阅读说明：本技术 单晶硅片碱抛光用添加剂及其应用 (Additive for alkali polishing of monocrystalline silicon piece and application thereof ) 是由 杨勇 章圆圆 陈培良 于 2021-08-19 设计创作，主要内容包括：本发明公开了一种单晶硅片碱抛光用添加剂,其各组分的质量百分含量为：抛光成分0.01%～1%,分散剂1%～3%,防沉剂1%～5%,保护剂0.05%～0.1%,余量为去离子水。在单晶硅片碱抛光的抛光液中添加本发明的添加剂,可使硅片的背抛面具有高平整度、低比表面积,无线痕,外观呈镜面效果,反射率高,最终电池效率提升0.03%～0.05%,满足PERC电池对抛光的需求。(The invention discloses an additive for alkali polishing of a monocrystalline silicon piece, which comprises the following components in percentage by mass: 0.01 to 1 percent of polishing component, 1 to 3 percent of dispersant, 1 to 5 percent of anti-settling agent, 0.05 to 0.1 percent of protective agent and the balance of deionized water. The additive is added into the polishing solution for alkali polishing of the monocrystalline silicon piece, so that the back polished surface of the silicon piece has high flatness, low specific surface area and no linear trace, the appearance has a mirror surface effect and high reflectivity, the final battery efficiency is improved by 0.03-0.05%, and the requirement of the PERC battery on polishing is met.)

1. The additive for alkali polishing of the monocrystalline silicon piece is characterized by comprising the following components in percentage by mass: 0.01 to 1 percent of polishing component, 1 to 3 percent of dispersant, 1 to 5 percent of anti-settling agent, 0.05 to 0.1 percent of protective agent and the balance of deionized water;

the polishing component is selected from one or more of ethyl vanillin, vanillic element, isotridecanol ether, alcohol ether phosphate and isomeric decaalcohol ether.

2. The additive for alkali polishing of a single-crystal silicon wafer as set forth in claim 1, wherein the dispersant is one or more selected from the group consisting of polyphosphate, polycarboxylate sulfonate and polyvinyl alcohol.

3. The additive for alkali polishing of a single crystal silicon wafer according to claim 1, wherein the anti-settling agent is selected from one or more of disodium tetraacetate, ethylene glycol bistetraacetate, and thiodiglycolic acid.

4. The additive for alkali polishing of a monocrystalline silicon piece according to claim 1, wherein the protective agent is one or more selected from benzotriazole, sodium hypophosphite and 2-mercaptobenzothiazole.

5. A polishing solution for alkali polishing of a silicon single crystal wafer, characterized by comprising an alkali solution and the additive according to any one of claims 1 to 4, wherein the mass ratio of the additive to the alkali solution is 2.3-4.5: 100.

6. The polishing solution for alkali polishing of a single crystal silicon wafer according to claim 5, wherein the alkali solution is NaOH solution or KOH solution.

7. The polishing solution for alkali polishing of a single-crystal silicon wafer as set forth in claim 6, wherein the mass concentration of NaOH in the NaOH solution is 5-8.5%, and the mass concentration of KOH in the KOH solution is 8-15%.

8. A method for alkali polishing a silicon single crystal wafer, characterized in that the silicon single crystal wafer is subjected to polishing treatment using the polishing liquid according to any one of claims 5 to 7.

9. The alkali polishing method for a single crystal silicon wafer according to claim 8, wherein the temperature of the polishing treatment is controlled to be 60 to 70 ℃.

10. The alkali polishing method for a single crystal silicon wafer according to claim 8, wherein the time of the polishing treatment is controlled to be 2 to 5 min.

Technical Field

The invention relates to the field of photovoltaics, in particular to an additive for alkali polishing of a monocrystalline silicon piece and application thereof.

Background

At present, a solar cell etching and polishing process is a crucial step in a solar efficient cell manufacturing process, and has a significant influence on the electrical performance and EL yield of finished cells, the uniformity of the reflectivity of the back of an etched silicon wafer determines the uniformity of a back passivation coating, and the uniformity of the coating determines the uniformity of the laser aperture ratio and size; therefore, etching plays a very important role in the production process of PERC (Passivated emitter rear contact) cells.

Alkali polishing is a common technical means at present, but the alkali polishing often has the following problems: 1) pyramid residues are not generated completely in the alkali polishing process; 2) the alkali polishing reflectivity is difficult to improve, and the stability is poor; 3) the tower footing formed by alkali polishing is small.

The prior alkaline polishing additive mainly adopts a polishing agent, a chelating agent and a protective agent, and still has the following problems: 1) the stability of the alkali polishing additive is poor, and the effective period is within 3 months; 2) the tower footing formed by polishing is small; 3) the polished surface has poor flatness and low reflectivity.

Disclosure of Invention

In order to improve the stability of the alkali polishing additive, the flatness and the reflectivity of an etched back surface after polishing and further better improve the conversion efficiency of a finished battery piece, the invention provides the alkali polishing additive for the monocrystalline silicon piece, which comprises the following components in percentage by mass: 0.01 to 1 percent of polishing component, 1 to 3 percent of dispersant, 1 to 5 percent of anti-settling agent, 0.05 to 0.1 percent of protective agent and the balance of deionized water;

the polishing component is selected from one or more of ethyl vanillin, vanillic element, isotridecanol ether, alcohol ether phosphate and isomeric decaalcohol ether.

Preferably, the dispersant is selected from one or more of polyphosphate, polycarboxylic acid sulfonate and polyvinyl alcohol.

Preferably, the anti-settling agent is selected from one or more of disodium tetraacetate, ethylene glycol bistetraacetic acid and thiodiglycolic acid.

Preferably, the protective agent is selected from one or more of benzotriazole, sodium hypophosphite and 2-mercaptobenzothiazole.

The invention also provides polishing solution for polishing the monocrystalline silicon piece by using the alkali, which contains alkali liquor and the additive, wherein the mass ratio of the additive to the alkali liquor is 2.3-4.5: 100.

Preferably, the alkali liquor is NaOH solution or KOH solution.

Preferably, the mass concentration of NaOH in the NaOH solution is 5-8.5%, and the mass concentration of KOH in the KOH solution is 8-15%.

The invention also provides an alkali polishing method of the monocrystalline silicon piece, which utilizes the polishing solution to polish the monocrystalline silicon piece.

Preferably, the temperature of the polishing treatment is controlled to be 60-70 ℃.

Preferably, the polishing time is controlled within 2-5 min.

The invention has the advantages and beneficial effects that:

the additive for alkali polishing of the monocrystalline silicon piece can control the crystal face direction and speed of etching of the silicon piece by inorganic alkali, and achieves the back polishing effect of larger tower footing and higher reflectivity; the size of the polished silicon wafer tower base is 23-28 micrometers, and the reflectivity is 41-43%.

The polishing component used by the additive can improve the selectivity of OH < - > to the etched surface of the silicon chip, thereby obtaining a polished surface with better flatness. The polishing component mainly influences the selection of OH < - > on the crystal face of the monocrystalline silicon through the chemical structure of the polishing component, and preferentially etches the 111 crystal face, so that the tower footing is displayed to be smoother.

The dispersant used in the additive of the present invention enables the polishing component to be better dispersed in the polishing solution.

The anti-settling agent used by the additive can lock some metal ions in the solution through the structure of the anti-settling agent, and prevents the metal ions from combining with sodium silicate to form insoluble silicate precipitates in the solution of high-concentration sodium silicate.

The protective agent used by the additive is mainly formed by combining a substance with a phosphorosilicate glass layer to form a compact passivation film so as to prevent OH < - > from corroding the front surface of silicon, and the back surface of the additive does not have the structure of the phosphorosilicate glass layer, so that alkali only etches the back surface of the additive; however, the performance of the protective agent is affected after a trace amount of metal ions in the solution are precipitated, so that an anti-precipitation agent is required to prevent precipitation.

The additive has high stability, and the polishing duration can reach 24-48 hours by adding the additive into alkali liquor. Because the additive does not contain a strong oxidant commonly used in the market, the whole formula does not have self decomposition or reaction with other chemical substances no matter under normal temperature condition or in polished high-alkali environment, and therefore, the additive has strong stability.

By adopting the polishing solution to perform back polishing on the silicon wafer, the back polished surface of the silicon wafer has high flatness, low specific surface area, no linear trace, mirror surface effect in appearance, high reflectivity and flatter back polishing, and the requirements of the PERC battery on polishing are met.

The components of the additive for alkali polishing of the monocrystalline silicon piece are easy to clean and do not remain on the silicon piece.

The battery piece prepared by the additive can increase the electrical performance of the battery piece, and the efficiency can be improved by 0.03-0.05% by matching the front process and the back process.

Drawings

FIG. 1 is a graph of the surface flatness of silicon wafers after polishing in example 1 and comparative example 1;

FIG. 2 is a schematic view of the silicon wafer after polishing in example 1 and comparative example 1;

FIG. 3 is a schematic view of the silicon wafer after polishing in example 2 and comparative example 2;

fig. 4 shows performance data for finished cells made in example 3 and comparative example 3.

Detailed Description

The following description of the embodiments of the present invention will be made with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

The invention provides an alkali polishing method of a monocrystalline silicon piece, which comprises the following specific steps:

1) preparing an additive: adding 0.01-1 wt% of polishing component, 1-3 wt% of dispersant, 1-5 wt% of anti-settling agent and 0.05-0.1 wt% of protective agent into the balance of water, and mixing to obtain additive;

the polishing component is selected from one or more of ethyl vanillin, vanillic element, isotridecanol ether, alcohol ether phosphate and isomeric deca-alcohol ether;

the dispersing agent is selected from one or more of polyphosphate, polycarboxylic acid sulfonate and polyvinyl alcohol;

the anti-settling agent is selected from one or more of disodium tetraacetate, ethylene glycol bistetraacetic acid and thiodiglycolic acid;

the protective agent is selected from one or more of benzotriazole, sodium hypophosphite and 2-mercaptobenzothiazole;

2) preparing a polishing solution: adding the additive prepared in the step 1) into alkali liquor, and uniformly mixing to prepare polishing solution; the mass ratio of the additive to the alkali liquor is 2.3-4.5: 100; the alkali liquor is NaOH solution or KOH solution, the mass concentration of NaOH is 5-8.5%, and the mass concentration of KOH is 8-15%;

3) polishing the back of the silicon wafer by using the polishing solution prepared in the step 2), wherein the temperature of the polishing treatment is controlled to be 60-70 ℃, and the time is controlled to be 2-5 min.

The specific embodiment of the invention is as follows:

example 1

Taking 2.5L of alkali for polishing, adding 2L of water, raising the temperature to 65 ℃, adding 100mL of 48 percent NaOH, and adding 30mL of the additive (the formula is 0.05 percent of vanillin, 1 percent of polyphosphate, 3 percent of disodium tetraacetate, 0.08 percent of benzotriazole and the balance of deionized water) after the temperature is stable; after stirring uniformly, taking the silicon wafer with PSG removed, carrying out precleaning for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, after precleaning is completed, putting the silicon wafer into a water tank for cleaning for 2min, then putting the silicon wafer into an alkali polishing tank for polishing for 4min, after polishing is completed, putting the silicon wafer into the water tank for cleaning for 2min, and completing the alkali polishing etching process.

Comparative example 1

2.5L of alkali is taken to be thrown into a groove, 2L of water is added, the temperature is raised to 65 ℃, then 100mL of 48 percent NaOH is added, and after the temperature is stabilized, 30mL of additive (the formula is 5 weight percent of sodium perchlorate, 3 weight percent of sodium citrate, 3 weight percent of palmitic acid, 0.001 weight percent of hexadecyl trimethyl amine oxide, 0.1 weight percent of tween and the balance of deionized water) used in the current market is added; after stirring uniformly, taking the silicon wafer with PSG removed, carrying out precleaning for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, after precleaning is completed, putting the silicon wafer into a water tank for cleaning for 2min, then putting the silicon wafer into an alkali polishing tank for polishing for 4min, after polishing is completed, putting the silicon wafer into the water tank for cleaning for 2min, and completing the alkali polishing etching process.

The flatness profile of the silicon wafer surface after polishing of example 1 and comparative example 1 is shown in fig. 1, and it can be seen from fig. 1 that: the silicon wafer polished by the additive is obviously better than the silicon wafer polished by the additive sold in the market in the aspect of mirror surface effect, and the surface of the silicon wafer polished by the additive is smoother.

The pyramid diagram of the polished silicon wafer of example 1 and comparative example 1 is shown in fig. 2, and it can be seen from fig. 2 that: the size of the tower footing of the silicon wafer polished by the additive is obviously larger than that of the silicon wafer polished by the additive in the market from the microstructure, and the planar bulges are less.

Example 2

Adding 2L of water into a 2.5L alkali polishing tank, raising the temperature to 65 ℃, adding 100mL of 48% NaOH, and adding 30mL of the additive (the formula is 0.05wt% of vanillin, 1wt% of polyphosphate, 3wt% of disodium tetraacetate, 0.08wt% of benzotriazole, and the balance of deionized water) after the temperature is stable to prepare polishing solution; the polishing solution is used after being placed for three months, when the polishing solution is used, the polishing solution is uniformly stirred, a silicon wafer with PSG removed is taken out, pre-cleaned for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, the silicon wafer is placed in a water tank for cleaning for 2min after the pre-cleaning is finished, then the silicon wafer is placed in an alkali polishing tank for polishing for 4min, the silicon wafer is placed in the water tank for cleaning for 2min after the polishing is finished, and the alkali polishing etching process is finished.

Comparative example 2

Adding 2L of water into a 2.5L alkali polishing tank, raising the temperature to 65 ℃, adding 100mL of 48% NaOH, and adding 30mL of additives (the formula is 5wt% of sodium perchlorate, 3wt% of sodium citrate, 3wt% of palmitic acid, 0.001wt% of hexadecyl trimethyl amine oxide, 0.1wt% of tween and the balance of deionized water) used in the current market after the temperature is stable to prepare the polishing solution; the polishing solution is used after being placed for three months, when the polishing solution is used, the polishing solution is uniformly stirred, a silicon wafer with PSG removed is taken out, pre-cleaned for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, the silicon wafer is placed in a water tank for cleaning for 2min after the pre-cleaning is finished, then the silicon wafer is placed in an alkali polishing tank for polishing for 4min, the silicon wafer is placed in the water tank for cleaning for 2min after the polishing is finished, and the alkali polishing etching process is finished.

The pyramid images of the polished silicon wafers of example 2 and comparative example 2 are shown in FIG. 3, and it can be seen from FIG. 3 that: after the additive is placed for 3 months, the using effect is completely the same as that of the initial time distribution, and pyramid residues do not exist; whereas the additives sold in the market have substantially lost polishing effectiveness, the pyramid remains much; the additive of the invention has good stability.

Example 3

Taking 150L of alkali for polishing, adding 140L of water, raising the temperature to 65 ℃, adding 6L of 48 percent NaOH, and adding 3.5L of the additive (the formula is 0.05 percent of vanillin, 1 percent of polyphosphate, 3 percent of disodium tetraacetate, 0.08 percent of benzotriazole and the balance of deionized water) after the temperature is stable; after stirring uniformly, polishing 1200 silicon wafers without PSG, pre-cleaning for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, after the pre-cleaning is finished, putting the silicon wafers into a water tank for cleaning for 2min, then putting the silicon wafers into an alkali polishing tank for polishing for 4min, after the polishing is finished, putting the silicon wafers into the water tank for cleaning for 2min, and finishing the alkali polishing etching process; and then, carrying out a subsequent solar cell preparation process to obtain a finished product cell.

Comparative example 3

Taking 150L of alkali to throw a groove, adding 140L of water, raising the temperature to 65 ℃, adding 6L of 48% NaOH, and adding 3.5L of additives (the formula is 5wt% of sodium perchlorate, 3wt% of sodium citrate, 3wt% of palmitic acid, 0.001wt% of hexadecyl trimethyl amine oxide, 0.1wt% of tween and the balance of deionized water) used in the current market after the temperature is stable; after stirring uniformly, polishing 1200 silicon wafers without PSG, pre-cleaning for 2min in a 45 ℃ NaOH and hydrogen peroxide tank, after the pre-cleaning is finished, putting the silicon wafers into a water tank for cleaning for 2min, then putting the silicon wafers into an alkali polishing tank for polishing for 4min, after the polishing is finished, putting the silicon wafers into the water tank for cleaning for 2min, and finishing the alkali polishing etching process; and then, carrying out a subsequent solar cell preparation process to obtain a finished product cell.

The performance data of the finished cells obtained in example 3 and comparative example 3 are shown in fig. 4, and it can be seen from fig. 4 that: the average cell efficiency of the additive of the invention is 22.7045%, and the average cell efficiency of the commercially available additive is 22.6768%; in contrast, the average cell efficiency of the additive of the invention was improved by 0.0277%.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the technical principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.