WO2015030361A1 - Composition for forming solar cell electrode and electrode produced from same - Google Patents

Abstract

The present invention relates to a composition for forming a solar cell electrode, comprising: silver (Ag) powder; a glass frit comprising silver (Ag) and tellurium (Te) elements; and an organic vehicle, wherein the glass frit has a mole ratio of 1:01 to 1:25 of Ag to Te. The solar cell electrode produced from the composition has excellent fill factor and conversion efficiency as contact resistance (Rc) and series resistance (Rs) are minimized.

Description

Composition for forming solar cell electrode and electrode prepared therefrom

The present invention relates to a composition for forming a solar cell electrode and an electrode prepared therefrom.

Solar cells generate electrical energy using the photoelectric effect of pn junctions that convert photons of sunlight into electricity. In the solar cell, front and rear electrodes are formed on the upper and lower surfaces of the semiconductor wafer or substrate on which the pn junction is formed. The photovoltaic effect of the pn junction is induced by solar light incident on the semiconductor wafer, and electrons generated therefrom provide a current flowing through the electrode to the outside. The electrode of the solar cell may be formed on the wafer surface by coating, patterning and firing the composition for forming a solar cell electrode.

Recently, as the thickness of the emitter is continuously thinned to increase the efficiency of the solar cell, it may cause a shunting phenomenon that may degrade the performance of the solar cell, and to increase the conversion efficiency. It is gradually increasing the area of the solar cell, which can increase the contact resistance of the solar cell can reduce the efficiency of the solar cell.

Therefore, there is an urgent need to develop a composition for forming a solar cell electrode capable of manufacturing a solar cell electrode having excellent conversion efficiency by improving contactability with a wafer to minimize contact resistance (Rc) and series resistance (Rs).

An object of the present invention is to provide a composition for forming a solar cell electrode excellent in contact between the electrode and the wafer surface.

Another object of the present invention is to provide a composition for forming a solar cell electrode which can minimize contact resistance and series resistance.

Still another object of the present invention is to provide a solar cell electrode having excellent fill factor and conversion efficiency.

Another object of the present invention is to provide an electrode made of the composition.

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

One aspect of the invention relates to a composition for forming a solar cell electrode. The composition for forming a solar cell electrode is silver (Ag) powder; Glass frits containing silver (Ag) and tellurium (Te) elements; And an organic vehicle, wherein the glass frit has a molar ratio of Ag and Te of about 1: 0.1 to about 1:25.

The glass frit is lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga), antimony (Sb), cerium (Ce), iron (Fe), lithium (Li), silicon (Si), Zinc (Zn), Tungsten (W), Magnesium (Mg), Cesium (Cs), Strontium (Sr), Molybdenum (Mo), Titanium (Ti), Tin (Sn), Indium (In), Vanadium (V), ruthenium (Ru), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese It may further include one or more elements selected from the group consisting of (Mn), neodymium (Nd), chromium (Cr) and aluminum (Al).

The silver (Ag) element included in the glass frit may be derived from one or more silver compounds selected from the group consisting of silver cyanide, silver nitrate, silver halide, silver carbonate, and silver acetate.

The glass frit may be formed from a metal oxide including the silver compound and tellurium (Te) oxide.

The metal oxide is lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga), antimony (Sb), cerium (Se), iron (Fe), lithium (Li), silicon (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), ruthenium (Ru), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese It may further include one or more selected from the group consisting of (Mn), neodymium (Nd), chromium (Cr) and aluminum (Al).

The composition comprises about 60 to about 95 weight percent of the silver powder; About 0.1 to about 20 weight percent of the glass frit; And about 1 to about 30% by weight of the organic vehicle.

The glass frit may include about 0.1 to about 50 mol% of silver (Ag) element relative to the total number of moles of glass frit.

The glass frit may have an average particle diameter (D50) of about 0.1 μm to about 10 μm.

The composition may further include one or more additives selected from the group consisting of dispersants, thixotropic agents, plasticizers, viscosity stabilizers, antifoams, pigments, ultraviolet stabilizers, antioxidants and coupling agents.

Another aspect of the invention relates to a solar cell electrode prepared from the composition for forming a solar cell electrode.

The composition for forming a solar cell electrode of the present invention introduced a silver compound having an ion decomposition temperature of about 1000 ° C. or lower into a glass frit to improve contact between the electrode and the wafer, and the solar cell electrode made of the composition had a contact resistance (Rc). Excellent fill factor and conversion efficiency due to minimization of series resistance (Rs).

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

Composition for forming solar cell electrode

Composition for forming a solar cell electrode of the present invention is silver (Ag) powder; Glass frits containing silver (Ag) and tellurium (Te) elements; And an organic vehicle, wherein the glass frit may have a molar ratio of Ag and Te of about 1: 0.1 to about 1:25. Hereinafter, the present invention will be described in detail.

(A) silver powder

The composition for solar cell electrode formation of this invention uses silver (Ag) powder as electroconductive powder. The silver powder may be a powder having a particle size of nano size or micro size. For example, the silver (Ag) powder may have a size of several tens to hundreds of nanometers or a size of several tens of micrometers. In the specific example, silver powders having different sizes of # 2 or more may be mixed and used.

The silver powder may have a spherical, plate or amorphous shape in particle shape.

The silver powder may have an average particle diameter (D50) of about 0.1 μm to about 10 μm, and more preferably about 0.5 μm to about 5 μm. The average particle diameter was measured using a 1064LD model manufactured by CILAS after dispersing the conductive powder in isopropyl alcohol (IPA) at 25 ° C. for 3 minutes with ultrasonic waves. Within this range, the contact resistance and the wire resistance can be lowered.

Silver powder may comprise from about 60 to about 95 weight percent of the total weight of the composition. Within this range, it is possible to prevent the conversion efficiency from lowering due to an increase in the resistance, and to prevent pasting from becoming difficult due to the relative decrease in the amount of the organic vehicle. Preferably from about 70 to about 90 weight percent, for example 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90 wt% may be included.

(B) glass frit

The glass frit etches the anti-reflection film during the firing process of the composition for forming a solar cell, generates silver crystal particles in the emitter region to melt the silver particles and lowers the resistance, and It improves the adhesion between the wafers and softens during sintering to induce an effect of lowering the firing temperature.

Increasing the area of the solar cell in order to increase the efficiency of the solar cell can increase the contact resistance of the solar cell to minimize damage to the pn junction (pn junction) and at the same time minimize the series resistance. In addition, since the variation in the firing temperature increases with the increase of the wafer of various sheet resistances, it is preferable to use a glass frit that can sufficiently secure thermal stability even at a wide firing temperature.

The glass frit of the present invention is formed from silver (Ag) compounds and metal oxides. Specifically, the glass frit of the present invention may be prepared by mixing, melting, and pulverizing a silver compound and a metal oxide having a temperature of about 1000 ° C. or less decomposed into silver (Ag) ions. The metal oxide may be one or more.

The silver compound may be used alone or as a mixture of silver cyanide (AgCN), silver nitrate (AgNO3), silver halide (Ag-X), silver carbonate (Ag2CO3), silver acetate (AgC2H302) and the like as the ion-bonding compound. In the silver halide (Ag-X), X may be iodine, fluorine, chlorine or bromine, preferably iodine.

In one embodiment, the metal oxide comprises tellurium (Te) oxide, and lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga) in addition to the tellurium (Te) oxide ), Antimony (Sb), cerium (Ce), iron (Fe), lithium (Li), silicon (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Cs), strontium (Sr) ), Molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), ruthenium (Ru), barium (Ba), nickel (Ni), copper (Cu), sodium (Na) ), Potassium (K), arsenic (As), cobalt (Co), zirconium (Zr), manganese (Mn), neodymium (Nd), chromium (Cr) and one selected from the group consisting of oxides of aluminum (Al) It may further include the above.

The glass frit of the present invention made of the silver compound and the metal oxide may include silver (Ag) and tellurium (Te) elements, and the molar ratio of Ag and Te present in the glass frit is about 1: 0.1 to about 1 : 25. Low series resistance and contact resistance can be ensured in the above range. In embodiments, the molar ratio of Ag and Te present in the glass frit may be 1: 0.3 to 1:24, for example, 1: 1 to 1:21. As used herein, the molar ratio means the molar ratio of each element.

As another example, the glass frit may include lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga), antimony (Sb), cerium (Ce), iron (Fe), and lithium ( Li, silicon (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium ( In), vanadium (V), ruthenium (Ru), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K), arsenic (As), cobalt (Co), zirconium ( It may further include one or more elements selected from the group consisting of Zr), manganese (Mn), neodymium (Nd), chromium (Cr) and aluminum (Al).

In addition, the glass frit may contain about 0.1 to about 50 mol% of silver (Ag) element relative to the total number of moles of glass frit, and preferably about 0.5 to about 40 mol%.

The content of each metal element included in the glass frit can be measured by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). Since the inductively coupled plasma-atomic emission spectroscopy (ICP-OES) uses a very small amount of sample, it can shorten the sample preparation time, reduce the error due to sample pretreatment, and have an excellent analysis sensitivity.

Specifically, the inductively coupled plasma-atomic emission spectroscopy (ICP-OES) is a step of pre-treating a sample, preparing a standard solution, and measuring and converting the concentration of the element to be measured to determine the content of each element present in the glass frit. Can be measured precisely.

The pretreatment of the sample may carbonize the sample by dissolving and heating the sample in an appropriate amount using an acid solution capable of dissolving the glass frit as a sample. As the acid solution, for example, a sulfuric acid (H 2 SO 4) solution or the like may be used.

The carbonized sample may be appropriately diluted to a range of analytical concentration of the element to be analyzed with a solvent such as distilled water and hydrogen peroxide (H 2 O 2). The analytical concentration range may be used in a diluted state of about 10,000 times in consideration of the element detection capability of the applied ICP-OES device.

The pretreated sample may be calibrated with a standard solution, for example, a standard solution of an element to be analyzed for element measurement when measured with an ICP-OES instrument.

For example, by introducing the standard solution into the ICP-OES measuring device to create a calibration curve by an external standard method (concentration) of the metal element to be analyzed of the sample pre-treated with the ICP-OES measuring device ( ppm) can be measured and converted to calculate the molar ratio of each element in the glass frit.

The glass frit can be prepared from the silver compounds and metal oxides described above using conventional methods. For example, it mixes with the composition of the said silver compound and a metal oxide. Mixing can be performed using a ball mill or planetary mill. The mixed composition is melted at conditions of about 800 ° C. to about 1300 ° C. and quenched at 25 ° C. The obtained result can be ground by a disk mill, planetary mill or the like to obtain a glass frit.

The glass frit may have an average particle diameter (D50) of about 0.1 to about 10㎛, the shape of the glass frit may be spherical or irregular.

The glass frit is about 0.1 to about 20% by weight, preferably about 0.5 to about 10% by weight, for example 1, 2, 2.5, 3, 3.5, 4, 4.5, It is preferably included in 5, 5.5, 6, 6.5, 7, 8, 9, 10% by weight. When it is contained in the above range, it is possible to ensure the pn junction stability under various sheet resistance, to minimize the series resistance value, and finally to improve the efficiency of the solar cell.

(C) organic vehicle

The organic vehicle imparts suitable viscosity and rheological properties to the composition through mechanical mixing with the inorganic component of the composition for forming a solar cell electrode.

The organic vehicle may be an organic vehicle that is typically used in a composition for forming a solar cell electrode, and may include a binder resin and a solvent.

As the binder resin, an acrylate-based or cellulose-based resin can be used. In embodiments, ethyl cellulose may be used as the binder resin. In another embodiment, the binder resin is ethyl hydroxyethyl cellulose, nitro cellulose, a mixture of ethyl cellulose and phenol resin, alkyd resin, phenol resin, acrylic ester resin, xylene resin, polybutene resin, polyester resin. , Urea-based resins, melamine-based resins, vinyl acetate-based resins, wood rosins, or polymethacrylates of alcohols.

As the solvent, for example, hexane, toluene, ethyl cellosolve, cyclohexanone, butyl cellosolve, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) Butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexylene glycol, terpineol, methyl ethyl ketone, benzyl alcohol, gamma butyrolactone or ethyl lactate alone or the like It can mix and use 2 or more types.

The organic vehicle may be included in about 1 to about 30% by weight based on the total weight of the composition for forming a solar cell electrode. It is possible to secure sufficient adhesive strength and excellent printability in the above range.

(D) additive

The composition for forming a solar cell electrode of the present invention may further include a conventional additive as needed to improve the flow characteristics, process characteristics and stability in addition to the components described above. The additive may be used alone or in combination of two or more of a dispersant, thixotropic agent, plasticizer, viscosity stabilizer, antifoaming agent, pigment, ultraviolet stabilizer, antioxidant, coupling agent and the like. They may be included in about 0.1 to about 5% by weight relative to the total weight of the composition for forming a solar cell electrode, but may be changed in content as necessary.

Solar cell electrode and solar cell comprising same

Another aspect of the invention relates to an electrode formed from the composition for forming a solar cell electrode and a solar cell comprising the same. 1 illustrates a structure of a solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a composition for forming an electrode is printed and baked on a wafer 100 or a substrate including a p layer (or n layer) 101 and an n layer (or p layer) 102 as an emitter. Thus, the rear electrode 210 and the front electrode 230 may be formed. For example, the electrode forming composition may be printed on the back side of the wafer and then dried at a temperature of about 200 ° C. to 400 ° C. for about 10 to 60 seconds to perform a preliminary preparation step for the back electrode. In addition, the composition for forming an electrode on the front surface of the wafer may be printed and dried to perform a preliminary preparation step for the front electrode. Thereafter, a firing process may be performed at about 400 ° C. to about 950 ° C., preferably about 700 ° C. to about 950 ° C., for about 30 seconds to about 210 seconds to form a front electrode and a rear electrode.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Examples 1-93 and Comparative Examples 1-2

Example 1

Spherical silver powder (Dowa Hightech CO) having an average particle diameter of 2.0 μm after dissolving 3.0 wt% of ethyl cellulose (DTH chemical company, ETHOCEL STD4) as an organic binder in 6.5 wt% of solvent butyl carbitol at 60 ° C. LTD, AG-4-8) 86.90% by weight, 3.1% by weight of glass frit using silver cyanide (AgCN) as a silver compound and prepared in the composition of Table 1, 0.2% by weight of dispersant DISPER BYK102 (BYK-chemie) as an additive And thixoatrol ST (Elementis co.) 0.3 wt% was added and mixed evenly after mixing evenly mixed with a three-roll kneader to prepare a composition for forming a solar cell electrode.

Examples 2-18

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that the glass frit prepared with the composition of Table 1 was used.

Examples 19-36

Silver nitrate (AgNO3) was used as the silver compound, and a composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except for using the glass frit prepared with the composition of Table 2 below.

Examples 37-54

Silver iodide (AgI) was used as the silver compound, and a composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except for using the glass frit prepared with the composition of Table 3 below.

Examples 55-72

Silver carbonate (Ag2CO3) was used as the silver compound, and a composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except for using the glass frit prepared with the composition of Table 4 below.

Examples 73-93

A silver compound (AgC 2 H 3 O 2) was used as the silver compound, and a composition for forming a solar cell electrode was prepared in the same manner as in Example 1 except for using the glass frit prepared in the composition of Table 5 below.

Comparative Examples 1 and 2

A composition for forming a solar cell electrode was prepared in the same manner as in Example 1, except that the glass frit prepared with the composition of Table 6 was used.

Determination of the molar ratio of Ag to Te in glass frit using inductively coupled plasma-atomic emission spectroscopy (ICP-OES)

Pretreatment of the sample: 0.5g of glass frit, the sample to be analyzed, is placed in a beaker and accurately weighed to 0.0001g. 5 ml of sulfuric acid (H 2 SO 4) was added to a beaker containing the sample, and the sample was completely carbonized by heating at 220 ° C. for 3 hours using a hot plate. Pretreatment was completed by adding hydrogen peroxide (H 2 O 2) until the beaker containing the carbonized sample became transparent.

Preparation of Standard Solution : Standard solutions of the silver (Ag) and tellurium (Te) elements, which are the analysis target elements, were prepared, respectively.

Measurement of the molar ratio of Ag: Te : Nitric acid (HNO 3) was added to a beaker containing the pretreated sample, followed by heating for 5 minutes, followed by air cooling. The prepared standard solution was introduced into an ICP-OES measuring instrument (PerkinElmer, Inc.) to prepare a calibration curve by an external standard method, and Ag and Ag, which are analytes included in the sample, were measured by the ICP-OES measuring instrument. The molar ratio of Ag: Te in the glass frit was calculated by measuring the element concentration (ppm) of Te, respectively. Some of the results are representatively shown in Table 7 below.

Content (%) of each element = concentration (ppm) of each element x Dilution Factor (DF) / 10000

Mole of each element = content of each element / molecular weight of each element

Mole ratio of Ag: Te = 1: (mole of Te / mole of Ag)

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

Measurement method of contact resistance

The composition for forming a solar cell electrode prepared in Examples and Comparative Examples was printed by screen printing in a predetermined pattern on the entire surface of a crystalline mono wafer (Wafer), and dried using an infrared drying furnace. The cell formed by the above process was calcined for 30 seconds to 210 seconds between 700 to 950 ° C. using a belt type kiln, and the cell thus manufactured was contacted (Rc) of the solar cell using a TLM (Transfer Length Method) measuring equipment. ) Was measured and shown in Tables 8 to 13, respectively.

Method of measuring series resistance, fill factor and efficiency

The composition for forming a solar cell electrode according to the above Examples and Comparative Examples was printed by screen printing in a predetermined pattern on the entire surface of a crystalline mono wafer (Wafer), and dried using an infrared drying furnace. After printing the aluminum paste on the back of the back of the wafer and dried in the same manner. The cell formed by the above process was fired for 30 seconds to 210 seconds in a temperature range of 700 to 950 ° C. using a belt-type kiln, and the cell thus manufactured was manufactured using a solar cell efficiency measuring device (Pasan, CT-801). The series resistance (Rs), fill factor (FF,%) and conversion efficiency (%) of the solar cell were measured and shown in Tables 8 to 13, respectively.

TABLE 8

TABLE 9

TABLE 10

TABLE 11

TABLE 12

TABLE 13

As can be seen from the results of Tables 8 to 13, the electrodes of Examples 1 to 93 in which the molar ratio of Ag and Te in the glass frit is 1: 0.1 to 1:25 are Comparative Examples 1 in which the molar ratio of Ag and Te is outside the above range. And compared with the electrode of the comparative example 2 which does not contain a silver (Ag) element, it can be seen that it is low in contact resistance and series resistance, and excellent in Fill Factor and conversion efficiency.

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (10)

Silver (Ag) powder; Glass frits containing silver (Ag) and tellurium (Te) elements; And Including an organic vehicle, The glass frit is a composition for forming a solar cell electrode, characterized in that the molar ratio of Ag and Te is 1: 0.1 to 1: 25. The method of claim 1, The glass frit is lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Ce), iron (Fe), lithium (Li), silicon (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), ruthenium (Ru), Barium (Ba), Nickel (Ni), Copper (Cu), Sodium (Na), Potassium (K), Arsenic (As), Cobalt (Co), Zirconium (Zr), Manganese (Mn), Neodymium (Nd), chromium (Cr) and aluminum (Al) composition for forming a solar cell electrode, characterized in that it further comprises at least one element selected from the group consisting of. The method of claim 1, The silver (Ag) element included in the glass frit is a silver cyanide, silver nitrate, silver halide, silver carbonate, and silver acetate is a composition for forming a solar cell electrode, characterized in that derived from at least one silver compound selected from the group consisting of. The method of claim 3, The glass frit is a composition for forming a solar cell electrode, characterized in that formed from a metal oxide containing the silver compound and tellurium (Te) oxide. The method of claim 4, wherein The metal oxide is lead (Pb), bismuth (Bi), phosphorus (P), germanium (Ge), gallium (Ga), cerium (Se), iron (Fe), lithium (Li), silicon (Si), zinc (Zn), tungsten (W), magnesium (Mg), cesium (Ce), strontium (Sr), molybdenum (Mo), titanium (Ti), tin (Sn), indium (In), vanadium (V), ruthenium (Ru), Barium (Ba), Nickel (Ni), Copper (Cu), Sodium (Na), Potassium (K), Arsenic (As), Cobalt (Co), Zirconium (Zr), Manganese (Mn), Neodymium The composition for forming a solar cell electrode, characterized in that it further comprises at least one selected from the group consisting of oxides of (Nd), chromium (Cr) and aluminum (Al). The method of claim 1, 60 to 95 wt% of the silver powder; 0.1 to 20% by weight of the glass frit; And The composition for forming a solar cell electrode, characterized in that it comprises 1 to 30% by weight of the organic vehicle. The method of claim 1, The glass frit is a composition for forming a solar cell electrode, characterized in that containing 0.1 to 50 mol% of silver (Ag) element relative to the total number of moles of glass frit. The method of claim 1, The glass frit has a composition for forming a solar cell electrode, characterized in that the average particle diameter (D50) is 0.1㎛ to 10㎛. The method of claim 1, The composition is a composition for forming a solar cell electrode, characterized in that it further comprises at least one additive selected from the group consisting of dispersants, thixotropic agents, plasticizers, viscosity stabilizers, defoamers, pigments, ultraviolet stabilizers, antioxidants and coupling agents. . 10. A solar cell electrode prepared from the composition for forming a solar cell electrode of claim 1.

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