CN113502163B

CN113502163B - Chemical auxiliary agent for forming solar cell back structure, and preparation method and application thereof

Info

Publication number: CN113502163B
Application number: CN202111058843.3A
Authority: CN
Inventors: 陈鹏; 李晓强
Original assignee: Hangzhou Jingbao New Energy Technology Co ltd
Current assignee: Hangzhou Jingbao New Energy Technology Co ltd
Priority date: 2021-09-10
Filing date: 2021-09-10
Publication date: 2021-12-03
Anticipated expiration: 2041-09-10
Also published as: CN113502163A

Abstract

The invention discloses a chemical auxiliary agent for forming a back structure of a solar cell, a preparation method and application thereof, and relates to the technical field of solar cell manufacturing. The raw materials of the chemical auxiliary agent comprise 0.5-10 parts of a first component, 0.5-10 parts of a second component and 0.01-1 part of a third component; the first component is water soluble polysaccharide colloid; the second component is a water-soluble high molecular polymer with strong polarity; the third component is an alcohol ether surfactant. By improving the chemical auxiliary agent adopted by alkaline corrosion and utilizing the matching of the first component, the second component and the third component, the silicon wafer back structure after corrosion presents a novel back surface structure between a pyramid-shaped suede and a flat surface, so as to meet the special requirements of performances such as light absorption, tunneling oxide layer passivation and metallization on the surface structure.

Description

Chemical auxiliary agent for forming solar cell back structure, and preparation method and application thereof

Technical Field

The invention relates to the technical field of solar cell manufacturing, in particular to a chemical auxiliary agent for forming a back structure of a solar cell, and a preparation method and application thereof.

Background

Currently, the mainstream solar cell is based on semiconductor single crystal silicon material, the technology development is rapid, and the conversion efficiency of the industry volume production is over 23% from the conventional aluminum back surface field cell to the double-sided passivated cell (PERC cell). Meanwhile, a new generation of solar cell technology, for example: the tunnel oxide layer passivation contact battery (TOPCon battery) is maturing rapidly, the mass production efficiency exceeds 24%, the highest efficiency reaches 25%, and the TOPCon battery is expected to become a technical route of next-generation industrialization.

The surface structure of the cell has an important influence on the performance of the TOPCon cell, and the back surface of the TOPCon cell at present has two common structures, namely a flat surface and a textured structure with a pyramid appearance.

The advantage of the pyramid structure is: the incident light can be utilized to the maximum extent, and the light absorption is increased; its disadvantages are: the pyramid surface is a silicon (111) surface, has a larger density of states than a (100) surface, and the surface is not completely flat but has microscopic undulations, so that the surface state is not favorable for the passivation effect of the tunneling oxide layer.

In contrast, a flat back surface has the advantages of: better passivation is easily obtained but has the disadvantage of not favouring light absorption. In addition, the flat back surface has a significant technical difficulty, and the contact resistance between the silver grid lines and the flat silicon surface is far higher than a normal value due to the poor matching of the back conductive paste and the flat surface, so that the efficiency of the battery is reduced.

Therefore, neither the pyramid structure nor the flat surface structure can have optical performance, passivation performance, and electrode contact performance.

Disclosure of Invention

The invention aims to provide a chemical auxiliary agent for forming a back structure of a solar cell and a preparation method thereof, and aims to obtain a novel back surface structure between a pyramid-shaped suede and a flat surface, and obtain a better passivation effect and a better silver grid line contact performance.

Another object of the present invention is to provide an alkaline etchant for forming a back structure of a solar cell and a method for preparing the same, which can form a special back structure on the surface of a silicon wafer through an etching reaction to improve the overall performance of the silicon wafer.

The third purpose of the invention is to provide the prepared solar cell based on the novel back structure, wherein the back surface of the cell has a structure between the pyramid-shaped texture surface and the flat surface, and the special requirements of light absorption, passivation of a tunneling oxide layer and metallization on the surface structure can be considered.

The invention is realized by the following steps:

according to a first aspect, the invention provides a chemical auxiliary agent for forming a back structure of a solar cell, which comprises, by mass, 0.5-10 parts of a first component, 0.5-10 parts of a second component and 0.01-1 part of a third component; the first component is water soluble polysaccharide colloid; the second component is a water-soluble high molecular polymer with strong polarity; the third component is an alcohol ether surfactant.

In a second aspect, the present invention provides a method for preparing a chemical assistant for forming a back structure of a solar cell, which is prepared by using the raw materials of the chemical assistant in the foregoing embodiments.

In a third aspect, the present invention provides an alkaline etching solution for forming a back structure of a solar cell, which is obtained by mixing the chemical auxiliary agent prepared by the preparation method in the foregoing embodiment with the alkaline solution.

In a fourth aspect, the present invention provides a method for preparing a back structure of a solar cell, which uses the alkaline etchant in the foregoing embodiment to etch a silicon wafer.

In a fifth aspect, the invention provides a monocrystalline silicon solar cell, which is prepared by adopting the solar cell back structure.

The invention has the following beneficial effects: the inventor improves the chemical auxiliary agent adopted for alkaline corrosion, and utilizes the matching of the first component, the second component and the third component to ensure that the corroded silicon wafer back structure presents a novel back surface structure between a pyramid-shaped suede and a flat surface, so that the silicon wafer back structure is suitable for a TOPCon battery, special requirements of performances such as light absorption, tunneling oxide layer passivation and metallization on the surface structure are considered, and the comprehensive performance is ideal.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a microscopic structure view (a photograph of a front surface of an electron scanning microscope) of the back surface of a sample obtained in examples 1 to 4 of the present invention;

FIG. 2 is a microscopic structure view (cross-sectional photograph of an electron scanning microscope) of the back surface of a sample obtained in examples 1 to 4 of the present invention;

FIG. 3 is a scanning electron microscope photograph of a sample obtained in comparative example 1 of the present invention;

FIG. 4 is a scanning electron microscope photograph of a sample obtained in comparative example 2 of the present invention;

FIG. 5 is a scanning electron microscope photograph of a sample obtained in comparative example 3;

FIG. 6 is a scanning electron microscope photograph of a sample obtained in comparative example 4;

FIG. 7 is an optical photograph of the back surface of the silicon wafer after the etching reaction in example 4 and comparative example 5;

FIG. 8 is a graph showing the results of the spectral reflectance tests of the samples obtained in example 4 and comparative examples 1-2;

FIG. 9 is an optical photograph of the samples obtained in example 4 and comparative examples 1 to 2.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Based on the drawbacks of the two structures on the back surface of the TOPCon cell, the inventor believes that in order to achieve the objectives of combining optical performance, passivation performance and contact performance of the electrodes, and further to achieve the optimal efficiency of the TOPCon cell, a novel back surface structure needs to be developed.

The inventor continuously explores for a long time, improves additives adopted in the corrosive liquid, utilizes the chemical auxiliary agent provided by the embodiment of the invention to be matched with alkali liquor to form the corrosive liquid, can form a novel back surface structure between a pyramid-shaped suede and a flat surface after a silicon wafer is treated, is suitable for a TOPCon battery, and has special requirements of light absorption, passivation of a tunneling oxide layer and metallization on the surface structure.

The embodiment of the invention provides a chemical auxiliary agent for forming a back structure of a solar cell, which comprises the following raw materials of 0.5-10 parts by mass of a first component, 0.5-10 parts by mass of a second component and 0.01-1 part by mass of a third component; the first component is water soluble polysaccharide colloid; the second component is a water-soluble high molecular polymer with strong polarity; the third component is an alcohol ether surfactant.

Specifically, the first component is selected from at least one of locust bean gum, dextran, konjac gum and pectin; the second component is selected from at least one of polyhexamethylene guanidine, polyethyleneimine, sodium poly-p-styrene sulfonate and sodium polyethylene sulfonate; the third component is at least one selected from alkylphenol ethoxylate, fatty alcohol polyoxyethylene ether and isomeric alcohol polyoxyethylene ether.

It should be noted that, the inventors have found that, by using the first component, the second component, and the third component as the effective ingredients of the additive: after the silicon wafer is processed by the alkaline corrosive liquid formed by the chemical auxiliary agent provided by the embodiment of the invention, a novel back surface structure can be formed, and the special requirements of light absorption, passivation of a tunneling oxide layer and metallization on the surface structure can be considered.

It is necessary to supplement that in the chemical assistant formula system, the colloidal molecules in the first component have strong bonding force with silicon surface atoms in the solution. When its concentration in alkaline etching solutions is low and in strong electrolyte solutions, these molecules are "wrapped" by ions and water molecules in the aqueous solution and randomly distributed in isolation in the solution. These isolated molecules will adsorb to bind on the silicon surface when the silicon wafer is reacted in an etching solution. However, these isolated molecules have small particle sizes, similar to isolated "anchor points," and cover only a very small fraction of the surface area, and therefore follow the silicon surface atoms with OH' s^-The reaction proceeds and falls off quickly, failing to form a stable bond for a long time. Meanwhile, the colloid molecules contain a large number of hydrophilic groups such as hydroxyl groups, and when the second component is added, the charges of the high-polarity polymer are mutually attracted with the hydrophilic groups of the colloid molecules in the first component. These polymers can link a plurality of colloidal molecules, and thus form network-like adsorption on the surface of the silicon wafer. Therefore, a layer of polymer layer can be uniformly adsorbed on the surface of the silicon chip in a large area, and the protective layer can be kept for a long time in the process of corrosion reaction due to a plurality of anchor points. The effective adsorption area can block silicon and OH^-To avoid corrosion, non-adsorbed or weakly adsorbed areas on the silicon surface follow the silicon with OH^-Is etched by the reaction of (a). The third component (i.e., the alcoholic surfactant) favors silicon and OH^-Reaction of (2)The generated hydrogen bubbles are discharged, so that the surface appearance of the silicon chip obtained by the reaction is uniform and consistent and has no air flow traces. Due to the synergistic effect of the three components, a uniform and specific back surface structure can be formed. The back surface structure exhibits a structure of "peaks" + "basins," the "peak" sidewalls approximating exposed (111) silicon facets, and the "basins" approximating exposed (100) silicon facets. The structure has a high proportion of (100) crystal faces, and is beneficial to obtaining a good passivation effect compared with a pyramid textured structure. Meanwhile, the structure has certain micro roughness, is large in contact area and is easier to contact with conductive silver paste. Therefore, the contact resistance of the material is obviously lower than that of a flat surface structure, and better efficiency is easily obtained.

In order to further improve the comprehensive performance of the silicon wafer after corrosion treatment, the inventor further optimizes the use amount of each component: the raw materials comprise, by mass, 0.5-5 parts of a first component, 0.5-3 parts of a second component and 0.01-0.5 part of a third component. It should be noted that by further optimizing the selection of the raw materials of the three components, the optical performance, passivation performance and contact performance of the electrode after the etching treatment can be further improved, so that the TOPCon battery can obtain the optimal efficiency.

In an alternative embodiment, the method comprises the following steps: mixing the raw materials of the chemical auxiliary agent and water to obtain an aqueous solution, wherein the mass fractions of the first component, the second component and the third component in the aqueous solution are 0.5-10%, 0.5-10% and 0.01-0.5% in sequence. For example, the mass fraction of the first component may be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10%, or the like, or may be any value between the above values. The mass fraction of the second component may be the same as or different from that of the first component, which is also a value in the range of 0.5-10%. The mass fraction of the third component may be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc., and may be any value between the above values.

It should be noted that the chemical auxiliary agent as a product can be in the form of an aqueous solution, or can form an alkaline corrosion solution with alkali liquor to be sold as a product, but the dosage ratio of the three components needs to be controlled. On the premise of accurately controlling the dosage proportion of the three components, the three components can be prepared into an aqueous solution or form an alkaline corrosive solution by adopting a conventional method, and the product form can be various, so that the product falls into the protection scope of the application as long as the mixture ratio of the three components is within the range defined by the application.

The embodiment of the invention provides an alkaline etching solution for forming a back structure of a solar cell, which is obtained by mixing the chemical auxiliary agent prepared by the preparation method in the embodiment with an alkaline solution, and the amount of the total chemical auxiliary agent can be controlled within a conventional range.

In some embodiments, the chemical auxiliary is mixed with the alkaline solution in the form of an aqueous solution, the mass fraction of the alkaline solution is controlled to be 1-2% (e.g., 1%, 1.5%, 2%, etc.), and the volume ratio of the alkaline solution to the chemical auxiliary aqueous solution is 100:0.5-100:2 (100: 0.5, 100:1.0, 100:1.5, 100:2, etc.).

In other embodiments, the chemical auxiliary agent may not be added in the form of an aqueous solution, but the first component, the second component and the third component may be directly added to the alkali solution, and the dosage ratio of the first component, the second component and the third component is controlled within the range defined in the present application.

Specifically, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

The embodiment of the invention also provides a preparation method of the novel back structure of the solar cell, which is characterized in that the alkaline corrosive liquid is adopted to corrode a silicon wafer, so that a novel back surface structure between a pyramid-shaped suede and a flat surface can be obtained, and the optical performance, the passivation performance and the contact performance of an electrode can be considered at the same time.

In some embodiments, the method of making comprises: reacting the silicon wafer in alkaline corrosive liquid for 120-600 seconds, and controlling the temperature of the alkaline corrosive liquid to be 50-95 ℃. Specifically, the reaction temperature may be 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 95 ℃ or the like, and the reaction time may be 120s, 200s, 300s, 400s, 500s, 600s or the like.

In some embodiments, the silicon wafer is pre-cleaned and then reacted with an alkaline etchant, and the surface impurities are removed by pre-cleaning and then the etching reaction is performed.

In some embodiments, after the reaction with the alkaline corrosive liquid, the silicon wafer is soaked and washed by hydrogen peroxide, and residual organic matters adsorbed on the surface of the silicon wafer are thoroughly removed by the hydrogen peroxide washing. After the washing, the washing may be performed again with water and dried.

The embodiment of the invention provides a preparation method of a novel back structure of a solar cell, which is prepared by adopting the preparation method, so that the solar cell has a special novel back structure, is particularly suitable for TOPCon solar cells, can overcome the defects of the two existing structures, has excellent comprehensive performance and has good market application prospect. However, the TOPCon solar cell is not limited to this.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The embodiment provides a preparation method of a novel back structure of a solar cell, which comprises the following steps:

(1) preparation of chemical adjuvant solution

Mixing and stirring 1.5 parts by mass of locust bean gum and water to obtain a clear colloidal solution, then sequentially adding 0.5 part by mass of polyhexamethylene guanidine and 0.1 part by mass of nonylphenol polyoxyethylene ether, and fully and uniformly mixing to obtain a chemical assistant solution. Wherein, in the chemical additive solution, the mass fraction of the locust bean gum is 1.5 percent, the mass fraction of the polyhexamethylene guanidine is 0.5 percent, and the mass fraction of the polyoxyethylene nonyl phenyl ether is 0.1 percent.

(2) Preparation and corrosion reaction of alkaline corrosive liquid

Preparing a potassium hydroxide solution with the mass fraction of 1.5% as an alkaline corrosive solution, and keeping the temperature of the solution at 70 ℃. And (2) adding the chemical additive solution prepared in the step (1) into the alkaline corrosive liquid, controlling the volume ratio of the alkaline corrosive liquid to the chemical additive solution to be 100:1, and uniformly stirring.

The silicon wafer after the front surface diffusion (boron diffusion is a common technique in TOPCon solar cell manufacturing process) was pre-cleaned and put into the above alkaline etching solution to react for 200 seconds.

(3) Post-treatment

And taking out the silicon wafer after reaction, immediately washing the silicon wafer by using deionized water, and fully diluting the corrosive solution attached to the surface. Immersing the silicon wafer after immersion in a hydrogen peroxide solution with the mass fraction of 1.5%, maintaining the temperature of the hydrogen peroxide solution at 60 ℃, and adding potassium hydroxide with the mass fraction of 0.5%. And cleaning and drying the silicon wafer again to obtain a test sample.

Example 2

The embodiment provides a method for preparing a novel back structure of a solar cell, which is different from embodiment 1 only in step (1), and specifically comprises the following steps:

mixing and stirring 2.0 parts by mass of glucan and water, then sequentially adding 0.5 part by mass of polyethyleneimine and 0.2 part by mass of fatty alcohol-polyoxyethylene ether, and fully and uniformly mixing to obtain a chemical assistant solution. Wherein, in the chemical auxiliary solution, the mass fraction of glucan is 2.0%, the mass fraction of polyethyleneimine is 0.5%, and the mass fraction of fatty alcohol-polyoxyethylene ether is 0.2%.

Example 3

mixing 1.0 part by mass of konjac glucomannan and water, stirring, then sequentially adding 0.5 part by mass of sodium poly-p-styrene sulfonate and 0.1 part by mass of isomeric tridecanol polyoxyethylene ether, and fully and uniformly mixing to obtain a chemical assistant solution. Wherein, in the chemical auxiliary agent solution, the mass fraction of konjac gum is 1.0%, the mass fraction of sodium poly-p-styrene sulfonate is 0.5%, and the mass fraction of isomeric tridecanol polyoxyethylene ether is 0.1%.

Example 4

mixing and stirring 3.0 parts by mass of pectin and water, then sequentially adding 1.0 part by mass of sodium polyvinyl sulfonate and 0.1 part by mass of isomeric tridecanol polyoxyethylene ether, and fully and uniformly mixing to obtain a chemical assistant solution. Wherein, in the chemical auxiliary agent solution, the mass fraction of pectin is 3.0%, the mass fraction of sodium polyvinyl sulfonate is 1.0%, and the mass fraction of isotridecanol polyoxyethylene ether is 0.1%.

Example 5

The embodiment provides a method for preparing a novel back structure of a solar cell, which is different from embodiment 1 only in step (1), and specifically comprises the following steps: mixing and stirring 10 parts by mass of locust bean gum and water to obtain a clear colloidal solution, then sequentially adding 10 parts by mass of polyhexamethylene guanidine and 5 parts by mass of nonylphenol polyoxyethylene ether, and fully and uniformly mixing to obtain a chemical assistant solution. Wherein, in the chemical additive solution, the mass fraction of the locust bean gum is 10 percent, the mass fraction of the polyhexamethylene guanidine is 10 percent, and the mass fraction of the nonylphenol polyoxyethylene ether is 0.5 percent.

Comparative example 1

The comparative example provides a conventional texturing additive, and the back of a silicon wafer is subjected to secondary texturing to obtain a pyramid-shaped textured structure.

The etching process comprises preparing 1% potassium hydroxide solution as alkaline etching solution, adding texturing additive (commercially available), maintaining the solution temperature at 80 deg.C, and reacting according to conventional texturing procedure. And cleaning and drying the textured silicon wafer to obtain a test sample.

Comparative example 2

And (3) selecting the existing alkaline polishing additive in the industry, and chemically polishing the back surface of the silicon wafer to obtain an approximately flat surface structure.

The etching process comprises preparing 1% potassium hydroxide solution as alkaline etching solution, adding alkaline polishing additive (commercially available), maintaining the solution temperature at 65 deg.C for 200s, and reacting according to etching and polishing procedure. And cleaning and drying the polished silicon wafer to obtain a test sample.

Comparative example 3

The present comparative example provides a method for preparing a novel back structure of a solar cell, which is different from example 4 only in that: the pectin in the first component is replaced by water-soluble cellulose. The other components remained the same.

Comparative example 4

The present comparative example provides a method for preparing a novel back structure of a solar cell, which is different from example 4 only in that: no second component (sodium polyvinyl sulfonate) was added to the chemical adjuvant.

Comparative example 5

The present comparative example provides a method for preparing a novel back structure of a solar cell, which is different from example 4 only in that: isomeric tridecanol polyoxyethylene ether is not added.

Test example 1

The back structures of the silicon wafers obtained after the etching reactions in examples 1 to 4 and comparative examples 1 to 2 were tested by scanning electron microscopy, and the results are shown in fig. 1 to 4.

The microstructures (scanning electron microscope front photographs) of the back surfaces of the samples obtained in examples 1 to 4 are shown in (a) to (d) of FIG. 1. The microstructures (scanning electron microscope sectional photographs) of the back surfaces of the samples obtained in examples 1 to 4 are shown in (a) to (d) of FIG. 2. As can be seen from fig. 1-2, these structures exhibit a structure of "peaks" + "basins," the "peak" sidewalls approximating the exposed (111) silicon facets, and the "basins" approximating the exposed (100) silicon facets. The "mountains" and "basins" uniformly cover the entire back surface of the cell in a random manner. In the four embodiments, the proportion of the exposed surface of the "basin" to the total surface area of the back surface is different, thus resulting in different surface reflectivities.

The photograph of the front surface of the sample obtained in comparative example 1 is shown in fig. 3 (a), and the photograph of the cross section is shown in fig. 3 (b). The surface can be seen to be a randomly distributed pyramidal structure, exposing the (111) facets.

The scanning electron micrograph of the sample obtained in comparative example 2 is shown in fig. 4. FIG. 4 is a back surface of a nearly flat structure with slightly square etch pits on the surface, but with very small etch pits (< 1 um) in depth. The surface of the structure is predominantly the (100) plane.

Comparing the examples with comparative examples 1 and 2, it can be seen that the novel backside structure obtained by the examples of the present invention is intermediate between the surfaces of the pyramidal texture structure and the flat structure, and has moderate reflectivity. The structure has a high proportion of (100) crystal faces, and is beneficial to obtaining a good passivation effect compared with a pyramid textured structure. Meanwhile, the structure has certain micro roughness, is large in contact area and is easier to contact with conductive silver paste. Therefore, its contact resistance is significantly lower than that of a flat surface structure, and it is easy to obtain more excellent efficiency.

Test example 2

In comparative example 3, the locust bean gum in the first component of the adjuvant was replaced with water-soluble cellulose, and the rest was the same as in example 4. The back surface of the silicon wafer after the etching reaction was observed by a scanning electron microscope, and the results are shown in FIG. 5, in which (a) is a front view of the sample and (b) is a side view of the cross section. Although water-soluble cellulose is also a water-soluble colloid, it has a weak force with the silicon surface, and cannot effectively inhibit the reaction of silicon atoms with alkali, forming random fluctuations, and does not form the more regular structure of "mountain peak" + "basin" shape as embodied in examples 1-4.

In comparative example 4, the sodium polyvinylsulfonate of the second component of the adjuvant was eliminated and the first component was still pectin, the rest being the same as in example 4. The back surface of the silicon wafer after the etching reaction was observed by a scanning electron microscope, and the results are shown in FIG. 6, in which (a) is a front view of the sample and (b) is a side view of the cross section. It can be seen that the pectin molecules in the etching solution are randomly and in isolated association with the atoms of the surface of the single crystal silicon. During the etching process, the areas where pectin molecules bind are protected and become the tips of the pyramids. The silicon atoms of the unbound regions are gradually replaced by OH^-And (111) surfaces which are etched downwards and have slow etching rate are exposed, and a pyramid structure is formed. Due to the absence of the second component, pectin molecules cannot form a network-like adsorption layer but isolated adsorption points, so that the surface state after the final reaction is that pyramids are randomly distributed on a plane, and the more regular structures of 'mountain peak' + 'basin' embodied in examples 1-4 are not formed.

In comparative example 5, the surfactant isomeric tridecanol polyoxyethylene in the adjuvant third component was eliminated, leaving the first and second components, and the remainder was the same as in example 4. FIG. 7 shows optical photographs of the back surfaces of the silicon wafers after etching reaction in example 4 and comparative example 5, wherein (a) is example 4 and (b) is comparative example 5. As can be seen from the photographs, the appearance of the back surface was uniform in example 4, while the back surface in comparative example 5, although having a similar effect, had uneven spots on the surface due to adsorption of hydrogen bubbles generated during etching on the surface, which blocked the reaction of silicon and alkali. After the addition of the third component, the surfactant aids in the desorption of the bubbles from the surface, thereby obtaining a surface with a uniform appearance.

Test example 3

As can be seen from examples 1-4, different reflectivities can be obtained for different ratios of "mountain" and "basin". Samples obtained in example 4 and comparative examples 1 and 2 were selected and tested for spectral reflectance, and the results are shown in fig. 8. Meanwhile, the optical photographs of the three back surface samples are shown in fig. 9, (a) is the pyramidal textured structure in comparative example 1, (b) is the novel structure in example 4, and (c) is the flat surface structure in comparative example 2.

The results of the spectral testing showed that the pyramidal textured structure of comparative example 1 had the lowest reflectivity, with an average reflectivity of 11.1%. The flat surface structure in comparative example 2 had the highest reflectance, and the average reflectance at 300-1000nm was 47.8%. The average reflectivity of the novel structure obtained in the embodiment 4 of the invention is 32.8%. As can be seen from the photograph of fig. 9, comparative example 1 exhibited a bluish black color due to significant light absorption, comparative example 2 was a mirror-like bright light effect, and the sample obtained in example 4 exhibited a uniformly uniform light gray color, which was shown to correspond to the test results of spectral reflectance.

Therefore, the novel back surface structure obtained by the invention mixes the (100) crystal face and the (111) crystal face, the more uniform 'mountain peak' and 'basin' structures are between the pyramid texture structure and the flat surface structure, and the reflectivity is between the two structures.

Test example 4

Solar cells were prepared based on the novel back structure of single-crystal silicon obtained in example 4 and the back structures in comparative examples 1 and 2, and electrical parameters thereof were tested as shown in table 1.

Table 1 solar cell efficiency test results

As can be seen from table 1: the conversion efficiency of the solar cell with the flat back surface in the comparative example 2 is 23.42%, the conversion efficiency of the cell with the back pyramid textured structure in the comparative example 1 is 23.59%, and the conversion efficiency of the cell with the back structure treated by the embodiment 4 of the invention is 23.64%.

The contact resistance Rs is reduced from 0.0037 Ω to 0.0016 Ω compared to a flat surface structure, improving the fill factor FF. The efficiency is obviously improved by combining with the improvement of the short-circuit current, and the efficiency is increased by 0.22 percent.

Compared with the back structure of the pyramid texture, the method is mainly characterized in that the open-circuit voltage is improved, so that the efficiency is improved by 0.05%. Therefore, from the efficiency comparison of the solar cell, the chemical composition and the technical scheme for manufacturing the novel back surface structure of the solar cell are suitable for the TOPCon solar cell and have obvious technical advantages.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The chemical auxiliary agent for forming the back structure of the solar cell is characterized in that the raw materials comprise, by mass, 0.5-10 parts of a first component, 0.5-10 parts of a second component and 0.01-1 part of a third component;

the first component is selected from at least one of locust bean gum, konjac gum and pectin; the second component is selected from at least one of polyhexamethylene guanidine, polyethyleneimine, sodium polytereene sulfonate and sodium polyethylene sulfonate; the third component is at least one selected from alkylphenol ethoxylates, fatty alcohol-polyoxyethylene ether and isomeric alcohol-polyoxyethylene ether.

2. The chemical auxiliary agent according to claim 1, wherein the raw materials comprise, by mass, 0.5-5 parts of the first component, 0.5-3 parts of the second component, and 0.01-0.5 part of the third component.

3. A method for preparing a chemical assistant for forming a back structure of a solar cell, which is prepared by using the raw material of the chemical assistant according to any one of claims 1 to 2.

4. The method of claim 3, comprising: mixing the raw materials of the chemical auxiliary agent and water to obtain an aqueous solution, wherein the mass fractions of the first component, the second component and the third component in the aqueous solution are 0.5-10%, 0.5-10% and 0.01-0.5% in sequence.

5. An alkaline etching solution for forming a back structure of a solar cell, which is obtained by mixing the chemical auxiliary agent prepared by the preparation method of claim 3 or 4 with an alkaline solution.

6. The alkaline etching solution of claim 5, wherein the mass fraction of the alkaline solution is controlled to be 1-2%, and the volume ratio of the alkaline solution to the aqueous solution of the chemical auxiliary agent is 100:0.5-100: 2;

the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

7. A preparation method of a solar cell back structure is characterized in that the alkaline etchant of claim 5 or 6 is used for etching a silicon wafer.

8. The method of manufacturing according to claim 7, comprising: reacting the silicon chip in the alkaline corrosive liquid for 120-600s, wherein the temperature of the alkaline corrosive liquid is 50-95 ℃;

firstly, pre-cleaning the silicon wafer, and then reacting the silicon wafer with the alkaline corrosive liquid;

after reacting with the alkaline corrosive liquid, adopting hydrogen peroxide to perform immersion cleaning to remove residual organic matters on the surface.

9. A monocrystalline silicon solar cell, characterized in that the solar cell back structure prepared by the preparation method of claim 7 or 8 is used.