Monochromatic photovoltaic cell, photovoltaic energy storage device and photovoltaic energy storage system

Abstract

The invention provides a monochromatic photovoltaic cell which can be applied to scenes of radio communication, industrial sensors, national defense, aviation, medicine, energy and the like. The photovoltaic cell provided by the invention is relatively high in photoelectric conversion efficiency, relatively large in open-circuit voltage and good in cell performance. Specifically, the monochromatic photovoltaic cell provided by the invention comprises a window layer and a plurality of sub-junction regions which are vertically stacked, each sub-junction region in the plurality of sub-junction regions comprises an absorption layer and a back reflection layer, and the refractive index difference of the plurality of sub-junction regions except the bottom sub-junction region in the plurality of sub-junction regions is gradually increased along a first direction. The refractive index difference is the refractive index difference between the absorption layer and the back reflection layer of each sub-junction region, the first direction is the direction from the window layer of the monochromatic photovoltaic cell to the direction away from the window layer, and the bottom sub-junction region is the last sub-junction region along the first direction.

Description

Technical Field

[0001] The present application relates to the field of laser photovoltaic cells, and specifically, to a monochromatic photovoltaic cell, a photovoltaic energy storage device and a photovoltaic energy storage system. Background Art

[0002] The laser energy supply system transmits the light emitted by the laser light source to the laser photovoltaic cell through optical fiber, which can provide a stable power output. Among them, the working principle of the laser photovoltaic cell is similar to that of the solar cell, but because it is a monochromatic light source, the former can obtain a higher conversion efficiency. Unlike ordinary solar cells, the light source uses a laser with a wavelength of 790nm-850nm.

[0003] The conversion efficiency of photovoltaic cells refers to the efficiency of converting light energy into electrical energy, and is an important indicator for measuring the performance of photovoltaic cells. The photon-to-electron conversion efficiency (PCE) of existing monochromatic photovoltaic cells is around 50%. How to improve the photon-to-electron conversion efficiency of photovoltaic cells is a problem that needs to be solved. Summary of the invention

[0004] The present application provides a monochromatic photovoltaic cell, a photovoltaic energy storage device and a photovoltaic energy storage system. The photovoltaic cell provided in the present application has a high photoelectric conversion efficiency, a large open circuit voltage and good battery performance. It can be applied to lasers in the wavelength range of 800nm ​​to 900nm and has the excellent characteristic of a conversion efficiency greater than 50%.

[0005] In a first aspect, an embodiment of the present application provides a monochromatic photovoltaic cell. The monochromatic photovoltaic cell comprises a window layer and a plurality of vertically stacked sub-junction regions, each of the plurality of sub-junction regions comprises an absorption layer and a back reflection layer, wherein: the refractive index difference of the plurality of sub-junction regions except the bottom layer sub-junction region among the plurality of sub-junction regions gradually increases along a first direction, the refractive index difference being the refractive index difference between the absorption layer and the back reflection layer of each sub-junction region, the first direction being a direction from the window layer to a direction away from the window layer, and the bottom layer sub-junction region being the last sub-junction region along the first direction.

[0006] It should be noted that when the monochromatic photovoltaic cell provided in the present application is working, it can convert the light energy of the incident laser into electrical energy, wherein the direction of the incident laser is incident from the window layer of the monochromatic photovoltaic cell, and reaches the conductive layer after passing through a plurality of vertically stacked sub-junction regions in sequence. Therefore, the first direction mentioned above is the same as the incident direction of the incident laser.

[0007] In addition, the refractive index difference of the plurality of sub-junction regions gradually increases along the first direction means that, among the plurality of sub-junction regions arranged along the first direction, the refractive index difference corresponding to the latter sub-junction region increases compared to the refractive index difference corresponding to the former sub-junction region.

[0008] Based on the method provided in the present application, by gradually increasing the refractive index difference between the absorption layer and the back reflection layer, the reflection of the incident laser is gradually enhanced, thereby enhancing the photon absorption efficiency, thereby achieving the effect of improving the photoelectric conversion efficiency.

[0009] In combination with the first aspect, in some implementations of the first aspect, the absorption layer of each sub-junction region is aluminum gallium arsenide Al y Ga 1-y As material, the back reflection layer of each of the plurality of sub-junction regions except the bottom sub-junction region is made of aluminum gallium arsenide Al x Ga 1-x As material, wherein the value of x along the first direction gradually increases, the value of y along the first direction is the same, x and y are used to represent the proportion of aluminum element in the aluminum gallium arsenide material, 1-x is used to represent the proportion of gallium element in the aluminum gallium arsenide material of the absorption layer, 1-y is used to represent the proportion of gallium element in the aluminum gallium arsenide material of the back reflection layer, x and y are real numbers greater than or equal to 0 and less than 1, and x is greater than y.

[0010] In some embodiments, the material of the absorption layer of each sub-junction region can be set to AlGaAs Al 0.08 Ga 0.92 As material, which can effectively match 808nm laser and improve conversion efficiency. In other embodiments, the material of the absorption layer of each sub-junction region can be set to gallium arsenide GaAs material, which can effectively match 850nm laser and improve conversion efficiency.

[0011] In combination with the first aspect, in certain implementations of the first aspect, each sub-junction region also includes an emission layer, and the multiple sub-junction regions include at least one non-identical sub-junction region, and the non-identical sub-junction region is a sub-junction region in which the material of the emission layer is different from the material of the absorption layer.

[0012] It can be understood that the sub-junction region corresponding to the non-identical sub-junction region can be called an identical sub-junction region, that is, the identical sub-junction region is a sub-junction region where the material of the emission layer and the material of the absorption layer are the same.

[0013] By providing at least one non-identical junction region, the output voltage can be precisely controlled while further optimizing the photoelectric conversion efficiency of the battery.

[0014] In combination with the first aspect, in some implementations of the first aspect, the at least one non-identical sub-junction region is at least one sub-junction region that is arranged adjacent to the underlying sub-junction region.

[0015] By arranging at least one non-identical subjunction region adjacent to the last few junctions of a photovoltaic cell, the photoelectric conversion efficiency of the cell can be ensured.

[0016] In combination with the first aspect, in some implementations of the first aspect, a tunnel layer is provided between two adjacent sub-junction regions among the plurality of sub-junction regions.

[0017] By providing a tunneling layer, vertical series connection of various sub-junction regions of the battery can be achieved.

[0018] In combination with the first aspect, in certain implementations of the first aspect, the emission layer and the absorption layer of each sub-junction region form a PN junction.

[0019] In combination with the first aspect, in certain implementations of the first aspect, the emitter layer of each subjunction region is N-type aluminum gallium arsenide AlGaAs material, the absorption layer of each subjunction region is P-type aluminum gallium arsenide AlGaAs material, and the multiple tunneling layers include N-type aluminum gallium arsenide AlGaAs material and P-type aluminum gallium arsenic AlGaAs material; or, the emitter layer of each subjunction region is P-type aluminum gallium arsenic AlGaAs material, the absorption layer of each subjunction region is N-type aluminum gallium arsenic AlGaAs material, and the multiple tunneling layers include P-type aluminum gallium arsenic AlGaAs material and N-type aluminum gallium arsenic AlGaAs material.

[0020] In combination with the first aspect, in some implementations of the first aspect, the emitter layer of the non-isotropic junction region is aluminum gallium arsenide Al 0.3 Ga 0.7 As material.

[0021] Aluminum gallium arsenide (AlGaAs) is used to fix the composition of the emitter layer in the non-isotropic junction region. 0.3 Ga 0.7 As material can increase the open circuit voltage and enhance battery performance.

[0022] In combination with the first aspect, in certain implementations of the first aspect, the photocurrent generated by each sub-junction region is the same.

[0023] In combination with the first aspect, in some implementations of the first aspect, the thicknesses of the plurality of sub-junction regions along the first direction gradually increase.

[0024] It is understandable that as the incident laser is transmitted in the battery, the energy of the laser will gradually decrease due to loss. Taking into account the photon absorption efficiency of each junction sub-junction region, and in order to ensure that the photocurrent generated by each sub-junction region is the same, the thickness of the sub-junction region is designed to be larger, closer to the bottom layer of the photocell, so as to ensure that the number of photons absorbed by each sub-junction region is the same.

[0025] In combination with the first aspect, in certain implementations of the first aspect, the number of sub-junction regions of the monochrome photovoltaic cell is 3, and the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, and a third sub-junction region along the first direction, and the second sub-junction region and the third sub-junction region are non-identical sub-junction regions.

[0026] In combination with the first aspect, in certain implementations of the first aspect, the number of sub-junction regions of the monochrome photovoltaic cell is 4, the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region and a fourth sub-junction region along the first direction, and the non-identical sub-junction region is the fourth sub-junction region.

[0027] In combination with the first aspect, in some implementations of the first aspect, the number of the plurality of sub-junction regions is 6, the monochromatic photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region, a fourth sub-junction region, a fifth sub-junction region and a sixth sub-junction region along the first direction, and the thickness range of each sub-junction region is respectively: 87nm≤H 1 ≤154nm、115nm≤H 2 ≤181nm、158nm≤H 3 ≤224nm、236nm≤H 4 ≤303nm、321nm≤H 5 ≤495nm、1997nm≤H 6 ≤4μm, where H 1 is the thickness of the first subjunction region, H 2 is the thickness of the second subjunction region, H 3 is the thickness of the third sub-junction region, H 4 is the thickness of the fourth subjunction region, H 5 is the thickness of the fifth subjunction region, H 6 is the thickness of the sixth sub-junction region.

[0028] In combination with the first aspect, in some implementations of the first aspect, the number of the plurality of sub-junction regions is 5, the monochromatic photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region, a fourth sub-junction region and a fifth sub-junction region along the first direction, and the thickness range of each sub-junction region is respectively: 115nm≤H 1 ≤181nm、158nm≤H 2 ≤224nm、236nm≤H 3 ≤303nm、321nm≤H 4 ≤495nm、1997nm≤H 5 ≤4μm, where H 1 is the thickness of the first subjunction region, H 2 is the thickness of the second subjunction region, H3 is the thickness of the third sub-junction region, H 4 is the thickness of the fourth subjunction region, H 5 is the thickness of the fifth sub-junction region.

[0029] In combination with the first aspect, in some implementations of the first aspect, the number of the plurality of sub-junction regions is 4, the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region and a fourth sub-junction region along the first direction, and the thickness range of each sub-junction region is respectively: 158nm≤H 1 ≤224nm、236nm≤H 2 ≤303nm、321nm≤H 3 ≤495nm、1997nm≤H 4 ≤4μm, where H 1 is the thickness of the first subjunction region, H 2 is the thickness of the second subjunction region, H 3 is the thickness of the third sub-junction region, H 4 is the thickness of the fourth sub-junction region.

[0030] In combination with the first aspect, in some implementations of the first aspect, the number of the plurality of sub-junction regions is 3, the monochromatic photovoltaic cell includes a first sub-junction region, a second sub-junction region and a third sub-junction region along the first direction, and the thickness range of each sub-junction region is respectively: 236nm≤H 1 ≤303nm、321nm≤H 2 ≤495nm、1997nm≤H 3 ≤4μm, where H 1 is the thickness of the first subjunction region, H 2 is the thickness of the second subjunction region, H 3 is the thickness of the third sub-junction region.

[0031] Combined with the design of absorption layer and emission layer with corresponding thickness, the photon absorption efficiency can be further enhanced, achieving the effect of improving the photoelectric conversion efficiency.

[0032] In combination with the first aspect, in certain implementations of the first aspect, the wavelength of the laser that excites the monochromatic photovoltaic cell is 808 nm or 850 nm.

[0033] In combination with the first aspect, in some implementations of the first aspect, the thickness w of the window layer is in the range of 20 nm≤w≤60 nmm.

[0034] In combination with the first aspect, in some implementations of the first aspect, the back reflection layer of the bottom sub-junction region is aluminum gallium arsenide Al 0.6 Ga 0.4As material.

[0035] In a second aspect, an embodiment of the present application provides a battery pack, which includes a monochrome photovoltaic cell according to the first aspect or various implementations of the first aspect.

[0036] In a third aspect, an embodiment of the present application provides a photovoltaic energy storage device. The photovoltaic energy storage device includes a battery pack and a battery controller according to the second aspect. The battery controller controls the charging or discharging of the battery pack, and the battery controller controls the opening or closing of the photovoltaic energy storage device.

[0037] In a fourth aspect, a photovoltaic energy storage system is provided, which is connected to an inverter system and stores the electric energy output by the inverter system or outputs the stored electric energy to the inverter system. The photovoltaic energy storage system includes the battery pack and the battery controller of the second aspect, the battery controller controls the switching of the charging state and the discharging state of the battery pack, and the battery controller controls the opening or closing of the photovoltaic energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic structural diagram of a photovoltaic cell 100 provided in an embodiment of the present application.

[0039] Figure 2 For Al x Ga 1-x The corresponding relationship between the value of x in As and the band gap.

[0040] Figure 3 A schematic structural diagram of a triple-junction photovoltaic cell 300 provided in an embodiment of the present application.

[0041] Figure 4 Schematic diagram of simulation results of the photovoltaic cell 300.

[0042] Figure 5 A schematic structural diagram of a four-junction photovoltaic cell 500 provided in an embodiment of the present application.

[0043] Figure 6 Schematic diagram of simulation results of photovoltaic cell 500.

[0044] Figure 7 A schematic structural diagram of a double-junction photovoltaic cell 700 provided in an embodiment of the present application.

[0045] Figure 8 A schematic structural diagram of a single-junction photovoltaic cell 800 provided in an embodiment of the present application.

[0046] Fig. 9 A schematic diagram of an application scenario of a photovoltaic energy storage system provided for this application.

[0047] Fig.10A schematic diagram of the structure of a photovoltaic energy storage system provided in this application. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0049] In order to facilitate understanding of the embodiments of the present application, the following explanation is made.

[0050] First, the terms "first", "second", etc. and various numbers in the text descriptions or drawings of the embodiments of the present application shown below are only used for the convenience of description, and are not necessarily used to describe a specific order or sequence, and are not used to limit the scope of the embodiments of the present application. For example, to distinguish different sub-junction areas, etc.

[0051] Second, the terms "including" and "having" and any variations thereof in the embodiments of the present application shown below are intended to cover non-exclusive inclusions. For example, a system, product or device comprising a series of units is not necessarily limited to those units explicitly listed, but may include other units that are not explicitly listed or inherent to these products or devices.

[0052] Third, in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions, and the embodiments or designs described as "exemplary" or "for example" should not be interpreted as being more preferred or more advantageous than other embodiments or designs. The use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way for easy understanding.

[0053] Fourth, in the drawings of this application, the thickness, size and shape of each layer of the battery device have been slightly exaggerated for the sake of convenience. Specifically, the shape of the battery device shown in the drawings is shown by way of example. For example, the shape of the battery device in this application is not limited to the shape shown in the drawings. Moreover, the drawings are only examples and are not drawn strictly to scale. In addition, the same reference numerals are used in the embodiments of this application to represent the same component or the same structural member.

[0054] Fifth, unless otherwise defined, all terms (including technical terms and scientific terms) used in this application have the same meaning as commonly understood by a person of ordinary skill in the art to which this application belongs. It should also be understood that terms (such as terms defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0055] Sixth, in the description of the embodiments of the present application, the terms "upper", "lower", "vertical", etc. indicate directions or positional relationships that are defined relative to the directions or positions of the components schematically placed in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, rather than indicating or implying that the device or structure referred to must have a specific direction, or be constructed and operated in a specific direction. They may change accordingly according to the changes in the directions of the components placed in the drawings, and therefore cannot be understood as limitations on the present application.

[0056] Seventh, the character “ / ” generally indicates that the previous and next associated objects are in an “or” relationship.

[0057] Eighth, in the description of the embodiments of the present application, "photovoltaic cell" and "photovoltaic cell" are used to express the same meaning without distinction.

[0058] Ninth, the present application relates to aluminum gallium arsenide materials (also referred to as aluminum gallium arsenide materials) and gallium arsenide materials (also referred to as gallium arsenide materials). When describing materials in general, the proportion of each element in the material is not distinguished, and it is only used to describe the elements contained in the material. 0.4 Ga 0.6 As, aluminum gallium arsenide Al 0.01 Ga 0.99 As are aluminum gallium arsenide materials. It can be understood that for aluminum gallium arsenide materials, the subscript of the element represents the proportion of the corresponding element in the material, and the subscripts of all elements together determine the band gap width of the material. For example, for aluminum gallium arsenide Al 0.4 Ga 0.6 For As material, the subscript 0.4 corresponds to the proportion of aluminum element in the AlGaAs material, and the subscript 0.6 corresponds to the proportion of gallium element in the AlGaAs material.

[0059] For ease of understanding, the technical terms involved in this application are first briefly explained and illustrated.

[0060] 1. Laser photovoltaic cells

[0061] Laser photovoltaic cells are a new type of photovoltaic technology that uses laser technology to improve the efficiency of photovoltaic cells. The working principle of laser photovoltaic cells is to use the high energy and high focusing properties of lasers to focus light energy more concentratedly on the surface of photovoltaic cells, thereby improving the absorption efficiency of photovoltaic cells. Laser photovoltaic cells can optimize the performance of photovoltaic cells by adjusting the wavelength, power and focusing method of the laser. Laser photovoltaic cells can be used in many devices and scenarios, including but not limited to: photovoltaic panels for power supply to homes, commercial and industrial buildings; mobile device power supply systems, such as smartphones, tablets and wearable devices, to provide them with renewable electricity. Vehicles and transportation vehicles, such as electric vehicles, electric bicycles and other electric vehicles, provide them with clean energy drive. Power supply to remote areas, such as mountains, deserts or islands, to provide these areas with renewable electricity.

[0062] 2. Band Gap

[0063] The band gap of a photovoltaic cell refers to the energy difference between the valence band and the conduction band in a semiconductor material. In a photovoltaic cell, after the semiconductor material absorbs light energy, electrons will jump from the valence band to the conduction band to form a current. The band gap determines the photovoltaic cell's ability to absorb light of different wavelengths, and therefore affects the efficiency of the photovoltaic cell. Among them, materials with a smaller band gap can absorb light in a larger energy range, but are also prone to heat loss and low efficiency; while materials with a larger band gap can absorb light in a smaller energy range, but are also prone to reflection and transmission, which also leads to a decrease in efficiency. Therefore, the band gap of a photovoltaic cell needs to be selected within an appropriate range to balance absorption and conversion efficiency. For monochromatic photovoltaic cells, different materials have different band gaps and are suitable for absorbing light of different wavelengths. Therefore, in practical applications, appropriate materials will be selected according to demand.

[0064] 3. Common structures and functions of photovoltaic cells

[0065] Anti-reflection layer: can reduce the reflection of light on the surface of the battery, allowing the light to penetrate deeper into the battery so that more light can be absorbed, thereby improving the photoelectric conversion efficiency.

[0066] Contact layer: This layer is in contact with the metal electrode and usually has a high doping concentration. It can improve the transmission efficiency of electrons inside the photovoltaic cell, thereby reducing the recombination loss of electrons and achieving the purpose of improving the photoelectric conversion efficiency. The electrode-free part needs to be etched away.

[0067] Window layer: Its main function is to reduce the recombination rate at the upper surface of the battery and it needs to be transparent to the input light.

[0068] Emission layer: It forms a PN junction with the absorption layer and is usually thin. Its main function is to enhance the light absorption capacity and photoelectric conversion efficiency of the photovoltaic cell. The emission layer can increase the absorption capacity of the photovoltaic cell to the laser. It can change the propagation path of light, make the light reflect multiple times inside the photovoltaic cell, increase the interaction between light and materials, and thus improve the light absorption efficiency.

[0069] Absorption layer: refers to a layer of material that can absorb light energy and convert it into electrical energy. It is thick and weakly doped.

[0070] Back reflection layer: (1) It can increase the light absorption capacity of photovoltaic cells. It can reflect the light that passes through the cell from the front and make it absorbed by the cell again, thereby improving the light absorption efficiency of photovoltaic cells. (2) It can reduce the reflection loss on the surface of photovoltaic cells. By selecting appropriate materials and designs, the back reflection layer can reduce the proportion of light reflected from the cell surface, so that more light is absorbed by the cell, and the photoelectric conversion efficiency of photovoltaic cells is improved. (3) It can protect the cell, prevent the external environment from eroding and damaging the cell, extend the service life of the photovoltaic cell, and ensure the stability of the photovoltaic cell.

[0071] Tunneling layer: The connecting part between multi-junction cells, composed of highly doped PN junction.

[0072] Conductive layer: serves as a buffer layer in contact with the substrate.

[0073] The laser power supply system can convert the light emitted by the laser light source into electrical energy by transmitting it to the laser photovoltaic cell through optical fiber, and can provide stable power output. Compared with the traditional metal wire and coaxial cable power transmission technology, since the laser power supply system transmits light through optical fiber, it can be used in scenarios where electromagnetic interference needs to be eliminated or electronic devices need to be isolated from the surrounding environment. It has important applications in radio communications, industrial sensors, national defense, aviation, medicine, energy and other fields. The working principle of laser photovoltaic cells is similar to that of solar cells, but it can achieve higher conversion efficiency, greater output voltage, and can transmit more energy.

[0074] At present, in order to improve the photoelectric conversion efficiency of laser photovoltaic cells, some schemes use NPN structure laser photovoltaic cells based on reverse junction technology. Among them, the photovoltaic cell uses semi-insulating gallium arsenide GaAs material as the substrate, and the P-type conductive layer connects the GaAs P\N junction cell to the reverse P / N junction. The reverse P / N junction avoids the generation of substrate leakage, thereby improving the efficiency of photoelectric conversion. In other schemes, the thickness of multiple sub-cell layers is changed, and an internal reflection layer is set in each GaAs sub-cell layer to improve the photoelectric conversion efficiency. In addition to the scheme described above, there are many different cell designs to improve the photoelectric conversion efficiency, which will not be listed in detail.

[0075] However, no matter which solution is adopted, the materials of each sub-cell of the existing laser photovoltaic cell will not change, that is, the existing solution adopts a fully isotropic sub-cell structure design, which limits the further improvement of the photoelectric conversion efficiency.

[0076] In view of this, the present application provides a monochromatic laser photovoltaic cell, which improves the photon absorption efficiency and increases the open circuit voltage by gradually increasing the refractive index difference between the absorption layer and the reflected layer of multiple sub-junction regions from top to bottom, and using large bandgap emission layer materials in some sub-junction regions, thereby achieving the purpose of improving the photoelectric conversion efficiency of the cell.

[0077] Figure 1 Schematic diagram of the structure of the photovoltaic cell 100 provided in the embodiment of the present application. Figure 1 As shown, the photovoltaic cell 100 includes a plurality of sub-junction regions vertically stacked along a first direction, namely, the first sub-junction region #1, the second sub-junction region #2...the Nth sub-junction region #N, where N is an integer greater than or equal to 3. Among the N sub-junction regions, the refractive index difference of the plurality of sub-junction regions except the bottom sub-junction region (i.e., the Nth sub-junction region #N) gradually increases along the first direction, and the refractive index difference is the refractive index difference between the material of the absorption layer and the back reflection layer of each sub-junction region. Among them, the first direction is the direction from the window layer of the photovoltaic cell 100 to the direction away from the window layer, and can also be understood as the direction from the first sub-junction region #1 to the Nth sub-junction region #N, or can also be understood as the incident direction of the incident light (wherein, the incident light is incident from the window layer and passes through the first sub-junction region #1 to the Nth sub-junction region #N in sequence). The material of the back reflection layer of the bottom sub-junction region is aluminum gallium arsenide Al 0.6 Ga 0.4 As.

[0078] Exemplarily, when N is equal to 4, that is, the photovoltaic cell 100 includes 4 sub-junctions, and the 4 sub-junctions are arranged vertically stacked along the first direction, namely the first sub-junction #1, the second sub-junction #2, the third sub-junction #3 and the fourth sub-junction #4, and the fourth sub-junction #4 is the bottom sub-junction. Among them, each sub-junction of the first sub-junction #1 to the fourth sub-junction #4 includes an absorption layer and a back reflection layer. If the refractive index difference between the absorption layer and the back reflection layer of the first sub-junction #1 is Δ1, the refractive index difference between the absorption layer and the back reflection layer of the second sub-junction #2 is Δ2, and the refractive index difference between the absorption layer and the back reflection layer of the third sub-junction #3 is Δ3, then the relationship between Δ1, Δ2 and Δ3 satisfies Δ1<Δ2<Δ3. The material of the back reflection layer of the fourth sub-junction #4 is Al 0.6 Ga 0.4 As.

[0079] In some embodiments, in order to further improve the photoelectric conversion efficiency of the photovoltaic cell 100, the absorption layer of each sub-junction region of the photovoltaic cell 100 is AlGaAs. y Ga 1-yAs material, the back reflection layer of each sub-junction region of the plurality of sub-junction regions except the bottom sub-junction region is aluminum gallium arsenide Al x Ga 1-x As material, wherein the value of x along the first direction gradually increases, the value of y along the first direction is the same, x and y are real numbers greater than or equal to 0 and less than 1, and x is greater than y. Specifically, Figure 2 Aluminum Gallium Arsenide Al x Ga 1-x The corresponding relationship between the value of x and the band gap in As material shows that as the value of x increases, the AlGaAs x Ga 1-x As material has a larger band gap. As the band gap gradually increases, the refractive index difference between the absorption layer and the back reflection layer gradually increases, so that the reflection of photons in the battery gradually increases, thereby enhancing the photon absorption efficiency, thereby achieving the purpose of improving the photoelectric conversion efficiency. It can be understood that the absorption layer of each sub-junction region of the photovoltaic cell 100 is AlGaAs. y Ga 1-y As material, and the same value along the first direction y means that, for a specific photovoltaic cell, the material of the absorption layer of each sub-junction region is the same; for different photovoltaic cells, the material of the absorption layer may be the same or different between different photovoltaic cells. In some embodiments, when the photovoltaic cell 100 is a triple-junction photovoltaic cell comprising three sub-junction regions, the material of the absorption layer of each sub-junction region can be set to GaAs, and excited by an 850nm laser. In other embodiments, when the photovoltaic cell 100 is a multi-junction photovoltaic cell comprising four or more sub-junction regions, the material of the absorption layer of each sub-junction region can be set to aluminum gallium arsenide Al 0.08 Ga 0.92 As, and excited by 808nm laser.

[0080] In some embodiments, in order to further improve the photoelectric conversion efficiency of the photovoltaic cell 100, the multiple sub-junction regions of the photovoltaic cell 100 include at least one non-identical sub-junction region, wherein the non-identical sub-junction region is a sub-junction region with different emission layer and absorption layer materials.

[0081] It should be noted that, in order to always ensure the photoelectric conversion efficiency of the photovoltaic cell 100, in the present application, at least one non-identical sub-junction region is at least one sub-junction region that is arranged adjacently including the bottom sub-junction region. That is, the position of at least one non-identical sub-junction region is based on the position of the bottom sub-junction region of the monochromatic photovoltaic cell 100 as the starting position, and is arranged adjacently in the opposite direction of the first direction according to the number of at least one non-identical sub-junction region. In other words, in the present application, at least one non-identical sub-junction region is arranged adjacently upward from the bottom sub-junction region, so that the non-identical sub-junction region of the photovoltaic cell 100 provided in the present application is located in the last few sub-junction regions of the photovoltaic cell 100. Exemplarily, when the photovoltaic cell 100 includes 4 sub-junction regions, they are arranged in sequence along the first direction as the first sub-junction region #1, the second sub-junction region #2, the third sub-junction region #3 and the fourth sub-junction region #4. If the 4 sub-junction regions include two non-identical sub-junction regions, the two non-identical sub-junction regions are the third sub-junction region #3 and the fourth sub-junction region #4, respectively.

[0082] Optionally, the emitter layer of the non-isotropic junction region is AlGaAs 0.3 Ga 0.7 As material.

[0083] like Figure 1 As shown, each subjunction region of the photovoltaic cell 100 includes an emission layer, an absorption layer, and a back reflection layer arranged in sequence along a first direction, wherein for each subjunction region, when its emission layer and the absorption layer form an NP junction, the material of the emission layer of each subjunction region is an N-type aluminum gallium arsenide AlGaAs material, and the material of the absorption layer of each subjunction region is a P-type aluminum gallium arsenide AlGaAs material. When its emission layer and the absorption layer form a PN junction, the material of the emission layer of each subjunction region is a P-type aluminum gallium arsenide AlGaAs material, and the material of the absorption layer of each subjunction region is an N-type aluminum gallium arsenide AlGaAs material.

[0084] In order to connect adjacent sub-junction regions together, in some embodiments, a tunneling layer is provided between two adjacent sub-junction regions, and the tunneling layer is composed of a highly doped PN junction or NP junction. Exemplarily, when the emission layer of each sub-junction region forms a PN junction with the absorption layer, the tunneling layer is composed of a highly doped NP junction; when the emission layer of each sub-junction region forms an NP junction with the absorption layer, the tunneling layer is composed of a highly doped PN junction. Exemplarily, when the emission layer of each sub-junction region forms an NP junction with the absorption layer, the material of the tunneling layer near the upper sub-junction region is P-type aluminum gallium arsenide Al 0.3 Ga 0.7 As, the material of the tunnel layer near the lower sub-junction region is N-type aluminum gallium arsenide Al 0.01 Ga 0.99 As material.

[0085] In addition, the photovoltaic cell further comprises a window layer, and a thickness w of the window layer is in the range of 20 nm≤w≤60 nmm.

[0086] In the present application, the thickness of each sub-junction region is different, and the thickness of multiple sub-junction regions along the first direction gradually increases. That is, multiple sub-junction regions in the present application have different thicknesses. The top sub-junction region has the thinnest thickness, and the bottom sub-junction region has the thickest thickness. Among them, the thickness distribution principle of each sub-junction region is designed according to the wavelength of the incident light, the material absorption coefficient and the number of junctions to ensure that the currents of each sub-battery match each other.

[0087] In one achievable manner, according to the Lambert-Beer law, in order to make the absorption efficiency corresponding to the thickness of the last junction sub-junction region 97%, the current of each sub-junction region in the longitudinal direction uniform (i.e. the same), and the absorption efficiency of each sub-junction region differing within ±5%, the present application provides the following range of the thickness H of each junction: ..., 87nm≤H N-5 ≤154nm、115nm≤H N-4 ≤181nm、158nm≤H N-3 ≤224nm、236nm≤H N-2 ≤303nm、321nm≤H N-1 ≤495nm、1997nm≤H N ≤4μm. Among them, H N is the thickness range of the Nth subjunction region, H N-1 is the thickness of the N-1th subjunction region, H N-2 is the thickness of the N-2 subjunction region, H N-3 is the thickness of the N-3 subjunction region, H N-4 is the thickness of the N-4th subjunction region, H N-5 is the thickness of the N-5th sub-junction region. It can be understood that the N-5th sub-junction region is located above the N-4th sub-junction region, the N-4th sub-junction region is located above the N-3th sub-junction region, the N-3th sub-junction region is located above the N-2th sub-junction region, the N-2th sub-junction region is located above the N-1th sub-junction region, and the N-1th sub-junction region is located above the Nth sub-junction region.

[0088] It is understood that the above thickness range only lists the thickness of each sub-junction region of the photovoltaic cell including the 6-junction sub-junction region. For example, when the photovoltaic cell 100 includes a 5-junction cell, the thickness ranges of the 5 sub-junction regions of the photovoltaic cell 100 from top to bottom along the vertical direction are 115nm≤H 1 ≤181nm、158nm≤H 2 ≤224nm、236nm≤H 3 ≤303nm、321nm≤H 4 ≤495nm、1997nm≤H 5When the number of sub-junction regions included in the photovoltaic cell 100 is greater than 6, the thickness ranges of more sub-junction regions can be calculated in sequence according to this method, wherein the thickness of the last junction is calculated based on a photon absorption rate greater than or equal to 95%.

[0089] It can also be understood that, due to the differences in the physical properties of the materials themselves and the thickness errors during the preparation and deposition process, the thickness range given above is only for reference and does not limit the scope of application of the present application.

[0090] It should be noted that the size of the photovoltaic cell 100 provided in the present application can have various specifications, corresponding to different power requirements. For example, the cross-sectional shape is a square of 5.2 mm×5.2 mm, or the cross-sectional shape is a circle of 5.2 mm in diameter, etc., the grid line spacing is 300 μm, when the effective input power is 4 to 10 W, the effective excitation power density is 105 to 106 W / m 2 , and obtain a power output of 2 to 6W.

[0091] In addition, during the preparation process, the steps may include metal-organic chemical vapor deposition (MOCVD) epitaxial growth, photolithography, N-electrode preparation, annealing, etching of the contact layer exposed to the air, P-electrode preparation, annealing, preparation of an anti-reflective layer, etc.

[0092] Optionally, the photovoltaic cell 100 further includes an anti-reflection layer, which is disposed on the window layer by a process such as evaporation and does not cover the electrode. The material may be 50nm ZnS and 100nm MgF 2 .

[0093] Optionally, the substrate material of the photovoltaic cell 100 is highly doped GaAs, and when preparing the electrode, a lateral electrode can be prepared so that it is in direct contact with the conductive layer; or a tunneling layer can be grown on the conductive layer to prepare an NPN junction, and then the electrode can be prepared on the substrate.

[0094] Figure 3 Schematic diagram of the structure of a triple-junction photovoltaic cell 300 provided in an embodiment of the present application. Figure 3As shown, the photovoltaic cell 300 includes three sub-junction regions, namely, the first sub-junction region #1, the second sub-junction region #2 and the third sub-junction region #3. The photovoltaic cell 300 is arranged in sequence along the first direction as a contact layer 301, a window layer 302, an emission layer 303, an absorption layer 304, a back reflection layer 305, a tunneling layer 306, an emission layer 307, an absorption layer 308, a back reflection layer 309, a tunneling layer 310, an emission layer 311, an absorption layer 312, a back reflection layer 313 and a conductive layer 314. Among them, the emission layer 303, the absorption layer 303 and the back reflection layer 305 constitute the first sub-junction region #1, the emission layer 307, the absorption layer 308, the back reflection layer 309 constitute the second sub-junction region #2, and the emission layer 311, the absorption layer 312, and the back reflection layer 313 constitute the third sub-junction region #3. A tunneling layer 306 is provided between the first sub-junction region #1 and the second sub-junction region #2, and a tunneling layer 310 is provided between the second sub-junction region #2 and the third sub-junction region #3.

[0095] Table 1

[0096]

[0097]

[0098] It should be noted that the materials of each layer in the above Table 3 are only examples and not limitations.

[0099] Optionally, the photovoltaic cell 300 may further include a buffer layer, which may be disposed between the back reflection layer 313 and the conductive layer 314, and the material of the buffer layer may be aluminum gallium arsenide Al 0.1 Ga 0.9 As.

[0100] It should be noted that the positive and negative electrodes of the battery 300 are respectively arranged on the outer surface (ie, the upper side) of the contact layer 301 and the outer surface (ie, the lower side) of the conductive layer 314 , which will not be described in detail here.

[0101] In the photovoltaic cell 300 provided in the present application, the non-identical sub-junction regions are the second sub-junction region #2 and the third sub-junction region #3. The open circuit voltage Voc of the photovoltaic cell 300 is 3.6V, and the optimal output voltage Vm is 3.3V. The thickness of the first sub-junction region #1 is 240nm, wherein the thickness of the emission layer 303 is 40nm, and the thickness of the absorption layer 304 is 200nm. The thickness of the second sub-junction region #2 is 560nm, wherein the thickness of the emission layer 307 is 160nm, and the thickness of the absorption layer 308 is 400nm. The thickness of the third sub-junction region #3 is 2260nm, wherein the thickness of the emission layer 311 is 160nm; the thickness of the absorption layer 312 is 2100nm. In the photovoltaic cell 300 provided in the present application, the thickness of the window layer is 60nm.

[0102] Optionally, the photovoltaic cell 300 further includes an anti-reflection layer, the material of which may be zinc sulfide ZnS and magnesium fluoride MgF 2 .

[0103] Figure 4 Schematic diagram of simulation results of photovoltaic cell 300. The circle line is current data, and the dotted line is power data. Figure 4 It can be seen that when the 808nm laser is used for excitation, the photocell 300 is at a temperature of 298K and 2×10 5 W / m 2 Under the excitation power density, an output voltage of 3.3 V was obtained, and the photoelectric conversion efficiency was 50.5%.

[0104] Figure 5 Schematic diagram of the structure of a four-junction photovoltaic cell 500 provided in an embodiment of the present application. Figure 5 As shown, the photovoltaic cell 500 includes four sub-junction regions, namely the first sub-junction region #1, the second sub-junction region #2, the third sub-junction region #3 and the fourth sub-junction region #4. The photovoltaic cell 500 includes a contact layer 501, a window layer 502, an emission layer 503, an absorption layer 504, a back reflection layer 505, a tunneling layer 506, an emission layer 507, an absorption layer 508, a back reflection layer 509, a tunneling layer 510, an emission layer 511, an absorption layer 512, a back reflection layer 513, a tunneling layer 514, an emission layer 515, an absorption layer 516, a back reflection layer 517 and a conductive layer 518 in sequence along a first direction. The emission layer 503, the absorption layer 504 and the back reflection layer 505 constitute the first sub-junction region #1, the emission layer 507, the absorption layer 508 and the back reflection layer 509 constitute the second sub-junction region #2, the emission layer 511, the absorption layer 512 and the back reflection layer 513 constitute the third sub-junction region #3, and the emission layer 515, the absorption layer 516 and the back reflection layer 517 constitute the fourth sub-junction region #4. The tunneling layer 506 is between the first sub-junction region #1 and the second sub-junction region #2, the tunneling layer 510 is between the second sub-junction region #2 and the third sub-junction region #3, and the tunneling layer 514 is between the third sub-junction region #3 and the fourth sub-junction region #4. The materials of each layer can be as shown in Table 2.

[0105] Table 2

[0106]

[0107]

[0108] It should be noted that the materials of each layer in Table 2 are only examples and not limitations. For example, the window layer material can also be indium gallium phosphide Ga 0.5 In 0.5 P material.

[0109] Optionally, the photovoltaic cell 500 may further include a buffer layer, which may be disposed between the back reflection layer 517 and the conductive layer 518, and the material of the buffer layer may be aluminum gallium arsenide Al 0.1 Ga 0.9 As.

[0110] It should be noted that the positive and negative electrodes of the battery 500 are respectively arranged on the outer surface (ie, the upper side) of the contact layer 501 and the outer surface (ie, the lower side) of the conductive layer 518, which will not be described in detail here.

[0111] In the photovoltaic cell 500 provided in the present application, the non-identical sub-junction region is the fourth sub-junction region #4. The open circuit voltage Voc of the photovoltaic cell 500 is 5.3V, and the optimal output voltage Vm is 5V. The thickness of the first sub-junction region #1 is 210nm, wherein the thickness of the emission layer 503 is 40nm, and the thickness of the absorption layer 504 is 170nm. The thickness of the second sub-junction region #2 is 250nm, wherein the thickness of the emission layer 507 is 60nm, and the thickness of the absorption layer 508 is 190nm. The thickness of the third sub-junction region #3 is 460nm, wherein the thickness of the emission layer 511 is 200nm, and the thickness of the absorption layer 512 is 260nm. The thickness of the fourth sub-junction region #4 is 2700nm, wherein the thickness of the emission layer 515 is 150nm, and the thickness of the absorption layer 516 is 2550nm. In the photovoltaic cell 500 provided in the present application, the thickness of the window layer is 60nm.

[0112] Figure 6 Schematic diagram of simulation results of photovoltaic cell 500. The circle line is current data, and the dotted line is power data. Figure 6 It can be seen that when the 808nm laser is used for excitation, the photocell 500 is 6 W / m 2 Under the excitation power density, an output voltage of 5V was obtained, and the photoelectric conversion efficiency was 66.4%.

[0113] Figure 7 Schematic diagram of the structure of a double-junction photovoltaic cell 700 provided in an embodiment of the present application. Figure 7 As shown, the photovoltaic cell 700 includes two sub-junction regions, namely, the first sub-junction region #1 and the second sub-junction region #2. The photovoltaic cell 700 includes, from top to bottom, a contact layer 701, a window layer 702, an emission layer 703, an absorption layer 704, a back reflection layer 705, a tunneling layer 706, an emission layer 707, an absorption layer 708, a back reflection layer 709, and a conductive layer 710. Specifically, the emission layer 703, the absorption layer 704, and the back reflection layer 705 constitute the first sub-junction region #1, the emission layer 707, the absorption layer 708, and the back reflection layer 709 constitute the second sub-junction region #2, and the tunneling layer 706 is between the first sub-junction region #1 and the second sub-junction region #2. The materials of each layer can be as shown in Table 3.

[0114] Table 3

[0115]

[0116]

[0117] It should be noted that the materials of each layer in the above Table 3 are only examples and not limitations.

[0118] Optionally, the photovoltaic cell 700 may further include a buffer layer, which may be disposed between the back reflection layer 709 and the conductive layer 710, and the material of the buffer layer may be aluminum gallium arsenide Al 0.1 Ga 0.9 As.

[0119] It should be noted that the positive and negative electrodes of the battery 700 are respectively arranged on the outer surface (ie, the upper side) of the contact layer 701 and the outer surface (ie, the lower side) of the conductive layer 710 , which will not be described in detail here.

[0120] In addition, the cross-sectional shape of the photovoltaic cell 700 along the horizontal plane may be a circle, a square, a regular polygon, etc., which is not limited in the present application.

[0121] It should be noted that the positive and negative electrodes of the battery 500 are respectively arranged on the outer surface (ie, the upper side) of the contact layer 501 and the outer surface (ie, the lower side) of the conductive layer 518, which will not be described in detail here.

[0122] In the photovoltaic cell 700 provided in the present application, the non-identical subjunction region is the second subjunction region #2. The open circuit voltage Voc of the photovoltaic cell 700 is 2.72V, and the optimal output voltage Vm is 2.49V. The thickness of the first subjunction region #1 is 460nm, wherein the thickness of the emission layer 703 is 200nm, and the thickness of the absorption layer 704 is 260nm. The thickness of the second subjunction region #2 is 2400nm, wherein the thickness of the emission layer 707 is 150nm, and the thickness of the absorption layer 708 is 2250nm.

[0123] In addition, in the photovoltaic cell 700 provided in the present application, the thickness of the window layer is 60 nm, and the photoelectric conversion efficiency is 75.8%.

[0124] Figure 8 Schematic diagram of the structure of a single-junction photovoltaic cell 800 provided in an embodiment of the present application. Figure 8 As shown, the photovoltaic cell 800 includes a subjunction region, namely, subjunction region #1. The photovoltaic cell 100 includes a contact layer 801, a window layer 802, an emission layer 803, an absorption layer 804, a back reflection layer 805 and a conductive layer 806 from top to bottom, and the emission layer 803, the absorption layer 804 and the back reflection layer 805 constitute the first subjunction region #1. The materials of each layer can be as shown in Table 4.

[0125] Table 4

[0126] name Material type Contact layer 801 Gallium Arsenide GaAs N Window layer 802 <![CDATA[Aluminum gallium arsenide Al 0.4 Ga 0.6 As]]> N Emission layer 803 <![CDATA[Aluminum gallium arsenide Al 0.3 Ga 0.7 As]]> N Absorption layer 804 <![CDATA[Aluminum gallium arsenide Al 0.08 Ga 0.92 As]]> P Back reflection layer 805 <![CDATA[Aluminum gallium arsenide Al 0.6 Ga 0.4 As]]> P Conductive layer 806 Gallium Arsenide GaAs P

[0127] It should be noted that the materials of each layer in the above Table 4 are only examples and not limitations.

[0128] Optionally, the photovoltaic cell 800 may further include a buffer layer 807, which is located between the back reflection layer 805 and the conductive layer 806, and is used to improve the band gap matching and lattice matching. The material of the buffer layer 807 may be aluminum gallium arsenide Al 0.1 Ga 0.9 As.

[0129] It should be noted that the outer surface of the contact layer 801 (i.e., the top) and the outer surface of the conductive layer 806 (i.e., the bottom) are respectively provided with positive and negative electrodes. For example, the outer surface of the contact layer 801 is provided with a positive electrode, and the outer surface of the conductive layer 806 is provided with a negative electrode.

[0130] In addition, the cross-sectional shape of the photovoltaic cell 800 along the horizontal plane may be a circle, a square, a regular polygon, etc., which is not limited in the present application.

[0131] In the photovoltaic cell 800 provided in the present application, the non-identical subjunction region is the first subjunction region #1. The open circuit voltage Voc of the photovoltaic cell 700 is 1.27 V, and the optimal output voltage Vm is 1.19 V. The thickness of the first subjunction region #1 is 3500 nm, wherein the thickness of the emission layer 803 is 200 nm, and the thickness of the absorption layer 804 is 3300 nm.

[0132] In addition, in the photovoltaic cell 800 provided in the present application, the thickness of the window layer is 20 nm and the photoelectric conversion efficiency is 58.3%.

[0133] Combination of the above Figure 1 , Figure 3 , Figure 5 , Figure 7 and Figure 8 The photovoltaic cell provided in the embodiment of the present application is described. In some embodiments, the embodiment of the present application further provides a photoelectric conversion device or a photoelectric conversion device, which includes any one of the photovoltaic cells provided in the above-mentioned embodiments of the present application. For example, the photoelectric conversion device or the photoelectric conversion device can be a photoelectric conversion joint. Exemplarily, after the photovoltaic cell provided in the embodiment of the present application is prepared, the transistor outline (TO) packaging process can be used to package the photovoltaic cell, add heat dissipation teeth and other structures, and make a photoelectric conversion joint including a heat dissipation device, for example.

[0134] Fig. 9A schematic diagram of an application scenario of a photovoltaic energy storage system provided by the present application. Among them, the photovoltaic power generation system includes a photovoltaic power generation device and an inverter device. The photovoltaic power generation device is used to convert light energy into electrical energy. The photovoltaic power generation device may include a plurality of photovoltaic cells provided in the embodiments of the present application. The inverter device is used to convert the direct current output by the photovoltaic power generation device into alternating current, and transmit the electrical energy to the load and the power grid. The inverter device may also be configured with a communication device for communicating with the photovoltaic power generation system and the photovoltaic energy storage system, and further realizing the regulation of electrical energy. The photovoltaic energy storage system may receive instruction information issued by the communication device in the inverter device, and store and release electrical energy according to the requirements of the instruction information. The electrical energy converted by the photovoltaic power generation system is used to power the load. When the electrical energy converted by the photovoltaic power generation system is higher than the electrical energy required for the load to work, the photovoltaic energy storage system, under the regulation of the inverter device, can store the excess electrical energy of the photovoltaic power generation system; when the electrical energy converted by the photovoltaic power generation system is insufficient to power the load, the photovoltaic energy storage system, under the regulation of the inverter device, can output the stored electrical energy to the load through the inverter device.

[0135] Fig.10 The photovoltaic energy storage system provided in the present application is a schematic diagram of the structure. The photovoltaic energy storage system includes a battery controller (battery control unit, BCU) and a battery pack PACK, wherein the battery pack includes a plurality of photovoltaic cells provided in the embodiments of the present application (such as the above Figure 1 , Figure 3 , Figure 5 , Figure 7 or Figure 8 ). BCU is connected to the inverter device. When there is surplus electric energy converted by the photovoltaic power generation system, BCU, under the control of the inverter device, uses the electric energy converted by the photovoltaic power generation device to charge the battery pack PACK and stores the excess electric energy in the PACK; when the electric energy converted by the photovoltaic power generation device is sufficient to supply power to the load, BCU controls the PACK to supply power to the load and outputs the electric energy stored in the PACK to the load through the inverter.

[0136] In the photovoltaic energy storage system, the BCU can control the on / off function of the circuit. When the BCU main switch is turned off, the power connection circuit between the BCU and the inverter, and between the BCU and the battery pack PACK can be cut off. At this time, if the photovoltaic energy storage system is in the shutdown state, it will not be awakened by the high voltage. When the BCU main switch is turned on, the entire photovoltaic energy storage system is awakened by the high voltage. When the BCU main switch is turned on and then turned off, the entire photovoltaic energy storage system will be powered off and will not be able to continue to supply power to the load.

[0137] It should be understood that the photovoltaic energy storage system can also be called an energy storage system, a battery energy storage system, a household energy storage system, a battery system, etc., which does not constitute any limitation on the scope of protection of this application.

[0138] Unless otherwise stated, all technical and scientific terms used in the embodiments of the present application have the same meaning as those generally understood by those skilled in the art of the technical field of the present application. The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit the scope of the present application. It should be understood that the above is for illustration, and the examples above are only to help those skilled in the art understand the embodiments of the present application, rather than to limit the application embodiments to the specific numerical values ​​or specific scenarios illustrated. It is obvious that various equivalent modifications or changes can be made by those skilled in the art according to the examples given above, and such modifications and changes also fall within the scope of the embodiments of the present application.

[0139] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A monochrome photovoltaic cell, characterized in that: The method comprises a window layer and a plurality of vertically stacked sub-junction regions, each of the plurality of sub-junction regions comprising an absorption layer and a back reflection layer, wherein: The refractive index difference of the multiple sub-junction regions except the bottom sub-junction region among the multiple sub-junction regions gradually increases along the first direction, and the refractive index difference is the refractive index difference between the absorption layer and the back reflection layer of each sub-junction region. The first direction is the direction from the window layer to the direction away from the window layer, and the bottom sub-junction region is the last sub-junction region along the first direction.

2. The monochromatic photovoltaic cell according to claim 1, characterized in that: The absorption layer of each sub-junction region is aluminum gallium arsenide Al y Ga 1-y As material, the back reflection layer of each of the plurality of sub-junction regions except the bottom sub-junction region is made of aluminum gallium arsenide Al x Ga 1-x As material, wherein the value of x along the first direction gradually increases, the value of y along the first direction is the same, x and y are used to represent the proportion of aluminum element in the aluminum gallium arsenide material, 1-x is used to represent the proportion of gallium element in the aluminum gallium arsenide material of the absorption layer, 1-y is used to represent the proportion of gallium element in the aluminum gallium arsenide material of the back reflection layer, x and y are real numbers greater than or equal to 0 and less than 1, and x is greater than y.

3. The monochromatic photovoltaic cell according to claim 1 or 2, characterized in that: Each of the sub-junction regions further includes an emission layer, The plurality of sub-junction regions include at least one non-identical sub-junction region, where the non-identical sub-junction region is a sub-junction region where the material of the emission layer is different from the material of the absorption layer.

4. The monochromatic photovoltaic cell according to claim 3, characterized in that: The at least one non-identical sub-junction region is at least one sub-junction region that includes the adjacent arrangement of the underlying sub-junction regions.

5. The monochromatic photovoltaic cell according to any one of claims 1 to 4, characterized in that: A tunneling layer is located between two adjacent sub-junction regions among the plurality of sub-junction regions.

6. The monochromatic photovoltaic cell according to any one of claims 1 to 5, characterized in that: The emission layer and the absorption layer of each sub-junction region form a PN junction.

7. The monochromatic photovoltaic cell according to claim 6, characterized in that: The emitter layer of each subjunction region is an N-type aluminum gallium arsenide AlGaAs material, the absorption layer of each subjunction region is a P-type AlGaAs material, and the plurality of tunnel layers include a P-type aluminum gallium arsenide AlGaAs material and an N-type aluminum gallium arsenide AlGaAs material; or, The emission layer of each subjunction region is P-type aluminum gallium arsenide AlGaAs, the absorption layer of each subjunction region is N-type aluminum gallium arsenide AlGaAs material, and the multiple tunneling layers include N-type aluminum gallium arsenide AlGaAs material and P-type aluminum gallium arsenide AlGaAs material.

8. The monochromatic photovoltaic cell according to any one of claims 3 to 7, characterized in that: The emitter layer of the non-isotropic junction region is AlGaAs 0.3 Ga 0.7 As material.

9. The monochromatic photovoltaic cell according to any one of claims 1 to 8, characterized in that: The photocurrent generated by each sub-junction region is the same.

10. The monochromatic photovoltaic cell according to any one of claims 1 to 9, characterized in that: The thicknesses of the plurality of sub-junction regions along the first direction gradually increase.

11. The monochromatic photovoltaic cell according to any one of claims 3 to 10, characterized in that: The number of sub-junction regions of the monochrome photovoltaic cell is 3. The monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region and a third sub-junction region along the first direction. The second sub-junction region and the third sub-junction region are the non-identical sub-junction regions.

12. The monochromatic photovoltaic cell according to any one of claims 3 to 10, characterized in that: The number of sub-junction regions of the monochrome photovoltaic cell is 4. The monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region and a fourth sub-junction region along the first direction. The non-identical sub-junction region is the fourth sub-junction region.

13. The monochromatic photovoltaic cell according to any one of claims 1 to 10, characterized in that: The number of the multiple sub-junction regions is 6, and the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region, a fourth sub-junction region, a fifth sub-junction region and a sixth sub-junction region along the first direction, and the thickness ranges of each sub-junction region are: 87nm≤H1≤154nm, 115nm≤H2≤181nm, 158nm≤H3≤224nm, 236nm≤H4≤303nm, 321nm≤H5≤495nm, 1997nm≤H6≤4μm, wherein H1 is the thickness of the first sub-junction region, H2 is the thickness of the second sub-junction region, H3 is the thickness of the third sub-junction region, H4 is the thickness of the fourth sub-junction region, H5 is the thickness of the fifth sub-junction region, and H6 is the thickness of the sixth sub-junction region.

14. The monochromatic photovoltaic cell according to any one of claims 1 to 10, characterized in that: The number of the multiple sub-junction regions is 5, and the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region, a fourth sub-junction region and a fifth sub-junction region along the first direction, and the thickness ranges of each sub-junction region are: 115nm≤H1≤181nm, 158nm≤H2≤224nm, 236nm≤H3≤303nm, 321nm≤H4≤495nm, 1997nm≤H5≤4μm, wherein H1 is the thickness of the first sub-junction region, H2 is the thickness of the second sub-junction region, H3 is the thickness of the third sub-junction region, H4 is the thickness of the fourth sub-junction region, and H5 is the thickness of the fifth sub-junction region.

15. The monochromatic photovoltaic cell according to any one of claims 1 to 10, characterized in that: The number of the multiple sub-junction regions is 4, and the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region, a third sub-junction region and a fourth sub-junction region along the first direction, and the thickness ranges of each sub-junction region are: 158nm≤H1≤224nm, 236nm≤H2≤303nm, 321nm≤H3≤495nm, 1997nm≤H4≤4μm, respectively, wherein H1 is the thickness of the first sub-junction region, H2 is the thickness of the second sub-junction region, H3 is the thickness of the third sub-junction region, and H4 is the thickness of the fourth sub-junction region.

16. The monochromatic photovoltaic cell according to any one of claims 1 to 10, characterized in that: The number of the multiple sub-junction regions is 3, and the monochrome photovoltaic cell includes a first sub-junction region, a second sub-junction region and a third sub-junction region along the first direction, and the thickness ranges of each sub-junction region are respectively: 236nm≤H1≤303nm, 321nm≤H2≤495nm, 1997nm≤H3≤4μm, wherein H1 is the thickness of the first sub-junction region, H2 is the thickness of the second sub-junction region, and H3 is the thickness of the third sub-junction region.

17. The monochromatic photovoltaic cell according to any one of claims 1 to 16, characterized in that: The wavelength of the incident laser for exciting the monochromatic photovoltaic cell is 808 nm or 850 nm.

18. The monochromatic photovoltaic cell according to any one of claims 1 to 17, characterized in that: The thickness w of the window layer is in the range of 20 nm ≤ w ≤ 60 nm.

19. The monochromatic photovoltaic cell according to any one of claims 1 to 18, characterized in that: The back reflection layer of the bottom sub-junction region is aluminum gallium arsenide Al 0.6 Ga 0.4 As material.

20. A battery pack, characterized in that: include: A plurality of monochromatic photovoltaic cells as claimed in any one of claims 1 to 19.

21. A photovoltaic energy storage device, characterized in that: include: A battery controller and a battery pack as claimed in claim 20, wherein the battery controller controls charging or discharging of the battery pack, and the battery controller controls turning on or off the photovoltaic energy storage device.

22. A photovoltaic energy storage system, characterized in that: The photovoltaic energy storage system is connected to an inverter system and stores the electric energy output by the inverter system, or outputs the stored electric energy to the inverter system. The photovoltaic energy storage system comprises: a battery controller and a battery pack as described in claim 20, wherein the battery controller controls the switching of the charging state and the discharging state of the battery pack, and the battery controller controls the opening or closing of the photovoltaic energy storage system.

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