TWI731243B - Composition for forming solar cell electrode and electrode prepared using the same - Google Patents

Abstract

Disclosed herein are a composition for solar cell electrodes and a solar cell electrode. The composition for solar cell electrodes includes: a conductive powder; a tellurium (Te)-silver (Ag)-boron (B)-based glass frit; and an organic vehicle, wherein the glass frit has a molar ratio of tellurium (Te) to boron (B) of 70:1 to 5:1.

Description

Composition for forming solar cell electrode and electrode prepared using the same

The present invention relates to a composition used for solar cell electrodes and an electrode formed using the same.

Solar cells use the photovoltaic effect of the p-n junction (p-n junction) that converts sunlight photons into electricity to generate electricity. In a solar cell, a front electrode and a back electrode are respectively formed on the upper surface and the lower surface of a semiconductor wafer or substrate with a p-n junction. Then, sunlight entering the semiconductor wafer induces a photovoltaic effect at the p-n junction, and electrons generated by the photovoltaic effect at the p-n junction provide current to the outside through the electrodes. The electrode of the solar cell is formed on the wafer by applying, patterning, and baking the composition for the electrode of the solar cell.

As the composition used for the solar cell electrode, a conductive paste composition containing conductive powder, glass frit, and organic vehicle is used. The glass frit is used to melt the anti-reflection film on the semiconductor wafer to form electrical contact between the conductive powder and the wafer.

Specifically, the glass frit not only affects the electrical characteristics of the solar cell (such as the open circuit voltage (Voc) and series resistance (Rs) of the electrode), but also affects the aspect ratio of the electrode that determines the conversion efficiency and fill factor of the solar cell. influences.

Therefore, there is a need for a composition for solar cell electrodes that can improve the electrical characteristics of solar cells.

The background art of the present invention is disclosed in Japanese Unexamined Patent Publication No. 2012-084585.

An object of the present invention is to provide a composition for solar cell electrodes that can ensure high contact efficiency between the electrode and the surface of the wafer, thereby minimizing the contact resistance and series resistance of the electrode, and a composition using the composition Manufactured electrodes.

Another object of the present invention is to provide a composition for solar cell electrodes that can ensure a high fill factor and high conversion efficiency of the solar cell, and an electrode made using the composition.

These and other objects of the present invention can be achieved by the present invention described below.

One aspect of the present invention relates to a composition for solar cell electrodes.

The composition for the solar cell electrode includes: conductive powder; tellurium (Te)-silver (Ag)-boron (B) series glass frit; and an organic carrier, wherein the glass frit is The molar ratio of tellurium (Te) to boron (B) is 70:1 to 5:1.

The glass frit may include 50 mol% to 80 mol% tellurium oxide (TeO2), 0.5 mol% to 20 mol% boron oxide (B ₂ O ₃ ), and 1 mol% to 30 mol% silver nitrate (AgNO ₃ ).

The molar ratio of silver nitrate (AgNO ₃ ) to boron oxide (B ₂ O ₃ ) of the glass frit may be 1:3 to 3:1.

The molar ratio of silver nitrate (AgNO ₃ ) to tellurium oxide (TeO ₂ ) of the glass frit may be 1:80 to 1:9.

The glass frit may not contain bismuth (Bi) or lead (Pb).

The glass frit may have a particle size of 0.1 μm to 10 μm.

The glass frit may further include at least one of oxides of the following elements: sodium (Na), lithium (Li), zinc (Zn), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Ce) ), iron (Fe), silicon (Si), tungsten (W), magnesium (Mg), molybdenum (Mo), cesium (Cs), strontium (Sr), titanium (Ti), tin (Sn), indium (In ), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), potassium (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn) and aluminum (Al ).

The composition may include: 60wt% to 95wt% of the conductive powder; 0.1wt% to 20wt% of the glass frit; and 1wt% to 30wt% of the organic carrier.

The composition may also include at least one additive selected from the group consisting of a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, a defoamer, a pigment, an ultraviolet (UV) stabilizer, an antioxidant, and a coupling agent.

Another aspect of the present invention relates to a solar cell electrode.

The solar cell electrode can be produced using the above-mentioned composition for solar cell electrodes.

The present invention provides a composition for a solar cell electrode that can minimize the contact resistance and series resistance of the electrode while ensuring the high filling factor and high conversion efficiency of the solar cell, and an electrode made using the composition.

10: substrate

11: Semiconductor substrate

12: Ejector

21: back electrode

23: front electrode

100: solar cell

Fig. 1 is a schematic diagram of a solar cell according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be explained in detail.

A detailed description of known functions and configurations that would unnecessarily obscure the subject of the present invention will be omitted.

Unless the context clearly indicates otherwise, the singular forms "a, an" and "the" used herein are intended to also include the plural forms. In addition, when the term "comprises, comprising, includes and/or including" is used in this specification, it refers to the presence of the features, integers, steps, operations, elements, components, and/or The group, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In addition, unless stated otherwise, margins of error are taken into account when analyzing components.

The term "metal oxide" as used herein may refer to one metal oxide or multiple metal oxides.

In addition, "X to Y" used herein to indicate a range of certain values means "greater than or equal to X and less than or equal to Y".

Composition for solar cell electrodes

A composition for solar cell electrodes according to the present invention includes conductive powder, tellurium (Te)-silver (Ag)-boron (B) glass frit, and an organic carrier, wherein the tellurium (Te) of the glass frit is opposite to boron The molar ratio of (B) is 70:1 to 5:1.

Now, each component of the composition for solar cell electrodes according to the present invention will be explained in more detail.

Conductive powder

The conductive powder is used to impart conductivity to the composition used for the solar cell electrode. The composition for solar cell electrodes according to the present invention may contain metal powder such as silver (Ag) or aluminum (Al) as the conductive powder. For example, the conductive powder may be silver powder. The conductive powder may have nano-level fineness or micron-level fineness. For example, the conductive powder may be silver powder with an average particle size of tens of nanometers to hundreds of nanometers or an average particle size of several micrometers to tens of micrometers. Alternatively, the conductive powder may be a mixture of two or more types of silver powders having different finenesses.

The conductive powder may have various particle shapes, such as spherical, flake-shaped, or amorphous particle shapes, without limitation.

The conductive powder may have an average particle diameter (D50) of 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm. Within this range, the composition can reduce the contact resistance and line resistance of the solar cell. Here, the conductive powder can be dispersed in isopropyl alcohol (IPA) at 25°C for 3 minutes by ultrasonication, and then a 1064D particle size analyzer (CILAS Co., Ltd. (CILAS) can be used to disperse the conductive powder in isopropyl alcohol (IPA) for 3 minutes. Co., Ltd.)) measured the average particle size.

In the composition for the solar cell electrode, the conductive powder may be present in an amount of 60 wt% to 95 wt%, specifically 70 wt% to 90 wt%. Within this range, the composition can improve the conversion efficiency of the solar cell and can be easily prepared into a paste form.

Tellurium (Te)-Silver (Ag)-Boron (B) glass frit

The glass frit is used to form silver crystal grains in the emitter region by etching the anti-reflective layer and melting the conductive powder during the baking process of the composition for the solar cell electrode. In addition, the glass frit improves the adhesion between the conductive powder and the chip, and is softened during the baking process to lower the baking temperature.

As the glass frit according to the present invention, a tellurium (Te)-silver (Ag)-boron (B) series glass frit is used, wherein the molar ratio of tellurium (Te) to boron (B) ranges from 70:1 to 5:1 Within range. The glass frit can improve the contact efficiency between the electrode and the surface of the wafer, thereby minimizing the contact resistance and series resistance of the electrode while improving the fill factor and conversion efficiency of the solar cell. Specifically, the molar ratio of tellurium (Te) to boron (B) of the glass frit may be 35:1 to 8:1, more specifically, 20:1 to 10:1.

The tellurium (Te)-silver (Ag)-boron (B) glass frit may include tellurium oxide (TeO ₂ ), silver nitrate (AgNO ₃ ), and boron oxide (B ₂ O ₃ ). Here, in addition to silver nitrate (AgNO ₃ ), silver may also be derived from silver oxide, silver cyanide, silver halide, silver carbonate, or silver acetate. For example, the glass frit can be prepared by using a ball mill or planetary mill to mix the above-mentioned raw materials, melting the mixture at 900°C to 1,300°C, and quenching the molten mixture to 25°C, and then using a disc mill , Planetary mill, etc. to crush the obtained product. The glass frit may have an average particle diameter (D50) of 0.1 μm to 10 μm.

In one embodiment, the glass frit may include 50 mol% to 80 mol% tellurium oxide (TeO ₂ ), 0.5 mol% to 20 mol% boron oxide (B ₂ O ₃ ), and 1 mol% to 30 mol% silver nitrate (AgNO ₃ ) .

In one embodiment, the glass frit may include 0.5 mol% to 20 mol%, specifically 0.5 mol% to 7 mol%, more specifically 0.5 mol% to 5 mol% of boron oxide (B ₂ O ₃ ). The glass frit may contain 1 mol% to 30 mol%, specifically 1 mol% to 10 mol%, more specifically 2 mol% to 7 mol% of silver nitrate (AgNO ₃ ). The glass frit may contain 50 mol% to 80 mol%, specifically 60 mol% to 75 mol% of tellurium oxide (TeO ₂ ). Within these ranges, the glass frit can increase the fill factor of the solar cell while minimizing the contact resistance and series resistance of the electrode.

The molar ratio of silver nitrate (AgNO ₃ ) to boron oxide (B ₂ O ₃ ) of the glass frit can be 3:1 to 1:3. Within this range, the glass frit can increase the fill factor of the solar cell.

The molar ratio of silver nitrate (AgNO ₃ ) to tellurium oxide (TeO ₂ ) of the glass frit can be 1:80 to 1:9. Within this range, the glass frit can increase the fill factor of the solar cell.

The glass frit may not contain bismuth (Bi) or lead (Pb). Does not contain bismuth (Bi) or lead (Pb) The glass frit can minimize the contact resistance and series resistance of the electrode without deteriorating other properties.

The glass frit may further include at least one of oxides of the following elements: sodium (Na), lithium (Li), zinc (Zn), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Ce) ), iron (Fe), silicon (Si), tungsten (W), magnesium (Mg), molybdenum (Mo), cesium (Cs), strontium (Sr), titanium (Ti), tin (Sn), indium (In ), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), potassium (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn) and aluminum (Al ).

In the composition for the solar cell electrode, the glass frit may be present in an amount of 0.1 wt% to 20 wt%, specifically 0.5 wt% to 10 wt%. Within this range, the glass frit can ensure the stability of the p-n junction under various sheet resistances, minimize the resistance, and ultimately improve the efficiency of the solar cell.

Organic carrier

The organic carrier is mechanically mixed with the inorganic components of the composition used for the solar cell electrode to impart viscosity and rheological properties suitable for printing to the composition.

The organic vehicle may be any typical organic vehicle used in the composition of the solar cell electrode, and generally includes a binder resin, a solvent, and the like.

The binder resin may be one or more of acrylate resin or cellulose resin. Ethyl cellulose is generally used as the binder resin. In addition, the binder resin may be one or more of the following: ethyl hydroxyethyl cellulose, nitrocellulose, a blend of ethyl cellulose and phenol resin, alkyd resin, phenol resin, acrylic resin Grease, xylene resin, polybutene resin, polyester resin, urea resin, melamine resin, vinyl acetate resin, wood rosin, alcohol polymethacrylate, etc.

The solvent can be one or more of the following: for example, hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl card Alcohol (Diethylene Glycol Dibutyl Ether), Butyl Carbitol Acetate (Diethylene Glycol Monobutyl Ether Acetate), Propylene Glycol Monomethyl Ether, Hexylene Glycol, Terpineol, Methyl Ethyl Ketones, benzyl alcohol, gamma-butyrolactone, and ethyl lactate. These solvents can be used alone or as a mixture thereof.

In the composition for the solar cell electrode, the organic vehicle may be present in an amount of 1 wt% to 30 wt%. Within this range, the organic vehicle can provide sufficient adhesion strength and good printability to the composition.

additive

The composition for solar cell electrodes according to the present invention may further include any typical additives as needed to enhance fluidity, handleability and stability. Additives may include dispersants, thixotropic agents, plasticizers, viscosity stabilizers, defoamers, pigments, ultraviolet stabilizers, antioxidants, coupling agents, and the like. These additives can be used alone or as a mixture thereof. Based on the total weight of the composition for the solar cell electrode, the additive may be present in an amount of 0.1 wt% to 5 wt%, but the content of the additive may be changed as needed.

Solar cell electrode and solar cell including the solar cell electrode

Another aspect of the present invention relates to an electrode formed of a composition for a solar cell electrode and a solar cell including the electrode. Fig. 1 shows a solar cell according to an embodiment of the present invention.

1, the solar cell 100 according to the present embodiment includes a substrate 10, a front electrode 23 formed on the front surface of the substrate 10, and a rear electrode 21 formed on the back surface of the substrate 10.

In one embodiment, the substrate 10 may be a substrate with a p-n junction formed thereon. Specifically, the substrate 10 may include a semiconductor substrate 11 and an emitter 12. More specifically, the substrate 10 may be a substrate prepared by doping one surface of the p-type semiconductor substrate 11 with an n-type dopant to form the n-type emitter 12. Alternatively, the substrate 10 may be a substrate prepared by doping one surface of the n-type semiconductor substrate 11 with a p-type dopant to form the p-type emitter 12. Here, the semiconductor substrate 11 may be a p-type substrate or an n-type substrate. The P-type substrate may be a semiconductor substrate 11 doped with p-type dopants, and the n-type substrate may be a semiconductor substrate 11 doped with n-type dopants.

In the description of the substrate 10, the semiconductor substrate 11, etc., the surface through which the light of such a substrate enters the substrate is referred to as the front surface (light-receiving surface). In addition, the surface of the substrate opposite to the front surface is referred to as the back surface.

In one embodiment, the semiconductor substrate 11 may be formed of crystalline silicon or compound semiconductor. Here, the crystalline silicon may be single crystal or polycrystalline. As crystalline silicon, for example, a silicon wafer can be used.

Here, the p-type dopant may include group III elements such as boron, aluminum, or gallium. s material. In addition, the n-type dopant may be a material containing a group V element such as phosphorus, arsenic, or antimony.

The front electrode 23 and/or the back electrode 21 can be made using the composition for solar cell electrodes according to the present invention. Specifically, the front electrode 23 can be made using a composition containing silver powder as a conductive powder, and the back electrode 21 can be made using a composition containing aluminum powder as a conductive powder. The front electrode 23 may be formed by printing the composition for solar cell electrodes on the emitter 12 and then baking, and the rear electrode 21 may be formed by applying the composition for solar cell electrodes to the back of the semiconductor substrate 11 The surface is then baked to form.

Next, the present invention will be explained in more detail with reference to examples. However, it should be noted that these examples are provided for illustration only, and should not be construed as limiting the present invention in any way.

In addition, for the sake of clarity, details that are obvious to those skilled in the art will not be repeated.

Example 1

As an organic binder, 3.0wt% ethyl cellulose (STD4, Dow Chemical Company) was fully dissolved in 6.5wt% butyl carbitol at 60°C, and then added to the binder 87.5wt% of spherical silver powder with an average particle size of 2.0μm (AG-4-8, Dowa Hightech Co., Ltd.) was added to the solution, 2.5wt% of which had an average particle size of 2.0μm And has a glass frit with the composition shown in Table 1, 0.2wt% dispersant (BYK 102, BYK-chemie) and 0.3wt% thixotropic agent (Chicosat (Thixatrol ST, Elementis Co., Ltd.), and then mixed and kneaded in a 3-roll kneader to prepare a composition for solar cell electrodes.

Example 2 to Example 7 and Comparative Example 1 to Comparative Example 3

A composition for solar cell electrodes was prepared in the same manner as in Example 1, except that the composition of the glass frit was changed to be as listed in Table 1.

Property evaluation

(1) Contact resistance (Rc, mΩ), series resistance (Rs, mΩ) and open circuit voltage (Voc, mV): screen printing with a predetermined pattern, and then drying in an infrared (IR) drying oven, Each of the compositions for solar cell electrodes prepared in the Examples and Comparative Examples was deposited on the front surface of the wafer. The battery formed according to this formula is subjected to baking in a belt-type baking furnace at 600°C to 900°C for 60 seconds to 210 seconds, and then a transfer length method (TLM) tester is used for contact resistance ( Rc), series resistance (Rs) and open circuit voltage (Voc) were evaluated. The results are shown in Table 2.

(2) Filling factor (%) and efficiency (%): by using a predetermined pattern Screen printing and then drying in an infrared drying oven, each of the compositions for solar cell electrodes prepared in the Examples and Comparative Examples were deposited on the front surface of the wafer. Next, aluminum paste was printed on the back surface of the wafer and dried in the same manner as described above. The battery formed according to this program was subjected to baking in a belt-type baking oven at 400°C to 900°C for 30 seconds to 180 seconds, and then a solar cell efficiency tester CT-801 (Pasan Co. ., Ltd.)) evaluated the filling factor (FF, %) and conversion efficiency (Eff., %). The results are shown in Table 2.

As shown in Table 2, it can be seen that the solar cell electrodes made with the composition for solar cell electrodes in which the molar ratio of tellurium to boron falls within the range described herein can exhibit high contact with the surface of the wafer Efficiency, thereby minimizing contact resistance and series resistance while improving the fill factor and conversion efficiency of the solar cell.

On the contrary, it can be seen that the solar cell electrodes of Comparative Example 1 and Comparative Example 2 in which the molar ratio of tellurium to boron is outside the range described herein have high series resistance and contact resistance, and Comparative Example 3 without silver Of solar cell electrodes exhibited high Resistance and low fill factor.

Although some embodiments have been described herein, it should be understood that various modifications, variations, and changes can be made by those skilled in the art without departing from the spirit and scope of the present invention. Therefore, it should be understood that the foregoing embodiments are provided for illustrative purposes only, and should not be regarded as limiting the present invention in any way.

10‧‧‧Substrate

11‧‧‧Semiconductor substrate

12‧‧‧Ejector

21‧‧‧Back electrode

23‧‧‧Front electrode

100‧‧‧Solar cell

Claims (9)

A composition for solar cell electrodes, comprising: conductive powder; glass frit, containing 50 mol% to 80 mol% tellurium oxide, 0.5 mol% to 5 mol% boron oxide, and 1 mol% to 30 mol% silver nitrate; and an organic carrier, The molar ratio of tellurium to boron of the glass frit is 70:1 to 10:1. The composition for solar cell electrodes as described in item 1 of the scope of patent application, wherein the molar ratio of silver nitrate to boron oxide of the glass frit is 1:3 to 3:1. The composition for solar cell electrodes as described in item 1 of the scope of patent application, wherein the molar ratio of silver nitrate to tellurium oxide of the glass frit is 1:80 to 1:9. The composition for solar cell electrodes as described in item 1 of the scope of patent application, wherein the glass frit does not contain bismuth or lead. The composition for solar cell electrodes as described in item 1 of the scope of patent application, wherein the glass frit has a particle size of 0.1 μm to 10 μm. The composition for solar cell electrodes as described in item 1 of the scope of patent application, wherein the glass frit further includes at least one of the oxides of the following elements: sodium, lithium, zinc, phosphorus, germanium, gallium, cerium, Iron, silicon, tungsten, magnesium, molybdenum, cesium, strontium, titanium, tin, indium, vanadium, barium, nickel, copper, potassium, arsenic, cobalt, zirconium, manganese and aluminum. The composition for solar cell electrodes as described in the first item of the patent application includes: 60wt% to 95wt% of the conductive powder; 0.1wt% to 20wt% of the glass frit; and 1wt% to 30wt% The organic vehicle. The composition for solar cell electrodes as described in item 1 of the scope of patent application, further includes: dispersant, thixotropic agent, plasticizer, viscosity stabilizer, defoamer, pigment, ultraviolet stabilizer, antioxidant, and At least one additive in the coupling agent. A solar cell electrode, which is produced using the composition for a solar cell electrode as described in any one of items 1 to 8 in the scope of the patent application.

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