TW201338029A - Manufacture method of crystalline silicon solar cell substrate - Google Patents

Abstract

A manufacture method of crystalline silicon solar cell substrate comprising: immersing the crystalline silicon bulk material in a solution of Silver Nitrate and watery Hydrofluoric acid so that silver particles and a first silicon oxide layer are generated continuously by the Silver Nitrate and the crystalline silicon bulk material. Simultaneously, the first silicon oxide layer is continuously removed by the watery Hydrofluoric acid so that a plurality of inwardly hollow nano-scale trenches on the surface of crystalline silicon bulk material; then immersing the crystalline silicon bulk material in a nitrate aqueous solution to remove silver particles in nano-scale trenches and oxidizing the crystalline silicon bulk material simultaneously to form a second silicon oxide layer; finally, immersing the crystalline silicon bulk material in the hydrofluoric acid solution to remove the second silicon oxide layer so as to obtain the crystalline silicon solar cell substrate. The Silver Nitrate concentration is at least equal to 0.01 M so that inwardly hollow nano-scale trenches are formed on the crystalline silicon solar cell substrate and the average reflectivity of 300~800nm light source incident to substrate is less than 6%.

Description

Silicon crystal solar cell substrate manufacturing method

The invention relates to a method for fabricating a substrate, in particular to a method for fabricating a silicon-based solar cell substrate.

As the problem of the energy crisis becomes more serious, the green energy industry is constantly seeking to replace the renewable resources of oil. The most common one is solar cells. Among the solar cell related industries, the twin crystal solar cells have excellent photon-to-current conversion efficiency (PCE) and are widely recognized.

As far as the operation principle of solar cells is concerned, the factors affecting PCE depend not only on the amount of sunlight incident, but also on the solar band incident on the solar cell. The higher the amount of sunlight incident on the solar cell for absorption and thus the photoelectric effect, the higher the PCE. However, not all of the wavelengths of sunlight can be absorbed by the twinned solar cells and converted to electrical energy by the photoelectric effect. As far as the energy gap of the twin is concerned, it is about 1.15 eV at room temperature, so only sunlight with a wavelength of less than 1100 nm can produce a photoelectric effect with the twinned solar cell. As can be seen from the foregoing description, in order to increase the PCE of a twinned solar cell, those skilled in the art of silicon solar cells are all aiming toward the goal of reducing the light reflectance below the 1100 nm band.

In a currently common and commercialized technique, a potassium hydroxide (KOH) solution is used to wet-etch a twin-crystal substrate to form a surface of the wet-etched twinned substrate. There is a pyramid structure, and thereby the anti-reflection structure of the twinned substrate is completed. However, the average reflectance of the anti-reflective structure between 300 nm and 500 nm is still higher than 20%, which not only has the problem of low external wavelength efficiency of external quantum efficiency, but also reduces the 矽. Short-circuit current density (Jsc) of a crystalline solar cell.

In addition, the Republic of China No. 201020347 Early Disclosure Invention Patent (hereinafter referred to as the first case 1) discloses a method for producing a nanoporous crystalline ruthenium. In the technical means disclosed in the first case, the crystallization enthalpy is first immersed in an acidic oxidant mixed with silver nitrate (AgNO ₃ ) and hydrofluoric acid (HF) to carry out a redox reaction, forcing the surface of the crystallization ruthenium to be reduced and precipitated. The nano silver particles are oxidized to form SiO ₂ at the corresponding precipitated nano silver particles. Finally, the crystal ruthenium is subjected to acid etching to form nanopores on the surface of the crystal ruthenium relative to the respective nano silver particles. Although the technical means disclosed in the previous case 1 can form nanopores on the surface of the crystalline ruthenium; however, the first case 1 does not specifically disclose the composition concentration ratio of the acidic oxidant, the reaction temperature and the final completed nanometer in the specification. The reflectivity of porous crystalline germanium. Therefore, from the technical content disclosed in the previous case 1, there is still a large distance to be overcome for the purpose of achieving low reflectance.

Further, the Republic of China No. 201121085 early publication invention patent case (hereinafter referred to as the former case 2) discloses a method of manufacturing a solar cell. In the technical means disclosed in the previous case 2, the main steps include the following steps:

(A) performing a dry surface treatment on a substrate to have an irregular surface of the germanium substrate;

(B) immersing the ruthenium substrate having an irregular surface in a solution mixed with sodium persulfate (Na ₂ S ₂ O ₈ ) and silver nitrate for selective oxidation reaction;

(C) immersing the ruthenium substrate after the selective oxidation reaction in a hydrofluoric acid solution to have a microtextured surface of the ruthenium substrate (ie, forming the ruthenium substrate to form a nanoporous ruthenium layer);

(D) immersing the ruthenium substrate having a microtextured surface in an aqueous KOH solution to remove the nanoporous ruthenium layer;

(E) immersing the ruthenium substrate after removing the nanoporous ruthenium layer in a concentrated nitric acid (HNO ₃ ) solution to remove residual silver;

(F) performing a dopant diffusion process on the germanium substrate after the step (E) to form a P-N junction in the germanium substrate;

(G) depositing an anti-reflection layer on the germanium substrate after the step (F);

(H) Finally, an electrode is formed on the germanium substrate.

According to the reflectance analysis data shown in the specification of the foregoing case 2, the average reflectance of the experimental example 5 of the previous case 2 in the band of 300 nm to 800 nm is still formed under the condition that the antireflection layer is formed. It is maintained at around 10.5%, especially its average reflectance between 300 nm and 400 nm is still as high as 20%. Compared with the technical means of the pyramid structure mentioned above, the former case 2 not only has the problem of low utilization of external quantum efficiency of short wavelength, but the program on the overall process is more than the technical means of the pyramid structure. A deposition step of the antireflection layer. Therefore, the technical means disclosed in the previous case 2 does not contribute much to the substantial reduction of the reflectance.

According to the above description, the process of simplifying the twinned solar cell substrate is reduced in consideration of reducing the average reflectance of the twinned solar cell substrate, so that the sunlight is effectively absorbed by the twinned solar cell substrate and thereby the PCE is improved. The subject of improvement required by the field.

Accordingly, it is an object of the present invention to provide a method of fabricating a twinned solar cell substrate.

Therefore, the method for fabricating the twinned solar cell substrate of the present invention comprises the following steps:

(a) immersing a crystallization block in a mixed solution containing silver nitrate and a hydrous hydrofluoric acid to continuously generate a redox reaction with the crystallization block to form a plurality of nano silver particles and a a first ruthenium oxide layer, at the same time, the aqueous hydrofluoric acid is continuously removed from the first ruthenium oxide layer, so that one surface of the crystallization block is recessed inward with a plurality of nano-scale grooves;

(b) after the step (a), immersing the twin bulk material in an aqueous solution of nitric acid (HNO ₃ ) to remove nano silver particles remaining in the nano-scale grooves and simultaneously oxidizing the Crystallizing the block to form a second layer of ruthenium oxide;

(c) after the step (b), immersing the crystallization block in a hydrofluoric acid aqueous solution to remove the second ruthenium oxide layer, and thereby preparing the twinned solar cell substrate;

Wherein, the concentration of the silver nitrate is at least equal to 0.01 M, so that the twin crystal block is recessed inward from the surface thereof with the nano-scale grooves, and a light source between 300 nm and 800 nm is incident on the light source. The average reflectance caused by the twinned solar cell substrate is less than 6%.

The effect of the invention is that under the deposition step of omitting the anti-reflection layer, the reflectivity of the twinned solar cell substrate can be maintained below 6%, so that the light source is effectively absorbed by the twinned solar cell substrate for photoelectric operation. effect.

<Detailed Description of the Invention>

The above and other technical contents, features and effects of the present invention will be apparent from the following detailed description of the preferred embodiments of the accompanying drawings.

Referring to FIG. 1, a preferred embodiment of a method for fabricating a twinned solar cell substrate of the present invention comprises the following steps:

(a) immersing a crystallization block in a mixed solution containing silver nitrate and a hydrous hydrofluoric acid to continuously generate a redox reaction with the crystallization block to form a plurality of nano silver particles and a a first ruthenium oxide layer, at the same time, the aqueous hydrofluoric acid is continuously removed from the first ruthenium oxide layer, so that one surface of the crystallization block is recessed inward with a plurality of nano-scale grooves;

(b) after the step (a), immersing the crystallization block in an aqueous solution of nitric acid to remove nano silver particles remaining in the nano-scale grooves and simultaneously oxidizing the crystallization block Forming a second layer of ruthenium oxide; and

(c) after the step (b), immersing the crystallization block in a hydrofluoric acid aqueous solution to remove the second ruthenium oxide layer, and thereby preparing the twinned solar cell substrate;

Wherein, the concentration of the silver nitrate is at least equal to 0.01 M, so that the twin crystal block is recessed inward from the surface thereof with the nano-scale grooves, and a light source between 300 nm and 800 nm is incident on the light source. The average reflectance caused by the twinned solar cell substrate is less than 6%.

It should be noted here that when the reaction temperature of the step (a) is too high, the redox reaction between the silver nitrate and the twins will be too intense, resulting in the ingot not being effectively recessed inward. Nano-scale trenches having such small width dimensions and high aspect ratios, resulting in an average reflectance of less than 6% for light sources of this band (ie, 300 nm to 800 nm); Preferably, the reaction temperature of the step (a) is lower than a sufficient amount of the nano-scale grooves to cause the germanium block to be recessed inward from the surface thereof to cause an average reflection of less than 6% of the light source of the band. The predetermined temperature of the rate; more preferably, the predetermined temperature of the step (a) is between 20 ° C and 35 ° C.

It is worth mentioning here that when the concentration of the silver nitrate in the mixed solution is too large, excessive etching will occur, so that the surface morphology of the twin crystal block cannot form the nano-scale grooves, and the reflectance is increased. Therefore, preferably, the concentration of silver nitrate in the step (a) is between 0.01 M and 0.5 M.

Preferably, the concentration of the aqueous solution of nitric acid in the step (b) is between 40% and 70%.

The germanium bulk material suitable for use in the preferred embodiment of the present invention may be an N-type doped or P-type doped germanium substrate, and the germanium substrate is a single crystal germanium selected from the <100> crystal orientation ( Monocrystalline Si), <100> crystal orientation of quasi-monocrystalline Si, or polycrystalline Si. It should be further noted here that the definition of a single crystal germanium such as a <100> crystal orientation refers to a polycrystalline germanium having a preferred orientation of <100>.

It should be further noted herein that the main purpose of the step (c) of the present invention is to prevent the final solar cell element from reducing the short-circuit current (Isc) due to the residual second ruthenium oxide layer reacted in the step (b). .

<Specific Example 1 (E1)>

A specific example 1 (E1) of the method for producing a twinned solar cell substrate of the present invention is carried out according to the following procedure.

A single crystal germanium substrate was immersed in a mixed solution of 0.7 g of AgNO ₃ , 2 ml of aqueous hydrofluoric acid (concentration: 55%) and 100 ml of H ₂ O to carry out a redox reaction. In this specific example 1 (E1) of the present invention, a reaction temperature of the mixed solution is maintained at 25 ° C, and the concentration of AgNO ₃ in the mixed solution is calculated to be about 0.04 M.

Further, the single crystal germanium substrate is washed, and the cleaned single crystal germanium substrate is immersed in an aqueous solution of HNO _{3 having a} concentration of 68% to remove silver particles generated in the aforementioned redox reaction, and oxidize the single The wafer substrate is formed to form a hafnium oxide layer.

Finally, the single crystal germanium substrate is immersed in a hydrofluoric acid aqueous solution having a concentration of 55% to remove the above-mentioned cerium oxide layer formed by the immersion of the HNO ₃ aqueous solution, thereby preparing the twin crystal of the specific example 1 (E1). Solar cell substrate.

<Specific example 2 (E2)>

A specific example 2 (E2) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 1 (E1), and the difference is that the specific example 2 (E2) uses a polysilicon. The substrate is used to produce a twinned solar cell substrate.

<Specific example 3 (E3)>

A specific example 3 (E3) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 1 (E1), and is different in that the mixed solution of the specific example 3 (E3) The H ₂ O content in the solution was 10 ml, and the concentration of AgNO ₃ in the mixed solution was calculated to be about 0.34 M.

<Specific example 4 (E4)>

A specific example 4 (E4) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 3 (E3), and the difference is that the specific example 4 (E4) uses a polysilicon. The substrate is used to produce a twinned solar cell substrate.

<Specific example 5 (E5)>

A specific example 5 (E5) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 3 (E3), and is different in that one of the specific examples 5 (E5) is a single crystal. The reaction temperature of the ruthenium substrate in a mixed solution containing AgNO ₃ was 35 °C.

<Comparative Example 1 (CE1)>

A comparative example 1 (CE1) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 3 (E3), and is different in that the mixed solution of the comparative example 1 (CE1) The AgNO ₃ content in the solution was 7.0 g, and the concentration of AgNO ₃ in the mixed solution was calculated to be about 1.31 M.

<Comparative Example 2 (CE2)>

A comparative example 2 (CE2) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the comparative example 1 (CE1), and the difference is that the comparative example 2 (CE2) uses a polysilicon. The substrate is used to produce a twinned solar cell substrate.

<Comparative Example 3 (CE3)>

A comparative example 3 (CE3) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 3 (E3), and is different in that one of the single crystals of the comparative example 3 (CE3) The reaction temperature of the ruthenium substrate in a mixed solution containing AgNO ₃ was 90 °C.

<Comparative Example 4 (CE4)>

A comparative example 4 (CE4) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the comparative example 3 (CE3), except that the comparative example 4 (CE4) uses a polysilicon. The substrate is used to produce a twinned solar cell substrate.

<Comparative Example 5 (CE5)>

A comparative example 5 (CE5) of the method for producing a twinned solar cell substrate of the present invention is substantially the same as the specific example 3 (E3), and is different in that one of the single crystals of the comparative example 5 (CE5) The reaction temperature of the ruthenium substrate in a mixed solution containing AgNO ₃ was 55 °C.

<Analysis data>

Referring to the scanning electron microscope (SEM) surface image shown in FIG. 1 , the surface of the twin crystal solar cell substrate of the specific example 1 (E1) of the present invention is formed with a plurality of nano-scale grooves, and The width of these nano-scale trenches is between 50 nm and 200 nm.

Referring to the SEM surface image shown in FIG. 2, the surface of the twinned solar cell substrate of the specific example 2 (E2) of the present invention is formed with a plurality of nano-scale trenches, and the depth of the nano-scale trenches is From 20 nm to 100 nm.

Referring to the SEM surface and the cross-sectional image shown in FIG. 3 and FIG. 4, the surface of the twin crystal solar cell substrate of the specific example 3 (E3) of the present invention is formed with a plurality of nano-scale grooves, and the nano-scales are formed. The depth and width of the trench are between 10 nm and 100 nm and between 20 nm and 200 nm.

Referring to the SEM surface image shown in FIG. 5, the surface of the twin crystal solar cell substrate of the specific example 4 (E4) of the present invention is formed with a plurality of nano-scale grooves, and the depth of the nano-scale grooves and The width is between 100 nm and 5 μm and between 10 nm and 100 nm.

In contrast, the SEM surface image shown in FIG. 6 shows that the twinned solar cell substrate of Comparative Example 1 (CE1) of the present invention is formed with a plurality of widths only on the surface thereof due to an excessively high concentration of AgNO ₃ (1.31 M). A groove between 100 nm and 1000 nm.

Referring to the SEM surface image shown in FIG. 7, the twinned solar cell substrate of Comparative Example 2 (CE2) of the present invention is formed with a plurality of widths only on the surface thereof due to an excessively high concentration of AgNO ₃ (1.31 M). A groove between 200 nm and 1000 nm.

Further, as shown in the SEM surface image shown in Fig. 8, the twinned solar cell substrate of Comparative Example 3 (CE3) of the present invention has a majority on the surface of the single crystal germanium substrate due to an excessively high reaction temperature (90 ° C). Grooves with a width between approximately 50 nm and 100 nm.

Referring to the SEM surface image shown in FIG. 9, it is understood that the twinned solar cell substrate of Comparative Example 4 (CE4) of the present invention is difficult to form the specific examples of the present invention on the surface of the polycrystalline germanium substrate due to an excessively high reaction temperature (90 ° C). Nano-level groove.

The SEM image shown in the above-mentioned FIGS. 1 to 9 shows that the nano-scale grooves of the twin-crystal solar cell substrate produced by the specific examples (E1 to E4) of the present invention have a small width dimension and a high aspect ratio; In contrast, the twin-crystal solar cell substrates produced by the comparative examples (CE1 to CE4) are due to excessively high reaction temperatures or excessively high AgNO ₃ concentrations, and the width of the grooves is large (E1~). E4), and by comparing the above SEM images, it can be estimated that the groove aspect ratios of the comparative examples (CE1~CE2, CE4) should be much smaller than the specific examples (E1~E4). The groove size of the comparative example 3 (CE3) was approximated to the specific example 1 (E1); however, the groove result of the comparative example 3 (CE3) exhibited a structure having a higher density and a smaller hole, which easily caused light. The scattering further increases the reflectivity.

The photoluminescence (PL) spectrum obtained by using the 325 nm laser light of the present invention is shown in Fig. 10 (refer to Appendix 1 in conjunction); wherein the laser light is twinned from the specific example 3 (E 3) The surface of the solar cell substrate was incident on the substrate to a depth of 1 μm, and the spectrum of the photoexcitation light was analyzed by taking the left, middle, and right points from the substrate (the distance between each adjacent two points was 5 mm). As shown in FIG. 10, the spectrum of the photoexcitation light of the specific example 3 (E3) of the present invention falls between 600 nm and 800 nm, and the band is converted into an energy gap (energy gap=1240/wavelength, ie, 1240/). 800~1240/600) is between 1.55 eV and 2.06 eV. Therefore, from the viewpoint of the twin crystal having an energy gap of about 1.15 eV, the analysis result of Fig. 10 preliminarily confirmed that the energy gap of the surface of the specific example 3 (E3) increased from 1.15 eV to 2.06 eV due to the nano-scale groove on the surface thereof. about. It can be inferred from the foregoing description that the nano-scale grooves on the surface of the specific example 3 (E3) of the present invention will be advantageous for increasing the absorption rate of the short-wavelength.

In addition, in order to facilitate the comparison of the implementation conditions of the embodiments of the present invention and the efficacy test of the results of the implementation, the implementation conditions of the redox reaction in the mixed solution of the embodiments of the present invention and the reflectance analysis data thereof are simply Consolidated in the following list 1.

In addition, referring to the reflectance graph shown in Fig. 11, the average reflectance of the comparative examples (CE1~CE4) in the range of 300 nm to 800 nm is about 9.1% to 15.8%, which is about 300 nm to 430. The average reflectance between the nm bands is between 4.8% and 14%. In contrast, the average reflectance of these specific examples (E1~E5) between 300 nm and 800 nm is less than 5.5%. The average reflectance between the 300 nm and 430 nm bands is less than 1.5%, and it is particularly worth mentioning that the average reflection of the specific examples (E1 to E3) of the present invention between 300 nm and 430 nm The rate is closer to 0%. Therefore, the specific examples (E1 to E5) of the present invention not only enhance the specific example of the twin crystal solar cell substrate for 300 nm to 800 nm under the premise that the deposition step of the antireflection layer is omitted (previous case 2). The absorption between the bands is more effective in increasing the utilization of external quantum efficiency for short wavelengths.

In summary, the method for fabricating the twinned solar cell substrate of the present invention can also cause the average reflection of the light source between the 300 nm and 800 nm bands of the twinned solar cell substrate under the deposition step of omitting the antireflection layer. The rate is maintained at 5% or less, so that the light source is effectively absorbed by the twinned solar cell substrate to perform the photoelectric effect, and the object of the present invention can be achieved.

The above is only the preferred embodiment and the specific examples of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent change according to the scope of the invention and the description of the invention. And modifications are still within the scope of the invention patent.

1 is a SEM surface image showing the surface microstructure of a specific example 1 (E1) of the method for fabricating a twinned solar cell substrate of the present invention;

2 is a SEM surface image showing the surface microstructure of a specific example 2 (E2) of the method for fabricating the twinned solar cell substrate of the present invention;

3 is a SEM surface image showing the surface microstructure of a specific example 3 (E3) of the method for fabricating the twinned solar cell substrate of the present invention;

Figure 4 is a SEM cross-sectional image showing the cross-sectional microstructure of the specific example 3 (E3) of the present invention;

5 is a SEM surface image showing the surface microstructure of a specific example 4 (E4) of the method for fabricating the twinned solar cell substrate of the present invention;

6 is a SEM surface image showing the surface microstructure of Comparative Example 1 (CE1) which is one of the methods for fabricating the twinned solar cell substrate of the present invention;

7 is a SEM surface image showing the surface microstructure of Comparative Example 2 (CE2) of one of the methods for fabricating the twinned solar cell substrate of the present invention;

8 is a SEM surface image showing the surface microstructure of Comparative Example 3 (CE3) of a method for fabricating a twinned solar cell substrate of the present invention;

9 is a SEM surface image showing the surface microstructure of Comparative Example 4 (CE4) of a method for fabricating a twinned solar cell substrate of the present invention;

Figure 10 is a PL spectrum diagram showing the results of photoexcitation of the surface of the twinned solar cell substrate of the specific example 3 (E3) of the present invention;

Fig. 11 is a graph showing the reflectance of the specific examples (E1 to E5) of the present invention and the comparative examples (CE1 to 4) between 300 nm and 800 nm.

Claims (4)

A method for fabricating a twinned solar cell substrate, comprising the steps of: (a) immersing a germanium block in a mixed solution containing silver nitrate and a hydrous hydrofluoric acid to cause the silver nitrate and the twin block to continue Producing a redox reaction to form a plurality of nano-silver particles and a first layer of tantalum oxide, while continuously removing the first layer of tantalum oxide from the aqueous hydrofluoric acid, and thereby from the surface of one of the twin blocks There are a plurality of nano-scale grooves in the inner recess; (b) after the step (a), the germanium block is immersed in an aqueous solution of nitric acid to remove the nanoparticles remaining in the nano-scale grooves. Silver particles, and simultaneously oxidizing the crystallization block to form a second ruthenium oxide layer; and (c) after the step (b), immersing the crystallization block in a hydrofluoric acid aqueous solution to remove the a second ruthenium oxide layer, and thereby preparing the twinned solar cell substrate; wherein the concentration of the silver nitrate in the mixed solution is at least equal to 0.01 M, such that the crystallization block is recessed inwardly from the surface thereof Nano-scale trenches and a source of light between 300 nm and 800 nm The average reflectance caused after being incident on the twinned solar cell substrate is less than 6%. The method for fabricating a twinned solar cell substrate according to claim 1, wherein a predetermined temperature of the step (a) is between 20 ° C and 35 ° C. The method for fabricating a twinned solar cell substrate according to claim 1, wherein the concentration of silver nitrate in the step (a) is between 0.01 M and 0.5 M. The method for producing a twinned solar cell substrate according to claim 1, wherein the concentration of the aqueous nitric acid solution in the step (b) is between 40% and 70%.