WO2016019767A1

WO2016019767A1 - Acidic texturing solution for etching solar cell silicon wafer, texturing method, solar cell and manufacturing method for solar cell

Info

Publication number: WO2016019767A1
Application number: PCT/CN2015/082249
Authority: WO
Inventors: 刘尧平; 王燕; 杨丽霞; 梅增霞; 陈伟; 梁会力; 库兹涅佐夫安德烈; 杜小龙
Original assignee: 中国科学院物理研究所
Priority date: 2014-08-06
Filing date: 2015-06-24
Publication date: 2016-02-11
Also published as: CN104195645A; CN104195645B

Abstract

An acidic texturing solution for etching a solar cell silicon wafer, a texturing method, a solar cell and a manufacturing method for the solar cell. The acidic texturing solution comprises a copper ion source for providing copper ions with a concentration of 0.1-25 mmol/L, a fluorine ion source for providing fluorine ions with a concentration of 0.5-10 mol/L, and an oxidant with a concentration of 0.1-1.0 mol/L that is capable of oxidizing copper into the copper ions. The surface of the silicon wafer can be textured well by means of the acidic texturing solution and thus an independent, complete and compactly arranged micron-size inverted pyramid-shaped structure is formed on the surface of the silicon wafer at relatively low temperature and in relatively short time. By using the inverted pyramid-shaped structure, the reflectivity of incident light on the textured surface is reduced to 5%-15% so that the efficiency of the solar cell is improved. The inverted pyramid-shaped structure is not limited to the preparation of an HIT and a conventional diffusion cell and can be also applied in other solar cells and optoelectronic devices using a silicon substrate.

Description

Acidic fluffing liquid for etching solar cell silicon wafer, method for making cashmere, solar cell sheet and manufacturing method thereof

Technical field

The present invention relates to the field of solar cell technologies, and in particular, to an acidic fluffing liquid, a method for forming a fabric, a solar cell sheet, and a method for fabricating the same.

Background technique

With the development and progress of human society, the demand for energy is increasing, and with the depletion of non-renewable energy, people are increasingly dependent on renewable energy, especially solar energy. Among them, solar cells have gradually entered the daily life of the public. In the photovoltaic industry, how to achieve the improvement of solar cell conversion efficiency and cost reduction has always been the focus of research, and an important means to improve the conversion efficiency of solar cells is to reduce the reflection of sunlight on the surface of the silicon wafer. In order to reduce the reflection loss, the surface of the silicon wafer is usually textured or an anti-reflection film is deposited on the surface of the battery. Among them, the method of forming the surface of the silicon wafer is favored.

At present, solar cell monocrystalline silicon wafer texturing is a relatively mature method. The traditional single crystal silicon or quasi-single crystal texturing process generally uses alkali liquid (such as sodium hydroxide) and texturing additive as the cashmere liquid. Make suede. The principle of alkaline texturing is the anisotropic etching of single crystal silicon or quasi-single crystal by alkali solution. The alkali solution has different corrosion rates on the surface of the silicon wafer, such as slower corrosion of the (111) crystal plane, and 100) The crystal face is corroded faster. When the surface of the silicon wafer is etched with an alkali solution, a random structure is formed on the surface of the silicon due to the anisotropic corrosion characteristics. The random pyramid structure can reflect sunlight twice, and the general reflectivity is about 10%.

In order to make the sunlight reflect on the surface of the silicon wafer multiple times, thereby improving the absorption of light by the solar cell and improving the efficiency of the battery, the inverted pyramid structure can also be prepared by the process of alkali velvet. The inverted pyramid structure can reflect sunlight three times, and the reflectivity can be reduced to about 5%. However, the lye softening process differs from the preparation of the random pyramid structure in that a mask layer needs to be prepared, that is, a high-temperature oxidation, an etching mask, a high-temperature etching, and the like are required, thereby limiting the large-scale process steps thereof. The scope of the application.

In view of the above problems, in order to reduce the reflectivity of incident light on the surface of the silicon wafer, improve the absorption of light by the solar cell, and the conversion efficiency of the solar cell, there is an urgent need for a new texturing process.

Summary of the invention

An object of the present invention is to provide an acidic fluffing liquid for etching a silicon wafer of a solar cell, a method for forming a fleece, a solar cell sheet, and a method for fabricating the same, which can use an inexpensive metal copper ion at a lower temperature The texturing is completed in a shorter temperature and in a shorter period of time, and an inverted pyramid structure of a micron-sized structure is obtained.

According to an aspect of the present invention, there is provided an acidic texturing liquid for etching a solar cell wafer, comprising: a copper ion source for providing copper ions at a concentration of 0.1 to 25 mmol/L; and a fluoride ion source. Providing a fluoride ion having a concentration of 0.5 to 10 mol/L; and an oxidizing agent having a concentration of 0.1 to 1.0 mol/L can oxidize copper to copper ions.

Further, the copper ion source is selected from one or more of copper chloride, copper sulfate, and copper nitrate.

Further, the oxidizing agent is selected from one or more of potassium permanganate, potassium bromide, persulfate and hydrogen peroxide.

Further, the concentration of copper ions is 4 to 15 mmol/L, the concentration of fluoride ions is 3 to 7 mol/L, and the concentration of the oxidizing agent is 0.3 to 0.7 mol/L.

Further, the copper ion source is copper nitrate, the fluoride ion source is hydrofluoric acid, and the oxidant is hydrogen peroxide.

Further, the concentration of copper ions was 7 mmol/L, the concentration of fluoride ions was 5 mol/L, and the concentration of hydrogen peroxide was 0.5 mol/L.

According to another aspect of the present invention, an acid texturing method for a solar cell wafer is provided, comprising the steps of: formulating an acidic texturing liquid of any of the above; and placing the silicon wafer in an acidic texturing liquid The acidic fluffing liquid is heated to a predetermined temperature and etched for a predetermined time to obtain a surface-finished silicon wafer; the predetermined temperature is 40 ° C to 80 ° C, and the predetermined time is 5 to 30 minutes.

Further, the predetermined temperature is 50 ° C to 70 ° C, and the predetermined time is 8 to 20 minutes.

Further, the predetermined temperature is 50 ° C, and the predetermined time is 8 minutes.

Further, before the silicon wafer is softened, the step of pre-cleaning and water washing the silicon wafer is further included, which comprises: firstly, the silicon wafer is ultrasonically cleaned in acetone and ethanol, and then placed in a mixture of a sulfuric acid solution and an aqueous hydrogen peroxide solution. The liquid is heated and boiled, and then ultrasonically cleaned in water; the mass percentage concentration of the sulfuric acid solution is 70%, the mass percentage concentration of the aqueous hydrogen peroxide solution is 35%; and the volume ratio of the sulfuric acid solution to the aqueous hydrogen peroxide solution is 3:1.

Further, the method further comprises: ultrasonically cleaning the softened silicon wafer in nitric acid or aqua regia to remove the metal covering on the surface of the textured surface; and ultrasonically cleaning the silicon wafer after removing the metal covering, and then using high purity Blow dry with nitrogen.

According to still another aspect of the present invention, a method of fabricating a solar cell sheet is provided, comprising the step of texturing a silicon wafer, the texturing step being prepared by any of the above-described acidic texturing methods.

According to still another aspect of the present invention, a solar cell sheet is provided which is fabricated by any of the above-described methods for fabricating a solar cell sheet.

The present invention also provides a silicon wafer having a textured surface formed by any of the above-described acidic texturing methods, the textured surface having a microstructure consisting of a plurality of inverted pyramids.

Further, the bottom of the inverted pyramid structure on the textured surface is rounded.

Further, the top of the inverted pyramid on the surface of the textured surface is quadrangular, the side length of the quadrilateral is 1 to 10 μm, and the depth of the inverted pyramid is 1 to 10 μm.

Further, the top of the inverted pyramid on the surface of the texturing is square.

Further, the average reflectance of the textured surface is 5% to 15%.

Further, the distribution density of the inverted pyramid on the surface of the pile is 10 ⁶ to 10 ⁸ /cm ² .

By applying the technical scheme of the present invention, the morphology and depth of the inverted pyramid structure on the surface of the textured fabric are controlled by controlling the concentration, etching temperature and time of the copper ion salt, the hydrofluoric acid and the oxidizing agent in the acidic fluffing liquid. The use of the acidic texturing process of the present invention results in a separate, complete and closely spaced micron-sized inverted pyramid structure on the surface of the wafer at lower temperatures and in a shorter period of time. Due to the presence of the textured surface on the silicon wafer, the incident light can be reflected and refracted multiple times on the textured surface, thereby changing the direction of the incident light in the silicon wafer, extending the optical path and reducing the incident light on the surface of the silicon wafer. The reflection reduces the reflectivity to 5% to 15%. It can be seen that the present invention completely obviates the process of preparing a complex mask layer and lithography during the alkali-based texturing in the prior art, and the inverted pyramid structure can be obtained in one step by simply immersing the silicon wafer in the acidic texturing liquid. Since mask etching is not required, an inverted pyramid-shaped pit structure can be formed on one side or both sides of the silicon wafer as needed. The acid texturing method of the invention simplifies the operation process, is convenient and widely used, and uses inexpensive copper instead of expensive gold or silver, thereby reducing the cost.

In addition, the inverted pyramid structure of the textured surface obtained by the present invention is pit-shaped, and the bottom of the inverted pyramid is rounded due to the etching of the metal nanoparticles, which eliminates the need for a heterojunction solar cell (HIT). The smooth etching process can directly deposit an amorphous silicon layer to prepare a HIT solar cell. And due to the existence of the bottom smooth structure, the metal electrode material is very easy to fill the structure when preparing the solar cell electrode, which is beneficial to increase the contact area, thereby effectively reducing the contact resistance and thereby increasing the conversion efficiency of the battery. In addition, the preparation of an inverted pyramid structure on both sides of the silicon wafer is very advantageous for preparing a symmetrical structure battery such as HIT. The smooth pit-shaped inverted pyramid structure is not limited to the application in the preparation of HIT and conventional diffusion cells, and can be applied to other solar cells that require the use of a silicon substrate and in optoelectronic devices.

The above as well as other objects, advantages and features of the present invention will become apparent to those skilled in the <

DRAWINGS

Some specific embodiments of the present invention are described in detail below by way of example, and not limitation. The same reference numbers in the drawings identify the same or similar parts. Those skilled in the art should understand that the drawings are not necessarily drawn to scale. In the figure:

1 is an SEM image of an inverted pyramid structure obtained on a textured surface after etching in Example 1 of the present invention;

Figure 2 is an enlarged SEM image of the single inverted pyramid structure of Figure 1;

3 is a schematic view showing a change trend of a reflectance of a textured surface obtained by etching in Example 1 of the present invention;

4 is an SEM image of the inverted pyramid structure obtained on the textured surface after etching in contact with the electrode in Example 1 of the present invention.

detailed description

In order to solve the problem of the prior art silicon wafer texturing process being complicated and having high reflectivity, the present invention proposes an acidic texturing liquid for etching a solar cell wafer. In one embodiment of the invention, the acidic texturing fluid comprises a source of copper ions, a source of fluoride ions, and an oxidizing agent capable of oxidizing copper to copper ions. The copper ion source is used to provide a copper ion concentration of 0.1 to 25 mmol/L, the fluoride ion source is used to provide a fluoride ion having a concentration of 0.5 to 10 mol/L, and the concentration of the oxidizing agent is 0.1 to 1.0 mol/L of the oxidizing agent.

By immersing the silicon wafer in an acidic fluffing liquid and controlling the etched morphology and depth by controlling the concentration of the copper ion source, the fluoride ion source, and the oxidant, the wafer surface is exposed at a lower temperature and in a shorter time. An inverted pyramid structure is formed on the dense arrangement. The reason is that, in the acidic fluffing liquid, the Cu ²⁺ -containing copper ion source mainly acts as a catalyst, and Cu ²⁺ can obtain electrons from the silicon surface due to the lower potential in the solution, thereby causing the silicon to lose electrons. It is oxidized to silica, and the fluoride ion source reacts with the oxidized silica to realize silicon wafer etching. Due to the high temperature during etching, Cu ²⁺ obtains electrons at a relatively high speed, so that it is easy to form a dense copper film on the surface of the silicon wafer, which hinders the etching of the silicon wafer by fluoride ions. The invention introduces an oxidizing agent into the acidic fluffing liquid, so that excess copper nanoparticles formed on the surface of the silicon are oxidized to form Cu ²⁺ , thereby avoiding the formation of a dense copper film on the surface of the silicon wafer to hinder the etching. The invention effectively controls the precipitation and dissolution of the metal copper nanoparticles by the use of the oxidant, thereby effectively controlling the etching effect and shortening the etching time.

In order to reduce the reflectance of incident light on the textured surface having an inverted pyramid structure to 5% to 15%, the present invention controls the concentration of copper ions in the acidic texturing liquid to be 0.1 to 25 mmol/L, and the concentration of fluoride ions. The control is 0.5 to 10 mol/L, and the concentration of the oxidizing agent is controlled to 0.1 to 1.0 mol/L. Among them, copper ions can obtain electrons from the surface of silicon, oxidize silicon into silicon dioxide, and at the same time reduce itself to copper nanoparticles, thereby achieving catalytic etching of silicon wafers. If the concentration of copper ions is high, there is a problem that copper nanoparticles are precipitated too fast, thereby forming a dense film on the surface of the silicon wafer, which hinders the etching. Conversely, if the copper ion concentration is low, the copper nanoparticles will precipitate less and will not effectively etch the silicon surface.

The main role of fluoride ions in the acidic fluffing liquid is to etch the silicon dioxide formed by the oxidation of silicon. If the solubility of the fluoride ion in the acidic fluffing liquid is high, the etching speed is too fast, and a nanopore structure is formed on the surface of the silicon wafer, so that the inverted pyramid structure is not obtained. If the solubility of the fluoride ion in the acidic fluffing liquid is low, the etching speed of the surface of the silicon wafer is too slow, and the inverted pyramid structure cannot be obtained. The main function of the oxidant is to oxidize the precipitated excess copper nanoparticles to copper ions. If the concentration of the oxidant is too high, there is a problem that the copper nanoparticles on the silicon surface cannot be precipitated, resulting in an etching efficiency that is too low to obtain an inverted pyramid structure. If the concentration of the oxidizing agent is too low, copper nanoparticles may not be oxidized, resulting in the appearance of a dense copper film, hindering the progress of etching.

Generally, the silicon wafer prepared by metal catalytic etching is a nanostructure, which is easy to form a large number of dead layer structures when preparing a solar emitter, resulting in an increase in surface recombination and Auger recombination, thereby hindering the conversion efficiency of the solar cell. In the present invention, although the metal catalytic etching method is also employed, since the concentration of the etching reagent in the acidic texturing liquid is creatively selected and controlled within the above range, a closely arranged and micron-sized inverted pyramid structure velvet is obtained. The surface, while effectively inhibiting the appearance of nanostructures. The densely arranged micro-sized inverted pyramid structure can avoid the appearance of a large number of dead layers, which can reduce the surface recombination and Auger recombination, and can match the existing solar cell preparation process, reducing the reflectivity of the incident light on the textured surface. , greatly improving the conversion efficiency of the battery.

In order to make the etching rate and the etching depth better meet the requirements of the texturing, the volume of the inverted pyramid on the surface of the textured surface is more uniform, and the reflectivity of the silicon wafer is better reduced, and further preferably, the acidic fluffing liquid is used. The concentration of copper ions is 4 to 15 mmol/L, the concentration of fluoride ions is 3 to 7 mol/L, and the concentration of the oxidizing agent is 0.3 to 0.7 mol/L.

In an exemplary embodiment of the invention, the source of copper ions is selected from one or more of the group consisting of copper chloride, copper sulfate, and copper nitrate. The oxidizing agent is selected from one or more of potassium permanganate, potassium bromide, persulfate and hydrogen peroxide. Illustratively, it will be readily understood by those skilled in the art that persulphates may include, but are not limited to, ammonium persulfate, potassium persulfate, and sodium persulfate. The present invention preferably uses the above copper ion source and oxidant, but Not limited to this, as long as the copper ion source can ionize the freely moving copper ions, the oxidant has a strong oxidation effect, and the copper nanoparticles can be oxidized to copper ions.

In an exemplary embodiment of the invention, the source of copper ions is copper nitrate, the source of fluoride ions is hydrofluoric acid, and the oxidant is hydrogen peroxide. That is, the acidic fluffing liquid is composed of copper nitrate, hydrofluoric acid and hydrogen peroxide. In a preferred embodiment of the invention, the concentration of copper nitrate is 7 mmol/L, the concentration of hydrofluoric acid is 5 mol/L, and the concentration of hydrogen peroxide is 0.5 mol/L. By using the acidic fluffing liquid of the preferred embodiment to form a fleece of the silicon wafer, a more complete and dense inverted pyramid structure can be obtained, and the suede surface is more effective, and the reflectance of the incident light can be reduced to a greater extent. Improve the conversion efficiency of solar cells.

According to another aspect of the present invention, there is also provided an acid texturing method for a solar cell wafer, comprising the steps of: first preparing an acidic texturing liquid, which may be any of the above mentioned An acidic fluffing liquid; the silicon wafer to be fluffed is placed in an acidic fluffing liquid, the acid fluffing liquid is heated to a predetermined temperature, and etched for a predetermined time to obtain a surface-finished silicon wafer. The predetermined temperature is 40 ° C to 80 ° C, and the predetermined time is 5 to 30 minutes.

The silicon wafer for solar cells referred to in the present invention includes single crystal silicon and quasi-single crystal, and is suitable for both N-type single crystal silicon and P-type single crystal silicon. After the silicon wafer to be processed is placed in the acidic fluffing liquid, the etch rate of the Si (100) and (111) faces of the Cu nanoparticles is different due to the combination of the fluorine ions, the strong oxidizing agents and the Cu nanoparticles. An anisotropic etch can be formed on the silicon surface at a lower temperature and for a shorter period of time to obtain an independent, complete, dense, micron-sized inverted pyramid structure on the silicon surface simply and quickly. At the same time, the reflectivity of the textured surface is effectively reduced, and the carrier surface recombination and Auger recombination on the silicon surface are greatly reduced, thereby improving the conversion efficiency of the solar cell. Preferably, during the etching process, the etching effect can be enhanced by heating, ultraviolet radiation, ultrasonication, and bubbling.

In order to obtain the textured surface of the inverted pyramid structure of the present invention, in an exemplary embodiment of the present invention, the predetermined temperature for etching the acidic fluffing liquid is controlled within a range of 40 to 80 ° C while controlling the etching time to 5 ~30 minutes. If the predetermined temperature of the etching is higher than 80 ° C, copper ions are precipitated too fast, and the silicon wafer is easily etched as a whole, resulting in failure to obtain a textured surface of the inverted pyramid structure. If the predetermined temperature of the etching is lower than 40 ° C, the etching rate is too slow, the nanostructure is liable to occur, and the micron-sized inverted pyramid structure textured surface which is closely arranged is also not obtained. If the etching time is higher than 30 minutes, the completed inverted pyramid structure will be damaged by over-etching. If the etching time is less than 5 minutes, the etching time will be too short to form a complete and independent inverted. Pyramid structure.

Further preferably, the predetermined temperature is from 50 ° C to 70 ° C and the predetermined time is from 8 to 20 minutes. Most preferably, the predetermined temperature for etching is 50 ° C for a predetermined time of 8 minutes.

Since some organic impurities are inevitably left on the silicon wafer during the process of cutting the silicon wafer, the silicon wafer is pre-cleaned and washed before being placed in the acidic fluffing liquid for etching. A step of. Specifically, the silicon wafer is firstly placed in acetone and ethanol for ultrasonic cleaning, and then heated and boiled in a mixture of a sulfuric acid solution and an aqueous hydrogen peroxide solution. After heating and boiling, it is kept for 0.5 to 1 hour, and then ultrasonically cleaned in water. The concentration of the sulfuric acid solution was 70% by weight, and the concentration of the aqueous hydrogen peroxide solution was 35% by weight. The volume ratio of the sulfuric acid solution to the aqueous hydrogen peroxide solution was 3:1. Ultrasonic cleaning with acetone and ethanol is aimed at removing organic impurities remaining on the silicon wafer, and cleaning with a mixture of sulfuric acid solution and aqueous hydrogen peroxide for the purpose of removing metal impurities on the surface of the silicon wafer. Finally, the purpose of ultrasonic cleaning with deionized water is to remove the pre-cleaned liquid remaining on the surface of the silicon wafer. Pre-cleaning and water washing increase the absorption of incident light by the silicon wafer, which is beneficial to improve the short-circuit current of the battery, and is of great significance for improving the photoelectric conversion efficiency of the battery.

In view of factors that match the existing solar cell preparation process, the acid texturing method provided by the present invention further comprises the step of ultrasonically cleaning the softened silicon wafer into nitric acid or aqua regia to remove the metal covering of the textured surface. The silicon wafer after removal of the metal covering was ultrasonically washed with deionized water, followed by drying with high purity nitrogen.

According to another aspect of the present invention, there is also provided a silicon wafer having a textured surface, the textured surface being formed by any of the above-described acidic texturing methods, the textured surface having a plurality of inverted pyramids The microstructure of the structure.

Among them, the inverted pyramid structure is in the shape of a pit. The bottom of the inverted pyramid structure on the textured surface is rounded. The top of the inverted pyramid is quadrilateral. The sides of the quadrilateral are 1 to 10 μm. The depth of the inverted pyramid is 1 to 10 μm. In an exemplary embodiment of the invention, the top of the inverted pyramid is square. The silicon wafer obtained by the present invention has an average reflectance of 5 to 15% on the textured surface. In a preferred embodiment of the invention, the distribution density of the inverted pyramid on the surface of the texturing is from 10 ⁶ to 10 ⁸ /cm ² .

In a preferred embodiment of the present invention, the bottom of the inverted pyramid is rounded due to the etching of the nano copper particles, which eliminates the need for a smooth etching process in a heterojunction solar cell (HIT). An amorphous silicon layer is directly deposited to prepare an HIT solar cell. Moreover, in the preparation of the solar cell electrode, due to the existence of the rounded structure at the bottom of the inverted pyramid, the metal electrode material is very easy to fill the structure, which is beneficial to increase the contact area between the metal electrode and the silicon surface, thereby effectively reducing the contact resistance. Increase the conversion efficiency of the battery. The smooth concave inverted pyramid structure is not limited to the application in the preparation of the above-mentioned HIT and conventional diffusion cells, and can also be applied in ion implantation solar cells, hybrid solar cells, and other solar cell structures requiring the use of silicon substrates and optoelectronic devices. .

According to still another aspect of the present invention, a method for fabricating a solar cell sheet is provided, including The single crystal silicon wafer is subjected to texturing, wherein the texturing step is prepared by any of the above-described acidic texturing methods. The use of the acid texturing method provided by the invention for texturing, shortening the manufacturing process of the solar cell sheet, reducing the cost, and mass production.

According to still another aspect of the present invention, there is provided a solar cell sheet produced by the method of fabricating the above solar cell sheet. The solar cell sheet obtained by the texturing method of the present invention obtains a solar cell sheet in comparison with a conventional texturing method, and has the advantages of low contact resistance, high short-circuit current, and high conversion efficiency of the solar cell.

The beneficial effects of the present invention are further illustrated below in conjunction with more specific embodiments:

Example 1

1) Surface cleaning steps

Take a P-type silicon wafer with a size of 156 × 156cm (resistance is 1 ~ 3 Ωcm), first ultrasonically cleaned in acetone for 5 minutes, ultrasonically washed in ethanol for 5 minutes, and then placed in a mixture of sulfur solution and hydrogen peroxide solution. In the liquid (the concentration of the sulfuric acid solution is 70wt%, the concentration of the aqueous solution of hydrogen peroxide is 35wt%, the volume ratio of the sulfuric acid solution to the aqueous solution of hydrogen peroxide is 3:1), the silicon wafer is heated and boiled for 0.5 hours, and finally ultrasonically cleaned with deionized water. clean.

2) Etching step

The pre-cleaned and water-washed silicon wafer in step 1) is immersed in an acidic fluffing liquid composed of copper nitrate, hydrofluoric acid and hydrogen peroxide (wherein the concentration of copper nitrate is 7 mmol/L, and the concentration of hydrofluoric acid is 5 mol/ L, the concentration of hydrogen peroxide was 0.5 mol/L), and the acidic fluffing liquid was heated to 60 ° C and then etched for 12 minutes.

3) Post-processing stage

The silicon wafer after the stepping in step 2) is taken out, ultrasonically cleaned with a concentration of 69 wt% of nitric acid to remove the surface-covered metal, and then ultrasonically washed with deionized water and dried with high-purity nitrogen gas to obtain a pour. A silicon substrate with a pyramid structure.

Example 2-3

The procedure was the same as in Example 1, except that the concentration of copper nitrate, hydrofluoric acid and hydrogen peroxide in the acid fluffing liquid was different from the temperature and time at the time of texturing.

In Example 2, the concentration of copper nitrate was 4 mmol/L, the concentration of hydrofluoric acid was 7 mol/L, and the concentration of hydrogen peroxide was 0.3 mol/L. The acid fluffing liquid was heated to 50 ° C and etched for 8 minutes.

In Example 3, the concentration of copper nitrate was 15 mmol/L, the concentration of hydrofluoric acid was 3 mol/L, and the concentration of hydrogen peroxide was 0.7 mol/L. The acidic texturing solution was heated to 70 ° C and etched for 8 minutes.

Example 4-5

In Example 4, the concentration of copper nitrate was 0.1 mmol/L, the concentration of hydrofluoric acid was 10 mol/L, and the concentration of hydrogen peroxide was 0.1 mol/L. The acidic fluffing liquid was heated to 40 ° C and etched for 30 minutes.

In Example 5, the concentration of copper nitrate was 25 mmol/L, the concentration of hydrofluoric acid was 10 mol/L, and the concentration of hydrogen peroxide was 0.1 mol/L. The acidic texturing liquid was heated to 80 ° C and etched for 5 minutes.

Comparative example 1-4

In Comparative Example 1, the concentration of copper nitrate was 0.05 mmol/L, the concentration of hydrofluoric acid was 13 mol/L, and the concentration of hydrogen peroxide was 0.05 mol/L. The acid fluffing liquid was heated to 50 ° C and etched for 8 minutes.

In Comparative Example 2, the concentration of copper nitrate was 30 mmol/L, the concentration of hydrofluoric acid was 0.3 mol/L, and the concentration of hydrogen peroxide was 1.4 mol/L. The acid fluffing liquid was heated to 50 ° C and etched for 8 minutes.

In Comparative Example 3, the concentration of copper nitrate was 30 mmol/L, the concentration of hydrofluoric acid was 0.3 mol/L, and the concentration of hydrogen peroxide was 1.4 mol/L. The acidic fluffing liquid was heated to 30 ° C and etched for 35 minutes.

In Comparative Example 4, the concentration of copper nitrate was 0.06 mmol/L, the concentration of hydrofluoric acid was 12 mol/L, and the concentration of hydrogen peroxide was 0.04 mol/L. The acid fluffing liquid was heated to 90 ° C and then etched for 3 minutes.

The single crystal silicon wafers after the texturing in Examples 1-5 and Comparative Examples 1-4 were prepared into solar cell sheets by a conventional method, including diffusion diffusion, dephosphorization, de-phosphorization, and anti-reflection. Membrane, preparation electrode, characterization test. The silicon wafer after diffusion has a square resistance of 80 Ω/sq, and the deposited silicon nitride anti-reflection film has a thickness of 80 nm.

The SEM of the inverted pyramid trapped structure obtained after the texturing in Example 1 is shown in Figures 1-2. It can be seen that the inverted pyramid structure obtained by the acidic texturing method of the present invention is independent, neat and densely arranged, and has a size of 1 to 5 μm. It can be seen from Fig. 2 that due to the etching of the copper nanoparticles, the bottom of the inverted pyramid is a rounded structure, which helps to increase the contact area between the electrode and the silicon surface and reduce the contact resistance.

The textured single crystal silicon wafer in Example 1 was detected by a D8J integral reflectometer, and its surface reflectance tendency is shown in Fig. 3. As can be seen from FIG. 3, the acidic texturing method of the present invention obtains a textured surface of an inverted pyramid structure on the surface of the silicon wafer, which increases the absorption of incident light on the surface of the silicon wafer, and significantly reduces the single crystal silicon. Surface reflectance with an average reflectance as low as 5%.

4 is an SEM image of the inverted pyramid structure of the surface of the silicon wafer prepared in Example 1 in contact with the electrode. Since the bottom of the inverted pyramid is a rounded structure, it helps to increase the contact area between the electrode and the silicon surface, and reduces the contact resistance. 4 can be seen that the bottom of the inverted pyramid is a smooth structure, metal electrodes and inverted gold The tower's contact is relatively tight, basically achieving full contact, which is conducive to the transmission of current.

The Uoc, Isc, FF, and Eff of the solar cell sheets were measured by a halm tester, and the specific properties are shown in Table 1.

Table 1

It can be seen from Table 1 that in the embodiment 1-5, the technical solution of the present invention is used to control the concentration of the copper ion salt solution, the fluorine-containing ions and the oxidant, the etching temperature and the time in the acidic fluffing liquid, preferably. Controlling the shape and depth of the etch, so that the surface of the velvet can be etched at a lower temperature and in a shorter time, thereby obtaining an independent, complete and closely arranged inverted pyramid structure suede, greatly reducing the reflectivity , improved solar cell effect.

In Comparative Examples 1-4, since the concentration of copper ions, fluoride ions and oxidizing agents in the acidic fluffing liquid, etching temperature and time, etc. are not within the scope of the present invention, micron-sized surfaces are not obtained on the textured surface. The inverted pyramid structure can only obtain local nanopore structure or irregular structure, and the local nanopore structure and irregular structure can not reduce the incident light reflection of the textured surface, and at the same time, it is easy to form a large number of dead layer structures when preparing the emitter, and increase Surface recombination and Auger recombination. Therefore, the conversion efficiency of the solar cell in Comparative Examples 1-4 was low.

Example 6

1) Surface cleaning steps

Take N-type silicon wafer with a size of 156×156cm (resistivity: 1～3Ωcm), firstly put it into acetone for ultrasonic cleaning for 5 minutes, then ultrasonically clean it in ethanol for 5 minutes, then put it in a mixture of sulfuric acid and hydrogen peroxide. (The volume ratio of sulfuric acid to hydrogen peroxide was 3:1, the concentration of sulfuric acid was 70 wt%, and the concentration of hydrogen peroxide was 35 wt%). The wafer was heated and boiled for 1 hour, and finally ultrasonically cleaned with deionized water.

2) Etching step

The pre-cleaned and water-washed silicon wafer in step 1) is immersed in an acidic fluffing liquid composed of copper nitrate, hydrofluoric acid and hydrogen peroxide (wherein the concentration of copper nitrate is 5 mmol/L, and the concentration of hydrofluoric acid is 3 mol/ L, the concentration of hydrogen peroxide was 0.7 mol/L), and the acidic fluffing liquid was heated to 55 ° C and then etched for 10 minutes.

3) Post-processing stage

The silicon wafer after the stepping in step 2) is taken out, ultrasonically cleaned with a concentration of 69 wt% of nitric acid to remove the surface-covered metal, and then ultrasonically washed with deionized water and dried with high-purity nitrogen gas to obtain a pour. Monocrystalline silicon wafer with pyramid structure.

On the single crystal silicon substrate obtained in the step 3), a 10 nm amorphous silicon layer is first deposited on the front and back sides, and then 10 nm of n-type doped and p-type doped amorphous silicon are deposited on the front and back sides, respectively. On the reverse side, a transparent electrode (ITO) of 80 nm was continuously deposited, and finally a silver electrode was printed to prepare a HIT solar cell.

Example 7

1) Surface cleaning steps

Take a P-type silicon wafer with a size of 156 × 156cm (resistance is 1 ~ 3 Ωcm), first ultrasonically cleaned in acetone for 5 minutes, ultrasonically cleaned in ethanol for 5 minutes, and then placed in a mixture of sulfuric acid and hydrogen peroxide. (The volume ratio of sulfuric acid to hydrogen peroxide was 3:1, the concentration of sulfuric acid was 70 wt%, and the concentration of hydrogen peroxide was 35 wt%). The wafer was heated and boiled for 0.5 hour, and finally ultrasonically cleaned with deionized water.

2) Etching step

The pre-cleaned and washed silicon wafer in step 1) is immersed in an acidic fluffing liquid composed of copper nitrate, hydrofluoric acid and hydrogen peroxide (wherein the concentration of copper nitrate is 10 mmol/L, and the concentration of hydrofluoric acid is 4 mol/ L, the concentration of hydrogen peroxide was 1.0 mol/L), and the acid fluffing liquid was heated to 45 ° C and then etched for 10 minutes.

3) Post-processing stage

The single crystal silicon wafer obtained in the step 3) is placed in an ion implanter for phosphorus ion implantation, the implantation energy is 10 KeV, the dose is 2.6×10 ¹⁵ /cm ^-2 , and after the injection is completed, the nitrogen atmosphere is protected at 900 ° C. After annealing for 40 minutes, the square resistance of the silicon wafer after annealing was 90 Ω/sq, and then a silicon nitride anti-reflection film was deposited, and the electrodes were printed to obtain a solar cell sheet.

Example 8

1) Surface cleaning steps

Take an N-type silicon wafer with a size of 156 × 156cm (resistivity is 1 ~ 3 Ωcm), first put acetone in order Ultrasonic cleaning for 5 minutes, ultrasonic cleaning in ethanol for 5 minutes, then placed in a mixture of sulfuric acid and hydrogen peroxide (volume ratio of sulfuric acid to hydrogen peroxide is 3:1, concentration of sulfuric acid is 70wt%, concentration of hydrogen peroxide is 35wt% The wafer was heated and boiled for 0.5 hours, and finally ultrasonically cleaned with deionized water.

2) Etching step

The pre-cleaned and water-washed silicon wafer in step 1) is immersed in an acidic fluffing liquid composed of copper chloride, hydrofluoric acid and ammonium persulfate (wherein the concentration of copper chloride is 4 mmol/L, hydrofluoric acid) The concentration was 6 mol/L, the concentration of ammonium persulfate was 0.5 mol/L, and the acid fluffing liquid was heated to 55 ° C and etched for 8 minutes.

3) Post-processing stage

The front side of the silicon wafer substrate obtained in the step 3) is spin-coated with a polystyrene sulfonic acid having a thickness of 60 nm, and after drying, a silver gate positive electrode having a thickness of 100 nm is thermally evaporated, and then the thickness is further evaporated on the reverse side. It is an aluminum electrode of 100 nm, and is further prepared as an organic-inorganic hybrid solar cell.

The Uoc, Isc, FF, and Eff of the solar cell sheets were measured by a halm tester, and the specific properties are shown in Table 2.

Table 2

It can be seen from Table 2 that the acid-textured silicon wafer of the present invention is applied to different solar cells, and it can be seen that a textured surface having an inverted pyramid structure is obtained on the surface of the silicon wafer, which greatly reduces Reflectivity increases solar cell efficiency.

Therefore, the acidic texturing process of the present invention is suitable for use in the manufacture of various types of solar cells. The utility model has the advantages of simple process, low cost, convenient operation, wide application conditions, no complicated mask and lithography process, and an inverted pyramid structure can be obtained on the silicon wafer in one step.

In this regard, it will be appreciated by those skilled in the <RTIgt;the</RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; The content directly determines or derives many other variations or modifications consistent with the principles of the invention. Cause Accordingly, the scope of the invention should be understood and construed as covering all such other modifications or modifications.

Claims

An acidic fluffing liquid for etching a solar cell wafer, comprising:

a copper ion source for providing copper ions at a concentration of 0.1 to 25 mmol/L;

a fluoride ion source for providing fluoride ions at a concentration of 0.5 to 10 mol/L;

The concentration of 0.1 to 1.0 mol/L of the oxidizing agent can oxidize copper to copper ions.
The acidic texturing liquid according to claim 1, wherein the copper ion source is one or more selected from the group consisting of copper chloride, copper sulfate, and copper nitrate.
The acidic texturing liquid according to any one of claims 1 to 2, wherein the oxidizing agent is selected from one or more of potassium permanganate, potassium bromide, persulfate and hydrogen peroxide.
The acidic fluffing liquid according to any one of claims 1 to 3, wherein the concentration of the copper ions is 4 to 15 mmol/L, and the concentration of the fluoride ions is 3 to 7 mol/L. The concentration is 0.3 to 0.7 mol/L.
The acidic texturing liquid according to any one of claims 1 to 4, wherein the copper ion source is copper nitrate, the fluoride ion source is hydrofluoric acid, and the oxidizing agent is hydrogen peroxide.
The acidic texturing liquid according to claim 5, wherein the concentration of the copper ions is 7 mmol/L, the concentration of the fluoride ions is 5 mol/L, and the concentration of the hydrogen peroxide is 0.5 mol/L.
An acid texturing method for a solar cell wafer includes the following steps:

Formulating the acidic texturing liquid of any of claims 1-6;

Depositing the silicon wafer in the acidic fluffing liquid, heating the acidic fluffing liquid to a predetermined temperature, and etching for a predetermined time to perform texturing on the silicon wafer, thereby obtaining surface-textured silicon sheet;

The predetermined temperature is 40 ° C to 80 ° C, and the predetermined time is 5 to 30 minutes.
The acidic texturing method according to claim 7, wherein the predetermined temperature is from 50 ° C to 70 ° C and the predetermined time is from 8 to 20 minutes.
The acidic texturing method according to claim 8, wherein the predetermined temperature is 50 ° C and the predetermined time is 8 minutes.
The acidic texturing method according to any one of claims 7 to 9, further comprising the steps of pre-cleaning and water-washing the silicon wafer before the silicon wafer is textured, comprising:

First, the silicon wafer is ultrasonically cleaned in acetone and ethanol, and then heated and boiled in a mixture of a sulfuric acid solution and an aqueous hydrogen peroxide solution, and then ultrasonically washed in water;

Wherein, the sulfuric acid solution has a mass percentage concentration of 70%, the hydrogen peroxide aqueous solution has a mass percentage concentration of 35%; and the volume ratio of the sulfuric acid solution to the hydrogen peroxide solution is 3:1.
The acidic texturing method according to any one of claims 7 to 10, further comprising:

The softened silicon wafer is placed in nitric acid or aqua regia to ultrasonically remove the metal covering on the textured surface;

The silicon wafer after removal of the metal cover was ultrasonically washed with water and then dried with high purity nitrogen.
A method of fabricating a solar cell sheet, comprising the step of texturing a silicon wafer, wherein the texturing step is prepared by the acidic texturing method according to any one of claims 7-11.
A solar cell sheet produced by the method for producing a solar cell sheet according to claim 12.
A silicon wafer having a textured surface, the textured surface being formed by the acidic texturing method according to any one of claims 7-11, wherein the textured surface has a plurality of inverted pyramids Microstructure.
The silicon wafer according to claim 14, wherein a bottom portion of said inverted pyramid structure on said textured surface is rounded.
The silicon wafer according to any one of claims 14 to 15, wherein a top of the inverted pyramid on the textured surface is a quadrangle, a side length of the quadrilateral is 1 to 10 μm, and a depth of the inverted pyramid is 1 to 10 μm.
A silicon wafer according to any one of claims 14 to 16, wherein the top of the inverted pyramid on the textured surface is square.
The silicon wafer according to any one of claims 14-17, wherein the textured surface has an average reflectance of 5% to 15%.
The silicon wafer according to any one of claims 14 to 18, wherein a distribution density of the inverted pyramid on the textured surface is from 10 6 to 10 8 /cm 2 .
The silicon wafer according to any one of claims 14 to 19, wherein a top of the inverted pyramid on the textured surface is a square, a side of the square is 1 to 10 μm, and a depth of the inverted pyramid is 1 to 10 μm.