KR101461830B1 - Substrate for ci(g)s solar cell and method for manufacturing the same - Google Patents

Abstract

One embodiment of the present invention relates to a stainless steel substrate; And a phosphate-based insulating layer formed on the stainless steel substrate, wherein the phosphate-based insulating layer contains 10 to 40% of aluminum phosphate (AlPO ₄ ) and 10% or less of aluminum hydroxide (Al (OH) ₃ ) (Excluding 0), not more than 10% of potassium phosphate (K ₄ P ₂ O ₇ ) (excluding 0), 1 to 5% of lithium phosphate (Li ₃ PO ₄ ), less than 2% of silica colloid And a residual phosphoric acid (H ₂ PO ₄ ), and a method of manufacturing the same.
According to the present invention, there is provided a substrate for a CI (G) S solar cell which is improved in heat resistance by using an inorganic material in place of a coating of an organic polymer series which is insensitive to heat resistance and is water- .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a substrate for a CI (G) S solar cell,

The present invention relates to a substrate for a CI (G) S solar cell and a method of manufacturing the same.

Traditional methods of collecting energy using fossil fuels are slowly reaching their limits due to global warming, depletion of fuel resources, and environmental pollution. Particularly in the case of petroleum fuels, the prognosis is that the forecast will reveal the floor within a very short period of time, albeit slightly different.

In addition, the energy-climate treaty, represented by the Kyoto Protocol, forcibly requires the reduction of carbon dioxide emissions resulting from the burning of fossil fuels. Therefore, it is clear that it will be restricted by the current use of fossil fuels, as well as the current contracting countries, and in the future to all countries around the world.

The most representative energy source used to replace fossil fuels is nuclear power. Nuclear power generation is an energetic alternative energy source that can substitute for fossil fuels such as petroleum, because it generates a large amount of energy that can be collected per unit weight of uranium or plutonium as a raw material and does not generate greenhouse gases such as carbon dioxide. I have received.

However, the explosion of the Chernobyl nuclear power plant in Sri Lanka and the Fukushima Nuclear Power Plant in Japan caused by the Great East Japan Earthquake has led to a reexamination of the safety of nuclear power, which has been regarded as an infinite clean energy source. As a result, The introduction of energy is desperately needed more than ever.

Hydropower can be used as an alternative energy source, but its use is limited because it is affected by geographical factors and climatic factors. In addition, other alternative energy sources are also difficult to use as alternative means of fossil fuels because of the limited amount of power generation or the limited use area.

However, since the solar cell can be used anywhere as long as only a proper amount of sunshine is ensured, the power generation capacity and the facility scale are almost linearly proportional to each other. Therefore, when the solar cell is used in a small- Production is possible, and the use thereof is increasing not only in the world but also in related research.

Solar cells are based on the principle of semiconductors. When a light having a certain energy level or more is irradiated to a pn-junction semiconductor, the electrons of the semiconductor are excited as freely movable electrons to form a pair of electrons and holes (EHP ) Is generated. The generated electrons and holes move to the electrode located on the opposite side to generate an electromotive force.

In the first type of the solar cell, a p-type semiconductor is formed by doping an impurity (B) into a silicon substrate, and then another impurity (P) is doped thereon to convert a part of the layer into an n-type semiconductor. It is a silicon-based solar cell, often referred to as a first-generation solar cell.

The silicon-based solar cell has the highest degree of commercialization because it has a relatively high energy conversion efficiency and a high cell conversion efficiency (ratio of conversion efficiency at the time of mass production to the highest energy conversion efficiency of the laboratory). However, in order to manufacture the silicon-based solar cell module, a complicated process step such as manufacturing an ingot from a raw material and making the ingot into a wafer and then manufacturing and modifying the cell must be performed, and a bulk material is used , There is a problem that the material consumption is increased and the manufacturing cost is high.

In order to solve the disadvantages of such a silicon solar cell, a so-called thin film solar cell called a second generation solar cell has been proposed. Since the thin film solar cell is manufactured by stacking the thin film layers sequentially required on the substrate, instead of manufacturing the solar cell by the above-described process, the process is simple, and the thin film solar cell has an advantage that the material cost is low.

However, in many cases, compared with the silicon-based solar cell, the energy conversion efficiency is not high enough to cause commercialization. However, some high-energy conversion solar cells have been developed and commercialized.

One of them is a CI (G) S solar cell. The solar cell may contain copper (Cu), indium (In), germanium (Ge) (germanium may not be included. (Hereinafter referred to as CIS), and CI (G) S compound semiconductors including selenium (Se).

Since the semiconductor contains three or four elements, the width of the bandgap can be controlled by controlling the content of the element, thereby increasing the energy conversion efficiency. Occasionally, selenium (Se) is replaced with sulfur (S) or selenium (Se) with sulfur (S). In the present invention, all of these cases are regarded as CI (G) S solar cells.

Fig. 1 shows an example of a stacked structure of CIGS (when germanium is contained) solar cell. As shown in the drawing, a substrate 10 is present in the lowest layer, and a back metal layer 20 used as an electrode is formed on the substrate 10. A buffer layer (for example, CdS) 40, a transparent window 50, and a front metal layer (electrode) 70 are formed on the rear metal layer 20 as a p- Respectively. In some cases, an antireflection film 60 may be additionally formed.

At this time, the substrate 10 is not only excellent in corrosion resistance, but also has flexibility, so that a stainless steel substrate which can be applied to a continuous process such as a roll-to-roll is often used. However, since the stainless steel substrate contains a large amount of Fe or other alloying elements, such alloying elements diffuse into the back metal layer 20 or the light absorbing layer 30 located on the back metal layer 20, have. In addition, since the substrate is made of a metal, when a solar cell is manufactured through a monolithic integration method in which an electrode layer is formed on a substrate, a cell is separated from a cell, and then the cell is electrically connected , There is a disadvantage in that the cell and the cell are not electrically short-circuited. In order to solve this problem, an insulating layer is formed between the substrate 10 and the rear metal layer 20 to manufacture a solar cell.

As such an insulating layer, conventionally, a polymer material having a low heat resistance such as polyimide has been used, but a CI (G) S solar cell requiring a high temperature process has a problem that a coating film is deformed or burned. In order to solve this problem, a technique using a silica-based inorganic coating material has been developed, but it is disadvantageous in that it is very harmful to humans and the environment because an organic solvent must be used to coat inorganic coating materials of the silica-based silica system. Therefore, it is preferable that an organic solvent is not used in forming the insulating layer. However, the stainless steel substrate, which is mainly used as a substrate, is poor in hydrophilicity and poor wettability because the surface thereof is made of a chromium oxide passivation film. have.

The present invention provides a substrate for a CI (G) S solar cell and a method of manufacturing the same, which can produce an insulating layer having excellent heat resistance as well as an insulating effect by a method not harmful to the environment.

One embodiment of the present invention relates to a stainless steel substrate; And a phosphate-based insulating layer formed on the stainless steel substrate, wherein the phosphate-based insulating layer contains 10 to 40% of aluminum phosphate (AlPO ₄ ) and 10% or less of aluminum hydroxide (Al (OH) ₃ ) (Excluding 0), not more than 10% of potassium phosphate (K ₄ P ₂ O ₇ ) (excluding 0), 1 to 5% of lithium phosphate (Li ₃ PO ₄ ), less than 2% of silica colloid And a residual phosphoric acid (H ₂ PO ₄ ).

Another embodiment of the present invention provides a method of manufacturing a semiconductor device, comprising: preparing a stainless steel substrate; Applying a phosphate coating solution to the stainless steel substrate; And heating the substrate coated with the phosphate coating solution to a temperature of 450 to 650 ° C, wherein the phosphate coating solution contains 10 to 40% of aluminum phosphate (AlPO ₄ ), aluminum hydroxide (Al (OH) ₃ ) : 10% or less (zero is not included), glass potassium phosphate _{(K 4 P 2 O 7)} : 10% or less (zero is not included), lithium phosphate _{(Li 3 PO 4): 1} ~ 5%, the silica colloidal: 2% (G) S solar cell substrate comprising an aqueous solution of residual phosphoric acid (H ₂ PO ₄ ) (excluding 0) and residual phosphoric acid (H ₂ PO ₄ ).

According to the present invention, there is provided a substrate for a CI (G) S solar cell which is improved in heat resistance by using an inorganic material in place of a coating of an organic polymer series which is insensitive to heat resistance and is water- .

1 is a cross-sectional view schematically showing a laminated structure of a CIGS solar cell.
2 is a process flow chart showing a manufacturing method for manufacturing the substrate of the present invention.

Hereinafter, the present invention will be described.

A CI (G) S solar cell substrate according to an embodiment of the present invention includes a stainless steel substrate; And a phosphate-based insulating layer formed on the stainless steel substrate, wherein the phosphate-based insulating layer contains 10 to 40% of aluminum phosphate (AlPO ₄ ) and 10% or less of aluminum hydroxide (Al (OH) ₃ ) (Excluding 0), not more than 10% of potassium phosphate (K ₄ P ₂ O ₇ ) (excluding 0), 1 to 5% of lithium phosphate (Li ₃ PO ₄ ), less than 2% of silica colloid , And residual phosphoric acid (H ₂ PO ₄ ).

In the present invention, the type of the stainless steel substrate used as the lower substrate of the substrate for the solar cell is not particularly limited, but for example, a stainless steel of 300 series or 400 series can be used.

The phosphate-based insulating layer formed on the solar cell substrate of the present invention may contain 10 to 40% of aluminum phosphate (AlPO ₄ ), 10% or less of aluminum hydroxide (Al (OH) ₃ ) Potassium phosphate (K ₄ P ₂ O ₇ ): not more than 10% (excluding 0), lithium phosphate (Li ₃ PO ₄ ): 1 to 5%, silica colloid: not more than 2% ₂ PO ₄ ).

Aluminum phosphate (AlPO ₄ ): 10 to 40 wt%

The aluminum phosphate forms a strong network structure at a high temperature above the vitrification temperature (about 300 ° C), thereby forming a basic skeleton of the insulating layer. If the content of aluminum phosphate is less than 10% by weight, the solid content concentration is low and it may become difficult to form an insulating layer having a sufficient thickness. If it exceeds 40% by weight, the content of other additives is relatively low, It may be difficult to ensure surface roughness, and adhesion between the insulating layer and the stainless steel substrate may be deteriorated. In addition, precipitation in the coating liquid may occur during the manufacturing process, which may make it difficult to form an insulating layer, or product defects may occur. Therefore, it is preferable that the aluminum phosphate has a range of 10 to 40 wt%.

Aluminum hydroxide (Al (OH) ₃ ): 10 wt% or less (excluding 0)

The aluminum hydroxide plays a role of supplementing the aluminum element in the insulating layer and at the same time improving the heat resistance. However, when the content of sodium hydroxide exceeds 10% by weight, the content of other additives such as aluminum phosphate is relatively low, which makes it difficult to control the thickness of the insulating layer, and in a severe case, the formation of the insulating layer itself may become difficult , Excellent surface roughness or adhesion between the insulating layer and the stainless steel substrate may be deteriorated. In addition, the pH of the coating solution is increased and the solubility of other additives is lowered. Therefore, it is preferable that the aluminum hydroxide has a range of 10 wt% or less (excluding 0).

Free potassium phosphate (K ₄ P ₂ O ₇ ): 10% by weight or less (excluding 0)

The glassy potassium phosphate is added to control the surface roughness of the insulating layer to a low level. However, if it is more than 10% by weight, defects such as stickiness on the surface of the insulating layer may occur. Therefore, it is preferable that the free potassium phosphate has a range of 10 wt% or less (excluding 0).

Lithium phosphate (Li ₃ PO ₄ ): 1 to 5 wt%

The lithium phosphate serves to lower the curing temperature. However, if it exceeds 5% by weight, precipitation in the coating liquid may occur during the manufacturing process, which may result in difficulty in forming an insulating layer or product failure, so that the lithium phosphate preferably has a range of 1 to 5% .

Silica colloid: 2% or less (excluding 0)

The silica colloid is an element for securing adhesion between the stainless steel substrate and the insulating layer. However, if it exceeds 2%, the problem of particle aggregation may occur during the curing process, and therefore it is preferable that the silica colloid has a range of 2% or less (excluding 0).

It is preferable that the phosphate-based insulating layer of the present invention has phosphoric acid (H ₂ PO ₄ ) other than the above-mentioned components. The phosphoric acid (H ₂ PO ₄ ) serves to supplement the concentration of phosphoric acid ions in the coating solution while lowering the pH so that aluminum phosphate can be dissolved.

On the other hand, the aluminum phosphate (AlPO ₄ ), aluminum hydroxide (Al (OH) ₃ ), potassium phosphate (K ₄ P ₂ O ₇ ), lithium phosphate (Li ₃ PO ₄ ) It is more preferable that the total amount of the colloid is 15 to 40% by weight. If it is less than 15% by weight, the solid content may be too low to control the formation of the insulating layer or the thickness of the insulating layer. When the content of the insulating layer exceeds 40% by weight, There is a possibility that the thickness control becomes difficult.

The phosphate-based insulating layer preferably has a surface roughness (Rz) of 50 to 120 nm. Normally, the stainless steel substrate has a surface roughness (Rz) of about 200 to 250 nm, and has a very high surface roughness. However, in the present invention, by forming an insulating layer having a surface roughness Rz of 50 to 120 nm and having a very low surface roughness as described above, the short circuit resistance of the CI (G) S solar cell is increased, Effect can be obtained. However, if the surface roughness of the phosphate-based insulating layer is less than 50 nm, adhesion to the upper layer may be lowered. If the surface roughness exceeds 120 nm, the short circuit resistance of the solar cell may be lowered, The electrode may be short-circuited and the cell may be broken. Therefore, it is preferable that the surface roughness of the phosphate-based insulating layer is in the range of 50 to 120 nm.

In addition, the phosphate-based insulating layer preferably has a thickness of 600 to 2000 nm. If the thickness of the phosphate-based insulating layer is less than 600 nm, there is a limit to improve the surface roughness of the stainless steel substrate. If the thickness exceeds 2000 nm, a boiling phenomenon may occur during the curing process to cause surface defects. The thickness of the insulating layer is preferably in the range of 600 to 2000 nm.

2 is a process flow chart showing a manufacturing method for manufacturing the substrate of the present invention. Hereinafter, the manufacturing method of the present invention will be described with reference to FIG.

First, a stainless steel substrate is prepared (S1). The stainless steel substrate has a disadvantage in that it is difficult to form a water-soluble coating because the surface of the stainless steel substrate is made of a chromium oxide passivation film and has low hydrophilicity and poor wettability. Therefore, in order to solve the problem of wettability of such a stainless steel substrate, it is preferable to carry out a surface modification treatment as a pretreatment process.

For example, a method of mixing a NaOH degreasing solution and distilled water in a water tank at a weight ratio of 1: 5 and mixing them, then immersing the stainless steel substrate at 60 to 75 ° C for about 5 to 10 minutes, and then taking out. The surface of the thus-treated stainless steel substrate becomes hydrophilic due to the OH functional group of the alkali degreasing solution, and the contact angle of 70 degrees or more drops to 25 degrees or less.

Alternatively, an RCA cleaning process, commonly known as a semiconductor cleaning process, may be utilized. Water, ammonia, and hydrogen peroxide in a water tank at a ratio of 5: 1: 1, mixing and then dipping the stainless steel substrate at 70 to 80 ° C for 10 to 20 minutes. Through this, various oxide layers such as chromium oxide and the like existing on the stainless steel substrate can be removed and the wettability of the surface can be improved.

Thereafter, a phosphate coating solution is applied to the prepared stainless steel substrate (S2). At this time, at least one method selected from the group consisting of bar coating, roll coating, slot die coating and spray coating may be used for the coating of the phosphate coating solution. The surface roughness, which is difficult to improve by the vacuum deposition method, can be lowered through the application method. In general, the level of surface roughness can be improved by only a few nanometers through vacuum deposition. However, if the solution process is used, the coating material in the liquid state will fill the ridged surface of the rough stainless steel surface, It is possible to obtain an improvement effect.

10% or less (excluding 0) of aluminum phosphate (AlPO ₄ ), 10 to 40% of aluminum hydroxide (Al (OH) ₃ ), potassium free phosphate (K ₄ P ₂ O ₇ ) : Not more than 10% (excluding 0), lithium phosphate (Li ₃ PO ₄ ): 1 to 5%, silica colloid: not more than 2% (excluding 0), and residual phosphoric acid (H ₂ PO ₄ ) .

At this time, the pH of the phosphate coating solution is preferably 1 to 3, and if the pH is more than 3, the solute in the aqueous solution may not dissolve and gelation or precipitation may occur. Therefore, it is preferable that the pH is lower, but it is difficult to lower the pH to less than 1, so that the phosphate coating solution of the present invention preferably has a pH of 1 to 3.

On the other hand, the phosphoric acid aqueous solution contained in the phosphate coating solution of the present invention preferably has a concentration of 0.001 to 2 mol / L. If the concentration of the aqueous phosphoric acid solution is less than 0.001 mol / L, the pH of the solution may be high and the solubility of the aluminum phosphate may be low. If the concentration exceeds 2 mol / L, the coating layer may be hardened. Therefore, the aqueous phosphoric acid solution preferably has a concentration of 0.001 to 2 mol / L.

Thereafter, the substrate coated with the phosphate coating solution is heated to 450 to 650 ° C (S3). The substrate coated with the coating solution is heat-treated, and the applied coating solution is dried and sintered to form a phosphate-based insulating layer. However, if the heating temperature is less than 450 ° C., the coating layer is not cured and thus the coating layer becomes sticky in a high humidity environment. If the heating temperature is more than 650 ° C., Defects that cause discoloration may occur. Therefore, the heating temperature is preferably in the range of 450 to 650 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples serve to illustrate the present invention in detail and do not limit the scope of the present invention.

(Example)

A stainless steel 430 substrate 0.1 mm in thickness was cut into a size of 100 mm x 100 mm to prepare specimens. The prepared specimens were cleaned by the RCE cleaning method as described below. The RCE cleaning was performed by heating the cleaning solution prepared by mixing distilled water, ammonia, and hydrogen peroxide in a ratio of 5: 1: 1 to 75 ° C, and immersing the specimen for about 15 minutes to remove surface oxides and contaminants. After the RCE cleaning, the specimen was rinsed with distilled water to remove surface residues. Thereafter, 50 g of aluminum phosphate (AlPO ₄ ), 50 g of aluminum hydroxide (Al (OH) ₃ ), 50 g of free potassium phosphate (K ₄ P ₂ O ₇ ) and 5 g of lithium phosphate (Li ₃ PO ₄ ) H ₂ PO ₄ ) aqueous solution, 20 g of a silica colloidal dispersion was added to prepare a phosphate coating solution. The specimen was sprayed with an appropriate amount using an eyedropper, and then uniformly coated with various thicknesses through a bar coater. The pH of the aqueous solution of phosphoric acid was 1.5. Thereafter, the substrate was heated at 450 DEG C for 1 minute to form a phosphate-based insulating layer. This, in weight percent, aluminum phosphate (AlPO _4): 14.3%, aluminum hydroxide _{(Al (OH) 3):} 3.5%, free potassium phosphate _{(K 4 P 2 O 7)} : 3.5%, lithium phosphate (Li ₃ PO ₄ ): 3.5%, and silica colloid: 1.4%. Subsequently, the substrate was subjected to a heat treatment at 550 ° C. for 1 hour in a vacuum furnace having a vacuum of 10 mTorr or less, and then a Mo electrode having a thickness of 1 μm was coated thereon by sputtering. Subsequently, CIGS, CDS layer, ZnO The upper electrode layer was deposited and then coated with a silver grid to produce a solar cell. As a result of measuring the cell efficiency through the photomultiplier of the solar cell, the efficiency was improved by about 5% as compared with the solar cell having no insulating layer.

In addition, as a result of manufacturing 25 conventional solar cells to which the substrate proposed by the present invention is applied and the substrate on which the insulating layer is not formed, the defective rate is 20% , But only 5% when the phosphate-based insulating layer proposed by the present invention was formed.

On the other hand, in order to evaluate the heat resistance, an organic insulating layer was formed on the stainless steel 430 substrate prepared above as comparison data with the phosphate-based insulating layer, followed by coating 1 μm of Mo as a lower electrode and heating in a 10 mtorr vacuum environment . As a result, when the organic insulating layer was formed, discoloration and cracking occurred at a temperature of 300 ° C or higher. However, when the phosphate-based insulating layer proposed by the present invention was formed, cracking and discoloration did not occur even at 550 ° C or higher It can be confirmed that heat resistance is secured.

Claims (9)

Stainless steel substrate; And
And a phosphate-based insulating layer formed on the stainless steel substrate,
The phosphate-based insulating layer contains 10 to 40% by weight of aluminum phosphate (AlPO ₄ ), 10% or less (excluding 0) of aluminum hydroxide (Al (OH) ₃ ), potassium free phosphate (K ₄ P ₂ O ₇ ): CI consisting of not more than 10% (excluding 0), lithium phosphate (Li ₃ PO ₄ ): 1 to 5%, silica colloid: not more than 2% (excluding 0), and residual phosphoric acid (H ₂ PO ₄ ) G) S Solar cell substrate. The method according to claim 1,
Wherein the phosphate-based insulating layer has a surface roughness (Rz) of 50 to 120 nm. The method according to claim 1,
Wherein the phosphate-based insulating layer has a thickness of 600 to 2000 nm. The method according to claim 1,
The total amount of aluminum phosphate (AlPO ₄ ), aluminum hydroxide (Al (OH) ₃ ), potassium phosphate (K ₄ P ₂ O ₇ ), lithium phosphate (Li ₃ PO ₄ ) and silica colloid is 15 to 40% CI (G) S Substrate for solar cell. Preparing a stainless steel substrate;
Applying a phosphate coating solution to the stainless steel substrate; And
And heating the substrate coated with the phosphate coating solution to 450 to 650 ° C,
10% or less (excluding 0) of aluminum phosphate (AlPO ₄ ), 10 to 40% of aluminum hydroxide (Al (OH) ₃ ), potassium free phosphate (K ₄ P ₂ O ₇ ) : CI consisting of 10% or less (excluding 0), lithium phosphate (Li ₃ PO ₄ ) 1 to 5%, silica colloid 2% or less (excluding 0) and residual phosphoric acid (H ₂ PO ₄ ) Method for manufacturing a solar cell substrate. The method of claim 5,
Wherein the step of preparing the stainless steel substrate comprises modifying the surface of the stainless steel substrate. The method of claim 5,
Wherein the step of applying the phosphate coating solution is performed by using at least one method selected from the group consisting of bar coating, roll coating, slot die coating and spray coating. The method of claim 5,
Wherein the phosphate coating solution is a CI (G) S solar cell having a pH of 1 to 3. The method of claim 5,
Wherein the aqueous phosphoric acid solution has a concentration of 0.001 to 2 mol / L.

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