CN111244218B - Solar cell and preparation method thereof - Google Patents

Abstract

The invention provides a solar cell and a preparation method thereof. The solar cell includes a substrate, an epitaxial layer and a metal electrode sequentially arranged from bottom to top, the solar cell also includes a light guide structure arranged on a surface of the metal electrode away from the epitaxial layer, and the light guide structure includes a sequence along the direction away from the metal electrode. At least two layers of light guide layers are stacked, and the refractive index of the light guide layers increases sequentially along the direction away from the metal electrode. The light guide structure is arranged on the metal electrode of the solar cell. Since the refractive index of the light guide layer of the light guide structure increases in turn along the direction away from the metal electrode, the sunlight projected on the metal electrode can be guided by the refraction of light to be able to absorb light. The position of the solar cell is used to make use of the part of the sunlight that was not originally absorbed, thereby effectively improving the utilization efficiency of light per unit area of the solar cell.

Description

Solar cell and preparation method thereof

technical field

The present invention relates to the field of solar cells, in particular, to a solar cell and a preparation method thereof.

Background technique

GaAs has a forbidden band width of 1.43 eV and is one of the most preferred materials for absorbing sunlight. Solar cells prepared from gallium arsenide have the characteristics of high conversion efficiency, good temperature characteristics, and strong radiation resistance. With the development of metal organic compound vapor deposition (MOCVD) and molecular beam epitaxy (MBE) technologies, GaAs solar cells Applications are becoming more and more widespread.

Gallium arsenide solar cell chips are generally fabricated after the epitaxial layer structure is prepared, and the front electrode is usually made of gold, silver, copper, aluminum and other metal electrodes with good conductivity, which can collect current and turn on the battery. Purpose. The layout of the front electrode is designed according to the needs, which occupies about 5% of the area of the battery chip. Since the metal electrode is opaque to light, the sunlight projected on the front electrode on the battery chip cannot be utilized, which reduces the utilization efficiency of light per unit area of the gallium arsenide solar cell.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a solar cell and a preparation method thereof, so as to solve the problem of low utilization rate of light per unit area of the solar cell in the prior art.

In order to achieve the above object, according to one aspect of the present invention, a solar cell is provided. The solar cell includes a substrate, an epitaxial layer and a metal electrode sequentially arranged from bottom to top. A light guide structure on the surface of the layer, the light guide structure includes at least two light guide layers stacked in sequence along the direction away from the metal electrode, and the refractive index of the light guide layers increases sequentially along the direction away from the metal electrode.

Further, the above-mentioned light guide structure includes: a first light guide layer, disposed on the surface of the metal electrode away from the epitaxial layer; the second light guide layer, disposed on the surface of the first light guide layer away from the metal electrode, the The ratio is less than the refractive index of the second light guide layer.

Further, the refractive index of the first optical guide layer is between 1.3 and 1.7, preferably the thickness of the first optical guide layer is between 50 and 200 nm, and preferably the first optical guide layer is a magnesium fluoride layer, an aluminum fluoride layer, a fluoride A composite layer of any one or more of the barium layer, the yttrium fluoride layer, the lanthanum fluoride layer and the silicon oxide layer.

Further, the refractive index of the second optical guide layer is between 1.7 and 2.05, preferably the thickness of the second optical guide layer is between 50 and 200 nm, and preferably the second optical guide layer is a silicon nitride layer, a zirconium oxide layer, and a hafnium oxide layer. and a composite layer of any one or more of the zinc oxide layers.

Further, the above-mentioned light guide structure further includes a third light guide layer, and the third light guide layer is disposed on the surface of the second light guide layer away from the first light guide layer. Preferably, the refractive index of the third light guide layer is between 2.02 and 2.5, and more preferably The thickness of the third optical guide layer is between 50 and 200 nm, and more preferably the third optical guide layer is a composite layer of any one or more of a titanium dioxide layer, a titanium pentoxide layer, a cerium oxide layer and a zinc sulfide layer.

Further, a part of the surface of the above-mentioned epitaxial layer is provided with a metal electrode, and another part of the surface is exposed, the solar cell also includes an anti-reflection layer and a third light guide layer, the anti-reflection layer is provided on the exposed surface of the epitaxial layer, and the third light guide layer is provided. On the surface of the second light guide layer away from the first light guide layer, and the refractive index of the anti-reflection layer is the same as that of the third light guide layer and both are greater than the refractive index of the second light guide layer, preferably the refractive index of the anti-reflection layer is Between 2.02 and 2.5, it is further preferred that the thickness of the anti-reflection layer is between 50 and 200 nm, and it is more preferred that the anti-reflection layer is any one or more of a titanium dioxide layer, a titanium pentoxide layer, a cerium oxide layer and a zinc sulfide layer. composite layer.

Further, the above-mentioned solar cell is a silicon-based solar cell, a heterojunction solar cell or a compound semiconductor thin film type solar cell. Preferably, the compound semiconductor thin film type solar cell is a gallium arsenide solar cell or a copper indium gallium selenide solar cell. A single junction consisting of a buffer layer, a back field layer, a base layer, an emission layer, a window layer and an ohmic contact layer stacked away from the substrate, or including a plurality of single junctions connected by tunnel junctions.

Further, the above-mentioned substrate is a GaAs substrate, a Ge substrate or a SiC substrate, and the metal electrode is preferably a gold electrode, a copper electrode or a silver electrode.

According to another aspect of the present invention, there is provided a preparation method of any one of the above solar cells, the preparation method includes sequentially forming an epitaxial layer and a metal electrode on a substrate, and characterized in that, the preparation method further includes forming an epitaxial layer on the metal electrode. A light guide structure is arranged on the surface away from the epitaxial layer, and the light guide structure includes at least two layers of light guide layers stacked in sequence along the direction away from the metal electrode, and the refractive index of the light guide layers increases sequentially along the direction away from the metal electrode.

Further, the above-mentioned process of disposing the light guide structure on the surface of the metal electrode away from the epitaxial layer includes: disposing a mask layer on the epitaxial layer; disposing the first light guide layer, the second light guide layer and the third light guide layer on the metal electrode in sequence The process of removing the mask layer, setting an anti-reflection layer on the epitaxial layer, or setting a light guide structure on the surface of the metal electrode away from the epitaxial layer includes: setting a mask layer on the epitaxial layer; The light guide layer and the second light guide layer; the mask layer is removed, and a refractive material is arranged on the epitaxial layer and the second light guide layer to form a third light guide layer on the second light guide layer, and an antireflection layer is formed on the epitaxial layer; preferably The first light guide layer, the second light guide layer, the third light guide layer and the refracting material are independently provided by vapor deposition or sputtering.

Applying the technical solution of the present invention, a light guide structure is arranged on the metal electrode of the solar cell. Since the refractive index of the light guide layer of the light guide structure increases in turn along the direction away from the metal electrode, the sunlight projected on the metal electrode can be refracted by the refraction of light. The light is guided to a position where light can be absorbed, and the part of sunlight that is not originally absorbed can be utilized, thereby effectively improving the utilization efficiency of light per unit area of the solar cell.

Description of drawings

The accompanying drawings forming a part of the present application are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

FIG. 1 shows a schematic diagram of a solar cell structure according to a preferred embodiment of the present invention; and

FIG. 2 shows a schematic diagram of light conduction in the light guide structure of the solar cell shown in FIG. 1 .

Wherein, the above-mentioned drawings include the following reference signs:

10, substrate; 20, epitaxial layer; 30, metal electrode; 41, first light guide layer; 42, second light guide layer; 43, third light guide layer; 50, anti-reflection layer.

Detailed ways

It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

As analyzed in the background art of this application, in the prior art, since the metal electrodes are opaque to light, the sunlight projected on the metal electrodes on the battery chips cannot be utilized, which reduces the utilization efficiency of light per unit area of the solar cells. In order to solve this problem Problem, the present application provides a solar cell and a preparation method thereof.

In a typical embodiment of the present application, a solar cell is provided. As shown in FIG. 1 , the solar cell includes a substrate 10 , an epitaxial layer 20 and a metal electrode 30 arranged in sequence from bottom to top. Including a light guide structure disposed on the surface of the metal electrode 30 away from the epitaxial layer 20, the light guide structure includes at least two layers of light guide layers stacked in sequence along the direction away from the metal electrode 30, and the light guide layer along the direction away from the metal electrode 30 The refractive index increase sequentially.

A light guide structure is arranged on the metal electrode 30 of the solar cell. Since the refractive index of the light guide layer of the light guide structure increases in turn in the direction away from the metal electrode 30, the sunlight projected on the metal electrode 30 can be guided to a direction that can be The position where the light is absorbed then utilizes the portion of sunlight that was not originally absorbed (see Figure 2), thereby effectively improving the utilization efficiency of light per unit area of the solar cell.

In an embodiment of the present application, as shown in FIG. 1 , preferably, the above-mentioned light guide structure includes a first light guide layer 41 and a second light guide layer 42 , and the first light guide layer 41 is disposed on the surface of the metal electrode 30 away from the epitaxial layer 20 . ; The second optical guide layer 42 is arranged on the surface of the first optical guide layer 41 away from the metal electrode 30 , and the refractive index of the first optical guide layer 41 is smaller than the refractive index of the second optical guide layer 42 . The structure of the above-mentioned light guide structure is simple, and the amount of sunlight entering the light absorption position can be effectively changed by adjusting the refractive index difference between the first light guide layer 41 and the second light guide layer 42, and the utilization efficiency of light per unit area of the solar cell can be improved.

There are many kinds of materials used for the first light guide layer 41 in the present application. It is preferable to control the refractive index of the first light guide layer 41 to be between 1.3 and 1.7, which is the lowest range of the currently commonly used solid refractive index materials. In order to introduce as much long-wavelength sunlight (380 nm to 870 nm) into the absorbable position as possible, the thickness of the first light guide layer 41 is preferably between 50 and 200 nm. In order to better adapt to the material of the solar cell, preferably the first optical guide layer 41 is a magnesium fluoride layer, an aluminum fluoride layer, a barium fluoride layer, a yttrium fluoride layer, a lanthanum fluoride layer and a silicon oxide layer. Any one or more of the composite layers.

There may be various materials for the first light guide layer 41 of the present application, and it is preferable to control the refractive index of the second light guide layer 42 to be between 1.7 and 2.05. In addition, in order to cooperate with the refractive index of the first optical guide layer 41 to introduce as much long-wavelength sunlight (380 nm to 870 nm) into the absorbable position, the thickness of the second optical guide layer 42 is preferably between 50 and 200 nm. In order to better match the material of the first optical guide layer 41, the second optical guide layer 42 is preferably a composite layer of any one or more of a silicon nitride layer, a zirconium oxide layer, a hafnium oxide layer and a zinc oxide layer.

In another embodiment of the present application, as shown in FIG. 1 , the above-mentioned light guide structure further includes a third light guide layer 43 , and the third light guide layer 43 is disposed on the surface of the second light guide layer 42 away from the first light guide layer 41 , Preferably, the refractive index of the third optical guide layer 43 is between 2.02 and 2.5, and more preferably the thickness of the third optical guide layer 43 is between 50 and 200 nm. A composite layer of any one or more of a cerium layer and a zinc sulfide layer. As shown in FIG. 2 , by arranging the third light guide layer 43 , the refraction angle of light is further increased, so that more light is introduced into the absorbable position, and the utilization efficiency of light per unit area is further improved.

In another embodiment of the present application, it is preferable that a part of the surface of the epitaxial layer 20 is provided with a metal electrode 30, and another part of the surface is exposed. The solar cell further includes an anti-reflection layer 50 and a third light guide layer 43, and the anti-reflection layer 50 is disposed on the On the exposed surface of the epitaxial layer 20, the third light guide layer 43 is disposed on the surface of the second light guide layer 42 away from the first light guide layer 41, and the refractive index of the antireflection layer 50 is the same as that of the third light guide layer 43 and are larger than the refractive index of the second light guide layer 42, preferably the refractive index of the anti-reflection layer 50 is between 2.02 and 2.5, more preferably the thickness of the anti-reflection layer 50 is between 50 and 200 nm, and more preferably the anti-reflection layer 50 is a titanium dioxide layer , a composite layer of any one or more of the titanium pentoxide layer, the cerium oxide layer and the zinc sulfide layer. Disposing the anti-reflection layer 50 on the light guide structure and using it as a light guide layer can also have the effect of changing the light path and improving the light utilization efficiency.

Of course, the number of light guide layers in the light guide structure of the present application is not limited to the above two or three layers, and those skilled in the art can also adjust the light guide according to the area of the metal electrode, the area of the epitaxial layer and the refractive index of each light guide layer used. The number of layers, whether adjusted to several layers, is within the scope of protection of the present application.

The light-guiding structure of the present application can be used in various solar cells, preferably the above-mentioned solar cells are silicon-based solar cells, heterojunction solar cells or compound semiconductor thin-film solar cells.

In a preferred embodiment, the compound semiconductor thin film solar cell is a gallium arsenide solar cell or a copper indium gallium selenide solar cell, and the epitaxial layer 20 includes a buffer layer, a back field layer, and a base layer that are stacked away from the substrate 10 in sequence. , a single junction composed of an emission layer, a window layer and an ohmic contact layer, or a plurality of single junctions connected by a tunnel junction. That is, the above-mentioned solar cell may be a single-junction solar cell or a multi-junction solar cell.

The substrate 10 used for the above-mentioned solar cell can be selected according to the specific type of solar energy, and preferably, the above-mentioned substrate 10 is a GaAs substrate, a Ge substrate or a SiC substrate.

The metal electrode 30 used in the solar cell of the present application can be a metal electrode 30 commonly used in solar cells. In order to improve the electrical conductivity, the metal electrode 30 is preferably a gold electrode, a copper electrode or a silver electrode.

In another typical embodiment of the present application, there is provided a preparation method of any one of the above solar cells, the preparation method includes sequentially forming an epitaxial layer 20 and a metal electrode 30 on the substrate 10, and in addition, the preparation method The method further includes disposing a light guide structure on the surface of the metal electrode 30 away from the epitaxial layer 20 , the light guide structure includes at least two light guide layers stacked in sequence along the direction away from the metal electrode 30 , and the light guide layer is refracted along the direction away from the metal electrode 30 . rate increases sequentially.

In the preparation method of the present application, a light guide structure is arranged on the metal electrode 30 of the solar cell. Since the refractive index of the light guide layer of the light guide structure increases sequentially along the direction away from the metal electrode 30, the light projected on the metal electrode 30 can be projected on the metal electrode 30 through the refraction of light. The sunlight is guided to a position where light can be absorbed, and the part of the sunlight that is not originally absorbed can be used (refer to Figure 2), thereby effectively improving the utilization efficiency of light per unit area of the solar cell.

Those skilled in the art can refer to the prior art for the fabrication method of the above-mentioned epitaxial layer and metal electrode of the solar cell, for example, the epitaxial layer is formed by epitaxial growth, which will not be repeated here.

In an embodiment of the present application, the process of disposing the light guide structure on the surface of the metal electrode away from the epitaxial layer 20 includes: disposing a mask layer on the epitaxial layer; disposing a first light guide layer 41 and a second light guide layer on the metal electrode in sequence. The light guide layer 42 and the third light guide layer 43; the mask layer is removed, and the anti-reflection layer 50 is arranged on the epitaxial layer. In the above process, the third light guide layer 43 and the anti-reflection layer 50 are formed in steps, and their respective materials can be flexibly selected.

In another embodiment of the present application, the process of disposing the light guide structure on the surface of the metal electrode 30 away from the epitaxial layer 20 includes: disposing a mask layer on the epitaxial layer; disposing the first light guide layer 41 on the metal electrode 30 in sequence and the second light guide layer 42; the mask layer is removed, and a refractive material is arranged on the epitaxial layer 20 and the second light guide layer 42 to form a third light guide layer 43 on the second light guide layer 42, and a reduced light guide layer is formed on the epitaxial layer 20. Reflective layer 50 . In the above process, the third light guide layer 43 and the anti-reflection layer 50 are formed at the same time, which simplifies the manufacturing process.

Preferably, the first light guide layer 41 , the second light guide layer 42 , the third light guide layer 43 and the refractive material are provided independently by vapor deposition or sputtering.

The specific implementation process of the above evaporation or sputtering can refer to the prior art, such as using a mask to cover the position where the first optical guide layer does not need to be set, and then using the first optical guide layer material for evaporation or sputtering. Plating process parameters or sputtering process parameters can be adjusted according to thickness requirements on the basis of referring to the prior art, and details are not described herein again. The technical effects of the present application will be further described below with reference to the examples and comparative examples.

Example 1

1) The Ge substrate is introduced into the MOCVD equipment, and each epitaxial layer is grown as follows:

The Ge substrate was introduced into the MOCVD equipment, and the H ₂ gas was introduced to clean the substrate at a high temperature at 800 °C;

A back field layer is epitaxially grown on the cleaned substrate, and the back field layer is Al _0.5 Ga _0.5 As, wherein the thickness of the back field layer is 100 nm, and the growth temperature of the back field layer is 800°C;

The base layer is grown on the back field layer, the base layer is GaAs, the thickness of the base layer is 2000nm, and the growth temperature of the base layer is 800°C;

growing a C-doped GaAs emitting layer on the base layer, wherein the thickness of the emitting layer is 500 nm;

A window layer is grown on the emission layer, preferably the window layer is Al _0.5 Ga _0.5 As, the thickness of the window layer is 100nm, and the growth temperature of the window layer is 800°C;

A contact layer is grown on the window layer, the contact layer is a P-doped GaAs layer, the P-doped concentration is 1E20, the thickness of the contact layer is 100 nm, and the growth temperature of the contact layer is 800°C.

2) Define a metal electrode region on the epitaxial layer, cover the rest with a mask, and evaporate gold to make metal electrodes;

3) Evaporating magnesium fluoride (refractive index 1.38) on the metal electrode to form a first light guide layer with a thickness of 120 nm;

4) Vapor deposition of hafnium oxide (refractive index 1.95) on the first light guide layer to form a second light guide layer with a thickness of 90 nm;

5) Remove the mask;

6) Evaporate TiO ₂ (refractive index 2.35) on the surface of the metal electrode and the exposed epitaxial layer to form a third optical guide layer on the metal electrode, and form an anti-reflection layer on the surface of the exposed epitaxial layer with a thickness of 70 nm.

Example 2

The difference from Example 1 is that the first light guide layer is aluminum fluoride with a refractive index of 1.35; the second light guide layer is zinc oxide with a refractive index of 2.0.

Example 3

The difference from Example 1 is that the first light guide layer is lanthanum fluoride with a refractive index of 1.58; the second light guide layer is zirconium oxide with a refractive index of 2.05; the third light guide layer is cerium oxide with a refractive index of 2.20.

Example 4

The difference from Example 1 is that the thickness of the first optical guide layer is 50 nm.

Example 5

The difference from Example 1 is that the thickness of the first optical guide layer is 200 nm.

Example 6

The difference from Example 1 is that the thickness of the second optical guide layer is 200 nm.

Example 7

The difference from Example 1 is that the thickness of the second optical guide layer is 50 nm.

Example 8

The difference from Example 1 is that the thickness of the third optical guide layer is 50 nm.

Example 9

The difference from Example 1 is that the thickness of the third optical guide layer is 200 nm.

Example 10

The difference from Example 1 is that the thickness of the second optical guide layer is 40 nm.

Example 11

The difference from Example 1 is that the thickness of the first optical guide layer is 210 nm.

Example 12

The difference from Example 1 is that the third optical guide layer is not provided on the second optical guide layer, and only titanium dioxide is provided on the exposed surface of the epitaxial layer.

Comparative Example 1

The difference from Example 1 is that no optical guide layer is provided, and only titanium dioxide is provided on the exposed surface of the epitaxial layer.

The photoelectric conversion efficiency of the solar cells of each embodiment and the comparative example was tested by IV test, and the test results are shown in Table 1.

Table 1

From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects:

The light guide structure is arranged on the metal electrode of the solar cell. Since the refractive index of the light guide layer of the light guide structure increases in turn along the direction away from the metal electrode, the sunlight projected on the metal electrode can be guided by the refraction of light to be able to absorb light. The position of the solar cell is used to make use of the part of the sunlight that was not originally absorbed, thereby effectively improving the utilization efficiency of light per unit area of the solar cell.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (21)

1. A solar cell comprising a substrate (10), an epitaxial layer (20) and a metal electrode (30) arranged in sequence from bottom to top, wherein the solar cell further comprises a A light guide structure on the surface of the metal electrode (30) away from the epitaxial layer (20), the light guide structure comprising at least two light guide layers stacked in sequence along a direction away from the metal electrode (30), and The refractive index of the light guide layer increases sequentially along the direction away from the metal electrode (30); the light guide structure includes: a first optical guide layer (41), disposed on the surface of the metal electrode (30) away from the epitaxial layer (20); A second light guide layer (42) is disposed on the surface of the first light guide layer (41) away from the metal electrode (30), and the refractive index of the first light guide layer (41) is smaller than that of the second light guide the refractive index of the layer (42); A part of the surface of the epitaxial layer (20) is provided with the metal electrode (30), and another part of the surface is exposed; the solar cell further comprises an anti-reflection layer (50) and a third light guide layer (43), the anti-reflection layer (50) and the third light guide layer (43). A reflective layer (50) is arranged on the exposed surface of the epitaxial layer (20), and the third light guide layer (43) is arranged on the second light guide layer (42) away from the first light guide layer (41) On the surface of the antireflection layer (50), the refractive index of the antireflection layer (50) and the refractive index of the third light guide layer (43) are the same and both are greater than the refractive index of the second light guide layer (42). 2 . The solar cell according to claim 1 , wherein the refractive index of the first light guide layer ( 41 ) is between 1.3 and 1.7. 3 . 3. The solar cell according to claim 2, wherein the thickness of the first light guide layer (41) is between 50 and 200 nm. 4. The solar cell according to claim 3, wherein the first optical guide layer (41) is a magnesium fluoride layer, an aluminum fluoride layer, a barium fluoride layer, a yttrium fluoride layer, and a lanthanum fluoride layer and a composite layer of any one or more of the silicon oxide layers. 5 . The solar cell according to claim 1 , wherein the refractive index of the second light guide layer ( 42 ) is between 1.7 and 2.05. 6 . 6. The solar cell according to claim 5, wherein the thickness of the second light guide layer (42) is between 50 and 200 nm. 7. The solar cell according to claim 6, wherein the second light guide layer (42) is any one or more of a silicon nitride layer, a zirconium oxide layer, a hafnium oxide layer and a zinc oxide layer composite layer. 8. The solar cell according to any one of claims 1 to 7, wherein the light guide structure further comprises a third light guide layer (43), and the third light guide layer (43) is arranged on the first light guide layer (43). On the surfaces of the two light guide layers (42) away from the first light guide layer (41). 9 . The solar cell according to claim 8 , wherein the refractive index of the third light guide layer ( 43 ) is between 2.02 and 2.5. 10 . 10 . The solar cell according to claim 9 , wherein the thickness of the third light guide layer ( 43 ) is between 50 and 200 nm. 11 . 11. The solar cell according to claim 10, wherein the third light guide layer (43) is any one or more of a titanium dioxide layer, a titanium pentoxide layer, a cerium oxide layer and a zinc sulfide layer composite layer. 12. The solar cell according to any one of claims 1 to 11, wherein the refractive index of the anti-reflection layer (50) is between 2.02 and 2.5. 13. The solar cell according to claim 12, wherein the thickness of the anti-reflection layer (50) is between 50 and 200 nm. 14. The solar cell according to claim 13, wherein the anti-reflection layer (50) is any one or more of a titanium dioxide layer, a titanium pentoxide layer, a cerium oxide layer and a zinc sulfide layer composite layer. 15 . The solar cell according to claim 1 , wherein the solar cell is a silicon-based solar cell, a heterojunction solar cell or a compound semiconductor thin film solar cell. 16 . 16 . The solar cell according to claim 15 , wherein the compound semiconductor thin film solar cell is a gallium arsenide solar cell or a copper indium gallium selenide solar cell, and the epitaxial layer ( 20 ) comprises a layer that is separated from the A single junction composed of a buffer layer, a back field layer, a base layer, an emission layer, a window layer and an ohmic contact layer stacked on the substrate (10), or a plurality of the single junctions connected by tunnel junctions. 17. The solar cell according to claim 1, wherein the substrate (10) is a GaAs substrate, a Ge substrate or a SiC substrate. 18. The solar cell according to claim 17, wherein the metal electrode (30) is a gold electrode, a copper electrode or a silver electrode. 19. A method for preparing a solar cell according to any one of claims 1 to 18, the preparation method comprising sequentially forming an epitaxial layer (20) and a metal electrode (30) on a substrate (10), wherein In that, the preparation method further comprises arranging a light guide structure on the surface of the metal electrode (30) away from the epitaxial layer (20), the light guide structure including stacking sequentially along a direction away from the metal electrode (30) At least two light guide layers are disposed, and the refractive index of the light guide layers increases sequentially along the direction away from the metal electrode (30). 20. The preparation method according to claim 19, wherein the process of disposing the light guide structure on the surface of the metal electrode away from the epitaxial layer (20) comprises: disposing a mask layer on the epitaxial layer; A first light guide layer (41), a second light guide layer (42) and a third light guide layer (43) are arranged on the metal electrode in sequence; removing the mask layer, disposing an antireflection layer (50) on the epitaxial layer, Or the process of disposing the light guide structure on the surface of the metal electrode (30) away from the epitaxial layer (20) includes: disposing a mask layer on the epitaxial layer; A first light guide layer (41) and a second light guide layer (42) are arranged on the metal electrode (30) in sequence; The mask layer is removed, and a refractive material is provided on the epitaxial layer (20) and the second light guide layer (42), so as to form a third light guide layer (43) on the second light guide layer (42) ), and an anti-reflection layer (50) is formed on the epitaxial layer (20). 21. The preparation method according to claim 20, wherein the first light guide layer (41), the second light guide layer (42), the third light guide layer (43) and the refractive material They are installed independently by vapor deposition or sputtering.

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