Front structure of Topcon solar cell, Topcon solar cell and preparation

Abstract

The invention discloses a front structure of a Topcon solar cell, the Topcon solar cell and preparation, and belongs to the technical field of solar cells. The front surface contact structure comprises a first conductive layer, a passivation antireflection layer and a first metal electrode which are arranged on the front surface of the silicon wafer; wherein the first metal electrode penetrates through the passivation antireflection layer and is in contact with the first conductive layer; in addition, other media exist on the interface of the first metal electrode and the first conductive layer; meanwhile, metal points containing aluminum do not exist, the other media have a passivation effect, the passivation effect is improved, contact recombination between the first metal electrode and the first conductive layer can be effectively reduced, and the conversion efficiency of the Topcon solar cell is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a front structure of a Topcon solar cell, a Topcon solar cell and a preparation method thereof. Background Art

[0002] Solar cells generally include a substrate and an emitter region formed by semiconductors having different conductivity types (e.g., p-type and n-type), and electrodes connected to the substrate and emitter regions of different conductivity types, respectively. In this case, the substrate and the emitter region form a pn junction. When light is incident on the solar cell, a plurality of electron-hole pairs are generated in the semiconductor by the incident light, and they are separated into electrons and holes. The electrons move to the n-type semiconductor (e.g., the emitter region), and the holes move to the p-type semiconductor (e.g., the substrate). Then, the electrons and holes are collected by the electrodes electrically connected to the substrate and the emitter region, and the electrodes are connected to each other using wires, thereby obtaining electricity. Tunnel Oxide Passivated Contact solar cell (Topcon cell) is one of the most promising and efficient solar cell structures. This type of cell usually prepares a thin tunnel oxide layer on the back of the silicon wafer, and then deposits a doped polysilicon layer on the surface of the tunnel oxide layer. The two together form a passivation contact structure. On this basis, a hydrogenated dielectric layer (such as SiN x 、SiO2 / SiN x The laminated film, Al2O3 film), can further provide good interface passivation effect and field passivation effect for the back of the silicon wafer, significantly improve the internal transport of carriers, and reduce the recombination and contact resistance of the metal electrode contact area. The boron diffusion is carried out on the front of the Topcon battery to form a conductive layer, and has a passivation anti-reflection layer. At the same time, in order to establish a better ohmic contact, the preparation of the electrode structure on the front of the Topcon battery often requires the use of silver-containing metal paste (hereinafter referred to as Ag paste). The metal paste penetrates the passivation layer at high temperature and forms an ohmic contact with the doped layer. However, the Ag paste used contains Al elements, and the sintering process after printing is often accompanied by the formation of AgAl spikes, which causes very serious damage to the passivation layer and the front diffusion area. The damage is also relatively serious, resulting in very large recombination. Among the many factors that limit the efficiency of silicon-based solar cells, the contact recombination between the metal electrode and the silicon-based area is a key factor affecting the photoelectric conversion efficiency. Summary of the invention

[0003] 1. Problem to be solved One of the purposes of the present invention is to provide a front structure of a Topcon solar cell, aiming to improve the conversion efficiency of the solar cell; at the same time, the present invention also provides a front contact structure of the solar cell and a preparation process of the solar cell.

[0004] 2. Technical solution In order to solve the above problems, the technical solution adopted by the present invention is as follows: According to the purpose of the present invention, a first aspect of the present invention provides a front structure of a Topcon solar cell, wherein the front contact structure comprises a first conductive layer, a passivation anti-reflection layer and a first metal electrode arranged on the front of a silicon wafer; Wherein, the first metal electrode contacts the first conductive layer through the passivation anti-reflection layer; Furthermore, other media exist at the interface between the first metal electrode and the first conductive layer (may be referred to as the interface for short).

[0005] According to the purpose of the present invention, a first aspect of the present invention provides a front structure of a Topcon solar cell, wherein no metal point containing aluminum exists in the first metal electrode and the first conductive layer region; More specifically, there are no metal spots containing the same metal as the metal electrode and aluminum; For example, if the first metal electrode is a silver electrode, there are no metal points containing silver and aluminum (hereinafter referred to as AgAl points) between the first metal electrode and the first conductive layer region.

[0006] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the material of the other medium includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0007] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the material of the other medium contains the material of the passivation anti-reflection layer.

[0008] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the other medium is in a layered form, and the layered form includes a quasi-layered form.

[0009] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the other medium is less than the thickness of the passivation anti-reflection layer.

[0010] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the other medium is 1-120 nm.

[0011] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the area of ​​the interface between the first metal electrode and the first conductive layer is S; The coverage area of ​​the other medium is S1; Calculated with S, the proportion of S1 does not exceed 99%; preferably, the proportion of S1 is 10-99%; further preferably, the proportion of S1 is 10-90%.

[0012] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the doping concentration of the first conductive layer is 1e18-1e20cm -3 .

[0013] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the sheet resistance of the first conductive layer is 100-600 ohm / sqr.

[0014] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, doped silicon dioxide also exists at the interface between the first metal electrode and the first conductive layer.

[0015] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the doped silicon dioxide is doped in any one, two or more of the following ways: PbO, B2O3, Al2O3, Ga2O3, AgO, NaO, and LiO2.

[0016] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the doped silicon dioxide is 2-800 nm.

[0017] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the doped silicon dioxide is layered or quasi-layered; Alternatively, the layer has a thickness of 2 to 800 nm.

[0018] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the area of ​​the interface between the first metal electrode and the first conductive layer is S; The coverage area of ​​the doped silicon dioxide is S2; Calculated with S, the proportion of S2 is not less than 2%; preferably, the proportion of S2 is 2-100%; further preferably, the proportion of S2 is 2-99%.

[0019] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the first conductive layer is an element diffusion layer; The thickness of the first conductive layer is 300-1500 nm; The element doping concentration of the first conductive layer is 1E18 cm -3 ~1E20 cm -3 ; The element doping depth (junction depth) of the first conductive layer is 300-1500nm.

[0020] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the first conductive layer is a boron element diffusion layer.

[0021] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the passivation anti-reflection layer is 20-120 nm.

[0022] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the passivation anti-reflection layer comprises a passivation layer and an anti-reflection layer.

[0023] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the passivation layer is 2-10 nm; preferably, the thickness of the passivation layer is 2-5 nm.

[0024] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the thickness of the anti-reflection layer is 40-120 nm; preferably, the thickness of the anti-reflection layer is 50-120 nm.

[0025] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the passivation anti-reflection layer includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0026] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the passivation layer includes any one or two or more of oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon carbide).

[0027] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the anti-reflection layer includes any one or two or more of oxides (such as aluminum oxide) and silicides (such as silicon dioxide, silicon nitride, silicon carbide).

[0028] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, there are metal dots at the interface between the first metal electrode and the first conductive layer; The metal dots contain silver and silicon.

[0029] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the size of the metal dots is 20-800 nm.

[0030] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the embedding depth of the metal dots in the silicon wafer is 20-500 nm.

[0031] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, metal particles (or also referred to as metal particles) are present at the interface between the first metal electrode and the first conductive layer.

[0032] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the metal particles are present in the doped silicon dioxide.

[0033] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the first metal electrode includes a plurality of first finger electrodes extending along a first direction and a plurality of first bus bar electrodes extending along a second direction intersecting the plurality of first finger electrodes.

[0034] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the first finger electrode includes a first portion and a second portion alternately distributed along the first direction.

[0035] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the area of ​​the interface between the first part of the first finger electrode and the first conductive layer is S A ; The area proportion of the metal point is S1 A ; S A Calculate the S1 A The proportion of does not exceed 5%; or, the S1 A The proportion is 0.001%~5%.

[0036] According to the front structure of the Topcon solar cell of any embodiment of the first aspect of the present invention, the area of ​​the interface between the second portion of the first finger electrode and the first conductive layer is S B ; The area proportion of the metal point is S1 B ; S B Calculate the S1 B The proportion of does not exceed 10%; or, the S1 B The proportion is 0.001%~10%; Among them, S1 B Greater than or equal to S1 A .

[0037] The second aspect of the present invention provides a method for preparing a front structure of a Topcon solar cell as described in any embodiment of the first aspect of the present invention, comprising: Step S1: performing texturing treatment on the front side of the silicon wafer; Step S2: performing element diffusion and high-temperature oxidation treatment on the front side of the silicon wafer; Step S3: depositing a passivation anti-reflection layer on the front side of the silicon wafer; Step S4: using electrode slurry, printing and sintering to form a first metal electrode on the front side of the silicon wafer; and forming a second metal electrode on the back side; The amount of glass powder contained in the electrode paste for forming the first metal electrode does not exceed 3wt%, and the electrode paste does not contain aluminum powder; and the content of PbO in the glass powder is 20-45% by mole percentage; In this step, the glass powder in the electrode slurry slightly corrodes the passivation anti-reflection layer at high temperature to form a structure in which the passivation anti-reflection layer is partially retained, that is, the other medium; Step S5: applying a reverse voltage between the first metal electrode and the second metal electrode and being less than the breakdown voltage of the silicon solar cell, and illuminating the front side of the silicon solar cell in the presence of the voltage, thereby inducing a current within the illumination range, wherein the induced current has a current of 10 A / cm2 with respect to the illumination range. 2 Up to 1000A / cm 2 The current density is 10ns to 10ms, and the illumination light source is guided until the entire width of the cell is covered; In this step, through voltage and current, where the passivation anti-reflection layer is completely corroded, the silver ions in the slurry diffuse with the silicon to form metal points.

[0038] According to the method for preparing the front structure of a Topcon solar cell according to any embodiment of the second aspect of the present invention, in step S2, the element diffused is boron.

[0039] According to the method for preparing the front structure of a Topcon solar cell in any embodiment of the second aspect of the present invention, in step S2, the process parameters of the element diffusion are: Temperature: 800~900℃; Time: 10~40min.

[0040] According to the method for preparing the front structure of a Topcon solar cell in any embodiment of the second aspect of the present invention, in step S2, the process parameters of the high temperature oxidation treatment are: Insulation temperature: 900~1050℃; Insulation time: 30~120min.

[0041] According to the method for preparing the front structure of a Topcon solar cell in any embodiment of the second aspect of the present invention, in step S4, the process parameters of the sintering treatment are: Sintering temperature: 700~800℃; Sintering time: 1~2min.

[0042] A third aspect of the present invention provides a Topcon solar cell, wherein the Topcon solar cell has a front structure of a Topcon solar cell as described in any embodiment of the first aspect of the present invention, or a front structure of a Topcon solar cell prepared by a method according to any embodiment of the second aspect of the present invention; and a back structure, the back structure comprising: A tunneling oxide layer, a second conductive layer, a passivation anti-reflection layer, and a second metal electrode in contact with the second conductive layer are arranged on the back side of the silicon wafer.

[0043] According to the Topcon solar cell of any embodiment of the third aspect of the present invention, the second conductive layer is a doped polycrystalline silicon layer; The second conductive layer has an opposite polarity to the first conductive layer.

[0044] According to the Topcon solar cell of any implementation scheme of the third aspect of the present invention, the thickness of the tunneling oxide layer is 0.5-3 nm.

[0045] According to the Topcon solar cell of any embodiment of the third aspect of the present invention, the thickness of the second conductive layer is 20-300 nm.

[0046] The element doping concentration of the second conductive layer is 0.5~9E20 cm -3 .

[0047] According to the Topcon solar cell of any embodiment of the third aspect of the present invention, the thickness of the passivation anti-reflection layer is 50-150 nm.

[0048] According to the Topcon solar cell of any embodiment of the third aspect of the present invention, the passivation anti-reflection layer includes any one or two or more of oxide (such as aluminum oxide) and silicide (such as silicon dioxide, silicon nitride, silicon carbide).

[0049] According to the Topcon solar cell of any embodiment of the third aspect of the present invention, the second metal electrode includes a plurality of second finger electrodes extending along a third direction and a plurality of second bus bar electrodes extending along a fourth direction intersecting the plurality of second finger electrodes.

[0050] A fourth aspect of the present invention provides a method for preparing a Topcon solar cell, comprising: Step A1: performing texturing and polishing on the front side of the silicon wafer; Step A2: performing element diffusion and high-temperature oxidation treatment on the front side of the silicon wafer; Step A3: etching and polishing the back side of the silicon wafer; Step A4: depositing a tunnel oxide layer and a doped polysilicon layer on the surface of the silicon wafer; Step A5: depositing a passivation anti-reflection layer on the surface of the silicon wafer; Step A6: using electrode slurry to print and sinter on the front side of the silicon wafer to form a first metal electrode; The amount of glass powder contained in the electrode slurry for forming the first metal electrode does not exceed 3wt%, and the electrode slurry does not contain aluminum powder; and the content of PbO in the glass powder is 20-45% by mole percentage; in this step, the glass material in the electrode slurry slightly corrodes the passivation anti-reflection layer at high temperature to form a structure in which the passivation anti-reflection layer is partially retained, that is, the other medium; Printing and sintering a second metal electrode on the back side of the silicon wafer; Step A7: applying a reverse voltage between the first metal electrode and the second metal electrode and being less than the breakdown voltage of the silicon solar cell, and illuminating the front side of the silicon solar cell in the presence of the voltage, thereby inducing a current within the illumination range, wherein the induced current has a current of 10 A / cm2 with respect to the illumination range. 2 Up to 1000A / cm 2 The current density is 10ns to 10ms, and the illumination light source is guided until the entire width of the cell is covered; In this step, through voltage and current, where the passivation anti-reflection layer is completely corroded, the silver ions in the slurry diffuse with the silicon to form metal points.

[0051] Beneficial Effects (1) The present invention provides a front structure of a Topcon solar cell, in which other dielectrics exist at the interface between the first metal electrode and the first conductive layer, and the dielectrics have a passivation effect, thereby improving the passivation effect, effectively reducing the contact recombination between the first metal electrode and the first conductive layer, and improving the conversion efficiency of the Topcon solar cell.

[0052] (2) The front structure of the existing Topcon solar cell has metal points containing the metal of the metal electrode and aluminum during the sintering process. For example, if the first metal electrode is a silver electrode, the metal points are metal points containing silver and aluminum (hereinafter referred to as AgAl points). Usually, such metal points are in a spike state, which will cause serious damage to the passivation anti-reflection layer on the front side, and will also cause damage to the first conductive layer on the front side, resulting in a large composite of the metal area of ​​the first metal electrode; The present invention provides a front structure of a Topcon solar cell, wherein the metal region of the first metal electrode has no AgAl points, thereby avoiding the problem of increased contact recombination caused by AgAl spikes.

[0053] (3) The front contact structure of the Topcon solar cell provided by the present invention, the interface between the first metal electrode and the first conductive layer also has metal points, the metal points mainly include an alloy of silver and silicon, the presence of the metal points effectively increases the conductive channel between the first metal electrode and the first conductive layer, can reduce the contact resistance between the first metal electrode and the first conductive layer, while improving passivation, ensuring a low contact resistance of the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of the front structure of a Topcon solar cell provided in Example 1 of the present invention; Figure 2 A partial enlarged view of the first metal electrode of the front structure of the Topcon solar cell provided in Example 1 of the present invention; Figure 3 A partial enlarged view of the first metal electrode of the front structure of a Topcon solar cell provided in Example 2 of the present invention; Figure 4 A partial enlarged view of the first metal electrode of the front structure of a Topcon solar cell provided in Comparative Example 2 of the present invention; Figure 5A schematic diagram of the structure of a Topcon solar cell provided in Example 3 of the present invention; Figure 6 A schematic diagram of the structure of a Topcon solar cell provided in Example 3 of the present invention; In the figure: 100, silicon wafer; 110, second tunneling oxide layer; 120, second passivation anti-reflection layer; 130, second conductive layer; 140, second metal electrode; 141, second finger electrode; 142, second bus bar electrode; 150, first conductive layer; 160, first passivation anti-reflection layer; 170, first metal electrode; 171, first finger electrode; 171A, first part of first finger electrode; 171B, second part of first finger electrode; 172, first bus bar electrode; 180, interface; 181, metal point; 182, other dielectric layer; 183, glass layer; 184, metal particles; DIR1, first direction; DIR2, second direction; DIR3, third direction; DIR4, fourth direction. DETAILED DESCRIPTION

[0055] The present disclosure may be more easily understood by reference to the following description in conjunction with the accompanying drawings and examples, all of which constitute a part of the present disclosure. It should be understood that the present disclosure is not limited to the specific products, methods, conditions or parameters described and / or shown herein. Further, the terms used herein are only used for the purpose of describing specific embodiments by way of example and are not intended to be limiting unless otherwise stated.

[0056] It should also be understood that, for the sake of clarity, certain features of the present disclosure may be described herein in the context of separate embodiments, but may also be provided in combination with each other in a single embodiment. That is, unless clearly incompatible or specifically not included, each separate embodiment is considered to be combinable with any other embodiment, and the combination is considered to represent another different embodiment. Conversely, for the sake of simplicity, the various features of the present disclosure described in the context of a single embodiment may also be provided individually or in any sub-combination. Finally, although a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or sub-structure itself may also be considered to be an independent embodiment.

[0057] Unless otherwise indicated, it should be understood that each individual element in a list and each combination of individual elements in the list will be interpreted as a different embodiment. For example, a list of embodiments expressed as "A, B, or C" should be interpreted to include embodiments "A", "B", "C", "A or B", "A or C", "B or C", or "A, B, or C".

[0058] In the present disclosure, the singular forms of the articles "a", "an", and "the" also include the corresponding plural references, and references to a specific value include at least that specific value unless the context clearly indicates otherwise. Thus, for example, reference to "a substance" is a reference to at least one of that substance and its equivalents.

[0059] When items are described by using conjunction terms such as “… and / or…”, the description should be understood to include any one of the associated listed items and all combinations of one or more thereof; for example, A and / or B should be interpreted as an embodiment including “A” but not including “B”, an embodiment including “B” but not including “A”, and an embodiment including “A” and “B”.

[0060] In general, the use of the term "about" indicates an approximate value that may vary depending on the desired properties obtained by the disclosed subject matter, and will be interpreted in a context-dependent manner based on function. Therefore, one of ordinary skill in the art will be able to interpret a certain degree of difference on a case-by-case basis. In some cases, the number of significant figures used when expressing a particular value can be a representative technique for determining the difference allowed by the term "about". In other cases, a gradient in a range of values ​​can be used to determine the range of differences allowed by the term "about". Further, all ranges in this disclosure are inclusive and combinable, and reference to the values ​​stated in the range includes each value within the range.

[0061] Throughout the specification of this application document, when a certain part is described as “including” a certain constituent element, unless otherwise clearly described to the contrary, it does not mean that other constituent elements are excluded but that other constituent elements may also be included.

[0062] Throughout the specification of the present invention, when a certain step is recorded as being "above" or "before" other steps, it not only includes the case where a certain step has a direct time series relationship with other steps, but also includes the same rights as the case where a certain step has an indirect time series relationship where the time series of the order of two steps is changed, such as a mixing step after each step.

[0063] Throughout the specification of the present invention, when it is recorded as "according to any embodiment of the ... aspect of the ... object of the present invention...", unless otherwise clearly stated to the contrary, it does not mean that the constituent elements of the described scheme that appear before and after it are excluded, but that other constituent elements may also be included.

[0064] Throughout the specification of the present invention, when "quasi-layer" is described, a typical example is a layer formed by dots or a collection of dots connected to each other.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs; the terms used herein and / or include any and all combinations of one or more of the listed items. In order to make the technical solutions and advantages of the present invention clear, the technical solutions in the embodiments of the present invention will be fully described below.

[0066] Example 1 The embodiment of the present invention provides a contact structure of the front side of a Topcon solar cell (labeled as Front-1). For the convenience of description, only the part related to the embodiment of the present invention is shown. Figure 1 shown.

[0067] The front contact structure of the solar cell provided in this embodiment includes: A first conductive layer 150, a first passivation anti-reflection layer 160 and a first metal electrode 170 are arranged on the front side of the silicon wafer 100; The first passivation anti-reflection layer 160 includes: a first passivation layer and a first anti-reflection layer disposed on the first conductive layer 150; The first metal electrode 170 passes through the first passivation anti-reflection layer 160 and contacts the first conductive layer 150 to form an interface 180 (the interface described herein, i.e., the interface between the first metal electrode and the first conductive layer, the same as herein below), and the area of ​​the interface 180 is S. There are other dielectrics, metal dots, glass layers, and metal particles between the interface 180 between the first metal electrode 170 and the first conductive layer 150.

[0068] A specific method for preparing the front contact structure of a solar cell provided in this embodiment is as follows: Step S1: performing texturing and polishing on the front side of the silicon wafer; Step S2: performing element diffusion and high-temperature oxidation treatment on the front side of the silicon wafer; The reference element diffusion temperature is 800~900℃ and the time is 10~40min; The reference temperature of high temperature oxidation treatment is 900~1050℃ and the time is 30~120min; Step S3: depositing a passivation anti-reflection layer on the front side of the silicon wafer; Step S4: Use electrode paste to print and sinter on the front side of the silicon wafer to form a first metal electrode 170; and form a second metal electrode 140 on the back side. The reference sintering temperature is 700~800℃, and the time is 1~2min. In addition, compared with the traditional silver-aluminum paste for P-type emitters (such as DuPont's PV3N2, Shanghai Silver Paste's 995PFB, and Dico DK71A), the amount of glass powder contained in the electrode paste used to form the first metal electrode 170 in this embodiment does not exceed 3wt%; and the electrode paste does not contain aluminum powder; and, calculated in molar percentage, the content of PbO in the glass powder is 20~45%; Step S5: applying a reverse voltage between the first metal electrode 170 and the second metal electrode 140 and being smaller than the breakdown voltage of the silicon solar cell, and illuminating the front side of the silicon solar cell in the presence of the voltage, thereby inducing a current within the illumination range, wherein the induced current has a current of 10 A / cm2 with respect to the illumination range. 2 Up to 1000A / cm 2 The current density is 10ns to 10ms, and the illumination light source is guided until the entire width of the cell is covered. Specifically in this embodiment, the reverse voltage is 10V, and the front of the silicon solar cell is illuminated by laser. The light spot formed by the illumination is the local area, and finally 300A / cm is formed at the local position. 2 The current density is 100ns, and the illumination light source is guided until it covers the entire width of the cell.

[0069] Through the above steps, the glass powder in the slurry will produce controllable micro-corrosion on the first passivation anti-reflection layer 160 at high temperature, forming other dielectric layers 182 that partially retain the first passivation anti-reflection layer 160, forming a glass layer 183, and through voltage and current, where the passivation anti-reflection layer is completely corroded, the silver ions in the slurry diffuse with silicon to form AgSi alloy metal points (i.e., metal points 181), forming a conductive channel for Si and Ag. At the same time, metal particles 184 are formed at the glass layer 183.

[0070] More specifically: Regarding the "silicon wafer 100", it has a front side facing the sun during normal operation and a back side opposite to the front side, the front side is the light-receiving side, and the back side is located on the other side of the silicon wafer 100 relative to the front side; wherein, the silicon wafer 100 can be a P-type or N-type silicon wafer, and can be a polycrystalline silicon wafer or a quasi-single-crystalline silicon wafer, and the corresponding type of silicon wafer 100 can be selected according to actual use needs.

[0071] It should be pointed out that the surface of the silicon wafer 100 can be made into a velvet structure (referred to as velvet) by using surface texturing technology, based on which the reflection loss of surface light can be further reduced, the utilization rate of incident light by the silicon wafer 100 can be improved, and the short-circuit current of the battery can be increased. The surface texturing method can generally adopt mechanical grooving, chemical corrosion, plasma etching, etc., and finally obtain a velvet structure, which includes but is not limited to alkali polishing surface, mechanical polishing surface, random pyramid, inverted pyramid, spherical crown, V-shaped groove, and morphology between the above morphologies. In addition, it can usually form an irregular hemispherical velvet texture by acid velvet, form a pyramid velvet texture by alkali velvet, or first form a pyramid velvet texture by alkali velvet and then smooth the pyramid tip by acid velvet. At this time, the surface morphology formed at the groove on the back of the silicon wafer 100 is conducive to increasing the absorption and reuse of light by the silicon wafer 100, so as to increase the short-circuit current density, thereby improving the conversion efficiency of solar cells.

[0072] In addition, based on the above, it is not difficult to see that the height of the velvet texture of the velvet structure will also affect the reflectivity of the silicon wafer 100. As for the thickness of the "silicon wafer 100", it should be noted that reducing the thickness of the silicon wafer 100 can effectively reduce the carrier recombination rate and thus obtain a higher open circuit voltage. However, due to the low absorption coefficient of crystalline silicon to incident light, after reducing the thickness of the silicon wafer, the silicon wafer will absorb less sunlight, thereby causing a reduction in the short-circuit current of the battery. In summary, based on actual needs, corresponding adjustments can be made to the thickness of the silicon wafer 100, the height of the velvet texture, the reflectivity, etc. For example, in certain embodiments of the present invention, the silicon wafer 100 may selectively satisfy any one or a combination of the following conditions (I) to (IV): (I) the thickness of the silicon wafer 100 is 130 to 200 um; (II) the height of the velvet texture of the silicon wafer 100 is 1 to 5 um; (III) the resistivity of the silicon wafer 100 is 0.5 to 5 ohm·cm; (IV) the reflectivity of the silicon wafer 100 is 9 to 11%.

[0073] Specifically in this embodiment, the silicon wafer 100 is a phosphorus-doped N-type single crystal silicon wafer, and the surface of the phosphorus-doped N-type single crystal silicon wafer is textured by an alkali texturing method, and a pyramid-shaped textured surface is formed on the surface. More specifically, the silicon wafer 100 in this embodiment has a resistivity of 0.8 ohm·cm, a thickness of 130 um, a textured surface height of 1 um, and a reflectivity of 10.2%.

[0074] The first conductive layer 150 needs to have the opposite polarity to the silicon wafer 100. For example, if the silicon wafer 100 is a phosphorus-doped N-type single crystal silicon wafer, the first conductive layer 150 is a P-type doped region containing diffused P-type dopants, and the sheet resistance of the P-type doped region in the present invention is 100-600 ohm / sq and the doping concentration is 1e18-1e20cm -3 .

[0075] Specifically in this embodiment, the first conductive layer 150 is located on the front side of the silicon wafer 100. The first conductive layer 150 is decomposed by boron trichloride and oxygen by tubular diffusion, so that it is deposited on the surface of the velvet texture to form a BSG layer, and a PN junction with a depth of 1.0um is formed. At this time, a part of the silicon wafer 100 is diffused to become the first conductive layer 150 in this embodiment, and the doping concentration of the first conductive layer 150 is 3e18cm -3 , square resistance is 280 ohm / sq.

[0076] Regarding the "first passivation anti-reflection layer 160", in some embodiments of the present invention, the first passivation anti-reflection layer 160 is prepared and formed on the first conductive layer 150, and the first passivation anti-reflection layer 160 includes a first passivation layer and a first anti-reflection layer arranged on the first conductive layer 150. As some examples of the present invention, the first passivation layer can be an oxide layer of a single material, or a combination of oxide layers of multiple materials and amorphous silicon layers, or a combination of multiple layers of amorphous silicon with different refractive indices of a single material. In addition, the first anti-reflection layer can be a silicon oxynitride layer, a silicon nitride layer, etc. It can be understood that the specific structure of the first passivation anti-reflection layer 160 includes but is not limited to the several methods listed above, and the first passivation anti-reflection layer 160 can be arranged accordingly according to actual use needs, and is not specifically limited here.

[0077] Further, the thickness of the first passivation anti-reflection layer 160 may be between 20nm and 120nm; in some preferred embodiments of the present invention, the first passivation anti-reflection layer 160 is preferably between 50nm and 80nm, and the refractive index is 1.9-2.1. In some other preferred embodiments of the present invention, the first passivation anti-reflection layer 160 is preferably composed of an oxide layer with a thickness of 2-10nm as the first passivation layer and a silicon nitride layer with a thickness of 40-120nm as the first anti-reflection layer, in which case the oxide layer and the silicon nitride layer are arranged in sequence from the silicon wafer 100 outward, the oxide layer is in contact with the first conductive layer 150 on the inner side, and the silicon nitride layer is in contact with the oxide layer.

[0078] Furthermore, the oxide layer is preferably composed of one or more layers of a silicon oxide layer (also abbreviated as SiO2 layer) and an aluminum oxide layer (also abbreviated as Al2O3 layer). Therefore, the first passivation layer may also be a combination of the silicon oxide layer and the aluminum oxide layer in the oxide layer. x The first passivation anti-reflection layer 160 is substantially a hydrogenated silicon nitride layer. At this time, hydrogen in the hydrogenated silicon nitride layer can enter the silicon wafer 100 under the action of diffusion mechanism and thermal effect, so as to neutralize the dangling bonds on the front side of the silicon wafer 100, passivate the defects of the silicon wafer 100, and thus transfer the energy band in the forbidden band to the valence band or the conduction band, so as to increase the probability of carriers entering the first conductive layer 150 through the first passivation anti-reflection layer 160.

[0079] Regarding the “formation method” of the first passivation anti-reflection layer 160, the silicon oxide layer therein can be prepared by thermal oxidation (including dry oxygen oxidation, wet oxygen oxidation), chemical vapor deposition (CVD) (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method), room temperature wet oxidation method, etc., which are prepared according to actual use needs and are not specifically limited here; the silicon nitride layer can be prepared by chemical vapor deposition (CVD) (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method) The silicon nitride layer can be prepared by chemical vapor deposition (CVD) method, magnetron sputtering technology, etc., and it is prepared according to the actual use needs. If conditions permit, it is preferred to use chemical vapor deposition (CVD) method (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method) to prepare the silicon nitride layer; the aluminum oxide layer can be prepared by atomic layer deposition (ALD) method, plasma assisted ALD method, pyrolysis deposition method, delocalized PECVD method, molecular beam epitaxy, deposition A1 plus oxidation method, etc., and it is prepared according to the actual use needs, and no specific limitation is made here. A large amount of hydrogen will be generated when aluminum oxide and silicon nitride are deposited in the thin film, which can form a good hydrogen passivation.

[0080] Specifically in this embodiment, Figure 1 As shown, the first passivation anti-reflection layer 160 includes an aluminum oxide (Al2O3) layer with a thickness of 5 nm as the first passivation layer and a hydrogenated silicon nitride (SiN X ) layer as the first anti-reflection layer. At this time, the first passivation layer and the first anti-reflection layer are arranged in sequence from the silicon wafer 100 to the outside. The first passivation layer is superimposed on the first conductive layer 150, and the first anti-reflection layer is superimposed on the first passivation layer. Finally, the first passivation anti-reflection layer 160 presents a refractive index of 2.1.

[0081] The first metal electrode 170 is usually a silver electrode and includes a plurality of first finger electrodes 171 extending along a first direction DIR1 and a plurality of first bus bar electrodes 172 extending along a second direction DIR2 crossing the plurality of first finger electrodes 171 .

[0082] like Figure 1 , 2 As shown, the first metal electrode 170 passes through the first passivation anti-reflection layer 160 and contacts the first conductive layer 150 to form a junction interface 180, and the area of ​​the junction interface 180 is S. There are other dielectrics, metal dots 181, glass layers 183 and metal particles 184 between the junction interface 180 between the first metal electrode 170 and the first conductive layer 150.

[0083] Regarding the "other medium", in some examples of the present invention, it can be an oxide layer of a single material, a combination of oxide layers of multiple materials and an amorphous silicon layer, a combination of multiple layers of amorphous silicon with different refractive indices of a single material, or a silicon oxynitride layer, a silicon nitride layer, etc. It can be understood that the "other medium" includes but is not limited to the several methods listed above; or, the basic material composition and formation method of the other medium can be the same as the first passivation anti-reflection layer 160. The existence form of the "other medium" can be layered, point-like distribution, and a layer-like structure formed by the aggregation of points. In some examples of the present invention, the "other medium" is the "other medium layer 182", the thickness of the other medium layer 182 is 1~120nm, the coverage area of ​​the other medium layer 182 is S1, and calculated by S, the proportion of S1 does not exceed 99%; preferably, the proportion of S1 is 10~99%. Specifically, the “other medium” described in this embodiment is the “other medium layer 182”. The basic material composition and formation method of the other medium layer 182 are the same as those of the first passivation anti-reflection layer 160. The thickness of the other medium layer 182 is 1-80 nm, 550 is calculated as S, and the proportion of S1 is 80%.

[0084] The "metal dots" are dispersed between the interface 180 between the first metal electrode 170 and the first conductive layer 150, contain silver and silicon but do not contain aluminum, the size of the metal dots is 20-800 nm, and the embedding depth of the metal dots in the silicon wafer 100 is 20-500 nm. Specifically, in this embodiment, the metal dots 181 contain silver and silicon, the size of the metal dots 181 is 550 nm, and the embedding depth of the metal dots 181 in the silicon wafer 100 is 500 nm.

[0085] The "glass layer" is actually doped silicon dioxide, and its doping includes any one, two or more doping methods of PbO, B2O3, Al2O3, Ga2O3, AgO, NaO, and LiO2. The existence form of the "doped silicon dioxide" can be layered, point-like distribution, or a quasi-layered structure formed by the aggregation of points. In some examples of the present invention, the "doped silicon dioxide (also called doped silicon glass)" is a "doped silicon dioxide layer", the thickness of the doped silicon dioxide layer is 2~800nm, the coverage area of ​​the doped silicon dioxide layer is S2, and calculated by S, the proportion of S2 is not less than 2%, preferably the proportion of S2 is 2~100%, and further preferably the proportion of S2 is 2~99%, and the doped silicon dioxide also contains metal particles 184. Specifically in this embodiment, the glass layer 183 is a doped silicon dioxide layer, and the doped silicon dioxide also contains metal particles 184. The thickness of the doped silicon dioxide layer is 40 nm, and its doping includes PbO, B2O3, Al2O3, Ga2O3, AgO, NaO, and LiO2. Calculated with S, the proportion of S2 is 95%.

[0086] Example 2 like Figure 3 As shown, an embodiment of the present invention provides a contact structure (labeled: Front-2) for the front side of a Topcon solar cell. The structure is basically the same as that of embodiment 1, except that: In this embodiment, the first finger electrode 171 includes a first portion 171A of the first finger electrode and a second portion 171B of the first finger electrode alternately distributed along the first direction DIR1. The area of ​​the interface between the first portion of the first finger electrode and the first conductive layer is S A , the coverage area of ​​the metal point 181 is S1 A , with S A Calculate the S1 A The proportion of S1 is no more than 5%; A The area of ​​the interface between the second portion of the first finger electrode and the first conductive layer is S B , the coverage area of ​​the metal point 181 is S1 B , with S B Calculate the S1 B The proportion of S1 is no more than 10%, preferably A The coverage area S1 of the metal dot 181 is 0.001-10%. A , S BThis can be achieved by adjusting the illumination parameters of step S5. Specifically, in this embodiment, step S1 A The proportion of S1 is 0.2%. B The proportion is 1%.

[0087] Comparative Example 1 This comparative example provides a front structure (labeled: Front-D1) of a Topcon solar cell prepared with a conventional paste. As mentioned above, the preparation process of the front structure (labeled: Front-D1) of this comparative example is basically the same as that of Example 1, except that the electrode paste used to form the first metal electrode 170 in this comparative example is replaced with the conventional paste DK71A.

[0088] Specifically speaking of the battery structure, the structure is basically the same as that of Example 1, with the only difference being that Front-D1 of this comparative example does not have other dielectric layers 182 and metal dots 181 as described in Example 1, and AgAl spikes are formed between the interface 180 between the first metal electrode 170 and the first conductive layer 150 .

[0089] Comparative Example 2 like Figure 4 As shown, the embodiment of the present invention provides a front structure of a Topcon solar cell (labeled as Front-D2), which is basically the same as that of embodiment 1, except that: There is only other medium between the interface 180 between the first metal electrode 170 and the first conductive layer 150 , and there is no metal dot 181 , glass layer 183 and metal particles 184 .

[0090] In terms of process, the contact structure Front-D2 on the front side of the Topcon solar cell of Comparative Example 2 can be obtained by adjusting the sintering process of step S4.

[0091] Comparative Example 3 The front structure of the Topcon solar cell provided in this comparative example (labeled as Front-D3) is as described above. The specific structure of the front structure Front-D3 of this comparative example is basically the same as that of Example 2, except that: A The proportion of S1 is 0.1%. B The proportion of S1 is 0.05%. B The proportion is lower than S1 A % of.

[0092] Example 3 The embodiment of the present invention provides a Topcon solar cell. For ease of description, only the part related to the embodiment of the present invention is shown. Figure 5 ,6 shown.

[0093] The Topcon solar cell provided in the embodiment of the present invention comprises: a silicon wafer 100; A front contact structure disposed on the front side of the silicon wafer 100; A second tunneling oxide layer 110 , a second conductive layer 130 , a second passivation anti-reflection layer 120 and a second metal electrode 140 are disposed on the back side of the silicon wafer 100 .

[0094] The preparation method of the Topcon solar cell is the same as that of Example 1. On this basis, a step of etching and polishing the back side of the silicon wafer 100 is added between steps S2 and S3; and a step of depositing a tunneling oxide layer and a doped polysilicon layer on the surface of the silicon wafer 100 is added.

[0095] More specifically: The "tunneling oxide layer" is mainly an ultra-thin oxide layer with a thickness of 0.5 to 3 nm, which has an important influence on the properties of the passivation contact, and good contact comes from defect-assisted tunneling mechanisms or micropores on the oxide layer. Preferably, the ultra-thin oxide layer is an ultra-thin silicon oxide layer. Regarding the formation of the ultra-thin silicon oxide layer, there are currently mainly thermal oxidation methods (including dry oxygen oxidation, wet oxygen oxidation), chemical vapor deposition (CVD) methods (including plasma chemical vapor deposition (PECVD) method, low pressure chemical vapor deposition (LPCVD) method), room temperature wet oxidation method, etc., preferably low pressure chemical vapor deposition (LPCVD) method. Specifically in this embodiment, the thickness of the second tunneling oxide layer 110 is 1.5 nm.

[0096] Regarding the "second conductive layer 130" described above, it is a doped polysilicon layer, and its doping type needs to be opposite to the polarity of the first conductive layer 150, and in order to achieve a better passivation effect, the second polysilicon layer 620 preferably has a thickness of not less than 50nm. In addition, in some preferred embodiments of the present invention, the second conductive layer 130 can optionally meet any one or a combination of the following (I) to (III) conditions: (I) thickness is 50~300nm; (II) square resistance is 20~200ohm / sq; (III) has a surface concentration of 0.5~9E20. Specifically in this embodiment, the silicon wafer 100 selects a phosphorus-doped N-type single crystal silicon wafer. At this time, the first conductive layer 150 in the structure located on the front of the silicon wafer 100 is a P-type doped region containing diffused P-type dopants, and the first conductive layer 150 is P-type doped. Based on this, in this embodiment, the second conductive layer 130 located on the back side of the silicon wafer 100 is phosphorus-doped N-type doped, the thickness of the second conductive layer 130 is 150nm, and the surface concentration is 4e20cm -3 , the square resistance is 40ohm / sq.

[0097] The second passivation anti-reflection layer 120 is basically the same as the first passivation anti-reflection layer 160. Specifically, in this embodiment, the second passivation anti-reflection layer 120 includes an aluminum oxide (Al2O3) layer with a thickness of 5 nm as a second passivation layer and a hydrogenated silicon nitride (SiN) layer with a thickness of 75 nm. X ) layer as the second anti-reflection layer. At this time, the second passivation layer and the second anti-reflection layer are arranged in sequence from the silicon wafer 100 to the outside. The second passivation layer is superimposed on the first conductive layer 150, and the second anti-reflection layer is superimposed on the second passivation layer. Finally, the second passivation anti-reflection layer 120 presents a refractive index of 2.12.

[0098] The “second metal electrode 140 ” is commonly a silver electrode, and includes a plurality of second finger electrodes 141 extending along a third direction DIR3 and a plurality of second bus bar electrodes 142 extending along a fourth direction DIR4 intersecting the plurality of second finger electrodes 141 .

[0099] Based on the above, the present embodiment provides the following five types of Topcon solar cells: The first Topcon solar cell (labeled as Topcon-1) has a back structure as described in this embodiment and a front structure Front-1 as described in embodiment 1; A second Topcon solar cell (labeled as Topcon-2) has a back structure as described in this embodiment and a front structure Front-2 as described in embodiment 2; A third Topcon solar cell (labeled as Topcon-D1) has a back structure as described in this embodiment and a front structure Front-D1 as described in Comparative Example 1; A fourth Topcon solar cell (labeled as Topcon-D2) has a back structure as described in this embodiment and a front structure Front-D2 as described in Comparative Example 2; The fifth Topcon solar cell (labeled: Topcon-D3) has the back structure as described in this embodiment and the front structure Front-D3 as described in Comparative Example 3.

[0100] The properties of each battery are shown in Table 1 below.

[0101] Table 1. Performance comparison parameters of various solar cells

[0102] It can be seen from Table 1 that the final cell conversion efficiency of the solar cell Topcon-1 provided in Example 3 of the present invention is improved by 0.26% compared with Topcon-D1.

[0103] The solar cell Topcon-2 provided in Example 3 of the present invention has a final cell conversion efficiency increased by 0.36% compared to Topcon-D1.

[0104] The solar cell Topcon-2 provided in Example 3 of the present invention has a final cell conversion efficiency increased by 1.93% compared to Topcon-D2.

[0105] The solar cell Topcon-2 provided in Example 3 of the present invention has a final cell conversion efficiency increased by 0.09% compared to Topcon-D3.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A front structure of a Topcon solar cell, characterized in that: The front structure includes a first conductive layer, a passivation anti-reflection layer and a first metal electrode arranged on the front of the silicon wafer; Wherein, the first metal electrode contacts the first conductive layer through the passivation anti-reflection layer; The first metal electrode includes a plurality of first finger electrodes extending along a first direction and a plurality of first bus bar electrodes extending along a second direction crossing the plurality of first finger electrodes; Furthermore, other dielectrics and metal points exist at the interface between the first metal electrode and the first conductive layer; The metal dots contain silver and silicon, but do not contain aluminum; The area of ​​the interface between the first metal electrode and the first conductive layer is S; The coverage area of ​​the other medium is S1; Calculated by S, the proportion of S1 does not exceed 99%; or, the proportion of S1 is 10-99%.

2. The front structure of the Topcon solar cell according to claim 1, characterized in that: The material of the other dielectric includes any one, two or more of oxide and silicide.

3. The front structure of the Topcon solar cell according to claim 2, characterized in that: The thickness of the other medium is 1-120 nm.

4. The front structure of the Topcon solar cell according to claim 1, characterized in that: Doped silicon dioxide also exists at the interface between the first metal electrode and the first conductive layer.

5. The front structure of the Topcon solar cell according to claim 4, characterized in that: The thickness of the doped silicon dioxide is 2-800 nm.

6. The front structure of the Topcon solar cell according to claim 4, characterized in that: The area of ​​the interface between the first metal electrode and the first conductive layer is S; The coverage area of ​​the doped silicon dioxide is S2; Calculated by S, the proportion of S2 is not less than 2%; or, the proportion of S2 is 2-100%.

7. The front structure of a Topcon solar cell according to any one of claims 1 to 6, characterized in that: The size of the metal dots is 20-800 nm; And / or, the embedding depth of the metal dots in the silicon wafer is 20-500 nm.

8. The front structure of the Topcon solar cell according to claim 7, characterized in that: The first finger electrode includes a first portion and a second portion alternately distributed along the first direction.

9. The front structure of the Topcon solar cell according to claim 8, characterized in that: The area of ​​the interface between the first portion of the first finger electrode and the first conductive layer is S A ; The area proportion of the metal point is S1 A ; S A Calculate the S1 A The proportion of does not exceed 5%; or, the S1 A The proportion is 0.001%~5%.

10. The front structure of the Topcon solar cell according to claim 9, characterized in that: The area of ​​the interface between the second portion of the first finger electrode and the first conductive layer is S B ; The area proportion of the metal point is S1 B ; S B Calculate the S1 B The proportion of does not exceed 10%; or, the S1 B The proportion is 0.001%~10%.

11. The front structure of the Topcon solar cell according to claim 10, characterized in that: The S1 B Greater than or equal to S1 A .

12. The method for preparing the front structure of a Topcon solar cell according to any one of claims 1 to 11, characterized in that: include: Step S1: performing texturing treatment on the front side of the silicon wafer; Step S2: performing element diffusion and high-temperature oxidation treatment on the front side of the silicon wafer; Step S3: depositing a passivation anti-reflection layer on the front side of the silicon wafer; Step S4: using electrode slurry, printing and sintering to form a first metal electrode on the front side of the silicon wafer; and forming a second metal electrode on the back side; The amount of glass powder contained in the electrode paste for forming the first metal electrode does not exceed 3wt%, and the electrode paste does not contain aluminum powder; and the content of PbO in the glass powder is 20-45% calculated by molar percentage.

13. The method for preparing the front structure of a Topcon solar cell according to claim 12, characterized in that: In step S2, the process parameters of the element diffusion are: Temperature: 800~900℃; Time: 10~40min; And / or, in step S2, the process parameters of the high temperature oxidation treatment are: Insulation temperature: 900~1050℃; Insulation time: 30~120min; And / or, in step S4, the process parameters of the sintering treatment are: Sintering temperature: 700~800℃; Sintering time: 1~2min.

14. Topcon solar cell, characterized in that The Topcon solar cell comprises the front structure of the Topcon solar cell according to any one of claims 1 to 11, or the front structure of the Topcon solar cell prepared by the method for preparing the front structure of the Topcon solar cell according to any one of claims 12 to 13.

Images