KR101604520B1 - Reflective solar cell and fabricating method thereof - Google Patents

Abstract

A solar cell and a manufacturing method thereof are disclosed. The method includes depositing a first conductive transparent electrode on one side of a transparent first substrate, depositing a reflective film on the other side of the first substrate, depositing an n-type limiting layer, an active layer and a p- The first conductive transparent electrode and the solar cell structural layer are bonded together, and then the second substrate is removed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a solar cell,

The present invention relates to a solar cell and a manufacturing method thereof.

In general, an Al _x Ga _{1 - x} As solar cell is a semiconductor device that converts light energy of about 650 to 850 nm wavelength band injected from the outside into electric energy.

The Al _x Ga _{1 - x} As solar cell is manufactured at a high temperature of 600 to 800 ° C. using a metalorganic chemical vapor deposition (MOCVD) system capable of growing a high quality thin film, and basically, an n-type AlGaAs material And a high efficiency undoped Al _x Ga _{1 - x} As active layer with a certain ratio of Al and Ga calculated for a specific wavelength between the p-type AlGaAs material.

In general, Al _x Ga _{1 - x} As solar cells are grown on an n - type GaAs absorption substrate with almost identical lattice constants. As the lattice constant of the grown solar cell almost coincides with the lattice constant of the substrate, it is possible to grow a solar cell with excellent crystal quality.

This Al _x Ga _1-x As n-type GaAs absorbent substrate that is essentially used for the growth of the solar cell is an Al _x Ga ₁ growing on top _- in the active layer it has a considerably lower band gap than the _x As solar cell structure layer And absorbs light traveling to the lower substrate. For example, the band gap of A _lx Ga _{1 -x} As is 1.5 eV when x is 0.1, 2.2 eV when x is 1, and the band gap of GaAs is 1.4 eV, so that the band gap of the substrate is extremely low You can check,

In a solar cell, the light energy injected is not used for the recombination of the 100% active layer, and a considerable part of the light energy moves to the absorption substrate through the active layer. In order to compensate for the disadvantages of the n-type GaAs absorption substrate in the Al _x Ga _{1 -x} As solar cell, GaP, sapphire (Al ₂ O ₃ ), or GaN substrates having high bandgaps are used. However, And defects are generated, thereby making it difficult to manufacture a high-efficiency AlGaAs solar cell.

Technical problem to be solved by the present invention, a reflective film and a conductive by a film applied to a transparent substrate, depositing on both faces, Al _x Ga _{1 -} proceeds to not recombined in the _x As the solar cell active layer substrate an active layer of the light energy is reduced and the absorption To increase the efficiency of the solar cell, and a manufacturing method thereof.

According to an aspect of the present invention, there is provided a solar cell comprising: a transparent substrate; A first conductive transparent electrode on the transparent substrate; A reflective film below the transparent substrate; A solar cell structural layer including a p-type confinement layer on the first conductive transparent electrode, an active layer, and an n-type confinement layer; An anti-reflection film on the solar cell structure layer; And a second conductive transparent electrode on the anti-reflection film.

In one embodiment of the present invention, the solar cell structure layer, the second reflective film, and the second conductive transparent electrode may be partly etched.

In one embodiment of the present invention, the transparent substrate may include a sapphire substrate.

In one embodiment of the present invention, the first and second conductive transparent electrodes may be composed of indium tin oxide (ITO), respectively.

In one embodiment of the present invention, the reflective film may be composed of silver (Ag).

According to another aspect of the present invention, there is provided a method of fabricating a solar cell, including: depositing a first conductive transparent electrode on one side of a transparent first substrate; depositing a reflective film on the other side of the first substrate; ; Growing a solar cell structural layer comprising an n-type limiting layer, an active layer and a p-type limiting layer on a second substrate; Bonding the first conductive transparent electrode to the solar cell structural layer; Removing the second substrate; Sequentially forming an antireflection film and a second conductive transparent electrode on the solar cell structure layer; And mesa etching the antireflection film, the second conductive transparent electrode, and the solar cell structural layer.

In one embodiment of the present invention, the bonding step may be wafer bonding using a eutectic material.

In one embodiment of the present invention, the eutectic material may be an AuIn eutectic material.

The present invention as described above has the effect of increasing the solar cell efficiency by reusing the light energy absorbed in the substrate by applying the reflective film and the conductive transparent substrate to the solar cell.

In addition, the present invention has an effect of manufacturing a high-efficiency solar cell by a simple process by bonding sapphire substrates having reflective films and transparent conductive films on both sides thereof to a solar cell structure on a wafer-by-wafer basis.

1 is a cross-sectional view schematically illustrating a solar cell manufactured by conventional MOCVD.
2 is a cross-sectional view schematically illustrating a solar cell according to an embodiment of the present invention.
3A to 3E are cross-sectional views schematically illustrating a manufacturing method of a solar cell according to an embodiment of the present invention.
4 is an exemplary view for explaining light emission characteristics of the Al _x Ga _{1 - x} As solar cell of the present invention.
5 and 6 are diagrams for explaining efficiency of an Al _x Ga _{1 - x} As solar cell according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view schematically illustrating a solar cell manufactured by conventional MOCVD.

As shown in the figure, a conventional Al _x Ga _{1 -x} As solar cell has a structure in which an n-type Al _x Ga _{1 -x} As (x> 0.8) limiting layer 120 is formed on a GaAs substrate 110 by MOCVD, Type active layer 130 and a p-type Al _x Ga _{1 -x} As (x> 0.8) limiting layer 140, and the p-type confinement layer 140 is composed of a doped Al _x Ga _{1 -x} As (0 <x < An Al anti-reflection film 150 and an indium tin oxide (ITO) 160, which is a transparent upper electrode, are stacked to prevent re-emission of light energy injected into the upper portion. Since the lower electrode 170 is independent of light energy, Au or Ni is used.

Such a conventional Al _x Ga _{1 -} In _x As solar cells, GaAs substrate 110 is considerably lower band gap than the Al _x Ga _1-x As solar cell structure layer (120, 130, 140) grown on top The light emitted from the active layer 130 is absorbed by the substrate 110, which results in a significant decrease in efficiency.

2 is a cross-sectional view schematically illustrating a solar cell according to an embodiment of the present invention.

As shown in the figure, the Al _x Ga _{1 -x} As solar cell of the present invention includes a transparent sapphire substrate 10, a conductive transparent electrode 20, a p-type confinement layer 30, an undoped active layer 40, an n-type confinement layer 50, an antireflection film 60, a conductive transparent electrode 70, and a reflective film 80.

The solar cell of the present invention includes a p-type confinement layer 30, a non-doped active layer 40, a n-type cladding layer 40, and a n-type cladding layer 40 in order to connect the conductive transparent electrode 20 on the substrate 10 to the conductive transparent electrode 70 on the top. Type limiting layer 50, the antireflection film 60, and the conductive transparent electrode 70 may be etched.

Hereinafter, a manufacturing method of the solar cell of the present invention shown in Fig. 2 will be described with reference to the drawings.

3A to 3E are cross-sectional views schematically illustrating a manufacturing method of a solar cell according to an embodiment of the present invention.

First, as shown in FIG. 3a, manufacturing method of the present invention, n-type on the n-type GaAs substrate _{(90) Al x Ga 1 -} x As (x> 0.8) confining layer 50, the undoped Al _x Ga _{1 -} forms the _x As solar cells _- Al _x Ga ₁ by growing the _x As (x> 0.8) confining layer _{(30) - x As (0} <x <0.8) active layer 40 and p-type Al _x Ga ₁ and that the separate, transparent to the one surface of the sapphire substrate 10 to form a transparent conductive electrode 20 to form a reflection film 80 on the other surface, the conductive transparent electrode 20 and the p-type Al _x Ga _{1 - x} As (x > 0.8) limiting layer 30 can be wafer bonded as shown in Fig. 3B.

The conductive transparent electrode 20 deposited on one surface of the transparent sapphire substrate 10 is, for example, ITO. The ITO thus formed serves as a bottom current diffusion layer of the Al _x Ga _{1 - x} As solar cell. May be deposited to a thickness of, for example, 200 nm, but the present invention is not limited thereto. ITO having a thickness of 200 nm has a high transmittance of 95% or more in a wavelength region of 350 to 1000 nm and is advantageous as a lower electrode of the transparent sapphire substrate 10. [

Further, since the transparent reflecting film 80 is formed on the other surface of the sapphire substrate 10 is, for example, a thickness of 100㎚ Ag, has a high reflectivity of 95% or more in the wavelength region of about 400 to 1000㎚, Al _x Ga It is possible to effectively reflect the light energy of 650 to 850 nm wavelength region injected into the substrate 10 from the _{1 - x} As solar cell.

That is, the transparent sapphire substrate 10 having the conductive transparent electrode 20 and the reflective film 80 of the present invention is formed on both surfaces of a transparent sapphire substrate 10 having a thickness of 250 μm, (ITO) having a thickness of 200 nm, which is the reflective layer 20, and Ag having a thickness of 100 nm, which is the reflective film 80, can be deposited.

On the other hand, a conductive transparent electrode 20 and the reflective film 80 is formed of transparent sapphire substrate 10 and Al _x Ga ₁ of the present _invention the bonding of the _x As solar cells, AuIn eutectic (eutetic) can be bonded using materials have. The AuIn eutectic material is an ohmic contact material itself when heat is applied at a temperature of about 200 [deg.] C or more, and has an advantage that an annealing process to be performed in a chip process is not necessary. At this time, the thickness of the AuIn eutectic material is preferably 100 nm or less. When AuIn eutectic material is 100 nm or more, incident light may be absorbed by AuIn eutectic material itself.

As described above, the transparent sapphire substrate 10 on which the conductive transparent electrode 20 and the reflective film 80 of the present invention are formed is made of Al _x Ga _{1 - x} As solar cell ₁₀ grown on the n-type GaAs substrate 90, by the bonding of the active layer and a wafer unit formed by the substrate, Al _x Ga _{1 -} has the advantage of not affecting the characteristics of the thin film solar cell _x as.

In the description of the present invention, a sapphire substrate is described as an example of a transparent substrate, but the present invention is not limited thereto, and various transparent substrates may be used.

After the transparent sapphire substrate 10 on which the conductive transparent electrode 20 and the reflective film 80 are formed is bonded to the Al _x Ga _{1 -x} As solar cell, the n-type GaAs substrate 90 is selectively etched Remove it in solution. At this time, for example, NH ₃ : H ₂ O ₂ : DI may be used as the selective etching solution.

Then, as shown in FIG. 3d, the n-type Al _x Ga ₁ located in the _upper-can be sequentially deposited a reflecting layer 60 and the conductive transparent electrode 70 to the upper _x As (x> 0.8), the restriction layer 50 . At this time, the reflective layer 60 may be made of Al, and the conductive transparent electrode 70 may be made of ITO.

3E, the conductive transparent electrode 70, the reflective layer 60, and the n-type electrode are formed through a photo-lithography process and an inductively coupled plasma (ICP) mesa etching process, The limiting layer 50, the undoped active layer 40 and a part of the p-type confinement layer 30 can be removed.

FIG. 4 is a view for explaining light emission characteristics of the Al _x Ga _{1 - x} As solar cell of the present invention, in which (a) shows a light emitting route of a conventional solar cell, (b) And shows the light emission route of the battery.

In the case of (a) of Figure 4, Al _x Ga _{1 - x} As upper light energy of a specific wavelength inputted to the solar cell, and recombination in the solar cell active layer 130, could not be recombined part of the light energy is in the upper or lower Reflection. It can be confirmed that most of the light energy is absorbed by the n-type GaAs substrate 110 although a part of the light energy that has been propagated to the upper part is sent to a part of the active layer 130 by the upper reflective layer 140.

However, FIG. 4 for the (b), Al _x Ga ₁ of the present invention comprising a conductive transparent electrode 20 and the reflective film transparent sapphire substrate 10, 80 is formed _{- x} As solar cells, light energy 4 (a), most of the light energy traveling to the substrate by the transparent sapphire substrate 10 and the reflective film 80 at the lower end of the substrate 10 is reflected again to the active layer 40, The efficiency of the solar cell can be increased.

5 and 6 one embodiment of a Al _x Ga ₁ of the present invention _{- x} As as an example for illustrating the efficiency of the solar cell, and Fig. 5 is an n-type GaAs substrate (B) and the transparent sapphire substrate of the present invention ( A shows transmittance data for respective wavelengths, and FIG. 6 shows reflectance data for each wavelength according to the thickness of the reflection film 80.

As shown in FIG. 5, the n-type GaAs substrate is hardly transparent (B), but the transparent sapphire substrate used in the present invention has a very high transmittance.

6, when the Ag reflective film 80 formed on the other side of the transparent sapphire substrate 10 has a thickness of 100 nm, the most favorable reflectance is obtained in all wavelength bands.

In the above description, Al _x Ga _{1 -} but for example the _x As solar cell example described and are therefore not to exclude that the present invention is a solar cell that is composed of other materials that are applied, to which the present invention to a solar cell consisting of a variety of materials .

Thus, by applying the reflective film and the conductive transparent substrate to the solar cell, the solar energy efficiency can be increased by reusing the light energy absorbed in the substrate, and the sapphire substrate having the reflective film and the transparent conductive film on both sides By bonding the cell structure and the wafer structure on a mutual wafer basis, a high efficiency solar cell can be manufactured by a simple process.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the true scope of the present invention should be determined by the following claims.

10, 90: plate 20, 70: conductive transparent electrode
30: p-type limiting layer 40: active layer
50: n-type limiting layer 60: antireflection film
80:

Claims (8)

delete delete delete delete delete Depositing a first conductive transparent electrode on one side of a transparent first substrate and depositing a reflective film on the other side of the first substrate;
Growing a solar cell structural layer comprising an n-type limiting layer, an active layer and a p-type limiting layer on a second substrate;
Bonding the first conductive transparent electrode to the solar cell structural layer;
Removing the second substrate;
Sequentially forming an antireflection film and a second conductive transparent electrode on the solar cell structure layer; And
And etching the antireflection film, the second conductive transparent electrode, and the solar cell structural layer by a mesa etching method.
7. The method of claim 6,
A solar cell manufacturing method for wafer bonding using a eutectic material.
8. The method of claim 7,
Fabrication method of solar cell which is AuIn eutectic material.

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