KR101029331B1 - Texturing method of silicon wafer for solar cell, thereby textured silicon wafer for solar cell and solar cell comprising same - Google Patents

Abstract

Provided are a method of texturing a silicon wafer for a solar cell, and a silicon wafer for a textured solar cell.

The method of texturing a silicon wafer for a solar cell according to the present invention includes controlling the pressure applied to the etching solution to a low pressure below normal pressure in a chemical etching process for texturing the silicon wafer. The texturing process at low pressure according to the present invention effectively removes the blocking effect of hydrogen gas to form a more regular and smaller pyramid on the silicon wafer surface. Compared to the prior art, the size of the pyramid is reduced by about 2 to 3 micrometers, the RMS roughness is reduced by about 200 nm, and an improved surface state is obtained, and the reflectance is also reduced by about 2 to 3% over the entire wavelength range.

Description

Texturing method of silicon wafer for solar cell, thereby textured silicon wafer for solar cell and solar cell comprising same {Texturing method of silicon wafer for solar cell, the silicon wafer for solar cell textured by the same and solar cell comprising the silicon wafer}

The present invention relates to a method for texturing a silicon wafer for a solar cell, a silicon wafer for a textured solar cell and a solar cell comprising the same, and more particularly, a more regular and dense pyramid is formed on the surface of the silicon wafer, the efficiency of the solar cell The present invention relates to a method for texturing a silicon wafer for a solar cell, thereby improving the texture of the silicon wafer for a solar cell and a solar cell including the same.

Recently, as the prediction of depletion of existing energy sources such as oil and coal is increasing, interest in alternative energy to replace them is increasing. Among them, solar cells are particularly attracting attention because they are rich in energy resources and have no problems with environmental pollution. Solar cells include solar cells that generate steam required to rotate turbines using solar heat, and solar cells that convert sunlight into electrical energy using the properties of semiconductors. Refers to.

Most common solar cells consist of large area p-n junction diodes. The basic requirement for solar cells for photovoltaic energy conversion is that the electrons must be asymmetric in the semiconductor structure. Referring to Figure 1, it shows the asymmetry of the p-n junction. The n-type region has a large electron density and a small hole density, and the p-type region is opposite to that. Therefore, in the thermal equilibrium, in the diode composed of the junction of p-type semiconductor and n-type semiconductor, diffusion due to the concentration gradient of carrier causes charge imbalance, which causes an electric field to be formed. No abnormal carrier diffusion occurs. When this diode is applied with light above the band gap energy, which is the energy difference between the conduction band and valence band of the material, it receives this light energy and the electrons are excited from the valence band to the conduction band. (excite) At this time, the electrons excited by the conduction band can move freely, and holes are generated in the valence band where electrons escape. This is called an excess carrier, and these excess carriers diffuse by concentration differences in the conduction band or the valence band.

At this time, electrons excited in p-type semiconductor and holes made in n-type semiconductor are called minority carriers, and carriers in p-type or n-type semiconductors before bonding (p-type holes, n-type electrons) are called majority carriers. At this time, the major carriers are interrupted by the flow of energy barriers caused by the electric field, but electrons, which are the minority carriers of the p-type, may move toward the n-type. Due to the diffusion of minority carriers, the electrical neutrality inside the material is broken, resulting in a voltage difference. When the electromotive force generated at the anode terminal of the p-n junction diode is connected to an external circuit, it acts as a solar cell.

On this principle, the performance of a solar cell capable of converting sunlight into electrical energy generally measures the efficiency of conversion to light energy, which is a ratio of the amount of incident light at the electrical output of the solar cell, usually expressed in%. .

Therefore, a lot of research is being conducted to increase the efficiency of solar cells, one of which is to maximize the absorption of light by texturing the wafer surface. Such texturing technology is one of important technologies for improving solar cell efficiency by reducing optical loss due to light confinement. As used herein, the term "texturing" is a term widely used in the art to which the present invention pertains, and refers to an overall process of treating a silicon wafer surface to have an uneven structure.

As the texturing method, a chemical etching method, a method using plasma etching, a mechanical scribing method, a photolithography method, and the like are used.

The plasma etching method is a method of forming a pattern by applying photoresist to a wafer, etching using a plasma, and removing a mask, which shows a fairly good reflectance, but requires a long time and requires expensive equipment. Because of this, industrial applicability is small. In addition, the mechanical scribing method is a method of forming a groove on the surface of the wafer and then texturing it using a chemical etching method. Difficult to produce and difficult to apply to thin films. In addition, the photo printing method is a method of forming a pattern by coating a photoresist on a wafer with an oxide film and texturing it through an isotropic / isotropic etching method, which is difficult to apply commercially because the process cost is too high.

Therefore, among the above methods, a chemical etching method capable of texturing a large amount of wafers at a low price in a short time has been in the spotlight.

Such chemical etching methods include isotropic etching and anisotropic etching, and anisotropic etching is preferred because anisotropic etching is less efficient than anisotropic etching in view of photoelectric conversion efficiency.

In general, the anisotropic etching method is performed by anisotropically etching the surface of a silicon wafer by immersing the silicon wafer in an etching solution prepared from a mixed solution of potassium hydroxide solution (KOH) and isopropylalcohol (IPA; isopropylalcohol, (CH ₃ ) ₂ CHOH). . The texturing process using the anisotropic etching method is known to be affected by the crystallographic properties of the wafer, the doping concentration, the process temperature, the solution ratio and the time. In addition, in order to form a pyramid having a uniform size and height closely related to the improvement of the efficiency of the solar cell, the above-listed conditions must be optimized, which makes it difficult for the worker to find such optimized conditions. In particular, there is a problem in that a pyramid having a non-uniform size (width) and height is formed because the texturing process does not proceed effectively by hydrogen generated during the texturing process. It will be described in more detail below.

On the other hand, the texturing process using a chemical etching method to increase the efficiency of the cell by reducing the reflection of sunlight incident to the front surface of the silicon solar cell mainly uses a potassium hydroxide (KOH) solution, which is a basic hydroxide etching solution.

The reaction process of silicon and etching solution (KOH) of silicon is shown in Chemical Formula 1.

Si + 2KOH + H ₂ O → K ₂ SiO ₃ + H ₂ ↑

In Formula 1, hydrogen gas (bubbles) is inevitably generated as a result of the etching reaction. Hydrogen bubbles inevitably generated during the texturing process are attached to the silicon substrate during etching, thereby interfering with etching, resulting in a non-uniform texture structure. This phenomenon is called a screen effect of hydrogen gas.

In more detail, the blocking effect of the hydrogen gas is trapped between the pyramid and the pyramid in which the hydrogen gas inevitably generated in the process is formed, and the etching reaction does not occur smoothly at the place where the hydrogen gas is trapped (that is, hydrogen gas Acts as a mask for the etching reaction.) Also, the etch reaction does not occur smoothly at the place where the trapped hydrogen rises to the surface and scratches the silicon. Therefore, the size and irregularity of the pyramid increases due to the blocking effect of hydrogen gas, which causes a problem in that the photoelectric conversion efficiency of the solar cell decreases.

Accordingly, the first problem to be solved by the present invention is to provide a method of texturing a silicon wafer for a solar cell having a dense and uniform pyramid.

The second problem to be solved by the present invention is to provide a silicon wafer for solar cells having a dense and uniform pyramid.

The third problem to be solved by the present invention is to provide a solar cell silicon wafer having a compact and uniform pyramid, thereby providing a solar cell with improved light efficiency.

In order to achieve the first object of the present invention,

In the chemical etching process for texturing a silicon wafer for solar cells,

It provides a method of texturing a silicon wafer for a solar cell comprising the step of adjusting the pressure applied to the etching solution to a low pressure less than the normal pressure.

According to one embodiment of the invention, the texturing method of the silicon wafer for solar cells

(a) immersing the silicon wafer in an etching solution located in the chamber and maintaining it under normal pressure; And

(b) controlling the pressure applied to the etching solution.

According to another embodiment of the present invention, the step of adjusting the pressure applied to the etching solution is

(c) lowering and maintaining the pressure applied to the etching solution to a low pressure below normal pressure; and

(d) increasing the pressure applied to the reduced pressure etching solution to normal pressure and then maintaining the same.

According to another embodiment of the present invention, the step of adjusting the pressure applied to the etching solution is

(C) and (d) may be repeated a plurality of times.

According to another embodiment of the present invention, the texturing method of the silicon wafer for solar cells

The time ratio of steps (a) and (b) may be 1: 2.

According to another embodiment of the present invention, the step of adjusting the pressure applied to the etching solution is

The time ratio of steps (c) and (d) may be 1: 1.

According to another embodiment of the present invention, the low pressure less than the normal pressure of the step (c) may be 0.01 ~ 0.1mPa lower than the normal pressure.

According to another embodiment of the present invention, the silicon wafer may be n-type single crystal silicon or p-type single crystal silicon.

According to another embodiment of the present invention, the silicon wafer may be n-type polycrystalline silicon or p-type polycrystalline silicon.

According to another embodiment of the present invention, the temperature of the etching solution may be 70 ~ 80 ℃.

According to another embodiment of the present invention, the etching solution may be composed of basic hydrate, additives and deionized water.

According to another embodiment of the present invention, the basic hydrate may be any one or more selected from the group of KOH, NaOH, CsOH, RbOH, (CH ₃ ) ₄ NOH and NH ₄ OH.

According to another embodiment of the present invention, the additive may be any one or more selected from the group (CH ₃ ) ₂ CHOH, Na ₂ CO ₃ and K ₂ CO ₃ .

According to another embodiment of the present invention, the volume% of the basic hydrate, additives and deionized water of the etching solution may be 0.5 to 5: 3.0 to 20.0: 75.0 to 96.5.

The present invention provides a solar cell silicon wafer textured in accordance with the silicon wafer texturing method for the solar cell in order to achieve the second object.

According to one embodiment of the invention, the surface of the silicon wafer for solar cells may have a pyramid structure.

According to another embodiment of the present invention, the width of the standard pyramid may be 0.1 to 5㎛.

According to another embodiment of the present invention, the roughness (RMS) of the silicon wafer for solar cells may be 100 ~ 645nm.

According to another embodiment of the present invention, the reflectivity of the silicon wafer may be 5 to 10% at a wavelength of 400 to 800 nm.

The present invention provides a solar cell comprising the silicon wafer for the solar cell in order to achieve the third object.

The texturing process at low pressure according to the present invention effectively removes the blocking effect of hydrogen gas to form a more regular and smaller pyramid on the silicon wafer surface. Compared to the prior art, the size of the pyramid was reduced by about 2 to 3 micrometers and the RMS roughness was reduced by about 200 nm to obtain an improved surface state. Reflectivity was also reduced by about 2-3% over the entire wavelength range. Based on these results, the texturing process at low pressure is expected to contribute to the improvement of efficiency in manufacturing high efficiency solar cell. Therefore, the present invention provides a texturing process at a low pressure, the manufacturing process is simple and the manufacturing time is short, has an excellent effect in the industrial aspect, the silicon wafer manufactured by the present invention has the effect of increasing the efficiency of the solar cell silicon It can provide significant advantages in the field of texturing of wafers.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples. However, these Examples and Test Examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these Examples and Test Examples. .

In order to solve the problems of the prior art, the present invention provides a method for reducing the cost and improving the efficiency of a texturing process using a chemical etching method. Provides a texturing process.

To this end, the present invention is to effectively remove the hydrogen gas generated in the reaction process by adjusting the pressure applied to the etching solution for texturing the silicon wafer to less than normal pressure, as a result for a solar cell having a uniform and compact pyramid structure Silicon wafers can be textured.

The texturing method of the silicon wafer for solar cells according to the present invention will be described in more detail with reference to the following drawings.

A schematic of the entire texturing process of the present invention is shown in FIG. 2. Referring to FIG. 2, the entire texturing process includes a wafer cleaning step using a sulfuric acid-hydrogen peroxide mixture (SPM); Washing with deionized water (DIW); A wafer cleaning step using a hydrochloric acid-hydrogen peroxide-water mixture (HPM); Washing with deionized water; Saw damage etching (SDE); Washing with deionized water; Etching with dilute HF; Washing with deionized water; Texturing; Washing with deionized water; and drying.

Saw Damage Etching (SDE) refers to the use of suitable chemical methods to remove the defect-rich layer resulting from the silicon wafer cutting process. In general, isotropic etching is performed using KOH. In FIG. 2, since SDE was used using a basic hydroxide etching solution, it was expressed as "alkali SDE".

In addition, the SPM or HPM is typically a cleaning solution for removing contaminants in a semiconductor process using a silicon substrate, SPM is for removing organic matter and HPM is for removing metal impurities. In addition, the diluted hydrofluoric acid is a buffered oxide etching solution (BOE; Buffered Oxide Echant).

The previous step of the texturing step of FIG. 2 is commonly referred to as a pretreatment process and is a process for cleaning the surface of a silicon wafer. The pretreatment process of the present invention is not particularly limited and is conventionally performed in the art.

As described above, the texturing process according to the prior art has its limitations in making the surface pyramid structure more dense and uniform, and the inventors pay close attention to this, and the limitation of the prior art is due to the hydrogen gas generated during the texturing process. It will be apparent that the following description will be made in detail with reference to the accompanying drawings.

Figure 3 shows the increase in irregularities of the pyramid due to the hydrogen gas blocking effect.

Referring to FIG. 3, it can be seen that the light confinement phenomenon decreases as the size and irregularity of the pyramid increase due to the hydrogen gas blocking effect as described above, thereby decreasing the efficiency of the solar cell. In order to remove the hydrogen gas blocking effect to increase the efficiency of the solar cell, the present invention focuses on the fact that when the hydrogen gas is quickly removed from the silicon wafer surface, the texturing structure becomes more dense and uniform. In order to reduce the concentration of hydrogen gas in the solution, to achieve this purpose, the effect of blocking the hydrogen gas was effectively achieved by reducing the pressure exerted on the etching solution. This is because the solubility of gases in liquids increases with higher pressure.

Therefore, the texturing process should be performed at low pressure to reduce the pressure applied to the etching solution.

4 is a schematic diagram of an apparatus for implementing a texturing method at low pressure according to the present invention.

4, an air inlet 410 and an air outlet 420 are connected to the vacuum chamber 400, and a vacuum pump 430 is connected to the air outlet. A pressure gauge 440 was also installed in the vacuum chamber for measuring the pressure in the vacuum chamber. At the lower end of the vacuum chamber, there is a heating part 450, and an etch bath 460 is placed on the heating part.

Hereinafter, the texturing process at low pressure will be described in more detail.

The etching solution was placed on a heating unit in a vacuum chamber and the etching solution was heated.

The heating unit is not particularly limited and is commonly used in the art. Accordingly, the heating part may be a hot water heating part using a hot plate or silicone oil. In one embodiment of the present invention was used a hot plate.

In addition, the etching solution is not particularly limited and is commonly used in the art. In general, an etching solution uses a basic solution, which includes basic hydrates, additives, and deionized water, and the basic hydrates serve to etch silicon wafers, and the additives are added for etching rate control. The basic hydrate may be any one selected from the group of KOH, NaOH, CsOH, RbOH, (CH ₃ ) ₄ NOH (tetramethyl ammonium hydroxide, TMAH) and NH ₄ OH, the additive is IPA, Na ₂ CO ₃ and K ₂ It may be any one selected from the group CO ₃ .

The composition ratio of the etching solution is a requirement that has a major influence in forming uniform and dense pyramids. The composition ratio is optimized for forming a uniform and dense pyramid, depending on the material selected, the material being etched and the texturing environment. In the present invention, it is preferable to mix and use the composition of the etching solution in a volume% of KOH: IPA: DIW = 0.5 to 5.0: 3.0 to 20.0: 75.0 to 96.5, because the blocking effect of hydrogen gas in the above composition ratio This can be effectively prevented.

In an embodiment of the present invention, an etching solution using KOH, IPA, and DIW in a volume ratio of 1: 6: 55 was used.

The temperature of the etching solution is preferably maintained at 70 ~ 80 ℃, because the break point of the IPA is 82.5 ℃, when the temperature of the etching solution is more than 80 ℃ IPA evaporates to change the composition of the etching solution Because it comes. In one embodiment of the present invention it was set to 80 ℃.

Next, the pre-treated silicon wafer 470 is placed on the fixed plate in the heated etching solution and then immersed in the etching solution to perform an etching process.

The silicon wafer used in the present invention is not particularly limited and may be any one selected from the group consisting of n-type single crystal silicon, n-type polycrystalline silicon, p-type single crystal silicon and p-type polycrystalline silicon. In one embodiment of the present invention, n-type polycrystalline silicon was used.

The etching process

(a) immersing the silicon wafer in an etching solution located in a chamber applied to the etching solution and maintaining it under normal pressure; And

(b) adjusting the pressure applied to the etching solution.

Maintaining the pressure applied to the solution at atmospheric pressure is performed at a constant pressure in the chamber for a predetermined time, because chemical etching is performed on the surface of the pretreated silicon wafer to form a pyramid. The time to maintain the atmospheric pressure is the time until hydrogen gas is generated and its diameter becomes 1 mm, until the hydrogen gas blocking effect occurs.

Next, the step of controlling the pressure applied to the etching solution is

(c) lowering and maintaining the pressure applied to the etching solution to a low pressure below normal pressure; and

(d) increasing the pressure applied to the reduced pressure etching solution to normal pressure and maintaining the same.

Step (c) is carried out by using a vacuum pump to make the pressure in the chamber 0.01 to 0.1 mPa lower than the normal pressure. As described above, when the pressure in the chamber is lowered, the pressure inside the chamber is lower than the pressure outside the chamber, and a pressure difference occurs. This pressure difference lowers the pressure applied to the etching solution so that the hydrogen gas quickly exits the etching solution. Therefore, the hydrogen gas blocking effect can be effectively blocked.

In the present invention, the pressure applied to the etching solution is 0.01 to 0.1 mPa lower than the normal pressure. The reason is that when the pressure in the chamber applied to the etching solution is less than 0.1 mPa lower than the normal pressure, the IPA of the etching solution evaporates rapidly. This is because the change in the composition of the etching solution is not able to achieve the desired texturing, and when the pressure in the chamber applied to the etching solution is more than 0.01 mPa lower than the normal pressure, the hydrogen gas blocking effect is insufficient.

In the step (c) of the embodiment of the present invention, the pressure in the chamber was maintained at 0.015 mPa lower than the normal pressure, and the texturing was performed.

In the step (d), when the step (c) is performed and all of the hydrogen gas is released from the etching solution, the pressure in the chamber is maintained at atmospheric pressure again to allow etching to occur in the portion where the etching is not performed.

Next, the steps (c) and (d) were repeated a plurality of times to texture the entire surface of the silicon wafer while effectively preventing the hydrogen gas blocking effect to form a uniform and small pyramid.

As described above, the time ratios of steps (a) and (b) and the time ratios of steps (c) and (d) are determined. These time ratios may vary depending on the size of the silicon wafer and the texturing environment. It is not particularly limited.

 In an embodiment of the present invention, the time ratio of steps (a) and (b) is 1: 2, and the time ratio of steps (c) and (d) is 1: 1.

On the other hand, in general, the texturing process by chemical etching is performed between 30 to 40 minutes because it must be completed before the composition change by evaporation of the IPA occurs.

In the present invention, the texturing process was performed for 30 minutes. As described above, the time ratios of steps (a) and (b) were set to 1: 2, and the time ratios of steps (c) and (d) were set to 1: 1. In order to maintain the initial pressure for 10 minutes in step (a) and to adjust the pressure applied to the etching solution in the latter 20 minutes in step (b), the pressure control in the latter 20 minutes in step (b) A low pressure holding step (5 minutes) → (d) is a normal pressure holding step (5 minutes) → (c) a low pressure holding step (5 minutes) → (d) step is a normal pressure holding step (5 minutes).

Next, the silicon wafer was removed from the etching solution, washed with deionized water, and dried.

Silicon wafers textured by the present invention are described in more detail below.

The standard pyramid size, RMS roughness, and reflectance of a silicon wafer textured by the present invention depend on the composition of the etching solution, the temperature of the etching solution, the pressure during the etching process, and the like.

The size, RMS roughness and reflectance of the standard pyramid of the silicon wafer textured by the above method may be adjusted to a level desired by the user according to the etching solution and the texturing process conditions, and are not particularly limited.

As described above, the size of the standard pyramid according to the present invention is not particularly limited, but is preferably 0.1 to 5 mu m. This is because the texturing of the standard pyramid having a size of 0.1 μm or less has a practical difficulty in the texturing process, and when the size of the standard pyramid is 5 μm or more, the reflectance increases and the efficiency of the solar cell decreases.

 The "standard pyramid size" is a value corresponding to the length of one side of the bottom surface of the pyramid formed on the silicon wafer. As described above, the texturing method according to the present invention has an advantage of controlling the texturing form of a desired dimension by simply adjusting the low pressure condition.

In addition, the root mean square roughness and reflectivity of the silicon wafer textured by the above method is not particularly limited, but the RMS roughness is preferably 100 to 645 nm, and the reflectivity is preferably 5 to 10%. The reason is as described above.

Example  One

Example  1- (1)

Pretreatment process

In order to texturize the silicon wafer, a 270 탆 thick silicon wafer was cut into a shape of 2 cm wide and 2 cm long. The cut silicon wafer was washed with SPM (H ₂ SO ₄ : H ₂ O ₂ = 2: 1, volume ratio) at 85 ° C., followed by deionized water. The cleaned silicon wafer was washed again using HPM (HCl: H ₂ O ₂ : DIW = 1: 2: 5, volume ratio) at 80 ° C. Thereafter, the washed silicon wafer was washed with deionized water and then SDE was used using a 45% purity KOH solution heated to 85 ° C. The SDE-treated silicon wafer was washed with deionized water and then treated with BOE for 30 seconds using dilute hydrofluoric acid (HF: DIW = 1: 10, volume ratio) at 25 ° C., followed by deionized water.

Example  1- (2)

Texturing  fair

An etching solution containing KOH, IPA and deionized water in a volume ratio of 1: 6: 55 was placed in a vacuum chamber and heated to 80 ° C using a hot plate. The pre-treated silicon wafer of Example 1- (1) was immersed in the heated etching solution, followed by a texturing process for 30 minutes. The initial 10 minutes were maintained at atmospheric pressure and the pressure was adjusted for the latter 20 minutes. The pressure control was performed by repeating the low pressure maintaining step of keeping the pressure in the chamber at 0.015 mPa lower than the normal pressure and maintaining the pressure in the chamber at normal pressure again to adjust the pressure applied to the etching solution. In other words, the pressure in the chamber was regulated by the low pressure holding step (5 minutes)-normal pressure holding step (5 minutes)-low pressure holding step (5 minutes)-normal pressure holding step (5 minutes).

Comparative example  One

The conditions different from those of Example 1- (2) were the same, and the difference was only in the point of texturing at normal pressure as Comparative Example 1.

Comparative example  2

The silicon wafer which performed only the pretreatment process of Example 1- (1) was made into the comparative example 2.

Test Example

Test Example  One

Texturing  In process Generated  Visual observation of the amount of hydrogen gas

Figure 5a is a visual observation of the amount of hydrogen gas generated during the texturing process at low pressure of Example 1- (2), Figure 5b shows the amount of hydrogen gas generated during the texturing process at normal pressure of Comparative Example 1 It was observed with the naked eye. 5A and 5B, it can be seen that the amount of hydrogen gas of FIG. 5A is significantly reduced than the amount of hydrogen gas of FIG. 5B. This is because the hydrogen gas blocking effect is blocked at low pressure as described above.

Test Example  2

Surface analysis

Figure 6a is a photograph of the surface of Example 1- (2), Figure 6b is a photograph of the surface of Comparative Example 1.

6A and 6B, in the case of Comparative Example 1, traces of scratching of hydrogen gas may be found. This is because the hydrogen gas blocking effect occurred in Comparative Example 1.

SEM ( Scanning Electron Microscopy A) analysis and measurement of standard pyramid sizes

7A is an SEM photograph of Example 1- (2), and FIG. 7B is an SEM photograph of Comparative Example 1. FIG.

7A and 7B, it can be seen that the pyramids of Examples 1- (2) are small in size and uniform. In addition, the standard pyramid size was measured using SEM, and the standard pyramid size is a value corresponding to the length of one side of the bottom surface of the pyramid formed on the silicon wafer.

The measured standard pyramid size was 3 to 4 µm for Example 1- (2) and 5 to 7 µm for Comparative Example 1.

AFM ( Atomic Force Microscopy Analysis and RMS  Roughness ( Root Mean Square  roughness analysis

 8A is an AFM photograph of Example 1- (2), and FIG. 8B is an AFM photograph of Comparative Example 1. FIG.

8A and 8B, it can be seen that the size of the pyramid of Example 1- (2) is small and uniform. In addition, in order to measure the uniformity of the pyramid of Example 1- (2) and the comparative example 1, RMS roughness was measured using the said AFM.

The RMS roughness value measured using the AFM was 640.8 nm in Example 1- (2) and 825.3 nm in Comparative Example 1. In other words, it can be seen that the RMS roughness of Example 1- (2) was reduced by about 200 nm than that of Comparative Example 1. This is because the hydrogen gas blocking effect is effectively blocked by the pressure adjusting step according to the present invention to form a uniform pyramid.

Test Example 3

Reflectivity measurement

FIG. 9 shows the reflectivity of Examples 1- (2), Comparative Examples 1 and 2 using an UV-VIS spectrophotometer.

Referring to FIG. 9, it can be seen that the reflectivity of Example 1- (2) decreased by about 2 to 3% over the entire wavelength range. This is because in the case of Example 1- (2), a uniform and small pyramid is formed by the texturing method according to the present invention, thereby reducing optical loss due to an increase in light confinement. This texturing technology maximizes the absorption of light, improving solar cell efficiency.

Important measurements of the test examples are shown in Table 1.

Comparative Example 1 Example 1- (2) Standard pyramid size 5-7㎛ 3 ~ 4㎛ RMS roughness 825.5 nm 640.8 nm Reflectivity (% R at 400 ~ 800nm) 9.73% 7.64%

Therefore, the silicon wafer textured according to the present invention from the above test results effectively removed the hydrogen gas blocking effect through the texturing process at low pressure, thereby forming a regular and smaller pyramid than the textured silicon wafer at normal pressure. The standard pyramid size was reduced by about 2-3 μm and the RMS roughness was also reduced by about 200 nm to obtain an improved surface condition. Reflectivity also decreased by about 2 to 3% over the entire wavelength range. Based on these results, the texturing process at low pressure is expected to contribute to the improvement of efficiency in manufacturing high efficiency solar cell.

1 shows the asymmetry of the p-n junction.

Figure 2 shows a schematic diagram of the entire texturing process of the present invention.

Figure 3 shows the increase in irregularities of the pyramid due to the hydrogen gas blocking effect.

4 is a schematic diagram of a texturing method at low pressure according to the present invention.

5a visually observes the amount of hydrogen gas generated during the texturing process at low pressure of Example 1- (2).

Figure 5b is a visual observation of the amount of hydrogen gas generated during the texturing process at normal pressure of Comparative Example 1.

6A is a photograph of the surface of Example 1- (2).

6B is a photograph of the surface of Comparative Example 1. FIG.

7A is a SEM photograph of Example 1- (2).

7B is a SEM photograph of Comparative Example 1. FIG.

8A is an AFM photograph of Example 1- (2).

8B is an AFM photograph of Comparative Example 1. FIG.

9 is a measured value of reflectivity of Example 1- (2), Comparative Example 1 and Comparative Example 2. FIG.

Claims (20)

In the chemical etching process for texturing a silicon wafer for solar cells, (a) immersing the silicon wafer in an etching solution located in the chamber and maintaining it under normal pressure; And (b) adjusting the pressure applied to the etching solution, Step (b) is (c) lowering and maintaining the pressure applied to the etching solution to a low pressure below normal pressure; and (d) increasing the pressure applied to the etching solution lowered to a low pressure below the normal pressure again to normal pressure and maintaining the same. delete delete The method of claim 1, A method of texturing a silicon wafer for a solar cell, comprising repeating steps (c) and (d) a plurality of times. The method of claim 1, wherein the time ratio of steps (a) and (b) is 1: 2. The method of claim 1, wherein the time ratio of steps (c) and (d) is 1: 1. The method of texturing a silicon wafer for solar cells according to claim 1, wherein the low pressure below the normal pressure of step (c) is 0.01 to 0.1 mPa lower than the normal pressure. The method of claim 1, wherein the silicon wafer is n-type single crystal silicon or p-type single crystal silicon. The method of claim 1, wherein the silicon wafer is n-type polycrystalline silicon or p-type polycrystalline silicon. The method of claim 1, wherein the etching solution has a temperature of about 70 ° C. to about 80 ° C. 6. The method of claim 1, wherein the etching solution comprises a basic hydrate, an additive, and deionized water. The method of claim 11, wherein the basic hydrate is at least one selected from the group consisting of KOH, NaOH, CsOH, RbOH, (CH ₃ ) ₄ NOH, and NH ₄ OH. The method of claim 11, wherein the additive is at least one selected from the group (CH ₃ ) ₂ CHOH, Na ₂ CO _3, and K ₂ CO ₃ . The method of claim 11, wherein the etching solution has a volume percentage of basic hydrate, additive, and deionized water of 0.5 to 5: 3.0 to 20.0: 75.0 to 96.5. delete delete delete delete delete delete

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