Smoothing modification method for crystalline silicon solar cells and smoothing modification liquid therefor

Abstract

The present invention discloses a method for smoothly modifying a crystalline silicon solar cell and a smooth modification liquid thereof. The textured crystalline silicon wafer is placed in the smooth modification liquid and etched at a temperature of 8°C to 40°C for 15 s to 180 s. The top and bottom positions of the pyramid morphology structure of the crystalline silicon wafer are etched and modified into a smooth transition structure, which is beneficial to the deposition of the passivation film and reduces the recombination at the junction of the tip and the bottom. The method for smoothly modifying a crystalline silicon solar cell provided by the present invention has a simple process. The modified pyramid structure is more conducive to the conformal deposition of the thin film. The reflectivity of the modified pyramid increases by less than 1%. At the same time, the optical and electrical properties of the battery are taken into account. At the same time, the smooth modification liquid used does not contain nitrogen, effectively avoiding the emission of nitric acid in the prior art smooth treatment liquid, having a low waste liquid treatment cost, a small environmental protection pressure, and a low cost of the raw material chemical liquid, being easy to obtain, reducing the production cost and also reducing the environmental pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline silicon solar cells, and particularly relates to a method for rounding and modifying a crystalline silicon solar cell and a rounding and modifying solution therefor. Background Art

[0002] High efficiency and low cost have always been the driving forces for the development of solar cells. High-efficiency crystalline silicon solar cells have always occupied the mainstream of the photovoltaic power generation market. Heterojunction solar cells have the characteristics of high conversion efficiency, low cost per degree of electricity, simple process flow, no attenuation, and high bifaciality, and are one of the development directions of high-efficiency crystalline silicon cells.

[0003] Texturing is the first process in the crystalline silicon solar cell process, and a good textured surface structure plays a crucial role in subsequent processes. Usually, single-crystalline silicon solar cells use anisotropic etching of alkali to prepare a regular pyramid structure, which increases the number of reflections of light on the silicon wafer surface and greatly reduces the surface reflectivity. However, the tips and bottoms of the pyramids are relatively sharp, and a large number of defects are likely to occur at the tips and bottoms during subsequent thin film deposition, resulting in battery leakage and thus affecting the conversion efficiency of the solar cell.

[0004] For heterojunction solar cells, the currently common method in the industry is to use a mixed solution of hydrofluoric acid and nitric acid to etch the pyramid textured surface, and round the tips and bottoms of the pyramids, which is beneficial to subsequent conformal deposition of thin films and reduces recombination. In addition, the rounded pyramid textured surface can reduce the risk of the pyramid tips being worn off due to silicon wafer friction.

[0005] The existing rounding process requires the preparation of nitric acid with a concentration of 50%-80%, and the chemical cost is relatively high. The waste water in nitric acid contains a large amount of nitrogen elements, which causes great pressure on environmental protection, and the treatment of nitrogen-containing waste acid is relatively high. On the other hand, the reaction rate of the HF / HNO 3 mixed solution is relatively fast, and generally the reaction rate needs to be controlled by reducing the reaction temperature to 8°C. On the other hand, the reflectivity of the silicon wafer after rounding treatment will increase by more than 1%, reducing the short-circuit current. Summary of the Invention

[0006] Aiming at the above deficiencies, the purpose of the present invention is to provide a method for rounding and modifying a crystalline silicon solar cell and a rounding and modifying solution therefor, which have a simple process, controllable reflectivity, can round the top and bottom of the pyramid, and the reflectivity of the crystalline silicon wafer surface does not increase significantly, reducing recombination while taking into account the reflectivity.

[0007] To achieve the above purpose, the technical solution provided by the present invention is:

[0008] A method for rounding and modifying a crystalline silicon solar cell, which comprises the following steps:

[0009] (1) The crystalline silicon wafer after pre-texturing, the textured surface of the crystalline silicon wafer has a pyramid morphology structure, the bottom side length of the pyramid morphology structure is 1-10 microns, and the height is 0.7-7 microns;

[0010] (2) Prepare a smoothing modifier: Mix a fluoride ion source, a chlorine-containing ion source, an oxidant and deionized water to obtain a smoothing modifier, wherein the concentration of the fluoride ion source is 0.1 mol / L - 8 mol / L, the concentration of the chlorine-containing ion source is 0.01 mol / L - 13 mol / L, and the concentration of the oxidant is 0.01 mol / L - 3 mol / L;

[0011] (3) Smoothing modification: Place the textured crystalline silicon wafer in the smoothing modifier, etch at a temperature of 8°C - 40°C for 15 s - 180 s, preferably etch at a temperature of 15°C - 30°C for 30 s - 90 s, which can etch and modify the top and bottom positions of the pyramid morphology structure of the crystalline silicon wafer into a smooth transition structure, which is beneficial to subsequent thin film deposition and reduces the carrier recombination at the junction of the tip and the bottom. The surface reflectivity of the modified silicon wafer does not increase significantly, and the reflectivity increase is less than 1%, taking into account the reflectivity while reducing recombination. The modified inverted pyramid structure is beneficial to the conformal deposition of subsequent thin films, thereby improving the performance of solar cells.

[0012] As a preferred embodiment of the present invention, the crystalline silicon wafer is a P-type silicon wafer or an N-type silicon wafer.

[0013] As a preferred embodiment of the present invention, after the smoothing modification is completed, the etching depth at the top of the pyramid morphology structure and the junction of the bottoms of two adjacent pyramid morphology structures is 10 nm - 100 nm.

[0014] As a preferred embodiment of the present invention, the fluoride ion source is selected from hydrofluoric acid.

[0015] As a preferred embodiment of the present invention, the chlorine-containing ion source is selected from hydrochloric acid, sodium hypochlorite, sodium chlorite, chlorine dioxide, chlorine gas, sodium chlorate or sodium perchlorate.

[0016] As a preferred embodiment of the present invention, the oxidant is selected from one or more of sodium persulfate, hydrogen peroxide, acetic acid, peracetic acid, potassium permanganate, concentrated sulfuric acid.

[0017] As a preferred embodiment of the present invention, an additive is further added in the step (2), and the mass ratio of the additive to the smoothing modifier is 0.2 - 5:100. After adding the additive, the smoothing modification process can be made more stable and the smoothing modification effect can be improved.

[0018] As a preferred embodiment of the present invention, the additive is composed of the following components in proportion by weight: 0.1 to 5 parts by weight of benzyltrimethylammonium chloride, 1 to 3 parts by weight of sodium citrate, 0.5 to 3 parts by weight of guar gum, and 100 parts by weight of water.

[0019] As a preferred embodiment of the present invention, the additive is a mixture of one or more of benzyltrimethylammonium chloride, sodium citrate and guar gum.

[0020] A rounding modification liquid used in a rounding modification method for a crystalline silicon solar cell has a reasonable formula, does not contain nitrogen, has low waste liquid treatment cost, has low environmental pressure, has low chemical liquid cost, and reduces production cost.

[0021] The beneficial effects of the present invention are as follows: the method for rounding modification of crystalline silicon solar cells provided by the present invention has a simple process and is compatible with the current texturing process; the modified pyramid structure is more conducive to the conformal deposition of the thin film; the reflectivity of the modified pyramid increases by less than 1%, while taking into account both the optical and electrical properties of the battery; at the same time, the rounding modification liquid used does not contain nitrogen, which effectively avoids the discharge of nitric acid in the rounding treatment liquid of the prior art, has a low waste liquid treatment cost, has a small environmental pressure, and has a low cost of raw chemical liquid and is easy to obtain, which reduces production costs while also reducing pollution to the environment.

[0022] The present invention is further described below in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM surface structure of the crystalline silicon wafer before smoothing.

[0024] Figure 2 This is the SEM cross-sectional structure of the crystalline silicon wafer before rounding modification.

[0025] Figure 3 This is a SEM cross-sectional structural diagram of a crystalline silicon wafer after smooth modification using the technical solution of the present invention.

[0026] Figure 4 This is a SEM cross-sectional structural diagram of a crystalline silicon wafer after smooth modification using the technical solution of the present invention. DETAILED DESCRIPTION

[0027] In the embodiment of the present invention, taking the N-type single crystal silicon wafer after texturing as an example, the single crystal silicon wafer has a textured surface covered with pyramid morphology structures, the bottom side of the pyramid morphology structure is 1 to 10 microns long, and the height is The side length, i.e. the height, is about 0.7 to 7 microns, preferably 2 to 5 microns. Figure 1 In other embodiments, the single crystal silicon wafer may also be a P-type silicon wafer.

[0028] Example 1: This example provides a method for rounding and modifying a crystalline silicon solar cell. Hydrofluoric acid, sodium hypochlorite, deionized water, and an additive are prepared. In this example, sodium hypochlorite simultaneously has the function of an oxidant, so there is no need to add an additional oxidant. Of course, in other examples, an oxidant can also be added. After mixing hydrofluoric acid, sodium hypochlorite, and deionized water, a rounding and modifying solution is obtained, where the concentration of sodium hypochlorite is 0.1 mol / L and the concentration of the hydrofluoric acid is 1.0 mol / L. The additive is added to the rounding and modifying solution, and the mass ratio of the additive to the rounding and modifying solution is 3:100. Among them, the additive is composed of 1 part by mass of benzyltrimethylammonium chloride, 2 parts by mass of sodium citrate, 0.5 part by mass of guar gum, and 100 parts by mass of water.

[0029] The textured monocrystalline silicon wafer is placed in the rounding and modifying solution, and it is modified for 30 s at a reaction temperature of 25 °C to etch and modify the top and bottom positions of the pyramid-shaped morphology structure of the crystalline silicon wafer into a smooth transition structure. See Figure 3 and Figure 4 , the tips and bottoms of the pyramid-shaped morphology structure are modified into a smooth transition, which is beneficial to the conformal deposition of the subsequent thin film. After testing, the reflectivity of the modified pyramid-shaped textured surface is 11.3%.

[0030] Example 2: This example provides a method for rounding and modifying a crystalline silicon solar cell, which is basically the same as that in Example 1, except that hydrofluoric acid, hydrogen peroxide, hydrochloric acid, and an additive are prepared. After mixing hydrofluoric acid, hydrogen peroxide, and hydrochloric acid, a rounding and modifying solution is obtained, where the concentration of hydrofluoric acid is 0.3 mol / L, the concentration of hydrogen peroxide is 0.4 mol / L, and the concentration of hydrochloric acid is 10 mol / L; the additive is added to the rounding and modifying solution, and the mass ratio of the additive to the rounding and modifying solution is 2:100. The additive is composed of 2 parts by mass of benzyltrimethylammonium chloride, 1 part by mass of sodium citrate, 1 part by mass of guar gum, and 100 parts by mass of water.

[0031] The textured monocrystalline silicon wafer is placed in the rounding and modifying solution, and it is modified for 90 s at a reaction temperature of 15 °C to etch and modify the top and bottom positions of the pyramid-shaped morphology structure of the crystalline silicon wafer into a smooth transition structure. After testing, the reflectivity of the modified pyramid-shaped textured surface is 11.7%.

[0032] Example 3: This example provides a method for rounding and modifying a crystalline silicon solar cell, which is basically the same as that in Example 1, except that hydrofluoric acid, sodium perchlorate, and hydrochloric acid are prepared. In this example, sodium perchlorate has the function of an oxidant at the same time, so there is no need to add an additional oxidant. Of course, in other examples, an oxidant can also be added. Mix hydrofluoric acid, sodium perchlorate, and hydrochloric acid to obtain a rounding and modifying solution, where the concentration of hydrofluoric acid is 1 mol / L, the concentration of sodium perchlorate is 0.2 mol / L, and the concentration of hydrochloric acid is 8 mol / L;

[0033] Place the textured monocrystalline silicon wafer in the rounding and modifying solution and modify it for 60 s at a reaction temperature of 30 °C to etch and modify the top and bottom positions of the pyramid morphology structure of the silicon wafer into a smooth transition structure. After testing, the reflectivity of the modified pyramid texture is 11.5%.

[0034] Comparative Example 1

[0035] Place the textured monocrystalline silicon wafer in a mixed acid solution of HF and HNO 3 and treat it for 90 s at a reaction temperature of 8 °C; among them, the mass percentage of HF in the mixed acid solution is 1%, and the mass percentage of HNO 3 is 70%; after testing, the reflectivity of the modified pyramid texture is 12.5%.

[0036] Prepare the solar cells from Examples 1-3 and Comparative Example 1 according to the HIT process flow and conduct a comparative test on the performance of the solar cells. The specific results are shown in Table 1:

[0037] Table 1

[0038] ΔUoc (mV) <![CDATA[ΔJsc (mA / cm 2 )]]> ΔFF (%) ΔEff (%) Example 1 1.2 0.02 0.21 0.106 Example 2 1.5 0.01 0.12 0.084 Example 3 1.6 0.01 0.20 0.111 Comparative Example 1 0 0 0 0

[0039] Through the comparison in Table 1, the performance of the solar cells prepared from the monocrystalline silicon wafers treated by the rounding and modifying method of the crystalline silicon solar cell of the present invention according to the HIT process flow is basically better than that of the traditional process. Moreover, the formula of the rounding and modifying solution used in the rounding and modifying method of the crystalline silicon solar cell of the present invention is reasonable, does not contain nitrogen, effectively avoids the nitrogen emission in the HF / HNO 3 mixed acid modifying solution, has a low waste liquid treatment cost, small environmental protection pressure, reduces the production cost and also reduces the environmental pollution.

[0040] The method for smoothly modifying a crystalline silicon solar cell of the present invention is compatible with the current production line texturing process, and the process is simple. It has a good smoothing effect on the tips and bottoms of the pyramid-shaped structures, which is more conducive to conformal deposition of subsequent thin films. The reflectivity is controllable, achieving a better balance between the optical and electrical properties of the solar cell, and ultimately improving the cell efficiency. The above embodiments are only the preferred embodiments of the present invention. The present invention cannot list all the embodiments. Any technical solution using one of the above embodiments or equivalent changes made according to the above embodiments is within the protection scope of the present invention.

[0041] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention. Other methods obtained by using the same or similar methods are all within the protection scope of the present invention.

Claims

1. A method for smoothly modifying a crystalline silicon solar cell, characterized in that, it includes the following steps: (1) Prepare a textured crystalline silicon wafer. The textured surface of the crystalline silicon wafer has a pyramid-shaped morphology structure with a bottom side length of 1 to 10 micrometers and a height of 0.7 to 7 micrometers; (2) Configure a smooth modification solution: Mix a fluoride ion source, a chlorine-containing ion source, an oxidant, and deionized water to obtain a smooth modification solution, wherein the concentration of the fluoride ion source is 0.1 mol / L to 8 mol / L, the concentration of the chlorine-containing ion source is 0.01 mol / L to 13 mol / L, and the concentration of the oxidant is 0.01 mol / L to 3 mol / L; An additive is further added in the step (2), and the mass ratio of the additive to the smooth modification solution is 0.2 to 5:100; the additive is composed of the following components in a mass fraction ratio: 0.1 to 5 parts by mass of benzyltrimethylammonium chloride, 1 to 3 parts by mass of sodium citrate, 0.5 to 3 parts by mass of guar gum, and 100 parts by mass of water; (3) Smooth modification: Place the textured crystalline silicon wafer in the smooth modification solution and etch it at a temperature of 8 °C to 40 °C for 15 s to 180 s to etch and modify the top and bottom positions of the pyramid-shaped morphology structure of the crystalline silicon wafer into a smooth transition structure, which is beneficial to the deposition of the passivation film and reduces the recombination at the junction of the tip and the bottom.

2. The method for smoothly modifying a crystalline silicon solar cell according to claim 1, characterized in that, the crystalline silicon wafer is a P-type silicon wafer or an N-type silicon wafer.

3. The method for smoothly modifying a crystalline silicon solar cell according to claim 1, characterized in that, after the smooth modification is completed, the etching depth at the top of the pyramid-shaped morphology structure and the junction of the bottoms of two adjacent pyramid-shaped morphology structures is 10 nm to 100 nm.

4. The method for smoothly modifying a crystalline silicon solar cell according to claim 1, characterized in that, the fluoride ion source is selected from hydrofluoric acid.

5. The method for smoothly modifying a crystalline silicon solar cell according to claim 1, characterized in that, the chlorine-containing ion source is selected from hydrochloric acid, sodium hypochlorite, sodium chlorite, chlorine dioxide, chlorine gas, sodium chlorate, or sodium perchlorate.

6. The method for smoothly modifying a crystalline silicon solar cell according to claim 1, characterized in that, the oxidant is selected from one or more of sodium persulfate, hydrogen peroxide, acetic acid, peracetic acid, potassium permanganate, and concentrated sulfuric acid.

7. A smooth modification solution used in the method for smoothly modifying a crystalline silicon solar cell according to any one of claims 1-6.

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