TWI605109B - Wet etching surface treatment method and the method of preparing a porous silicon wafer - Google Patents

Description

Microporous germanium wafer prepared by wet etching surface treatment method and method thereof

The present invention relates to an etching solution, and more particularly to a microetched wafer obtained by a wet etching surface treatment method and a method thereof.

In view of the growing problem of the energy crisis, the green energy industry is constantly seeking a variety of alternative energy sources to replace the oil in order to cope with the energy crisis. The most common ones are non-solar batteries. In the solar cell-related industries, polycrystalline germanium (Si) solar cells have been widely recognized by the industry because of their simplicity in process compared to single crystal germanium solar cells and good photo-to-current conversion efficiency (PCE). It is well known to those skilled in the solar cell related industry that only reducing the reflectance of the light-receiving surface of the solar cell is advantageous for increasing the light absorption of the light-receiving surface, and thereby improving the PCE of the solar cell.

Referring to FIG. 1, the invention patent case No. I538986 of the Republic of China (hereinafter referred to as the first case 1) discloses a method of surface roughening, which comprises a step S11, a step S12, a step S13, and a step S14 in sequence.

The step S11 is to provide a tantalum substrate obtained by cutting a diamond wire, before The diamond wire cut is also referred to as a fixed abrasive grain cut. In detail, the step S11 of the first case 1 is to cut a silicon brick by using a diamond wire and a diamond cutting line coated on the surface of the steel wire to cut a silicon brick (Si brick); The twinned bricks are obtained by squaring a squaring ingot (Si ingot). However, the surface roughness of the tantalum substrate obtained by the transverse sectioning of the diamond line is low, in particular, the strip surface has a plurality of strip-shaped incisions, and the strip-shaped incisions belong to a smooth surface, which cannot effectively reduce the tantalum substrate. The reflectivity of the glossy surface. Therefore, this step S12 needs to be further implemented.

The step S12 is an acid etching of the germanium substrate by using an etchant; wherein the acid etching is performed for a time of 5 seconds or less, and a temperature of 15 ° C or less, and the etchant contains hydrofluoric acid (HF) and nitric acid. (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ) and water (H ₂ O). In terms of weight percent of the etchant (wt%), 10<HF 17;35<HNO ₃ 40;0<H ₂ SO ₄ 10;65<H ₂ O 70.

This step S13 is to rinse the acid-etched tantalum substrate with deionized water to terminate the etching reaction. Finally, the step S14 is to dry the crucible substrate.

The analysis data of the foregoing case 1 shows that although the method of roughening the surface disclosed in the first case 1 can eliminate the strip-shaped cut marks of the light-receiving surface of the substrate, the roughness of the light-receiving surface can be improved. However, the reflectivity of the method of the first case for the light-receiving surface of the substrate is not found in the previous case 1.

According to the above description, the composition ratio of the modified acid etchant is applied to make it apply. The surface treatment of the polycrystalline silicon wafer, and thereby reducing the reflectance of the surface of the polycrystalline silicon wafer after the surface treatment, is a subject to be solved by those skilled in the art.

Accordingly, it is an object of the present invention to provide an acid etching solution capable of reducing the reflectance of the light-receiving surface of a polycrystalline silicon wafer.

Another object of the present invention is to provide a wet etching surface treatment method for the aforementioned acid etching solution.

It is still another object of the present invention to provide a microporous wafer produced by the above method.

Thus, the acid etching solution of the present invention contains hydrofluoric acid, nitric acid, a buffer, and water in weight percent (wt%). Hydrofluoric acid is between 35 wt% and 60 wt%; nitric acid is between 20 wt% and 30 wt%; buffer is greater than 0 wt% and less than or equal to 5 wt%; water is between 20 wt% and 40 wt%.

In addition, the wet etching surface treatment method of the present invention comprises an acid etching step, an alkali etching step, a pickling step, and a drying step. The acid etching step is to apply an acid etching to the polycrystalline silicon wafer obtained by cutting a fixed particle by using an acid etching solution as described above, so that a light-receiving surface of the polycrystalline silicon wafer is formed with a plurality of micropores. The alkali etching step is performed by applying an alkali etching solution to the polycrystalline germanium sheet after the acid etching step to remove incomplete by-products and residual acid from the acid etching step. An etching solution containing potassium hydroxide, an oxidizing agent, and water. The acid The washing step is to pickle the polycrystalline tantalum sheet after the alkali etching step using a water-based acid pickling solution to remove the cerium oxide generated in the alkali etching step from the light collecting surface. The drying step is drying the polycrystalline crucible after the pickling step.

Further, the microporous germanium wafer of the present invention comprises a polycrystalline germanium sheet prepared by the wet etching surface treatment method as described above, comprising a polycrystalline germanium body and a light collecting surface connecting the polycrystalline germanium body. The light-receiving surface is formed with a plurality of micro-holes recessed toward the polycrystalline body, and a width (W) of the micro-holes is between 0.571 μm and 1.638 μm, and a depth (H) of the micro-holes is Between 0.165μm and 0.49μm.

The utility model has the advantages that the composition ratio of the acid etching solution is improved, and the acid etching solution contains a low content of HNO ₃ and a high content of HF, so that the pore size on the light receiving surface of the polycrystalline silicon sheet can be controlled in the deep submicron ( <0.25 μm) to sub-micron (~1 μm) to reduce the average reflectance of the light-receiving surface.

S20‧‧‧Washing steps

S21‧‧‧ Acid etching step

S22‧‧‧ Alkali etching step

S23‧‧‧ pickling step

S24‧‧‧ drying step

Other features and effects of the present invention will be apparent from the following description of the drawings, wherein: FIG. 1 is a flow chart illustrating a method of surface roughening disclosed in the Patent No. I538986 of the Republic of China; 2 is a flow chart illustrating an embodiment of the wet etching surface treatment method of the present invention; and FIG. 3 is a low magnification scanning electron microscope (scanning electron microscope) Microscope (hereinafter referred to as SEM) surface image, which illustrates the surface topography of a polycrystalline silicon wafer obtained by one of the wet etching surface treatment methods of the present invention (E2) before the acid etching step is performed; FIG. 4 is a low magnification SEM. The surface image shows the surface topography of the specific example 2 (E2) of the present invention after the wet etching surface treatment method is completed; and FIG. 5 is a high-magnification SEM surface image, illustrating the specific example 2 (E2) of the present invention. The surface topography after the wet etching surface treatment method; FIG. 6 is a high-magnification SEM surface image, illustrating the surface topography of the specific example 2 (E2) of the present invention after the wet etching surface treatment method is completed; Is a high-magnification SEM cross-sectional image, illustrating the cross-sectional morphology of the specific example 2 (E2) of the present invention after the wet etching surface treatment method is completed; FIG. 8 is a high-magnification SEM cross-sectional image, illustrating the specific example 2 of the present invention. (E2) a cross-sectional morphology after the wet etching surface treatment method is performed; FIG. 9 is a reflectance versus wavelength graph, illustrating a comparative example 1 (CE1) and a wet etching surface treatment method of the present invention. Specific Example 1 (E1), Specific Example 2 (E2), and Specific Example 3 (E3) a reflectance of a microporous germanium wafer prepared in Comparative Example 2 (CE2); and FIG. 10 is a reflectance versus wavelength graph illustrating a comparative example 3 (CE3) of the wet etching surface treatment method of the present invention and the specific The reflectance of the microporous germanium wafer prepared in Example 2 (E2).

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same reference numerals.

<Detailed Description of the Invention>

An embodiment of the acid etchant of the present invention contains hydrofluoric acid, nitric acid, a buffer, and water in weight percent (wt%). Hydrofluoric acid is between 35 wt% and 60 wt%; nitric acid is between 20 wt% and 30 wt%; buffer is greater than 0 wt% and less than or equal to 5 wt%; water is between 20 wt% and 40 wt%.

Preferably, the buffer contains water, a surfactant, and an acid. The acid is a group selected from the group consisting of phosphoric acid (H ₃ PO ₄ ), sulfuric acid, acetic acid (CH ₃ COOH), and a combination of the foregoing acids; the surfactant is a group selected from the group consisting of Organic solvents: polyalcohols, aldehydes, ketones, esters, and combinations of the foregoing organic solvents. More preferably, the content of water is between 93% by weight and 98% by weight based on the weight percent of the buffer; the content of the surfactant is between 0.5% and 2% by weight; the content of the acid is between 1.5% by weight Between % and 5 wt%.

The correlation of the composition range of the acid etching liquid of the present invention will be described later.

As shown in FIG. 2, an embodiment of the wet etching surface treatment method of the present invention comprises an acid etching step S21, an alkali etching step S22, a pickling step S23, and a dry Drying step S24.

The acid etching step S21 is an acid etching of a polycrystalline silicon wafer obtained by cutting a fixed particle by using an acid etching solution as described above, so that a light-receiving surface of the polycrystalline silicon wafer is formed with a plurality of micropores. . Preferably, the acid etching step S21 has a processing temperature (T _S21 ) and a processing time (t _S21 ). In an embodiment of the wet etching surface treatment method of the present invention, T _S21 32 ° C, and t _S21 90 seconds.

The alkali etching step S22 is performed by using an alkali etching solution to apply alkali etching to the polycrystalline silicon wafer after the acid etching step S21 to remove incomplete by-products and residues from the acid etching step when the acid etching step is removed. Acid etchant. The alkali etching solution contains potassium hydroxide (KOH), an oxidizing agent, and water. Preferably, the oxidant in the alkali etching solution of the alkali etching step S22 is hydrogen peroxide (H ₂ O ₂ ); the alkali etching step S22 has a processing temperature (T _S22 ) and a processing time (t _S22 ). More preferably, the content of potassium hydroxide is between 10% by weight and 70% by weight, the content of hydrogen peroxide is more than 0% by weight and less than or equal to 10% by weight, and the water content is Between 30 wt% and 90 wt%. In an embodiment of the wet etch surface treatment method of the present invention, T _S22 50 ° C, and t _S22 60 seconds.

The pickling step S23 is performed by pickling the polycrystalline silicon wafer after the alkali etching step S22 with a water-based acid pickling liquid to remove the alkali etching step S23 from the light collecting surface. Yttrium oxide. Preferably, the acid washing liquid of the pickling step S23 contains hydrofluoric acid, hydrochloric acid (HCl), and water; the pickling step S23 has a processing temperature (T _S23 ) and a processing time (t _S23 ). More preferably, the content of hydrofluoric acid is between 1% by weight and 10% by weight, the content of hydrochloric acid is between 1% by weight and 10% by weight, and the water content is between 80% by weight. Between % and 98% by weight. In an embodiment of the wet etch surface treatment method of the present invention, T _S23 25 ° C, and t _S23 300 seconds.

The drying step S24 is to dry the polycrystalline silicon wafer after the pickling step S23.

Preferably, the embodiment of the wet etching surface treatment method of the present invention further comprises a water washing step S20 after the acid etching step S21, the alkali etching step S22 and the pickling step S23.

An embodiment of the microporous wafer of the present invention comprises a polycrystalline tantalum sheet prepared by the embodiment of the wet etching surface treatment method as described above, comprising a polycrystalline germanium body and a light collecting surface connecting the polycrystalline germanium body. The light-receiving surface is formed with a plurality of micro-holes recessed toward the polycrystalline body. A width (W) of the micropores is between 0.571 μm and 1.638 μm, and a depth (H) of the micropores is between 0.165 μm and 0.49 μm.

Preferably, the micropores have an aspect ratio (H/D) of between 0.10 and 0.86 such that an average reflectance of a source between 400 nm and 1000 nm incident on the microporous wafer is Less than or equal to 26%.

It should be noted that the HNO ₃ in the acid etching solution of the acid etching step S21 is for oxidizing the germanium atoms on the light-receiving surface of the polycrystalline germanium sheet into cerium oxide (SiO ₂ ) molecules; the acid etching step The purpose of the HF in the acid etching solution of S21 is to react the SiO ₂ molecules formed on the light-receiving surface of the polycrystalline silicon wafer into hexafluoroantimonic acid (H ₂ SiF ₆ ), so that the SiO ₂ molecules on the light-receiving surface are removed. Dropping to form the micropores; the buffer in the acid etching solution of the acid etching step S21 is for controlling the etching reaction rate of the twinned surface, permeating a hydrophilic group having a carbon-hydrogen bond, and having a hydrogen-oxygen bond The hydrophobic base acid etchant easily contacts the surface of the polycrystalline silicon wafer to achieve a uniform etching effect, and defoaming is achieved in the acid etching step S21.

Based on the above description, when the HNO ₃ ratio in the acid etching solution of the acid etching step S21 is less than 20% by weight, the reaction rate of the deuterium atom to SiO ₂ is lowered, and the processing time of the acid etching step S21 cannot be performed (t _S21 ; The reaction is completed in 90 seconds. When the HNO ₃ ratio in the acid etching solution of the acid etching step S21 is more than 30% by weight, the micropores are widened, and the reflectance of the light-receiving surface cannot be lowered. When the HF ratio in the acid etching solution of the acid etching step S21 is less than 35 wt%, the reaction rate of SiO ₂ to H ₂ SiF ₆ is lowered, and the processing time of the acid etching step S21 cannot be performed (t _S21 ; 90 seconds). When the reaction is completed, when the HF ratio in the acid etching solution of the acid etching step S21 is more than 60% by weight, smaller pores are formed in the acid etching step S21, which can effectively reduce the reflection of the light-receiving surface thereof. However, the passivation effect of the tantalum nitride (SiN) layer formed by chemical vapor deposition (CVD) in the downstream battery process is not good, resulting in a decrease in electrical properties and thus a decrease in the PCE of the solar cell. In addition, when the buffer ratio in the acid etching solution of the acid etching step S21 is more than 5% by weight, the concentration of HF in the acid etching solution is lowered, which affects the reaction rate of the acid etching.

It should be additionally noted here that the purpose of the alkali etching step S22 is to remove by-products whose residual light-receiving surface is not completely reacted with residual acid etching liquid.

When the KOH ratio in the alkali etching solution of the alkali etching step S22 is less than 10% by weight, the reaction rate is lowered, and the reaction cannot be completed within the treatment time (t _S22 ; 60 seconds) of the alkali etching step S22, resulting in the light collection thereof. The surface remains with incompletely reacted by-products and acid etching solution, thus affecting the open circuit voltage (Voc) and short circuit current (Isc) of the solar cell completed by the downstream battery factory; When the KOH ratio in the alkali etching solution of the alkali etching step S22 is more than 70% by weight, it is difficult to effectively control the treatment time (t _S22 ), thereby destroying the microporous structure formed by the acid etching step S21, and remaining in the collection. The smooth alkali etchant will also lengthen the time required for the water washing step S20 after the alkali etching step S22. In addition, when the alkali etching solution of the alkali etching step S22 does not contain H ₂ O ₂ , the reaction activity cannot be increased to increase the reaction rate, and it is difficult to effectively remove the acid etching liquid remaining on the light-receiving surface thereof, when the alkali etching When the ratio of H ₂ O ₂ in the alkali etching solution of step S22 is more than 10% by weight, the reaction activity is too high and the reaction rate is too fast, so that it is difficult to control the alkali etching reaction, so that the micro-formation formed by the acid etching step S21 is broken. The pore structure increases the reflectivity of its light-receiving surface.

Finally, it should be additionally noted that the HF in the pickling liquid of the pickling step S23 is for removing the SiO ₂ generated by the light-receiving surface in the alkali etching step S22; the pickling liquid of the pickling step S23 The purpose of the HCl is to remove the metal impurities remaining on the light-receiving surface of the polycrystalline silicon crucible when the fixed crucible is cut.

When the HF ratio in the pickling liquid of the pickling step S23 is less than 1% by weight, the SiO ₂ generated by the alkali etching step S22 cannot be effectively removed, and thus the processing time of the pickling step S23 needs to be extended (t _S23 When the HF ratio in the pickling liquid of the pickling step S23 is more than 10% by weight, although the removal of the SiO ₂ generated by the alkali etching step S22 can be accelerated, an excessively fast reaction rate is disadvantageous to the pickling. The device control of step S23. When the HCl ratio in the pickling liquid of the pickling step S23 is less than 1% by weight, the metal impurities remaining on the light-receiving surface cannot be effectively removed, and thus the processing time (t _S23 ) of the pickling step S23 needs to be relatively When the HCl ratio in the pickling liquid of the pickling step S23 is more than 10% by weight, the metal impurities remaining on the light-receiving surface can be accelerated, but the excessively fast reaction rate is also unfavorable to the pickling step. S23 device control.

<Comparative Example 1 (CE1)>

A comparative example 1 (CE1) of the microporous wafer obtained by the acid etching solution of the present invention, the wet etching surface treatment method and the method thereof is briefly described below.

First, a polycrystalline tantalum piece obtained by cutting a fixed granule is subjected to a 30 ° C using an acid etching solution containing 61 wt% of HF, 25 wt% of HNO ₃ , 1 wt% of a buffering agent and 13 wt% of deionized water. A 30 second acid etching treatment is maintained to form a plurality of micropores on a light-receiving surface of the polycrystalline silicon wafer. In Comparative Example 1 (CE1) of the present invention, the buffer was an additive having a product name of MULTI-TEX manufactured by GP Solar GmbH, which contained about 3% of CH ₃ COOH. After the acid etching treatment, the polycrystalline silicon wafer is subjected to a water washing treatment.

Next, using an alkali etching solution containing 67 wt% of KOH, 3 wt% of H ₂ O ₂ and 30 wt% of deionized water, the acid-etched polycrystalline crucible was subjected to an alkali etching at 30 ° C for 10 seconds. deal with. After the alkali etching treatment, the polycrystalline silicon wafer is subjected to a water washing treatment.

Subsequently, the alkali-etched polycrystalline tantalum sheet was subjected to a pickling treatment at 25 ° C for 60 seconds using an acid pickling solution containing 7 wt% of HF, 9 wt% of HCl and 84 wt% of deionized water. After the pickling treatment, the polycrystalline tantalum sheet was also subjected to a water washing treatment. Finally, the pickled polycrystalline tantalum sheet is dried.

<Specific Example 1 (E1)>

A specific example 1 (E1) of the microporous germanium wafer obtained by the acid etching liquid of the present invention, the wet etching surface treatment method thereof, and the method thereof is substantially the same as Comparative Example 1 (CE1), and the difference is that The content of HF and deionized water in the acid etching solution used in the specific example 1 (E1) for performing the acid etching treatment was 60% by weight and 14% by weight, respectively.

<Specific example 2 (E2)>

A specific example 2 (E2) of the microporous germanium wafer obtained by the acid etching liquid of the present invention, the wet etching surface treatment method and the method thereof is substantially the same as the comparative example 1 (CE1), and the difference is that This specific example 2 (E2) is subjected to an acid etching treatment The content of HF and deionized water in the monoacid etching solution used was 44% by weight and 20% by weight, respectively.

<Specific example 3 (E3)>

A specific example 3 (E3) of the microporous germanium wafer obtained by the acid etching liquid of the present invention, the wet etching surface treatment method and the method thereof is substantially the same as that of the comparative example 1 (CE1), and the difference is that The content of HF and deionized water in the acid etching solution used in the specific example 3 (E3) for performing the acid etching treatment was 35 wt% and 39 wt%, respectively.

<Comparative Example 2 (CE2)>

A comparative example 2 (CE2) of the microporous germanium wafer obtained by the acid etching liquid of the present invention, the wet etching surface treatment method thereof, and the method thereof is substantially the same as Comparative Example 1 (CE1), and the difference is that The content of HF and deionized water in the acid etching liquid used in Comparative Example 2 (CE2) for performing an acid etching treatment was 34% by weight and 40% by weight, respectively.

<Comparative Example 3 (CE3)>

A comparative example 3 (CE3) of the microporous germanium wafer obtained by the acid etching liquid of the present invention, the wet etching surface treatment method and the method thereof is substantially the same as the comparative example 1 (CE1), and the difference is that The acid etching solution used in Comparative Example 3 (CE3) for performing an acid etching treatment contained 17 wt% of HF, 36 wt% of HNO ₃ , 1 wt% of a buffer, and 65 wt% of deionized water. In the comparative example 3 (CE3) of the present invention, the buffer is H ₂ SO ₄ . In other words, the composition of the acid etching solution used in the comparative example 3 (CE3) when the acid etching treatment was carried out was the composition of the first case.

The composition of the acid etching solution used in the comparative examples (CE1, CE2, CE3) and the specific examples (E1, E2, E3) of the present invention for performing the acid etching treatment thereof and the corresponding reflectance correlation analysis thereof The data is simply summarized in the following list 1.

<Analysis data>

^The buffer contains 3% CH ₃ COOH.

^b Buffer is H ₂ SO ₄ .

^The composition of the acid etching solution is the first case.

It can be seen from the low-magnification SEM surface image shown in FIG. 3 that the light-receiving surface of the polycrystalline silicon wafer obtained by the specific example 2 (E2) of the present invention before the acid etching treatment is performed, and the strip is cut by the fixed tantalum. Shaped cuts. Further, the magnification shown in FIG. 4 is higher than that of the low-magnification SEM surface image of FIG. 3, and at the same time, FIG. 3, the polycrystalline silicon wafer of the specific example 2 (E2) of the present invention is subjected to the wet etching surface treatment method. The surface topography of the light-receiving surface continues along the contour of the strip-shaped incision and etches toward the polycrystalline body and removes the strip-shaped incisions left by the cutting of the fixed niobium, thereby allowing the light-receiving surface to reach The effect of roughening.

The high-magnification SEM surface image shown in FIG. 5 and FIG. 6 shows that the polycrystalline silicon wafer of the specific example 2 (E2) of the present invention has a complex micropore width of the light-receiving surface after the wet etching surface treatment method is completed. It is between 0.517μm and 1.638μm. In addition, the high-magnification SEM cross-sectional image shown in FIG. 7 and FIG. 8 shows that the microporous film of the specific example 2 (E2) of the present invention has the micropores on the light-receiving surface after the wet etching surface treatment method is completed. The depth is between 0.165 μm and 0.49 μm.

According to the SEM-related analysis data, the micropore width formed on the light-receiving surface of the polycrystalline silicon wafer after the wet etching surface treatment method is performed by using the acid etching solution, the alkali etching solution and the pickling liquid. It is between the second half micron (<0.5μm) and the submicron (~1μm), and the micropore depth is between the deep submicron (<0.25μm) and the second half micron (<0.5μm). Micron-sized micropores that increase reflectivity. It is presumed that when a light source between 400 nm and 1000 nm is incident on the light-receiving surface of the polycrystalline silicon wafer prepared by the wet etching surface treatment method of the present invention, the reflectance can be effectively reduced.

The reflectance versus wavelength plots shown in Figure 9 are known (see also Table 1 above). These specific examples (E1, E2, E3) of the present invention use low HNO ₃ content (20 wt% to 30 wt%). With an acid etchant with a high HF content (35wt%~60wt%), the polycrystalline ruthenium can react with the acid etch solution to form SiO ₂ molecules and H ₂ SiF ₆ molecules to form micropores, which can make the micropore width fall. The required half-micron (<0.5 μm) to sub-micron (~1 μm) does not cause a problem of widening the microporous structure due to the high HNO ₃ content of the acid etchant to increase the reflectance. Therefore, it is confirmed that the average reflectances of the specific examples (E1, E2, E3) of the present invention are all lower than 26%, which is advantageous for increasing the amount of light entering the polycrystalline silicon wafer receiving surface and increasing the PCE after subsequent fabrication into a solar cell. .

Further, from the reflectance versus wavelength graph shown in Fig. 10 (see also Table 1 above), the average reflectance of this specific example 2 (E2) of the present invention has been lowered to 24.0%. In contrast, Comparative Example 3 (CE3) was used because of the use of an acid etchant having a high HNO ₃ content (36 wt%) and a low HF content (17 wt%), so that its polycrystalline ruthenium was in an acid etchant with Comparative Example 3 (CE3). When the reaction forms SiO ₂ molecules and H ₂ SiF ₆ molecules to form micropores, the microporous structure is broadened and the average reflectance is as high as 27.5%.

The microporous germanium wafers prepared by the specific examples (E1, E2, E3) and the comparative example 3 (CE3) of the present invention are further separately fabricated into a solar cell, and the solar cells are subjected to electrical analysis results. Display (see Table 2. below). These specific examples (E1~E3) are based on their average reflectance only between 24.4% and 25.4%, so the maximum values of open circuit voltage (Voc) and short circuit current (Isc) are respectively 0.6329V and 9.0253mA, and the fill factor (FF) and average photoelectric conversion efficiency (PCE) are between 79.904 and 79.251 and between 18.557 and 18.375, respectively. In contrast, Comparative Example 3 (CE3) has an average reflectance of 27.5%, so that its open circuit voltage (Voc) and short circuit current (Isc) are only 0.6034V and 8.7311mA, respectively, and the fill factor (FF) and average photoelectricity. Conversion efficiency (PCE) is reduced to 77.653 and 16.655%.

^The composition of the acid etching solution is the first case.

It can be seen from the analysis of the above paragraphs that the acid etching solution with low HNO ₃ content and high HF content of the present invention and the wet etching surface treatment method thereof can be used to remove micropores on the surface of the polycrystalline silicon wafer after wet etching. The size falls between the deep sub-micron (<0.25μm) to the sub-micron (~1μm) to obtain an average reflectance between 24.4% and 25.4%, and the solar cell fabricated in the subsequent one is more due to its average reflectance. The maximum open circuit voltage (Voc) and maximum short circuit current (Isc) are 0.6329V and 9.0253mA, respectively, and the fill factor (FF) and average photoelectric conversion efficiency (PCE) are between 79.904 and 79.251 and between 18.557, respectively. To 18.375 rooms.

In summary, the microporous germanium wafer prepared by the acid etching solution of the present invention, the wet etching surface treatment method and the method thereof can be used for the polycrystalline germanium film by using an acid etching solution having a low HNO ₃ content and a high HF content. The size of the micropores on the surface can be controlled between deep sub-micron (<0.25μm) and sub-micron (~1μm), so that the average reflectance of the light-receiving surface can be less than or equal to 26%, and after subsequent fabrication of solar cells The highest open circuit voltage (Voc) and maximum short circuit current (Isc) are 0.6329V and 9.0253mA, respectively, and the fill factor (FF) and average photoelectric conversion efficiency (PCE) are between 79.904 and 79.251 and between 18.557 and 18.375, respectively. Therefore, the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the simple equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still Within the scope of the invention patent.

S20‧‧‧Washing steps

S21‧‧‧ Acid etching step

S22‧‧‧ Alkali etching step

S23‧‧‧ pickling step

S24‧‧‧ drying step

Claims (6)

A wet etching surface treatment method comprising: an acid etching step of applying an acid etching to a polycrystalline silicon wafer obtained by cutting a fixed particle using an acid etching solution containing hydrofluoric acid, nitric acid, a buffering agent and water, so as to a light-receiving surface of the polycrystalline silicon wafer is formed with a plurality of micropores; an alkali etching step is performed by using an alkali etching solution to apply alkali etching to the polycrystalline silicon wafer after the acid etching step to remove the light-receiving surface In the acid etching step, the reaction is incomplete by-products and residual acid etching solution, the alkali etching solution contains potassium hydroxide, an oxidizing agent, and water; and an acid washing step uses a water-based acid washing solution The polycrystalline silicon wafer after the alkali etching step is subjected to pickling to remove the cerium oxide generated during the alkali etching step from the light receiving surface; and a drying step of drying the polycrystalline silicon wafer after the pickling step; Wherein, the hydrofluoric acid is between 35 wt% and 60 wt%, the nitric acid is between 20 wt% and 30 wt%, the buffer is greater than 0 wt% and less than or equal to 5 wt%, and the water is between 20 wt%. Between 40% by weight; wherein the buffer contains water, The active agent, and the acid, the acid is a group selected from the group consisting of phosphoric acid, sulfuric acid, acetic acid, and a combination of the foregoing, and the surfactant is an organic solvent selected from the group consisting of polyhydric alcohols, a combination of an aldehyde, a ketone, an ester, and the foregoing organic solvent; wherein, in a weight percentage of the buffer, the water content is between 93 wt% and 98 wt%, and the surfactant content is between 0.5 wt% Between % and 2 wt%, the content of the acid is between 1.5 wt% and 5 wt%; wherein the acid etching step has a processing temperature (T _S21 ) and a processing time (t _S21 ), T _S21 32 ° C, and t _S21 90 seconds; wherein the alkali etching step has a processing temperature (T _S22 ) and a processing time (t _S22 ), T _S22 50 ° C, and t _S22 60 seconds; and wherein the pickling step has a processing temperature (T _S23 ) and a processing time (t _S23 ), T _S23 25 ° C, and t _S23 300 seconds. The wet etching surface treatment method according to claim 1, wherein the oxidizing agent in the alkali etching solution of the alkali etching step is hydrogen peroxide; and the acid washing liquid of the pickling step contains hydrofluoric acid, hydrochloric acid, and water. The wet etching surface treatment method according to claim 2, wherein the content of potassium hydroxide is between 10% by weight and 70% by weight, and the content of hydrogen peroxide is more than 0% by weight based on the weight percentage of the alkali etching solution. 10% by weight or less, and water content is between 30% by weight and 90% by weight; and wherein, in the weight percentage of the acid washing liquid, the content of hydrofluoric acid is between 1% by weight and 10% by weight, and the content of hydrochloric acid It is between 1 wt% and 10 wt%, and the water content is between 80 wt% and 98 wt%. The wet etching surface treatment method according to claim 1, further comprising a water washing step after the acid etching step, the alkali etching step, and the pickling step. A microporous germanium wafer comprising: The polycrystalline silicon wafer obtained by the wet etching surface treatment method according to any one of claims 1 to 4, comprising a polycrystalline germanium body and a light collecting surface connecting the polycrystalline germanium body, wherein the light collecting surface is formed with a plurality of The micropores of the polycrystalline body body are recessed, and a width (W) of the micropores is between 0.571 μm and 1.638 μm, and a depth (H) of the micropores is between 0.165 μm and 0.49 μm. The microporous silicon wafer according to claim 5, wherein the micropores have an aspect ratio (H/D) of between 0.10 and 0.86, such that a light source between 400 nm and 1000 nm is incident on the micro An average reflectance after the aperture wafer is 26% or less.