Voltage-adjustable photovoltaic cell and preparation method thereof

Abstract

The invention provides a voltage-adjustable photovoltaic cell and a preparation method thereof, and relates to the technical field of photovoltaic cells. The voltage-adjustable photovoltaic cell includes: a substrate; the sub-cells are sequentially arranged on the substrate in a stacked mode, and the upper surface of each sub-cell is provided with a step face located outside the upper adjacent sub-cell; a plurality of tunnel junctions, wherein one tunnel junction is arranged between every two adjacent sub-cells; the bottom electrode is arranged on one side, deviating from the sub-battery, of the substrate; and a plurality of adjustable electrodes, each of which is connected to each of the sub-cells, and is located on the corresponding step surface corresponding to the adjustable electrode. According to the photovoltaic cell, different circuit access points can be selected according to requirements, so that flexible adjustment of the output voltage is realized, and the photovoltaic cell is simple to manufacture, high in reliability and better in economical efficiency.

Description

[0001] The present application claims priority to the Chinese patent application No. 202510828874.4, filed on June 19, 2025, entitled "Voltage-tunable photovoltaic cell and preparation method thereof", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of photovoltaic cells, in particular to a voltage-tunable photovoltaic cell and a preparation method thereof. BACKGROUND

[0003] Laser Wireless Power Transfer (LWPT) provides a powerful solution for efficient wireless charging and has become the focus of the energy field. Laser photovoltaic cells, as key components of laser wireless power transfer, have a band gap that matches the photon energy of the target wavelength, allowing them to maximize the absorption and conversion of photon energy and still output high photoelectric conversion efficiency under low photon flux.

[0004] To meet the differentiated needs of driving voltage for different application scenarios, the existing technology usually adopts the following solutions: one is to prepare laser photovoltaic cells with different band gaps to achieve customized voltage output; two is to use a multi-junction laser photovoltaic cell series structure to adjust the output voltage by changing the number of series; three is to adjust the voltage by regulating external parameters such as operating temperature or input light source power. However, these traditional technical solutions have poor versatility and flexibility, resulting in high production costs of the cells. SUMMARY

[0005] The present application provides a voltage-tunable photovoltaic cell and a preparation method thereof. The photovoltaic cell can select different circuit access points according to requirements, thereby achieving flexible adjustment of output voltage, and is simple to make, high in reliability, and better in economy.

[0006] One aspect of the present application provides a voltage-tunable photovoltaic cell, comprising: a substrate; a plurality of sub-cells, each sub-cell being sequentially stacked on the substrate, and each sub-cell having a stepped surface above the adjacent sub-cell; a plurality of tunnel junctions, one tunnel junction being arranged between each adjacent two sub-cells; a bottom electrode arranged on a side of the substrate away from the sub-cells; and a plurality of adjustable electrodes, each adjustable electrode being connected to each sub-cell, and the corresponding adjustable electrode being located on the corresponding stepped surface.

[0007] In one possible implementation, the stepped surface includes at least a first stepped portion located on a first side of the sub-cell; and the adjustable electrode includes at least a first terminal, and the corresponding first terminal is located on the corresponding first stepped portion.

[0008] In a possible implementation, the stepped surface further comprises a second stepped portion on the second side of the sub-cell; and the adjustable electrode further comprises a second terminal corresponding to the second stepped portion.

[0009] In a possible implementation, an insulating layer is arranged between the adjustable electrode and the sidewall of the sub-cell arranged in the same layer.

[0010] In a possible implementation, along a direction of the sub-cell pointing to the substrate, the sub-cell comprises, in sequence, a window layer, an emission region, a base region and a back field layer.

[0011] In a possible implementation, along a direction of the sub-cell pointing to the substrate, the total thickness of the emission region and the base region in each sub-cell increases in sequence.

[0012] In a possible implementation, the sub-cell further comprises an ohmic contact layer arranged on the window layer.

[0013] In a possible implementation, the photovoltaic cell further comprises a grid line electrode arranged on the top surface of the sub-cell of the top layer.

[0014] Another aspect of the present application provides a preparation method of a voltage-adjustable photovoltaic cell, comprising:

[0015] A substrate is provided.

[0016] A plurality of sub-cells are grown on the substrate in sequence, and a tunnel junction is grown between each two sub-cells; wherein, along a direction of the sub-cell pointing to the substrate, the plurality of sub-cells are in sequence a first sub-cell, a second sub-cell, …, an Nth sub-cell.

[0017] A photolithography process is used to etch the first sub-cell, the second sub-cell, …, and the N-1th sub-cell, so as to form a stepped surface on the upper surface of each sub-cell below the first sub-cell.

[0018] An adjustable electrode is formed on the upper surface of each sub-cell, so that the corresponding adjustable electrode is located on the corresponding stepped surface.

[0019] In a possible implementation, the photolithography process used to etch the first sub-cell, the second sub-cell, …, and the N-1th sub-cell comprises:

[0020] A first mask plate is arranged on the first sub-cell, and the first sub-cell is etched along the first mask plate.

[0021] A second mask plate is arranged on the upper surface of the first sub-cell and the second sub-cell, and the second sub-cell is etched along the second mask plate.

[0022] Similarly, until the N-1 mask plate is arranged on the first sub-cell, the second sub-cell, …, the N-1 sub-cell, the N-1 sub-cell is etched along the N-1 mask plate.

[0023] The application provides a voltage-adjustable photovoltaic cell and a preparation method thereof. The photovoltaic cell sequentially stacks a plurality of sub-cells on a substrate, and the adjacent sub-cells are connected in series through a tunnel junction, so that the photovoltaic cell can realize a larger output voltage. Moreover, for each sub-cell below the top sub-cell, a step surface outside the upper adjacent sub-cell is formed on the upper surface of each sub-cell. By connecting an adjustable electrode to the upper surface of each sub-cell, the corresponding adjustable electrode is arranged on the corresponding step surface, the bottom electrode below the substrate can be connected to any adjustable electrode. In this way, the output voltage of the photovoltaic cell can be flexibly adjusted, the photovoltaic cell can meet the demand of different driving voltages, and can be applied to different application scenarios. Thus, the versatility of the photovoltaic cell is improved, the production cost of the photovoltaic cell can be significantly reduced, and the economy of the photovoltaic cell is improved. Moreover, the photovoltaic cell is simple in manufacturing mode and high in reliability. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 A structural schematic diagram of a voltage-adjustable photovoltaic cell provided by an embodiment of the present application is shown in the figure.

[0026] Figure 2 A structural schematic diagram of another voltage-adjustable photovoltaic cell provided by an embodiment of the present application is shown in the figure.

[0027] Figure 3 A hierarchical structure diagram of a sub-cell provided by an embodiment of the present application is shown in the figure.

[0028] Figure 4 A top view structural diagram of a photovoltaic cell provided by an embodiment of the present application is shown in the figure.

[0029] Figure 5 A step flow chart of a preparation method of a photovoltaic cell provided by an embodiment of the present application is shown in the figure.

[0030] Figure 6 A process flow chart of a photovoltaic cell provided by an embodiment of the present application is shown in the figure.

[0031] Explanation of reference signs:

[0032] 100 - substrate;

[0033] 200 - sub-cell; 200a - first sub-cell; 200b - second sub-cell; 200c - third sub-cell; 200d - N-1th sub-cell; 200e - Nth sub-cell; 210 - window layer; 220 - emission region; 230 - base region; 240 - back field layer; 250 - ohmic contact layer; 260 - gate line electrode; 201 - step surface; 2011 - first step part; 2012 - second step part;

[0034] 300 - tunnel junction;

[0035] 400 - bottom electrode;

[0036] 500 - adjustable electrode; 500a - first electrode; 500b - second electrode; 500c - third electrode; 500d - N-1th electrode; 500e - Nth electrode; 501 - first terminal; 502 - second terminal;

[0037] 600 - insulating layer;

[0038] 10 - first mask plate; 20 - second mask plate; 30 - N-1th mask plate. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0040] Laser wireless energy transmission technology is a technology that uses laser as a carrier to transmit energy to a remote device through space. Laser photovoltaic cells, as key components of laser wireless energy transmission, have a band gap that matches the photon energy of the target wavelength, enabling maximum absorption and conversion of photon energy, and still outputting high photoelectric conversion efficiency under low photon flux.

[0041] In traditional laser wireless energy transmission technology, the high conversion efficiency and driving voltage of laser photovoltaic cells are one of the key elements to solve the charging and endurance problems of various aerospace applications such as unmanned aerial vehicles, spacecraft, and robots working in extreme conditions. However, with the rise of the Internet of Things, new requirements have been placed on laser wireless energy transmission technology. Some micro sensors, detectors, and other devices only require a few hundred millivolts or even tens of millivolts of driving voltage each time, and it is very convenient to use a laser beam to charge these electronic devices without the need for long-term power supply. Laser wireless energy transmission technology will also become an ideal power supply technology for micro-power electronic devices.

[0042] To meet the driving voltage requirements of laser photovoltaic cells in different application scenarios, common solutions for preparing laser photovoltaic cells with different voltages include: (1) selecting multiple absorption layer materials with different bandgap widths to prepare multiple laser photovoltaic cells with different output voltages. (2) achieving different voltage outputs by connecting different numbers of laser photovoltaic cells in series. Among them, the series connection method can be divided into two types. One is multi-junction lobe series connection. This series connection method involves etching isolation trenches and evaporating metal electrodes, and then connecting the upper and lower electrodes using lead wire technology. The process is complex and requires high beam uniformity. The other is multi-junction stacked series connection. The multi-junction stacked series connection structure is completed during the epitaxial layer growth process. This method does not require metal leads or deep etching for isolation. The process is simple and the fabrication cycle is short. Moreover, the series resistance introduced by the tunnel junction connection is very small. At present, the multi-junction stacked series connection method has become the mainstream solution to improve the output voltage.

[0043] However, the rated output voltage of laser photovoltaic cells prepared by these methods is also uniquely determined. To meet the varying driving voltage requirements of different applications, it is often necessary to prepare multiple cells with different voltages to satisfy customized output needs. Therefore, traditional laser photovoltaic cells cannot be universally applied to different scenarios, which increases production costs and hinders their efficient use.

[0044] In view of this, embodiments of this application provide a voltage-adjustable photovoltaic cell and its fabrication method. This photovoltaic cell comprises multiple sub-cells stacked sequentially on a substrate, with adjacent sub-cells connected in series via tunnel junctions, enabling the photovoltaic cell to achieve a larger output voltage. Furthermore, for each sub-cell below the top layer, a stepped surface is formed on the upper surface of each sub-cell, located outside the adjacent sub-cell above it. By connecting adjustable electrodes to the upper surface of each sub-cell and placing corresponding adjustable electrodes on the corresponding stepped surfaces, the bottom electrode below the substrate can be connected to a circuit along with any of the adjustable electrodes.

[0045] This configuration allows for flexible adjustment of the photovoltaic cell's output voltage, enabling it to meet the demands of different driving voltages and be suitable for various application scenarios. This improves the versatility of the photovoltaic cell, significantly reduces its production cost, and enhances its economic viability. Furthermore, photovoltaic cells are simple to manufacture and highly reliable.

[0046] The voltage-adjustable photovoltaic cell provided in this embodiment will be described in detail below with reference to the accompanying drawings.

[0047] Figure 1 This is a schematic diagram of the structure of a voltage-adjustable photovoltaic cell provided in an embodiment of this application. Figure 2This is a schematic diagram of another voltage-adjustable photovoltaic cell provided in an embodiment of this application. (Refer to...) Figure 1 or Figure 2 As shown, this application provides a voltage-adjustable photovoltaic cell, which includes a substrate 100, a plurality of sub-cells 200 and a plurality of tunnel junctions 300. The plurality of sub-cells 200 are sequentially disposed on the substrate 100, and a tunnel junction 300 is disposed between every two layers of sub-cells 200.

[0048] The substrate 100 serves as a basic support layer, providing fundamental support for the structural layers formed thereon (including sub-cells 200 and tunnel junctions 300), and also protecting these structural layers. Each sub-cell 200 converts light energy into electrical energy for storage and can transmit the stored electrical energy to electrical devices. The tunnel junction 300 enables the series connection between the sub-cells 200, utilizing the quantum tunneling effect to transport charge carriers while maintaining optical transmittance, thus achieving continuous transmission of photocurrent within each sub-cell 200.

[0049] The tunnel junction 300 can be formed using a heavily doped semiconductor material, and the tunnel junction 300 includes N... ++ Type semiconductor layer and P ++ Type semiconductor layer. N ++ The N-type semiconductor layer and the N-type semiconductor in the sub-cell 200 are connected, P ++ The heavily doped tunnel junction 300 connects the P-type semiconductor layer and the P-type semiconductor in the sub-cell 200. This low-resistance connection between the sub-cells 200 helps reduce internal electrical losses and thus improves the overall photoelectric conversion efficiency of the photovoltaic cell.

[0050] Continue to refer to Figure 1 or Figure 2 The photovoltaic cell provided in this embodiment also includes a bottom electrode 400 and a plurality of adjustable electrodes 500. The bottom electrode 400 is disposed on one side of the back ion cell 200 of the substrate 100, and each adjustable electrode 500 is connected to each sub-cell 200. The bottom electrode 400 can be used as the positive electrode of the photovoltaic cell in the circuit, and each adjustable electrode 500 can be used as the negative electrode of the photovoltaic cell in the circuit.

[0051] Regarding the arrangement of the adjustable electrodes 500, the entire upper surface of the top sub-cell 200 of the photovoltaic cell is exposed, and the corresponding adjustable electrode 500 can be connected to its upper surface. For each sub-cell 200 below the top sub-cell 200, to reserve connection positions for the adjustable electrodes 500 in these sub-cells 200, a stepped surface 201 is formed on the upper surface of each sub-cell 200, exposed outside the adjacent sub-cell 200 above. The adjustable electrode 500 corresponding to each sub-cell 200 below the top sub-cell 200 can be connected to the stepped surface 201 of the corresponding sub-cell 200.

[0052] In fabricating photovoltaic cells, multiple sub-cells 200 and tunnel junctions 300 between adjacent sub-cells 200 can be grown on a substrate 100 first. Then, the sub-cells 200 above the bottom sub-cells 200 and the tunnel junctions 300 are etched to remove portions of these sub-cells 200 and tunnel junctions 300, forming step surfaces 201 on the upper surface of the sub-cells 200 below the top sub-cells 200. Next, tunable electrodes 500 are formed on each sub-cell 200 through deposition and photolithography processes. The tunable electrodes 500 corresponding to each sub-cell 200 below the top sub-cell 200 are all formed on the step surfaces 201 of the corresponding sub-cells 200.

[0053] like Figure 1 or Figure 2 As shown, for ease of explanation, this embodiment defines N sub-cells 200 located on the substrate 100. Along the direction from the sub-cell 200 to the substrate 100, these N sub-cells 200 are sequentially arranged as a first sub-cell 200a, a second sub-cell 200b, a third sub-cell 200c, ..., an (N-1)th sub-cell 200d, and an Nth sub-cell 200e. Correspondingly, the adjustable electrodes 500 connected to the first sub-cell 200a, the second sub-cell 200b, the third sub-cell 200c, ..., the (N-1)th sub-cell 200d, and the Nth sub-cell 200e are defined as the first electrode 500a, the second electrode 500b, the third electrode 500c, ..., the (N-1)th electrode 500d, and the Nth electrode 500e, respectively. For example, N can be a positive integer greater than or equal to 5. That is, the photovoltaic cell provided in this embodiment can have more than 5 sub-cells 200 connected in series.

[0054] The first sub-cell 200a, the second sub-cell 200b, the third sub-cell 200c, …, the N-1th sub-cell 200d (and the tunnel junction 300 below the sub-cells 200) can be etched to remove part of the first sub-cell 200a, the second sub-cell 200b, the third sub-cell 200c, …, the N-1th sub-cell 200d, so that the stacked structure of the sub-cells 200 forms a stepped structure, and the upper surfaces of the second sub-cell 200b, the third sub-cell 200c, …, the N-1th sub-cell 200d, and the Nth sub-cell 200e all form stepped surfaces 201. The first electrode 500a is formed on the top surface of the photovoltaic cell, and the second electrode 500b, the third electrode 500c, …, the N-1th electrode 500d, and the Nth electrode 500e are respectively formed on the stepped surfaces 201 of the corresponding sub-cells 200.

[0055] In this embodiment, the plurality of sub-cells 200 are sequentially grown on the substrate 100, and the adjacent sub-cells 200 are connected by the tunnel junction 300. The plurality of sub-cells 200 are stacked in series, so that the photovoltaic cell can have a larger output voltage. On this basis, the stacked structure of the sub-cells 200 is etched to form a stepped structure, and the adjustable electrode 500 is connected to each sub-cell 200, and any adjustable electrode 500 can be connected to the circuit according to requirements.

[0056] In this way, the output voltage of the photovoltaic cell can be flexibly adjusted to meet different requirements for driving voltage in different application scenarios, and the photovoltaic cell can be applied to different application scenarios. For example, the photovoltaic cell can be applied to the aerospace field such as unmanned aerial vehicles and spacecraft, and the photovoltaic cell can also be applied to the field of micro devices such as micro sensors and detectors. Compared with the related art, which needs to prepare a plurality of batteries with different voltages to meet the requirements of different driving voltages, the photovoltaic cell of the present embodiment can output different voltages, improve the versatility of the photovoltaic cell, and significantly reduce the production cost of the photovoltaic cell and improve the economy of the photovoltaic cell.

[0057] For example, when the bottom electrode 400 and the first electrode 500a of the first sub-cell 200a are connected to the circuit, the photovoltaic cell outputs the total voltage of the N sub-cells 200. When the bottom electrode 400 and the second electrode 500b of the second sub-cell 200b are connected to the circuit, the photovoltaic cell outputs the total voltage of the N-1 sub-cells 200. Similarly, when the bottom electrode 400 and the Nth electrode 500e of the Nth sub-cell 200e are connected to the circuit, the photovoltaic cell outputs the total voltage of a single sub-cell 200.

[0058] And, after the growth of the stack of multiple sub-cells 200 on the substrate 100, the step-like structure is formed by etching the stack structure, and then the adjustable electrodes 500 are connected to each sub-cell 200 to form the photovoltaic cell. The photovoltaic cell is simple in manufacturing, low in manufacturing cost, high in manufacturing efficiency, and high in reliability.

[0059] In addition, since the step surface 201 is formed on the upper surface of the sub-cell 200 based on the etching process in the embodiment, and then the adjustable electrode 500 is connected to the step surface 201. This method has obvious technical universality and can be widely used in various types of photovoltaic device fields. For example, the photovoltaic cell of the embodiment can be a laser photovoltaic cell, and the light source supplied to the photovoltaic cell can be a laser beam. Alternatively, the photovoltaic cell of the embodiment can also be a solar photovoltaic cell, and the light source supplied to the photovoltaic cell can be sunlight.

[0060] For example, the substrate 100 of the laser photovoltaic cell can use germanium (Ge), GaAs (gallium arsenide), AlGaAs (aluminum gallium arsenide), or (Al) GaInP (aluminum gallium indium phosphorus) and other materials. When the photovoltaic cell is a solar photovoltaic cell, the substrate 100 of the photovoltaic cell mainly considers support and reliability. For example, the substrate 100 of the solar photovoltaic cell can use single crystal silicon, polycrystalline silicon, silicon carbide (SiC), silicon oxide (SiO2), glass, stainless steel, etc.

[0061] As for the specific structure of the step-like structure formed by the stack structure of the photovoltaic cell, the planar shape of the photovoltaic cell is mostly rectangular, and the edge regions of the first sub-cell 200a, the second sub-cell 200b, …, the N-1th sub-cell 200d can be etched, and by controlling the etching amount, the stack structure of the sub-cell 200 forms a step-like structure, and the step surface 201 is formed on the edge region of the upper surface of the second sub-cell 200b, the third sub-cell 200c, …, the Nth sub-cell 200e.

[0062] Referring to Figure 1 As an embodiment, only one side edge of the photovoltaic cell can be etched, and the etched side of the photovoltaic cell is defined as the first side in the embodiment. The step surface 201 formed on the second sub-cell 200b, the third sub-cell 200c, …, the Nth sub-cell 200e includes a first step portion 2011 located at the first side of the corresponding sub-cell 200. At this time, the adjustable electrode 500 connected to each sub-cell 200 includes a first terminal 501, and the first terminal 501 connected to the second sub-cell 200b, the third sub-cell 200c, …, the Nth sub-cell 200e is located at the first step portion 2011 of the corresponding sub-cell 200.

[0063] In this way, the number of terminals of the adjustable electrode 500 connected to each sub-cell 200 is one, and each sub-cell 200 has only one circuit access point. The access point of the sub-cell 200 can be quickly located, and the accuracy and reliability are high.

[0064] Referring to Figure 2 As another embodiment, as shown in FIG. 2B, the two side edges of the photovoltaic cell can be etched. Based on etching the first side of the photovoltaic cell, the second side of the photovoltaic cell is also etched. The step surface 201 formed on the second sub-cell 200b, the third sub-cell 200c, …, and the Nth sub-cell 200e includes the first step part 2011 on the first side of the corresponding sub-cell 200 and the second step part 2012 on the second side of the corresponding sub-cell 200. At this time, the adjustable electrode 500 connected to each sub-cell 200 can include the first terminal 501 and the second terminal 502. The first terminal 501 and the second terminal 502 connected to the second sub-cell 200b, the third sub-cell 200c, …, and the Nth sub-cell 200e are respectively located at the first step part 2011 and the second step part 2012 of the corresponding sub-cell 200.

[0065] Figure 2 For example, the first step part 2011 and the second step part 2012 are located at opposite sides of the photovoltaic cell, and the first terminal 501 and the second terminal 502 are respectively connected to the opposite side edges of the sub-cell 200, for example, the first terminal 501 and the second terminal 502 are symmetrically arranged at the opposite sides of the sub-cell 200. Of course, the first step part 2011 and the second step part 2012 can also be located at adjacent sides of the photovoltaic cell, and the first terminal 501 and the second terminal 502 are respectively connected to the adjacent side edges of the sub-cell 200.

[0066] In this way, the number of terminals of the adjustable electrode 500 connected to each sub-cell 200 is two, and each sub-cell 200 has two circuit access points. Either the first terminal 501 or the second terminal 502 can be selected to access the circuit, thereby providing a more flexible voltage regulation mode. The first terminal 501 and the second terminal 502 are designed in a redundant manner, and when one of the terminals is damaged, the other terminal can still connect the sub-cell 200 to the circuit.

[0067] In other embodiments, based on the first step part 2011 and the second step part 2012, the step surface 201 can also include a third step part located at a third side of the sub-cell 200 and / or a fourth step part located at a fourth side of the sub-cell 200. Correspondingly, the adjustable electrode 500 connected to each sub-cell 200 can also include a third terminal and / or a fourth terminal. The third terminal is connected to the third step part, and the fourth terminal is connected to the fourth step part. The embodiments of the present application do not limit this.

[0068] As shown in Figure 1 and Figure 2 The tunable electrode 500 can also be provided with an insulating layer 600 between the sidewall of the tunable electrode 500 and the sidewall of the sub-cell 200 in the same layer. The insulating layer 600 is, for example, a silicon oxide layer, and the tunable electrode 500 is electrically isolated from the sub-cell 200 in the same layer by the insulating layer 600. The insulating layer 600 can effectively block the parasitic current path and ensure that the voltage gradient is determined only by the selected number of series connections of the tunable electrode 500, thereby achieving precise voltage regulation. Taking the tunable electrode 500 as an example, the Xth electrode connected to the Xth sub-cell 200, the parasitic current is blocked by the insulating layer 600, and it can be ensured that the output voltage is determined only by the number of series connections of the Xth sub-cell 200 to the Nth sub-cell 200e.

[0069] Before forming the tunable electrode 500, the insulating layer 600 can be formed on the stepped surface 201 of the second sub-cell 200b, the third sub-cell 200c, …, and the Nth sub-cell 200e. Then the tunable electrode 500 is deposited on the side of the insulating layer 600 away from the sub-cell 200. The insulating layer 600 can serve as the basis for forming the tunable electrode 500, and it fills the gap between the tunable electrode 500 and the sub-cell 200 in the same layer. The insulating layer 600 can support the sidewall of the tunable electrode 500 and improve the reliability of the tunable electrode 500.

[0070] It can be understood that, due to the tunnel junction 300 provided between adjacent sub-cells 200, the side of the tunable electrode 500 is the stacked structure of the tunnel junction 300 and the sub-cell 200. For the insulating layer 600 provided between the tunable electrode 500 and the sub-cell 200, the insulating layer 600 also covers the sidewall of the corresponding tunnel junction 300. For example, the insulating layer 600 can completely cover the sidewall of the tunnel junction 300 and cover part of the sidewall of the sub-cell 200.

[0071] Figure 3 A hierarchical structure diagram of the sub-cell provided in the embodiments of the present application is provided. Referring to Figure 3 As shown in

[0072] The window layer 210 is located on top of the sub-cell 200, and its main function is to reduce surface recombination, preventing photo-generated electrons and holes from recombining before reaching the tunable electrode 500. The window layer 210 is usually made of a material that is lattice-matched to the material of the absorber layer. Such a material has high optical transparency and low electrical resistivity, allowing light to enter the sub-cell 200 while also allowing electrons to easily escape from the sub-cell 200.

[0073] The emitter region 220 is located next to the base region 230, and the emitter region 220 is usually N-type doped.

[0074] The base region 230 is located between the back surface field layer 240 and the emitter region 220, and the base region 230 is usually P-type doped.

[0075] The back surface field layer 240 is located at the bottom of the sub-cell 200, and its main function is to reduce the surface recombination rate, increase the lifetime of minority carriers, and help collect photo-generated carriers generated in the base region 230.

[0076] When the photovoltaic cell is in operation, the light source is incident from the side where the first sub-cell 200a is located. The first sub-cell 200a absorbs part of the light, and the remaining light then enters the second sub-cell 200b, which in turn absorbs part of the light. In this way, the last remaining light eventually enters the Nth sub-cell 200e and is fully absorbed by the Nth sub-cell 200e. In order to make the photo-generated current generated by the N sub-cells 200 the same, according to Lambert-Beer's law, the thickness of the PN junction light-absorbing layer of the first sub-cell 200a to the Nth sub-cell 200e needs to be designed to increase in turn.

[0077] That is, in the direction of the sub-cell 200 pointing to the substrate 100, the total thickness of the emitter region 220 and the base region 230 in each sub-cell 200 increases in turn. Along the direction of the light source incident, the total thickness of the emitter region 220 and the base region 230 of each sub-cell 200 arranged in turn increases in the order of the first sub-cell 200a to the Nth sub-cell 200e, which satisfies Lambert-Beer's law to keep the light absorption of each sub-cell 200 consistent. Along the direction of the sub-cell 200 pointing to the substrate 100, since the total thickness of the emitter region 220 and the base region 230 in each sub-cell 200 increases in turn, the overall thickness of each sub-cell 200 can also increase in turn (as shown in Figure 1 or Figure 2 ).

[0078] Continuing to refer to Figure 3 , the sub-cell 200 can also include an ohmic contact layer 250, which is disposed on the window layer 210, and the tunable electrode 500 can be connected to the ohmic contact layer 250. The ohmic contact layer 250 can reduce the contact resistance between the tunable electrode 500 and the semiconductor material layer of the sub-cell 200, thereby improving the fill factor of the sub-cell 200 and improving the overall power supply efficiency of the photovoltaic cell.

[0079] Figure 4 This is a top view of the photovoltaic cell provided in an embodiment of this application. (Refer to...) Figure 4 As shown, the top surface of the photovoltaic cell is also provided with grid electrodes 260, which can be disposed on the top surface of the top sub-cell 200. For example, the grid electrodes 260 are disposed on the window layer 210 of the top sub-cell 200. Alternatively, when the top sub-cell 200 is provided with an ohmic contact layer 250 on the window layer 210, the grid electrodes 260 can be disposed on the ohmic contact layer 250 of the top sub-cell 200. The grid electrodes 260 are used to collect photogenerated electrons generated on the surface of the sub-cell 200 and effectively transmit them to an external circuit, thereby realizing the conversion of light energy into electrical energy.

[0080] By reducing lateral resistance loss through the gate electrode 260, low-resistance and high-efficiency collection of photogenerated carriers can be achieved. The gate electrode 260 can be formed using a highly conductive metallic material, such as gold (Au), silver (Ag), titanium (Ti), or platinum (Pt).

[0081] The design parameters of the grid lines, such as their number, width, height, and shape, all affect the photoelectric conversion efficiency of photovoltaic cells. For example, the number and width of the grid lines affect the transmission path of lateral current and shading losses, while the height and shape affect the resistance and contact resistance of the grid lines. Therefore, by optimizing the geometric arrangement of the grid lines, such as their width, spacing, and height, a balance can be found between reducing series resistance and shading losses, thus achieving optimal performance of the sub-cell 200.

[0082] This application also provides a method for preparing a voltage-adjustable photovoltaic cell, which is used to prepare the aforementioned photovoltaic cell.

[0083] Figure 5 A flowchart illustrating the steps of a photovoltaic cell fabrication method provided in this application embodiment. Figure 6 This is a process flow diagram for preparing photovoltaic cells provided in the embodiments of this application.

[0084] Reference Figure 5 As shown, the preparation method provided in this application includes the following steps:

[0085] S100. Provides a substrate.

[0086] Reference Figure 6 As shown in the figure, the adjustable electrode 500 is provided on one side edge of the photovoltaic cell as an example for illustration. It can be understood that the manufacturing process of the adjustable electrode 500 provided on two, three, or four sides of the photovoltaic cell is similar to the manufacturing process of the adjustable electrode 500 provided on one side edge.

[0087] Referring to Figure 6 (a) of FIG. 1, a substrate 100 is first provided as a base support structure.

[0088] S200. A plurality of sub-cells are sequentially grown on the substrate, and a tunnel junction is grown between each two sub-cells; wherein, along the direction of the sub-cells pointing to the substrate, the plurality of sub-cells are sequentially a first sub-cell, a second sub-cell, …, an Nth sub-cell.

[0089] Continuing to refer to Figure 6 (a) of FIG. 1, a plurality of sub-cells 200 are sequentially grown on the substrate 100 by using a Metal-Organic Chemical Vapor Deposition (MOCVD) process, and a tunnel junction 300 is grown between each two sub-cells 200. Wherein, along the direction of the sub-cells 200 pointing to the substrate 100, the plurality of sub-cells 200 are sequentially a first sub-cell 200a, a second sub-cell 200b, …, an Nth sub-cell 200e.

[0090] S300. A photolithography process is used to etch the first sub-cell, the second sub-cell, …, the N-1th sub-cell, so as to form a step surface on the upper surface of each sub-cell below the first sub-cell.

[0091] Next, a photolithography process is used to sequentially etch the first sub-cell 200a, the second sub-cell 200b, …, the N-1th sub-cell 200d, so as to etch away part of the regions of the first sub-cell 200a, the second sub-cell 200b, …, the N-1th sub-cell 200d. In this way, a step surface 201 is formed on the upper surface of each sub-cell 200 below the first sub-cell 200a, i.e., the second sub-cell 200b, the third sub-cell 200c, …, the Nth sub-cell 200e.

[0092] It should be noted that, since a tunnel junction 300 is provided between each two sub-cells 200, the etching of the first sub-cell 200a as described herein includes synchronously etching the tunnel junction 300 below the first sub-cell 200a. Similarly, the etching of the second sub-cell 200b includes synchronously etching the tunnel junction 300 below the second sub-cell 200b. … The etching of the N-1th sub-cell 200d includes synchronously etching the tunnel junction 300 below the N-1th sub-cell 200d.

[0093] The photolithography process used to etch the first sub-cell 200a, the second sub-cell 200b, …, the N-1th sub-cell 200d specifically includes the following steps:

[0094] A first mask 10 is disposed on the first sub-cell 200a, and the first sub-cell 200a is etched along the first mask 10.

[0095] Referring to (b) of FIG. 1, a photoresist layer is coated on the upper surface of the first sub-cell 200a, and the photoresist layer is exposed and developed to form the first mask 10. Figure 6 Referring to (c) of FIG. 1, the first sub-cell 200a and the tunnel junction 300 thereunder are etched along the first mask 10, and part of the first sub-cell 200a and the tunnel junction 300 thereunder are removed to expose part of the upper surface of the second sub-cell 200b. Figure 6 A second mask 20 is disposed on the first sub-cell 200a and the second sub-cell 200b, and the second sub-cell 200b is etched along the second mask 20.

[0096] Referring to (d) of FIG. 1, a photoresist layer is coated on the upper surface of the first sub-cell 200a and the exposed region of the upper surface of the second sub-cell 200b, and the photoresist layer is exposed and developed to form the second mask 20.

[0097] Referring to (e) of FIG. 1, the second sub-cell 200b and the tunnel junction 300 thereunder are etched along the second mask 20, and part of the second sub-cell 200b and the tunnel junction 300 thereunder are removed to expose part of the upper surface of the third sub-cell 200c. Figure 6 Figure 6 Referring to (f) of FIG. 1, a photoresist layer is coated on the upper surface of the first sub-cell 200a, the exposed region of the upper surface of the second sub-cell 200b, …, the exposed region of the upper surface of the N-1th sub-cell 200d, and the photoresist layer is exposed and developed to form the N-1th mask 30. Referring to (g) of FIG. 1, the N-1th sub-cell 200d and the tunnel junction 300 thereunder are etched along the N-1th mask 30, and part of the N-1th sub-cell 200d and the tunnel junction 300 thereunder are removed to expose part of the upper surface of the Nth sub-cell 200e.

[0098] Figure 6 In this way, the stacked structure of the sub-cells 200 forms a stepped structure, and the upper surfaces of the second sub-cell 200b, the third sub-cell 200c, …, and the Nth sub-cell 200e each form a stepped surface 201. Figure 6 S400. An adjustable electrode is formed on the upper surface of each sub-cell, so that the corresponding adjustable electrode is located on the corresponding stepped surface.

[0099] Referring to (h) of FIG. 1, a photoresist layer is coated on the upper surface of the first sub-cell 200a, the exposed region of the upper surface of the second sub-cell 200b, …, the exposed region of the upper surface of the Nth sub-cell 200e, and the photoresist layer is exposed and developed to form the Nth mask 40.

[0100] Referring to (i) of FIG. 1, the Nth sub-cell 200e and the tunnel junction 300 thereunder are etched along the Nth mask 40, and part of the Nth sub-cell 200e and the tunnel junction 300 thereunder are removed to expose part of the upper surface of the (N+1)th sub-cell 200f.

[0101] Figure 6 ​​As shown in (h), after a stepped surface 201 is formed on the upper surface of the second sub-cell 200b, the third sub-cell 200c, ..., the Nth sub-cell 200e, each tunable electrode 500 is prepared by deposition and photolithography, so that the first electrode 500a is formed on the top surface of the photovoltaic cell, and the second electrode 500b, the third electrode 500c, ..., the Nth electrode 500e are respectively formed on the stepped surface 201 of the corresponding sub-cell 200.

[0102] A metal electrode layer can be deposited on the photovoltaic cell first, covering the surface of the first sub-cell 200a and the step surface 201 of the second sub-cell 200b, the third sub-cell 200c, ..., the Nth sub-cell 200e. Then, through a photolithography process, each adjustable electrode 500 is formed on each sub-cell 200.

[0103] It should be noted that the figure does not show the formation of an insulating layer 600 between the adjustable electrode 500 and the co-layer sub-cell 200 (see [reference]). Figure 1 or Figure 2 The process is as follows: When an insulating layer 600 is provided between the tunable electrode 500 and the sidewall of the sub-cell 200 in the same layer, before fabricating each tunable electrode 500, the insulating layer 600 can be formed on the sidewall of the first sub-cell 200a, the second sub-cell 200b, ..., the N-1th sub-cell 200d by deposition and photolithography.

[0104] Reference Figure 6 As shown in (i), after the tunable electrodes 500 are fabricated, a bottom electrode 400 is deposited on the back side of the substrate 100. Finally, the photovoltaic cell is fabricated by an annealing process.

[0105] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not 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 application.

[0106] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A voltage adjustable photovoltaic cell, characterized by, The application relates to a solar cell, comprising: a substrate; a plurality of sub-cells, each of which is sequentially stacked on the substrate, and each of the sub-cells has a stepped surface above an adjacent sub-cell; a plurality of tunnel junctions, each of which is arranged between two adjacent sub-cells; a bottom electrode arranged on a side of the substrate away from the sub-cells; and a plurality of adjustable electrodes, each of which is connected to a corresponding sub-cell and located on a corresponding stepped surface. The stepped surface comprises at least a first stepped portion on a first side of the sub-cell.

2. The voltage adjustable photovoltaic cell of claim 1, wherein, The adjustable electrode comprises at least a first terminal located on the corresponding first stepped portion. The stepped surface further comprises a second stepped portion on a second side of the sub-cell.

3. The voltage adjustable photovoltaic cell of claim 2, wherein, The adjustable electrode further comprises a second terminal located on the corresponding second stepped portion. An insulating layer is arranged between the adjustable electrode and a sidewall of the sub-cell.

4. Voltage adjustable photovoltaic cell according to any of claims 1 to 3, characterized in that In a direction of the sub-cell pointing to the substrate, the sub-cell comprises, sequentially from top to bottom, a window layer, an emitter region, a base region and a back field layer.

5. Voltage adjustable photovoltaic cell according to any of claims 1-3, characterized in that, In a direction of the sub-cell pointing to the substrate, the total thickness of the emitter region and the base region in each of the sub-cells increases sequentially from top to bottom.

6. The voltage adjustable photovoltaic cell of claim 5, wherein, The sub-cell further comprises:

7. The voltage adjustable photovoltaic cell of claim 5, wherein, an ohmic contact layer arranged on the window layer. The application further relates to a solar cell, comprising:

8. The voltage adjustable photovoltaic cell of claim 5, wherein, a gate line electrode arranged on a top surface of a top layer of the sub-cell. The application further relates to a method for manufacturing a solar cell, comprising:

9. A method for producing a voltage-tunable photovoltaic cell, characterized by, providing a substrate; sequentially growing a plurality of sub-cells and a tunnel junction between each two of the sub-cells on the substrate, wherein in a direction of the sub-cell pointing to the substrate, the plurality of sub-cells are sequentially a first sub-cell, a second sub-cell,..., and an Nth sub-cell; etching the first sub-cell, the second sub-cell,..., and an N-1th sub-cell by using a photolithography process to form a stepped surface on a top surface of each of the sub-cells below the first sub-cell; forming an adjustable electrode on the top surface of each of the sub-cells so that a corresponding adjustable electrode is located on a corresponding stepped surface. forming a stepped surface on a top surface of each of the sub-cells below a top layer of the sub-cell, comprising:

10. The method for preparing a voltage-adjustable photovoltaic cell according to claim 9, characterized in that, arranging a first mask on the first sub-cell, and etching the first sub-cell along the first mask; arranging a second mask on the first sub-cell and the second sub-cell, and etching the second sub-cell along the second mask; and so on, until arranging an N-1th mask on the first sub-cell, the second sub-cell,..., and the N-1th sub-cell, and etching the N-1th sub-cell along the N-1th mask. ​

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