Preparation method of silicon substrate and heterojunction solar cell

Abstract

The invention provides a preparation method of a silicon substrate and a heterojunction solar cell, and the preparation method of the silicon substrate comprises the steps: an initial silicon substrate comprises a first surface and a second surface, a first mask layer is formed on the first surface, and a second mask layer is formed on the second surface; performing first dot matrix laser etching treatment on the first mask layer to form a first intermediate mask layer; the second surface is provided with a target area, the target area is used for arranging a grid line, and second dot matrix laser etching processing is carried out on the second mask layer corresponding to the target area to form a second middle mask layer; performing alkali etching treatment on the first surface through the first intermediate mask layer, and performing alkali etching treatment on the target area through the second intermediate mask layer; and removing the first intermediate mask layer to obtain a first suede, and removing the second intermediate mask layer to obtain the silicon substrate with the target area as the second suede. The silicon substrate with excellent adhesiveness between the second surface and the grid lines and ultralow reflectivity on the first surface is prepared by using the method.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell preparation, and in particular to a method for preparing a silicon substrate and a heterojunction solar cell. Background Art

[0002] Under the background of energy structure transformation and dual carbon, the new energy industry is booming, and photovoltaics as a new energy source has also ushered in unprecedented prosperity. Silicon substrate heterojunction solar cells are one of the current key focus of photovoltaic solar cells. In order to improve the light utilization of silicon substrate heterojunction solar cells, the silicon substrate is currently mainly treated by texturing to form a pyramid structure on the surface of the silicon substrate, so that the surface of the silicon substrate is a velvet surface with low reflectivity, thereby improving the light trapping effect of the silicon substrate, facilitating the silicon substrate to better absorb light and improving the light utilization of silicon substrate heterojunction solar cells.

[0003] At present, the silicon substrate of silicon substrate heterojunction solar cells is usually double-sided, and the back velvet surface will cause uneven deposition of the mask layer, which will affect the passivation effect. At the same time, the velvet structure on the back is not conducive to the secondary reflection absorption of the incident light, which is not conducive to the improvement of the conversion rate of the silicon substrate heterojunction solar cell. The existing method is to polish the back of the silicon substrate to form a polished surface, thereby reducing the reflectivity, increasing the secondary reflection absorption of the incident light, and enhancing the absorption of light by the silicon substrate; at the same time, because the back is a polished surface, it is conducive to the uniform deposition of the back passivation layer. However, at present, the grid line is mainly formed by coating a low-temperature silver paste (paste) on the back of the silicon substrate. The adhesion between the back of the silicon substrate and the paste is poor in the case of the light surface, which easily causes the paste to have poor contact with the silicon wafer, and it is easy to cause the phenomenon of partial main grid falling off during the component welding process of preparing the heterojunction solar cell. Summary of the invention

[0004] The present invention provides a method for preparing a silicon substrate, by which a silicon substrate having excellent adhesion between a second surface and a gate line and an ultra-low reflectivity on a first surface can be prepared. The method has a simple process and a short flow, and is suitable for wide promotion and application.

[0005] The present invention also provides a method for preparing a heterojunction solar cell, comprising preparing a silicon substrate using the above-mentioned method for preparing a silicon substrate, so that the heterojunction solar cell prepared by the method has a high light utilization rate.

[0006] The present invention provides a method for preparing a silicon substrate, comprising:

[0007] S1: set the mask layer;

[0008] The initial silicon substrate comprises a first surface and a second surface which are arranged opposite to each other, a first mask layer is formed on the first surface, and a second mask layer is formed on the second surface;

[0009] S2: dot laser etching treatment;

[0010] Performing a first dot matrix laser etching process on the first mask layer to form a first intermediate mask layer with holes;

[0011] The second surface has a target area, the target area is used to set the gate line, and the second mask layer corresponding to the target area is subjected to a second dot matrix laser etching process to form a second intermediate mask layer with holes;

[0012] S3: alkali etching treatment;

[0013] performing alkaline etching on the first surface through the holes in the first intermediate mask layer, and performing alkaline etching on the target area through the holes in the second intermediate mask layer;

[0014] S4: removing the mask layer;

[0015] The first intermediate mask layer is removed to obtain a first velvet surface, and the second intermediate mask layer is removed to obtain a second velvet surface located in a target area.

[0016] In the method for preparing the silicon substrate as described above, in S2, in the first dot matrix laser etching process, the size of a single light spot is 0.5-50 microns, and the minimum distance between any two adjacent light spots is 0.1-3 microns; and / or,

[0017] In the second dot matrix laser etching process, the size of a single light spot is 0.5-50 microns, and the minimum distance between any two adjacent light spots is 0.1-3 microns.

[0018] In the method for preparing the silicon substrate as described above, in S2, the time of the first lattice laser etching process is 1-30 seconds, and the power of the first lattice laser etching process is 1-100W; and / or,

[0019] The time of the second dot matrix laser etching process is 1-30s, and the power of the second dot matrix laser etching process is 1-100W.

[0020] In the method for preparing a silicon substrate as described above, the first mask layer and / or the second mask layer are each independently an oxide layer or a silicon nitride layer.

[0021] In the method for preparing the silicon substrate as described above, the thickness of the oxide layer is 5nm-300nm.

[0022] In the method for preparing the silicon substrate as described above, the thickness of the silicon nitride layer is 30nm-300nm.

[0023] The method for preparing the silicon substrate as described above, before S1, further comprises: sequentially performing a pre-cleaning process, an RCA cleaning process, and a drying process on the initial silicon substrate;

[0024] Wherein, the pre-cleaning treatment comprises: performing a first cleaning treatment on the initial silicon substrate using a first solution, and then performing a second cleaning treatment on the initial silicon substrate using a second solution;

[0025] The first solution comprises: 1-15wt% alkali solution, 1-15wt% hydrogen peroxide, the temperature of the first solution is 45-65°C, and the time of the first cleaning treatment is 1-4min;

[0026] The second solution comprises: 0.1-10wt% of alkaline solution, the cleaning temperature of the second solution is 45-80°C, and the time of the second cleaning treatment is 0.5-4min.

[0027] In the method for preparing the silicon substrate as described above, the alkali etching treatment comprises: using an alkali solution with a mass percentage of 1-5% to perform the alkali etching treatment.

[0028] In the method for preparing the silicon substrate as described above, the temperature of the alkali etching treatment is 40-80° C., and the time of the alkali etching treatment is 60-300 seconds.

[0029] In the method for preparing the silicon substrate as described above, S4 further includes:

[0030] The first intermediate mask layer and the second intermediate mask layer are removed respectively using hydrofluoric acid with a mass percentage of 0.001-38%.

[0031] The present invention also provides a method for preparing a heterojunction solar cell, comprising preparing a silicon substrate using the method for preparing a silicon substrate as described above;

[0032] A first passivation layer is provided on the first velvet surface of the silicon substrate, and a second passivation layer is provided on the surface where the second velvet surface of the silicon substrate is located;

[0033] A first doping layer is disposed on a surface of the first passivation layer away from the silicon substrate, and a second doping layer is disposed on a surface of the second passivation layer away from the silicon substrate, wherein the first doping layer and the second doping layer have opposite conductivity types;

[0034] A first transparent conductive film is disposed on a surface of the first doped layer away from the silicon substrate, and a second transparent conductive film is disposed on a surface of the second doped layer away from the silicon substrate;

[0035] The heterojunction solar cell is obtained by arranging an electrode on a surface of the first transparent conductive film away from the silicon substrate, and arranging an electrode on a surface of the second transparent conductive film corresponding to the second velvet surface away from the silicon substrate.

[0036] The method for preparing a silicon substrate of the present invention comprises the following steps: forming a first mask layer on a first surface of an initial silicon substrate, performing a first dot matrix laser etching treatment on the first mask layer to form a first intermediate mask layer having holes, performing an alkali etching treatment on the first surface through the holes of the first intermediate mask layer, the alkali solution can contact the initial silicon substrate through the holes of the first intermediate mask layer to achieve texturing of the first surface, and removing the first intermediate mask layer to obtain a first texture surface; forming a second mask layer on a second surface of the initial silicon substrate, the second surface having a target area for setting gate lines, performing a second dot matrix laser etching treatment on the second mask layer corresponding to the target area to form a second intermediate mask layer having holes, performing an alkali etching treatment on the target area through the holes of the second intermediate mask layer, the alkali solution can contact the initial silicon substrate through the holes of the second intermediate mask layer, and removing the second intermediate mask layer to obtain a second texture surface located in the target area, and the second texture surface is used for setting gate lines. The present invention can improve the adhesion between the gate line and the target area by performing texturing in the target area for setting the gate line, thereby improving the tension between the gate line and the target area; and the present invention only performs texturing on the target area for setting the gate line on the back side (other areas outside the target area are smooth surfaces), which can not only ensure that the passivation layer can be uniformly deposited on the back side of the silicon substrate, but also does not affect the back side reflectivity of the silicon substrate; at the same time, since the method of the present invention omits the step of polishing the back side of the initial silicon substrate after texturing, the process flow is shortened, and the phenomenon of thinning the initial silicon substrate due to polishing can be avoided, thereby avoiding the waste of the thickness of the initial silicon substrate and reducing the probability of silicon wafer fragmentation in subsequent processes. It is worth mentioning that since the first dot matrix laser etching process in the present invention can form a first intermediate mask layer with holes of high regularity morphology, when the alkali solution performs alkali etching on the first surface through the holes of high regularity morphology, the first surface can be formed into a first velvet surface with a more uniform morphology, thereby reducing the front side reflectivity of the silicon substrate.

[0037] The method for preparing a heterojunction solar cell of the present invention comprises preparing a silicon substrate using the method for preparing a silicon substrate, so that the heterojunction solar cell prepared by the method has a high utilization rate of light. The method is simple, efficient and has excellent practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic structural diagram of an initial silicon substrate according to Embodiment 1 of the present invention;

[0039] Figure 2 This is a schematic structural diagram of a first intermediate silicon substrate according to Embodiment 1 of the present invention;

[0040] Figure 3 This is a schematic structural diagram of a second intermediate silicon substrate according to Embodiment 1 of the present invention;

[0041] Figure 4 This is a schematic structural diagram of a silicon substrate according to Embodiment 1 of the present invention;

[0042] Figure 5 Schematic diagram of the structure of a heterojunction solar cell according to Example 1 of the present invention;

[0043] Description of reference numerals:

[0044] 1-Silicon substrate;

[0045] 2-a first intrinsic amorphous silicon layer;

[0046] 3-N-type amorphous silicon layer;

[0047] 4-a first transparent conductive film;

[0048] 5-a second intrinsic amorphous silicon layer;

[0049] 6-P-type amorphous silicon layer;

[0050] 7- a second transparent conductive film;

[0051] 8-Metal electrode;

[0052] 11- initial silicon substrate;

[0053] 12- a first mask layer;

[0054] 13- a second mask layer;

[0055] 14-a first intermediate mask layer;

[0056] 15-Second intermediate mask layer. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] The present invention provides a method for preparing a silicon substrate, comprising:

[0059] S1: set the mask layer;

[0060] The initial silicon substrate comprises a first surface and a second surface which are arranged opposite to each other, a first mask layer is formed on the first surface, and a second mask layer is formed on the second surface;

[0061] S2: dot laser etching treatment;

[0062] Performing a first dot matrix laser etching process on the first mask layer to form a first intermediate mask layer with holes;

[0063] The second surface has a target area, the target area is used to set the gate line, and the second mask layer corresponding to the target area is subjected to a second dot matrix laser etching process to form a second intermediate mask layer with holes;

[0064] S3: alkali etching treatment;

[0065] Performing alkali etching on the first surface through the holes in the first intermediate mask layer, and performing alkali etching on the target area through the holes in the second intermediate mask layer;

[0066] S4: removing the mask layer;

[0067] The first intermediate mask layer is removed to obtain a first velvet surface, and the second intermediate mask layer is removed to obtain a second velvet surface located in a target area.

[0068] The initial silicon substrate of the present invention has two oppositely disposed first and second surfaces. In the present invention, the first surface can be used as the front side of the initial silicon substrate, and the second surface can be used as the back side of the initial silicon substrate.

[0069] A first mask layer is formed on the first surface, and similarly, a second mask layer is formed on the second surface. The first mask layer and the second mask layer function to protect specific areas of the silicon substrate from being etched in subsequent processing steps.

[0070] The present invention does not limit the shape, size and thickness of the initial silicon substrate, which can be selected according to actual needs.

[0071] The first dot matrix laser etching process is to form holes penetrating the first mask layer on the surface of the first mask layer by a laser beam. When performing the first dot matrix laser etching process, the laser beam can etch the surface of the first mask layer to form holes penetrating the first mask layer and exposing the first surface of the silicon substrate, thereby obtaining a first intermediate mask layer. Among them, the first intermediate mask layer is resistant to alkali but not acid, and its alkali resistance is better than that of the silicon substrate. Therefore, the first intermediate mask layer can always cover the above-mentioned first surface in the subsequent alkali etching process as a "mask", and the holes provide a position for etching for preparing the first velvet surface on the first surface of the silicon substrate.

[0072] The second surface of the present invention has a target area, and the target area is used to set the gate line. The second dot matrix laser etching process is to form holes penetrating the second mask layer on the surface of the second mask layer corresponding to the above-mentioned target area by a laser beam. When performing the second dot matrix laser etching process, the laser beam can etch the surface of the second mask layer corresponding to the target area to form holes, and the holes penetrate the second mask layer to expose the target area of ​​the silicon substrate, thereby obtaining a second intermediate mask layer. Among them, the second intermediate mask layer is alkali-resistant but not acid-resistant, and its alkali resistance is better than that of the silicon substrate. Therefore, the second intermediate mask layer can be covered on the second surface in the subsequent alkali etching process as a "mask", and the holes provide a position for etching for preparing the second velvet surface for the gate line portion set in the target area.

[0073] In some embodiments, the holes include various shapes, such as square and circular.

[0074] The first surface is alkali-etched with alkali. Since the first intermediate mask layer is alkali-resistant but not acid-resistant, the first intermediate mask layer will not be dissolved by the alkali etching, and the alkali can texturize the first surface of the silicon substrate through the through holes that penetrate the first mask layer. The target area of ​​the second surface is alkali-etched with alkali. Since the second intermediate mask layer is alkali-resistant but not acid-resistant, the second intermediate mask layer will not be dissolved by the alkali etching, and the alkali can texturize the target area of ​​the second surface of the silicon substrate through the through holes that penetrate the second mask layer.

[0075] After the above-mentioned first surface is subjected to alkaline etching treatment, the first intermediate mask layer is removed to expose the first surface subjected to alkaline etching treatment, thereby obtaining a first velvet surface; similarly, after the above-mentioned target area is subjected to alkaline etching treatment, the second intermediate mask layer is removed to expose the second surface subjected to etching treatment, thereby obtaining a second velvet surface located in the target area, and finally obtaining a silicon substrate.

[0076] The preparation method of the present invention can obtain a silicon substrate with a velvet surface on the front side and a velvet surface in the target area on the back side (other areas outside the target area on the back side are smooth surfaces). When the silicon substrate sets the grid lines, the velvet surface formed in the target area on the back side has excellent adhesion to the grid lines, which can avoid the phenomenon that the efficiency of the heterojunction solar cell is affected by the poor contact of the grid lines. In addition, the velvet surface on the front side and the smooth surfaces in other areas on the back side can reduce the reflectivity of the silicon substrate and enhance the absorption of light by the silicon substrate, especially the absorption of long waves. It is worth mentioning that there is no alkali polishing treatment in the preparation method of the present invention, which can avoid the thinning of the silicon substrate due to the alkali polishing treatment, thereby avoiding the occurrence of the phenomenon that the fragmentation rate of the silicon substrate is too high. The preparation method of the present invention also has the advantages of simple process and short flow, and is suitable for wide promotion and application.

[0077] The present invention does not impose any special limitation on the first lattice laser etching process, as long as the first mask layer can form a first intermediate mask layer with holes; the present invention does not impose any special limitation on the second lattice laser etching process, as long as the second mask layer can form a second intermediate mask layer with holes.

[0078] In some embodiments, when the size of a single spot is 0.5-50 microns and the minimum distance between any two adjacent spots is 0.1-3 microns during the first dot matrix laser etching process, the velvet roughness of the front surface of the silicon substrate can be made appropriate, thereby reducing the reflectivity of the silicon substrate.

[0079] When the size of a single spot is 0.5-50 microns and the minimum distance between any two adjacent spots is 0.1-3 microns during the second dot matrix laser etching process, the velvet roughness of the back surface of the silicon substrate can be made appropriate to ensure the adhesion between the gate line and the silicon substrate.

[0080] In some embodiments of the present invention, when the time of the first dot matrix laser etching process is 1-30s and the power of the first dot matrix laser etching process is 1-100W, a portion of the first mask layer can be more thoroughly removed without damaging the initial silicon substrate to form a first intermediate mask layer with holes.

[0081] When the second dot matrix laser etching process lasts for 1-30 seconds and the power of the second dot matrix laser etching process is 1-100W, part of the second mask layer can be more thoroughly removed without damaging the initial silicon substrate to form a second intermediate mask layer with holes.

[0082] In the present invention, specific process parameters of the first lattice laser etching process and the second lattice laser etching process may be the same or different.

[0083] In a specific embodiment, the first mask layer and / or the second mask layer are each independently an oxide layer or a silicon nitride layer. For example, in the present invention, the first mask layer can be an oxide layer or a silicon nitride layer; the second mask layer can be an oxide layer or a silicon nitride layer. The oxide layer includes a silicon dioxide layer, the silicon nitride layer includes a SiNx layer, and x is a positive integer.

[0084] In some embodiments, the oxide layer may be formed by a thermal oxidation method; and the silicon nitride layer may be formed by a CVD deposition method.

[0085] In the present invention, when the first mask layer includes an oxide layer or a silicon nitride layer, during the alkaline etching process, the first intermediate mask layer formed by the first mask layer can better protect the first surface to form a first velvet surface; when the second mask layer includes an oxide layer or a silicon nitride layer, during the alkaline etching process, the second intermediate mask layer formed by the second mask layer can better protect the second surface to form a second velvet surface in the target area, and after the alkaline etching process, the first intermediate mask layer including the oxide layer or the silicon nitride layer and the second intermediate mask layer can be more easily removed, thereby obtaining a silicon substrate with a velvet surface on the front side and a velvet surface in the target area on the back side.

[0086] In a specific embodiment, when the first mask layer and / or the second mask layer is an oxide layer, the thickness of the oxide layer is 5nm-300nm. For example, the thickness of the oxide layer includes but is not limited to 5nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm or a range consisting of any two of them.

[0087] The present invention can fully protect the first surface and the second surface in the alkali etching process by controlling the thickness of the oxide layer, and more efficiently obtain a silicon substrate with a velvet surface on the first surface and a velvet surface in the target area of ​​the second surface.

[0088] In a specific embodiment, when the first mask layer and / or the second mask layer is a silicon nitride layer, the thickness of the silicon nitride layer is 30nm-300nm. For example, the thickness of the silicon nitride layer includes but is not limited to 30nm, 100nm, 150nm, 200nm, 250nm, 300nm or a range consisting of any two of them.

[0089] The present invention controls the thickness of the silicon nitride layer, can fully protect the first surface and the second surface in the alkali etching process, and more efficiently obtains a silicon substrate with a velvet surface on the first surface and a velvet surface in the target area of ​​the second surface.

[0090] In a specific implementation, the alkali etching treatment includes: using an alkali solution with a mass percentage of 1-5% to perform the alkali etching treatment.

[0091] The alkali in the alkali solution includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia water, sodium carbonate, and potassium carbonate. For example, the mass percentage of the alkali solution includes but is not limited to 1%, 2%, 3%, 4%, 5wt% or a range consisting of any two of them.

[0092] The present invention uses an alkali solution with a mass percentage within the above range, and can more fully etch the first surface and more fully etch the target area of ​​the second surface without damaging the first intermediate mask layer and the second intermediate mask layer, thereby forming a silicon substrate with a velvet surface on the first surface and a velvet surface on the target area of ​​the second surface.

[0093] In a specific embodiment, the temperature of the alkali etching treatment is 40-80°C, and the time of the alkali etching treatment is 60-300s. For example, the temperature of the alkali etching treatment includes but is not limited to 40°C, 50°C, 60°C, 70°C, 80 or any two thereof; the time of the alkali etching treatment includes but is not limited to 60s, 100s, 150s, 200s, 250s, 300s or any two thereof.

[0094] The present invention controls the temperature and time of the alkali etching treatment within the above range, so that the target areas corresponding to the first surface and the second surface can be etched more uniformly while saving energy consumption, thereby more efficiently obtaining a silicon substrate including the first velvet surface and the second velvet surface.

[0095] In a specific embodiment, removing the first intermediate mask layer and the second intermediate mask layer respectively includes: using hydrofluoric acid with a mass percentage of 0.001-38% to remove the first intermediate mask layer and the second intermediate mask layer respectively. For example, the mass percentage of the hydrofluoric acid used to remove the first intermediate mask layer and the second intermediate mask layer includes but is not limited to 0.001%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 38% or a range consisting of any two thereof.

[0096] The present invention uses hydrofluoric acid with a mass percentage within the above range to respectively remove the first intermediate mask layer and the second intermediate mask layer, thereby more efficiently removing the first intermediate mask layer and the second intermediate mask layer without almost affecting the first velvet surface and the second velvet surface.

[0097] In some embodiments of the present invention, before S1, the method further includes: sequentially performing a pre-cleaning process, an RCA cleaning process, and a drying process on the initial silicon substrate;

[0098] The pre-cleaning treatment includes: performing a first cleaning treatment on the initial silicon substrate using a first solution, and then performing a second cleaning treatment on the initial silicon substrate using a second solution;

[0099] The first solution comprises: 1-15wt% alkali solution, 1-15wt% hydrogen peroxide, the temperature of the first solution is 45-65°C, and the time of the first cleaning treatment is 1-4min;

[0100] The second solution includes: 0.1-10 wt % of alkaline solution, the temperature of the second solution is 45-80° C., and the time of the second cleaning treatment is 0.5-4 minutes.

[0101] Specifically, before S1, it may also include: using a first solution to perform a first cleaning treatment on the initial silicon substrate to remove grease and other dirt on the surface of the initial silicon substrate; then using a second solution to perform a second cleaning treatment on the initial silicon substrate to remove the surface damage layer of the initial silicon substrate; then performing an RCA cleaning treatment to further remove the oxide layer of the initial silicon substrate, and finally performing a drying treatment to obtain a clean and dry initial silicon substrate.

[0102] The present invention also includes performing the above-mentioned pre-cleaning treatment, RCA cleaning treatment and drying treatment on the initial silicon substrate in sequence before S1, so as to obtain a clean and dry initial silicon substrate, thereby promoting the subsequent formation of the first mask layer and the second mask layer, and further obtaining a silicon substrate with better comprehensive performance.

[0103] In the present invention, the RCA cleaning process can be a standard RCA cleaning process. In some embodiments, the RCA cleaning process can include a first RCA cleaning process, a second RCA cleaning process, and a hydrofluoric acid treatment, wherein in the first RCA cleaning process, the solution includes: 1-15wt% alkali solution, 1-15wt% hydrogen peroxide, the temperature is 45-65°C, and the time is 1-4min; in the second RCA cleaning process, the solution includes: 1-15wt% hydrochloric acid, 1-15wt% hydrogen peroxide, the temperature is 25-65°C, and the time is 1-4min; in the hydrofluoric acid treatment, the solution is 1-10wt% HF, the temperature is 25°C, and the time is 2-4min.

[0104] The base in the present invention may be a base commonly used in the art. For example, the base may be at least one of KOH and NaOH.

[0105] The present invention also provides a method for preparing a heterojunction solar cell, comprising preparing a silicon substrate using the above-mentioned method for preparing a silicon substrate;

[0106] A first passivation layer is provided on the first suede surface of the silicon substrate, and a second passivation layer is provided on the surface where the second suede surface of the silicon substrate is located;

[0107] A first doping layer is disposed on a surface of the first passivation layer away from the silicon substrate, and a second doping layer is disposed on a surface of the second passivation layer away from the silicon substrate, wherein the first doping layer and the second doping layer have opposite conductivity types;

[0108] A first transparent conductive film is disposed on a surface of the first doped layer away from the silicon substrate, and a second transparent conductive film is disposed on a surface of the second doped layer away from the silicon substrate;

[0109] An electrode is arranged on the surface of the first transparent conductive film away from the silicon substrate, and an electrode is arranged on the surface of the second transparent conductive film corresponding to the second velvet surface away from the silicon substrate to obtain a heterojunction solar cell.

[0110] Specifically, the heterojunction solar cell of the present invention includes, in the stacking direction, an electrode, a first transparent conductive film, a first doped layer, a first passivation layer, a silicon substrate, a second passivation layer, a second doped layer, a second transparent conductive film, and an electrode.

[0111] The method for preparing a heterojunction solar cell of the present invention comprises preparing a silicon substrate using the method for preparing a silicon substrate, wherein the heterojunction solar cell prepared by the method has a high utilization rate of light. The method is simple, efficient and has excellent practical value.

[0112] The present invention does not specifically limit the first passivation layer and the second passivation layer. The first passivation layer and the second passivation layer may be passivation layers commonly used in the art. For example, the first passivation layer may be a first intrinsic amorphous silicon doped layer, and the second passivation layer may be a second intrinsic amorphous silicon doped layer.

[0113] The present invention does not specifically limit the first doping layer and the second doping layer, as long as the conductivity type of the first doping layer is opposite to that of the second doping layer. For example, the first doping layer may be an N-type doping layer (an N-type amorphous silicon layer or an N-type microcrystalline silicon layer), and the second doping layer may be a P-type doping layer (a P-type amorphous silicon layer or a P-type crystalline silicon layer). In the present invention, the N-type doping layer is arranged on the front side, and the P-type doping layer is arranged on the back side.

[0114] The present invention also does not limit the arrangement of the first passivation layer, the second passivation layer, the first doping layer, and the second doping layer, and the first passivation layer, the second passivation layer, the first doping layer, and the second doping layer can be formed respectively by methods commonly used in the art. For example, at least one of the first passivation layer, the second passivation layer, the first doping layer, and the second doping layer can be formed by chemical vapor deposition.

[0115] The present invention does not limit the specific formation method of the first transparent conductive film and the second transparent conductive film. The first transparent conductive film and the second transparent conductive film can be formed by a method commonly used in the art. For example, the first transparent conductive film and / or the second transparent conductive film can be formed by physical vapor deposition.

[0116] Hereinafter, the present invention will be further described in detail through specific embodiments.

[0117] Example 1

[0118] Figure 1 is a schematic structural diagram of an initial silicon substrate according to Embodiment 1 of the present invention; Figure 2This is a schematic structural diagram of a first intermediate silicon substrate according to Embodiment 1 of the present invention; Figure 3 This is a schematic structural diagram of a second intermediate silicon substrate according to Embodiment 1 of the present invention; Figure 4 This is a schematic structural diagram of a silicon substrate according to Embodiment 1 of the present invention; Figure 5 Schematic diagram of the structure of the heterojunction solar cell according to Example 1 of the present invention, Figure 1-5 As shown, the method for preparing the heterojunction solar cell of this embodiment includes the following steps:

[0119] 1. Preparation of silicon substrate

[0120] 1) First, the initial silicon substrate 11 is placed in a mixed solution of 2wt% potassium hydroxide and 2wt% hydrogen peroxide, and cleaned at 65°C for 4 minutes, and then placed in a 5wt% KOH solution and cleaned at 50°C for 2 minutes; then, an RCA cleaning process is performed to obtain a clean initial silicon substrate; then, the clean initial silicon substrate 11 is dried to obtain a clean and dry initial silicon substrate 11;

[0121] 2) a first mask layer 12 and a second mask layer 13 are respectively provided on two surfaces of the initial silicon substrate 11 to obtain a first intermediate silicon substrate;

[0122] The first mask layer 12 is a SiNx layer formed by CVD deposition method, and has a thickness of 150 nm; the second mask layer 13 is a SiNx layer formed by CVD deposition method, and has a thickness of 150 nm;

[0123] 3) Selecting a circular spot to perform a first dot matrix laser etching process on the first mask layer 12 to form a first intermediate mask layer 14 having holes; selecting a circular spot to perform a second dot matrix laser etching process on the second mask layer 13 corresponding to the target area (the target area is used to set the grid line) to form a second intermediate mask layer 15 having a second hole;

[0124] In the first dot matrix laser etching process, the time is 10 s, the power is 5 W, the minimum distance between any two adjacent light spots is 1 micron, and the diameter of a single light spot is 2 microns;

[0125] In the second spot array laser etching process, the time was 10 s, the power was 5 W, the minimum distance between any two adjacent spots was 1 μm, and the diameter of a single spot was 2 μm;

[0126] 4) performing alkaline etching treatment at 50° C. for 3 min using a 1 wt % KOH solution to obtain a second intermediate silicon substrate, removing the first intermediate mask layer using 8 wt % hydrofluoric acid to obtain a first velvet surface, and removing the second intermediate mask layer using 8 wt % hydrofluoric acid to obtain a second velvet surface located in a target area, thereby obtaining a silicon substrate 1;

[0127] Finally, the silicon substrate is subjected to RCA cleaning and drying treatments.

[0128] 2. Preparation of heterojunction solar cells

[0129] 1) using chemical vapor deposition (CVD) to sequentially deposit a first intrinsic amorphous silicon layer 2 and an N-type amorphous silicon layer 3 on a first textured surface of a silicon substrate 1;

[0130] Using a CVD method, a second intrinsic amorphous silicon layer 5 and a P-type amorphous silicon layer 6 are sequentially deposited on the plane where the second textured surface of the silicon substrate 1 is located;

[0131] 2) using physical vapor deposition (PVD) to deposit a first transparent conductive film 4 on a surface of the N-type amorphous silicon layer 3 away from the silicon substrate 1, and using PVD to deposit a second transparent conductive film 7 on a surface of the P-type amorphous silicon layer 6 away from the silicon substrate 1;

[0132] A metal electrode 8 is disposed on the surface of the first transparent conductive film 4 away from the silicon substrate 1, and a metal electrode 8 is disposed on the surface of the second transparent conductive film 7 corresponding to the second velvet surface away from the silicon substrate 1 to form a heterojunction solar cell.

[0133] Example 2

[0134] The method for preparing the heterojunction solar cell provided in this embodiment is basically the same as that in Embodiment 1, except that:

[0135] Select a square light spot to perform a first dot matrix laser etching process on the first mask layer 12 to form a first intermediate mask layer 14; select a square light spot to perform a second dot matrix laser etching process on the second mask layer 13 corresponding to the target area (the target area is used to set the grid line) to form a second intermediate mask layer 15;

[0136] In the first dot matrix laser etching process, the time is 10 s, the power is 5 W, the minimum distance between any two adjacent light spots is 1 micron, and the side length of a single light spot is 2 microns;

[0137] In the second point array laser etching process, the time is 10 s, the power is 5 W, the minimum distance between any two adjacent light spots is 1 micron, and the side length of a single light spot is 2 microns.

[0138] Comparative Example

[0139] This comparative example provides a method for preparing a heterojunction solar cell, comprising the following steps:

[0140] 1. Preparation of silicon substrate

[0141] 1) firstly placing the initial silicon substrate in a mixed solution of 2wt% potassium hydroxide and 2wt% hydrogen peroxide, cleaning at 65°C for 4min, and then placing it in a 5wt% KOH solution, cleaning at 50°C for 2min; then performing RCA cleaning treatment to obtain a clean initial silicon substrate; then drying the clean initial silicon substrate to obtain a clean and dry initial silicon substrate;

[0142] 2) At 80° C., a mixed solution of 1 wt % KOH and 1 % texturing additive (JY-106S) was used to perform positive pyramid texturing-alkali etching on both surfaces of the initial silicon substrate for 480 s to obtain a double-sided texturing sheet;

[0143] 3) The double-sided velvet sheet was subjected to a tube furnace thermal oxidation treatment at a temperature of 900 degrees, an oxygen flux of 300L / min, and a time of 20 minutes, so that an oxide layer was formed on both sides of the double-sided velvet sheet; then the oxide layer on one side was removed by a chain pickling device, the HF concentration of the chain device was 5%, and then 1wt% KOH was used for alkaline polishing at 80°C for 2 minutes to obtain a silicon substrate with a velvet surface on the front side and a polished surface on the back side;

[0144] Finally, the silicon substrate is cleaned and dried by RCA.

[0145] 2. Preparation of heterojunction solar cells

[0146] The preparation of the heterojunction solar cell provided in this comparative example is basically the same as that in Example 1, except that: the silicon substrate prepared in this comparative example is used.

[0147] Performance Testing

[0148] The following performance tests were performed on the silicon substrate and the heterojunction solar cell of the embodiment and the comparative example, and the results are shown in Table 1;

[0149] 1) Suede reflectivity test

[0150] The D8 reflectivity test equipment was used to obtain the reflectivity of the front suede surface of the silicon substrate.

[0151] 2) Tension between the gate line and the silicon substrate

[0152] The grid line tension test equipment is used to test the tension between the front grid line and the silicon substrate, and the tension between the back grid line and the silicon substrate in the heterojunction solar cell.

[0153] Table 1 Test results

[0154] project Front suede reflectivity Front tension / N Back tension / N Comparative Example 11.72％ 1.2 0.5 Example 1 5.78％ 1.5 1.45 Example 2 6.20％ 1.4 1.41

[0155] According to Table 1, 1) compared with the comparative example, the silicon substrate obtained in the embodiment of the present invention has a lower front velvet reflectivity. The reason is that compared with the velvet making method in the comparative example, the first dot matrix laser etching process in the present invention can form a first intermediate mask layer with holes of high regularity morphology. When the alkaline solution performs alkaline etching on the first surface through the holes of high regularity morphology, the first surface can form a first velvet with a more uniform morphology, thereby reducing the front reflectivity of the silicon substrate.

[0156] 2) Compared with the comparative example, the silicon substrate obtained in the embodiment of the present invention can improve the tension between the front grid line and the silicon substrate, and the tension between the back grid line and the silicon substrate when used to prepare a heterojunction solar cell. The reason is that the present invention can form a first velvet surface with a more uniform morphology, which helps to improve the tension between the front grid line and the silicon substrate, and because the back area of ​​the present invention for setting the grid line is a velvet surface, the tension between the back grid line and the silicon substrate can be further improved.

[0157] 3) At the same time, since the present invention only textures the area on the back side of the silicon substrate for setting the gate lines, and the other areas on the back side are smooth, the back side reflectivity of the heterojunction solar cell including the embodiment of the present invention can be basically consistent with the back side reflectivity of the heterojunction solar cell of the comparative example.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a silicon substrate, characterized in that: include: S1: set the mask layer; The initial silicon substrate comprises a first surface and a second surface which are arranged opposite to each other, a first mask layer is formed on the first surface, and a second mask layer is formed on the second surface; S2: dot laser etching treatment; Performing a first dot matrix laser etching process on the first mask layer to form a first intermediate mask layer with holes; The second surface has a target area, the target area is used to set the gate line, and the second mask layer corresponding to the target area is subjected to a second dot matrix laser etching process to form a second intermediate mask layer with holes; S3: alkali etching treatment; performing alkaline etching on the first surface through the holes in the first intermediate mask layer, and performing alkaline etching on the target area through the holes in the second intermediate mask layer; S4: removing the mask layer; The first intermediate mask layer is removed to obtain a first velvet surface, and the second intermediate mask layer is removed to obtain a second velvet surface located in a target area.

2. The method for preparing a silicon substrate according to claim 1, characterized in that: In S2, in the first dot matrix laser etching process, the size of a single light spot is 0.5-50 microns, and the minimum distance between any two adjacent light spots is 0.1-3 microns; and / or, In the second dot matrix laser etching process, the size of a single light spot is 0.5-50 microns, and the minimum distance between any two adjacent light spots is 0.1-3 microns.

3. The method for preparing a silicon substrate according to claim 2, characterized in that: In S2, the time of the first lattice laser etching process is 1-30s, and the power of the first lattice laser etching process is 1-100W; and / or, The time of the second dot matrix laser etching process is 1-30s, and the power of the second dot matrix laser etching process is 1-100W.

4. The method for preparing a silicon substrate according to claim 1, characterized in that: The first mask layer and / or the second mask layer are each independently an oxide layer or a silicon nitride layer.

5. The method for preparing a silicon substrate according to claim 4, characterized in that: The thickness of the oxide layer is 5nm-300nm; and / or, The thickness of the silicon nitride layer is 30nm-300nm.

6. The method for preparing a silicon substrate according to any one of claims 1 to 5, characterized in that: Before S1, the following step further includes: sequentially performing a pre-cleaning process, an RCA cleaning process, and a drying process on the initial silicon substrate; Wherein, the pre-cleaning treatment comprises: performing a first cleaning treatment on the initial silicon substrate using a first solution, and then performing a second cleaning treatment on the initial silicon substrate using a second solution; The first solution comprises: 1-15wt% alkali solution, 1-15wt% hydrogen peroxide, the temperature of the first solution is 45-65°C, and the time of the first cleaning treatment is 1-4min; The second solution comprises: 0.1-10 wt % of alkaline solution, the temperature of the second solution is 45-80° C., and the time of the second cleaning treatment is 0.5-4 min.

7. The method for preparing a silicon substrate according to any one of claims 1 to 5, characterized in that: The alkali etching treatment comprises: using 1-5% by mass alkali solution for alkali etching treatment.

8. The method for preparing a silicon substrate according to claim 7, characterized in that: The temperature of the alkali etching treatment is 40-80° C., and the time of the alkali etching treatment is 60-300 seconds.

9. The method for preparing a silicon substrate according to any one of claims 1 to 5, characterized in that: S4 also includes: The first intermediate mask layer and the second intermediate mask layer are removed respectively using hydrofluoric acid with a mass percentage of 0.001-38%.

10. A method for preparing a heterojunction solar cell, characterized in that: include: Prepare a silicon substrate using the method for preparing a silicon substrate according to any one of claims 1 to 9; A first passivation layer is provided on the first velvet surface of the silicon substrate, and a second passivation layer is provided on the surface where the second velvet surface of the silicon substrate is located; A first doping layer is disposed on a surface of the first passivation layer away from the silicon substrate, and a second doping layer is disposed on a surface of the second passivation layer away from the silicon substrate, wherein the first doping layer and the second doping layer have opposite conductivity types; A first transparent conductive film is disposed on a surface of the first doped layer away from the silicon substrate, and a second transparent conductive film is disposed on a surface of the second doped layer away from the silicon substrate; An electrode is arranged on the surface of the first transparent conductive film away from the silicon substrate, and an electrode is arranged on the surface of the second transparent conductive film corresponding to the second velvet surface away from the silicon substrate to obtain the heterojunction solar cell.

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