TWI511318B - Silicon substrate for solar cell and manufacturing method thereof - Google Patents

Description

Solar cell substrate and method of manufacturing same

The present invention relates to a solar cell, and more particularly to a method of manufacturing a germanium substrate for a solar cell, and a solar cell produced by the method.

According to different materials, the current tantalum solar cells are mainly divided into three categories: single crystal germanium solar cells, polycrystalline germanium thin film solar cells, and amorphous germanium thin film solar cells, among which the more efficient twinned solar cells are the mainstream.

Due to the principle of solar cell power generation, the photoelectric energy is directly converted into electrical energy by using the photoelectric effect. Therefore, how to effectively improve the anti-reflection rate of the solar cell, thereby reducing the optical loss to improve the photoelectric conversion efficiency, is actually improving the efficiency of the solar cell. important topic.

At present, there are two main methods for improving the antireflection rate of a solar cell. One is to coat the surface of the ruthenium substrate with an antireflection coating, and the other is to form a texturization on the surface of the ruthenium substrate.

In the case where the surface of the ruthenium substrate is coated with an antireflection layer, Reference 1 discloses deposition of a tantalum nitride film (SiNx:H) on the surface of a ruthenium substrate by plasma enhanced chemical vapor deposition (PECVD). In order to have a better anti-reflection effect in a specific wavelength range. However, the coated anti-reflective layer can only have a better anti-reflection effect for a specific wavelength range, so if you want to make a crystalline solar energy The battery has an anti-reflection effect in different wavelength ranges such as ultraviolet light, visible light, and infrared light, and the multilayer anti-reflection layer needs to be coated to obtain an anti-reflection effect, resulting in an increase in cost, complicated process, and difficulty in the above method. Area production and other issues.

In the case of making a roughened structure on the surface of the tantalum substrate, reference 2 discloses that a roughened structure is formed on the surface of the tantalum substrate by a physical method using a reactive ion etch technique to reduce the reflectance in the visible wavelength range. Up to 20% or less; Reference 3 discloses a chemical method of alkaline etching using potassium hydroxide (KOH) to form a pyramid structure on the surface of the ruthenium substrate to reduce the reflectance in the visible wavelength range to 17%. . However, compared to physical etching, although the chemical etching method has the advantages of lower cost, faster process, and large-area production, the reflectance can only be reduced to 17%, and the wavelength in the visible range cannot be completely absorbed. In order to improve its anti-reflection ability, it is necessary to coat a layer of tantalum nitride on the surface of the aforementioned pyramid structure, resulting in an increase in cost and an increase in process time.

[Reference 1] Zhong Yunsheng, Discussion on Anti-reflective Coating Technology and Equipment for Silicon Crystal Solar Cells vol. 290: Journal of Machinery Industry, 2007.

[Reference 2] S. Winderbaum, O. Reinhold, and F. Yun, "Reactive ion etching (RIE) as a method for texturing polycrystalline silicon solar cells," Solar Energy Material and Solar Cells, vol. 46, pp. 239 -248, 1997.

[Reference 3] P. Panek, M. Lipi Ski, and J. Dutkiewicz, "Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells," Journal of Materials Science, vol. 40, pp. 1459-1463, 2005/03/01 2005.

In view of the above, an object of the present invention is to provide a method for manufacturing a tantalum substrate for a solar cell, which can produce a tantalum substrate capable of effectively suppressing light reflection in the ultraviolet, visible, and infrared wavelength ranges, in other words, by the method of the present invention. The prepared substrate has good light absorption properties for ultraviolet light, visible light, and infrared light.

In order to achieve the above object, a method for manufacturing a tantalum substrate for a solar cell according to the present invention mainly comprises the following steps: first, preparing a tantalum substrate having a concave-convex microstructure on a surface; and secondly, immersing the tantalum substrate in the a first acidic etching solution, wherein metal particles are deposited on the surface of the uneven microstructure of the germanium substrate, the first acidic etching solution contains a first concentration of metal ions and an acidic solution; and then, the germanium substrate is dipped Forming, in a second acidic etching solution, a plurality of nanogrooves for the concave and convex microstructure of the germanium substrate, the second acidic etching solution containing the metal having a second concentration lower than the first concentration The ions and the acidic solution; finally, the metal particles deposited on the surface of the textured microstructure of the tantalum substrate and each of the nanoholes are removed.

In the manufacturing method provided by the present invention, the uneven microstructure is preferably composed of a plurality of conical bodies integrally connected. In addition, in an embodiment of the present invention, the ruthenium substrate having the uneven microstructure is obtained by immersing a ruthenium wafer in an aqueous solution of potassium hydroxide (KOH) for alkaline etching.

In the manufacturing method provided by the present invention, the ruthenium substrate is immersed in the first acidic etchant for preferably from 20 seconds to 45 seconds, thereby uniformly depositing the metal particles. On the surface of the uneven microstructure of the base material, the rate of redox reaction between each metal particle and the tantalum substrate is relatively average. Further, the time during which the ruthenium substrate is immersed in the second acidic etchant is preferably from 1 minute to 5 minutes, thereby forming a nanopore having a predetermined depth.

In the manufacturing method provided by the present invention, the metal ion is preferably silver ion, and the acidic solution is preferably hydrofluoric acid (HF). Further, the first concentration of the silver ions is preferably 0.34 M (mole/L), and the second concentration is preferably 0.03 M (mole/L). Further, according to a manufacturing method of an embodiment of the present invention, the first and second acidic etching liquids are obtained by dissolving silver nitrate (AgNO ₃ ) in hydrofluoric acid.

In the manufacturing method provided by the present invention, the step of removing one of the tantalum oxides formed on the surface of the textured microstructure of the tantalum substrate may be further included.

Another object of the present invention is to provide a tantalum substrate for a solar cell obtained by the above-described manufacturing method.

The tantalum substrate of the solar cell provided by the present invention comprises a base layer and a concave-convex microstructure integrally formed on one surface of the base layer, the concave and convex microstructure having a plurality of nano-holes.

In the germanium substrate of the solar cell provided by the present invention, the germanium base layer and the uneven microstructure are preferably lightly doped n-type germanium materials to reduce the electrical conductivity.

In the crucible substrate of the solar cell provided by the present invention, the concavo-convex microstructure is preferably composed of a plurality of conical bodies integrally connected. Further, each of the tapered bodies preferably has a size range of 3 to 5 μm and an area of 3 × 3 to 8 × 8 μm ² .

In the substrate of the solar cell provided by the present invention, the depth of each of the nanoholes is preferably between 1 μm and 5 μm, and further, each of the nanoholes is preferably perpendicular to the base layer, thereby further reducing The light reflectance of the germanium substrate.

The detailed construction of the crucible substrate of the solar cell provided by the present invention and the manufacturing method thereof will be exemplified in the following examples, and the drawings can be made within the scope of the embodiments of the present invention which can be easily implemented by those skilled in the art. Be explained.

10‧‧‧矽 substrate

11‧‧‧矽 grassroots

20‧‧‧ concave microstructure

21‧‧‧Nami Slots

23‧‧‧Nami Line

30‧‧‧矽 substrate

S1~S5‧‧‧Steps

FIG. 1 is a flow chart showing a method of manufacturing a germanium substrate for a solar cell according to an embodiment of the present invention.

Fig. 2 is a perspective view showing the substrate of the present invention.

Fig. 3 is a scanning electron microscope (SEM) photograph of the substrate of Examples 11 to 14.

Figure 4 is a scanning electron microscope (SEM) photograph of the substrate of Examples 5, 10, 15, 20, 25 and 30.

Fig. 5 is a graph showing the reflectance wavelength of the substrate of Examples 5, 10, 15, 20, 25 and 30.

Fig. 6 is a graph showing the average reflectance of the substrates of Examples 1 to 30.

Please refer to FIG. 1 . The method for manufacturing a tantalum substrate for a solar cell according to the present invention mainly includes the following steps: In step S1, please refer to FIG. 2 simultaneously to prepare a substrate 10 for the substrate 10 . Having a base layer 11 and integrally formed on one surface of the base layer 11 A concave-convex microstructure 20. The tantalum substrate 10 may be, for example, a mono-crystalline silicon having a lattice direction of (100), (110) or (111), or a polysilicon. The tantalum substrate 10 having the uneven microstructure 20 may use a commercially available tantalum wafer having a micro-pyramid array structure, or may be obtained by immersing a silicon wafer in potassium hydroxide (KOH). The alkaline etching is performed in the aqueous solution so that the tantalum wafer has a concave-convex microstructure of a plurality of integrally connected cones. In addition, in an example of the present invention, a lightly doped n-type germanium wafer is used to reduce the conductivity of the germanium substrate, making it applicable to solar cells.

In steps S2 and S3, the tantalum substrate 10 is first immersed in a first acidic etching solution until the surface of the uneven microstructure 20 of the tantalum substrate 10 is deposited with metal particles, and then the tantalum substrate is further deposited. 10 is immersed in a second acidic etching solution to form a plurality of nanopore holes 21 in the uneven microstructure 20 of the tantalum substrate 10.

Wherein, the first acidic etching solution comprises a first concentration of metal ions and an acidic solution, the second acidic etching solution comprises a second concentration of the metal ions and the acidic solution, and the second concentration is lower than the first The concentration, and the metal ion is preferably silver ion, and the acidic solution is preferably hydrofluoric acid. In an embodiment of the invention, the first and second acidic etching solutions are obtained by dissolving silver nitrate (AgNO ₃ ) in hydrofluoric acid.

Thus, when the ruthenium substrate 10 is immersed in the first acidic etchant, the silver ions dispersed in the acidic etchant will first acquire electrons from the ruthenium atoms on the surface of the substrate 10, and the ruthenium substrate 10 The surface of the uneven microstructure 20 is reduced to silver particles, and then deposited on the surface of the uneven microstructure 20, and the uneven microstructure 20 of the tantalum substrate 10 is oxidized to cerium oxide (SiO ₂ ) due to loss of electrons. It is etched by hydrofluoric acid and a nanopore appears. Then, when the ruthenium substrate 10 is immersed in the second acidic etchant, the lower concentration of silver ions in the second acidic etchant can continue the aforementioned redox reaction at a relatively slow rate to assist deposition. The silver particles on the surface of the concave-convex microstructure 20 continue to be etched. Finally, as shown in FIG. 2, a plurality of uniformly distributed nano-slots 21 are formed in the concave-convex microstructure 20 of the base material 10, that is, a plurality of uniformly distributed Nano line 23.

In step S2, the time during which the tantalum substrate 10 is immersed in the first acidic etching solution is preferably from 20 seconds to 45 seconds. If the immersion time exceeds 45 seconds, excessive silver particles are deposited on the surface of the embossed microstructure 20, causing the embossed microstructure 20 to be rapidly oxidized and completely etched by hydrofluoric acid; if the immersion time is less than 20 seconds, the embossed microstructure 20 and silver ions The redox reaction rate is uneven, resulting in the inability of the silver particles to uniformly deposit on the surface of the uneven microstructure 20, affecting the second-stage etching of step S3.

In step S3, the time during which the tantalum substrate 10 is immersed in the second acidic etching solution is preferably from 1 minute to 5 minutes. If the immersion time exceeds 5 minutes or less than 1 minute, the nanopore hole 21 cannot be etched (that is, the nanowire 23 cannot be produced), and only the nanopore structure is formed.

Further, in steps S2 and S3, the first concentration of the silver ions is preferably 0.34 M (mole/L), and the second concentration is preferably 0.03 M (mole/L). If the first concentration is higher than 0.34 M, excessive silver particles are deposited on the surface of the textured microstructure 20, causing the textured microstructure 20 to be rapidly oxidized and completely etched by hydrofluoric acid. If the second concentration is higher than 0.03 M, the redox reaction of the uneven microstructure 20 and the silver ions is not uniform, and the etched nanopore 21 is unstable in structure and easily collapses.

In step S4, the metal particles deposited on the surface of the uneven microstructure 20 of the tantalum substrate 10 and each of the nanopore holes 21 are removed. The manner of removing the metal particles is not particularly limited, but if the metal ions of the first and second acidic etching solutions are derived from silver nitrate, it is preferable to remove the uneven microstructure 20 using nitric acid (HNO ₃ ). The surface and the metal particles (silver particles) in each of the nanopore holes 21, for example, the ruthenium substrate 10 are immersed in a nitric acid solution, whereby the deposited silver particles are removed as much as possible.

In addition, if the step S4 is performed by immersing the ruthenium substrate 10 in a nitric acid solution to remove silver particles, an oxide layer may be formed on the surface of the embossed microstructure 20, that is, cerium oxide (SiO ₂ ) may be present. Preferably, the manufacturing method of the present invention further comprises a step S5 of removing the cerium oxide on the surface of the textured microstructure 20. Of course, there is no particular limitation on the manner in which the cerium oxide is removed, and for example, diluted hydrofluoric acid can be used.

The ruthenium substrate 30 obtained by the above-described manufacturing method has the ruthenium base layer 11 and the uneven microstructure 20 integrally formed on one surface of the ruthenium base layer 11 as shown in FIG. 2, and the unevenness is such that the structure 20 has a plurality of Nano slot 21.

In order to further understand the present invention, a method of preparing a tantalum substrate for a solar cell of the present invention will be described in further detail below with reference to examples. However, the various embodiments of the present invention are not to be construed as being limited to the scope of the present invention. The embodiments are only more fully described by those of ordinary skill in the art.

[Examples of Preparation of Substrate]

6吋n-type矽 wafer (1~3Ω-cm, thickness 200μm, supplied by Hejing Technology Co., Ltd.) is sequentially cleaned with acetone solution, alcohol solution, and deionized water. The cleaning is performed on ultrasonic waves. Performed in the oscillator, after which the wafer is dipped Soak the diluted hydrofluoric acid for about 2 to 3 minutes to remove the oxide layer on the surface of the tantalum wafer, and then perform final cleaning with deionized water.

Next, the tantalum wafer is etched with a potassium hydroxide aqueous solution to make the tantalum wafer have a concave-convex microstructure on its surface. The aqueous potassium hydroxide solution is prepared by deionized water in a ratio of 70:2:5, 40% by weight of potassium hydroxide, and isopropyl alcohol (IPA). The germanium wafer is again immersed in the diluted hydrofluoric acid for about 2 to 3 minutes to remove the oxide layer on the surface of the germanium wafer.

The ruthenium wafer is first immersed in a first acid etchant prepared by using silver nitrate and hydrofluoric acid for the first etching, and then the ruthenium wafer is immersed in the same silver nitrate and hydrofluoric acid. A second etching is performed in the diacid etchant. The first and second acidic etching solutions are prepared by dissolving a silver nitrate solid (99.8%, a joint chemical reagent for sale) in 4.6 M hydrofluoric acid (55%, supplied by CHONEYE PURE CHEMICALS). A first acidic etchant of 0.34M silver ions and a second acidic etchant containing 0.03M silver ions.

After the etching is completed, the germanium wafer is immersed in nitric acid to remove silver particles deposited on the surface of the concave-convex microstructure and each nanopore.

Finally, the cerium oxide on the surface of the ruthenium wafer is removed with diluted hydrofluoric acid and rinsed with deionized water. The ruthenium substrate of the present invention was obtained by removing moisture remaining on the surface of the ruthenium wafer with nitrogen (nitrogen, N2) and a hot plate.

The tantalum substrates of Examples 1 to 30 were prepared in the above manner, and the first etching time and the second etching time of each of the examples are shown in Table 1 below.

[Table 1]

The structure of the tantalum substrate of each example was taken by a scanning electron microscope (SEM, JSM-6700F cold cathode field emission scanning electron microscope of Japan JEOL), and each example was measured at a wavelength of 200 nm. Light reflectance in the range of (ultraviolet light) to wavelength 1000 nm (infrared light).

Please refer to FIG. 3 and FIG. 4 , wherein FIG. 3 ( a ) to ( d ) are SEM photographs of the substrates of Examples 11 to 14, respectively, and FIGS. 4 ( a ) to ( f ) are respectively examples. SEM photographs of the substrates of 5, 10, 15, 20, 25, and 30. As is apparent from FIGS. 3 and 4, the tantalum substrate produced by the manufacturing method of the present invention has a nanopore having a depth of about 1 to 5 μm, and each nanopore has excellent verticality. Figure 3 (a) ~(d) A small image in the lower right corner can also confirm that the manufacturing method of the present invention can produce a tantalum substrate having a tapered structure (pyramid structure) and a nanopore structure on the surface. Thus, when the germanium substrate of the present invention is applied to a solar cell, light incident on the surface of the germanium substrate can pass not only through the tapered body structure, but also the light reflectance of the germanium substrate can be reduced to 5 by the respective nanopore structure. Below %, that is, improving light absorption characteristics.

Please refer to FIG. 5 , which is the analysis results of the reflectance and the wavelength of the incident light of Examples 15, 20 and 25, and it can be seen that the reflectances of Examples 15, 20 and 25 are in the range of 200 nm to 1000 nm. Below 2%. Referring to FIG. 6 , the first etching time is 30, 35, and 40 seconds, and the average reflectance in the range of 200 nm to 1000 nm is less than 6%, and the average reflectance of Example 15 is as follows. Can be reduced to 1.2%. The above results prove that the substrate of the present invention does have high light absorption characteristics.

In addition, although the first etching time is 20, 25, and 45 seconds, and the second etching time is 1 to 3 minutes (that is, Examples 1 to 3, Examples 6 to 8, and Examples 26 to 28) The average reflectance in the range of 200 nm to 1000 nm is relatively high (about 6% to 18%), but it also exhibits an approximation or even better light reflectance with a conventional germanium substrate having a pyramid structure on the surface, and more When the second etching time is increased to 5 minutes (i.e., Examples 5, 10, and 30), the average reflectance can also be reduced to 3% to 6%.

Furthermore, the average reflectances of the examples 11 to 15 in the different wavelength ranges are shown in Table 2 below. It can be seen from Table 2 that the germanium substrate of the present invention has ultraviolet light (200 to 400 nm) and visible light (401 to 800 nm). Both have an average reflectance of less than 6%, and for near-infrared light (801-1000 nm), there is also an average reflectance equal to or lower than 8.16%, which is apparent from the present invention. The substrate prepared by the method has good light absorption characteristics for ultraviolet light, visible light and infrared light.

In summary, since the manufacturing method of the present invention can produce a tantalum substrate having uniformly distributed nanopore grooves, the tantalum substrate of the present invention can effectively suppress light reflection in the ultraviolet, visible, and infrared wavelength ranges, in other words, The germanium substrate of the present invention has good light absorption properties for ultraviolet light, visible light, and infrared light. In addition, the manufacturing method of the present invention has the advantages of shortened process time and reduced manufacturing cost compared to the prior art, and the resulting substrate has better light reflectance.

S1~S5‧‧‧Steps

Claims (10)

A method for manufacturing a tantalum substrate for a solar cell, comprising the steps of: (a) preparing a tantalum substrate having a concave and convex microstructure on the surface; and (b) immersing the tantalum substrate in a first acidic etching solution until The surface of the uneven microstructure of the germanium substrate is deposited with metal particles, the first acidic etching solution comprises a metal ion of a first concentration and an acidic solution; (c) the germanium substrate is immersed in a second acidic etching solution. Forming a plurality of nano-slots in the concave-convex microstructure of the ruthenium substrate, the second acidic etchant comprising a second concentration of the metal ions and the acidic solution, the second concentration being lower than the first concentration; (d) removing metal particles deposited on the surface of the textured microstructure of the tantalum substrate and each of the nanoholes. The method for manufacturing a tantalum substrate for a solar cell according to claim 1, wherein in the step (a), the concavo-convex microstructure is composed of a plurality of conical bodies integrally connected. The method for manufacturing a substrate for a solar cell according to claim 1, wherein in the step (a), the substrate having the uneven microstructure is subjected to alkaline etching by immersing a wafer in an aqueous potassium hydroxide solution. And made. The method for producing a tantalum substrate for a solar cell according to claim 1, wherein the metal ion is silver ion and the acidic solution is hydrofluoric acid. The method for manufacturing a substrate for a solar cell according to claim 4, wherein in the step (b), the ruthenium substrate is immersed in the first acidic etchant for a time of 20 seconds to 45 seconds. The method of manufacturing a substrate for a solar cell according to claim 4, wherein in the step (c), the ruthenium substrate is immersed in the second acidic etchant for a period of from 1 minute to 5 minutes. The method for producing a tantalum substrate for a solar cell according to claim 4, wherein the first concentration of the silver ions is 0.34 M. The method for producing a tantalum substrate for a solar cell according to claim 4, wherein the second concentration of the silver ions is 0.03 M. The method for producing a tantalum substrate for a solar cell according to claim 4, wherein the first and second acidic etching solutions are obtained by dissolving silver nitrate in hydrofluoric acid. The method for manufacturing a tantalum substrate for a solar cell according to claim 1, further comprising the step (e) of removing a tantalum oxide formed on the surface of the uneven microstructure of the tantalum substrate.