CN111599895A - Preparation method of crystalline silicon solar passivated contact cell - Google Patents

Abstract

A preparation method of a crystalline silicon solar passivated contact cell belongs to the field of solar cells. The preparation method comprises the following steps: manufacturing a tunneling layer on the back of the N-type crystalline silicon to obtain a first structure body; manufacturing an n + doped polycrystalline silicon passivation layer on the back surface of the tunneling layer, and then etching the edge and the front surface to obtain a second structural body; carrying out P + doping on the front surface of the second structure body to manufacture a P-type layer, and then carrying out edge and back etching to obtain a third structure body; manufacturing a passivation film on the front surface of the third structure body to obtain a fourth structure body; respectively manufacturing antireflection films on the front surface and the back surface of the fourth structural body to obtain a fifth structural body; electrodes are formed on the front and back surfaces of the fifth structure body, respectively. The battery has simple manufacturing process and high photoelectric efficiency.

Description

A kind of preparation method of crystalline silicon solar energy passivation contact cell

technical field

The present application relates to the field of solar cells, and in particular, to a method for preparing a crystalline silicon solar passivation contact cell.

Background technique

In recent years, as a green and environmentally friendly energy technology, crystalline silicon solar power has developed rapidly, and various new crystalline silicon technologies have emerged one after another.

At present, Passivated Emitter and RearCell (PERC for short) is mainly used in the market. The photoelectric conversion efficiency of mainstream PERC solar cells can exceed 22%. However, the conversion efficiency of PERC solar cells will be more limited. Therefore, a technique called passivation contact was developed, which can be used to further improve the photoelectric conversion efficiency of the cell. Passivation contact technology is highly compatible with existing PERC technology, so it is more and more favored by the market and various research institutions.

However, in the practice of the existing passivation contact technology, the solar cell is prone to failure.

SUMMARY OF THE INVENTION

In view of the above deficiencies, the present application provides a method for preparing a crystalline silicon solar passivation contact cell, so as to partially or fully improve or even solve the problems in the related art.

This application is implemented like this:

In a first aspect, examples of the present application provide a method of fabricating a crystalline silicon solar passivation contact cell. The method includes: forming a tunneling layer on the back of N-type crystalline silicon to obtain a first structure; forming an n+ doped polysilicon passivation layer on the back of the tunneling layer, and then performing edge and front etching to obtain a second structure ; Carry out p+ doping on the front of the second structure to make a P-type layer, and then perform edge and back etching to obtain a third structure; Make a passivation film on the front of the third structure to obtain a fourth structure; respectively; Antireflection films are formed on the front and back of the fourth structure to obtain a fifth structure; electrodes are respectively formed on the front and back of the fifth structure.

In combination with the first aspect, in a first possible implementation manner of the first aspect of the present application, the material of the tunneling layer is silicon dioxide.

In combination with the first aspect, in a second possible implementation manner of the first aspect of the present application, the tunneling layer is fabricated by thermal oxidation, ozone, wet oxidation or atomic layer deposition.

In combination with the first aspect or the first or second embodiment of the first aspect, in a third possible implementation of the first aspect of the present application, the thickness of the tunneling layer is 0.5 nanometers to 3 nanometers.

With reference to the first aspect, in a fourth possible implementation manner of the first aspect of the present application, making an n+ doped polysilicon passivation layer includes making a polysilicon film and n+ doping, and the polysilicon film is formed by low pressure chemical vapor deposition, plasma Volume enhanced chemical vapor deposition is performed, and n+ doping is performed by low pressure ion implantation or thermal diffusion; alternatively, p+ doping is performed by low pressure ion implantation or thermal diffusion.

In combination with the first aspect or the four embodiments of the first aspect, in a fifth possible implementation of the first aspect of the present application, the thickness of the n+ doped polysilicon passivation layer is 20 nanometers to 300 nanometers.

With reference to the first aspect, in a sixth possible implementation manner of the first aspect of the present application, the surface square resistance of the P-type layer is 80 ohms/□ to 300 ohms/□.

With reference to the first aspect, in a seventh possible implementation manner of the first aspect of the present application, the material of the passivation film is aluminum oxide, and/or the material of the anti-reflection film is silicon nitride.

In combination with the first aspect, in an eighth possible implementation manner of the first aspect of the present application, the edge and front side etching, and the edge and back side etching are independently performed by chemical wet etching or dry etching, respectively.

In a second aspect, examples of the present application provide a method of fabricating a crystalline silicon solar passivation contact cell. The battery includes: a base body and upper and lower electrodes respectively located on the top surface and bottom surface of the base body; the base body includes N-type crystalline silicon, a front surface structure and a back surface structure respectively located on the front surface and back surface of the base body; p+-doped p-type layer, aluminum oxide passivation film, silicon nitride anti-reflection film; the backside structure includes silicon dioxide tunneling layer, n+-doped polysilicon passivation layer, nitrided Silicon anti-reflection coating.

The above-mentioned preparation method includes: before fabricating the p+-doped p-type layer, firstly fabricating the silicon dioxide tunneling layer and the n+-doped polysilicon passivation layer in sequence.

In the above implementation process, in the preparation method of the crystalline silicon solar passivation contact cell provided by the embodiment of the present application, in the passivation contact cell, doped polysilicon is firstly plated on the back side, and then boron diffusion is performed on the front side. Such a process can effectively avoid the problem of wrapping plating, and can also improve the photoelectric conversion efficiency of the solar cell.

Description of drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art.

1 is a schematic structural diagram of a crystalline silicon solar passivation contact cell prepared by the method in the example of the application;

Fig. 2 shows a known process flow chart for making the crystalline silicon solar passivation contact cell of Fig. 1;

FIG. 3 shows another process flow diagram of manufacturing the crystalline silicon solar passivation contact cell of FIG. 1 in an example of the present application.

Icon: 100-solar cell; 101-lower electrode; 102-silicon nitride antireflection film; 103-polysilicon passivation layer; 104-silicon dioxide tunneling layer; 105-N-type crystalline silicon; 106-doped P type layer; 107-alumina passivation film; 108-silicon nitride antireflection film; 109-top electrode; 201-substrate; 202-PN junction; 203-front structure; 204-back structure.

Detailed ways

The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not indicated in the examples, it is carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used without the manufacturer's indication are conventional products that can be purchased from the market.

The following is a specific description of the preparation method of the crystalline silicon solar passivation contact cell of the embodiment of the present application:

Crystalline silicon solar passivation contact cell is a solar cell based on PN junction using silicon material and combined with passivation contact technology. Usually, N-type crystalline silicon is used as the substrate, and a PN junction is formed by doping on the front side, and then corresponding subsequent operations are performed to fabricate various functional layers on the front side and the back side. For example, where the PN junction is implemented as a passivation contact scheme, a relatively thin oxide film is made, which acts as a tunneling layer. At the same time, it also has a polysilicon layer cooperating with the tunneling layer, which serves as a passivation layer. The combination of the tunneling layer and the passivation layer can hinder the recombination of the minority carriers and allow the separation of the majority carriers at the same time. Through such a solution, the photoelectric conversion efficiency can be improved to a certain extent. However, the current type of batteries often show low efficiency (lower than design expectations) during use, and have a relatively short service life or even failure.

In order to facilitate the understanding of the preparation method of the crystalline silicon solar passivation contact cell proposed in this application, in the example, the inventor presents a crystalline silicon solar passivation contact cell (hereinafter referred to as solar cell 100 ) and its craftsmanship.

The structure of the solar cell 100 is shown in FIG. 1 , which is based on an N-type crystalline silicon 105 , and a PN junction 202 is formed by a p+-doped P-type layer 106 on the front side.

In general, the solar cell 100 includes a substrate 201 and upper and lower electrodes 109 and 101 on top and bottom surfaces thereof.

Wherein, the base body includes N-type crystalline silicon 105, a front side structure 203 and a back side structure 204 located on the front side and back side respectively.

The front structure 203 includes a p+ doped P-type layer 106 , an aluminum oxide passivation film 107 , and a silicon nitride antireflection film 108 that are stacked in sequence. The backside structure 204 includes a silicon dioxide tunneling layer 104 , an n+ doped polysilicon passivation layer 103 , and a silicon nitride antireflection film 102 that are stacked in sequence.

The manufacturing process flow of the solar cell 100 is shown in FIG. 2 and includes the following steps.

Step S10. Cleaning and texturing

First, the substrate is cleaned and textured. For example, the substrate can be cleaned and textured with an acid solution (such as a mixed acid of HF and HNO ₃ ), an alkaline solution (such as a sodium hydroxide or potassium hydroxide solution) to remove metal ions on the surface of the substrate silicon wafer and cut Damage layer and form wormhole-like suede or pyramid-like suede. Alternatively, electrochemical texturing, reactive ion etching, laser texturing, mask texturing, and the like can also be used.

The surface impurities and defects (such as residues) of the silicon wafer can be removed by cleaning, and the surface can be roughened by texturing, thereby forming a light trapping structure, which can improve the incidence of light.

During the texturing process, the front surface of the substrate forms a rough surface structure through the texturing. Therefore, the subsequent P-type layer on the front, the aluminum oxide passivation film on the front and the nitrogen on the front are subsequently fabricated on the front. The silicide anti-reflection films all have similar textured structures, such as the aforementioned pyramid textured textures.

Step S11. Front Boron Diffusion

Boron element is diffused into the substrate by means of thermal diffusion or ion implantation, thereby forming a P-type surface (p+-doped P-type layer) doped with phosphorus, and forming a PN junction.

Step S12. Backside cleaning

The backside of the PN junction, that is, the side surface of the base silicon wafer away from the N-type surface, is cleaned.

Step S13. Backside plating SiO ₂ and doped polysilicon

On the above-mentioned back surface after cleaning, SiO ₂ is fabricated by thermal oxidation, ozone, wet oxidation or atomic layer deposition (Atomic Layer Deposition, ALD) to form a silicon dioxide tunneling layer. Then, a polysilicon film is formed on the bottom surface of the silicon dioxide tunneling layer (the surface away from the substrate) by low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical VaporDeposition, PECVD). , and then doped with phosphorus by means of ion implantation or thermal diffusion to form an n+ doped polysilicon passivation layer.

Step S14. Edge and Front Etching

Since in step S13, phosphorus doping of the polysilicon on the backside is performed, a phosphorus-doped structure will also be formed on the side (edge) and front surface of the substrate. Therefore, in order to avoid phosphorus doping on the side, the chemical wet method or Dry etching removes the doped layer. As a result, only the phosphorus doping at the bottom remains.

Step S15. Al ₂ O ₃ plating on the front side

After etching, aluminum oxide is deposited on the front side by thermal oxidation, ozone or wet oxidation or atomic layer deposition, etc., to form an aluminum oxide passivation film.

Step S16. Front/Back SiNx

A silicon nitride film is respectively formed on the aluminum oxide passivation film and the n+-doped polysilicon passivation layer by means of plasma enhanced chemical vapor deposition to form a silicon nitride anti-reflection film.

Step S17. Front/back electrode printing and sintering

Through the above steps, the substrate of the crystalline silicon solar cell with passivation contact technology is fabricated, and then the grid finger-shaped metal material is fabricated by screen printing, and then the upper electrode and the lower electrode are formed by sintering. The battery obtained according to this example can achieve Voc performance of 697.0 mV, Jsc performance of 40.3 A, FF performance of 81.4%, and Eff performance of 22.86%.

Experiments show that the crystalline silicon solar passivation contact cell fabricated through the above steps has the problem of easy failure. In-depth investigation of the reason, the inventor found that: since the diffusion coefficient of phosphorus is larger than that of boron, in the above-mentioned phosphorus doping process (step S13 ), the doping of phosphorus on the front side will destroy the previous processes (steps S10 and S11 ). ) in the PN junction formed by the P-type thin layer (ie, p+ doped P-type layer), correspondingly, the PN will be destroyed, resulting in low efficiency or even failure of the solar cell.

In view of the above problems, the inventor tried to coat a protective film on the front-side emitter (in the PN junction, the base silicon wafer is the base, and the doped layer with the opposite polarity to the base is the emitter), such as SiNx, SiC, etc. Due to the existence of the protective film, when the backside is doped, the protective film can prevent the doping of the emitter. Therefore, after the N+-doped polysilicon on the back is plated, the protective film on the front is washed off. This process can effectively avoid the damage to the front PN junction caused by phosphorus wrapping. However, this requires additional coating and cleaning processes, which increases the manufacturing cost of solar cells and is not conducive to the application and development of passivation contact cell technology.

In view of this, the present application provides a novel technical solution to improve or even solve the above problems. This new technical solution can realize another solution different from the above-mentioned technology while applying the passivation contact technology (in the example, Tunnel Oxide Passivated Contact, TOPCon). It can not only apply passivation contact technology in crystalline silicon solar cells, but also avoid the problem of phosphorus wrapping during the process, thereby avoiding the damage to the front PN junction, and at the same time avoiding the introduction of more process steps. That is, with a relatively simpler preparation process, the crystalline silicon solar passivation contact cell can be fabricated, and the photoelectric conversion efficiency can be improved.

On the whole, the solution exemplified in this application is used for the first time in a passivation contact cell: firstly, doped polysilicon is plated on the back side, and then the front side boron is diffused to prepare the cell, which completely subverts the traditional process technology route. In this process, since phosphorus-doped polysilicon on the backside is prepared first (at this time, the PN junction has not yet been formed on the front side), even if phosphorus is plated around the front side during the doping process, it will not destroy the PN junction. In addition, since the diffusion coefficient of boron is much smaller than that of phosphorus, the n+-doped polysilicon on the backside will not be damaged during the boron diffusion process on the front side.

For the preparation method of the crystalline silicon solar passivation contact cell in the example of the present application, please refer to FIG. 3 .

Step S300. Cleaning and texturing; Step S301. Plating SiO ₂ on the back and doped polysilicon; Step S302. Etching the edge and front; Step S303. Diffusion of boron on the front; Step S304. Etching the edge and back; Al ₂ O ₃ ; Step S306. Front/back SiNx; Step S307. Front/back electrode printing and sintering. The above steps can be performed through existing semiconductor processes, such as the specific process methods mentioned above in the process route shown in FIG. 2 , such as thermal oxidation, low pressure chemical vapor deposition, ion implantation, and the like.

The SiO ₂ and the doped polysilicon (n+ doped, ie heavily doped n-type) formed in the above step S301 together constitute the tunnel oxide passivation contact. The tunneling oxide is silicon dioxide, which can be called a tunneling layer, a passivation tunneling layer or a passivation oxide layer. Due to the thin thickness of the silicon dioxide layer, the passage of minority carriers can be prevented, while the multi-carriers can be passed through through the tunneling effect. Silica can significantly inhibit the recombination of the backside (metal/lower electrode contact area) and thus has an outstanding passivation effect.

With reference to Fig. 2 and Fig. 3, it can be found that the overall process steps of the improved solution proposed in the present application (the solution in Fig. 3) are roughly equivalent compared with the known solution implemented by the inventor (the solution in Fig. 2), and Not significantly increased. The main difference between the two is the process steps defined by the dashed boxes in FIG. 3 .

Alternatively, the preparation method exemplified in this application can also be explained by the following description:

A tunnel layer is formed on the backside of the cleaned and textured N-type crystalline silicon (the backside is plated with SiO ₂ ) to obtain a first structure. The thickness of the tunneling layer is 0.5 nm to 3 nm.

An n+-doped polysilicon passivation layer (doped polysilicon) is formed on the backside of the tunneling layer, followed by edge and front side etching to obtain a second structure. The thickness of the n+ doped polysilicon passivation layer is significantly larger than the thickness of the tunneling layer (20nm-300nm).

On the front side of the second structure, p+ doping is performed (boron diffusion on the front side) to form a P-type layer to form a PN junction, and then edge and backside etching is performed to obtain a third structure. After boron diffusion on the front side, the surface resistance of the formed P-type layer is 80 ohms/square to 300 ohms/square, that is, its diffusion square resistance.

A passivation film was formed on the front surface of the third structure (the front surface was plated with Al ₂ O ₃ ) to obtain a fourth structure.

Antireflection films were formed (SiNx plated) on the front and back surfaces of the fourth structure, respectively, to obtain a fifth structure. Electrodes were fabricated (printed and sintered) on the front and back of the fifth structure, respectively.

The battery obtained according to this example can achieve Voc performance of 710.2mV, Jsc performance of 40.2A, FF performance of 81.6%, and Eff performance of 23.30%.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (10)

1. a preparation method of crystalline silicon solar energy passivation contact cell, is characterized in that, comprises: A tunneling layer is formed on the backside of the N-type crystalline silicon to obtain a first structure; An n+-doped polysilicon passivation layer is formed on the backside of the tunneling layer, followed by edge and frontside etching to obtain a second structure; Perform p+ doping on the front side of the second structure to form a P-type layer, and then perform edge and backside etching to obtain a third structure; A passivation film is formed on the front surface of the third structure to obtain a fourth structure; respectively making anti-reflection films on the front and back of the fourth structure to obtain a fifth structure; Electrodes are fabricated on the front and back surfaces of the fifth structure, respectively. 2 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein the material of the tunneling layer is silicon dioxide. 3 . 3 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein the tunneling layer is fabricated by thermal oxidation, ozone, wet oxidation or atomic layer deposition. 4 . 4 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein the tunneling layer has a thickness of 0.5 nanometers to 3 nanometers. 5 . 5 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein making the n+ doped polysilicon passivation layer comprises making a polysilicon film and n+ doping, and the polysilicon film passes through the Low pressure chemical vapor deposition, plasma enhanced chemical vapor deposition are implemented, and the n+ doping is implemented by low pressure ion implantation or thermal diffusion; Alternatively, the p+ doping is performed by low pressure ion implantation or thermal diffusion. 6 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 or 5 , wherein the n+ doped polysilicon passivation layer has a thickness of 20 nanometers to 300 nanometers. 7 . 7 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein the surface square resistance of the P-type layer is 80 ohms/□ to 300 ohms/□. 8 . 8. The method for preparing a crystalline silicon solar passivation contact cell according to claim 1, wherein the material of the passivation film is aluminum oxide, and/or the material of the antireflection film is nitride silicon. 9 . The method for preparing a crystalline silicon solar passivation contact cell according to claim 1 , wherein the edge and front etching, the edge and the back etching are independently performed by chemical wet etching or dry etching. 10 . Etching is performed. 10. A method for preparing a crystalline silicon solar passivation contact cell, the cell comprising: a base body and an upper electrode and a lower electrode respectively located on a top surface and a bottom surface of the base body; the base body comprises N-type crystalline silicon and The front side structure and the back side structure on its front side and back side; the front side structure comprises p+ doped p-type layer, aluminum oxide passivation film, silicon nitride antireflection film which are stacked in sequence; the back side structure It includes a silicon dioxide tunneling layer, an n+-doped polysilicon passivation layer, and a silicon nitride anti-reflection film that are stacked in sequence, wherein the preparation method includes: Before forming the p+-doped P-type layer, the silicon dioxide tunneling layer and the n+-doped polysilicon passivation layer are sequentially formed.

Images