Screen printing screen plate for solar cells and improved method thereof

Abstract

The application relates to the technical field of solar cells and discloses a screen printing screen plate for a solar cell and an improved method thereof. The improved method comprises the following steps: dividing a screen cloth into a plurality of distribution areas with equal intervals along an x axis, taking the distribution area in the middle of the x axis of the screen cloth as a reference area; analyzing the stress on the left and right sides of each distribution area to obtain the stress of each distribution area; through three-dimensional space stress analysis, according to stress balance, and in combination with the secondary projection method of the stress, the stress components corresponding to x, y and z are obtained; the shear stress of the reference area is obtained by ignoring the z direction; in order to keep the shear stress of the reference area consistent with the shear stress of the rest of the distribution areas of the screen cloth, the tungsten steel longitudinal wire content of the rest of the distribution areas is increased to balance the corresponding shear stress to offset the stress of each distribution area, so that the stress of each distribution area of the screen cloth is consistent; the line width difference of the metal grid lines is reduced, the poor confluence and the fragment rate are reduced, the battery efficiency is improved, and the feeding is convenient.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a screen printing screen plate for solar cells and an improved method thereof. BACKGROUND

[0002] A solar cell is a product that directly converts solar energy into electric energy. When exposed to light, a solar cell generates photo-generated carriers, and it is necessary to converge and guide the generated photo-generated carriers. The usual method is to prepare metal grid lines on the surface of a solar cell as metal electrodes to converge and guide the photo-generated carriers. In the prior art, the mainstream method for preparing metal electrodes is to use a screen printing process. The specific process of the screen printing process is as follows: first, open 23 the screen plate for screen printing in the shape of the metal electrode 41 (for example, as shown in Figure 1-2 The screen plate includes a screen frame 10 and a screen cloth 20 formed by weaving a plurality of screen lines 21, and the non-opening part of the screen cloth 20 is filled with polyimide 22; then, during screen printing, under the action of the scraper 30 such as a doctor blade, the electrode paste 40 is squeezed out from the opening 23 of the screen cloth 20, and then printed on the cell piece 50 (for example, as shown in Figure 2 ), to complete the printing of the metal electrode pattern; and then, the electrode paste 40 is sintered to form the metal electrode 41 on the cell piece 50.

[0003] However, in order to squeeze out the electrode paste 40, a downward force needs to be generated on the electrode paste 40. Therefore, during actual screen printing, a certain gap d2 (as shown in Figure 2 ) must be left between the screen cloth 20 and the cell piece 50. At this time, when the scraper 30 pushes the electrode paste 40 forward, a relatively large downward stress will inevitably be generated on the screen cloth 20. The strain generated by this stress on the horizontal screen (i.e., the screen line 21 in the screen cloth 20 distributed along the x-axis direction) and the vertical screen (i.e., the screen line 21 in the screen cloth 20 distributed along the y-axis direction) is not the same, and the strain generated by this stress in different distribution areas of the screen cloth 20 (for example, a plurality of distribution areas of the screen cloth 20 divided along the x-axis direction at equal intervals) is also not the same. Moreover, even if the screen cloth 20 is made of a material with a very high elastic modulus, such as stainless steel or tungsten steel, the screen cloth 20 will still generate stress and corresponding strain under the downward action of the scraper 30. This stress will first cause the pattern actually screen printed on the cell piece to slightly expand or deform, thereby causing differences between the actually screen printed pattern and the screen pattern (for example, as shown in Figure 3);secondly, due to the different strain of each distribution area of the screen cloth 20, it also causes the uneven line width of the printed metal grid line of each distribution area of the screen cloth 20. Moreover, in order to reduce the light shielding area of the metal grid line on the surface of the battery piece, the current trend of the preparation of the metal grid line is to make it thinner (i.e. the line width of the prepared metal grid line is smaller), which is also prone to cause the broken grid phenomenon of the printed metal grid line on the battery piece. Therefore, the inconsistency of the screen printing pattern, the uneven line width of the metal grid line, and even the broken grid phenomenon will cause poor confluence, affect the ability of the metal electrode to collect the photo-generated carriers, and ultimately affect the battery efficiency.

[0004] In view of the above defects of screen printing the metal electrode, referring to Figure 4 , the current solution is to use a double-layer roller (which includes an upper roller and a lower roller) for screen printing. Referring to Figure 4 b, the roller 60 (such as the upper roller) has openings 23 like a screen plate, and the inside of the roller 60 carries the electrode paste 40; the rotating upper roller and lower roller together drive the movement of the battery piece 50 (as shown in Figure 4 a, the direction of the arrow on the battery piece 50 represents the direction of the movement of the battery piece 50 driven by the double-layer roller), and under the action of the scraper 30 inside the roller 60 (such as the upper roller), the electrode paste 40 is extruded through the openings 23 on the battery piece 50 to complete the printing of the metal electrode pattern. In this double-layer roller, both the upper roller and the lower roller are cylindrical structures, the upper roller serves as a printing carrier (i.e. the inside of the upper roller carries the electrode paste 40), and the lower roller provides support to reduce stress. In this way, although the pattern of the screen printing is still deformed, for each point on the double-layer roller of the cylindrical structure, the deformation is consistent; therefore, the actual screen printed metal electrode pattern can be the same or similar to the screen cloth pattern, thereby improving the poor confluence of the metal electrode caused by the existing screen printing.

[0005] However, the double-layer roller solution still has many problems: 1. The filling of the electrode paste 40 is complicated: screen plate printing is open, and the electrode paste can be easily supplemented; while the roller 60 is a semi-closed device, the supplementing step of the electrode paste 40 is complicated, which causes waste of labor and low production. 2. The double-layer roller reduces the contact area of the printing device and the battery piece 50, which easily leads to an increase in the fragment rate of the battery piece 50 during the printing process.

[0006] In addition, the existing screen printing screen plate, such as the screen plate for printing provided in the publication No. CN210821351U, although the material of the screen can be stainless steel, tungsten steel alloy, etc. However, the existing screen printing screen plate, whether the longitudinal screen in each distribution area is made of stainless steel, or the longitudinal screen in each distribution area is made of tungsten steel alloy, or the proportion of the tungsten steel alloy longitudinal screen and the stainless steel longitudinal screen in each distribution area is consistent. Therefore, the existing screen printing screen plate still cannot solve the defect that the line width of the metal grid printed in each distribution area is not uniform, and even the grid is broken, due to the different stresses and strains of each distribution area caused by the pressure of the squeegee during screen printing, thereby still causing poor convergence and affecting the battery efficiency. SUMMARY

[0007] The present application aims to overcome the shortcomings of the prior art and provide a screen printing screen plate for solar cells and an improved method thereof.

[0008] Based on this, the present application discloses an improved method of a screen printing screen plate for solar cells, comprising the following improvement steps:

[0009] S1, the screen cloth of the screen printing screen plate is divided into several distribution areas along the x-axis direction in turn at equal intervals, the number of distribution areas is a base number greater than or equal to 3; wherein the screen cloth includes a plurality of horizontal wires distributed along the x-axis direction and a plurality of vertical wires distributed along the y-axis direction, and the distribution area in the middle of the x-axis of the screen cloth is taken as the reference area;

[0010] S2, when the squeegee of screen printing pushes the electrode paste to advance to different distribution areas of the screen cloth, the left and right sides of different distribution areas of the screen cloth are analyzed according to the constant pressure of the squeegee on the screen cloth, the screen distance between the screen cloth and the battery piece, the screen cloth length and the distance of the squeegee moving along the x-axis advancing direction, and the stress of different distribution areas is obtained;

[0011] S3, the stress of different distribution areas is analyzed in three-dimensional space, the corresponding stress components in x, y and z directions are obtained according to the stress balance and combined with the secondary projection method of stress;

[0012] S4, for the planar screen cloth, only the x and y directions are considered, and the z direction is ignored, and according to the relationship between the stress component and the shear strain corresponding to the shear stress, and the relationship between the stress and the strain, the shear stress of different distribution areas of the screen cloth is obtained; the shear stress of the reference area of the screen cloth is obtained;

[0013] S5, according to the influence relationship of the mesh wire material of the mesh cloth on the stress, combining the mutual influence of the transverse stress and the shear stress, in order to keep the shear stress of each distribution area of the mesh cloth consistent with the shear stress of the reference area, without changing the number of longitudinal wires of each distribution area, replacing the stainless steel longitudinal wires of each distribution area with corresponding number of tungsten steel longitudinal wires, to correspondingly increase the content of tungsten steel longitudinal wires replaced in each distribution area, to balance the corresponding shear stress of each distribution area, to correspondingly offset the stress suffered by the different distribution areas of the mesh cloth along the x-axis transverse direction, so that the stress of each distribution area of the mesh cloth is consistent.

[0014] Preferably, in step S2, the stress F suffered by the different distribution areas of the mesh cloth is obtained, including the following steps:

[0015] S21, according to the constant pressure F0 of the scraper on the mesh cloth, the mesh distance D between the mesh cloth and the battery piece, the length L of the mesh cloth and the distance e of the scraper moving along the x-axis forward direction, the left and right sides of the different distribution areas of the mesh cloth are analyzed, and the middle part of the distribution area is taken as the stress analysis point, and the following stress relationship formula (4) of the middle part of the different distribution areas is obtained:

[0016] F0 / Sin(180°-α-β)=F L / Sinβ=F R / Sinα (4),

[0017] (4) In the formula, F L is the tension on the left side of the distribution area, F R is the tension on the right side of the distribution area, α is the included angle between the pressure F0 and the left tension F L , and β is the included angle between the pressure F0 and the right tension F R ;

[0018] S22, the numerical value of the left tension F L and the right tension F R of the same distribution area is compared, and the left tension F L or the right tension F R with larger numerical value is taken as the stress F of the scraper on the distribution area.

[0019] Further preferably, step S21 specifically includes:

[0020] S211, when the scraper of screen printing pushes the electrode paste to a distribution area of the mesh cloth, according to the constant pressure F0 of the scraper on the mesh cloth, combining the mesh distance D between the mesh cloth and the battery piece, the length L of the mesh cloth and the distance e of the scraper moving along the x-axis forward direction, the left and right sides of the middle part of the distribution area are analyzed, and the following expressions (1) and (2) are obtained respectively:

[0021] α=arctan(e / D) (1),

[0022] (1) In the formula, α is the downward force F0 and the left-side tension F L The angle between them;

[0023] β=arctan((Le) / D) (2),

[0024] (2) In the formula, β is the downward force F0 and the right-side tension F R The angle between them;

[0025] S212. According to the trigonometric function sine theorem, in any triangle, we obtain the following equation (3):

[0026] a / SinA=b / SinB=c / SinC (3),

[0027] (3) In the formula, a, b, and c are the three sides of the triangle, and A, B, and C are the opposite angles of the three sides of the triangle.

[0028] S213. Based on the downward pressure F0 of the mesh and equations (1) to (3), the force relationship (4) in the middle of the distribution area is obtained: F0 / Sin(180°-α-β)=F L / Sinβ=F R / Sinα (4).

[0029] Preferably, in step S3, the stress components σ corresponding to the stress F in the x, y, and z directions are obtained respectively. x σ y σ z It includes the following steps:

[0030] S31. In a three-dimensional rectangular coordinate system, the projected components F of stress F in the x, y, and z directions are obtained by the second projection method. x F y F z ;

[0031] S32. The stress F in different distribution areas of the mesh is analyzed in three-dimensional space. When the stress equilibrium is reached, the following partial differential equation (6) is obtained:

[0032]

[0033]

[0034]

[0035] (6) In the formula, F x F y Fz Let σ be the projected components of stress F in the x, y, and z directions after applying the second projection method; x Let τ be the normal stress component of stress F along the x-axis. xy τ xz Let F be the shear stress components along the y-axis and z-axis, respectively; σ y Let τ be the normal stress component of stress F along the y-axis. yx τ yz Let F be the shear stress components along the x-axis and z-axis, respectively; σ z Let τ be the normal stress component of stress F along the z-axis. zx τ zy Let F be the shear stress components of stress F in the x-axis and y-axis directions, respectively;

[0036] Based on the partial differential equation (6), and combined with the projected component force F x F y F z Obtain the normal stress components σ of stress F in x, y, and z. x σ y σ z .

[0037] More preferably, in step S3, in the three-dimensional rectangular coordinate system, the stress F is decomposed into projected component forces F in the x, y, and z directions by the second projection method. x F y F z The expression (5) is as follows:

[0038]

[0039] (5) In the formula, F is the stress on different distribution areas of the mesh, F xy Let F be the projected component of stress F in the Oxy plane, and λ be the angle between the line of action of stress F and the coordinate axis z. z Let F be the projected component of stress F on the z-axis. x For F xy The projected component of the force on the x-axis, F y For F xy The projected component of the force on the y-axis; θ is the angle between the line of action of stress F and the coordinate axis z; λ, stress F and the z-axis, these three factors determine the angle between the plane and the coordinate axis x.

[0040] More preferably, step S4 specifically includes:

[0041] Step S41: For the mesh fabric, only the x and y directions are considered, while the z direction is ignored. Combined with the following equations (7) and (8), the shear strain γ corresponding to the stress F is obtained.xy Expression (10):

[0042]

[0043] where, when the force is balanced, according to partial differential equation (6), the following partial differential equation (7) is obtained:

[0044]

[0045]

[0046]

[0047]

[0048] In equation (7), ε is the strain corresponding to stress F, where ε x is the strain corresponding to normal stress component σ x is the strain corresponding to normal stress component σ y is the strain corresponding to normal stress component σ y is the strain corresponding to normal stress component σ z is the strain corresponding to normal stress component σ z ; the strain components of strain ε corresponding to stress F in x, y, z directions correspond to u, v, w; γ is the shear strain corresponding to shear stress, where γ xy is the shear strain corresponding to shear stress component τ xy is the shear strain corresponding to shear stress component τ xz is the shear strain corresponding to shear stress component τ xz is the shear strain corresponding to shear stress component τ yz is the shear strain corresponding to shear stress component τ yz ;

[0049] According to strain = stress / elastic modulus, and equations (6) to (7), the following constitutive equation (8) is obtained:

[0050]

[0051]

[0052]

[0053]

[0054] In equation (8), E is the tensile and compressive elastic modulus, G is the shear elastic modulus, and μ is the Poisson's ratio;

[0055] S42, the shear strain γ xy of the reference area m of the mesh cloth is obtained again; xywherein the shear stress component of the reference region m is denoted as shear stress τ m and the shear stress component of the rest of the distribution regions n of the screen cloth is denoted as shear stress τ n .

[0056] More preferably, the step S42 is specifically:

[0057] According to the constitutive equations (8) and (10) and in combination with the following relationship (9) of tensile elastic modulus E, shear elastic modulus G and Poisson's ratio μ, the shear stress component τ xy of the reference region m of the screen cloth is obtained;

[0058] G = E / 2(1 + μ) (9).

[0059] More preferably, the step S5 specifically includes:

[0060] S51, after calculating the shear stress τ m numerical value of the reference region m, in order to keep the shear stress τ n of the rest of the distribution regions consistent with the shear stress τ m of the reference region, τ n must be equal to the numerical value τ m , and in combination with the constitutive equations (8), (9) and (10), the following equation (11) is obtained:

[0061]

[0062] In equation (11), γ n is the shear strain of the rest of the distribution regions n; μ is the strain component of the strain ε corresponding to the stress F in the x-axis direction; σ xn is the normal stress component of the stress F in the x-axis direction when screen printing to the rest of the distribution regions n; σ yn is the normal stress component of the stress F in the y-axis direction when screen printing to the rest of the distribution regions n; E Cn is the tensile elastic modulus of the mixed screen line of tungsten steel longitudinal wires and stainless steel longitudinal wires of the rest of the distribution regions n; γ m is the shear strain of the reference region m; σ xm is the normal stress component of the stress F in the x-axis direction when screen printing to the reference region m; σ ym is the normal stress component of the stress F in the y-axis direction when screen printing to the reference region m; E2 is the tensile elastic modulus of the stainless steel screen line of the reference region m; wherein all the longitudinal wires of the reference region m are stainless steel screen lines;

[0063] S52, according to the shear stress τ mThe numerical value, the tensile and compressive elastic modulus E2 of the stainless steel screen line, in combination with the constitutive equations (8) and (9), calculates the tensile and compressive elastic modulus E of the mixed screen line corresponding to each of the remaining distribution areas n Cn ;

[0064] S53, according to the tensile and compressive elastic modulus E of the mixed screen line corresponding to each of the remaining distribution areas Cn , the tensile and compressive elastic modulus E1 of the tungsten steel screen line, the tensile and compressive elastic modulus E2 of the stainless steel screen line, and in combination with the following relationship (12), the tungsten steel longitudinal wire content c in each of the remaining distribution areas n is calculated:

[0065]

[0066] Preferably, in step S1, the number of distribution areas divided along the x-axis direction is 9, and the distribution area 5 is the reference area.

[0067] The present application also discloses a silk screen printing screen plate for solar cells, which is prepared by the improved method of the silk screen printing screen plate for solar cells.

[0068] Compared with the prior art, the present application has at least the following beneficial effects:

[0069] (1) The improved method of the present application replaces the stainless steel longitudinal wires in the remaining distribution areas with corresponding number of tungsten steel longitudinal wires without changing the number of longitudinal wires in each distribution area, so as to increase the tungsten steel longitudinal wire content in the replaced distribution areas, balance the shear stress corresponding to each of the remaining distribution areas, and make the stress in each distribution area of the screen cloth consistent. The silk screen printing screen plate prepared by the improved method of the present application can effectively avoid the defects of different stress in different distribution areas caused by the different stress in different distribution areas, which leads to different line width of the metal grid lines printed in different distribution areas, even to the broken grid, so that the line width of the metal grid lines printed by the improved silk screen printing screen plate is more uniform, the production defect is reduced, the actual silk screen printed metal electrode pattern is the same as the improved screen cloth pattern, the defect of poor metal electrode convergence caused by the existing silk screen printing is improved, and the battery efficiency is improved.

[0070] (2) Moreover, the silk screen printing screen plate prepared by the improved method of the present application is still an open printing method, so compared with the semi-closed printing method of double-layer rolling rod, it is more convenient to replace the electrode paste, can effectively avoid the defects of artificial waste and low yield, can increase the contact between the battery piece (or silicon piece) and the printing device during silk screen printing, reduce the force on the unit area of the battery piece surface, and effectively reduce the broken piece rate of the battery piece.

[0071] (3) The improved method of the present application is an improvement made specifically for the screen cloth of the screen printing screen plate, and does not require additional changes to the battery production equipment, so the improved method of the present application will be more convenient to promote in mass production. BRIEF DESCRIPTION OF DRAWINGS

[0072] Figure 1 It is a schematic diagram of the screen cloth structure of the existing screen printing screen plate.

[0073] Figure 2 It is a screen printing process diagram for preparing a metal electrode using the existing screen printing screen plate.

[0074] Figure 3 It is a schematic diagram of the expansion and deformation of the metal electrode pattern actually printed using the existing screen printing screen plate.

[0075] Figure 4 It is a schematic diagram of the existing double-layer roller screen printing of a metal electrode; wherein, Figure 4 a is a schematic diagram of the upper and lower layer rollers rotating to drive the battery piece to move; Figure 4 b is a schematic diagram of the structure of the screen printing roller.

[0076] Figure 5 It is a schematic diagram of the screen cloth in Example 1 being divided into 9 distribution areas along the x-axis direction in sequence and at equal intervals; Figure 5 Among them, the numbers 1, 2, 3, 4, 5, 6, 7, 8, and 9 respectively represent distribution area 1, distribution area 2, distribution area 3, distribution area 4, distribution area 5, distribution area 6, distribution area 7, distribution area 8, and distribution area 9.

[0077] Figure 6 It is a schematic diagram of the force analysis of the screen cloth under the pressing force F0 of the squeegee on the screen cloth in Example 1.

[0078] Figure 7 It is a schematic diagram of the secondary projection of the stress F in the three-dimensional rectangular coordinate system in Example 1.

[0079] Figure 8 It is a schematic diagram of the force analysis of the three-dimensional space object in Example 1.

[0080] Figure 9 It is a comparison data diagram of the width of the metal grid line obtained by screen printing the 520-mesh screen printing screen plate obtained by the improved method of Example 1 and the 520-mesh screen printing screen plate obtained by the existing standard process, respectively.

[0081] BRIEF DESCRIPTION OF DRAWINGS: screen frame 10; screen cloth 20; screen line 21; polyimide 22; opening 23; squeegee 30; electrode paste 40; metal electrode 41; battery piece 50; roller 60. DETAILED DESCRIPTION

[0082] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0083] Embodiment 1

[0084] The improved method of the screen printing screen plate of a solar cell in this embodiment, as shown in Figures 5-8 , includes the following improvement steps:

[0085] Step S1, the screen cloth 20 of the screen printing screen plate is sequentially divided into a plurality of distribution areas along the x-axis direction, and the number of the distribution areas is a base number greater than or equal to 3; the distribution area in the middle of the x-axis of the screen cloth 20 is taken as the reference area m, and the remaining distribution areas in the x-axis direction of the screen cloth 20 are recorded as the distribution area n.

[0086] Among them, as shown in Figures 5-6 , the screen printing screen plate includes a screen frame 10 and a screen cloth 20 formed by a plurality of screen lines 21; as shown in Figure 5 , and its screen cloth 20 includes a plurality of horizontal wires and a plurality of vertical wires, the horizontal wire is the screen line 21 in the screen cloth 20 along the x-axis direction, and the vertical wire is the screen line 21 in the screen cloth 20 along the y-axis direction.

[0087] In an example of this embodiment, as shown in Figure 5 , the screen cloth 20 is sequentially and equally spaced divided into 9 distribution areas along the x-axis direction, and the 9 distribution areas are recorded as distribution area 1, distribution area 2, distribution area 3, distribution area 4, distribution area 5, distribution area 6, distribution area 7, distribution area 8 and distribution area 9 respectively; moreover, the distribution area 1 and the distribution area 9 are symmetrically distributed, the distribution area 2 and the distribution area 8 are symmetrically distributed, the distribution area 3 and the distribution area 7 are symmetrically distributed, and the distribution area 4 and the distribution area 6 are symmetrically distributed; and the distribution area 5 is the distribution area in the middle of the x-axis of the screen cloth 20, that is, the distribution area 5 is the reference area.

[0088] S2, when the squeegee of the screen printing pushes the electrode paste to advance to different distribution areas of the screen cloth 20, the left and right sides of different distribution areas of the screen cloth 20 are analyzed according to the constant pressing force F0 of the squeegee on the screen cloth 20, the screen distance D between the screen cloth 20 and the cell piece 50, the screen cloth length L and the distance e of the squeegee moving along the x-axis advancing direction, and the stress F of different distribution areas of the screen cloth 20 is obtained.

[0089] In practice, the line width and pattern of the metal grid in the metal electrode for collecting the photo-generated carriers (such as photo-generated current) generated by the solar cell are determined by parameters such as mesh number and opening width of the screen printing screen plate when the metal electrode is prepared by using a screen printing process. The mesh number of the screen printing screen plate refers to the number of screen lines 21 contained on the screen cloth 20 per 1 square inch.

[0090] When the squeegee of the screen printing pushes the electrode paste to different distribution areas of the screen cloth 20, the pressing force of the squeegee on the screen cloth 20 is denoted as F0 (F0 is a constant value), at this time, the stress generated by the pressing force F0 on the screen cloth 20 in different distribution areas is different. Therefore, the tension on a certain distribution area (such as distribution area 1) of the screen cloth 20 is analyzed as shown in Figure 2 Figure 6 Since the force is mutual, according to the pressing force F0, the tension on a certain distribution area (such as distribution area 1) of the screen cloth 20 is analyzed as shown in Figure 6

[0091] The thickness of the screen cloth 20 is denoted as d1; the gap between the screen cloth 20 and the cell piece 50 during screen printing is denoted as d2; the screen distance D between the screen cloth 20 and the cell piece 50 during screen printing is d1+d2; the length of the screen cloth is denoted as L; the distance (referred to as the squeegee moving distance) that the squeegee moves along the x-axis forward direction of the screen cloth 20 is denoted as e; at this time, referring to Figure 6 , the tension on the left side of the distribution area is denoted as F L , and the tension on the right side of the distribution area is denoted as F R .

[0092] Referring to Figure 6 , the following expressions (1) and (2) can be obtained at any running moment of the squeegee:

[0093] α=arctan(e / D) (1);

[0094] In formula (1), α is the included angle between the pressing force F0 and the left tension F L .

[0095] β=arctan((L-e) / D) (2);

[0096] In formula (2), β is the included angle between the pressing force F0 and the right tension F R .

[0097] According to the sine theorem of trigonometric functions, it is known that in any triangle, the following formula (3) exists:

[0098] a / SinA=b / SinB=c / SinC (3); ​​

[0099] (3) In the formula, a, b, and c are the three sides of the triangle, and A, B, and C are the opposite angles of the three sides of the triangle.

[0100] Based on the downward pressure F0 and equations (1) to (3), the following force relationship equation (4) for the distribution area is obtained:

[0101] F0 / Sin(180°-α-β)=F L / Sinβ=F R / Sinα (4).

[0102] Further, see Figures 5-6 It can be seen that, taking the middle of each distribution area as the force analysis point, when the scraper moves to the middle of the mesh 20 (such as distribution area 5 at the middle of the x-axis of the mesh 20), the left and right tensions on distribution area 5 are symmetrical, and the left tension F on the middle of distribution area 5 is... L Equal to the tension F on the right side R Therefore, in one example of this embodiment, see... Figures 5-6 ,Will Figure 5 Distribution area 5 as Figure 6 The analysis of the reference area of ​​the stress is used to balance the shear stress corresponding to the other distribution areas, and it is only necessary to analyze the left and right tensions of half of the distribution areas in the mesh 20 (such as analyzing distribution areas 1 to 4 and distribution area 5).

[0103] Therefore, in summary, step S2, obtaining the stress F in different distribution areas of the mesh 20, specifically includes the following steps:

[0104] Step S21: When the squeegee of the screen printing pushes the electrode paste forward to a certain distribution area of ​​the mesh 20, based on the mesh spacing D between the mesh 20 and the battery cell 50, the mesh length L, and the distance e that the squeegee moves along the x-axis, the following steps are taken: Figure 6 From the force analysis shown, equations (1) and (2) can be obtained; then, based on the downward force F0 and equations (1) to (3), the left-side tension F of the distribution area of ​​the mesh 20 can be obtained. L and the right-side tension F R .

[0105] Step S22, apply a pulling force F to the left side of the same distribution area. L With the right-side tension F R Compare the numerical values ​​and assign the larger value (i.e., the greater impact on the distribution area) to the left-hand tension F. L Or the right-side tension F R The stress F is the stress on the distribution area caused by the scraper.

[0106] In one example of the embodiment, a 520 mesh silk screen printing screen plate suitable for M10 solar cell is taken as an example, see Figure 5 , to illustrate the calculation process of the stress F suffered by the distribution area 1 when the squeegee runs to the middle of the distribution area 1 of the 520 mesh silk screen printing screen plate.

[0107] The parameters of the 520 mesh silk screen printing screen plate are as follows: see Figure 2 , the thickness d1 of the silk screen printing screen plate is 3.5±1.5um; the gap d2 between the screen cloth 20 and the cell 50 during silk screen printing is 1.5±0.5mm; the screen cloth length L is 182mm; the squeegee pressing force F0 during silk screen printing is 50±30N. The mesh number K of the silk screen printing screen plate is 520 meshes; that is, in the silk screen printing screen plate, the number of x-axis direction horizontal wires per 1 inch of the screen cloth 20 is 520, and the number of y-axis direction vertical wires is also 520. When the squeegee runs to the middle of the distribution area 1, according to the screen cloth length L=182mm and the mesh number K=520 meshes of the silk screen printing screen plate, the moving distance e1 of the squeegee can be measured as 10.11mm; when the squeegee runs to the middle of the distribution area 5, according to the screen cloth length L=182mm and the mesh number K=520 meshes of the silk screen printing screen plate, the moving distance e5 of the squeegee can be measured as 91mm. Therefore, when the squeegee pressing force F0 is a known constant, according to the above parameters and equations (1) to (4), the left side force F L1 and the right side force F R1 of the middle of the distribution area 1 are calculated.

[0108] The sizes of the left side force F L1 and the right side force F R1 of the middle of the distribution area 1 are compared; when the left side force F L1 is greater than the right side force F R1 , the left side force F L1 is taken as the stress F of the distribution area 1 (or, when the right side force F R1 is greater than the left side force F L1 , the side force F R1 is taken as the stress F of the distribution area 1).

[0109] S3, the stress F suffered by different distribution areas of the plane screen cloth 20 is analyzed in three-dimensional space, according to the force balance, and combined with the secondary projection method of the stress F, the corresponding normal stress components σ x , σ y , σ z in x, y, z directions are obtained.

[0110] The secondary projection method of the stress F suffered by different distribution areas of the plane screen cloth 20 is as follows:

[0111] like Figure 7 As shown, in a three-dimensional Cartesian coordinate system, the stress F can be decomposed into Fx, Fy, Fz in the x, y, and z directions respectively. x F y F z These are the three component forces. The magnitudes of these three component forces can be calculated using the method of second projection.

[0112] From trigonometric relationships, we know that if the magnitude of stress F is known, the angle λ between the line of action of F and the coordinate axis z, and the plane determined by stress F and the z-axis (i.e., ...) Figure 7 If the angle between the shaded area (shown) and the coordinate axis x is θ, then the stress F can be projected onto the z-axis and the coordinate plane Oxy, respectively, thus obtaining the projected component F on the z-axis. z and the projected component F on the Oxy plane xy Then, F xy Projected onto the x-axis and y-axis respectively, the projected force F on these two coordinate axes is obtained. x and F y This method requires the stress F to be projected twice to obtain F. z F x and F y Therefore, it is called the double projection method. The stress F is obtained by the double projection method. z F x and F y The expression (5) is as follows:

[0113]

[0114] (5) In the formula, F is the stress on different distribution areas of the mesh fabric 20; F xy Let F be the projected component of stress F in the Oxy plane; λ be the angle between the line of action of stress F and the coordinate axis z; F z Let F be the projected component of stress F on the z-axis; x For F xy Projected component of force on the x-axis; F y For F xy The projected component of the force on the y-axis; θ is the angle λ between the line of action of F and the coordinate axis z; the plane determined by the stress F and the z-axis (i.e., Figure 7 The angle between the shaded area shown and the x-axis.

[0115] Furthermore, in practice, the mesh fabric 20 is not subjected to a single force. The mesh fabric 20 is woven from intersecting horizontal and vertical fibers; therefore, the stress on the mesh fabric 20 must also consider shear stress in other directions. The calculation principle for the stress and strain of a three-dimensional object is as follows: Figure 8 As shown, in three-dimensional space (such as...) Figure 8When a point in a cube of a three-dimensional rectangular coordinate system is subjected to a stress in one coordinate axis direction (e.g. z-axis direction), shear stresses in the other two coordinate axis directions (e.g. x-axis and y-axis directions) are generated. Figure 8 In the above equation, x, y, z represent the coordinate axis directions; σ represents the normal stress component of the stress F in one coordinate axis direction (e.g. the normal stress component of the stress F in its z-axis direction is σ z ); τ represents the shear stress; the shear stress τ is decomposed into two shear stress components parallel to the other two coordinate axes, as shown in the partial differential equation (6) below, in which the two subscript letters of the shear stress component represent the coordinate axis of the normal line direction of the plane under consideration and the coordinate axis of the decomposition direction of the shear stress component (e.g. when the edge perpendicular to the y-axis is studied, the normal stress component of the stress F in the y-axis direction is σ y , the shear stress component of the stress F in the x-axis direction is represented by τ yx , and the shear stress component of the stress F in the z-axis direction is represented by τ yz ).

[0116] According to Figure 8 , when the object reaches force balance, the following partial differential equation (6) is obtained:

[0117]

[0118]

[0119]

[0120] In equation (6), F x , F y , and F z represent the projection components of the stress F in the x, y, and z directions, respectively, after the stress F in different distribution regions is projected twice according to the above equation (5); σ x is the normal stress component of the stress F in the x-axis direction, τ xy and τ xz are the shear stress components of the stress F in the y-axis and z-axis directions, respectively; σ y is the normal stress component of the stress F in the y-axis direction, τ yx and τ yz are the shear stress components of the stress F in the x-axis and z-axis directions, respectively; σ z is the normal stress component of the stress F in the z-axis direction, τ zx and τ zy are the shear stress components of the stress F in the x-axis and y-axis directions, respectively.

[0121] Therefore, as can be seen from the above, in step S3, the stress F is decomposed into stress components σ x , σ y , and σ z in the x, y, and z directions respectively, which specifically includes the following steps:

[0122] Step S31, in a three-dimensional rectangular coordinate system, the stress F is decomposed into projection components F x , F y , and F z in the x, y, and z directions respectively by using the quadratic projection method of formula (5).

[0123] Step S32, according to the partial differential equation (6) and in combination with the projection components F x , F y , and F z , the normal stress components σ x , σ y , and σ z corresponding to the stress F in the x, y, and z directions are obtained.

[0124] S4, for the planar mesh 20, only the x and y directions are considered, and the z direction is ignored; according to the relationship between the stress components and the shear strain corresponding to the shear stress, and the relationship between the stress and the strain, the shear stress of each distribution area of the mesh 20 is obtained (such as the shear stress τ m of the reference area m). The shear stress corresponding to each distribution area n of the mesh 20 except the reference area m is denoted as τ n .

[0125] In practice, after being subjected to stress, the object will generate corresponding strain. ε represents the strain corresponding to the stress F (wherein ε x is the strain corresponding to the normal stress component σ x , ε y is the strain corresponding to the normal stress component σ y , and ε z is the strain corresponding to the normal stress component σ z ). The strain components u, v, and w of the strain ε corresponding to the stress F in the x, y, and z coordinate directions correspond to the shear strain γ (specifically, γ xy is the shear strain corresponding to the shear stress component τ xy , γ xz is the shear strain corresponding to the shear stress component τ xz , and γ yz is the shear strain corresponding to the shear stress component τ yz ). When the force is balanced, according to the partial differential equation (6), the following partial differential equation (7) is obtained:

[0126]

[0127]

[0128]

[0129]

[0130] According to Hooke's law (strain = stress / elastic modulus) and the above (6) to (7) formula, the following constitutive equation (8) can be obtained:

[0131]

[0132]

[0133]

[0134]

[0135] Wherein, the following relationship (9) is known:

[0136] G = E / 2 (1 + μ) (9) ;

[0137] In the formula (8) and (9), E is the tensile elastic modulus, G is the shear elastic modulus, and μ is the Poisson's ratio (Poisson's ratio refers to the ratio of transverse normal strain to axial normal strain when the material is subjected to uniaxial tension or compression, also known as transverse deformation coefficient, which is an elastic constant reflecting the transverse deformation of the material).

[0138] In an example of the embodiment, in the screen cloth 20 of the screen printing screen plate of the purpose 520, the material of the screen wire 21 is stainless steel or tungsten steel with higher strength, and the stainless steel screen wire is usually used; the tensile elastic modulus E2 of the stainless steel screen wire is 200 Gpa, and the Poisson's ratio μ is 0.3; the tensile elastic modulus E1 of the tungsten steel screen wire is 510 Gpa, and the Poisson's ratio μ is 0.28-0.311. As shown in the formula (8), the material of the rest of the screen cloth 20 except the screen wire 21 is usually polyimide 22, and the elastic modulus of the polyimide 22 is 3-4 Gpa (such as 3 Gpa), which is only 1.5% of the tensile elastic modulus E2 of the stainless steel screen wire and 0.6% of the tensile elastic modulus E1 of the tungsten steel screen wire; therefore, in the screen cloth 20 of the screen printing screen plate, the main body of the elastic modulus is provided by the stainless steel screen wire and the tungsten steel screen wire. Therefore, for the convenience of calculation, the elastic modulus contributed by PI is ignored. Figure 1-2

[0139] In summary, step S4 specifically includes:

[0140] ​Step S41, for the planar mesh cloth 20, only the x and y directions are considered, and the z direction is ignored, and the shear strain γ corresponding to the stress F can be obtained by combining (7) and (8) xy :

[0141]

[0142] Step S42, the shear stress component τ of the reference area m of the mesh cloth 20 can be obtained by combining the constitutive equations (8), (9) and (10) xy . Wherein, the shear stress component τ of the reference area m of the mesh cloth 20 xy is called the shear stress τ of the reference area m m , and the shear stress component τ of the remaining distribution areas n of the mesh cloth 20 xy is called the shear stress τ of the remaining distribution areas n n .

[0143] S5, according to the influence relationship of the mesh wire material of the mesh cloth 20 on the stress, and the mutual influence of the transverse stress and the shear stress, in order to keep the shear stress of the remaining distribution areas of the mesh cloth 20 consistent with the shear stress of the reference area, without changing the number of longitudinal wires of each distribution area of the mesh cloth 20, the remaining stainless steel longitudinal wires of each distribution area of the mesh cloth 20 are replaced by corresponding number of tungsten steel longitudinal wires, and the content of the replaced tungsten steel longitudinal wires in the remaining distribution areas is correspondingly increased, so as to balance the different shear stresses of the remaining distribution areas, and correspondingly offset the stress of the different distribution areas of the mesh cloth 20 along the x-axis, so as to keep the stress of each distribution area of the mesh cloth 20 consistent.

[0144] It should be noted that since the force is mutual (such as the transverse stress and the shear stress are mutually influenced), only the stress position needs to be increased in the longitudinal direction (i.e. Figure 5 the y-axis direction) of each distribution area of the mesh cloth 20, such as keeping the number of longitudinal wires of each distribution area of the mesh cloth 20 unchanged, replacing the remaining stainless steel longitudinal wires of each distribution area of the mesh cloth 20 with corresponding number of tungsten steel longitudinal wires, so as to change the proportion of the number of tungsten steel longitudinal wires in the remaining distribution areas and the number of longitudinal wires in the distribution area. Because the strength of the tungsten steel material of the mesh wire 21 is higher than that of the stainless steel material of the original mesh wire 21 of the mesh cloth 20, the tungsten steel longitudinal wire can balance a certain shear stress, so as to correspondingly offset the stress (i.e. the transverse stress) of the different distribution areas of the mesh cloth 20 caused by the downward pressure F0 of the scraper on the mesh cloth 20.

[0145] Since changing the number of both horizontal and vertical wires in the mesh 20 simultaneously alters the mesh count of the screen printing stencil, significantly changing its parameters, this embodiment can, based on shear stress, replace a portion of the stainless steel vertical wires in each distribution area with tungsten carbide vertical wires, without changing the total number of horizontal wires in the mesh 20 or the number of vertical wires in each distribution area (where the total number of vertical wires in the mesh 20 remains constant). This increases the ratio of the number of tungsten carbide vertical wires to the total number of vertical wires in different distribution areas of the mesh 20 (using...). Figure 5 Taking distribution area 1 as an example, in order to make the shear stress τ1 of distribution area 1 consistent with the shear stress τ5 of reference area 5, the ratio of the number of tungsten steel longitudinal wires in distribution area 1 to the number of longitudinal wires in distribution area 1 is increased. Thus, under the constant pressure F0 of the squeegee on the mesh 20, the stress of each distribution area is consistent, and finally the line width difference of the metal grid lines printed by the screen printing stencil obtained by the improved method of this embodiment is reduced, production defects are reduced, and the actual screen-printed metal electrode pattern is the same as the improved mesh pattern. This improves the defect of poor metal electrode current convergence caused by the existing screen printing, thereby improving battery efficiency.

[0146] Ignoring edge effects, if the stress is evenly distributed among each wire 21, then the strain will also be distributed among each wire 21.

[0147] Based on this, step S5 specifically includes:

[0148] Step S51: Calculate the shear stress τ in the reference region m. m After numerical calculation, in order to ensure that the shear stress τ corresponding to the remaining distribution areas of the mesh 20 is... n Shear stress τ in the reference region m To maintain consistency, τ needs to be... n Equal to the value τ m Combining the constitutive equations (8), (9) and (10), we obtain the shear strain formula in equation (11) as follows:

[0149]

[0150] (11) In the formula, γ n σ represents the shear strain corresponding to each of the remaining distribution regions n; μ represents the strain component of the strain ε corresponding to stress F along the x-axis; σ xn Let σ be the normal stress component of stress F in the x-axis direction when the screen printing extends to the remaining distribution area n; yn Let E be the normal stress component of stress F in the y-axis direction when the screen printing extends to the remaining distribution area n; Cn γ represents the tensile and compressive modulus of elasticity of the mixed mesh containing both tungsten steel and stainless steel longitudinal wires in each of the remaining distribution areas n; mis the shear stress of the reference region m; σ xm is the normal stress component of the stress F in the x-axis direction when screen printing to the reference region m; σ ym is the normal stress component of the stress F in the y-axis direction when screen printing to the reference region m; E2 is the tensile and compressive elastic modulus of the stainless steel screen line of the reference region m. It should be noted that all the longitudinal wires of the reference region m are stainless steel screen lines.

[0151] Step S52, according to the shear stress τ m of the reference region m, the numerical value, the tensile and compressive elastic modulus E2 of the stainless steel screen line, combined with the constitutive equations (8) and (9), the tensile and compressive elastic modulus E Cn of the mixed screen line corresponding to each of the remaining distribution regions is calculated.

[0152] Step S53, according to the tensile and compressive elastic modulus E Cn of the mixed screen line corresponding to each of the remaining distribution regions, the tensile and compressive elastic modulus E1 of the tungsten steel screen line, and the tensile and compressive elastic modulus E2 of the stainless steel screen line, combined with the following relationship (12) of the mixed screen line and the tungsten steel screen line and the stainless steel screen line, the tungsten steel longitudinal wire content c corresponding to the replacement in each of the remaining distribution regions n is calculated (the tungsten steel longitudinal wire content c corresponding to each of the remaining distribution regions n refers to the ratio of the number of replaced tungsten steel longitudinal wires in each of the remaining distribution regions n to the number of longitudinal wires in the distribution region) :

[0153]

[0154] In an example of the present embodiment, a 520-mesh screen printing screen plate suitable for M10 solar cells is taken as an example, and as Figure 5As shown, the screen cloth 20 is sequentially and equally spacedly divided into 9 distribution areas along the x-axis direction; after calculation, the number of screen lines of the screen cloth 20 remains unchanged, and the original stainless steel longitudinal wires in each remaining distribution area are replaced by a corresponding number of tungsten steel longitudinal wires to increase the proportion of the number of tungsten steel longitudinal wires in each remaining distribution area to the number of longitudinal wires in the distribution area, specifically as follows: the proportion of the number of tungsten steel longitudinal wires in the distribution area 5 is 0; the proportion of the number of tungsten steel longitudinal wires in the distribution areas 1 and 9 is increased to 7.6%; the proportion of the number of tungsten steel longitudinal wires in the distribution areas 2 and 8 is increased to 5%; the proportion of the number of tungsten steel longitudinal wires in the distribution areas 3 and 7 is increased to 2.9%; and the proportion of the number of tungsten steel longitudinal wires in the distribution areas 4 and 6 is increased to 1.3%. In this way, when the screen printing screen plate is subjected to the downward pressure F0 of the squeegee on the screen cloth 20, the increase in the content c of tungsten steel longitudinal wires in the y direction of each distribution area of the screen cloth 20 causes the x direction transverse strain corresponding to the transverse stress of the x direction transverse wires to be shared; and in the x direction of the screen cloth 20, the content c of tungsten steel longitudinal wires increases in a stepped manner from the distribution area in the middle of the screen cloth 20 to the distribution areas on both sides of the screen cloth 20, offsetting the different stresses (i.e. transverse stresses) borne by each distribution area, so that the metal grid line width printed and prepared by the screen printing screen plate obtained by using the improved method of the present embodiment tends to be uniform, and therefore the metal grid line with uniform width can improve the battery efficiency and reduce the production defects and poor convergence of the metal electrode.

[0155] The present embodiment also provides a screen printing screen plate for a solar cell, which is prepared by using the improved method of the screen printing screen plate for a solar cell described above in the present embodiment.

[0156] Referring to Figure 9 , the width of the metal grid line prepared by screen printing using the 520 mesh screen printing screen plate obtained by the existing standard process and the 520 mesh screen printing screen plate improved according to the above example of the present embodiment is counted, and the results show that the variance of the width of the metal grid line obtained by printing using the 520 mesh screen printing screen plate obtained by the existing standard process is 0.011, while the variance of the width of the metal grid line obtained by printing using the 520 mesh screen printing screen plate improved according to the above example of the present embodiment is only 0.009. Obviously, the variance of the width of the metal grid line after printing using the 520 mesh screen printing screen plate improved according to the above example of the present embodiment is more convergent, which indicates that screen printing using the screen printing screen plate obtained by using the improved method of the present embodiment can make the width of the metal grid line more uniform.

[0157] In addition, the screen printing screen plate obtained by using the improved method of the present application is still an open printing method, so it is more convenient to replace the electrode paste compared with the semi-closed printing method of the double-layer roller, which can effectively avoid the defects of artificial waste and low yield, and also can increase the contact between the battery piece 50 (or silicon wafer) and the printing device during screen printing, effectively reducing the fragment rate of the battery piece 50.

[0158] While preferred embodiments of the application have been described, those skilled in the art will appreciate that other modifications and variations to the preferred embodiments are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the preferred embodiments of the application, modifications and variations thereof can be made by those skilled in the art upon acquiring the present teachings and that such modifications and variations are to be considered as equivalent to the preferred embodiments of the application.

[0159] The above describes the technical solutions provided by the present application in detail, and the principles and implementation manners of the present application are described by applying specific examples. The above description of the embodiments is only used to help understand the method of the present application and its core idea; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges will be changed, and the above description should not be understood as a limitation on the present application.

Claims

1. An improved method for screen printing stencils in solar cells, characterized in that, The following improvement steps are included: S1. Divide the screen printing stencil into several distribution areas at equal intervals along the x-axis, with the number of distribution areas being a base number greater than or equal to 3; wherein, the screen fabric includes multiple horizontal yarns distributed along the x-axis and multiple vertical yarns distributed along the y-axis, and the distribution area in the middle of the x-axis of the screen fabric is taken as the reference area. S2. When the squeegee of the screen printing pushes the electrode paste forward to different distribution areas of the mesh, the stress analysis is performed on the left and right sides of the different distribution areas of the mesh based on the constant downward pressure of the squeegee on the mesh, the mesh distance between the mesh and the battery cell, the length of the mesh, and the distance the squeegee moves along the x-axis, so as to obtain the stress on the different distribution areas. S3. Perform stress analysis on the stress in different distribution areas in three-dimensional space. Based on the stress balance and combined with the second projection method of stress, obtain the stress components corresponding to the stress in the x, y, and z directions respectively. S4. For planar mesh, only the x and y directions are considered, while the z direction is ignored. Based on the relationship between the strain corresponding to the stress component and the shear strain corresponding to the shear stress, as well as the relationship between stress and strain, the shear stress of the reference area of ​​the mesh is obtained. S5. Based on the influence of the mesh material on stress, and considering the interaction between transverse stress and shear stress, in order to ensure that the shear stress in the remaining distribution areas of the mesh remains consistent with that in the reference area, the stainless steel longitudinal wires in the remaining distribution areas are replaced with a corresponding number of tungsten steel longitudinal wires without changing the number of longitudinal wires in each distribution area. This increases the content of tungsten steel longitudinal wires in the remaining distribution areas to balance the shear stress in the remaining distribution areas, thereby offsetting the stress on different distribution areas of the mesh along the x-axis and ensuring that the stress on each distribution area of ​​the mesh is consistent.

2. An improved method for screen printing stencils of solar cells according to claim 1, characterized in that, In step S2, obtaining the stress F experienced by different distribution areas of the mesh fabric includes the following steps: S21. Based on the constant downward pressure F0 of the scraper on the mesh, the mesh distance D between the mesh and the battery cell, the mesh length L, and the distance e that the scraper moves along the x-axis, the force analysis is performed on the left and right sides of different distribution areas of the mesh, and the middle of the distribution area is taken as the force analysis point to obtain the following force relationship (4) in the middle of different distribution areas: F0 / Sin(180°-α-β)=F L / Sinβ=F R / Sina (4), (4) In the formula, F L F is the tensile force on the left side of the distribution area. R The force on the right side of the distribution area is α, where α is the downward force F0 and the left side tension F. L The angle between them, β is the downward force F0 and the right-side tension F R The angle between them; S22, the tension F on the left side of the same distribution area L With the right-side tension F R Compare the numerical values ​​and assign the larger value to the left-hand tension F. L Or the right-side tension F R The stress F exerted by the scraper on the distribution area.

3. An improved method for screen printing stencils of solar cells according to claim 2, characterized in that, Step S21 specifically includes: S211. When the squeegee of the screen printing pushes the electrode paste forward to a distribution area of ​​the screen fabric, based on the constant downward pressure F0 of the squeegee on the screen fabric, combined with the screen distance D between the screen fabric and the battery cell, the screen fabric length L, and the distance e that the squeegee moves along the x-axis, the force analysis is performed on the left and right sides of the middle of the distribution area, and the expressions shown in (1) and (2) are obtained respectively: α=arctan(e / D) (1), (1) In the formula, α is the downward force F0 and the left-side tension F L The angle between them; β=arctan((Le) / D) (2), (2) In the formula, β is the downward force F0 and the right-side tension F R The angle between them; S212. According to the trigonometric function sine theorem, in any triangle, we obtain the following equation (3): a / SinA=b / SinB=c / SinC (3), (3) In the formula, a, b, and c are the three sides of the triangle, and A, B, and C are the opposite angles of the three sides of the triangle. S213. Based on the downward pressure F0 of the mesh and equations (1) to (3), the force relationship (4) in the middle of the distribution area is obtained: F0 / Sin(180°-α-β)=F L / Sinβ=F R / Sinα (4).

4. An improved method for screen printing stencils of solar cells according to claim 1, characterized in that, In step S3, the stress components σ corresponding to the stress F in the x, y, and z directions are obtained respectively. x σ y σ z It includes the following steps: S31. In a three-dimensional rectangular coordinate system, the projected components F of stress F in the x, y, and z directions are obtained by the second projection method. x F y F z ; S32. The stress F in different distribution areas of the mesh is analyzed in three-dimensional space. When the stress equilibrium is reached, the following partial differential equation (6) is obtained: (6) In the formula, F x F y F z Let σ be the projected components of stress F in the x, y, and z directions after applying the second projection method; x Let τ be the normal stress component of stress F along the x-axis. xy τ xz Let F be the shear stress components along the y-axis and z-axis, respectively; σ y Let τ be the normal stress component of stress F along the y-axis. yx τ yz Let F be the shear stress components along the x-axis and z-axis, respectively; σ z Let τ be the normal stress component of stress F along the z-axis. zx τ zy Let F be the shear stress components of stress F in the x-axis and y-axis directions, respectively; Based on the partial differential equation (6), and combined with the projected component force F x F y F z Obtain the normal stress components σ of stress F in x, y, and z. x σ y σ z .

5. An improved method for screen printing stencils of solar cells according to claim 4, characterized in that, In step S3, in the three-dimensional rectangular coordinate system, the stress F is decomposed into projected component forces F in the x, y, and z directions using the second projection method. x F y F z The expression (5) is as follows: (5) In the formula, F is the stress on different distribution areas of the mesh, F xy Let F be the projected component of stress F in the Oxy plane, and λ be the angle between the line of action of stress F and the coordinate axis z. z Let F be the projected component of stress F on the z-axis. x For F xy The projected component of the force on the x-axis, F y For F xy The projected component of the force on the y-axis; θ is the angle between the line of action of stress F and the coordinate axis z; λ, stress F and the z-axis, these three factors determine the angle between the plane and the coordinate axis x.

6. An improved method for screen printing stencils of solar cells according to claim 4, characterized in that, Step S4 specifically includes: Step S41: For the mesh fabric, only the x and y directions are considered, while the z direction is ignored. Combined with the following equations (7) and (8), the shear strain γ corresponding to the stress F is obtained. xy Expression (10): When the forces are in equilibrium, according to the partial differential equation (6), the following partial differential equation (7) is obtained: (7) In equation (7), ε is the strain corresponding to stress F, where ε x Normal stress component σ x The corresponding strain, ε y Normal stress component σ y The corresponding strain, ε z Normal stress component σ z The corresponding strain; the strain components ε corresponding to stress F in the x, y, and z directions are u, v, and w; γ is the shear strain corresponding to shear stress, where γ xy For the shear stress component τ xy The corresponding shear strain, γ xz For the shear stress component τ xz The corresponding shear strain, γ yz For the shear stress component τ yz The corresponding shear strain; Based on strain = stress / elastic modulus and equations (6) to (7), the constitutive equation (8) is obtained as follows: (8) In the formula, E is the tensile and compressive elastic modulus, G is the shear elastic modulus, and μ is Poisson's ratio; S42. Obtain the shear strain γ of the reference region m of the mesh. xy The corresponding shear stress component τ xy The shear stress component of the reference region m is denoted as shear stress τ. m The shear stress components corresponding to the remaining distribution areas n of the mesh are denoted as shear stress τ. n .

7. An improved method for screen printing stencils of solar cells according to claim 6, characterized in that, Step S42 is as follows: Based on constitutive equations (8) and (10), and combined with the following relationship (9) between the tensile and compressive elastic moduli E, the shear elastic moduli G, and the Poisson's ratio μ, the shear stress component τ of the reference region m of the mesh is obtained. xy ; G = E / 2(1+μ) (9).

8. An improved method for screen printing stencils of solar cells according to claim 6 or 7, characterized in that, Step S5 specifically includes: S51. Calculate the shear stress τ in step S4. m After numerical calculation, in order to ensure that the shear stress τ corresponding to the remaining distribution regions is... n Shear stress τ in the reference region m To maintain consistency, τ needs to be... n Equal to the value τ m Combining constitutive equations (8), (9), and (10), we obtain the following equation (11): (11) In the formula, γ n σ represents the shear strain corresponding to each of the remaining distribution regions n; μ represents the strain component of the strain ε corresponding to stress F along the x-axis; σ xn Let σ be the normal stress component of stress F in the x-axis direction when the screen printing extends to the remaining distribution area n; yn Let E be the normal stress component of stress F in the y-axis direction when the screen printing extends to the remaining distribution area n; Cn γ represents the tensile and compressive modulus of elasticity of the mixed mesh containing both tungsten steel and stainless steel longitudinal wires in each of the remaining distribution areas n; m σ is the shear strain in the reference region m; xm σ represents the normal stress component of stress F along the x-axis when the screen printing reaches the reference area m; ym E1 represents the normal stress component of stress F in the y-axis direction when the screen printing reaches the reference area m; E2 represents the tensile and compressive elastic modulus of the stainless steel mesh wire in the reference area m; where all longitudinal wires in the reference area m are stainless steel mesh wires. S52, based on shear stress τ m Numerical values ​​and the tensile and compressive elastic modulus E2 of the stainless steel mesh wire are used to calculate the tensile and compressive elastic modulus E of the hybrid mesh wire corresponding to each of the other distribution regions n, in conjunction with constitutive equations (8) and (9). Cn ; S53. Based on the tensile and compressive elastic modulus E of the hybrid network corresponding to the remaining distribution areas. Cn The tensile and compressive elastic modulus E1 of tungsten steel wire mesh and E2 of stainless steel wire mesh are used to calculate the content c of the tungsten steel longitudinal wires that are replaced in each of the other distribution areas n, in conjunction with the following relationship (12):

9. An improved method for screen printing stencils of solar cells according to claim 1, characterized in that, In step S1, the mesh fabric is divided into 9 distribution areas at equal intervals along the x-axis direction, of which distribution area 5 is the reference area.

10. A screen printing stencil for a solar cell, characterized in that, It is prepared by an improved method for screen printing stencils of a solar cell according to any one of claims 1-9.

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