WO2023065650A1

WO2023065650A1 - Method for preparing monocrystalline silicon cell and monocrystalline silicon cell

Info

Publication number: WO2023065650A1
Application number: PCT/CN2022/092293
Authority: WO
Inventors: 赵赞良; 王茹; 王武林; 韩晓辉; 陈宇晖; 史晨燕
Original assignee: 宁夏隆基乐叶科技有限公司
Priority date: 2021-10-20
Filing date: 2022-05-11
Publication date: 2023-04-27
Also published as: CN115995501A

Abstract

Provided are a monocrystalline silicon cell and a preparation method thereof, comprising the following steps: texturing at least one surface of a monocrystalline silicon wafer substrate, and obtaining on said at least one surface a monocrystalline silicon wafer having a plurality of continuously arranged pyramidal structures with pyramid textured surfaces; performing dopant diffusion on at least one pyramid textured surface of the obtained monocrystalline silicon wafer, thus obtaining a monocrystalline silicon wafer having a PN junction; using a slurry containing spherical metal particles to perform electrode grid line printing and sintering on the side of the at least one pyramid textured surface having a monocrystalline silicon wafer with a PN junction, thus causing the spherical metal particles and the pyramid textured surface to form an ohmic contact. Further comprised is the use of a laser SE process to strengthen the ohmic contact between metal particles and a tip of a pyramid. The present application improves a filling factor, reduces open-circuit voltage loss, and improves battery conversion efficiency; and satisfies the dual requirements of reducing the contact resistance of a contact area while reducing carrier recombination in a non-contact area, thus reducing the electrical loss of a solar cell.

Description

A method for preparing monocrystalline silicon cells and monocrystalline silicon cells

Cross References to Related Applications

This application claims the priority of the Chinese patent publication with the application number 202111221272.0 and titled "A Method for Preparing Monocrystalline Silicon Cells and Monocrystalline Silicon Cells" submitted to the China Patent Office on October 20, 2021, all of which The contents are incorporated by reference in this application.

technical field

The present application belongs to the technical field of solar cells, and in particular, relates to a method for preparing a monocrystalline silicon cell and the monocrystalline silicon cell.

Background technique

As we all know, with the continuous improvement of solar cell efficiency, it is necessary to conduct in-depth research on various factors affecting efficiency in order to achieve higher conversion efficiency; and the contact resistance of semiconductors and metal grid lines in the electrical loss is an important influence Factors, so the existing production process uses the selective emission region to divide the front surface into two different doped regions to meet the needs of different regions for the emission region. A high dopant concentration is required in the grid line area where the electrode contacts to achieve good ohmic contact between the metal and the semiconductor to reduce the contact resistance, and heavy and deep doping is required in this area; in the light-absorbing area, low doping is required. Dopant concentration to meet the need to reduce carrier recombination, so light doping should be used in the non-electrode contact area.

At present, the commonly used method for preparing the selective emission region is to prepare a layer of oxide layer containing a higher dopant concentration on the front surface of the silicon wafer while diffusing to prepare the pn junction, and then add a high-energy laser to make electrodes. The gate line contact area is directly driven into the dopant; the dopant in the non-electrode contact area will not be affected by the laser and will remain in the oxide layer; in the subsequent etching process, the oxide layer on the front surface is removed to Realize selective emission regions with different doping concentrations in different regions; in the screen printing process, match the electrode grid pattern with the selective emission regions to achieve the dual advantages of reducing contact resistance and reducing carrier recombination. However, on the surface of the textured silicon wafer, the spire and the bottom of the pyramid exist. When the electrode grid is printed in the selective emission area driven by the laser, the slurry will preferentially corrode the spire and form contact with the spire; at this time, The high-concentration dopant at the bottom of the valley driven by the laser will not be able to play its role in reducing contact resistance. On the contrary, due to its high doping concentration, it will bring high carrier recombination and affect the efficiency of the cell.

In the existing production process, the laser pushes the dopant at the top and the bottom of the valley at the same time, so that the high dopant in the valley bottom area that is not corroded by the slurry will bring higher carrier recombination, thus affecting the efficiency.

overview

Aiming at the problems existing in the prior art, the present application provides a method for preparing monocrystalline silicon cells, a method for propulsing dopants differentially by laser, and monocrystalline silicon cells.

Specifically, this application involves the following aspects:

The present application provides a method for preparing a monocrystalline silicon cell, characterized in that the method comprises the following steps:

Texture is made on at least one surface of the single crystal silicon chip substrate to obtain a pyramid textured single crystal silicon chip with a plurality of continuously arranged pyramid structures on the at least one surface, wherein

The average length of the base of the triangular cross-section obtained by cutting the pyramid tip with the pyramid structure perpendicular to the silicon wafer base and parallel to the base of the pyramid is regarded as L,

The average angle of the angle formed by the sides of the triangular cross-section obtained by cutting the pyramid tip and the bottom edge with the pyramid structure perpendicular to the silicon wafer base and parallel to the bottom edge of the pyramid is regarded as θ;

performing dopant diffusion on at least one pyramid textured surface of the obtained monocrystalline silicon wafer to obtain a monocrystalline silicon wafer with a PN junction;

Using a slurry containing spherical metal particles to perform electrode grid printing and sintering on the side of the single crystal silicon wafer with a PN junction having the at least one pyramid texture, so that the spherical metal particles form an ohmic contact with the pyramid texture;

Wherein the spherical metal particles contained in the slurry have D90≥L/(4sinθ).

Optionally, the range of D90 of the metal particles is L/(4sinθ)≤D90≤2L.

Optionally, θ is 45-75°, preferably 50-65°, more preferably 54.75-60°.

Optionally, L is 0.5-5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm.

Optionally, the range of D90 of the metal particles is 1 μm≤D90≤4 μm.

Optionally, obtaining a dopant-containing single crystal silicon wafer comprises the following steps:

Carrying out dopant diffusion to the monocrystalline silicon wafer with pyramid texture, forming a silicon dioxide layer containing dopant on the surface of the pyramid texture;

Laser propelling is used for the dopant in the silicon dioxide layer, the concentration of dopant being higher at the top of the pyramid than at the bottom of the pyramid.

Optionally, the power of the laser in laser propulsion is 18-32W.

Optionally, the marking speed in laser propulsion is 20000-30000 mm/s, and the laser frequency is 200-300 Hz.

Optionally, the dopant is phosphorus.

The present application also provides a monocrystalline silicon solar cell, characterized in that at least one surface of the monocrystalline silicon solar cell has a pyramid texture with a PN junction and a plurality of consecutively arranged pyramid structures,

There are electrode grid lines on the pyramid texture, wherein spherical metal particles forming ohmic contact with the pyramid texture are distributed in the electrode grid lines, and D90 of the spherical metal particles is greater than or equal to L/(4sinθ).

Optionally, the range of D90 of the metal particles is L/(4sinθ)≤D90≤2L.

Optionally, θ is 45-75°, preferably 50-65°, more preferably 54.75-60°.

Optionally, L is 0.5-5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm.

Optionally, the range of D90 of the metal particles is 1 μm≤D90≤4 μm.

Optionally, the apex of the pyramid suede is propelled by a laser to form a chamfered structure.

Optionally, the monocrystalline silicon cell is prepared by the above method.

In this application, by improving the selective emission level process, the degree of propulsion of the dopant by the laser at the apex and the bottom of the pyramid is different, so as to achieve the concentration of dopant in the apex region in contact with the slurry and the non-contact valley bottom region. Different, so as to improve the fill factor, reduce the open circuit voltage loss, and increase the conversion efficiency of the battery; compared with the existing technology, there is no higher requirement for the selective emission process, and it can meet the requirements of reducing the contact resistance of the contact area and reducing the recombination of carriers in the non-contact area The dual needs of the solar cell reduce the electrical loss.

Brief description of the drawings

Fig. 1 is the top view of pyramid suede structure formed after cashmere making;

Fig. 2 is the side view of pyramid suede surface structure formed after cashmere making;

Fig. 3 is the calculation schematic diagram of the relationship between metal particle size and pyramid size in the slurry;

Fig. 4 is the schematic diagram that metal particle in the slurry is in contact with the tip of the pyramid, and the bottom of the valley is not in contact;

Figure 5 is a schematic diagram of the differential advancement of the laser on the top and bottom of the pyramid;

Fig. 6 is the scanning electron microscope (SEM) result figure of the pyramid suede surface of the embodiment of the present application;

Fig. 7 is the scanning electron microscope (SEM) result figure that the laser of the embodiment 1 of the present application advances to the pyramidal tip;

Fig. 8 is the scanning electron microscope (SEM) result figure that the laser of the embodiment 2 of the present application advances to the pyramid spire;

Fig. 9 is the scanning electron microscope (SEM) result figure after the slurry of embodiment 1 and pyramid contact sintering;

Fig. 10 is the scanning electron microscope (SEM) result figure after the slurry of comparative example 1 and pyramid contact sintering;

Fig. 11 is the result of measuring the difference in series resistance and the difference in fill factor of the monocrystalline silicon cells prepared in Example 3 and Comparative Example 1.

A detailed description

The present application will be further described below in conjunction with the examples. It should be understood that the examples are only used to further illustrate and explain the present application, and are not intended to limit the present application.

Unless otherwise defined, technical and scientific terms in this specification have the same meaning as commonly understood by a person skilled in the art. Although methods and materials similar or identical to those described herein can be employed in experiments or practical applications, the materials and methods are described herein below. In case of conflict, the present specification, including definitions, will control and the materials, methods, and examples are presented for purposes of illustration only and not limitation. The present application will be further described below in conjunction with specific examples, but they are not used to limit the scope of the present application.

The present application provides a method for preparing a monocrystalline silicon solar cell, the method comprising the following steps:

Step 1: making texture on at least one surface of the monocrystalline silicon wafer substrate to obtain a pyramid textured monocrystalline silicon wafer with a plurality of continuously arranged pyramid structures on the at least one surface, wherein

Step 2: Carry out dopant diffusion to at least one pyramid textured surface of the obtained described monocrystalline silicon wafer, obtain the monocrystalline silicon wafer with PN junction;

Step 3: Use the slurry containing spherical metal particles to print and sinter electrode grid lines on the side of the single crystal silicon wafer having a PN junction with the at least one pyramid texture, so that the spherical metal particles and the pyramid texture form an ohmic touch.

Wherein, in step 1, the substrate of the single crystal silicon wafer may be a P-type single crystal silicon wafer or an N-type single crystal silicon wafer, which is not limited in this application. In a specific embodiment, the substrate of the single crystal silicon wafer used is a boron-doped single crystal silicon wafer. Before texturing, the single crystal silicon substrate can be cleaned to remove impurities adsorbed on the surface of the silicon substrate during slicing, grinding, chamfering, polishing and other processes.

The method of making texture can adopt the methods known in the prior art, and texture can be made on one surface of the single crystal silicon wafer substrate, and can also be textured on both surfaces of the single crystal silicon wafer substrate. The specific process conditions can be adjusted by those skilled in the art according to actual needs. For example, the corrosive solution of NaOH and isopropanol can be used for texturing in the tank type texturing equipment. In a specific embodiment, the conditions used for texturing are as follows: the organic matter on the surface of the silicon wafer can be oxidized by the hydrogen peroxide in the pre-cleaning tank, and the sodium hydroxide can dissolve the oxidation product while removing part of the mechanical damage layer; Use deionized water to wash the desorbed impurities and residual lye on the surface; use a certain proportion of sodium hydroxide and additive solution to corrode the monocrystalline silicon wafer in the texturing tank to form an uneven textured surface to increase the glossiness. Absorption; then enter the post-cleaning tank to remove some organic matter in the additives remaining on the surface of the silicon wafer; then wash the deionized impurities and residual lye on the surface with deionized water through the washing tank; finally, after slow pulling, remove The impurities and residual acid that have been desorbed on the surface complete the entire texturing process.

The top view of the "pyramid" in this application is shown in Figure 1, and the side view is shown in Figure 2, which is a regular quadrangular pyramid with a square bottom and four isosceles triangles on the sides with a common apex. As shown in Figure 3 and Figure 4, the average length of the base of the triangular cross-section obtained by cutting the pyramid structure in the direction perpendicular to the silicon wafer base and parallel to the base of the pyramid is regarded as L, that is, the base of the regular pyramid The average length of the sides is L. The average angle between the side and the base of the triangular cross-section obtained by cutting the pyramid structure in a direction perpendicular to the silicon wafer base and parallel to the base of the pyramid is regarded as θ.

In step 2, dopant diffusion is performed on at least one pyramid textured surface of the obtained single crystal silicon wafer to obtain a single crystal silicon wafer with a PN junction. The diffusion of dopant can adopt the method known in the prior art, and the specific process conditions can be adjusted according to actual needs by those skilled in the art. In a specific embodiment, the dopant is phosphorus.

In a specific embodiment, the conditions used for doping phosphorus can be as follows: using the North Huachuang tubular diffusion furnace, first insert the single crystal silicon wafer into the quartz boat and then put it on the silicon carbide paddle, and then send it into the inlet tube ; After ensuring that the furnace tube is properly sealed, nitrogen gas is passed into the liquid phosphorus oxychloride, and connected to the furnace tube, and phosphorus is diffused on the single crystal silicon wafer in a high-temperature environment; The internal diffusion of the silicon wafer increases the junction depth and reduces the surface concentration of the silicon wafer; after cooling down, oxygen is introduced to completely react and discharge the unreacted phosphorus source to prevent the external air from being polluted after the furnace door is opened, and finally nitrogen is charged to the furnace The tube is purged while the pressure is balanced and the furnace door is opened to carry the diffused single crystal silicon wafer out of the furnace tube.

In step three, during the electrode grid printing process, the glass frit in the paste is first dissolved into a liquid, and the silicon dioxide and silicon nitride layers formed in step two are etched, and then the emitter is exposed silicon surface. According to the electrode grid lines to be prepared, pastes containing different metal particles can be selected, for example, pastes containing silver particles.

As shown in Fig. 3, when θ and L are known, the average height H of the pyramid can be determined, that is, H=(L/2)*tanθ. If the metal particles in the slurry are in tangential contact with the pyramid hypotenuse from the bottom to the 1/4 position of the total length of the hypotenuse, and a is the vertical height from the tangent point to the bottom edge of the pyramid, then a=H/4=(L /8)*tanθ, taking b as the direct average distance between the center point of the slurry metal particle and the contact point of the two hypotenuses of the pyramid, then b/2=a*tan(90°-θ)=(L/8)*tanθ* tan(90°-θ)=L/8, b=L/4, the corresponding diameter of metal particles is D=2r=b/sinθ=L/(4sinθ).

Since the spire of the pyramid is higher than the bottom of the valley, the metal particles in the slurry will preferentially form contact with the spire with a higher concentration of dopant driven by the laser at this time, while the organic matter in the slurry will gather and flow due to the density. At the bottom of the valley, a layer of protection is formed for the bottom of the valley, and the size of the metal particles is basically greater than or equal to the distance between the spires, so that the particles will not easily fall into the bottom of the valley where the laser is driven into the low dopant concentration, forming a bad contact. The schematic diagram of the structure is as follows As shown in Figure 4; then, after high-temperature sintering in the sintering furnace, the metal particles will form a good ohmic contact with the tower tip with a small contact resistance, which will reduce the series resistance and increase the fill factor, which has a positive effect on the efficiency. There are basically no metal particles in the valley bottom area, and organic matter will also volatilize under the action of high temperature, which will reduce the recombination of carriers, reduce the loss of open circuit voltage, and play a positive role in efficiency. Therefore, the metal particles should be properly matched with the pyramid size, and the value range of the size D90 of the metal particles should be such that more than 90% of the metal particles are approximately the same as the position of more than a quarter of the hypotenuse of most of the pyramids. Cut contact, that is to say, the D90 range of the metal particles is D90≥L/(4sinθ), so as to ensure that the recombination of carriers in the valley area is reduced.

Further preferably, the D90 range of the metal particles is D90≤2L, that is, L/(4sinθ)≤D90≤2L, this is because, in the ideal situation where the pyramid size distribution is extremely concentrated, four adjacent pyramid structures correspond to one at most Metal particles, so that the top of each pyramid forms a good ohmic contact with the metal particles. When a large number of metal particles exceed the average size of the pyramid bottom by 2L, there will be extrusion between adjacent metal particles, resulting in the possibility of some pyramid tips The top of the pyramid cannot be contacted, thereby deteriorating the ohmic contact between the metal particles and the surface of the pyramid, and increasing the contact resistance.

The θ angle range is theoretically any acute angle, that is, 0-90 degrees. However, in order to further make the laser advance, it is easier to concentrate on the pyramid tip of the suede surface, and at the same time, it can also ensure 1/4 of the valley of the suede surface. Above to the spire position can fully contact with the metal particles, the angle is preferably 45-75°, for example can be 45°, 50°, 55°, 60°, 65°, 70°, 75°, more preferably 50- 65° to make the combined effect of contact performance and laser propulsion more prominent. Within this range of angles, 54.75°-60° can be further preferred, that is, the conventional inclination angle of the pyramid textured alkaline etching, which can be obtained by conventional existing alkaline etching without additional complicated Suede angle adjustment process can be obtained.

The average length of L may be 0.5-5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm. In some embodiments, L can be selected in the range of 1-2 μm. Under the minimum or maximum size of L in this range, the corresponding ranges of silver paste particles D90 are 0.5-2 μm and 1-4 μm, respectively. Under the condition that the above-mentioned dimensions cooperate with each other, the present application can ensure sufficient ohmic contact between the silver paste particles and the PN junction pyramid texture, and at the same time greatly reduce the carrier recombination at the bottom of the pyramid.

It should be noted that although the length of the base of each pyramid of the pyramid suede surface, the angle formed by the side of the triangular cross-section obtained by cutting the pyramid tip and the base will be relative to the average length L and the average There is a certain fluctuation in the angle θ, but this does not affect the implementation of the embodiment of the present application. Existing texturing does not lead to a particularly large degree of dispersion in the aforementioned lengths and included angles. Moreover, the actually used metal paste has a certain amount of low melting point conductive material and glass frit, and the distribution of metal particles has a certain degree of dispersion. Therefore, when the D90 of the metal particles of the metal paste satisfies the requirements, a large number of pyramid structures can already be formed at a higher position from the bottom of the tower, such as a position above 1/4 pyramid height and metal particles of suitable particle size. ohmic contact. In addition, the smaller-sized metal particles can supplement the ohmic contact near the top of the small-sized pyramid structure, and the low-melting point conductive material is fused between the metal particles to form a conductive connection during sintering. Therefore, although the pyramid suede of the present application may eventually have the unfavorable situation that a small amount of pyramid structures and small-sized metal particles form ohmic contacts at the bottom of the pyramids, it can be known from the above analysis that this will not lead to the present application as in the prior art. A large number of pyramid bases as shown in Figure 10 have degraded ohmic contacts.

In a preferred embodiment, the step of obtaining a dopant-containing single crystal silicon wafer may include the following steps:

performing dopant diffusion on at least one pyramidal texture of the obtained monocrystalline silicon wafer, and forming a dopant-containing silicon dioxide layer on the surface of at least one pyramidal texture;

When using laser propulsion, as shown in Figure 5, this application uses appropriate laser power to make the effect of matching the original metal particles with the size of the pyramid more prominent. The laser makes the doping effect of the spire more prominent to form an N ⁺⁺ doped region, which improves the conductivity of the spire. At the same time, the spire is more gentle and not sharp, that is, a chamfer structure is formed at the spire. Therefore, the effective ohmic contact area between the metal particles and the pyramid can be increased, and the resistance of the ohmic contact can be reduced, thereby reducing the series resistance and increasing the fill factor, which has a positive gain on efficiency.

Specifically, when the laser is used for dopant propulsion, since the atoms at the tip of the pyramid have more hanging bonds and lower bond energy, and there are four interfaces exposed to the outside, the energy of the atoms at the tip of the pyramid is higher at this time. In an active unstable state, therefore, when the laser advances, the laser will be more likely to drive the dopant at the top of the tower, forming a higher concentration of dopants at the top of the tower; and the bond of atoms at the bottom of the pyramid The energy is high, and only two interfaces are exposed to the outside. The probability of atoms being in a stable state is much greater than that of the spire, and the area of the valley bottom is much larger than that of the spire. Therefore, under the same laser energy, the doped atoms driven into the valley bottom There will be much less miscellaneous agent than at the spire.

It is particularly important to choose the appropriate laser propulsion conditions, because too high laser power will not only drive the active dopant atoms at the top of the tower, but also have enough energy to activate the stable dopant atoms at the bottom of the valley. At this time, the high dopant concentration at the top of the tower will be beneficial to react with the screen printing paste to form a good contact, while the high dopant concentration at the bottom of the valley will bring more carriers Recombination, which has a negative impact on the efficiency of the cell; and lower laser power, due to insufficient energy, may cause the dopant atoms at the tip of the tower to not be fully driven in, and cannot reach the formation of the slurry. Concentration requirements for good ohmic contact.

In order to achieve the best doping effect, in a specific embodiment, the power of the laser in laser propulsion is 18-32W, such as 18W, 19W, 20W, 21W, 22W, 23W, 24W, 25W, 26W, 27W, 28W, 29W, 30W, 31W, 32W.

In a specific embodiment, using the laser produced by Wuhan Teal, the marking speed in laser propulsion is 20000-30000mm/s, for example, it can be 20000mm/s, 21000mm/s, 22000mm/s, 23000mm/s, 24000mm /s, 25000mm/s, 26000mm/s, 27000mm/s, 28000mm/s, 29000mm/s, 30000mm/s.

In a specific embodiment, the laser frequency in laser propulsion is 200-300 Hz, for example, 200 Hz, 210 Hz, 220 Hz, 230 Hz, 240 Hz, 250 Hz, 260 Hz, 270 Hz, 280 Hz, 290 Hz, 300 Hz.

In a specific embodiment, the power of the laser in the laser propulsion is 18-32W, the marking speed is 20000-30000mm/s, and the laser frequency is 200-300Hz.

The laser-propelled pyramid suede surface can be observed by scanning electron microscopy on the laser damage to the pyramid suede surface and the effect of dopant propulsion.

The present invention also provides a monocrystalline silicon solar cell, at least one surface of the monocrystalline silicon solar cell has a pyramid texture with a PN junction and a plurality of consecutively arranged pyramid structures,

Further preferably, the range of D90 of the metal particles is D90≤2L, that is, L/(4sinθ)≤D90≤2L.

Wherein the angle range of θ can theoretically be any acute angle, that is, 0-90 degrees, preferably 45-75°, for example, 45°, 50°, 55°, 60°, 65°, 70°, 75°, more preferably 50-65°.

The length of L may be 0.5-5 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm. In some embodiments, L can be selected in the range of 1-2 μm. Under the minimum or maximum size of L in this range, the corresponding ranges of silver paste particles D90 are 0.5-2 μm and 1-4 μm, respectively.

Furthermore, due to the effect of laser propulsion, the tip of the pyramid texture of the monocrystalline silicon cell of the present application is more gentle and not sharp, forming a chamfered structure.

Further, the monocrystalline silicon cell can be prepared by the above method.

Example

Example 1

1. Using boron-doped single crystal silicon wafers as experimental silicon wafers, the pyramid textured surface is prepared in Jiejia Weichuang groove-type texturing equipment: firstly, the organic matter on the surface of the silicon wafer can be oxidized and hydrogenated by the hydrogen peroxide in the pre-cleaning tank. Sodium can dissolve the oxidation product and remove part of the mechanical damage layer at the same time; then use deionized water to wash the desorbed impurities and residual lye on the surface; use a certain proportion of sodium hydroxide and additive solution in the cashmere tank The monocrystalline silicon wafer undergoes a corrosion reaction to form an uneven suede surface to increase light absorption; then it enters the post-cleaning tank to remove some organic substances in the additives remaining on the surface of the silicon wafer; and then passes through the washing tank 2 to rinse the surface with deionized water The impurities that have been desorbed and the residual lye; finally, after slow pulling, the impurities that have been desorbed on the surface and the residual acid are removed to complete the entire texturing process.

The scanning electron microscope results of the prepared pyramid suede are shown in FIG. 6 . Among them, the average length L of the base of the triangular cross-section obtained by cutting the pyramid tip in the direction perpendicular to the silicon wafer base and parallel to the pyramid base is 1.7 μm. The average angle θ of the included angle formed by the sides of the triangular cross-section obtained by cutting the pyramid tip in the direction of the pyramid base and the base is 54.75°, and the height is 1.1 μm.

2. Put the textured silicon wafer into a tubular diffusion furnace for phosphorus diffusion to prepare a pn junction, and at the same time prepare a layer of phosphorus-containing silicon dioxide layer on the surface of the silicon wafer; Diffusion furnace, first insert the monocrystalline silicon wafer into the quartz boat and put it on the silicon carbide paddle, and then send it into the inlet tube; after ensuring that the furnace tube is properly sealed, inject nitrogen gas into the liquid phosphorus oxychloride In the furnace tube, phosphorous is diffused on the single crystal silicon wafer in a high temperature environment (750°C-880°C); then high-temperature advance is carried out to diffuse the impurity source into the silicon wafer to increase the junction depth and reduce the surface concentration of the silicon wafer; after that Lower the temperature (750°C-780°C), and then pass in phosphorus oxychloride again for diffusion to supplement the phosphorus doping concentration in the surface layer and provide a doped phosphorus source for the subsequent SE laser propulsion; then pass in oxygen to remove the unreacted Phosphorus oxychloride is completely reacted and discharged to prevent the outside air from being polluted after opening the furnace door. Finally, nitrogen gas is charged to purge the furnace tube while the pressure is balanced and the furnace door is opened to carry out the diffused single crystal silicon wafer from the furnace tube.

3. The diffused silicon wafer is prepared for the selective emission region. A laser is used to propel the dopants in the silicon dioxide layer. Specifically, the operating conditions of the laser propulsion are: the laser power is 32W, the marking speed is 28000mm/s, and the laser frequency is 250Hz. The monocrystalline silicon wafer after laser propulsion was characterized by scanning electron microscopy to observe the morphology of the pyramid texture. The results are shown in Figure 7. It can be seen that the damage on the top of the tower is larger and more dopants are driven in, so the resistance decreases more. , most of the driving points are located at the top of the pyramid, and the top of the tower is damaged so that the shape of the top of the tower is not so sharp, which can enhance the ohmic contact between the top of the tower and the silver particles in the subsequent sintered silver paste particles. However, a larger laser power will further damage the top of the pyramid suede in a large area, resulting in the deterioration of the original light-trapping structure. Therefore, the laser power should not be greater than 32W, otherwise the light reflectance of the finally formed cell will increase due to the deterioration of the light trapping effect, resulting in a decrease in the conversion efficiency of the cell.

4. Etching, annealing and coating the single crystal silicon wafer after laser propulsion. Jiejia Weichuang groove etching machine is used to etch the front and rear surfaces with HF acid and nitric acid to remove the phosphorus-containing silicon dioxide layer formed on the front surface during the diffusion process and the pyramid structure formed on the rear surface during texturing. The rear surface can be polished so that the coating can better grow the silicon nitride passivation layer; the silicon wafer is placed in the furnace tube for annealing process using the North Huachuang tube annealing machine, and the silicon wafer is placed in a high temperature environment (650°C- 780°C) Oxygen is used to oxidize the diffusion surface pushed by the laser to form a silicon dioxide film, which plays a passivation role; the northern Huachuang tube-type coating machine is used to put the silicon wafer into the furnace tube for the coating process, Using ammonia and silane to react under vacuum, silicon nitride films are grown on the front and rear surfaces of the annealed single crystal silicon wafer to achieve the effects of passivation and anti-reflection.

5. Screen-print the battery sheet with a chain printing machine, display the back electrode through the screen printing of the aluminum paste on the back, and display the positive electrode through the screen printing of the silver paste on the front; The sintering furnace sinters the electrodes printed on the single crystal silicon wafer; in the sintering process, firstly, the glass phase in the silver paste softens and melts, wets the surface of the silicon wafer, etches the anti-reflection film, and then etches the silicon emitter; at this time The oxidation-reduction reaction between silicon and metal oxide releases metal silver particles, forming corrosion pits; during the cooling process, Ag particles recrystallize near these corrosion pits, that is, silver particles grow to the surface of the silicon wafer; and the reacted glass frit and organic matter will Volatilize in a high temperature environment; after sintering, the metal and the silicon wafer form an ohmic contact with a small contact resistance; thus the finished monocrystalline silicon solar cell is prepared. Wherein the D90 of the silver particles in the front silver paste is greater than or equal to 1 μm and less than or equal to 4 μm. The scanning electron microscope of the finally prepared monocrystalline silicon cell is shown in Figure 9. The figure shows that the size of the silver particles in the slurry is much larger than the pitch spacing of the pyramids, and the silver particles cannot fall into the valley bottom area, so they will be directly on the adjacent Contact is formed at the top of the pyramid, but not at the bottom of the pyramid.

Example 2

The difference between embodiment 2 and embodiment 1 is that in step 3, the operating conditions of the laser propulsion are different. Specifically, the operating conditions of the laser propulsion are: the laser power is 18W, the marking speed is 28000mm/s, and the laser frequency is 250Hz.

Scanning electron microscopy was performed on the laser-propelled single crystal silicon wafer to observe its pyramid texture morphology. The results are shown in Figure 8. It can be seen that the damage is less and the drive-in is less. Contrary to Example 1, under the laser propulsion process, the damage range of the pyramid tip is smaller, and the pyramid suede maintains a better light-trapping suede surface. However, because the dopant at the top of the tower is driven into less, the resistance drops less, and the shape of the top of the tower is not conducive to the ohmic contact with the conductive particles, the ohmic contact between the top part of the tower and the silver particles in the subsequent sintered silver paste particles is phased Weakened compared to Example 1. Therefore, the laser power should not be lower than 18W, otherwise the final cell will increase the series resistance due to the deterioration of the ohmic contact of the paste, which will reduce the conversion efficiency of the cell.

Example 3

The difference between embodiment 3 and embodiment 1 is that in step 3, the operating conditions of the laser propulsion are different. Specifically, the operating conditions of the laser propulsion are: the laser power is 27W, the marking speed is 26000mm/s, and the laser frequency is 250Hz.

Comparative example 1

The difference between Comparative Example 1 and Example 3 lies in that the D90 of the silver particles in the silver paste in step 5 is different. Specifically, the D90 of the silver particles in the silver paste is less than 1 μm. Since the size of the silver particles in the paste is less than 1 μm, this type of silver particles falls into the bottom of the pyramid, and the concentration of the dopant phosphorus at the bottom of the valley is low due to the selective advancement of the laser, which is caused by the contact of the paste. A larger contact resistance causes an increase in the series resistance of the battery sheet and a decrease in the fill factor; the contact of such silver particles is shown in Figure 10. The specific operating conditions of each embodiment and comparative example are as shown in table 1:

Table 1

Test case

The difference in series resistance and the difference in fill factor were measured for the monocrystalline silicon cells prepared in Example 3 and Comparative Example 1, and the results are shown in Figure 11. The cells made of monocrystalline silicon wafers after texturing, diffusion, SE, etching, annealing, coating, screen printing, and sintering are passed through the I-V testing instrument to simulate sunlight to test the cells. After calculation, the output parameters, including series resistance and fill factor. The main difference in conversion efficiency of cells comes from the difference in series resistance and the difference in fill factor. The results in the figure show that, compared with the battery sheet of Comparative Example 1, the fill factor of the battery sheet of the present application is 0.33% higher, and the series resistance is lower by 0.13 milliohms.

The series resistance is mainly composed of the resistance of the battery base area, the lateral resistance of the emission area, the contact resistance between the silver electrode and the emission area, and the line resistance of the silver grid line. When the production process of other batteries remains unchanged, the reduction of the contact resistance between the silver electrode and the emitter region will lead to a reduction in the series resistance and an increase in the fill factor, thereby improving the conversion efficiency of the cell. The contact resistance between the silver electrode and the emitter region is mainly determined by the doping concentration of the emitter region. The series resistance in the battery sheet of this application is lower than that of the existing technology, which realizes the purpose of reducing the series resistance and improving the fill factor. At the same time, the selection of SE The positive advancement keeps the concentration of the valley bottom area not in contact with the slurry low, and also achieves a further increase in the open circuit voltage.

Claims

A method for preparing a monocrystalline silicon cell, characterized in that the method comprises the following steps:

Texture is made on at least one surface of the single crystal silicon chip substrate to obtain a pyramid textured single crystal silicon chip with a plurality of continuously arranged pyramid structures on the at least one surface, wherein

The average length of the base of the triangular cross-section obtained by cutting the pyramid tip with the pyramid structure perpendicular to the silicon wafer base and parallel to the base of the pyramid is regarded as L,

The average angle of the angle formed by the sides of the triangular cross-section obtained by cutting the pyramid tip and the bottom edge with the pyramid structure perpendicular to the silicon wafer base and parallel to the bottom edge of the pyramid is regarded as θ;

performing dopant diffusion on at least one pyramid textured surface of the obtained monocrystalline silicon wafer to obtain a monocrystalline silicon wafer with a PN junction;

Using a slurry containing spherical metal particles to carry out electrode grid printing and sintering on the side of the single crystal silicon wafer having a PN junction with the at least one pyramid texture, so that the spherical metal particles form an ohmic contact with the pyramid texture;

Wherein the spherical metal particles contained in the slurry have D90≥L/(4sinθ).
The method according to claim 1, characterized in that the range of D90 of the metal particles is L/(4sinθ)≤D90≤2L.
The method according to claim 1, characterized in that θ is 45-75°, preferably 50-65°, more preferably 54.75-60°.
The method according to claim 3, characterized in that L is 0.5-5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm.
The method according to claim 4, characterized in that the range of D90 of the metal particles is 1 μm≤D90≤4 μm.
The method according to claim 1, wherein obtaining a single crystal silicon wafer with a PN junction comprises the following steps:

performing dopant diffusion on at least one pyramidal texture of the obtained monocrystalline silicon wafer, and forming a dopant-containing silicon dioxide layer on the surface of at least one pyramidal texture;

Laser propelling is used for the dopant in the silicon dioxide layer, the concentration of dopant being higher at the top of the pyramid than at the bottom of the pyramid.
The method according to claim 6, characterized in that the power of the laser in the laser propulsion is 18-32W.
The method according to claim 7, characterized in that the marking speed during laser propulsion is 20000-30000 mm/s, and the laser frequency is 200-300 Hz.
The method of claim 1, wherein the dopant is phosphorus.
A monocrystalline silicon battery sheet, characterized in that at least one surface of the single crystal silicon battery sheet has a pyramid texture with a PN junction and a plurality of consecutively arranged pyramid structures,

The average length of the base of the triangular cross-section obtained by cutting the pyramid tip with the pyramid structure perpendicular to the silicon wafer base and parallel to the base of the pyramid is regarded as L,

The angle of the average included angle formed by the sides of the triangular cross-section obtained by cutting the pyramid tip and the bottom edge with the pyramid structure perpendicular to the silicon wafer base and parallel to the bottom edge of the pyramid is regarded as θ;

The pyramid textured surface has electrode grid lines, wherein spherical metal particles forming ohmic contact with the pyramid textured surface are distributed in the electrode grid lines, and D90 of the spherical metal particles is ≥ L/(4sinθ).
The monocrystalline silicon cell according to claim 10, characterized in that the range of D90 of the metal particles is L/(4sinθ)≤D90≤2L.
The monocrystalline silicon cell according to claim 10, wherein θ is 45-75°, preferably 50-65°, more preferably 54.75-60°.
The monocrystalline silicon cell according to claim 10, wherein L is 0.5-5 μm, preferably 1-3 μm, more preferably 1.2-1.8 μm.
The monocrystalline silicon cell according to claim 10, wherein the D90 range of the metal particles is 1 μm≤D90≤4 μm.
The monocrystalline silicon battery sheet according to claim 10, wherein the apex of the pyramid texture is propelled by a laser to form a chamfered structure.
The battery sheet according to claim 10, wherein the monocrystalline silicon battery sheet is prepared by the method according to any one of claims 1-9.