Preparation process of stable oxide layer of TOPCon battery

Abstract

The invention relates to a preparation process of a stable oxide layer of a TOPCon battery. The preparation process comprises the following steps: S01, pre-cleaning; s02, washing with water; s03, alkali polishing is conducted; s04, hydrogen peroxide alkali washing; s05, acid pickling; s06, hydrogen peroxide oxidation washing; s07, carrying out slow lifting; s08, performing drying; and S09, measuring the thickness of the oxide layer. The invention provides a novel oxide layer preparation step, specifically, an oxide layer on the back surface of a silicon wafer is completely removed through HF acid with a certain concentration during acid pickling, the effects of removing impurities of the silicon wafer and dehydrating the silicon wafer are achieved, then hydrogen peroxide is used for oxidizing the silicon wafer again, and a brand-new oxide layer grows. The cleaning defects in traditional preparation steps can be avoided, and the problems of poor cleaning effect, poor dehydration effect and poor oxide layer quality are fundamentally solved.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic technology, and in particular to a process for preparing a stable oxide layer of a TOPCon battery. Background Art

[0002] In recent years, with the continuous development of technology, the n-type tunnel oxide passivated contact (TOPCon) solar cell has accelerated its iteration with its technical advantages such as high mass production efficiency, high bifaciality, lower temperature coefficient, and lower light-induced degradation, and has basically replaced the selective emitter passivated back contact (PERC) solar cell and become the mainstream battery technology. The main structure of the TOPCon cell structure is to make an ultra-thin tunnel oxide layer on the back surface of the silicon wafer, and then superimpose a phosphorus-doped polysilicon layer to form a film layer that can be selectively penetrated by majority carriers, thereby improving the short-circuit current, open-circuit voltage and conversion efficiency of the solar cell.

[0003] At present, the preparation methods of the tunneling oxide layer of Topcon solar cells mainly include thermal oxidation, nitric acid oxidation, hydrogen peroxide oxidation, ozone oxidation, etc. Among them, the method of preparing the oxide layer by hydrogen peroxide oxidation is usually completed during the alkali polishing process. The traditional process flow is: pre-cleaning, water washing, alkali polishing, water washing, hydrogen peroxide oxidation, water washing, acid washing, water washing, slow pulling, and drying. In order to protect the wet oxide layer, the acid washing process selects HF-free pure HCL or micro HF plus HCL solutions. Among them, the method of cleaning with HF-free pure HCL will result in poor slow pulling and dehydration effect, and water vapor is easily left on the silicon wafer, resulting in poor EL. The method of cleaning with trace HF+HCL has a large change in the thickness of the retained oxide layer due to the influence of HF concentration. The uniformity of the oxide layer and the controllability of the film thickness are poor, which affects the efficiency and yield of the battery cell. Summary of the invention

[0004] The purpose of the present invention is to provide a TOPCon battery stable oxide layer preparation process, which can avoid the cleaning defects in the traditional preparation steps and fundamentally solve the problems of poor cleaning effect, poor dehydration effect and oxide layer quality.

[0005] The present invention achieves the above-mentioned purpose through the following technical scheme: A process for preparing a stable oxide layer of a TOPCon battery, comprising the following steps:

[0006] S01, pre-cleaning;

[0007] S02, washing;

[0008] S03, alkali polishing;

[0009] S04, hydrogen peroxide alkaline washing;

[0010] S05, pickling;

[0011] S06, hydrogen peroxide oxidation washing;

[0012] S07, slow pull;

[0013] S08, drying;

[0014] S09. Oxide layer thickness measurement.

[0015] Furthermore, the S01 is specifically for removing the acidic liquid remaining in the previous BSG process.

[0016] Furthermore, the S02 specifically refers to each water washing step, which is to remove the chemical liquid remaining in the previous step.

[0017] Furthermore, the S03 is specifically to use a mixture of additives, alkali and water to polish the back surface of the silicon wafer, and remove the back surface and edge PN junctions by etching and polishing.

[0018] Furthermore, the S04 is specifically to remove additive residues.

[0019] Furthermore, the S05 specifically includes: completely removing the back oxide layer produced during the previous hydrogen peroxide alkaline washing, removing the alkali remaining on the surface of the silicon wafer, and removing metal ions.

[0020] Furthermore, the S06 is specifically to prepare a new oxide layer on the surface.

[0021] Furthermore, the S07 is specifically a pre-dehydration treatment.

[0022] Furthermore, the step S08 is specifically to dry the silicon wafer at a high temperature of 80 to 100°C.

[0023] Furthermore, the S09 is specifically to control the thickness of the oxide layer to be 1.1-1.3 nm, and the thickness difference within a single chip is less than 0.2 nm.

[0024] Compared with the prior art, the beneficial effects of the TOPCon battery stable oxide layer preparation process of the present invention are: a new oxide layer preparation step is proposed, specifically, a certain concentration of HF acid is used during pickling to completely remove the oxide layer on the back surface of the silicon wafer, so as to achieve the effect of removing impurities and dehydrating the silicon wafer, and then hydrogen peroxide is used to re-oxidize the silicon wafer to grow a new oxide layer. The cleaning defects in the traditional preparation steps can be avoided, and the problems of poor cleaning effect, poor dehydration effect and oxide layer quality are fundamentally solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flower basket printing effect diagram of the present invention.

[0026] Figure 2This is a watermark effect diagram of the present invention. DETAILED DESCRIPTION

[0027] Example

[0028] A TOPCon battery stable oxide layer preparation process, the steps are:

[0029] S01, pre-cleaning: remove the acid solution remaining in the previous BSG process;

[0030] S02, water washing: Each water washing step is to remove the residual chemical liquid from the previous process;

[0031] S03, alkali polishing: Use a mixture of additives, alkali and water to polish the back surface of the silicon wafer, and remove the back and edge PN junctions by etching and polishing;

[0032] S04, hydrogen peroxide alkaline washing: remove additive residues;

[0033] S05, pickling: completely remove the back oxide layer produced during the previous hydrogen peroxide alkaline washing, remove the alkali remaining on the surface of the silicon wafer, and remove metal ions;

[0034] S06, hydrogen peroxide oxidation washing: re-prepare a new oxide layer on the surface;

[0035] S07, slow pulling: pre-dehydration treatment;

[0036] S08, drying: drying the silicon wafer at a high temperature of 80-100°C;

[0037] S09. Measure the oxide layer thickness, control the oxide layer thickness at 1.1-1.3nm, and the thickness difference within a single piece is less than 0.2nm.

[0038] Comparative Example 1

[0039] Traditional pickling is a pure HCL process without HF, and the steps are as follows:

[0040] 1. Pre-cleaning: remove the acid solution remaining in the previous BSG process;

[0041] 2. Water washing: Each water washing is to remove the residual chemical liquid from the previous process;

[0042] 3. Alkali polishing: Use a mixture of additives, alkali and water to polish the back surface of the silicon wafer, and remove the back and edge PN junctions by etching and polishing;

[0043] 4. Hydrogen peroxide oxidation: remove additive residues and prepare an oxide layer;

[0044] 5. Pickling: completely retain the back oxide layer produced by the previous hydrogen peroxide alkaline washing, remove the residual alkali on the surface of the silicon wafer, and remove the metal ions;

[0045] 6. Slow pulling: pre-dehydration treatment;

[0046] 7. Drying: Dry the silicon wafer at a high temperature of 80-100°C;

[0047] 8. Measure the oxide layer thickness and control the oxide layer thickness to be between 1.1-1.3nm. The thickness difference within a single film is less than 0.2nm.

[0048] Comparative Example 2

[0049] Traditional pickling is a process of adding trace HF and HCL, the steps are:

[0050] 1. Pre-cleaning: remove the acid solution remaining in the previous BSG process;

[0051] 2. Water washing: Each water washing is to remove the residual chemical liquid from the previous process;

[0052] 3. Alkali polishing: Use a mixture of additives, alkali and water to polish the back surface of the silicon wafer, and remove the back and edge PN junctions by etching and polishing;

[0053] 4. Hydrogen peroxide oxidation: remove additive residues and prepare an oxide layer;

[0054] 5. Pickling: Partially retain the back oxide layer produced during the previous hydrogen peroxide alkaline washing, remove the residual alkali on the surface of the silicon wafer, and remove metal ions;

[0055] 6. Slow pulling: pre-dehydration treatment;

[0056] 7. Drying: Dry the silicon wafer at a high temperature of 80-100°C;

[0057] 8. Measure the oxide layer thickness and control the oxide layer thickness to be between 1.1-1.3nm. The thickness difference within a single film is less than 0.2nm.

[0058] Experimental comparison results

[0059] Table 1 Oxide layer thickness and thickness difference between the embodiment and the comparative example

[0060] type Film thickness / nm Single film thickness difference / nm Comparative Example 1 1.1-1.3 0.05 Comparative Example 2 1.1-1.3 0.07 Example 1.1-1.3 0.03

[0061] Table 2 EL data comparison table of the embodiment and the comparative example

[0062] type OK Flower basket print Watermark Comparative Example 1 90.5 4.8 1.5 Comparative Example 2 97.9 0.4 0.09 Example 99.3 0 0

[0063] Table 3 Comparison of electrical properties of embodiments and comparative examples

[0064]

[0065] From Comparative Example 1, Comparative Example 2, and Example 1 to Table 3, it can be seen that the solution of the present application can completely solve the EL problems such as flower basket print and watermark. The flower basket print effect diagram of the present invention is shown in the attached Figure 1 , the watermark effect diagram of the present invention is shown in the attached Figure 2 The oxide layer has better uniformity, the open circuit voltage and short circuit current are better, and the efficiency is improved by 0.04-0.07% compared with the pure HCl pickling process and the HCl plus trace HF pickling process.

[0066] The present invention proposes a novel oxide layer preparation step, specifically, during pickling, a certain concentration of HF acid is used to completely remove the oxide layer on the back surface of the silicon wafer, so as to achieve the effect of removing impurities from the silicon wafer and dehydrating the silicon wafer, and then hydrogen peroxide is used to re-oxidize the silicon wafer to grow a new oxide layer. The specific steps are pre-cleaning, water washing, alkali polishing, water washing, hydrogen peroxide alkali washing, water washing, acid washing, water washing, hydrogen peroxide oxidation washing, slow pulling, and drying, which can avoid the cleaning defects in the traditional preparation steps and fundamentally solve the problems of poor cleaning effect, poor dehydration effect and oxide layer quality.

[0067] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0068] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A process for preparing a stable oxide layer of a TOPCon battery, characterized in that: The steps are: S01, pre-cleaning; S02, washing; S03, alkali polishing; S04, hydrogen peroxide alkaline washing; S05, pickling; S06, hydrogen peroxide oxidation washing; S07, slow pull; S08, drying; S09. Oxide layer thickness measurement.

2. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S01 is specifically to remove the acidic liquid remaining in the previous BSG process.

3. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S02 specifically refers to each water washing step, which is to remove the residual chemical liquid from the previous step.

4. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S03 is specifically to use a mixture of additives, alkali and water to polish the back surface of the silicon wafer, and remove the back and edge PN junctions by etching and polishing.

5. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S04 is specifically to remove the residual additives.

6. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S05 specifically includes: completely removing the back oxide layer produced during the previous hydrogen peroxide alkaline washing, removing the alkali remaining on the surface of the silicon wafer, and removing metal ions.

7. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S06 is specifically to prepare a new oxide layer on the surface.

8. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S07 is specifically a pre-dehydration process.

9. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The step S08 is specifically to dry the silicon wafer at a high temperature of 80 to 100°C.

10. The process for preparing a stable oxide layer of a TOPCon battery according to claim 1, characterized in that: The S09 is specifically to control the oxide layer thickness to be between 1.1 and 1.3 nm, and the thickness difference within a single wafer is less than 0.2 nm.

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