TWI537226B - Zno-based glass frit composition and aluminum paste composition for back contacts of solar cell using the same - Google Patents

Description

Zinc oxide-based glass medium composition and aluminum paste composition using the same for solar cell back contact

The disclosed subject matter relates to a zinc oxide-based glass dielectric composition, and an aluminum paste composition using the composition for use in a back junction of a solar cell, the glass dielectric composition being in the process of manufacturing a solar cell back contact It can reduce the bending phenomenon of the substrate after the substrate is fired, can exhibit moisture stability, and can improve the open circuit voltage and light conversion efficiency of the battery.

In recent years, solar cells with abundant energy resources and no environmental pollution problems have begun to attract attention. The solar cell has a junction structure of a P-type semiconductor and an N-type semiconductor. If light enters the solar cell, the negatively charged electrons will detach from the light and interact with the semiconductor material that makes up the solar cell, and a positively charged hole will be created, and the movement of the electron hole will generate a current. Specifically, the electrons are attracted by the N-type semiconductor, and the holes are attracted by the P-type semiconductor, so that the electrons and the holes are respectively moved to the N-type electrode bonded to the N-type semiconductor, and the P-type semiconductor is bonded. P-type electrode. If the aforementioned two electrodes are connected by wires, current flows to generate electric power.

In addition, according to materials and manufacturing technologies, solar cells are classified into a silicon solar cell and a compound semiconductor solar cell, and are further classified into a substrate type and a film type depending on the material.

The tantalum solar cell is formed by printing a paste containing a conductive metal on a substrate, drying, and baking, and aluminum powder is most commonly used to form back contacts.

The aforementioned aluminum paste containing aluminum powder can be used to manufacture a solar cell having a high conversion rate. Further, the aforementioned aluminum paste is classified into a lead-containing aluminum paste and a lead-free aluminum paste. Lead-containing aluminum pastes include lead-containing glass media and achieve high conversion efficiencies. However, as lead-containing glass media increases environmental pollution, there has recently been a trend to switch to a method using a lead-free glass medium in an aluminum paste.

The lead-free glass dielectric composition usually uses a fluorenyl (bismuth trioxide, Bi ₂ O ₃ ) glass. The basic component is antimony trioxide, and during the glass molding process, aluminum oxide (Al ₂ O ₃ ), boron trioxide (B ₂ O ₃ ), and hafnium oxide (SiO ₂ ) are included. In addition, at least one component as an additional additive may be used in the composition, which is selected from the group consisting of ferric oxide (Fe ₂ O ₃ ), phosphorus pentoxide (P ₂ O ₅ ), magnesium oxide (MgO), and trioxide. Di gallium (Ga ₂ O ₃ ), lithium dioxide (Li ₂ O), disodium pentoxide (Na ₂ O), zirconium dioxide (ZrO ₂ ), silver oxide (AgO), antimony pentoxide (Sc _{2 )} O ₅ ), strontium oxide (SrO), barium oxide (BaO), calcium oxide (CaO), palladium (Pd), platinum (Pt), and rhodium (Rh).

However, the aforementioned bismuth-based glass composition uses expensive antimony trioxide, and its high coefficient of thermal expansion causes the substrate to bend to increase the fracture rate of the wafer, and its moisture stability is low or exhibits relatively low cell efficiency. .

The present invention provides a zinc oxide-based glass dielectric composition which is used as an inorganic binder in an aluminum paste composition to reduce substrate bending caused by a difference in shrinkage during cooling after baking of a substrate. , thereby avoiding breakage of the substrate during the manufacture of the back contact of the solar cell, and exhibiting moisture stability to avoid fading of the aluminum fired film due to moisture, and also improving the open circuit voltage of the battery ( Open circuit voltage) and improve the light conversion efficiency of the battery.

The present invention also provides a lead-free aluminum paste composition for forming a back contact of a solar cell, which uses the glass dielectric composition as an inorganic bonding agent to improve battery characteristics.

The present invention provides a glass dielectric composition for forming an aluminum paste composition for a back junction of a solar cell, the glass media composition comprising:

(a) 45 to 60 weight percent (wt%) of zinc oxide;

(b) at least one metal oxide selected from the group consisting of 0.1 to 45 wt% ceria, 0.1 to 40 wt% boron trioxide, and 1 to 10 wt% aluminum oxide;

(c) 0.1 to 20 wt% of a transition metal oxide, a lanthanide oxide, or a mixture of the foregoing oxides;

(d) 3 to 5 wt% of phosphorus pentoxide;

(e) 3 to 5 wt% of cerium oxide.

The glass medium composition may have an average particle diameter of 0.5 to 20 μm, a moisture content of 5% or less, and a coefficient of thermal expansion of 50 × 10 ^-7 / ° C to 150 × 10 ^-7 / °C.

The transition metal oxide is at least one selected from the group consisting of manganese oxide (MnO), manganese dioxide (MnO ₂ ), cobalt trioxide (Co ₃ O ₄ ), cobalt dioxide (Co ₂ O ₃ ), and cobalt monoxide (CoO). An oxide in the group consisting of titanium dioxide (TiO ₂ ), vanadium pentoxide (V ₂ O ₅ ), and copper monoxide (CuO). Further, the lanthanide oxide is at least one selected from the group consisting of cerium oxide (CeO ₂ ), arsenic trioxide (Pr ₂ O ₃ ), antimony trioxide (Eu ₂ O ₃ ), and antimony trioxide (Tb _{2 ).} O _3), rubidium oxide groups (Nd ₂ O ₃₎ and samarium oxide (Sm ₂ O ₃₎ composed of the oxides.

The present invention also provides a lead-free aluminum paste composition for forming a back contact of a solar cell, comprising aluminum powder, an inorganic binder, and an organic vehicle, wherein the aluminum paste composition includes the inorganic The above zinc oxide-based glass dielectric composition of the bonding agent.

Hereinafter, the present invention will be described in further detail.

The present invention relates to a zinc oxide based glass dielectric composition useful as an inorganic binder for forming a composition of a back junction of a solar cell. The present invention also provides a lead-free aluminum paste composition using the glass dielectric composition, which is suitable for forming a back contact of a solar cell.

Unlike the conventional glass medium composition comprising lead oxide (PbO) or ruthenium as a main component, the present invention provides a lead-free glass medium composition containing no ruthenium.

Therefore, the glass dielectric composition of the present invention comprises zinc oxide as a main component, and at least one of cerium oxide, boron trioxide and aluminum oxide is used to form glass. Further, the glass dielectric composition of the present invention comprises a compound containing at least one transition metal element of manganese (Mn), cobalt (Co), copper (Cu), titanium (Ti), and vanadium (V), and/or a a compound of at least one lanthanide element of cerium (Ce), praseodymium (Pr), cerium (Eu), cerium (Tb), cerium (Nd), and cerium (Sm), and a specific content range of phosphorus pentoxide and cerium oxide Used to control the electrical properties (conversion efficiency) of the substrate as well as moisture reactivity.

Since the present invention uses a glass medium composition having a specific composition, it is possible to form a composition having a thermal expansion coefficient lower than that of the conventional ruthenium-based composition, so as to greatly reduce the difference in shrinkage ratio due to substrate baking and cooling. The substrate is bent and broken. Further, since the present invention does not contain a lead component, it is environmentally friendly, and since the present invention does not use an expensive antimony compound and uses a zinc oxide-based glass medium using a metal oxide which is easily obtained, the cost can be greatly reduced. Furthermore, the present invention comprises an oxide comprising a transition metal of at least one group selected from the group consisting of manganese, cobalt, copper, titanium and vanadium, and/or at least one selected from the group consisting of ruthenium, osmium, iridium, osmium, iridium. And an oxide of a lanthanide element in the group formed by the ruthenium, and can be effectively used to form a back P++ layer on the P-type substrate to increase the open circuit voltage. This is related to an increase in voltage (Voc) between the top and bottom of the substrate to improve conversion efficiency. Further, since the present invention includes phosphorus pentoxide and cerium oxide in a specific content range, the moisture stability and the bending phenomenon of the substrate can be further improved.

A glass dielectric composition for forming an aluminum paste composition for a back junction of a solar cell according to a preferred embodiment of the present invention comprises (a) 45 to 60 wt% of zinc oxide, (b) At least one metal oxide selected from the group consisting of 0.1 to 45% by weight of cerium oxide, 0.1 to 40% by weight of boron trioxide, and 1 to 10% by weight of aluminum oxide, (c) 0.1 to 20 wt% of a transition metal oxide, a lanthanide oxide, or a mixture of the foregoing oxides, (d) 3 to 5 wt% of phosphorus pentoxide, and (e) 3 to 5 wt% of ruthenium oxide.

Moreover, a glass medium composition for forming an aluminum paste composition for a back junction of a solar cell according to a preferred embodiment of the present invention comprises (a) 45 to 60 wt% of zinc oxide, (b) at least one metal oxide selected from the group consisting of 6 to 18 wt% of cerium oxide, 4 to 17 wt% of boron trioxide, and 5 to 10 wt% of aluminum oxide. c) 0.1 to 20 wt% of a transition metal oxide, a lanthanide oxide, or a mixture of the foregoing oxides, (d) 3 to 5 wt% of phosphorus pentoxide, and (e) 3 to 5 wt% of oxidation barium.

The glass composition having a specific composition is used to prepare an aluminum paste composition for forming a back contact of a solar cell, and is not used in a conventional plasma display panel (PDP). As described above, since the present invention has excellent moisture stability, fading of the aluminum fired film due to moisture and bending of the substrate can be avoided, and the open circuit voltage and light conversion efficiency of the solar cell can be greatly improved.

In the glass dielectric composition of the present invention, the zinc oxide of the component (a) is used as a main component, and forms a main structure with other basic components to increase stability, thereby improving thermal stability, water repellency, and moisture resistance. The content of the zinc oxide is preferably from 45 to 60% by weight, more preferably from 45 to 55% by weight based on the total amount of the glass medium composition. If the content of zinc oxide is less than 45 wt%, the relative proportion of other components may increase, resulting in failure to achieve the viscosity required for glass fluidity; if the content of zinc oxide exceeds 60 wt%, it may be difficult to form glass or glass. Excessive hardening increases the glass transition temperature. Therefore, the content of zinc oxide in the composition of the glass medium is preferably in the above range to enhance physical properties.

Next, in the glass medium composition of the present invention, the component (b) plays a basic function for stably forming the glass medium. Further, at least one metal oxide selected from the group consisting of cerium oxide, boron trioxide, and aluminum oxide may be used in combination, and may include, for example, cerium oxide or trioxide. A mixture of two or three of boron and aluminum oxide is selected. Cerium dioxide is used to reduce the coefficient of thermal expansion and the gelation frequency of the glass; aluminum oxide is used to reduce glass crystallization, reduce the coefficient of thermal expansion, and improve chemical durability; while boron trioxide is used Reduce the coefficient of thermal expansion and increase the stability of the glass. The (b) metal oxide may include 0.1 to 45 wt% of cerium oxide, 0.1 to 40 wt% of boron trioxide, and 1 to 10 wt%, respectively, based on the total amount of the glass dielectric composition. The aluminum oxide is more preferably 6 to 18 wt% of cerium oxide, 4 to 17% by weight of boron trioxide, and 5 to 10% by weight of aluminum oxide. Further, at least one of the foregoing metal oxides may be selected and used, and as described above, a mixture of two or three metal oxides selected from the group consisting of cerium oxide, boron trioxide, and aluminum oxide may also be used. . This is an essential component for forming glass, and if the content is less than or exceeds the above range, it is difficult to form glass.

Further, in the glass medium composition of the present invention, the component (c) can effectively form the P++ layer on the back contact on the P-type substrate, so that the light conversion efficiency and the open circuit voltage of the solar cell can be improved as described above. The type of the transition metal oxide and the lanthanoid oxide is not particularly limited. Preferably, the transition metal oxide is at least one oxide selected from the group consisting of manganese monoxide, manganese dioxide, cobalt trioxide, cobalt dioxide, cobalt monoxide, titanium dioxide, vanadium pentoxide, and copper monoxide. . Further, the lanthanide oxide may be at least one oxide selected from the group consisting of cerium oxide, antimony trioxide, antimony trioxide, antimony trioxide, antimony trioxide, and antimony trioxide. The (c) transition metal oxide, the lanthanide oxide or a mixture of the foregoing may be contained in a total amount of 100 wt% of the glass medium composition, and the total amount of the glass medium composition is The benchmark has an optimum content of 0.1 to 20 wt%. If the content is less than 0.1% by weight, the function of forming the P++ layer is attenuated; if the content exceeds 20% by weight, the content of other components is relatively reduced, resulting in difficulty in forming glass.

Further, the glass dielectric composition of the present invention substantially comprises (d) phosphorus pentoxide and (e) cerium oxide for stabilizing the structure of the glass, and avoiding moisture reactivity and improving electrical properties. That is, by using phosphorus pentoxide and cerium oxide, the moisture stability of the aluminum fired film is increased to avoid moisture penetration and fading, and the adhesion between the substrate and the fired film can be maintained. Avoid peeling off the fired film. If one of the above two components is missing, it may be impossible to obtain a glass having excellent bending resistance and being capable of controlling reactivity with moisture.

Preferably, the glass medium composition comprises from 3 to 5% by weight of (d) phosphorus pentoxide based on the total amount of the glass medium composition. Specifically, if the content of phosphorus pentoxide is between 3 and 5 wt%, the thermal properties suitable for the calcination temperature of the aluminum powder can be effectively exhibited; if the content is above or below the above range, the desired moisture stability cannot be obtained. Sex.

Further, the glass medium composition includes 3 to 5 wt% of (e) cerium oxide based on the total amount of the glass medium composition. Specifically, if the content of cerium oxide is from 3 to 5 wt%, the same effect as the above-described range of phosphorus pentoxide content can be obtained; if the content exceeds or falls below the above range, the desired moisture stability cannot be obtained. .

Therefore, even if the conventional glass medium composition includes phosphorus pentoxide and cerium oxide, which does not have a specific content range as in the present invention, the problem of improvement in the above-described moisture stability cannot be solved.

Specifically, even if phosphorus pentoxide and cerium oxide are added to improve the electrical properties of the solar cell, if the individual addition amount exceeds 5 wt%, the electrical properties of the solar cell are attenuated, and when the slurry is fired, The moisture reactivity of the fired film in which the aluminum powder particle film component reacts with the glass increases, and the stability is further lowered. Further, if the amount of the individual addition is less than 3 wt%, the improvement in electrical characteristics is not remarkable, and the reactivity between the aluminum fired film and moisture is increased to cause fading due to moisture.

The glass medium composition of the present invention has an average particle diameter of 0.5 to 20 μm, a water vapor content of 5% or less, and a coefficient of thermal expansion of 50 × 10 ^-7 / ° C to 150 × 10 ^-7 / ° C. Further, in order to control the bending of the substrate after baking, the average particle diameter of the glass medium is preferably from 0.5 to 10 μm. If the average particle diameter is less than 0.5 μm, the bending becomes too large; if it exceeds 10 μm, the dispersion stability in the slurry is lowered. Further, if the moisture content of the glass medium composition exceeds 5%, the viscosity of the slurry increases due to cross-linking of moisture and organic substances.

The glass medium composition preferably has a softening point (Ts) of from 400 ° C to 600 ° C and a glass transition temperature (Tg) of from 350 ° C to 550 ° C.

The glass medium composition of the present invention may further comprise disodium pentoxide depending on the requirements. The disodium oxynitride is used to compensate for electrical properties. The content may be from 1 to 10% by weight, preferably from 3 to 9% by weight based on the total amount of the glass medium composition. If sodium hexoxide is added, the content of the components described above is preferably controlled individually within the respective ranges of 100 wt% of the composition.

Preferably, the glass dielectric composition may have a composition selected from the group consisting of ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -CeO ₂ -CoO, ZnO -SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ ,ZnO- SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CoO, ZnO-SiO ₂ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Nd ₂ O ₃ -Co ₃ O ₄ , ZnO-SiO ₂ -B ₂ O ₃ -BaO- P ₂ O ₅ -MnO-Co ₂ O ₃ -Tb ₂ O ₃ -CuO, and ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO-Co ₂ O ₃ -Pr ₂ O ₃ . Preferably, the glass dielectric composition has a composition of ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-MnO ₂ -CoO-CeO ₂ because it can lift the battery The electrical characteristics have excellent moisture reaction stability, and the substrate can be greatly reduced in bending, and the substrate can be effectively prevented from being broken.

The glass medium composition of the present invention can be produced by a conventional method without particular limitation.

For example, the glass powder can be prepared by mixing the ingredients for a sufficient period of time, about 2 hours, to thoroughly mix the ingredients, melt, quenching, and pulverizing.

The melting can be carried out at a temperature of 1,000 to 1,500 ° C, preferably 1,300 to 1,450 ° C. The melting time can be from 10 to 60 minutes to allow the glass composition to be uniformly mixed in the molten state. If the melting temperature is lower than 1,000 ° C, the melt viscosity is too high so that the respective components cannot be uniformly mixed.

Quenching refers to rapid cooling of the molten state of the glass composition in the melting step. The glass composition may be subjected to one or both of dry quenching and wet quenching.

The pulverization means that the quenched glass melt is first pulverized using a conventional pulverizer such as a ball mill, and then pulverized to a fine particle of a desired size twice to prepare a glass powder.

Meanwhile, the present invention provides an aluminum paste composition for forming a back contact of a solar cell using the zinc oxide-based glass dielectric composition.

The aluminum paste composition is a lead-free composition comprising aluminum powder, an inorganic binder, and an organic vehicle, wherein the aluminum paste composition contains the zinc oxide-based glass medium composition as described above as an inorganic binder.

The aluminum paste composition may comprise 40 to 90 wt% of aluminum powder, 0.1 to 10 wt% of an inorganic binder, and 1 to 50 wt% of an organic vehicle. The organic vehicle may be a mixture comprising 1 to 50% by weight of an organic binder, 45 to 95% by weight of an organic solvent, and 0.1 to 10% by weight of an additive.

If the content of the aluminum powder is less than 40% by weight, the compactness is lowered to attenuate the electrical properties; if the content of the aluminum powder is more than 90% by weight, it is difficult to control the viscosity and it is difficult to prepare a slurry. Specifically, if the content of the inorganic binder in the aluminum paste composition is less than 0.1% by weight, the adhesion between the fired film and the wafer may be lowered; if the content of the inorganic binder exceeds 10 wt%, The reaction between the aluminum of the glass and the wafer during firing is suppressed, and the electrical properties are lowered. Further, if the content of the organic vehicle is less than 1% by weight, it is difficult to exhibit the rheological property of the slurry in the case where the aluminum powder content exceeds 90% by weight; if the content of the organic vehicle exceeds 50% by weight, the calcination may be Will increase the number of holes and attenuate the electrical characteristics.

As described above, in the aluminum paste composition of the present invention, the zinc oxide-based glass medium of the present invention can be used alone as the inorganic binder, and when it is contained in an amount of 10% by weight or less, the bending phenomenon can be further improved. Further, a tantalum trioxide-based glass medium and a zinc oxide-based glass medium may be used in combination as an inorganic binder as needed.

Further, in the aluminum paste composition of the present invention, in addition to the zinc oxide-based glass medium, any of the components in the aluminum paste composition may be any material known to those skilled in the art.

For example, the aluminum powder may be spherical, non-spherical or flake, and has a purity of 80% or more, and an average particle diameter of 1 to 30 μm, more preferably 1 to 20 μm. The aluminum powder may include at least one component selected from the group consisting of silver (Ag), boron (B), gallium (Ga), indium (In), antimony (Tl), and antimony (Si).

The organic binder may include a cellulose derivative such as methyl cellulose, ethyl cellulose, nitro cellulose or hydroxyl cellulose; an acrylic resin ( Acrylic resin; alkyd resin; polypropylene based resin; polyvinyl chloride based resin; polyurethane based resin; epoxy based Polyether based resin; rosin based resin; terpene based resin; phenol based resin; aliphatic petroleum resin );acrylic ester based resin; xylene based resin; coumarone indene based resin; styrene based resin; dicyclopentane Dicyclopentadiene based resin; polybutene based resin; polyether based resin; urea-based tree A urea based resin; a melamine based resin; a vinyl acetate based resin; a polyisobutyl based resin; and the foregoing composition.

The organic solvent may include butylcarbitol acetate, butylcarbitol, propyleneglycol monomethylether, dipropyleneglycol monomethylether, propylene glycol Propyleneglycol monomethylether propionate, ethylether propionate, propyleneglycol monomethylether acetate, terpenol, texanol, dimethylformamidine Aminoamino formaldehyde, methyl ethyl ketone, gamma-butyrolactone, ethyl lactate, and combinations thereof.

The additive may include fatty acids to improve wettability and fluidity, such as oleic acid, maleic acid, palmitic acid, myristic acid, lauric acid. (lauric acid), stearic acid; a defoaming agent for reducing foam; a dispersing agent for improving dispersibility; a plasticizer for controlling the solubility of the organic binder; and the combination thereof Things. If an additive is used alone, the content may be from 0.1 to 10% by weight. If two or more additives are used, the two or more additive components are suitably mixed so that the content of the resulting mixture is in the range of 0.1 to 10% by weight.

Meanwhile, the present invention provides a back contact of a solar cell obtained by using the lead-free aluminum paste composition. The solar cell can be a germanium solar cell.

The manufacturing method of the back contact of the solar cell is well known to those skilled in the art, and thus detailed description thereof is omitted here.

For example, the aluminum paste composition can be printed on a substrate and dried by a conventional method such as screen printing, doctor blade, inkjet printing, or gravure printing. And firing to form the back contact. The substrate is not particularly limited and may include any tantalum substrate for a front contact of a solar cell. Further, the aforementioned drying may be carried out at 150 ° C to 350 ° C for 1 to 30 minutes, and the above calcination may be carried out at a maximum temperature of 750 ° C to 950 ° C for several seconds to 5 minutes.

By the above method, a solar cell having a back contact having a thickness of 20 to 40 μm can be obtained, and the formed back contact has good adhesion to the substrate and has the same as that of the conventional back contact or Better mechanical strength. Further, by using the zinc oxide-based glass dielectric composition having a low coefficient of thermal expansion, the substrate bending and cracking due to the difference in shrinkage ratio during cooling after baking can be minimized.

Therefore, the present invention can use the back contact to produce a tantalum solar cell having excellent properties such as a front contact, an emitter layer, an anti-reflection layer, and the like.

According to the present invention, since the back contact of the solar cell is formed using a zinc oxide-based glass dielectric composition having a specific composition having a low thermal expansion coefficient, the open circuit voltage can be improved by increasing the voltage across the top and bottom ends of the substrate of the solar cell. Thereby, the light conversion efficiency is improved, and more specifically, the bending of the substrate can be greatly reduced. Further, since the zinc oxide-based glass dielectric composition of the present invention does not use an expensive mercapto compound having a high coefficient of thermal expansion, the manufacturing cost and the efficiency can be improved. Furthermore, the moisture reaction stability of the substrate can be improved to avoid fading of the fired film and to avoid peeling of the aluminum fired film.

Hereinafter, the present invention will be further described by way of examples and comparative examples. However, the following examples and comparative examples are only illustrative of the invention and are not intended to limit the scope of the invention.

Comparative Examples 1 to 6 and Examples 1 to 8

The metal oxide was mixed by the following method to have a composition shown in the following Table 1 to prepare a glass medium composition (the unit in Table 1 is wt%).

Specifically, the raw materials corresponding to the components of Table 1 were thoroughly mixed for 2 hours using a gravity-free mixing device (non-gravity mixer, SONGYOUNGTECH, model DC200W, experimental stirring device). Thereafter, the foregoing mixture was melted at 1500 ° C for 30 minutes.

Subsequently, a quenching procedure is performed to quench the aforementioned molten glass composition for rapid cooling. In the process, the glass composition was removed from the melting furnace through a conveyor belt, and the temperature was room temperature, and it was rapidly cooled in 10 seconds and maintained for 30 minutes to stabilize. The aforementioned rapidly cooled glass melt is subjected to a first pulverization process via a ball mill and then secondarily pulverized to a desired particle size to prepare a glass powder.

After the preparation of the glass powder, the glass transition temperature (Tg), the softening point (Ts), and the coefficient of thermal expansion (CTE) of each composition were measured, and the measurement results are shown in Table 2 below.

From the results of Table 2, it was confirmed that the thermal expansion coefficients of Examples 1 to 8 of the present invention were lower than those of Comparative Examples 1 to 6, so that the bending of the substrate after baking can be improved.

Comparative Examples 7 to 12 and Examples 9 to 16

Each of the aluminum paste compositions of the comparative examples and the examples was prepared using a glass medium, aluminum powder, and an organic vehicle according to the composition and composition ratios shown in Tables 3, 4, and 5 below (Tables 3, 4, and 5). The unit is wt%). Among them, aluminum powder having an average particle diameter of 3 μm is used, and the organic vehicle used includes ethyl cellulose as an organic binder, diethylene glycol butyl ether acetate as an organic solvent, and oleic acid as an additive. With dispersant (1.5%, disperbyk-183). Thereafter, the moisture reaction stability and the light conversion property were evaluated by a conventional method.

The moisture reaction stability evaluation results of Comparative Example 8 and Example 11 are as shown in the second drawing, and the substrate bending evaluation results of Comparative Example 7 and Example 11 are as shown in the first figure.

The evaluation method of the humidity reaction stability will be described later.

Deionized water (DI water) was filled in the beaker and maintained at 70 ° C in an oven or on a hot plate. The fired wafer was immersed in a constant temperature beaker for 10 minutes, and it was confirmed whether or not bubbles were generated. Thereafter, the wafer was taken out from the beaker and thoroughly dried, and the adhesion of the film was confirmed by a tape test (if the moisture reaction stability was low, film peeling occurred). The evaluation criteria are as follows.

○: no bubbles were formed and no film was peeled off.

△: There is bubble generation or peeling of the fired film

╳: A large number of bubbles are generated and there is a film peeling off.

As shown in Tables 3 to 5, the implementation of the present invention having a specific composition was used as compared with Comparative Example 7 and Comparative Example 9 using a glass medium (Comparative Example 1 and Comparative Example 3) not containing a transition metal oxide. Examples 9 through 16 exhibited higher open circuit voltages and better light conversion efficiencies.

Further, Embodiments 9 to 16 of the present invention have a small substrate curvature, thereby reducing substrate breakage, and the fired film thereof exhibits excellent moisture reaction stability.

In contrast, Comparative Examples 7 to 12 generally exhibited poor electrical characteristics, moisture stability, and bending phenomenon. As shown in the first figure, although the moisture reaction of Comparative Example 7 was stable, it was necessary to use a mercapto compound, and since the substrate was bent to a large extent, the substrate may be broken. Further, Comparative Examples 9 to 12 exhibited poor electrical characteristics and moisture reaction stability as compared with Example 11, and the degree of bending of the substrate was large. Further, as shown in the second figure, Comparative Examples 8 and 9 exhibited poor moisture reaction stability as compared with Example 11, and peeling of the substrate fired film occurred.

Examples 17 to 22

In order to further evaluate the optimum glass composition of the wafer, the aluminum paste composition (the unit in Table 6 is wt%) was prepared using the glass medium of Example 3 according to the composition and composition ratio shown in Table 6 below. Further, the same aluminum powders, organic binders, organic solvents, and additives as in Examples 9 to 16 were used.

As shown in Table 6, in Examples 17 to 22 in which the glass medium of Example 3 of the present invention was used, although the electrical characteristics slightly decreased as the content of the glass medium increased, the foregoing examples still have the comparative examples as compared with the comparative examples. More excellent characteristics.

The first graph is a photograph showing the results of the bending evaluation of Comparative Example 7 and Example 11.

The second graph is a photograph showing the results of moisture reaction stability of Comparative Example 8 and Example 11.

Claims (14)

A glass medium composition for forming an aluminum paste composition for a back junction of a solar cell, the glass medium composition comprising: (a) 45 to 60 weight percent (wt%) of zinc oxide; (b) At least one metal oxide selected from the group consisting of 0.1 to 45 wt% ceria, 0.1 to 40 wt% boron trioxide, and 1 to 10 wt% aluminum oxide; (c) 0.1 Up to 20 wt% of a transition metal oxide, a lanthanide oxide, or a mixture of the foregoing oxides; (d) 3 to 5 wt% of phosphorus pentoxide; and (e) 3 to 5 wt% Yttrium oxide. The glass medium composition according to claim 1, wherein the glass medium composition has an average particle diameter of 0.5 to 20 μm, a water vapor content of 5% or less, and a thermal expansion coefficient of 50 × 10 ^-7 /°C to 150 × 10 ^-7 / ° C. The glass medium composition according to claim 1, wherein the glass medium composition further comprises 1 to 10% by weight of disodium oxidate based on the total amount of the glass medium composition. The glass medium composition according to claim 1, wherein the transition metal oxide is at least one selected from the group consisting of manganese monoxide, manganese dioxide, cobalt trioxide, cobalt sulphate, cobalt monoxide, titanium dioxide, vanadium pentoxide, and An oxide in a group consisting of copper oxide; and the lanthanide oxide is at least one selected from the group consisting of cerium oxide, antimony trioxide, antimony trioxide, antimony trioxide, antimony trioxide, and antimony trioxide. An oxide in the group formed. The glass medium composition according to claim 1, wherein the glass medium composition has at least one composition selected from the group consisting of ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -CeO ₂ -CoO, ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -BaO- P ₂ O ₅ -MnO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CoO, ZnO-SiO ₂ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Nd ₂ O ₃ -Co ₃ O ₄ ,ZnO- SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO-Co ₂ O ₃ -Tb ₂ O ₃ -CuO, and ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O _5- MnO-Co ₂ O ₃ -Pr ₂ O ₃ . A lead-free aluminum paste composition for forming a back contact of a solar cell, comprising aluminum powder, an inorganic binder, and an organic vehicle; wherein the aluminum paste composition comprises any one of claims 1 to 5 The glass medium composition is used as the inorganic binder. The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 6, wherein the aluminum paste composition comprises 40 to 90% by weight of the aluminum powder, and 0.1 to 10% by weight of the inorganic bonding agent. And 1 to 50 wt% of the organic vehicle. The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 7, wherein the organic carrier is a mixture comprising 1 to 50 wt% of one organic binder, and 45 to 95 wt% An organic solvent and from 0.1 to 10% by weight of an additive. A lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 6, wherein the glass medium composition is at least one selected from the group consisting of ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -CeO ₂ -CoO, ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO,ZnO -SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CeO ₂ ,ZnO- SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-CoO, ZnO-SiO ₂ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO ₂ -CuO, ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Na ₂ O-MnO ₂ -CoO-CeO ₂ , ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -Nd ₂ O ₃ -Co ₃ O ₄ , ZnO-SiO ₂ -B ₂ O ₃ -BaO-P ₂ O ₅ -MnO-Co ₂ O ₃ -Tb ₂ O ₃ -CuO, and ZnO-SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ -BaO-P ₂ O ₅ -MnO-Co ₂ O ₃ -Pr ₂ O ₃ . The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 8, wherein the organic binder is at least one selected from the group consisting of methyl cellulose and ethyl cellulose. , cellulose derivative of nitrocellulose or hydroxy cellulose, acrylic resin, alkyd resin, polypropylene-based resin, polyvinyl chloride resin, polyurethane-based resin, epoxy resin, polyoxyalkylene resin, rosin-based Resin, mercapto-based resin, phenol-based resin, aliphatic petroleum resin, acrylate-based resin, xylyl resin, benzofuran-mercapto resin, styrene-based resin, dicyclopentadienyl resin, polybutenyl Resin, polyether based resin, urea based resin, melamine based resin, vinyl acetate based resin, and polyisobutyl resin. The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 8, wherein the organic solvent is at least one selected from the group consisting of diethylene glycol butyl ether acetate and diethyl phthalate. Alcohol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether propionate, diethyl ether propionate, propylene glycol monomethyl ether acetate, terpene alcohol, alcohol ester, dimethylformamide Methyl acetal, methyl ethyl ketone, γ-butyrolactone, and ethyl lactate. The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 6, wherein the aluminum powder is spherical, non-spherical or flake, and has a purity of 80% or more, 1 to 30 μm. The average particle diameter, and the aluminum powder contains at least one component selected from the group consisting of silver, boron, gallium, indium, antimony, and cerium. The lead-free aluminum paste composition for forming a back junction of a solar cell according to claim 8, wherein the additive is at least one selected from the group consisting of oleic acid, maleic acid, palmitic acid, and meat. Myristic acid, lauric acid, stearic acid, a defoaming agent, a dispersing agent, and a plasticizer. A back contact for a solar cell, which is made using the lead-free aluminum paste composition described in claim 6.