KR20130107904A - Manufacturing method of chalcogenide solar cell with double texture structure having a textured back contact and chalcogenide solar cell by the same - Google Patents

Abstract

PURPOSE: A method for manufacturing a chalcogenide solar cell with a double texture structure formed on the surface of a back electrode, and the chalcogenide solar cell manufactured by the same are provided to increase light capturing performance by forming a front texture and a back texture. CONSTITUTION: A back texture (32) is formed on the surface of a back electrode. A light absorption layer (40) of a chalcogenide semiconductor material is formed on the back electrode. A buffer layer (50) is formed on the light absorption layer. A transparent electrode is formed on the buffer layer. A front texture (62) is formed on the surface of the transparent electrode.

Description

MANUFACTURING METHOD OF CHALCOGENIDE SOLAR CELL WITH DOUBLE TEXTURE STRUCTURE HAVING A TEXTURED BACK CONTACT AND CHALCOGENIDE SOLAR CELL BY THE SAME}

The present invention relates to a method for manufacturing a chalcogenide-based solar cell, and more particularly, to a chalcogenide-based solar cell having an increased light capture capability, including a double texture structure having a texture formed on the back electrode surface. It relates to a manufacturing method.

In general, solar cells use diodes composed of p-n junctions and are classified into various types according to the materials used as the light absorbing layer.

Conventionally, solar cells using silicon as the light absorbing layer have become mainstream, but recently, efforts to use various compound semiconductors capable of controlling characteristics as light absorbing layers have been actively performed.

In particular, chalcogenide solar cells, which use direct-transition semiconductors with chalcogenide structures such as CIGS and CZTS, as light absorption layers, are attracting the most attention as materials that can be successfully oxidized in the future.

Chalcogenide means a compound containing chalcogen elements S, Se, and Te, and chalcogenide compounds widely applied in the field of solar cells are composed of group IB-IIIA-VIA elements, CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Ga) S ₂ (CIGS ), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS), and the like. Such chalcogenide-based compounds or thin films have a bandgap energy of 1 to 2 eV, which has the best light absorption coefficient (1x10 ⁵ cm ^-1 ) among semiconductors and is very optically stable, making it a very light absorbing layer of solar cells. Ideal material.

Another chalcogenide compound used in the solar cell industry is CdS, which is composed of group IIB-VIA elements, and is suitable as a buffer material located at an interface where PN junctions are formed. Typical chalcogenide-based solar cells use CIGS or CZTS as the light absorption layer and CdS as the buffer layer.

5 is a view showing the structure of a typical CIGS or CZTS solar cell.

In general, the Mo electrode back electrode 30 is formed on the soda-lime glass substrate 10 with the adhesive layer 20 interposed therebetween.

A light absorption layer 40 of CIGS-based or CZTS-based semiconductor material is formed on the rear electrode 30, and a front electrode 60 of TCO material is formed with a buffer layer 50 of CdS material therebetween. Finally, the anti-reflection layer 70 is formed on the front electrode 60.

The present invention is to solve the above-mentioned problems of the prior art, and to provide a method for manufacturing a chalcogenide-based solar cell having a double texture structure in order to improve the light trapping performance and the chalcogenide-based solar cell produced thereby Its purpose is to.

According to an aspect of the present invention, there is provided a method of manufacturing a chalcogenide-based solar cell having a double-textured structure having a texture on a back electrode surface, the method comprising: preparing a substrate; Forming a back electrode on the substrate; Forming a backside texture on a surface of the backside electrode; Forming a light absorption layer of chalcogenide-based semiconductor material on the rear electrode; Forming a buffer layer on the light absorption layer; Forming a transparent electrode on the buffer layer; And forming a front surface texture on the surface of the transparent electrode.

The inventors of the present invention invented a method for manufacturing a chalcogenide-based solar cell having improved light trapping ability by forming a texture structure on both sides of the chalcogenide-based light absorbing layer.

At this time, the step of forming the back electrode is carried out by depositing Mo in the DC sputtering process, the step of forming the back texture is performed by DC sputtering Mo under the conditions of increasing the particle energy deposited than the step of forming the back electrode. desirable.

The forming of the front electrode is performed by depositing a TCO by a DC sputtering or an RF sputtering process, and the forming of the front texture is performed by DC sputtering or RF sputtering under conditions that increase the deposited particle energy than forming the front electrode. It is preferable to proceed by.

Using the same equipment, but adjusting the process conditions so that the energy of the deposited particles is higher, the surface roughness becomes rough, thereby forming a texture structure.

On the other hand, the step of forming the front texture may be performed by wet etching the surface of the front electrode by immersion in an acid solution. Since the transparent conductive film used for the front electrode is anisotropically wet etched according to the fine physical density, a texture may be formed on the surface of the front electrode.

The chalcogenide-based solar cell having a double texture structure having a texture formed on the back electrode surface according to the present invention is characterized in that it is manufactured by the method described above.

In addition, a chalcogenide-based solar cell having a double texture structure having a texture formed on the back electrode surface according to the present invention, a substrate; A rear electrode formed on the substrate; A light absorption layer of chalcogenide-based semiconductor material formed on the rear electrode; A buffer layer formed on the light absorption layer; And a transparent electrode formed on the buffer layer, a back texture structure is formed on a surface of the back electrode in contact with the light absorbing layer, and a front texture structure is formed on the surface of the transparent electrode.

At this time, the light absorption layer is CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In It is preferable that the material is one selected from Ga, S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), and Cu ₂ ZnSnS ₄ (CZTS).

The present invention configured as described above has a double texture structure of the front texture and the back texture, so that the light trapping performance is greatly increased, thereby increasing the photoelectric conversion efficiency of the solar cell.

1 is a schematic diagram showing a process of manufacturing a chalcogenide-based solar cell having a double texture structure with a texture formed on the back electrode surface according to an embodiment of the present invention.
2 is an electron microscope photograph of a Mo thin film deposited under a sputtering process condition for forming a back electrode.
3 is an electron microscope photograph of a Mo thin film deposited under a sputtering process condition for forming a back texture.
4 is a view showing a light trapping state of the double texture structure chalcogenide solar cell of the present invention.
5 is a view showing the structure of a typical CIGS or CZTS solar cell.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.

1 is a schematic diagram showing a process of manufacturing a chalcogenide-based solar cell having a double texture structure with a texture formed on the back electrode surface according to an embodiment of the present invention.

The substrate 10 is prepared as shown in FIG. 1A and the surface is cleaned. The type of the substrate is not particularly limited, and materials such as glass, SUS, polymer, and metal may be applied. Recently, soda-lime glass substrates are mainly used in CIGS or CZTS solar cells for improvement of characteristics due to infiltration of Na. However, techniques for diffusing Na by different methods using different substrates have been studied. have.

In the cleaning of the substrate 10, acetone, methanol, and distilled water are generally washed sequentially, and the washing effect may be enhanced by using ultrasonic waves during the washing process.

An adhesive layer 20 is formed on the surface of the cleaned substrate 10 as shown in FIG. 1B. The adhesive layer 20 is formed to improve the adhesion between the substrate 10 and the back electrode, and may be omitted depending on the type of the substrate 10.

As shown in FIG. 1C, the back electrode 30 is formed on the adhesive layer 20.

CIGS or CZTS solar cells are generally formed with a rear electrode 30 of Mo material. Mo not only has a similar coefficient of thermal expansion to glass used as a substrate for recent CIGS or CZTS solar cells, but also has excellent adhesion and electrical conductivity.

DC sputtering is generally used as a method for forming the back electrode 30 Mo thin film. The DC sputtering process for forming the Mo back electrode 30 uses a DC power density per target area of 0.1 W / cm ² to 3 W / cm ² , and 10 minutes to 100 minutes at an Ar gas pressure of 5 mTorr to 100 mTorr. To perform. The Ar gas flow rate for pressure maintenance is selectively applied in the range of 1 sccm to several hundred sccm depending on the volume of the vacuum chamber and the pump capacity. The total DC power is also the size of the substrate and the target and the distance between the substrate and the target. It is selectively applied in the range of several W to several tens of kW.

The back electrode 30 may be changed into various configurations such as a double layer of a Na-doped Mo layer and a Na-doped Mo layer according to the type of the substrate 10, and may be used as the back electrode. If so, all configurations may apply.

As shown in FIG. 1D, a back texture 32 is formed on the back electrode 30.

In the present embodiment, the Mo back texture 32 is formed by changing the process conditions of the DC sputtering process used in the process of forming the Mo back electrode.

The above DC sputtering process conditions for forming the Mo back electrode are focused on forming a dense Mo layer having a sufficient thickness to act as an electrode. On the other hand, since the Mo back texture 32 is a surface uneven structure formed on the sufficiently formed Mo back electrode 30, by controlling the process conditions to adjust the size and energy of the sputtered Mo particles to form an irregular surface can do.

Specifically, the DC sputtering process for forming the Mo back texture 32 uses a DC power density per target area of 3 W / cm ² to 10 W / cm ² , and at an Ar gas pressure of 0.1 mTorr to 5 mTorr, 1 minute to It is performed for a relatively short time in the process for forming the Mo back electrode in the range of several tens of minutes. In addition, during the sputtering process, the temperature of the substrate is raised to a range of room temperature to several hundred degrees Celsius.

However, the Ar gas flow rate to maintain pressure is selectively applied in the range of 1 sccm to several hundred sccm depending on the volume of the vacuum chamber and the capacity of the pump, and the total DC power is also applied to the size of the substrate and the target and between the substrate and the target. A similar range to the case of forming the Mo rear electrode 30 is applied in that it can be selectively applied in the range of several W to several tens of kW depending on the interval of.

The sputtering process conditions for forming the backside texture 32 have higher DC power density per target area, a lower gas pressure in the chamber, and a higher temperature of the substrate than the case of forming the backside electrode 30. Is so high that irregularities are formed on the deposition surface. On the other hand, since the quality of the deposited layer may be degraded when the energy of the Mo particles to be deposited is high, the sputtering process for forming the backside texture 32 is performed relatively short.

2 is an electron microscope photograph of a Mo thin film deposited under a sputtering process condition for forming a back electrode. 2 is a cross-sectional and surface photograph of a Mo thin film formed by performing a DC sputtering process for 60 minutes at an Ar gas pressure of 20 mTorr using a DC power density per target area of 0.71 W / cm ² . Corresponds to the sputtering process conditions for forming the Mo back electrode 30 in the example. As shown, it was possible to form a Mo thin film having a thickness of about 952nm for 60 minutes, small grains are densely arranged on the surface to confirm that the surface is smooth.

3 is an electron microscope photograph of a Mo thin film deposited under a sputtering process condition for forming a back texture. 3 is a cross-sectional and surface photograph of a Mo thin film formed by performing a DC sputtering process for 30 minutes at an Ar gas pressure of 1 mTorr using a DC power density per target area of 3.47 W / cm ² . Corresponds to the sputtering process conditions for forming the Mo back texture 32 in the example. As shown, it was possible to form a Mo thin film having a thickness of about 1.12㎛ in 30 minutes, it can be confirmed that the surface is rough because large grains are irregularly arranged on the surface.

From this, it can be seen that by increasing the energy state of Mo deposited by changing the deposition conditions as in the present embodiment, a thin film having a rough surface can be formed instead of the rapid deposition of Mo. On the other hand, the process conditions of Figure 3 is a case where the Mo thin film is deposited in order to compare the characteristics of the Mo thin film, in the case of forming a back texture on the back electrode as in this embodiment, the sputtering process should be performed for a shorter time something to do.

As shown in FIG. 1E, a chalcogenide-based light absorbing layer 40 is formed on the back texture 32. In particular, a typical chalcogenide-based material, CIGS-based or CZTS-based semiconductor, is used as the light absorption layer.

The formation method of the CIGS-based or CZTS-based light absorbing layer 40 is largely divided into a vacuum method and a non-vacuum method, and the vacuum method and the non-vacuum method are also divided into various methods, respectively, but are not particularly limited in the present embodiment. Any method that can deposit on texture 32 can be applied.

As shown in FIG. 1F, the buffer layer 50 is formed on the light absorption layer 40. As the buffer layer 50, a CdS thin film is generally applied. The CdS buffer layer 50 is a chemical bath deposition (CBD) method for forming a film by immersing the substrate, which has been advanced to the stage of FIG. 1 (e), in an aqueous solution in which thiourea, cadmium sulfate, and alumina are mixed. Method).

In addition, the buffer layer 50 may be a ZnS or ZnSe thin film deposited by a CBD method, or an In _x Se _y or ZnIn _x Se _y thin film deposited by a process based on evaporation and a CVD based process. In _x Se _y or ZnSe thin film can be used.

As shown in FIG. 1G, the front electrode 60 is formed on the buffer layer 50. The front electrode 60 deposits a transparent conductive film (TCO) such as ITO, ZnO: Al, ZnO: Ga, and ZnO: B, and these transparent conductive films are generally deposited by DC or RF sputtering, but electron beam evaporation is performed. It can also deposit by other methods, such as a method and a thermal evaporation method.

The process of forming the front electrode 60 by DC or RF sputtering uses DC or RF power density per target area of 0.1 W / cm ² to 2 W / cm ² , and Ar gas or Ar gas at a pressure of 5 mTorr to 100 mTorr. Under a gas mixture of the doping element and 10 minutes to 100 minutes. The gas flow rate for pressure maintenance is selectively applied in the range of 1 sccm to several hundred sccm depending on the volume of the vacuum chamber and the pump capacity, and the total DC or RF power is also applied to the size of the substrate and the target and between the substrate and the target. Depending on the spacing, it is optionally applied in the range of several W to several tens of kW.

In addition, it is possible to change to a variety of configurations, such as forming a transparent conductive film of a double structure by sequentially depositing different types of transparent conductive film, all configurations can be applied as long as it can be used as the front electrode.

As shown in FIG. 1H, the front texture 62 is formed on the front electrode 60. The front texture 62 may be formed by etching the surface of the front electrode 60 to form irregularities and forming a transparent conductive film having irregularities formed on the surface of the front electrode 60.

The method of etching the surface of the front electrode 60 is a method of wet etching with an acid solution such as hydrochloric acid. When the wet etching is performed for several tens to hundreds of seconds by immersing the substrate advanced to the step of FIG. 1 (h) in 0.1 to several% of HCl solution, the surface is unevenly etched due to the difference in the physical strength of the surface of the front electrode 60. This creates a texture on the surface.

The method of additionally forming a transparent conductive film having irregularities on the surface of the front electrode 60 is performed by DC or RF sputtering. The above-described DC or RF sputtering process conditions for forming a transparent electrode focus on forming a thin transparent electrode thin film having a dense structure to act as an electrode. On the other hand, since the front texture 62 is a surface concave-convex structure formed on the sufficiently formed front electrode 60, by controlling the process conditions to adjust the size and energy of the sputtered transparent conductive film particles to form an irregular surface can do.

Specifically, the DC or RF sputtering process for forming the front texture 62 utilizes a DC power density per target area of 2 W / cm ² to 10 W / cm ² , and Ar gas or Ar gas of 0.1 mTorr to 5 mTorr pressure. In the gas conditions in which the doping elements are mixed, it is performed for a relatively short time in the process for forming the front electrode in the range of 1 minute to several tens of minutes. In addition, during the sputtering process, the temperature of the substrate is raised to a range of room temperature to several hundred degrees Celsius.

However, the Ar gas flow rate for pressure maintenance is selectively applied in the range of 1 sccm to several hundred sccm depending on the volume of the vacuum chamber and the pump capacity, and the total DC or RF power is also applied to the size and size of the substrate and target. A range similar to the case of forming the front electrode 60 is applied in that it can be selectively applied in the range of several W to several tens of kW depending on the distance between the targets.

The sputtering process conditions for forming the front texture 62 have higher DC power density per target area, lower gas pressure in the chamber, and higher substrate temperature than the front electrode 60, resulting in the energy of the deposited TCO particles. Is so high that irregularities are formed on the deposition surface. On the other hand, if the energy of the deposited TCO particles is high, the quality of the deposition layer may be degraded, so the sputtering process for forming the front texture 62 is performed relatively short.

Meanwhile, a technique of depositing a transparent electrode layer having its own surface texture on a surface by applying a low pressure CVD (LPCVD) process has been developed, which corresponds to forming a transparent electrode layer and a front surface texture in the present embodiment, respectively. Since it is a technique representing the present invention can be applied to this embodiment.

In addition, a configuration in which a grid electrode made of a metal material such as Al or Ag is added on the front surface texture 62 may be used to improve the performance of the electrode.

As shown in FIG. 1I, an antireflection layer 70 is formed on the front texture 62, and MgF ₂ and Al ₂ O ₃ are generally used as the antireflection layer 70.

An anti-reflection layer 70 of MgF ₂ material is deposited by thermal evaporation using a MgF ₂ pellets or, by using a Mg (thd) ₂ and TiF ₄ as a reaction gas to deposit an atomic layer deposition method (ALD, atomic layer deposition) .

The anti-reflection layer 70 made of Al ₂ O ₃ is deposited by atomic layer deposition using Al (CH ₃ ) ₃ and O ₃ as a reaction gas.

4 is a view showing a light trapping state of a double texture structure chalcogenide solar cell having a texture formed on the back electrode surface of the present invention.

The double-textured chalcogenide-based solar cell manufactured by the steps shown in FIG. 1 includes a back texture 32 formed on the back electrode 30 and a front texture 62 formed on the front electrode 60 at the same time.

Solar light incident on the front electrode 60 is reflected on the surface of the rear electrode 30 after the photovoltaic generation is performed through the light absorbing layer 40 through the buffer layer 50, and at this time, the back texture 32 formed on the surface. Diffuse reflection occurs.

The solar light diffused by the back texture 32 performs photovoltaic power passing through the light absorption layer 40, and passes through the buffer layer 50 and the front electrode 60 to the light absorption layer 40 again from the front texture 62. Is diffusely reflected.

While repeating the above process, since the sunlight stays in the light absorption layer 40 for a long time, the efficiency of the solar cell is greatly increased.

While the present invention has been described through the preferred embodiments, the above-described embodiments are merely illustrative of the technical idea of the present invention, and various changes may be made without departing from the technical idea of the present invention. Those of ordinary skill will understand. Therefore, the scope of protection of the present invention should be construed not only in the specific embodiments but also in the scope of claims, and all technical ideas within the scope of the same shall be construed as being included in the scope of the present invention.

10: substrate 20: adhesive layer
30: rear electrode 32: rear texture
40: light absorption layer 50: buffer layer
60: front electrode 62: front texture
70: antireflection layer

Claims (8)

Preparing a substrate;
Forming a back electrode on the substrate;
Forming a backside texture on a surface of the backside electrode;
Forming a light absorption layer of chalcogenide-based semiconductor material on the rear electrode;
Forming a buffer layer on the light absorbing layer;
Forming a transparent electrode on the buffer layer; And
A method of manufacturing a chalcogenide-based solar cell having a double-textured structure having a texture formed on a surface of a back electrode, characterized in that it comprises forming a front surface texture on the surface of the transparent electrode.
The method according to claim 1,
The forming of the back electrode is performed by depositing Mo in a DC sputtering process.
The step of forming the back texture is performed by DC sputtering Mo under the conditions of increasing the particle energy deposited than the step of forming the back electrode, the chalcogenide of the double texture structure formed with a texture on the back electrode surface Method for producing a solar cell.
The method according to claim 1,
Forming the front electrode is performed by depositing a TCO in a DC sputtering or RF sputtering process,
The double texture structure having the texture formed on the surface of the back electrode is characterized in that the forming of the front texture is performed by DC sputtering or RF sputtering the TCO under conditions of increasing the deposited particle energy than forming the front electrode. Method for producing a chalcogenide solar cell.
The method according to claim 1,
And forming the front texture by wet etching the surface of the front electrode by immersing in an acidic solution.
A chalcogenide-based solar cell having a double texture structure having a texture formed on a surface of a back electrode, which is manufactured by one of claims 1 to 4.
The method according to claim 5,
The light absorption layer is CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Double texture structure knife with a texture formed on the back electrode surface, characterized in that one of the materials selected from Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS) Cogenide solar cell.
Board;
A rear electrode formed on the substrate;
A light absorption layer of chalcogenide-based semiconductor material formed on the rear electrode;
A buffer layer formed on the light absorption layer; And
It comprises a transparent electrode formed on the buffer layer,
The back texture structure is formed on the surface of the back electrode in contact with the light absorption layer,
A chalcogenide-based solar cell having a double-textured structure having a texture formed on a backside electrode surface, wherein a frontside texture structure is formed on a surface of the transparent electrode.
The method of claim 7,
The light absorption layer is CuInS ₂ (CIS), CuGaS ₂ (CGS), CuInSe ₂ (CISe), CuGaSe ₂ (CGSe), CuAlSe ₂ (CASe), CuInTe ₂ (CITe), CuGaTe ₂ (CGTe), Cu (In, Double texture structure knife with a texture formed on the back electrode surface, characterized in that one of the materials selected from Ga) S ₂ (CIGS), Cu (In, Ga) Se ₂ (CIGSe), Cu ₂ ZnSnS ₄ (CZTS) Cogenide solar cell.

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