KR101381870B1 - Low temperature sintering paste for solar cell electrode and solar cell electrode - Google Patents

Abstract

Disclosed is a low temperature sintering paste for a solar cell electrode. The paste composition has oxidation resistance during low temperature sintering with the use of tin, prevents dispersion of copper in a PN junction and improves weldability of an electrode of a solar cell and a solder ribbon. Therefore, a paste for forming a high-efficiency solar cell electrode can be provided.

Description

LOW TEMPERATURE SINTERING PASTE FOR SOLAR CELL ELECTRODE AND SOLAR CELL ELECTRODE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of solar cell electrode materials, and more particularly to a low temperature firing paste for solar cell electrodes comprising a copper powder coated with tin as a low temperature firing paste, and a solar cell electrode produced using the same.

Photovoltaic is a powerful renewable and renewable energy source that replaces existing power sources that use fossil fuels and nuclear power, along with wind, biomass, geothermal, hydro, tidal, and more. Photovoltaic power generation uses solar power, which can be said to be virtually infinite, so once a system or device is built, it can produce electricity with minimal maintenance costs.

Therefore, the photovoltaic field is a lot of research and development, and the photovoltaic power generation and solar cell market is also rapidly growing every year. However, due to the high cost of construction and the need for higher photoelectric efficiency, governments in many countries are supporting the photovoltaic sector. As a result, a large number of companies producing solar modules and batteries have recently increased, and a price competition has occurred between them.

In terms of manufacturing costs, solar cells account for 70% of solar modules. Therefore, first of all, it is necessary to produce high efficiency solar cells at low cost. However, conventional solar cells have a fundamental limitation in cost reduction because they are manufactured using expensive silver (Ag) paste.

As a solution to this, various low-cost metal pastes have been proposed, and copper paste is one of them. However, there is a problem in that copper powder is oxidized during firing and copper is diffused in a PN junction, thereby reducing solar cell efficiency.

Korean Patent Registration Publication No. 10-0979509 B1

The present invention provides a low-temperature baking paste composition for a solar cell electrode based on copper powder to solve the problems as described above.

The present invention provides a low temperature baking paste composition for a solar cell electrode based on copper powder and having oxidation resistance in a baking process.

The present invention also provides a low temperature firing paste composition for a solar cell electrode based on copper powder in which copper is prevented from diffusing into the PN junction during firing.

The present invention provides a low temperature baking paste composition for a solar cell electrode having improved weldability with a solder ribbon.

The present invention also provides a solar cell electrode produced using a paste based on the above-described improved copper powder.

The present invention provides a low temperature baking paste composition for a solar cell electrode comprising a copper powder, an organic vehicle, a binder, and a dispersant, each coated with tin. The tin-coated copper powder includes a copper spherical body and tin coated on its surface, and the copper spherical body has a particle diameter of 0.1 to 8 탆. The tin has a thickness of 0.01 to 1 μm. The tin-coated copper powder is comprised between 35 and 60% by weight.

The organic vehicle includes 24 to 39% by weight, the binder is 15 to 25% by weight, and the dispersant is included in 1% by weight.

Further, the conductive metal powder is further included in an amount of 3 parts by weight or less based on the paste composition, and the conductive metal powder is selected from the group consisting of germanium, gallium, boron, nickel, tin, bismuth, lithium, indium, cadmium, phosphorus, and zinc. One or more selected. The said conductive metal powder has a particle diameter of 8 micrometers or less.

In addition, there is provided a solar cell electrode manufactured using a paste based on the above-described improved copper powder.

According to the present invention, the low temperature baking paste composition for solar cell electrodes based on copper powder has oxidation resistance at low temperature firing, prevents copper from diffusing into the PN junction during the firing process, and improves weldability with the solder ribbon. The present invention provides a solar cell electrode manufactured using a paste based on an improved copper powder.

1 is a photograph of a copper powder coated with tin contained in a low-temperature baking paste for a solar cell electrode according to the present invention.
2 is a graph showing the particle size distribution of the copper powder coated with tin contained in the low-temperature baking paste for solar cell electrodes according to the present invention.
3 is a cross-sectional view schematically illustrating a solar cell to which an electrode manufactured by using the low temperature baking paste for solar cell electrodes of the present invention is applied.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the embodiments of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The present invention relates to a paste for solar cell electrodes based on copper to which low-temperature firing is applied. Such pastes include copper powder, organic vehicles, binders and dispersants, each coated with tin. In addition, the paste of the present invention may further include a conductive metal powder.

Hereinafter, each element contained in the paste composition of this invention is demonstrated in detail.

Tin coated copper powder

The paste for solar cell electrodes of the present invention includes copper powder coated with tin, respectively, with reference to FIG. 1. The copper powder coated with tin thus includes a copper sphere and tin coated on its surface. The sheath of tin can be made by plating tin onto a copper sphere.

Copper used in the present invention may be applied to a metal containing copper as well as pure copper (Cu). Such copper may use commercially available spherical powder or flake powder. Alternatively, by using a flake type, it can be made into a copper powder according to a known method. Preferably the copper powder may be spherical.

Referring to FIG. 2, the particle size of the copper spherical powder may have a size of about 0.1 μm to about 8 μm. Here, when the particle size of the copper spherical powder is less than 0.1 mu m, the powders aggregate with each other, high dispersion is difficult, and there is a fear that paste formation is difficult due to high viscosity. When the particle size of the copper spherical powder exceeds 8 μm, there may be a problem that it is difficult to form a fine pattern when the conductor pattern is formed.

In addition, the purity of copper is not particularly limited as long as it is a purity for satisfying the conditions normally required as an electrode. In the case of copper used in the present invention, copper having a purity of 90% or more may be used, and preferably, copper having 95% or more. Can be used.

In the present invention, tin is coated on the surface of each of the copper spheres. The coating can be used by electroplating or chemical plating methods and can be implemented, for example, in the usual way by dipping copper spheres in a tin solution.

The thickness of the tin coated on the copper spheres may be 0.01 to 1 μm. When the tin thickness is less than 0.01 μm, the oxidation resistance of copper is lowered. When the tin thickness is more than 1 μm, the degree of diffusion due to the increase of the temperature of the tin film during firing decreases, thereby reducing the process efficiency. At low temperature firing with tin, which is more oxidative than copper, copper has oxidation resistance, thereby increasing the electrical efficiency of the electrode. In addition, it is possible to prevent the diffusion of copper in the PN junction. Furthermore, since the tin and the material of an electrode which are the main materials of the winding which make up a solder ribbon are the same, the weldability of the electrode of a solar cell and a solder ribbon can be improved.

In addition, when the copper powder coated with tin is less than 35% by weight, there is a problem of printability due to phase separation or a low viscosity, and when it exceeds 60% by weight, the viscosity of the paste becomes high, making printing difficult and increasing the price. There may be.

Organic vehicle

The paste composition of the present invention comprises an organic vehicle. The organic vehicle gives the paste suitable consistency for printing and rheological properties through mechanical mixing with the inorganic components of the low temperature fired paste for solar cell electrodes.

The organic vehicle can be included at 24 to about 39 weight percent. When the content of the organic vehicle is less than 24% by weight, the paste may be difficult to apply uniformly, whereas when it exceeds 39% by weight, sufficient conductivity of the electrode pattern may not be obtained and adhesion to the substrate may be inferior. .

The organic vehicle may be an organic vehicle that is commonly used in solar cell electrode pastes, and may be, for example, a mixture of a polymer and a solvent. Examples of the polymer include acrylate resins, ethyl cellulose, nitrocellulose, polymers of ethyl cellulose and phenol resins, wood rosin, and polymethacrylates of alcohols, but are not limited thereto. As the solvent, butyl carbitol acetate, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether propionate, ethyl ether propionate, terpinol, propylene glycol monomethyl ether Acetate, dimethylamino formaldehyde, methyl ethyl ketone, gamma butyrolactone, ethyl lactate, and copolymers thereof, but are not limited thereto.

bookbinder

A binder functions as a binder of each component before baking of an electrode pattern, and it is preferable to manufacture by suspension polymerization for uniformity. The binder includes, but is not limited to, cellulose resins, acrylic resins, alkyd resins, butyral resins, saturated polyester resins, and copolymers thereof.

The binder may be included in 15 to about 25% by weight. When the content of the binder is less than 15% by weight, the distribution of the binder in the electrode pattern to be formed may be uneven. On the other hand, when it exceeds 25% by weight, it is easy to cause pattern collapse during firing of the electrode, and resistance of the electrode may increase due to organic ash carbon after firing.

Other additives

Additives such as dispersants, midpoints, thixotropic agents, and leveling agents may be further included. Such additives may be added at 1% by weight relative to the total paste.

Conductive Metal Powder

The paste of the present invention may further include a conductive metal powder. The conductive metal powder may be, for example, at least one selected from the group consisting of germanium, gallium, boron, nickel, tin, bismuth, lithium, indium, cadmium, phosphorus, and zinc.

In addition, thixotropy is contained in the characteristic of a paste. The thixotropy described above refers to a property in which the paste may aggregate or disperse depending on the presence or absence of stress, and as a result, the state may change with a gel or a sol and exhibit a change in the viscosity of the composition. The thixotropic properties of the paste change depending on the size and shape of the conductive metal powder.

The conductive metal powder may be included in 3 parts by weight or less based on the total paste. If it is added more than that, it causes cost increase and economic efficiency decreases. In addition, when the particle diameter of the conductive metal powder exceeds 8 µm, since the viscosity of the paste decreases and causes a problem in forming the electrode pattern, the conductive metal powder may preferably have a particle diameter of 8 µm or less.

Hereinafter, a solar cell including an electrode manufactured using the paste composition of the present invention will be described in more detail.

Application to solar cell back electrode

The paste of the present invention may be preferably applied to the electrode of the solar cell, more preferably to the back electrode.

A solar cell in which a back electrode is formed of the paste of the present invention is shown in FIG. 3. Such a solar cell includes a substrate 1 of a first conductivity type, an emitter layer 2 of a second conductivity type formed on the substrate 1, an antireflection film 3 formed on the emitter layer 2, and a substrate 1. And a back contact layer 5 formed on the back of the back field layer 5, and a back contact layer 7 formed on the back of the back field layer 5. On the anti-reflection film 3, a front electrode 4 penetrating the anti-reflection film 3 and connected to the emitter layer 2 is formed, and a back electrode 6 formed on the back surface of the back contact layer 7 is formed.

Preferably, the front electrode 4 and the back electrode 5 of the heterojunction solar cell described above may be applied through a printing process and a low temperature baking process of the present invention. More preferably, the paste of the present invention may be applied to the back electrode 5.

Hereinafter, specific embodiments will be described with reference to Tables 1 to 3.

The low-temperature baking paste for solar cell electrodes according to the present invention was prepared by varying the weight of each element in Examples 1 to 10, and applied to the rear electrode of the solar cell, and then the electrical properties of the solar cell were investigated.

In particular, in Examples 1 to 5, the particle size of the copper powder was 50% for 1 µm and 50% for 3 µm, and the tin film thickness was 1 µm. In contrast, in the case of Examples 6 to 10, the copper powder had a particle diameter of 1 μm of 75% and 3 μm of 25%.

In Example 1, a paste prepared with 35 wt% of copper powder coated with tin, 25 wt% of binder resin, 39 wt% of organic vehicle, and 1 wt% of dispersant was prepared, and applied to the solar cell rear electrode.

In Example 2, a paste prepared with 40 wt% of copper powder coated with tin, 23 wt% of binder resin, 36 wt% of organic vehicle, and 1 wt% of dispersant was prepared, and applied to the solar cell rear electrode.

In Example 3, a paste prepared with 45 wt% tin powder coated with copper, 20 wt% binder resin, 34 wt% organic vehicle, and 1 wt% dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

In Example 4, a paste prepared with 50% by weight of copper powder coated with tin, 18% by weight of binder resin, 31% by weight of organic vehicle, and 1% by weight of a dispersant was prepared, and applied to the solar cell back electrode, and then examined for electrical properties.

In Example 5, a paste prepared with 60 wt% of copper powder coated with tin, 15 wt% of binder resin, 24 wt% of organic vehicle, and 1 wt% of dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

The components and compositions of the paste compositions of Examples 1 to 5 are summarized in Table 1 below.

ingredient Example 1
(wt%) Example 2
(wt%) Example 3
(wt%) Example 4
(wt%) Example 5
(wt%)
Copper powder 1.0㎛ 50%
And
3.0㎛ 50%

35

40

45

50

60 Tin membrane Thickness
1㎛ bookbinder 25 23 20 18 15 Organic vehicle 39 36 34 31 24 Dispersant One One One One One Sum 100 100 100 100 100

In Example 6, a paste prepared of 35 wt% tin powder coated with copper, 25 wt% binder resin, 39 wt% organic vehicle, and 1 wt% dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

In Example 7, a paste prepared with 40 wt% of copper powder coated with tin, 23 wt% of binder resin, 36 wt% of organic vehicle, and 1 wt% of dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

In Example 8, a paste prepared with 45 wt% tin powder coated with copper, 20 wt% binder resin, 34 wt% organic vehicle, and 1 wt% dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

In Example 9, a paste made of 50% by weight of copper powder coated with tin, 18% by weight of a binder resin, 31% by weight of an organic vehicle, and 1% by weight of a dispersant was prepared.

In Example 10, a paste prepared with 60 wt% of copper powder coated with tin, 15 wt% of binder resin, 24 wt% of organic vehicle, and 1 wt% of a dispersant was prepared, and applied to a solar cell back electrode, and then examined for electrical properties.

Constituents and compositions of the paste compositions of Examples 6 to 10 are summarized in Table 2 below.

ingredient Example 6
(wt%) Example 7
(wt%) Example 8
(wt%) Example 9
(wt%) Example 10
(wt%)
Copper powder 1.0 μm 75%
And
3.0㎛ 25%
35
40
45
50
60 Tin membrane Cover thickness 1㎛ bookbinder 25 23 20 18 15 Organic vehicle 39 36 34 31 24 Dispersant One One One One One Sum 100 100 100 100 100

7. Electrical Performance Evaluation

The electrical performance of solar cells prepared using the paste compositions obtained from Examples 1-10 was determined by NPC, Dumont, NJ, NJ, USA, under 1.5 solar conditions according to ASTM G-173-03. Measurement was performed using Incorporated's solar tester, Model NCT-M-180A. The results are shown in Table 3 below.

The firing temperature during the firing process of the solar cell is about 350 ℃.

In Table 3, Isc means short-circuit current density measured at zero output voltage, Voc means open circuit voltage measured at zero output current, and FF (%) is the fill factor, Eff (%). Means efficiency. Pmax is the electrical maximum output of the solar cell, calculated from the open voltage and short circuit current. Rs (10 ^-3 Ω) represents the contact resistance.

Eff
(%) Isc
(A) Voc
(V) FF
(%) Pmax
(W) Rs
(10 ^-3 Ω) Example 1 7.59 8.51 0.604 34.71 1.784 43.8 Example 2 14.26 8.46 0.619 52.95 3.350 11.8 Example 3 17.15 8.57 0.623 75.54 4.031 6.1 Example 4 17.36 8.55 0.623 76.52 4.080 5.1 Example 5 17.40 8.57 0.624 76.41 4.088 5.1 Example 6 6.67 8.10 0.602 32.17 1.568 50.6 Example 7 11.98 8.52 0.619 52.95 2.792 14.9 Example 8 17.19 8.56 0.622 75.81 4.039 5.4 Example 9 17.39 8.61 0.623 76.14 4.086 5.3 Example 10 17.50 8.55 0.625 77.01 4.113 5.1

As can be seen from Table 3, the solar cell using the paste of the present invention as an electrode shows good results in performance evaluation. Although only slightly lower values were obtained for Examples 1 and 6 which included 35 wt% tin coated copper powder in the efficiency (Eff), the other test figures showed overall improved results. .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

1: substrate of a first conductivity type
2: emitter layer of the second conductivity type
3: antireflection film
4: front electrode
5: back layer
6: rear electrode
7: back contact layer

Claims (9)

delete delete delete delete delete delete delete A solar cell electrode prepared by firing a paste composition, the paste composition comprising:
Copper powder each coated with a tin; Organic vehicle; bookbinder; And a dispersant;
The copper powder comprises copper spherical bodies and tin coated on the surface thereof and comprises 35 to 60% by weight,
The copper spheres have a particle diameter of 0.1 to 8㎛,
The organic vehicle is 24 to 39% by weight, the binder is 15 to 25% by weight, and the dispersant is included in 1% by weight,
The tin is one having a thickness of 0.01 to 1㎛,
To bake the paste composition at 350 ℃,
Solar cell electrode. The method of claim 8,
Further comprising 3 parts by weight or less of the conductive metal powder based on 100 parts by weight of the paste composition of claim 8,
The conductive metal powder is at least one selected from the group consisting of germanium, gallium, boron, nickel, tin, bismuth, lithium, indium, cadmium, phosphorus, zinc,
Solar cell electrode.

Images