KR20230084888A - Heterjunction solar cell, method for fabricating the same, and sputtering target used therefor - Google Patents

Abstract

A heterojunction solar cell may include an electrode layer containing more than 0 wt% and less than 3 wt% of tin oxide, more than 0 wt% and less than 1 wt% of germanium oxide, and more than 96 wt% and less than 100 wt% of indium oxide. The electrode layer may have an average transmittance of 86 % or more and a reflectance of 13.2 % or less for light with a wavelength of 300 to 1200 nm. A sputtering target is used to deposit the electrode layer of the heterojunction solar cell and may include a sintered body containing more than 0 wt% and less than 3 wt% of tin oxide, more than 0 wt% and less than 1 wt% of germanium oxide, and more than 96 wt% and less than 100 wt% of indium oxide, and having an average grain size of 5 micrometers or more. The sputtering target may include one or more phases from In_2O_3, SnO_2, In_4Sn_3O_12, In_1.91Sn_0.05O_3, and In_1.91Sn_0.09O_3.05. Accordingly, a transparent conductive film that can maximize the efficiency of a solar cell can be provided.

Description

Heterjunction solar cell, method for fabricating the same, and sputtering target used therefor}

The present invention relates to an oxide sputtering target for a solar cell and a low-reflection electrode layer of a heterojunction solar cell deposited therethrough. It relates to a target with a surface and an electrode layer of a heterojunction solar cell deposited therethrough.

A solar cell is a power generation that converts light energy received from the sun into electrical energy. In order to increase the efficiency of conversion into electrical energy, both the transmittance and conductivity of the transparent conductive film applied to the solar cell play an important role. Therefore, it is very important to effectively transmit light from the sun in order to apply it to a solar cell. It is important to improve the transmittance in order to send a large amount of light to the light absorption layer, but it is also very important to lower the reflectance. This is because there is a lot of reflected light and there is a limit to improving the transmittance of the thin film no matter how good the transmittance is.

One of the biggest issues of solar cells is to increase efficiency. In the field of heterojunction solar cells, various efforts have been made to increase efficiency. An object of the present invention relates to a sputtering target capable of depositing an electrode layer that helps to improve the efficiency of a heterojunction solar cell by lowering the reflectance of an electrode layer (TCO layer) and a thin film formed through the sputtering target. More specifically, to provide a transparent conductive film capable of improving the efficiency of a solar cell by lowering the reflectance by making the surface rougher than a thin film without a dopant by utilizing a dopant that has not been used in an electrode layer of a conventional solar cell.

In order to achieve the above object, according to the first aspect of the present disclosure, more than 0% by weight and less than or equal to 3% by weight of tin oxide, greater than 0% by weight and less than or equal to 1% by weight of germanium oxide, and 96% by weight or more , a heterojunction solar cell is provided, comprising an electrode layer containing less than 100 weight percent indium oxide.

In some embodiments, a heterojunction solar cell may include a first type silicon substrate, a second type silicon layer formed in front of the first type silicon substrate, and a first type silicon layer formed in the rear side of the first type silicon substrate. A type silicon layer may be additionally included.

In some embodiments, the electrode layer may be formed on a front side of the second type silicon layer and a rear side of the first type silicon layer, respectively.

In some embodiments, in a solar cell, the first-type silicon substrate, the first-type silicon layer, and the second-type silicon layer are each an n-type silicon substrate, an n-type silicon layer, and a p-type silicon layer, respectively. It may be a p-type silicon substrate, a p-type silicon layer, and an n-type silicon layer.

In some embodiments, the electrode layer may have an average transmittance of 86% or more and a reflectance of 13.2% or less for light having a wavelength of 300 to 1200 nm.

According to a second aspect of the present disclosure, it is used to deposit an electrode layer of a heterojunction solar cell, and is used to deposit greater than 0 weight percent and less than or equal to 3 weight percent tin oxide, greater than 0 weight percent and less than or equal to 1 weight percent germanium oxide, and 96 weight percent. As described above, a sputtering target for depositing an electrode layer of a heterojunction solar cell including a sintered body containing less than 100% by weight of indium oxide and having an average grain size of 5 micrometers or more is provided.

In certain embodiments, the sputtering target may include one or more phases of In ₂ O ₃ , SnO ₂ , In ₄ Sn ₃ O ₁₂ , In _1.91 Sn _0.05 O ₃ , In _1.91 Sn _0.09 O _3.05 .

In some embodiments, the sputtering target may further include a backing plate or backing tube bonded to a rear surface of the sintered body to support the sintered body.

In some embodiments, the sputtering target may be a sputtering target for DC magnetron sputtering.

According to a third aspect of the disclosure, a heterojunction solar cell manufacturing method is provided, including depositing an electrode layer of a heterojunction solar cell using the sputtering target for depositing an electrode layer of a heterojunction solar cell.

According to the configuration described above, there is an effect of providing a transparent conductive film capable of maximizing the efficiency of a solar cell by lowering the reflectance while maintaining the existing conductivity.

1 is a diagram schematically showing the structure of a heterojunction solar cell according to embodiments of the present disclosure.
2 and 3 are views showing crystal grains and crystal phases of a sintered body of a sputtering target according to an embodiment of the present disclosure, respectively.
4 to 7 are views showing characteristics of a transparent conductive film of an embodiment of the present disclosure and a transparent conductive film of a comparative example,
4 is a graph showing sheet resistance characteristics of a transparent conductive film of a comparative example;
5 is a graph showing the reflectance of transparent conductive films of Examples of the present disclosure and Comparative Examples;
6 is a 3D image of the surface of a transparent conductive film of a comparative example;
7 is a 3D image of a thin film surface of a transparent conductive film of an embodiment of the present disclosure.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

The present invention relates to depositing a low-reflection transparent conductive film using germanium oxide to increase the roughness of the surface of the transparent conductive film, thereby lowering the reflectance and not exhibiting a decrease in transmittance compared to a thin film without germanium oxide.

1 is a diagram schematically showing the structure of a heterojunction solar cell according to an embodiment of the present disclosure.

The basic structure of a heterojunction solar cell includes a first type silicon substrate 10, a second type silicon layer 21, a first type silicon layer 23, a first electrode layer 31, and a second electrode layer 33. ) may be included. In some embodiments, between the first type silicon substrate 10 and the second type silicon layer 21 and / or between the first type silicon substrate 10 and the second type silicon layer 21, respectively, A first protective layer 41 and a second protective layer 43 may be interposed therebetween. Also, in some embodiments, a first metal grid contact 51 and a second metal grid contact 53 may be formed. In some embodiments, the first type may be an n type and the second type may be a p type. However, in some alternative embodiments, the first type may be of p type and the second type may be of n type.

The first type silicon substrate 10 may be a crystalline silicon substrate. A second type silicon layer 21 may be formed in front of the first type silicon substrate 10 . In some embodiments, light may be incident from the front. A first type silicon layer 23 may be formed behind the first type silicon substrate 10 . The p-type second type silicon layer 21 may be, for example, an amorphous silicon layer made of a-Si:H or a-Si:H doped with a material capable of forming a p-type. The n-type first-type silicon layer 23 may be, for example, an amorphous silicon layer made of a material such as a-Si:H doped with phosphorus. The first protective layer 41 may be an intrinsic amorphous silicon layer made of a material such as a-Si:H or a-Si. The second passivation layer 43 may be an intrinsic amorphous silicon layer made of a material such as a-Si:H or a-Si. A first electrode layer 31 may be formed in front of the second type silicon layer 21 . A second electrode layer 33 may be formed behind the first type silicon layer 23 . As the first electrode layer 31 and/or the second electrode layer 33 , a low-reflection transparent conductive film according to an embodiment of the present disclosure as described below may be used. A first metal grid contact 51 may be formed in front of the first electrode layer 31 . A second metal grid contact 53 may be formed behind the second electrode layer 33 . Since the structure of such a heterojunction solar cell is known as a known technology, further detailed description is omitted.

2 and 3 are views showing crystal grains and crystal phases of a sintered body of a sputtering target according to an embodiment of the present disclosure, respectively.

The crystal grain size of the sintered body composed of 96% indium oxide, 3% tin oxide, and 1% germanium is shown in FIG. 2 . In some embodiments, the average grain size of the primary phase of the sintered body including germanium oxide may be 5 micrometers or more.

The crystal phase of the sintered body composed of 96% indium oxide, 3% tin oxide, and 1% germanium is shown in FIG. 3 . In some embodiments, the crystal phase of the sintered body containing germanium oxide irradiated through X-rays may include one or more of In2O3, SnO2, In4Sn3O12, (In1.91Sn0.05)O3, and In1.91Sn0.09O3.05. can Germanium oxide is completely dissolved and may not be detected in the examination of the crystal phase.

The sputtering target of the embodiment of the present disclosure is based on indium oxide and tin oxide contained in a predetermined ratio and has a sintered body containing germanium oxide, so DC sputter is possible because the target itself has conductivity.

That is, when the target according to the present invention is used, a transparent conductive film applied to a solar cell can be deposited in a DC sputter method, and the transparent conductive film deposited according to the present invention has high conductivity, thereby increasing solar cell efficiency. It becomes possible to help A target according to an embodiment of the present invention is a sputtering target applied to, for example, a DC magnetron sputtering device for forming a transparent conductive film applied to a solar cell. Such an oxide target may be formed by including a sintered body and a backing plate or backing tube.

A sintered body for forming a transparent conductive film having the above characteristics can be produced by a powder metallurgy method. That is, after mixing indium oxide, tin oxide, and germanium oxide powder according to the content ratio, cold press, slip casting, filter press, cold isostatic press, gel After molding through molding methods such as gel casting, centrifugal sedimentation, and gravimetric sedimentation, it may be manufactured through sintering.

As described above, the oxide target according to an embodiment of the present invention can be applied to a magnetron sputtering device. Since magnetron sputtering is generally used for depositing a large-area oxide thin film, the sintered body according to an embodiment of the present invention is tiled or tubed. It may be provided in a plurality of forms. The backing plate or backing tube serves to support one or a plurality of sintered bodies. To this end, the backing plate is disposed behind the sintered body, and the backing tube is bonded to the sintered body via a bonding material inside the tube-shaped sintered body. Such a backing plate or backing tube may be made of copper having excellent conductivity and thermal conductivity, preferably oxygen-free copper, titanium, or stainless steel. At this time, the bonding material disposed between the sintered body and the backing plate to bond them to each other may be made of, for example, indium. In addition, this bonding material may be applied to the entire surface of the backing plate in the form of a paste.

On the other hand, in order to bond the sintered body and the backing plate, the bonding material may be melted by heating means such as a hot plate, resistance heating, high frequency, electric coil or laser, and then cooled. At this time, the bonding material applied for melting Heat can be controlled at 170±10°C.

4 to 7 are diagrams showing characteristics of a transparent conductive film according to an embodiment of the present disclosure and a transparent conductive film according to a comparative example.

4 is a graph showing sheet resistance characteristics of the transparent conductive film of Comparative Example.

A transparent conductive film of a comparative example was obtained using a sputtering target having a composition of 97% indium oxide and 3% tin oxide, and the sputtering target of the embodiment of the present disclosure in FIG. 2 (96% indium oxide, 3% tin oxide, and 1 germanium oxide) %) was used to obtain a transparent conductive film according to an embodiment of the present disclosure, and the results of FIGS. 4 to 7 were obtained by comparing them.

The electrode layer used in the conventional heterojunction solar cell was made of indium oxide and tin oxide as in the comparative example, and the composition was composed of 97% indium oxide and 3% tin oxide. Even thin films with the same composition change their properties depending on the deposition conditions. In particular, the properties of the transmittance and sheet resistance of the thin film are changed according to the oxygen content during deposition. As shown in FIG. 4, if the oxygen content is excessively high, the resistance rapidly increases, and thus the transparent conductive film has no meaning. In order to select a range that has meaning as a transparent conductive film, evaluation was conducted while increasing the oxygen content during deposition, and it was found that an inflection point at which the resistance rapidly increased occurred in the range where the oxygen content was 2.0% or more. Therefore, in the embodiments of the present disclosure, the evaluation was performed in the section until the inflection point in which the conductivity rapidly changes.

5 is a graph showing the reflectance of transparent conductive films of Examples of the present disclosure and Comparative Examples.

Using the sputtering target of Comparative Example and the sputtering target of Example of the present disclosure, the oxygen content was less than 2% and the oxygen input ratio was adjusted from 0.0% to 2.0% to deposit a thin film, and then the reflectance was measured. Reflectance and transmittance were measured at a wavelength in the range of 300 to 1200 nm, and the results shown in Table 1 were obtained using average values.

The reflectance of the thin film deposited using the target of the comparative example was measured at a minimum of 11.1% to 15.8% depending on the oxygen input ratio used during deposition. In addition, the reflectance of the thin film deposited while adjusting the oxygen input ratio using the target of the embodiment of the present disclosure having a composition in which 1% of germanium oxide was added to 3% of tin oxide under the same conditions was found to be at least 10.8% to 13.2%. It can be seen that the reflectance in the region with the highest transmittance is lowered in the case of the composition in which germanium oxide is added compared to the thin film without germanium oxide. Although the minimum value of the reflectance of the thin film was lowered by the addition of germanium oxide, there was also a section in which the reflectance was higher than that of the composition without the addition of germanium oxide depending on the amount of oxygen input during deposition. From this, it can be seen that although germanium oxide is required to lower the thin film reflectance, the amount of oxygen input during deposition is also a very important variable. That is, it can be seen that in order to lower the reflectance of the thin film to which germanium oxide is added, an optimal oxygen input amount must be found. 5 shows a reflectance graph in the oxygen input section where the transmittance is the highest and the reflectance is the lowest.

6 is a thin film surface 3D image of a transparent conductive film of a comparative example, and FIG. 7 is a thin film surface 3D image of a transparent conductive film of an example of the present disclosure.

The surface roughness of the thin film was measured to find out the role in the thin film while the germanium oxide was included. As shown in Table 2, the surface roughness of the thin film made of 97% indium oxide and 3% tin oxide was 15.941 nm, and the surface roughness of the thin film made of 96% indium oxide, 3% tin oxide, and 1% germanium oxide was 20.898 nm. appear.

As germanium oxide was added, the surface roughness increased by about 24%. If the surface roughness is high, it is thought that the reflectance of the thin film is lowered as the incident light is reflected relatively less. It is presumed that the reason for the increase in the roughness of the thin film surface is that the germanium oxide suppresses the size of the crystal grains of the thin film from increasing in the plane direction, and the shape grows into a needle tower shape. This can be seen through the 3D images of the thin film surface using AFM in FIGS. 5 and 6 .

The transparent conductive film fabricated through the embodiments of the present disclosure was fabricated by ionizing argon gas and oxygen gas by direct current (DC) discharge and depositing a material protruding from a sputtering target on a substrate. More specifically, when a thin film is produced by placing a sputtering target and a substrate in a vacuum chamber, argon gas and oxygen gas may be mixed and injected in an appropriate volume ratio and DC voltage may be applied. In some embodiments, DC discharge applied The voltage density was about 2.6 W/cm 2 . Also, deposition may be performed through an in-line type sputtering facility. In the in-line sputtering facility, the substrate is moved and deposited on the substrate while passing the plasma discharged around the sputtering target.

Claims (8)

An electrode layer comprising more than 0 wt% and less than 3 wt% of tin oxide, more than 0 wt% and less than 1 wt% of germanium oxide, and more than 96 wt% and less than 100 wt% of indium oxide,
Heterojunction solar cell.
According to claim 1,
A first type silicon substrate;
a second type silicon layer formed in front of the first type silicon substrate;
Further comprising a first type silicon layer formed behind the first type silicon substrate,
The electrode layer is formed in front of the second type silicon layer and behind the first type silicon layer, respectively,
The first-type silicon substrate, the first-type silicon layer, and the second-type silicon layer may be an n-type silicon substrate, an n-type silicon layer, and a p-type silicon layer, respectively, or a p-type silicon substrate, a p-type silicon layer, and a p-type silicon layer, respectively. An n-type silicon layer,
Heterojunction solar cell.
According to claim 1,
The electrode layer has an average transmittance of 86% or more and a reflectance of 13.2% or less for light of a wavelength of 300 to 1200 nm,
Heterojunction solar cell.
It is used to deposit an electrode layer of a heterojunction solar cell,
It contains more than 0 weight percent and less than 3 weight percent tin oxide, more than 0 weight percent and less than 1 weight percent germanium oxide, and greater than 96 weight percent and less than 100 weight percent indium oxide, and has an average grain size of 5 micrometers or more. , containing a sintered body,
A sputtering target for deposition of an electrode layer of a heterojunction solar cell.
According to claim 4,
In ₂ O ₃ , SnO ₂ , In ₄ Sn ₃ O ₁₂ , In _1.91 Sn _0.05 O ₃ , In _1.91 Sn _0.09 O _3.05
A sputtering target for deposition of electrode layers of heterojunction solar cells.
According to claim 4,
Further comprising a backing plate or backing tube bonded to the rear surface of the sintered body to support the sintered body
A sputtering target for deposition of an electrode layer of a heterojunction solar cell.
According to claim 4,
A sputtering target for DC magnetron sputtering,
A sputtering target for deposition of electrode layers of heterojunction solar cells.
Including depositing an electrode layer of a heterojunction solar cell using the sputtering target for depositing an electrode layer of a heterojunction solar cell according to any one of claims 4 to 7,
Heterojunction solar cell manufacturing method.

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