Method for improving doping concentration of Topcon battery emitter metal contact region

Abstract

The invention provides a method for improving the doping concentration of a Topcon battery emitter metal contact area, which comprises the following steps of: cleaning and texturing a silicon wafer, performing diffusion reaction at high temperature and low pressure, and forming a first-stage silicon wafer with a three-layer structure based on a silicon substrate on the surface of the silicon wafer; performing deeper secondary high-temperature melting type doping reaction on the local area of the silicon wafer at normal temperature and normal pressure by using a laser beam emitted by a continuous laser which is started at high frequency to form a secondary silicon wafer which takes a silicon substrate as a basic part and is of a two-layer structure, most of which is of a three-layer structure; removing B2O3 on the surface layer after weak acid or weak base cleaning to form a third-stage silicon wafer, and oxidizing the third-stage silicon wafer to obtain a fourth-stage silicon wafer with an antireflection layer; and then silk-screen printing metal electrodes on the first surface and the second surface of the fourth-stage silicon wafer to form the Topcon battery with high photoelectric conversion efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic solar cell manufacturing, and in particular to a method for increasing the doping concentration of a metal contact region of an emitter of a Topcon cell. Background Art

[0002] Photovoltaic solar silicon cells can currently be divided into P-type PERC cells, N-type Topcon cells, heterojunction HJT cells, and XBC cells based on the above cells. P-type PERC cells are phosphorus-doped on P-type silicon wafers to form emitter metallization, while N-type Topcon cells are boron-doped on N-type silicon wafers to form emitter metallization.

[0003] During the boron diffusion doping process of N-type Topcon cells, due to the physical and chemical properties of boron and the physical and chemical properties of compounds containing boron, N-type silicon wafers and compounds containing boron undergo a replacement reaction under high temperature and low pressure conditions in order to perform doping to a certain depth and concentration. However, before the N-type silicon-based surface undergoes a replacement reaction with the boron compound, a bonding layer of the boron compound and silicon dioxide will quickly form on the silicon surface. This bonding layer prevents the boron compound from contacting the silicon atoms for a replacement reaction, resulting in the inability of boron doping to reach the desired concentration and depth. The concentration and depth of boron doping seriously affect the contact resistance of the cell. The greater the contact resistance, the lower the photoelectric conversion efficiency of the final Topcon cell.

[0004] Therefore, the present invention proposes a method for increasing the doping concentration of the emitter metal contact region of a Topcon cell to improve the photoelectric conversion efficiency of the cell. Summary of the invention

[0005] The present invention proposes a method for increasing the doping concentration of the emitter metal contact region of a Topcon cell, thereby reducing the contact resistance on the cell surface, thereby improving the photoelectric conversion efficiency of the cell and solving the aforementioned technical problems.

[0006] Description of terms in the present invention:

[0007] Topcon stands for Tunnel Oxide Passivating Contacts, which means tunnel oxide passivation contact cells. It is a cell made on the basis of N-shaped silicon wafers by heavily doping the electrode area with boron.

[0008] BSG is borosilicate glass that is doped with boron and diffused at the edge of the silicon wafer or climbs onto the surface of the edge of the silicon wafer.

[0009] B ++ Indicates that the concentration of boron doping is high, B +It means that the concentration of boron doped is low concentration. Low concentration is the concentration of boron doped into silicon after diffusion, and high concentration is the concentration of boron in silicon after laser doping based on diffusion.

[0010] The present invention provides a method for increasing the doping concentration of the emitter metal contact region of a Topcon battery, the method comprising the following steps:

[0011] S1, cleaning the silicon wafer and performing surface texturing treatment;

[0012] S2, subjecting the first surface of the silicon wafer after texturing to a boron source diffusion reaction at high temperature and low pressure to form a primary silicon wafer with a three-layer structure on the first surface;

[0013] S3, using a laser beam whose cross-sectional width is greater than a preset multiple of the metal electrode width to perform a secondary high-temperature melting diffusion reaction on a plurality of preset first areas of the first surface of the first-level silicon wafer at room temperature and pressure to form a secondary silicon wafer with a partially two-layer structure and a mostly three-layer structure;

[0014] S4, cleaning the secondary silicon wafer with a weak acid or a weak base to remove the B on the outermost layer of the secondary silicon wafer 2 O 3 After forming the BSG on the side of the secondary silicon wafer, a tertiary silicon wafer with a two-layer structure on the first side is formed;

[0015] S5, placing the three-level silicon wafer into an oxidation furnace for oxidation, forming a passivation layer or an anti-reflection layer on the outer surfaces of the first surface and the second surface, and the first area included in the first surface is a four-level silicon wafer with a three-layer structure;

[0016] S6. Screen-print a first metal electrode in the first sub-region in the middle of the first region of the four-level silicon wafer, and screen-print a second metal electrode in the second region symmetrical to the first sub-region on the second surface to obtain a battery cell, wherein the first surface of the battery cell including the first region has a three-layer structure.

[0017] Optionally, in S2, the first surface of the primary silicon wafer includes: B located on the surface layer 2 O 3 , located in the subsurface B + +SiO 2 , a Si base layer located below the secondary surface layer; in S3, the layer structure within the first surface of the secondary silicon wafer is located in the first region, including: a B layer located on the surface layer ++ +SiO 2 , a Si-based layer located below the surface layer; a three-layer structure within the first surface is located outside the first region, including: a B-based layer located on the surface layer 2 O 3 , located in the subsurface B + +SiO2 , the Si-based layer located below the subsurface layer.

[0018] Optionally, in S4, the first two-layer structure of the first surface of the three-level silicon wafer is located in the first region, including: B located on the surface layer ++ +SiO 2 , Si located in the subsurface; the second two-layer structure is located outside the first region, including: B located in the surface + +SiO 2 , Si in the subsurface; B 2 O 3 Removed by weak acids or bases.

[0019] Optionally, in S3, the laser beam is generated by a high-frequency started continuous laser with a laser wavelength of 1064nm-1090nm.

[0020] Optionally, the temperature range of the laser heating the first region is 1400°C-1800°C.

[0021] Optionally, when the temperature in the first region is greater than 1400° C., the B 2 O 3 、SiO 2 and Si is in a molten state, so that B of the first surface of the primary silicon wafer 2 O 3 Through B and SiO 2 The layer reacts with the Si below the subsurface layer to form B in the first region. ++ +SiO 2 .

[0022] Optionally, the first regions are distributed in a staggered array within the first plane, and the boron content of regions outside the first regions is lower than the boron content of the first regions.

[0023] Optionally, in S6, two sides of the first metal electrode in the first sub-region are 10 μm-20 μm away from a boundary line of the first region.

[0024] Optionally, the first regions are distributed discontinuously on the first surface.

[0025] The beneficial effects of the present invention are:

[0026] In the present invention, after cleaning and texturing the silicon wafer, a diffusion reaction is carried out at high temperature and low pressure to form a primary silicon wafer with a three-layer structure based on a silicon base on the surface of the silicon wafer; a laser beam emitted by a high-frequency continuous laser is then used to carry out a deeper secondary high-temperature melting type doping reaction on a local area of ​​the silicon wafer at normal temperature and pressure to form a secondary silicon wafer with a silicon base as the base and a two-layer structure in part and a three-layer structure in the majority; and a weak acid or weak alkali is further used to clean the surface B 2 O 3 The tertiary silicon wafer is cleared to form a tertiary silicon wafer, which is then oxidized to obtain a quaternary silicon wafer with an anti-reflection layer; and then the first and second surfaces of the quaternary silicon wafer are screen-printed with metal electrodes to form a Topcon cell with high photoelectric conversion efficiency.

[0027] The present invention uses the boron oxide on the outermost layer of the silicon wafer after boron diffusion as the boron source for laser doping, which not only increases the concentration of boron doping on the silicon wafer, but also reduces the contact resistance on the surface of the battery cell without adding additional process means, thereby improving the photoelectric conversion efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Steps S1 to S3 of the method for increasing the doping concentration of the metal contact region of the battery emitter provided by the present application are shown;

[0029] Figure 2 Indicates step S1;

[0030] Figure 3 Indicates step S2;

[0031] Figure 4 Indicates step S3;

[0032] Figure 5 Indicates step S4;

[0033] Figure 6 Indicates step S5;

[0034] Figure 7 Indicates step S6;

[0035] Figure 8 A schematic diagram showing the distances between two sides of a first metal electrode and a boundary line of a first region in a quadruple silicon wafer;

[0036] Fig. 9 A schematic diagram showing the array arrangement of the first region on the first surface of an N-type silicon wafer.

[0037] Among them, 10: first region; 20: first metal electrode. Specific embodiments

[0038] The technical solutions in the embodiments of the application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the application. Additionally, the phrase "in one embodiment" or "in an embodiment" that appears throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0039] It should also be noted that in this text, relative terms such as first and second are only used to distinguish one entity from another, and do not necessarily require or imply any actual relationship or order between these entities. Moreover, the term "comprising", "including", or any other variant thereof is intended to cover non-exclusive inclusion, such that an article or terminal device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or elements inherent to such an article. Without further limitation, an element defined by the statement "comprising one..." does not exclude the existence of additional identical elements in the article comprising the element.

[0040] Originally, the number of carriers in silicon is extremely small, so its electrical conductivity is very poor. By diffusion, trace amounts of impurity elements are doped into pure silicon, namely boron-doped P-type silicon wafers and phosphorus-doped N-type silicon wafers. The purpose of diffusion is to diffuse a layer of P-type semiconductor or N-type semiconductor on the silicon wafer base to form a PN junction at the interface. When sunlight shines on the PN junction, the PN junction absorbs light energy and excites electrons and holes. Under the constraint of the built-in electric field, the negatively charged electrons are pushed to flow towards the N region, and the positively charged holes move towards the P region, thereby causing the potential of the P region to increase and the potential of the N region to decrease. A measurable voltage will be generated between the P region and the N region. Wires are respectively welded to the P region and the N region, and when the load is connected, current will flow through the external circuit, thus forming an electronic component.

[0041] In the selective emitter (SE) laser doping technology, the SE crystalline silicon solar cell has high-concentration doping in the metal electrode region and low-concentration doping in the non-electrode region, that is, the light absorption region. In this way, a lateral n+ / n high-low junction can be obtained at the junction of the lightly doped region and the highly doped region, and an n+ / p junction can be obtained under the electrode grid lines. This structure can reduce the emitter contact resistance and the emitter dark saturation current, improve the fill factor, short-circuit current, and open-circuit voltage, thereby increasing the conversion efficiency of the battery.

[0042] In the present invention, as Figures 1 to 9 shown, the boron doping concentration and depth in the metal electrode region of the N-type silicon wafer are optimized by the following process method:

[0043] S1. Clean the silicon wafer and perform surface texturing treatment;

[0044] S2. Diffuse the first side of the textured silicon wafer under high temperature and low pressure with a boron source to form a first-level silicon wafer with a three-layer structure on the first side;

[0045] S3. Use a laser beam with a cross-sectional width greater than a preset multiple of the metal electrode width to perform a secondary high-temperature melting-type diffusion reaction on multiple preset first regions 10 on the first side of the first-level silicon wafer at normal temperature and pressure to form a second-level silicon wafer with a two-layer structure in part and a three-layer structure in the majority;

[0046] S4. Clean the second-level silicon wafer with weak acid or weak base to remove the outermost layer of B 2 O 3 and BSG on the side of the second-level silicon wafer, and then form a third-level silicon wafer with a two-layer structure on the first side;

[0047] S5. Put the third-level silicon wafer into an oxidation furnace for oxidation to form a passivation layer or an antireflection layer on the outer surfaces of the first side and the second side, and a fourth-level silicon wafer in which the first regions 10 included in the first side are all of three-layer structure;

[0048] S6. Screen-print a first metal electrode 20 in the middle first sub-region of the first region 10 in the fourth-level silicon wafer, and screen-print a second metal electrode in the second region symmetric to the first sub-region on the second side to obtain a battery cell, and the first side of the battery cell includes the first regions 10 all of three-layer structure.

[0049] The present invention is described by taking the production of a battery cell by doping an N-type silicon wafer with boron as an example. Of course, this method can also be used for similar doping processes of other silicon wafers to obtain a battery cell.

[0050] As Figures 1 to 7 shown, the N-type silicon wafer includes opposite first side and second side. After the surface of the first side and the second side is textured, the second sides of two N-type silicon wafers are brought close to each other and adhered tightly so that the first sides of the two N-type silicon wafers are both exposed outside and in direct contact with the internal environment of the diffusion equipment. After diffusion, the first sides of the two N-type silicon wafers are both first-level silicon wafers doped with a lower concentration of boron; then use a laser to perform concentrated high-temperature doping on the preset first regions 10 on the first side of the first-level silicon wafer to form a second-level silicon wafer. Among them, as Figure 3 and Figure 4 shown, the microstructure of the first side of the first-level silicon wafer includes three layers, specifically from the outermost layer to the innermost layer in sequence: B 2 O 3 、B + +SiO 2 、Si, and Si is the textured silicon layer after texturing.

[0051] Taking boron trichloride as the boron source as an example, the principle of the product on the first side of the first-level silicon wafer in the foregoing step S2 is: using BCl 3 as the boron source and introducing it into the diffusion furnace for reaction, BCl3 It reacts with oxygen at above 850℃ to produce B 2 O 3 and Cl 2 At this temperature, B 2 O 3 It is in a molten or nearly liquid state attached to the Si surface, and then the temperature of the diffusion furnace continues to rise. When it reaches 950℃ to 1050℃, the molten B 2 O 3 It starts to react with Si to produce B and Si. Because there is oxygen in the furnace, Si and O 2 Oxygen also reacts to produce SiO 2 , that is, Figure 3 As shown in the figure, the upper layer of Si is doped with a low concentration of B, but the doped layer also includes SiO 2 , that is, the doped layer is B + +SiO 2 ; Because of the barrier of the doping layer, the generated B 2 O 3 It cannot continue to react with the Si in the bottom layer, so the first side of the first-level silicon wafer after multiplication actually contains B on the surface layer. 2 O 3 , located in the subsurface B + and SiO 2 , the Si-based layer located below the subsurface layer.

[0052] The aforementioned primary silicon wafer is then partially doped with a laser for a second time to produce Figure 4 The secondary silicon wafer shown in the figure has a two-layer structure in part of the first surface of the secondary silicon wafer and a three-layer structure in most parts. The two-layer structure is located in the preset first area 10, that is, the laser doping area. Under the action of the laser, the B layer on the surface of the primary silicon wafer is 2 O 3 and the subsurface SiO 2 All are melted by high temperature, making B 2 O 3 It can contact with the Si of the bottom layer again and react to produce B, that is, the B concentration of the first region 10 increases, and the depth of the region containing B increases, which can be expressed as B ++ ,like Figure 4 As shown in B ++ +SiO 2 The undoped area is still a three-layer structure of the first-level silicon wafer, including the B 2 O 3 , located in the subsurface B + +SiO 2, the Si base layer below the subsurface layer. Subsequently, the metal electrode is screen-printed in the first region 10, so that the B concentration in the metal electrode region in the cell is increased and the depth is deepened.

[0053] Then, the first side of the laser-doped secondary silicon wafer is cleaned in a weak acid or weak base environment to remove the unreacted B 2 O 3 After being dissolved and removed, a three-level silicon wafer is obtained. In order to increase the light absorption capacity of the silicon wafer, an anti-reflection layer needs to be generated on the surface of the silicon wafer. This layer can make part of the light that passes through the silicon wafer be reflected back into the silicon to participate in the photovoltaic reaction again. Figure 6 As shown, the anti-reflection layer is the "anti-reflection SiO 2 " layer, because the anti-reflection layer is generated by oxidation of Si, that is, SiO 2 Finally, Figure 7 As shown, a first metal electrode 20 is screen-printed in a plurality of first regions 10 on the first surface of a quadruple silicon wafer, and a second metal electrode is screen-printed at a position opposite to the first region 10 on the second surface to form a Topcon cell with high doping concentration and depth.

[0054] In some embodiments, the laser beam used in step S3 is applied by a high-frequency continuous laser with a laser wavelength of 1064nm-1090nm. The energy of the laser in this wavelength range is stable and strong, which is suitable for rapid doping of silicon wafers. Of course, if it is a P-type silicon wafer doped with phosphorus, the wavelength range can be adaptively adjusted.

[0055] In addition, the temperature range of the laser acting on the first region 10 is preferably 1400°C-1800°C. 2 O 3 、SiO 2 And Si has the highest melting point of 1400°C. It is necessary to heat Si to a molten state, but the temperature should not be too high to damage Si. Therefore, 1400°C, 1500°C, or 1600°C is preferred. It can also be adjusted adaptively according to parameters such as the thickness of the silicon wafer.

[0056] In some embodiments, the relationship between the printing position of the first metal electrode 20 and the first region 10 satisfies that the two sides of the first metal electrode 20 are 10 μm-20 μm away from the boundary line of the first region 10. Figure 8As shown (the area indicated by the dotted line and the arrow in the figure is the relative position area between the first area 10 and the first metal electrode), the width of the first area 10 and the first metal electrode 20 is as follows: the width of the first area 10 is equal to at least 1 times or equal to 2 times or more than 2 times the width of the first metal electrode 20, so that the two sides of the first metal electrode 20 are 10μm-20μm away from the boundary line of the first area 10. Within this range, not only can the forward projection of the first metal electrode 20 be completely within the first area 10, but also the size of the first area 10 is most reasonable.

[0057] It should be noted that the array spacing of the first region 10 must also meet the following requirements: greater than the width of a first metal electrode 20 and less than 1.2 or 1.3 times the width of the first metal electrode 20, so as to ensure the passivation effect of the doped conductive layer outside the first metal electrode 20, while avoiding the area occupied by the heavily doped array being too large, which may lead to majority carrier recombination on the substrate surface.

[0058] It should also be noted that the boron source in the aforementioned S2 can also be boron bromide, i.e. BBr 3 , can also be compounds of other halogen elements and boron, which can be adjusted adaptively, and this embodiment does not make specific limitations on this.

[0059] In some other embodiments, the first regions 10 used for laser doping on the first surface may be distributed in a staggered array, and the array may include: an uninterrupted array or an intermittent array according to a preset length, such as Fig. 9 As shown, the uninterrupted array, i.e., the first region 10, is a series of long lines distributed in an array on the first surface of the silicon wafer; the discontinuous array, i.e., the first region 10, is a series of line segments on the first surface of the silicon wafer, and adjacent line segments are not connected. The specific first region 10 can be adaptively selected according to the structure of the actual silicon wafer and the specification parameters of the actual solar cell, and this embodiment does not impose specific restrictions on this.

[0060] Finally, the present application provides a method for increasing the doping concentration of the emitter metal contact area of ​​a Topcon cell, which comprises first cleaning the silicon wafer and performing a surface texturing treatment; then subjecting the first surface of the texturized silicon wafer to a boron source diffusion reaction at high temperature and low pressure to form a primary silicon wafer; then subjecting a laser beam to a secondary high-temperature melting diffusion reaction at room temperature and pressure on multiple preset first areas 10 of the first surface of the primary silicon wafer to form a secondary silicon wafer having a partially two-layer structure and a mostly three-layer structure; then subjecting the secondary silicon wafer to a weak acid or weak alkali cleaning to remove the outermost B on the secondary silicon wafer. 2 O 3and the BSG on the side; finally, the third-level silicon wafer is oxidized to form a passivation layer or an anti-reflection layer, and the first metal electrode 20 is screen-printed in the first sub-region in the middle of the first region 10 in the fourth-level silicon wafer, and the second metal electrode is screen-printed in the second region symmetrical to the first sub-region on the second surface to obtain a cell. The present invention uses the boron oxide on the surface of the silicon wafer after boron expansion as the boron source for laser doping, which not only increases the concentration of boron doping on the silicon wafer, but also reduces the contact resistance on the surface of the cell without adding additional process means, thereby improving the photoelectric conversion efficiency of the cell.

Claims

1. A method for increasing the doping concentration of the emitter metal contact area of ​​a Topcon cell, It is characterized in that The steps include: S1, cleaning the silicon wafer and performing surface texturing treatment; S2, subjecting the first surface of the silicon wafer after texturing to a boron source diffusion reaction at high temperature and low pressure to form a primary silicon wafer with a three-layer structure on the first surface; S3, using a laser beam whose cross-sectional width is greater than a preset multiple of the metal electrode width to perform a secondary high-temperature melting diffusion reaction on a plurality of preset first regions (10) on the first surface of the first-level silicon wafer at room temperature and pressure, to form a secondary silicon wafer having a partially two-layer structure and a mostly three-layer structure; S4, cleaning the secondary silicon wafer with a weak acid or a weak base to remove the B on the outermost layer of the secondary silicon wafer 2 O 3 After forming the BSG on the side of the secondary silicon wafer, a tertiary silicon wafer with a two-layer structure on the first side is formed; S5, placing the three-level silicon wafer into an oxidation furnace for oxidation, forming a passivation layer or an anti-reflection layer on the outer surfaces of the first surface and the second surface, and the first area (10) included in the first surface is a four-level silicon wafer with a three-layer structure; S6. Screen-printing a first metal electrode (20) in the first sub-region in the middle of the first region (10) in the quadruple silicon wafer, and screen-printing a second metal electrode in a second region symmetrical to the first sub-region on the second surface to obtain a battery cell, wherein the first surface of the battery cell including the first region (10) is a three-layer structure.

2. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 1, It is characterized in that In S2, the first surface of the primary silicon wafer includes: B located on the surface 2 O 3 , located in the subsurface B + +SiO 2 , a Si base layer located below the secondary surface layer; in S3, the two-layer structure within the first surface of the secondary silicon wafer is located within the first region (10), including: a B layer located on the surface layer ++ +SiO 2 , a Si-based layer located below the surface layer; a three-layer structure within the first surface located outside the first region (10), including: a B-based layer located on the surface layer 2 O 3 , located in the subsurface layer is B + +SiO 2 , the Si-based layer located below the subsurface layer.

3. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 2, It is characterized in that In S4, the first two-layer structure of the first surface of the three-level silicon wafer is located in the first region (10), including: B located on the surface layer ++ +SiO 2 , Si located in the subsurface layer; the second two-layer structure is located outside the first region (10), including: B located in the surface layer + +SiO 2 , Si in the subsurface; B 2 O 3 Removed by weak acids or bases.

4. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 3, It is characterized in that In S3, the laser beam is generated by a high frequency activated continuous laser with a laser wavelength of 1064nm-1090nm.

5. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 4, It is characterized in that The temperature range of the first region (10) heated by the laser is 1400°C-1800°C.

6. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 1, It is characterized in that When the temperature in the first region (10) is greater than 1400° C., the B 2 O 3 、SiO 2 and Si is in a molten state, so that B of the first surface of the primary silicon wafer 2 O 3 Through B and SiO 2 The layer reacts with the Si below the subsurface layer to form B in the first region (10). ++ +SiO 2 .

7. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 1, It is characterized in that In S6, the distance between the two sides of the first metal electrode (20) and the boundary line of the first region (10) is 10 μm-20 μm.

8. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 1, It is characterized in that The first regions (10) are distributed in a staggered array within the first plane, and the boron content of the region outside the first region (10) is lower than the boron content of the first region (10).

9. A method for increasing the doping concentration of the emitter metal contact region of a Topcon cell according to claim 1, It is characterized in that The first regions (10) are distributed discontinuously on the first surface.

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