TW201406644A - Structure of micro-nano anti-reflective layer and method for manufacturing the same - Google Patents

Abstract

A structure of micro/nano anti-reflective layer including a silicon substrate is provided. A surface of the silicon substrate has a micro-array structure, and a surface of the micro-array structure includes a plurality of nanostructures. The nanostructures extend along the Si<100> direction.

Description

Micro-nano anti-reflection layer structure and manufacturing method thereof

The invention relates to an anti-reflection layer structure and a manufacturing method thereof, and in particular to a micro-nano anti-reflection layer structure applicable to a solar cell and a manufacturing method thereof.

In recent years, with the rise of environmental awareness and the global energy crisis, pollution and shortage of petrochemical energy, how to develop energy-saving, environmentally-friendly and sustainable alternative energy sources has become the primary goal of technology research and development in various advanced countries. Among the many alternative energy solutions, solar cells account for more than 23% of the emerging markets of renewable energy. It is the most important alternative energy source at this stage, and it is also a promising energy technology.

At present, among various types of solar cells, germanium-based solar cells have a market share of more than 90%, and will remain the mainstream of solar cell technology in the future. However, the current development of germanium-based solar cells is still limited by the photoelectric conversion efficiency. Specifically, the conversion efficiency of germanium-based solar cells can theoretically reach about 24%, but the conversion efficiency of current commercial solar cells is only between 15% and 16%. Among them, the most important technical bottleneck is that the reflection loss of the solar cell itself is too large, and the photoelectric conversion efficiency cannot be raised to the theoretical value.

Many previous studies have attempted to improve the photoelectric conversion efficiency of germanium-based solar cells by improving the configuration or materials of the anti-reflective layer, but the process is often complicated, costly and often difficult to control. The system can not be combined with the front and back process. Therefore, how to effectively improve the reflective layer structure and process design of solar cells to further convert photoelectric efficiency is an important issue in solar cell technology.

The present invention provides a micro-nano anti-reflective layer structure which has good adhesion to a tantalum solar cell and can achieve excellent anti-reflection properties.

The invention further provides a manufacturing method of the micro-nano anti-reflection layer structure, which can quickly and low-cost manufacture of the micro-nano anti-reflection layer structure, and is easy to integrate into the current solar cell process.

The invention provides a micro-nano anti-reflective layer structure, comprising a germanium substrate having a micro-array structure on its surface, and the micro-array structure surface comprises a plurality of nanostructures, wherein the nanostructures extend along the 矽<100> direction.

In an embodiment of the invention, the nanostructure comprises a nanopore or a nanowire.

In an embodiment of the invention, the microarray structure comprises a plurality of pyramids composed of a group of 矽{111} planes.

In an embodiment of the invention, the height of the pyramid is in the range of 0.5 μm to 15 μm.

In an embodiment of the invention, the width of the pyramid is in the range of 0.5 μm to 15 μm.

In an embodiment of the invention, the height of the nanostructure is in the range of 20 nm to 15 μm.

In an embodiment of the invention, the cross-sectional line width of the nanostructure is In the range of 50 nm to 300 nm.

The invention further provides a method for manufacturing a micro-nano anti-reflection layer structure, comprising providing a germanium substrate, forming a micro-array structure on the surface of the germanium substrate; performing an electroless metal-assisted etching process to form a plurality of nanostructures on the micro-array structure, And the nanostructure extends along the 矽<100> direction.

In another embodiment of the invention, the nanostructure is a nanohole or a nanowire.

In another embodiment of the invention, the height of the nanostructure is in the range of 20 nm to 15 μm.

In another embodiment of the invention, the nanostructure has a profile line width in the range of 50 nm to 300 nm.

In another embodiment of the invention, the above method of forming a micro-array structure includes wet etching.

In another embodiment of the invention, the wet etching includes an anisotropic etching of the germanium substrate by an alkali etching method.

In another embodiment of the present invention, the electroless metal-assisted etching process includes: immersing the germanium substrate in the reaction solution to form a plurality of metal nanoparticles by a reduction reaction on the surface of the micro-array structure; The ruthenium under the metal nanoparticles is etched toward the 矽<100> direction to form a nanostructure; the metal nanoparticles are then removed.

In another embodiment of the invention, the above metal nanoparticles comprise gold, silver, platinum or copper.

In another embodiment of the invention, the above reaction solution comprises silver nitrate and hydrofluoric acid.

In another embodiment of the present invention, in the above electroless metal-assisted etching process, the temperature is controlled within a range of 10 ° C to 80 ° C.

Based on the above, the present invention provides a micro-nano anti-reflective layer structure and a manufacturing method thereof, which are combined with a micro-structure and a nano-structure to not only have good adhesion to a tantalum solar cell, but also can be manufactured at low cost and efficiently. A micro-nano anti-reflective layer structure with excellent anti-reflective properties.

The above described features and advantages of the present invention will be more apparent from the following description.

In the various figures referred to in the following examples, the dimensions and relative sizes of the layers may be exaggerated for clarity. In addition, it should be noted that the present invention may be practiced in many different forms and is not limited to the embodiments described herein.

1A-1D are schematic cross-sectional views showing a manufacturing process of a micro-nano anti-reflection layer structure according to an embodiment of the invention.

First, referring to FIG. 1A, a germanium substrate 100 is provided. The material of the tantalum substrate 100 is, for example, a single crystal germanium, but is not limited thereto.

Next, referring to FIG. 1B, a micro-array structure 110 is formed on the surface of the germanium substrate 100. The method of forming the micro-array structure 110 is, for example, wet etching. For example, the germanium substrate 100 may be anisotropically etched by an alkali etching method to obtain the micro-array structure 110. However, the invention is not limited thereto, and the micro-array structure 110 can be formed by other methods known to those of ordinary skill in the art.

The microarray structure 110 formed by the above method is, for example, a plurality of pyramids 112 composed of a group of 矽{111} planes. The height Hp of the pyramid 112 is, for example, in the range of 0.5 μm to 15 μm, and the width Wp of the pyramid is, for example, in the range of 0.5 μm to 15 μm, but the present invention is not limited thereto.

Then, an electroless metal assisted etching process is performed, please refer to FIG. 1C to FIG. 1D.

In FIG. 1C, the ruthenium substrate 100 is immersed in a reaction solution to form a plurality of metal nanoparticles 114 on the surface of the pyramid 112, and then through the metal nanoparticles 114 to assist the catalytic properties by controlling the reaction conditions (eg, The metal oxide nanoparticles 114 are used as an electrode to carry out a redox reaction, and the tantalum substrate 100 under the metal nanoparticles 114 (the portion to be etched 116 as shown in FIG. 1C) is gradually etched. The above metal nanoparticles 114 are, for example, gold, silver, platinum or copper, but the invention is not limited thereto. In the electroless metal-assisted etching process, for example, the reaction temperature is controlled in the range of 10 ° C to 80 ° C. Then, the surface of the crucible substrate 100 can be cleaned by, for example, concentrated nitric acid (concentration: 20 to 65%) to remove the metal nanoparticles 114.

The nanostructures 118 formed on the microarray structure 110 are shown in FIG. 1D, and all of the nanostructures 118 extend in the 矽<100> direction. It is worth noting that in the electroless metal-assisted etching process, the density of the metal nanoparticles distributed on the surface of the micro-array structure 110 can be changed by adjusting various reaction conditions (such as concentration of the reaction solution, reaction time, etc.), thereby changing the formation. The structure of the nanostructure 118. For example, when the metal nanoparticle 114 has a low distribution density (distribution density is less than 10 ⁸ cm ^-2 ), the nanostructure 118 can be in the form of a nanopore, and when the distribution density of the metal nanoparticle 114 is high ( The distribution density is greater than or equal to 10 ⁸ cm ^-2 ), and the nanostructure 118 is in the form of a nanowire. Further, the height Hn of the formed nanostructure 118 is, for example, in the range of 20 nm to 15 μm, and the cross-sectional line width Wn of the nanostructure 118 is, for example, in the range of 50 nm to 300 nm. Alternatively, the surface having the nanostructures 118 can be further passivated by wet oxidation.

As described above, with the manufacturing method of the micro-nano anti-reflection layer structure proposed in the present embodiment, the micro-nano anti-reflection layer structure can be manufactured quickly and inexpensively by only the wet etching and electroless metal-assisted etching processes. In addition, since the vacuum reaction environment is not required in the above reaction, and materials other than ruthenium are not required, there is no problem of poor material bondability, and it is also easy to integrate into the current solar cell process.

Experimental examples will be given below to explain the present invention in more detail. It should be noted that the data of each experimental example in the following is only for explaining the test effect of the micro-nano anti-reflective layer structure in the examples of the present invention in different experiments, and is not intended to limit the scope of the present invention.

Experimental Example 1: Fabrication of micro-nano anti-reflection layer structure

First, the tantalum substrate is anisotropically etched by an alkali etching method to form a plurality of pyramids composed of a group of 矽{111} planes.

Then, the ruthenium substrate was immersed in a reaction solution containing silver nitrate (AgNO ₃ ) and hydrofluoric acid (HF). Among them, the concentration of silver nitrate ranges from 0.005 to 0.2 M, and the concentration of hydrofluoric acid (HF) ranges from 2 to 6 M. The chemical reaction between the ruthenium substrate and the reaction solution is as follows: Cathodic reaction Ag ⁺ + e ^- → Ag E ⁰ = +0.79 V Anode reaction Si +6 F ^- → SiF ₆ ^2- +4 e ^- E ⁰ = -1.24 V Total reaction Si +4 Ag ⁺ +6 HF → H ₂ SiF ₆ +4 Ag +4 H ⁺

As shown in the above chemical reaction formula, in the electroless metal-assisted etching process at a reaction temperature of 10 to 80 ° C, the silver ions in the solution will pick up the electrons of the ruthenium and be reduced to silver nanoparticles, and precipitated in silver. The ruthenium under the nanoparticle is thus oxidized to SiO _x (x = 1 to 2), and simultaneously with the fluoride ion (F ^- ) provided by HF in the aqueous solution to form SiF ₆ ^2- dissolves, causing an etching reaction.

In this etching reaction, there are two main phenomena occurring for the etching of germanium. One is that the etching proceeds in relation to the lattice structure of germanium, that is, the etching proceeds in the direction of the most easy etching, that is, 矽<100 The direction is etched; the second is that subsequent silver precipitation occurs on the surface of the original nanoparticle, so that the etching progresses from the etching start position. Due to these two main phenomena, the silver nanoparticles originally located on the surface of the pyramidal surface gradually move toward the <100> direction, resulting in a single array of nanostructures oriented toward the <100> direction. Then, the surface of the crucible substrate can be cleaned by concentrated nitric acid to remove the silver nanoparticles.

As a result, as shown in the scanning electron micrograph of Fig. 2, a dense and uniformly distributed nanowire structure was formed on the surface of the pyramidal.

Experimental Example 2: Evaluation of refractive index

3 is a graph showing refractive index changes of the untreated tantalum wafer and the micro-nano anti-reflective layer structure of FIG. 2, respectively, theoretically. The calculation is based on Kramer Kronig relations (KK relations) (references: Zhongyi Guo, Jin-Young Jung, Keya Zhou, Yanjun Xiao, Sang-won Jee, SAMoiz, Jung-Ho Lee, "Optical properties of silicon nanowires array fabricated by metal-assisted electroless etching", Proc. of SPIE Vol.7772, 77721C (2010).), the formula is as follows:

Where n(ω) is the effective refraction index, R(ω) is the reflectance of the actually measured sample, and θ(ω) can be estimated from the measured reflectance. Therefore, by measuring the reflectance results of the structure of the germanium wafer and the micro-nano anti-reflective layer, the change in the equivalent refractive index can be known by bringing in the above-mentioned Cramer-Krönni relationship.

As shown in FIG. 2, the equivalent refractive index of the tantalum wafer calculated by the above calculation is 3.8 in the range of 400 nm to 700 nm, and the equivalent refractive index of the micro-nano anti-reflective layer structure of the present invention is 400. The average range from nanometer to 700 nm is 1.5, and it is obvious that the refractive index is much lower than that of the untreated tantalum wafer, which is also the main cause of the low reflectance of the micro-nano anti-reflective layer structure of the present invention.

As can be seen from FIG. 3, the micro-nano anti-reflective layer structure provided by the present invention has a lower equivalent refractive index than the tantalum wafer, and is suitable as an anti-reflective layer material for a solar cell.

Experimental Example 3: Evaluation of antireflection rate

The method of evaluating the refractive index of a sample is by attaching an integrating sphere. The ultraviolet-visible spectrometer (model: U-3010, Hitachi) of the integrating sphere is used to measure the reflectance of the sample in the wavelength range of 300 nm to 900 nm. In this experimental example, the wavelength range is used. The measured reflectance of the internal quantity is averaged to evaluate the anti-reflective ability of the sample.

4 is an untreated tantalum wafer (L1), a micron anti-reflective layer structure (L2) for making only a pyramid, and a micro-nano anti-reflective layer structure (L3) of FIG. 2 for a wavelength range of 300 nm to 900 nm. Reflectance map of light. The experimental results confirmed that the reflectance of the micro-nano anti-reflective layer structure (L3) was lower than 7% at any wavelength within this range, and both were much lower than the untreated tantalum wafer (L1) or only fabricated. The result of the micron anti-reflective layer structure (L2) of the pyramid.

Figure 5 shows an untreated tantalum wafer (Si), a micron anti-reflective layer structure (ML) that only produces pyramids, and a micro-nano anti-reflective layer structure (NML) of Figure 2 for wavelengths ranging from 300 nm to 900 nm. The average reflectance of light.

As can be seen from FIG. 5, the average reflectance of the tantalum wafer of the micro-nano anti-reflective layer structure of FIG. 2 to the full-wavelength range of solar energy is only about 3.6%, which is much lower than that of the germanium wafer (Si) of 52% or micron resistance. 15% of the reflective layer structure (ML), the experimental data clearly shows that the micro-nano anti-reflective layer structure (NML) of the present invention does have the most excellent anti-reflection characteristics among the three samples.

In summary, by the manufacturing method of the micro-nano anti-reflective layer structure of the present invention, the micro-nano anti-reflective layer structure can be mass-produced quickly and at low cost, and can be directly combined with the current solar cell process, and has high integration. Sex. In addition, the micro-nano anti-reflective layer structure can not only greatly reduce the interface reflection, provide the full-wave anti-reflection ability of the solar energy, and reduce the surface carrier recombination probability, and also has good bonding property with the tantalum solar cell. and It is stable and thus achieves excellent anti-reflection properties.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧矽 substrate

110‧‧‧microarray structure

112‧‧‧Corner

114‧‧‧Metal Nanoparticles

116‧‧‧ part to be etched

118‧‧‧Nano structure

120‧‧‧Micron anti-reflective layer structure

L1, L2, L3‧‧‧ curves

Wn‧‧‧ section line width

Wp‧‧‧Width

Hn, Hp‧‧‧ height

1A-1D are schematic cross-sectional views showing a manufacturing process of a micro-nano anti-reflection layer structure according to an embodiment of the invention.

2 is a scanning electron micrograph of the structure of the micro-nano antireflection layer of Experimental Example 1.

Fig. 3 is a graph showing the refractive index change of the structure of the tantalum wafer and the micro-nano anti-reflective layer, respectively, theoretically.

Figure 4 is a graph showing the reflectance of a germanium wafer, a micron anti-reflective layer structure, and a micro-nano anti-reflective layer structure for light in the wavelength range of 300 nm to 900 nm.

Figure 5 shows the average reflectance of a germanium wafer, a micron anti-reflective layer structure, and a micro-nano anti-reflective layer structure for light in the wavelength range of 300 nm to 900 nm.

100‧‧‧矽 substrate

112‧‧‧Corner

118‧‧‧Nano structure

120‧‧‧Micron anti-reflective layer structure

Wn‧‧‧ section line width

Wp‧‧‧Width

Hn, Hp‧‧‧ height

Claims (17)

A micro-nano anti-reflective layer structure comprising: a germanium substrate having a micron array structure on its surface, and the micro-array structure surface comprises a plurality of nanostructures, wherein the nanostructures extend along a 矽<100> direction . The micro-nano anti-reflective layer structure according to claim 1, wherein the nanostructures comprise nanopores or nanowires. The micro-nano anti-reflective layer structure of claim 1, wherein the micro-array structure comprises a plurality of pyramids composed of a group of 矽{111} planes. The micro-nano anti-reflective layer structure according to claim 3, wherein the height of the pyramids is in the range of 0.5 μm to 15 μm. The micro-nano anti-reflective layer structure according to claim 3, wherein the pyramids have a width in the range of 0.5 μm to 15 μm. The micro-nano anti-reflection layer structure according to claim 1, wherein the height of the nanostructures is in the range of 20 nm to 15 μm. The micro-nano anti-reflection layer structure according to claim 1, wherein the nanostructures have a profile line width ranging from 50 nm to 300 nm. A method for fabricating a micro-nano anti-reflective layer structure, comprising: providing a germanium substrate, forming a micron array structure on the surface of the germanium substrate; and performing an electroless metal-assisted etching process to form a plurality of layers on the micro-array structure Rice structure, and the nanostructures are extended along the 矽<100> direction Stretch. The method for manufacturing a micro-nano anti-reflective layer structure according to claim 8, wherein the nanostructures are nanopores or nanowires. The micro-nano anti-reflective layer structure as described in claim 8 wherein the height of the nanostructures is in the range of 20 nm to 15 μm. The method for fabricating a micro-nano anti-reflective layer structure according to claim 8, wherein the nanostructures have a profile line width in the range of 50 nm to 300 nm. The method of fabricating the micro-nano anti-reflective layer structure of claim 8, wherein the method of forming the micro-array structure comprises wet etching. The method for fabricating a micro-nano anti-reflective layer structure according to claim 12, wherein the wet etching comprises anisotropic etching of the germanium substrate by an alkali etching method. The method for fabricating a micro-nano anti-reflective layer structure according to claim 8 , wherein the electroless metal-assisted etching process comprises: immersing the germanium substrate in a reaction solution for the micro-array structure Forming a plurality of metal nanoparticles on the surface by a reduction reaction; and simultaneously etching the underside of the metal nanoparticles to the 矽<100> direction to form the nano structures; and removing the metal nanoparticles Particles. The method for producing a micro-nano anti-reflective layer structure according to claim 14, wherein the metal nanoparticles comprise gold, silver, platinum or copper. The method for producing a micro-nano anti-reflective layer structure according to claim 14, wherein the reaction solution comprises silver nitrate and hydrofluoric acid. The method for fabricating a micro-nano anti-reflective layer structure according to claim 14, wherein in the electroless metal-assisted etching process, the temperature is controlled within a range of 10 ° C to 80 ° C.