment of the first aspect of the present invention, a filter layer for testing the current of a solar cell sub-cell is provided, wherein the solar cell includes a substrate, a sub-cell under test, and an upper sub-cell disposed sequentially.

[0010] The upper sub-cell includes a back field, a base region, an emitter region, and a window layer that are stacked together.

[0011] The doping type of the filter layer is the same as the doping type of the emission region;

[0012] The filter layer includes a first filter layer, a second filter layer, and a third filter layer stacked together;

[0013] The material of the first filter layer is the same as the material of the back field;

[0014] The material of the second filter layer is the same as that of the emission region; the doping concentration of the second filter layer is ≥8×10⁻⁶. 18 / cm 3 ;

[0015] The material of the third filter layer is the same as that of the window layer; the doping concentration of the third filter layer is 5×10⁻⁶. 16 ~1×10 18 / cm 3 .

[0016] The design principle of the test piece in this invention is as follows:

[0017] In traditional techniques, testing the current of a subcell in a multi-junction solar cell, such as testing the current of the middle cell in a triple-junction solar cell, typically employs the following method, which will be illustrated below using the current testing of the GaAs subcell in a Ge / GaAs / GaInP subcell as an example:

[0018] To measure the photocurrent of a GaAs subcell, two additional bias light sources are needed to generate excess current in both the GaInP and Ge subcells, making the GaAs subcell a current-limited subcell, with the system output current equal to the photocurrent of the GaAs subcell. This allows for the measurement of the quantum efficiency curve of GaAs. The same method can be used to measure the quantum efficiency of the GaInP subcell, but not the Ge subcell.

[0019] After applying a bias voltage of approximately -2.0V, the EQE curve of the Ge sub-cell before irradiation was obtained. The results showed a high EQE value in the 700-880nm range, with a trough near 880nm. This measurement of the Ge sub-cell clearly does not reflect reality: First, photons in the 700-880nm wavelength range are primarily absorbed by the GaAs sub-cell, and the quantum efficiency of the GaAs sub-cell can reach over 85%. Even if a small portion of photons are not absorbed, the EQE caused by the bottom cell would not exceed 15%. Second, the absorption coefficient of the material used in the Ge sub-cell increases with decreasing wavelength, thus preventing the abnormal quantum efficiency trough near 880nm. However, the test results show that the quantum efficiency of the Ge sub-cell is approximately 60%, significantly lower than the actual level, indicating the presence of abnormal "artifacts."

[0020] The triple-junction solar cell was irradiated with 380 keV protons. The range of the particles was sufficient to cause significant damage to GaAs, but not enough to affect the Ge sub-cell. The spectral response of the irradiated Ge sub-cell was tested using the same testing method. The results showed that the Ge sub-cell exhibited opposite degradation patterns in the 700-880 nm and 880-1800 nm ranges. In the 700-880 nm range, the quantum efficiency almost decreased to zero; in the 880-1800 nm range, the quantum efficiency actually increased after irradiation. This result is clearly unusual, and the reason for this is the "coupling" effect between the Ge sub-cell and other sub-cells. The above anomaly can be explained using the physical model of fluorescence coupling in multi-junction solar cells established by researchers: the fluorescence coupling effect between sub-cells in III-V group multi-junction solar cells leads to a "spurious signal" in the quantum efficiency measurement of narrow bandgap cells. This phenomenon occurs when the photocurrent of the Ge sub-cell is less than that of the GaAs and GaInP sub-cells; in other words, it occurs when the infrared light flux is much less than the visible light flux. Because the spectrum during the test is different from AM0, the Ge sub-cell is in a reverse-biased breakdown state, reducing the conversion efficiency of the multi-junction solar cell.

[0021] In summary, traditional testing methods are insufficient for testing the current of the bottom cell or the cell with the lowest photocurrent, and cannot accurately reflect the performance of the cell after irradiation. Therefore, they cannot provide guidance for the design of high-efficiency multi-junction tandem solar cells.

[0022] However, in reality, radiative emission not only increases the open-circuit voltage of its own sub-cell but also affects other sub-cells. Considering the escape of radiated photons, these escaped secondary photons can be absorbed again by the materials of other sub-cells; this process is called photo recycling (PR). For example, secondary photons from a GaInP sub-cell are absorbed not only by itself but also by GaAs sub-cells. This causes an increase in the short-circuit current of the GaAs sub-cell. During the EQE test of multi-junction solar cells, the intensity of the EQE monochromatic light is much lower than that of the bias light, so the sub-cell under test is in a short-circuit state, while the sub-cell absorbing the bias light is in a quasi-open-circuit state. In the GaAs / Ge sub-cell system, when measuring the spectral response of the Ge sub-cell at 800 nm, GaAs has a larger short-circuit current and is in a quasi-open-circuit state with a higher bias voltage. In spectrally matched multi-junction cells, the difference in short-circuit current between sub-cells is not significant. Although some sub-cells are in an overcurrent state, the bias voltages on both sides are relatively small, insufficient to cause significant photoelectric coupling. For real multi-junction solar cells, the effect of photoelectric coupling between cells is mainly reflected in the contribution of radiated secondary photons to the lower sub-cells.

[0023] Therefore, to test the current of a cell under irradiation or after radiation, the test specimen should include the adjacent cells of the cell under test to provide a more accurate reference.

[0024] However, simply growing a filter layer on the cell under test, with the filter layer being equivalent to the upper sub-cell on the light-emitting side of the cell under test, fails to accurately simulate the light-receiving behavior of the cell within the entire structure. This is because the emitting region of the upper sub-cell lacks the built-in electric field of the PN junction to effectively separate the electron-hole pairs generated after light exposure. Furthermore, continuous radiative recombination within other auxiliary layers produces strong fluorescence peaks, leading to a significant rise in the EQE curve in the 400-600 nm wavelength range, deviating considerably from the normal range. In other words, if the cell under test and its adjacent upper sub-cell are extracted from the solar cell to form a test specimen, and the upper sub-cell is used as a filter layer, the results will deviate from the true values ​​due to an improperly designed doping concentration in the upper sub-cell.

[0025] There are two methods to eliminate or reduce photoelectric coupling effects: one is to avoid growing heterojunction materials that enhance fluorescence efficiency; the other is to reduce the fluorescence intensity of the filter layer material. However, materials that enhance fluorescence efficiency are usually part of the reflective coating. Without this material, the test specimen has high reflectivity to the received light, resulting in the spectrum entering the test specimen being different from the spectrum of the full cell of the solar cell, thus lacking practical reference value.

[0026] The filter layer according to embodiments of the present invention has at least the following beneficial effects:

[0027] The filter layer provided by this invention has similar performance to the upper sub-cell, which can fully simulate the performance of the sub-cell under test in the irradiation and light environment, providing a convenient and reliable experimental method for designing a battery with excellent radiation resistance. It also avoids the preparation of other sub-cells in the solar cell under test, thus saving costs.

[0028] This invention reduces the valence band top height of the second filter layer and increases the valence band top height of the third filter layer by designing the composition and doping concentration of the filter layers. This ultimately lowers the potential barrier height between the second and third filter layers. Furthermore, a window layer with a lower doping concentration is typically provided on the side of the sub-cell under test near the filter layer, thus reducing the potential barrier height between the window layer and the second filter layer. This weakens the confinement of minority carriers by the heterojunction, reducing the fluorescence effect and eliminating the photoelectric coupling effect or fluorescence coupling effect. In addition, the numerous defects generated by the heavily doped second filter layer cause nonradiative recombination of electron-hole pairs, thereby reducing the influence of the photoelectric coupling effect or fluorescence coupling effect. Therefore, the prepared test piece can be used to test the current of the sub-cell under test, and the test results are closer to the true value (i.e., solving the negative impact of the photon cycling effect in the filter layer on the integrated current of the sub-cell under test).

[0029] According to some embodiments of the present invention, the solar cell has ≥2 junctions. Specifically, for example, the solar cell may be a two-junction solar cell, a three-junction solar cell, a four-junction solar cell, a five-junction solar cell, or a six-junction solar cell.

[0030] According to some embodiments of the present invention, the solar cell further includes a first tunnel junction disposed on the side of the cell under test near the substrate, and a second tunnel junction disposed on the side of the cell under test away from the substrate.

[0031] According to some embodiments of the present invention, the solar cell further includes a buffer layer disposed between the substrate and the first tunnel junction.

[0032] According to some embodiments of the present invention, the substrate is a Ge substrate or a GaAs substrate.

[0033] According to some embodiments of the present invention, the substrate is p-type doped. Further, the thickness of the p-type doped portion of the substrate is 130-150 μm; the doping concentration is 8 × 10⁻⁶. 17 ~5×10 18 / cm 3 .

[0034] According to some embodiments of the present invention, the substrate is the first sub-cell of the solar cell. Specifically, N-type doping is performed on the surface of the substrate near the sub-cell under test, thereby forming a PN junction in the substrate, which exists as the first sub-cell.

[0035] According to some embodiments of the present invention, the method for forming N-type doping in the substrate includes atomic diffusion of phosphorus using PH3 as a phosphorus source, and the diffusion region forms the N-type emitter region of the first sub-cell. The doping concentration of the N-type emitter region in the first sub-cell is 8 × 10⁻⁶. 17 ~5×10 18 / cm 3 .

[0036] According to some embodiments of the present invention, the thickness of the N-type emitter region of the first sub-cell is 50–150 nm.

[0037] According to some embodiments of the present invention, the band gap of the first sub-cell is 0.66~0.67eV.

[0038] According to some embodiments of the present invention, the buffer layer is an N-type buffer layer.

[0039] The doping concentration of the N-type buffer layer is 1×10⁻⁶. 18 ~5×10 18 / cm 3 .

[0040] According to some embodiments of the present invention, the buffer layer is made of GaInAs.

[0041] According to some embodiments of the present invention, the thickness of the buffer layer is 300–800 nm.

[0042] According to some embodiments of the present invention, the thickness of the first tunnel junction is 10 to 100 nm.

[0043] The doping concentration of the first tunnel junction is ≥1×10 19 / cm 3 Specifically, the tunnel junction consists of two layers: an N-type doped structure and a P-type doped structure.

[0044] According to some embodiments of the present invention, the thickness of the sub-cell under test is 2000–3500 nm. For example, it can be 2900–3000 nm or 3000–3100 nm.

[0045] According to some embodiments of the present invention, the band gap of the sub-cell under test is 1.1~1.42eV.

[0046] According to some embodiments of the present invention, the cell under test includes a P-type back field layer, a P-type base region layer, an N-type emission region and an N-type window layer stacked sequentially; the N-type window layer is disposed on the side of the cell under test near the filter layer.

[0047] According to some embodiments of the present invention, the sub-cell under test includes a GaInAs sub-cell.

[0048] According to some embodiments of the present invention, the thickness of the P-type back field layer of the GaInAs sub-cell is 45~150 nm.

[0049] According to some embodiments of the present invention, the thickness of the P-type base layer of the GaInAs sub-cell is 1900~2500 nm. The doping concentration is 2×10⁻⁶. 18 ~5×10 18 / cm 3 .

[0050] According to some embodiments of the present invention, the thickness of the N-type emitter region of the GaInAs sub-cell is 50~300 nm. The doping concentration is 1×10⁻⁶. 17 ~2×10 18 / cm 3 .

[0051] According to some embodiments of the present invention, the thickness of the N-type window layer of the GaInAs sub-cell is 5~50 nm.

[0052] According to some embodiments of the present invention, the thickness of the second tunnel junction is 10~100 nm.

[0053] According to some embodiments of the present invention, the doping concentration of the second tunnel junction is >1×10⁻⁶. 19 / cm 3 .

[0054] According to some embodiments of the present invention, the thickness of the upper sub-cell is 600~800nm.

[0055] According to some embodiments of the present invention, in the upper sub-cell, the distance between the back field and the sub-cell under test is less than the distance between the window layer and the sub-cell under test.

[0056] According to some embodiments of the present invention, the back surface and base region of the upper sub-cell are made of P-type material.

[0057] According to some embodiments of the present invention, the emitter region and window layer of the upper sub-cell are made of N-type material.

[0058] According to some embodiments of the present invention, the band gap of the upper sub-cell is 1.8 to 1.95 eV.

[0059] According to some embodiments of the present invention, the upper sub-cell is selected from GaInP sub-cells.

[0060] According to some embodiments of the present invention, the solar cell further includes a cap layer disposed on the side of the upper sub-cell away from the substrate.

[0061] The cap layer is made of N-type GaInAs; the N-type doping concentration is >2×10⁻⁶. 18 / cm 3 .

[0062] The thickness of the cap layer is 300~500nm.

[0063] According to some embodiments of the present invention, the solar cell is a triple-junction solar cell, specifically comprising, in sequence: a substrate, a buffer layer, a first tunnel junction, a subcell under test, a second tunnel junction, an upper subcell, and a cap layer.

[0064] Furthermore, in the solar cell, a tunnel junction is provided between every two sub-cells; the solar cell is not limited to a three-junction configuration. The tunnel junction ensures that each sub-cell maintains lattice matching with the substrate.

[0065] According to some embodiments of the present invention, the thickness of the first filter layer is equal to the thickness of the back field.

[0066] Considering the compatibility between the second filter layer and the existing industrial structure of the sub-cell under test, the doping concentration of the first filter layer has a relatively small impact on the performance of the filter layer. For example, the doping concentration can specifically be 5 × 10⁻⁶. 16 ~5×10 18 / cm 3 Further, it could be 8×10 17 ~2×10 18 / cm 3 .

[0067] According to some embodiments of the present invention, the thickness of the second filter layer is equal to the sum of the thicknesses of the base region and the emission region.

[0068] According to some embodiments of the present invention, the thickness of the third filter layer is equal to the thickness of the window layer.

[0069] The thickness of each layer also affects the photon cycling phenomenon to some extent. If the thickness of the filter layer is set to the above thickness, the current of the sub-cell under test after space irradiation can be measured more accurately.

[0070] According to an embodiment of a second aspect of the present invention, a test piece is provided, the test piece comprising, in sequence, a substrate, a sub-cell under test, a filter layer as described in any one of claims 1 to 6, and a cap layer;

[0071] The distance between the first filter layer and the sub-cell under test is less than the distance between the third filter layer and the sub-cell under test.

[0072] The test specimen according to embodiments of the present invention has at least the following beneficial effects:

[0073] The test piece provided by this invention is applicable to multi-junction solar cells, allowing for current testing of all sub-cells except the top cell. Specifically, a filter layer can be designed based on the nearest upper sub-cell facing the light source of the sub-cell under test. Furthermore, this test piece can also be used to test the current of the bottom cell. It has high applicability to various types of solar cells and sub-cells within the same solar cell, thus showing broad prospects in industrial design and production.

[0074] According to some embodiments of the present invention, the doping type of the filter layer is N-type doping.

[0075] According to some embodiments of the present invention, the test piece further includes a buffer layer disposed between the substrate and the subcell under test.

[0076] According to some embodiments of the present invention, the test piece further includes a first tunnel junction disposed between the buffer layer and the sub-cell under test.

[0077] According to some embodiments of the present invention, the test piece further includes a second tunnel junction disposed between the sub-cell under test and the filter layer.

[0078] According to some embodiments of the present invention, the test piece includes a substrate, a buffer layer, a first tunnel junction, a cell under test, a second tunnel junction, a filter layer, and a cap layer, which are stacked sequentially.

[0079] The test piece can be used to test the current of intermediate cells in lattice-matched or lattice-mismatched solar cells.

[0080] According to an embodiment of a second aspect of the present invention, a method for preparing the test piece is provided, the method comprising designing the structure of the test piece according to the structure of the solar cell, and then sequentially disposing the sub-cell under test, a filter layer, and a cap layer on the substrate.

[0081] Since the preparation method adopts all the technical solutions of the test pieces in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments. Specifically, the test pieces can be produced using instruments and methods compatible with traditional solar cell preparation methods, without the need for additional new preparation instruments, and the resulting test pieces have a wide range of applications.

[0082] According to some embodiments of the present invention, the method of setting up includes at least one of metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE).

[0083] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0084] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0085] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0086] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0087] Figure 1 This is a schematic diagram of the structure of the solar cell used in Embodiment 1 of the present invention;

[0088] Figure 2 This is a schematic diagram of the structure of the test piece provided in Embodiment 1 of the present invention.

[0089] Figure 3 These are the EQE curves of the solar cell and the provided test specimen used in Example 1.

[0090] Figure label:

[0091] Substrate 100, buffer layer 200, first tunnel junction 310, second tunnel junction 320, sub-cell under test 400, upper sub-cell 500, cap layer 600;

[0092] First filter layer 710, second filter layer 720, third filter layer 730. Detailed Implementation

[0093] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0094] In the description of this invention, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of technical features indicated, or implicitly indicating the order of the technical features indicated.

[0095] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0096] In the description of this invention, it should be noted that, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0097] In specific implementations, if each parameter is a range value, it indicates that systematic errors from the test have been taken into account. For example, 90~110nm means that the actual designed thickness is approximately 100nm, but testing errors and possible errors during the fabrication process are taken into account, hence the representation as 90~110nm. Furthermore, within the above range, there will be no significant impact on the results of the solar cell.

[0098] Example 1

[0099] This embodiment prepares a test piece for testing the current of a solar cell sub-cell, as detailed below:

[0100] refer to Figure 1 The triple-junction solar cell fabrication test specimen shown is as follows: The triple-junction solar cell consists of a substrate 100, a buffer layer 200, a first tunnel junction 310, a sub-cell under test 400, a second tunnel junction 320, an upper sub-cell 500, and a cap layer 600, which are sequentially stacked. The parameters of each structure are shown in Table 1.

[0101] Table 1. Parameters of solar cells used in Example 1

[0102]

[0103] In Table 1:

[0104] The preparation method of N-type Ge is as follows: using PH3 as a phosphorus source to carry out atomic diffusion of phosphorus, and the diffusion region forms the N-type emission region of the first sub-cell (substrate).

[0105] The sub-cell under test comprises, sequentially stacked from the first tunnel junction, a P-type back field layer (90~110nm), a P-type base region layer (1900~2100nm), an N-type emitter region (80~120nm), and an N-type window layer (25~45nm) (undoped AlInP, with a doping concentration of 5×10⁻⁶). 16 ~2×10 18 Furthermore, the material of the N-type emitter region is N-type GaInAs.

[0106] In Table 1, blank areas indicate that the design of the test piece's structure and performance has no impact and can be designed according to industry practices, or that there are no corresponding parameters.

[0107] The structural reference of the test piece provided in this embodiment Figure 2 As shown, its sum Figure 1 The structural difference of the solar cell shown is that the upper sub-cell 500 is replaced with a light filter layer 700; wherein:

[0108] The filter layer includes a first filter layer 710, a second filter layer 720 and a third filter layer 730, which are stacked sequentially starting from the second tunnel junction 320.

[0109] Furthermore, the first filter layer and the upper sub-cell have the same P-type back surface thickness and material, but the latter is N-type doped with a doping concentration of 8 × 10⁻⁶. 17 ~2×10 18 / cm 3 ;

[0110] The thickness of the second filter layer is the same as the sum of the thicknesses of the P-type base region and the N-type emitter region of the upper sub-cell; the entire layer is N-type doped with a doping concentration of 2 × 10⁻⁶. 19 ~6×10 19 / cm 3 ;

[0111] The thickness and material of the third filter layer are the same as those of the N-type window layer of the upper sub-cell, and the specific concentration is 4×10⁻⁶. 17 ~6×10 17 / cm 3 Doping.

[0112] In this embodiment, apart from the substrate, the fabrication methods for each structure include metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). In this embodiment, metal-organic chemical vapor deposition (MOCVD) is preferred.

[0113] Test case

[0114] This test example tested the quantum efficiency (EQE) curves of the solar cell referenced in Example 1 and the prepared test piece, and obtained parameters such as Jsc, Voc, FF, Eff, and integral current for both. The tests were performed using a Bentham PV_ENCLOSURE system, which can be used to test the spectral responses of GaInAs neutron cells (sub-cells under test) and GaInP top-cell cells in the wavelength range of 300 nm to 1100 nm. The test results are as follows: Figure 3 As shown in Table 2.

[0115] Table 2 shows the electrical properties and EQE integral current of the solar cells and GaInAs sub-cells in different environments referenced in the embodiments.

[0116] Content Description <![CDATA[Jsc (mA / cm 2 )]]> Voc (mV) FF (%) Eff (%) GaInAs sub-cell EQE integral current Solar cell (triple junction) 17.69 2758.5 88.1 31.78 17.11 Sub-cell under test (before optimization) 27.45 1315.6 82.78 22.09 24.37 Sub-cell under test (after optimization) 19.64 1312.9 85.92 16.37 19.09

[0117] In Table 2, the solar cell (triple junction) refers to the solar cell used in Example 1 shown in Table 1; the sub-cell under test (after optimization) refers to the sub-cell under test tested in the test specimen provided in Example 1; in the sub-cell under test (before optimization), the difference between the test environment of the sub-cell under test and the test specimen of Example 1 is that the second filter layer was not heavily doped (doping concentration < 8 × 10⁻⁶). 18 / cm 3 The specific doping concentration is approximately 5 × 10⁻⁶. 18 / cm 3 .

[0118] The results show that the test specimen provided by this invention has a reasonably designed filter layer. Specifically, the valence band top height is reduced by using GaInP (second filter layer) in the heavily doped filter layer, and the valence band top height is increased by using AlGaInP (first filter layer) and AlInP (third filter layer) in the lightly doped filter layer. This reduces the potential barrier height between the second filter layer and the first filter layer (ΔEp1'<ΔEp1) and between the second filter layer and the third filter layer (ΔEp2'<ΔEp2), weakening the confinement of minority carriers by the heterojunction and thus reducing the fluorescence effect. At the same time, the large number of defects generated by the heavy doping of GaInP causes nonradiative recombination of electron-hole pairs, thereby reducing the influence of the "photoelectric coupling effect" or "fluorescence coupling effect".

[0119] Table 2 and Figure 3 The test results also show that the electrical performance information obtained from the test piece is closer to the actual value of the sub-cell under test in the solar cell.

[0120] Furthermore, the terminal efficiency of a solar cell is the efficiency measured after the cell has undergone performance degradation due to irradiation by the space environment (including charged particles, high and low temperatures, atomic oxygen, etc.). Since the terminal photoelectric conversion efficiency is related to the irradiation degradation mechanism of each sub-cell, determining the sub-cell integral current can provide a reliable basis for designing solar cells with high terminal efficiency. Therefore, the test piece and its preparation method provided by this invention can ensure accurate testing of the sub-cell integral current, thereby providing a foundation for designing solar cells with high terminal efficiency.

[0121] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A filter layer for testing the sub-cell current of a solar cell, the solar cell comprising a substrate, a sub-cell under test, and an upper sub-cell stacked sequentially; the upper sub-cell comprising a back surface region, a base region, an emitter region, and a window layer stacked sequentially; characterized in that, The doping type of the filter layer is the same as the doping type of the emission region; The filter layer includes a first filter layer, a second filter layer, and a third filter layer stacked together; The material of the first filter layer is the same as the material of the back field; The material of the second filter layer is the same as that of the emission region; the doping concentration of the second filter layer is ≥8×10⁻⁶. 18 / cm 3 ; The material of the third filter layer is the same as that of the window layer; the doping concentration of the third filter layer is 5×10⁻⁶. 16 ~1×10 18 / cm 3 ; The thickness of the first filter layer is equal to the thickness of the back field; the thickness of the second filter layer is equal to the sum of the thicknesses of the base region and the emission region; the thickness of the third filter layer is equal to the thickness of the window layer.

2. The filter layer according to claim 1, characterized in that, The filter layer is doped with N-type doping.

3. The filter layer according to claim 1, characterized in that, The solar cell has ≥2 junctions.

4. The filter layer according to claim 1, characterized in that, The substrate is a Ge substrate or a GaAs substrate.

5. The filter layer according to any one of claims 1 to 4, characterized in that, The sub-cell under test includes a P-type back field layer, a P-type base region layer, an N-type emission region layer, and an N-type window layer stacked sequentially; the N-type window layer is located on the side of the sub-cell under test near the filter layer.

6. A test piece, characterized in that, The test piece includes, in sequence, the substrate, the sub-cell under test, the filter layer as described in any one of claims 1 to 5, and the cap layer; The distance between the first filter layer and the sub-cell under test is less than the distance between the third filter layer and the sub-cell under test.

7. The test piece according to claim 6, characterized in that, The test piece also includes a buffer layer disposed between the substrate and the sub-cell under test.

8. The test piece according to claim 7, characterized in that, The test piece also includes a first tunnel junction disposed between the buffer layer and the sub-cell under test.

9. The test piece according to claim 6, characterized in that, The test piece also includes a second tunnel junction disposed between the sub-cell under test and the filter layer.

10. A method for preparing a test specimen as described in any one of claims 6 to 9, characterized in that, The preparation method includes designing the test piece structure according to the structure of the solar cell, and then sequentially setting the sub-cell under test, the filter layer, and the cap layer on the substrate.

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