KR101071412B1 - The patterned transparent electrode by lift-off and the solar cell using the same - Google Patents

Abstract

The present invention relates to a transparent electrode having a pattern formed by a lift-off process and a solar cell using the same, specifically, depositing a transparent electrode layer on a substrate (step 1); Forming a photoresist pattern on the transparent electrode layer prepared in step 1 (step 2); Further depositing a thin film transparent electrode layer on the transparent electrode layer on which the photoresist pattern prepared in step 2 is formed (step 3); And a transparent electrode having a pattern formed by using a lift-off process including removing the photoresist pattern (step 4) and a solar cell using the same. The transparent electrode according to the present invention has a pattern formed easily by a lift-off process to increase the surface area and the light absorbing layer volume compared to the conventional transparent electrode, and scattering light by depositing the light absorbing layer in the patterned transparent electrode when manufacturing a solar cell By reducing the solar cell can be manufactured with increased solar conversion efficiency.

Solar cell, transparent electrode, transparent electrode structure, surface area, solar conversion efficiency

Description

The patterned transparent electrode by lift-off and the solar cell using the same}

The present invention relates to a transparent electrode having a pattern formed by a lift-off process and a solar cell using the same.

Recently, the importance of developing the next generation of clean energy is increasing due to serious environmental pollution and depletion of fossil energy. Among them, solar cells are expected to be an energy source that can solve future energy problems due to the low pollution, infinite resources and semi-permanent lifespan.

A solar cell is a semiconductor device that converts solar energy directly into electrical energy. The solar cell is a crystalline silicon, an amorphous silicon, a compound semiconductor, an organic material, a dye-sensitized solar cell, etc., depending on the type and form of the photoelectric conversion material used. Classified as

Of these, more than 90% of the commercially available solar cells use single crystal and polycrystalline silicon wafers, which are called "first generation solar cells." The crystalline silicon solar cell has been forming the solar market by improving efficiency and reducing costs through steady technology development since the 1980s, and has been growing at an average annual rate of 50% over the past several years. Such demand growth is expected to maintain its growth trend in the future, but since silicon, which is a raw material, accounts for about 60% of the manufacturing cost of crystalline solar cells, it is sensitive to the impact of rising silicon prices and It is an obstacle to securing price competitiveness. In fact, the price of polysilicon for solar cells soared more than 10 times from US $ 23 / kg in 2003 to US $ 250 in early 2008, causing the solar cell manufacturing cost to increase. For this reason, there is increasing interest in thin-film solar cells, which are lower in manufacturing cost, consume less raw materials, and have a smoother supply of materials than crystalline silicon solar cells. Batteries, organic polymer solar cells, and the like. Thin-film silicon solar cells and thin-film compound solar cells show a certain level of conversion efficiency through continuous research and development, but dye-sensitized solar cells and organic polymer solar cells have low conversion efficiency (3-10% or less) despite low manufacturing cost. ) Is an obstacle to industrialization. Therefore, there is a need to improve the current low conversion efficiency.

On the other hand, the transparent electrode (transparent electrode) is a functional thin film electrode that transmits light in the visible light region and has electrical conductivity, and is a core material commonly used in various thin film solar cells. Most of the thin film materials for transparent electrodes currently used are n-type semiconductor materials composed of metal oxides and are called transparent conducting oxides (TCOs). The transparent conductive oxide may include zinc oxide (ZnO), tin oxide (SnO), indium oxide-tin oxide (In ₂ O ₃ -SnO: ITO), fluorinated tin oxide (FTO), indium oxide-zinc oxide _{(in 2 O 3 -ZnO: IZO} ) and using an oxide, such as.

In the case of a transparent electrode applied to a solar cell, the efficiency of converting sunlight into electricity is the most important. Therefore, it is essential for the conductive material to have a low resistivity along with a high light transmittance due to its characteristics. Therefore, in order to develop a high efficiency solar cell, it is essential that the conductive material layer deposited on the transparent base has a low specific resistance and high light transmittance, and in addition, has a low surface roughness as compared with the related art.

In general, the transparent electrode may be manufactured by depositing the transparent conductive oxide (TCO) on a glass substrate, because the surface of the TCO film is flat when the physical vapor deposition (PVD) method is most widely used for thin film deposition. The light incident on the solar cell is reflected and the light absorption rate is lowered.

Therefore, the present inventors while studying to solve the above problems, the surface area of the solar cell having a transparent electrode patterned by a lift-off process, the volume of the light absorbing layer is increased and It was confirmed that the scattering of light is reduced to increase the solar conversion efficiency and completed the present invention.

An object of the present invention is to provide a method for manufacturing a transparent electrode patterned using a lift-off process.

Another object of the present invention is to provide a transparent electrode having improved solar conversion efficiency manufactured by the manufacturing method.

Another object of the present invention to provide a solar cell using the transparent electrode.

In order to achieve the above object, the present invention

Depositing a transparent electrode layer on the substrate (step 1); Forming a photoresist pattern on the transparent electrode layer prepared in step 1 (step 2); Further depositing a thin film transparent electrode layer on the transparent electrode layer on which the photoresist pattern prepared in step 2 is formed (step 3); And a step of removing the photoresist pattern (step 4) to provide a method of manufacturing a transparent electrode having a pattern formed thereon.

In addition, the present invention provides a transparent electrode having a pattern formed by the manufacturing method.

Furthermore, the present invention provides a solar cell having a transparent electrode having the pattern formed thereon.

The transparent electrode according to the present invention has a pattern formed easily by a lift-off process to increase the surface area and the light absorbing layer volume compared to the conventional transparent electrode, and scattering light by depositing the light absorbing layer in the patterned transparent electrode when manufacturing a solar cell By reducing the solar cell can be manufactured with increased solar conversion efficiency.

Hereinafter, the present invention will be described in detail with reference to the drawings.

As shown in Figure 1 , the present invention comprises the steps of depositing a transparent electrode layer on a substrate (step 1);

Forming a photoresist pattern on the transparent electrode layer prepared in step 1 (step 2);

Further depositing a thin film transparent electrode layer on the transparent electrode layer on which the photoresist pattern prepared in step 2 is formed (step 3); And

Provided is a method of manufacturing a transparent electrode on which a pattern is formed using a liftoff process including removing the photoresist pattern (step 4).

First, step 1 is a step of depositing a transparent electrode layer on a substrate.

In the manufacturing method according to the present invention, the material used for the transparent electrode layer may be ZnO, In ₂ O ₃ , SnO ₂ , ITO, FTO, AZO, IZO, etc. commonly used in the art, the transparent electrode layer As a method of forming a solution, a solution deposition method including a physical vapor deposition method (PVD), a sol-gel method, etc., such as a direct current magnetron sputtering and a radio frequency magnetron sputtering, is used by using an evaporation method, a chemical vapor deposition method, and a vapor deposition method. It can be deposited in a thin film.

In the manufacturing method according to the present invention, the transparent electrode layer of step 1 can be adjusted according to the final thickness of the completed transparent electrode. At this time, it is preferable that the final thickness of the transparent electrode is 100 to 350 nm. If the final thickness is less than 100 nm, a sufficient pattern cannot be achieved. If the thickness is greater than 350 nm, the light absorbing layer and the amount of the electrolyte are reduced to decrease the solar cell efficiency. There is a problem.

For example, when the final thickness of the transparent electrode is 100 ~ 200 nm, the transparent electrode layer of the step 1 is preferably formed to a thickness of 10 to 50% of the final thickness of the transparent electrode, the final thickness of the transparent electrode is 200 ~ In the case of 350 nm, the thickness is preferably 20 to 70% of the final thickness of the transparent electrode. If the transparent electrode layer is less than 10% with respect to the final thickness of the transparent electrode, there is a problem that electricity does not flow sufficiently, and if the thickness is greater than 70%, the improvement of solar conversion efficiency may be insignificant.

Next, step 2 is a step of forming a photoresist pattern on the transparent electrode layer prepared in step 1.

In the manufacturing method according to the present invention, step 2 is also referred to as a lithography process, generally a method for forming a fine pattern in a semiconductor process, a light-sensitive photoresist is coated on the transparent electrode layer prepared in step 1 Afterwards, a patterning process is performed on the transparent electrode layer using a suitable mask or reticle and a stepper. The size and shape of the pattern can be formed according to the size and shape of the pattern designed for the mask or reticle.

Next, step 3 is a step of further depositing a thin film transparent electrode layer on the transparent electrode layer on which the photoresist pattern prepared in step 2 is formed.

In the manufacturing method according to the present invention, the transparent electrode layer deposition method includes physical vapor deposition (PVD), sol-gel (Sol-Gel) method, such as DC magnetron sputtering, radio frequency magnetron sputtering mentioned in step 1 Solution deposition, chemical vapor deposition, vapor deposition and the like can be used. At this time, in consideration of the thickness of the transparent electrode deposited in step 1, the remaining thickness of the final thickness of the transparent electrode is deposited.

Next, step 4 is to remove the photoresist pattern prepared in step 2.

In the manufacturing method according to the present invention, the step 4 is also referred to as a stripping (stripping) process, it is a process of removing the photoresist pattern prepared in the step 2.

Since the thickness of the photoresist pattern is greater than the thickness of the transparent electrode thin film to be formed and exposed to the outside, the photoresist pattern may be removed by a stripper solution or O ₂ ashing method, using an organic solvent such as acetone. You can also remove it.

Through such a manufacturing method, a transparent electrode on which a pattern is finally formed may be manufactured.

The transparent electrode is formed of a pattern, the deeper the depth of the pattern increases the amount of light absorbing layer and electrolyte provided in the solar cell and the surface area of the electrode (see Figs . 2 and 3 ), reducing the scattering of light It is possible to increase the solar conversion efficiency (see Table 1 and Figure 4 ).

In addition, the present invention provides a high efficiency solar cell provided with a transparent electrode having the pattern formed.

The solar cell according to the present invention increases the surface area of the transparent electrode using a patterned transparent electrode, increases the volume of the light absorbing layer and the electrolyte, and simultaneously reduces light scattering by depositing the light absorbing layer in the patterned transparent electrode. High efficiency can be obtained by utilizing the light efficiently. As the solar cell, a dye-sensitized solar cell, an organic molecular solar cell, a silicon thin film solar cell or a compound semiconductor thin film solar cell having a transparent electrode can be used.

In the solar cell according to an embodiment of the present invention, when the solar cell is a dye-sensitized solar cell, the solar cell

Depositing a catalyst thin film electrode on a transparent electrode on which a pattern is not formed, and then forming a hole to prepare an upper electrode (step A);

Preparing a lower electrode by depositing a light absorption layer on the transparent electrode on which the pattern is formed (step B);

Fixing the upper electrode of the step A to the lower electrode of the step B with a double-sided tape (step C); And

It can be prepared by a method comprising the step of injecting and sealing the electrolyte through the hole formed in the upper electrode (step D).

In the method of manufacturing a solar cell according to the present invention, step A is a step of manufacturing an upper electrode by forming a hole after depositing a catalyst thin film electrode on a transparent electrode having no pattern.

The hole is a space into which the hot melt foil is inserted to seal the solar cell. The hole may be manufactured by a drill, the diameter of which is preferably 0.5 to 3 mm. At this time, if the diameter of the hole exceeds 3 mm there is a problem that is difficult to seal, if less than 0.5 mm there is a problem that the hot melt foil is not inserted.

In the method of manufacturing a solar cell according to the present invention, step B is a step of manufacturing a lower electrode by depositing a light absorption layer on the transparent electrode on which the pattern is formed.

The light absorbing layer is deposited on the lower electrode, absorbs sunlight, excites photoelectrons, and sends the light to the transparent electrode. At this time, the light absorption layer deposition is preferably a solution deposition method, a vapor deposition method or a chemical coating method including a magnetron sputtering, Sol-Gel method and the like. The light absorbing layer may generally use single crystal, polycrystalline, amorphous silicon, cadmium sulfide (CdS), copper indium diselenide (CuInSe ₂ ), titanium oxide particles, niobium oxide (Nb ₂ O ₅ ) dye, or mixtures thereof. According to the light absorption layer material, one of a solution deposition method including a magnetron sputtering, a sol-gel method, a vapor deposition method, or a chemical coating method may be used.

In the method of manufacturing a solar cell according to the present invention, step C is a step of fixing the upper electrode of the step A to the lower electrode of the step B with a double-sided tape.

The step C is a step of assembling and fixing the upper and lower electrodes, to secure a space for the electrolyte is injected, and to fix without a void space between the electrode and the tape. At this time, if there is a blank space between the electrode and the tape in the step there is a problem that the electrolyte may leak.

In the method of manufacturing a solar cell according to the present invention, the step D is a step of injecting and sealing an electrolyte through a hole formed in the upper electrode.

In the step D, the electrolyte is injected into the hole formed in the step A into the solar cell in which the upper and lower electrodes are fixed in the step C, and the electrolyte is sealed to prevent leakage.

The sealing of step D is performed by inserting a hot melt sealing foil and attaching it with a thermal tape to heat the back surface of the heat conductive tape several times using a iron. At this time, the heat of the iron delivered through the heat conduction tape melts the inserted hot melt sealing foil to block holes formed in the upper electrode, thereby preventing the electrolyte from leaking.

Hereinafter, the embodiment of the present invention will be described in more detail. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited by the following examples.

< Manufacturing example  1> Polyethylene glycol  Preparation of Titanium Oxide Paste

0.5 g of titanium oxide particles (Degussa P25, 80% anatase-2-% rutile) were mixed with 1.5-2 ml of deionized water, and ground for about 10 minutes using a mortar and pestle. Next, 0.2 ml of acetylacetone, 0.2 ml of acetic acid, 0.15 g of polyethylene glycol (PEG) having a molecular weight of 20 000, and 0.5 g of PEG having a molecular weight of 500 000 were mixed sequentially, respectively. Grind about 15-20 minutes each time you add a solution. Finally, ethanol (absolute ethanol) was added to adjust the viscosity and grind for 20 minutes to prepare a titanium oxide paste.

< Manufacturing example  2> Triton  Preparation of Titanium Oxide Paste

After 1 g of titanium oxide particles were mixed with 3 ml of deionized water and stirred for 30 minutes, acetylacetone, acetic acid and triton (Triton, Polyoxyethylene (10) isooctlyphenyl ether, Mw = 646.85 g / mol) were sequentially added. At this time, each addition of the solution was stirred for 30 minutes each. Titanium oxide paste was prepared by adjusting the viscosity by adding ethanol and stirring for 15 minutes using a homogenizer.

< Manufacturing example  3> Preparation of Dye

Cis-bis (isothiocyanato) bis (2,2'-bipyridyl-4,4'-dicarboxylate) -ruthenium (II) bis-tetrabutylammonium (cis-bis (isothiocyanato) bis ( 2,2'-bipyridyl-4,4'-dicarboxylato) -ruthenium (II) bis-tetrabutylammonium, (N719)) A 0.3 mM solution of 35 mg dissolved in 100 ml of ethanol was heated to 50 ° C. plate was stirred vigorously for 12 hours to prepare a dye. The dye solution was used while stored in a light-blocked box at room temperature (25 ℃).

< Manufacturing example  4> Preparation of electrolyte solution

133.84 mg of lithium iodide (LiI), 126.905 g of iodine (I ₂ ), 0.73245 ml of 4-tert-butylpyridine and 1-hexyl-2,3-dimethyl-imidazolium (1-hexyl- 1.8492 g of 2, 3-dimethyl-imidazolium) was added to methoxyacetonitrile and mixed vigorously for 3 hours.

< Example  1> Lift-off  Fabrication of Transparent Electrode with Pattern Using Process

Step 1: depositing the transparent electrode

The glass substrate was placed 7.5 cm away from a target having a ratio of 9: 1 of In ₂ O ₃ : IZO, and a transparent electrode was deposited at 70 W rf magnetron power while flowing 50 sccm of pure argon at a process pressure of 3 mTorr. . At this time, the thickness of the deposited transparent electrode is 150 nm, 50% of the final thickness.

Step 2: Photoresist  Forming a pattern

In order to form a 3 μm wide vertical and horizontal line pattern on the transparent electrode deposited in step 1, an adhesion promoter reagent capable of improving the adhesion of the transparent electrode is coated on the transparent electrode, and a photoresister material After coating to a thickness of about 1.2 μm, a part of the organic solvent was removed by heating at 90 to 95 ° C. for 60 to 90 seconds on a hot plate. Thereafter, the part where the pattern is printed is exposed to light at an exposure time using a mask aligner or a stepper, which is an irradiation device of a light source, and then the photo is exposed to the light with a developer. The resist was removed to form a photoresist pattern on the transparent electrode.

Step 3: remove the transparent electrode Redeposited  step

Next, the glass substrate is placed 7.5 cm away from a target having a ratio of 9: 1 of In ₂ O ₃ : IZO, and then 50 sccm of pure argon is flowed at a process pressure of 3 mTorr, and the transparent electrode is powered by 70 W rf magnetron power. Was deposited. At this time, the thickness of the deposited electrode was 50% of the final thickness and was 150 nm.

Step 4: Photoresist  Steps to Remove a Pattern

Since the thickness of the photoresist pattern (~ 1200 nm) is much higher than the thickness of the formed thin film (300 nm), the remaining photoresist material can be removed by stripper solution or O ₂ ashing method. However, in order to protect the transparent electrode, a transparent electrode having a pattern formed by simply removing the acetone solution was prepared.

< Example  2>

A transparent electrode having a pattern was manufactured in the same manner as in Example 1, except that the deposition thickness of the thin film in step 1 was 210 nm and the deposition thickness of the thin film in step 3 was 90 nm.

< Example  3>

A transparent electrode having a pattern was prepared in the same manner as in Example 1 except that the deposition thickness of the thin film was 100 nm in step 1 and the deposition thickness of the thin film was 100 nm in step 2.

< Comparative example  1> Fabrication of Transparent Electrode without Pattern

By performing only Step 1 of Example 1, a transparent electrode having a thickness of 300 nm and no pattern was prepared.

< Example  4> Fabrication of Solar Cell with Patterned Electrode

Step A: preparing an upper electrode

After depositing platinum on the transparent electrode (Comparative Example 1), the pattern is not formed, an upper electrode was prepared by forming a hole in the transparent electrode on which platinum was deposited.

Step B: preparing a lower electrode

The titanium oxide prepared in Preparation Example 1 was coated on the patterned electrode layer prepared in Example 1, and heated at 100 ° C. for 20 minutes to evaporate moisture in the titanium oxide. Next, the mixture was heated at 50 ° C. for 5 minutes and then immersed in 0.3 mM of the dye prepared in Preparation Example 3 for 24 hours. After washing with ethanol to remove the dye not adsorbed on titanium oxide and dried in nitrogen gas to prepare a lower electrode.

Step C: Place the upper electrode on the lower electrode Fixed  step

The upper electrode prepared in step A was fixed to the lower electrode manufactured in step B with a double-sided tape (carbon tape).

Step D: Sealing After Injecting Electrolyte

After injecting the electrolyte solution prepared in Preparation Example 4 through a hole formed in the upper electrode, a high temperature molten sealing foil was put in the hole, a heat conductive tape was attached, and heat sealed to manufacture a solar cell according to the present invention. .

< Example  5>

In step B, a solar cell was manufactured in the same manner as in Example 4, except that the transparent electrode prepared in Example 2 was used.

< Example  6>

In step B, a solar cell was manufactured in the same manner as in Example 4, except that the transparent electrode prepared in Example 3 was used.

< Comparative example  2> Fabrication of Solar Cell with Transparent Electrode without Pattern

In step B, a solar cell was manufactured in the same manner as in Example 4, except that the transparent electrode prepared in Comparative Example 1 was used.

< Experimental Example  1> Electron scanning microscope

Examples 4,5 and Comparative Example 2 shows a cross-section of the transparent electrode of the lower substrate in the solar cell manufactured by the 3 by analyzing the scanning electron microscope (S-4300, Hitachi).

As shown in FIG . 3 , the transparent electrodes (Examples 4 and 5) having the pattern formed according to the present invention had increased surface area and increased light absorbing layer volume as compared with the transparent electrodes having no pattern of Comparative Example 2. Appeared in the dashed circle.

< Experimental Example  2> sunlight  Conversion rate measurement

In order to determine the photovoltaic conversion efficiency of the transparent electrode with a pattern formed according to the present invention, by measuring the photovoltaic conversion efficiency of the solar cells prepared in Examples 4, 5 and Comparative Example 2 in Table 1 and FIG . Indicated.

Open Voltage (Voc)
(mV) Short circuit current density (Jsc)
(mA / cm ² ) Fill factor (FF)
(%) Conversion efficiency
(%) Comparative Example 2 749.18 6.18 65.82 3.05 Example 4 756.77 7.20 70.14 3.82 Example 5 744.60 7.40 63.72 3.51

As shown in Table 1 and Figure 4 , it was confirmed that the solar cell having a transparent electrode with a pattern formed according to the present invention has a higher conversion efficiency than the solar cell with a general transparent electrode without a pattern is formed, carried out In the case of Example 4, it was confirmed that the conversion efficiency increased by about 25% or more.

Therefore, the transparent electrode according to the present invention has a pattern formed easily by a lift-off process to increase the surface area and the light absorbing layer volume compared to the conventional transparent electrode, and the light absorbing layer is deposited in the patterned transparent electrode in the manufacturing of solar cells By reducing the scattering of the solar cell can be manufactured with increased solar conversion efficiency.

1 is a conceptual diagram illustrating a method of manufacturing a transparent electrode having a pattern using a lift-off process according to the present invention.

2 is a conceptual diagram illustrating a volume difference when a light absorption layer is deposited on a transparent electrode having a pattern formed according to the present invention and a transparent electrode on which a conventional pattern is not formed.

3 is a photograph taken with a scanning electron microscope of a cross-section of a transparent electrode having a pattern formed according to the present invention ((a) Comparative Example 2, (b) Example 4, (c) Example 5).

Figure 4 is a graph measuring the solar conversion efficiency of the solar cell having a transparent electrode with a pattern formed according to the present invention.

Claims (10)

Depositing a thin film transparent electrode layer on the substrate (step 1); Coating a photoresist on the transparent electrode layer prepared in step 1, and then forming a photoresist pattern using a mask or a reticle and an exposure apparatus (step 2); Further depositing a thin film transparent electrode layer on the transparent electrode layer on which the photoresist pattern prepared in step 2 is formed (step 3); And The method of manufacturing a transparent electrode having a thickness of 100 ~ 350 nm formed pattern using a lift-off process comprising the step of removing the photoresist pattern (step 4). The method of claim 1, wherein the material used for the transparent electrode layers of steps 1 and 3 is any one selected from the group consisting of ZnO, In ₂ O ₃ , SnO ₂ , ITO, FTO, AZO and IZO or a mixed oxide thereof. Method of manufacturing a transparent electrode with a pattern formed using a lift-off process, characterized in that. The method of claim 1, wherein the method of forming the transparent electrode layers of steps 1 and 3 comprises a direct current magnetron sputtering, a radio frequency magnetron sputtering, a sol-gel method, an evaporation method, a chemical vapor deposition method, and a vapor deposition method. Method of manufacturing a transparent electrode with a pattern formed using a lift-off process, characterized in that selected from. The method of claim 1, wherein the transparent electrode layer of step 1 is formed in a thickness of 10 to 50% of the final thickness of the transparent electrode. The method of claim 1, wherein the step 4 comprises removing a photoresist pattern by using a stripper solution, acetone, or O ₂ ashing. A transparent electrode with a pattern formed by the method of any one of claims 1 to 5, wherein the thickness of the transparent electrode is 100 ~ 350 nm. delete delete The high efficiency solar cell provided with the transparent electrode in which the pattern of Claim 6 was formed. The high efficiency solar cell of claim 9, wherein the high efficiency solar cell is a dye-sensitized solar cell, an organic molecular solar cell, a silicon thin film solar cell, or a compound semiconductor thin film solar cell.

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