TWI603487B - Composition for forming electrode, electrode manufactured using the same and solar cell - Google Patents

Description

Composition for forming an electrode, electrode made using the composition, and solar cell

A composition for forming an electrode, an electrode made using the composition, and a solar cell are disclosed.

Solar cells can generate electricity using the photovoltaic effect of the p-n junction, which converts the photons of sunlight into electricity. In the solar cell, a front electrode and a rear electrode may be formed on the front surface and the rear surface of a semiconductor substrate (semiconductor wafer) having a p-n junction, respectively. The photovoltaic effect of the p-n junction can then be induced by sunlight entering the substrate, and electrons generated by the photovoltaic effect of the p-n junction can provide current to the outside via the electrode.

The electrode of the solar cell can be formed on the surface of the wafer in a predetermined pattern by coating the electrode composition and patterning and sintering the electrode composition.

The front electrode of the solar cell can increase the open circuit voltage when the damage of the front electrode to the wafer is minimized while maximizing the incident light. Thereby, the maximum efficiency of the solar cell can be achieved. Therefore, there is a need to develop a composition for forming an electrode that minimizes damage when the electrode contacts the wafer.

Embodiments provide a composition for forming an electrode that is capable of improving cell efficiency by minimizing damage when the electrode contacts a wafer and thereby increasing an open circuit voltage.

Embodiments provide an electrode made using the composition for forming an electrode.

Embodiments provide a solar cell including the electrode.

According to an embodiment, a composition for forming an electrode comprises a conductive powder, a glass frit, an organic vehicle, and a flame retardant, wherein the flame retardant is expressed at a temperature of 600 ° C based on an initial amount of 100 wt% Residual carbon is greater than or equal to 1 wt%, and the flame retardant exhibits an exothermic peak at 200 ° C to 500 ° C.

The flame retardant may be used in an amount of 0.05 wt% to 1.5 wt% based on the total amount of the composition for forming an electrode.

The flame retardant may be an organic compound selected from the group consisting of epoxy acrylate compounds, urethane acrylate compounds, and quinone compounds.

The composition for forming an electrode may include 60 wt% to 95 wt% of the conductive powder, 0.5 wt% to 20 wt% of the glass frit, and 0.05 wt% to 1.5 wt% of the flame retardant. And the balance is the organic carrier.

The glass frit may comprise one or more elements selected from the group consisting of lead (Pb), tellurium (Te), bismuth (Bi), lithium (Li), phosphorus (P), germanium (Ge), gallium (Ga). , cerium (Ce), iron (Fe), cerium (Si), zinc (Zn), tungsten (W), magnesium (Mg), cerium (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti) , tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K), arsenic (As), cobalt (Co) Zirconium (Zr), manganese (Mn), silver (Ag) and aluminum (Al).

The organic vehicle may comprise an organic binder and a solvent.

The composition for forming an electrode may further comprise at least one selected from the group consisting of a surface treatment agent, a dispersant, a thixotropic agent, a viscosity stabilizer, an antifoaming agent, a pigment, an ultraviolet (UV) stabilizer, and an anti-wear agent. Oxidizers and coupling agents.

Embodiments provide an electrode made using the composition for forming an electrode.

Embodiments provide a solar cell including the electrode.

The composition for forming an electrode can improve cell efficiency by minimizing damage when the electrode contacts the wafer and thereby increasing the open circuit voltage.

In the following, the invention will be explained more fully with reference to the accompanying drawings in which FIG. As will be appreciated by those skilled in the art, the described embodiments may be modified in various different ways without departing from the spirit and scope of the invention.

In the drawings, the thickness of layers, films, panels, regions, etc. are exaggerated for clarity. Throughout the specification, the same reference numerals indicate the same elements. It will be understood that when an element (such as a layer, a film, a region, or a substrate) is referred to as being "on" another element, the element may be directly on the other element or the intermediate element may be present. In contrast, when an element is referred to as being "directly on" another element, there is no intermediate element.

A composition for forming an electrode according to an embodiment is a ferable paste composition, and comprises a conductive powder, a glass frit, an organic vehicle, and a flame retardant, wherein the flame retardant is organic A compound which exhibits greater than or equal to 1 wt% of residual carbon at a temperature lower than or equal to 600 ° C and exhibits an exothermic peak at 200 ° C to 500 ° C based on an initial amount of 100 wt%.

Hereinafter, each component of the composition for forming an electrode will be described in detail.

The composition for forming an electrode may contain a metal powder as a conductive powder. The metal powder may include at least one metal selected from the group consisting of silver (Ag), gold (Au), palladium (Pd), platinum (Pt), ruthenium (Ru), rhodium (Rh), osmium (Os), ruthenium. (Ir), bismuth (Re), titanium (Ti), niobium (Nb), tantalum (Ta), aluminum (Al), copper (Cu), nickel (Ni), molybdenum (Mo), vanadium (V), zinc (Zn), magnesium (Mg), yttrium (Y), cobalt (Co), zirconium (Zr), iron (Fe), tungsten (W), tin (Sn), chromium (Cr) and manganese (Mn), but Not limited to this.

The particle size of the conductive powder may be on a nanometer scale or a micrometer scale. For example, the conductive powder may have a particle size of several tens of nanometers to several hundred nanometers, or several micrometers to several tens of micrometers. In an exemplary embodiment, the conductive powder may be a mixture of two or more silver powders having different particle sizes.

The conductive powder may have a spherical shape, a sheet shape, or an amorphous shape particle shape. The conductive powder may have an average particle diameter (D50) of 0.1 mm to 10 mm, for example, 0.5 mm to 5 mm. The conductive powder may be dispersed in isopropyl alcohol (IPA) at room temperature (20 ° C to 25 ° C) for three minutes by ultrasonic treatment, for example, using Model 1064D (CILAS Co., Ltd.) Ltd.)) Equipment to measure the average particle size. Within this average particle size range, the composition provides low contact resistance and low line resistance.

The conductive powder may be present in an amount of 60 wt% to 95 wt% based on 100 wt% of the composition for forming an electrode. Within this range, deterioration of conversion efficiency due to, for example, an increase in electrical resistance can be prevented, and hard formation of paste due to relative reduction of the organic carrier can also be prevented. In an embodiment, the conductive powder may be present in an amount of 70 wt% to 90 wt%.

The glass frit may be used to enhance adhesion between the conductive powder and the substrate, and used in the emitter region by etching the antireflection layer and melting the conductive powder during the sintering process of the composition for forming the electrode. Crystal grain is formed to lower the contact resistance. During the sintering process, the frit can be softened and the sintering temperature can be lowered.

When the area of the solar cell is increased to increase the efficiency of the solar cell, the contact resistance of the solar cell may increase. Therefore, it is desirable to minimize the influence on the p-n junction while minimizing the series resistance (Rs). In addition, as various wafers having different sheet resistances are increasingly used, the sintering temperature can be varied over a wide range. It may be desirable for the frit to ensure sufficient thermal stability to withstand a wide range of sintering temperatures.

The frit may be one or more of lead frit and lead-free frit that can be used in the electrode composition.

The glass frit may comprise one or more elements selected from the group consisting of lead (Pb), tellurium (Te), bismuth (Bi), lithium (Li), phosphorus (P), germanium (Ge), gallium (Ga). , cerium (Ce), iron (Fe), cerium (Si), zinc (Zn), tungsten (W), magnesium (Mg), cerium (Cs), strontium (Sr), molybdenum (Mo), titanium (Ti) , tin (Sn), indium (In), vanadium (V), barium (Ba), nickel (Ni), copper (Cu), sodium (Na), potassium (K), arsenic (As), cobalt (Co) Zirconium (Zr), manganese (Mn), silver (Ag) and aluminum (Al).

The frit may be prepared from the oxide of the element by any suitable method. For example, an oxide of the element can be obtained by mixing an oxide of a metal element at a predetermined ratio, melting the mixture, quenching the resultant, and then pulverizing the quenched product. Mixing can be carried out using a ball mill or a planetary mill. The melting can be carried out at 700 ° C to 1300 ° C, and the quenching can be carried out at room temperature (20 ° C to 25 ° C). The powdering can be carried out using a disk mill or a planetary mill, but is not limited thereto.

The glass frit may have an average particle diameter (D50) of 0.1 mm to 10 mm, and may be present in an amount of 0.5 wt% to 20 wt% based on 100 wt% of the composition for forming an electrode. Within this range, the glass frit can ensure excellent electrode bonding strength without deteriorating the electrical characteristics of the electrode.

The frit may have a spherical shape or an amorphous shape. In an embodiment, two different kinds of frits having different transition temperatures can be used. For example, the first frit having a transition temperature of greater than or equal to 200 ° C and less than or equal to 350 ° C and the second frit having a transition temperature of greater than 350 ° C and less than or equal to 550 ° C may be from 1: 0.2 to 1:1. The weight ratio is mixed.

The organic vehicle can be imparted to the composition for forming an electrode to be suitable for printing viscosity and rheological properties by mechanical mixing with the inorganic component of the composition for forming an electrode. The organic vehicle comprises an organic binder and a solvent.

The organic binder may be selected from an acrylate-based resin or a cellulose-based resin. In an embodiment, the organic binder may be selected from the group consisting of ethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and a phenolic resin, an alkyd resin, a phenolic resin, an acrylate. Acrylate ester-based resin, xylene resin, polybutene resin, polyester resin, urethane resin, melamine resin, vinyl acetate resin, wood rosin or alcohol Acrylate.

The organic binder may have a weight average molecular weight (Mw) of from 30,000 g/mol to 200,000 g/mol, for example from 40,000 g/mol to 150,000 g/mol. When the weight average molecular weight (Mw) is in this range, an excellent effect can be obtained in terms of printability.

The solvent may be, for example, hexane, toluene, Texanol (Dexanol (trade name), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), methylcellulose Agent, ethyl cellosolve, cyclohexanone, butyl cellosolve, fatty alcohol, butyl carbitol (diethylene glycol monobutyl ether), dibutyl carbitol (diethylene glycol dibutyl ether) , butyl carbitol acetate (diethylene glycol monobutyl ether acetate), propylene glycol monomethyl ether, hexanediol, terpineol, methyl ethyl ketone, benzyl alcohol, g-butyrolactone, ethyl lactate Or a combination thereof.

The organic vehicle may be present in an amount from 1 wt% to 30 wt%, such as from 5 wt% to 20 wt%, based on 100 wt% of the composition used to form the electrode. When the organic vehicle is used within this range, the bonding strength between the electrode pattern and the substrate can be improved and excellent continuous printability can be ensured.

The flame retardant may delay sintering of the organic material in the composition for forming an electrode, and adjust the fluidity of the frit and thereby adjust the etching properties of the anti-reflective coating. Therefore, damage to the electrode in contact with the emitter can be minimized, and the open circuit voltage can be increased.

The flame retardant is an organic compound having an amount of residual carbon of greater than or equal to 1 wt% at a temperature of 600 ° C based on an initial amount of 100 wt% thereof, for example, at 200 ° C to 500 ° C There is residual carbon of greater than or equal to 1.0 wt% and greater than or equal to 60.0 wt%, and exhibits an exothermic peak at 210 ° C to 450 ° C. In general, residual carbon in the organic binder can have a negative impact on the composition used to form the electrode and thus should be removed, but the residual carbon in the flame retardant can adjust the flowability of the frit and thus The etching properties are adjusted and as a result the open circuit voltage is increased. When the flame retardant has less than 1 wt% of residual carbon, the amount of residual carbon is too small to adjust the fluidity of the frit. The amount of residual carbon can be measured by Thermogravimetry-Differential Thermal Analysis (TG-DTA) at 600 ° C after raising the temperature from 10 ° C / min to 30 ° C / min to 600 ° C.

In addition, when the flame retardant has an exothermic temperature lower than 200 ° C, the flame retardant has an exothermic temperature lower than a temperature at which the glass starts to have fluidity, and thus may not exhibit a flame retarding function and cannot be increased. The open circuit voltage, but when the flame retardant has an exothermic temperature higher than 500 ° C, the combustion function is delayed too much, and the resistance of the electrode is increased, with the result that the efficiency of the solar cell is deteriorated. The exothermic temperature can be measured by Thermogravimetry-Differential Thermal Analysis (TG-DTA) under conditions of an elevated temperature of 5 ° C/min to 20 ° C/min. The exotherm temperature represents the temperature at the highest point of the peak accompanying the heavy loss in the TG-DTA chart.

The flame retardant may be used in an amount of 0.05 wt% to 1.5 wt%, for example, 0.1 wt% to 1.2 wt%, based on the total amount of the composition for forming the electrode. Within the range, the open circuit voltage can be increased and the efficiency of the solar cell can be improved.

The flame retardant may be an organic compound selected from the group consisting of an epoxy acrylate compound, a urethane acrylate compound, or a quinone compound.

The composition for forming an electrode may also contain typical additives as needed to enhance flow properties, processing properties, and stability. The additive may include a surface treatment agent, a dispersant, a thixotropic agent, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, an ultraviolet (UV) stabilizer, an antioxidant, a coupling agent, and the like. These additives may be used singly or in the form of a mixture thereof.

These additives may be present in an amount of from 0.1 wt% to 5 wt%, based on 100 wt% of the composition for forming an electrode. This amount can be changed as needed. The amount of the additive can be selected in consideration of the printing characteristics, dispersibility, and storage stability of the composition for forming an electrode.

Embodiments provide an electrode formed from the composition for forming an electrode.

Embodiments provide a solar cell including the electrode.

Referring to Figure 1, a solar cell according to an embodiment is illustrated. FIG. 1 illustrates a schematic diagram of a structure of a solar cell according to an embodiment.

Referring to FIG. 1, a front electrode 210 can be formed by printing an electrode composition on a substrate 100 including a p-layer (or n-layer) 101 and an n-layer (or p-layer) 102 as an emitter and then sintering the same. Rear electrode 230. For example, the electrode composition may be applied to the back side of the substrate 100 and heat-treated at 200 ° C to 400 ° C for 10 seconds to 60 seconds to perform a preliminary preparation step of the back electrode.

The preliminary preparation step of the front electrode can be carried out by printing the electrode composition on the front surface of the substrate 100 and then drying it. Next, the electrode composition may be sintered at 400 ° C to 980 ° C, for example, 700 ° C to 980 ° C for 30 seconds to 210 seconds to form the front and back electrodes.

The following examples and comparative examples are provided to highlight the characteristics of one or more embodiments, but it should be understood that the examples and comparative examples should not be construed as limiting the scope of the embodiments, and the comparative examples should not be construed as being Outside the scope of the example. Further, it should be understood that the described embodiments are not limited to the specific details described in the examples and the comparative examples. Preparation Examples 1 to 9 and Comparative Example 1 and Comparative Example 2 of a composition for forming an electrode

A composition for forming an electrode was prepared by disposing an organic binder at 60 ° C according to the composition provided in Table 1 (Mw = 50,000 g/mol, STD 4, Dow Chemical Company) )) sufficiently dissolved in a solvent (Texanol (trade name), Eastman) to add spherical silver (Ag) powder having an average particle diameter of 1.5 mm (AG-5-) 11F, Dowa Hightech Co., Ltd., Bi-Te-Ag-Li-Zn-O glass frit (Bi/Te/Ag/Li/Zn(mol%)=10/61 /9/8/12), according to Table 2, each flame retardant, dispersant (BYK-102, BYK-chemie), and thixotropic agent (Thixatrol ST, Elementis Co.), which is mixed and dispersed by a three roll mill. (Table 1) (Unit: wt%) (Table 2) Measurement of the amount of residual carbon in the flame retardant

The amount of residual carbon was obtained by raising the temperature of 30 mg of each of the flame retardants used in Examples 1 to 9 and Comparative Example 1 to about 600 ° C at about 20 ° C / min, followed by measurement at 600 ° C. The results of the measurement are shown in Table 2 above. Measurement of exothermic peak temperature of flame retardant

Flame retardant and organic carrier (organic binder) for each of Examples 1 to 9 and Comparative Example 1 were analyzed by Thermogravimetry-Differential Thermal Analysis (TG-DTA) at 10 ° C/min. The mixture of the solvent and the solvent was heated to measure the exothermic peak temperature, and the results are shown in Table 2. Organic carriers (organic binders and solvents) do not affect the exothermic peak temperature of the flame retardant. Solar cell efficiency assessment

The composition for forming an electrode according to each example and each comparative example was separately screen-printed to texture the front side of the wafer (p-type wafer doped with boron) and POCl ₃ A predetermined pattern is formed on the polycrystalline wafer obtained by forming an n+ layer, then forming an antireflection coating thereon with tantalum nitride (SiNx:H), and drying at 300 ° C to 400 ° C in an infrared drying oven. Subsequently, an aluminum paste was printed on the back side of the wafer and then dried using the same method as described above. The battery fabricated by the above process was sintered in a belt-type furnace at 400 ° C to 900 ° C for 30 seconds to 180 seconds to obtain a test battery.

The open cell voltage (V _oc , mV), series resistance (R _s , W), and conversion efficiency (Eff., %) of the test battery were measured using a solar cell efficiency measuring device (CT-801, Passan). measuring. The results are provided in Table 3. (table 3)

Referring to Table 3, each solar cell separately prepared using the composition for forming an electrode containing a flame retardant according to Examples 1 to 9 did not exhibit an increase too much as compared with the solar cell according to Comparative Example 2 The resistance, but exhibits an increased open circuit voltage and thus exhibits increased efficiency. The battery fabricated according to Comparative Example 1 using the composition for forming an electrode containing a flame retardant having residual carbon beyond the scope of the present invention exhibited a small open circuit voltage increasing effect.

The exemplified embodiments have been disclosed herein, and the specific terms are used and construed in a generic and descript In some instances, it will be apparent to those skilled in the art that the present disclosure, which is described in the application, the features, characteristics, and/or elements described in connection with the specific embodiments may be used alone or in combination with others. The features, characteristics, and/or combinations of elements set forth in the embodiments are used in combination. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention as described in the appended claims.

100‧‧‧Substrate
101‧‧‧p layer
102‧‧‧n layer
210‧‧‧ front electrode
230‧‧‧Back electrode

The features of the present invention will become apparent to those of ordinary skill in the art in the <RTIgt;

100‧‧‧Substrate

101‧‧‧p layer

102‧‧‧n layer

210‧‧‧ front electrode

230‧‧‧Back electrode

Claims (8)

A composition for forming an electrode, comprising: a conductive powder, a glass frit, an organic vehicle, and a flame retardant, wherein the flame retardant exhibits greater than or equal to 600 ° C based on an initial amount of 100 wt% 1 wt% of residual carbon, the flame retardant exhibits an exothermic peak at 200 ° C to 500 ° C, and is used in an amount of 0.05 wt% to 1.5 wt% based on the total amount of the composition for forming an electrode The flame retardant. The composition for forming an electrode according to claim 1, wherein the flame retardant is an organic compound selected from the group consisting of an epoxy acrylate compound, a urethane acrylate compound, and an anthracene compound. . The composition for forming an electrode according to claim 1, wherein the composition comprises 60% by weight to 95% by weight of the conductive powder, 0.5% by weight to 20% by weight of the glass frit, 0.05% by weight. Up to 1.5% by weight of the flame retardant, and the balance being the organic vehicle. The composition for forming an electrode according to claim 1, wherein the glass frit comprises one or more elements selected from the group consisting of lead, bismuth, antimony, lithium, phosphorus, antimony, gallium, antimony, Iron, bismuth, zinc, tungsten, magnesium, lanthanum, cerium, molybdenum, titanium, tin, indium, vanadium, niobium, nickel, copper, sodium, potassium, arsenic, cobalt, zirconium, manganese, silver and aluminum. The composition for forming an electrode according to claim 1, wherein the organic carrier comprises an organic binder and a solvent. The composition for forming an electrode according to claim 1, wherein the composition for forming an electrode further comprises at least one selected from the group consisting of a surface treatment agent, a dispersant, a thixotropic agent, Viscosity stabilizers, defoamers, pigments, UV stabilizers, antioxidants and coupling agents. An electrode produced by using the composition for forming an electrode according to any one of claims 1 to 6. A solar cell comprising the electrode as described in claim 7 of the patent application.