TWI657119B - Paste composition for rear electrode of solar cell - Google Patents

Abstract

The present invention provides a paste composition for a back electrode of a solar cell, and a solar cell formed using the paste composition.

Description

Back electrode paste composition for solar cells

The present invention relates to a paste composition for a back electrode of a solar cell, and a solar cell formed using the paste composition.

Solar cells generate current and voltage based on the photovoltaic effect, in which electrons and holes are generated by absorbing light energy generated from the sun. The solar cell includes a semiconductor substrate and an emitter layer, and a PN junction is formed in the semiconductor substrate and the emitter layer, and a front electrode electrically connected to the emitter is formed on the emitter, and is opposite to the light incident surface. On the other surface, a back electrode electrically connected to the substrate is formed.

Since the light absorbed to the solar cell has various wavelengths, the refractive index changes depending on the wavelength, so that there is a wavelength range in which light is favorably absorbed. Generally, light of a longer wavelength will not be advantageously absorbed due to the smaller refractive index, but will be transmitted through the solar cell. Therefore, a passivation layer which enhances light absorption by reflecting light to be transmitted and passing the light again through the solar cell is included.

Passivated emitter and rear cell (PERC) type solar cells include a passivation layer located at the back surface of the wafer, and can improve the absorption rate of light incident on the solar cell, and prevent electrons generated The loss that occurs when combined with the hole. Here, the passivation layer is usually constructed of an aluminum oxide layer (Al ₂ O ₃ layer) and a tantalum nitride layer (SiN _x layer), wherein the aluminum oxide layer generates a fixed negative charge at the back surface of the solar cell. These negative charges cause the holes generated from the solar cell to move toward the back electrode, and thus, the amount of recombination of generated electrons and holes can be reduced to collect more electrons and holes, thereby increasing the open circuit voltage (open) Circuit voltage; Voc) and improve the efficiency of solar cells.

In passivated emitter and back electrode type solar cells, the aluminum electrode is impermeable to the passivation layer, and thus a partial back surface field (BSF) layer is formed by using an aluminum paste through the opening. Here, due to the difference in diffusion speed between aluminum (Al) and bismuth (Si), voids may occur, which lowers the open circuit voltage (Voc) and deteriorates the conversion efficiency. The occurrence of voids is usually higher than the diffusion rate of aluminum. Therefore, there is a need to develop a technique for changing the components in the paste.

Further, when the aluminum paste does not react with the passivation layer, fine aluminum particles are generated due to poor adhesion to the aluminum electrode, and the generated particles cause contamination on the front surface portion, which lowers the conversion efficiency. This also causes problems when manufacturing solar cell modules. In addition, conventional aluminum pastes have weak waterproof stability.

Therefore, it is necessary to study and develop an aluminum paste which has excellent waterproof stability and attains a predetermined level or higher adhesion to an electrode.

An aspect of the present invention is directed to a paste composition for a back electrode of a solar cell, which is capable of having excellent water resistance stability and improved adhesion to an electrode, thereby achieving high conversion efficiency. And high open circuit voltage.

Another aspect of the present invention is directed to a solar cell formed using the paste composition for a back electrode of a solar cell as described above.

In a general aspect, a paste composition for a back electrode of a solar cell includes: (a) an aluminum conductive powder, (b) a glass frit containing SiO ₂ , ZnO, Bi ₂ O ₃ , And B ₂ O ₃ , and (c) an organic vehicle.

In the paste composition for a back electrode of a solar cell according to an exemplary embodiment of the present invention, the glass frit may include 5% by weight to 30% by weight of SiO ₂ and 1% by weight to 20% by weight of ZnO. 10% to 60% by weight of Bi ₂ O ₃ and 5% by weight to 20% by weight of B ₂ O ₃ .

In another general aspect, a paste composition for a back electrode of a solar cell includes: (a) an aluminum conductive powder, (b ' ) a glass frit containing SiO ₂ , ZnO, Bi ₂ O ₃ , B ₂ O ₃ , PbO, and Al ₂ O ₃ , and (c) an organic carrier.

In the paste composition for a back electrode of a solar cell according to an exemplary embodiment of the present invention, the glass frit includes 5% by weight to 30% by weight of SiO ₂ , and 1% by weight to 20% by weight of ZnO, 10 From wt% to 60% by weight of Bi ₂ O ₃ , from 5% by weight to 20% by weight of B ₂ O ₃ , from 5% by weight to 50% by weight of PbO, and from 1% by weight to 20% by weight of Al ₂ O ₃ .

In the paste composition for the back electrode of a solar cell according to an exemplary embodiment of the present invention, the glass frit may have an average particle diameter of 0.5 μm to 5.0 μm.

In the paste composition for the back electrode of a solar cell according to an exemplary embodiment of the present invention, the glass frit may have a content of 0.6% by weight to 20% by weight based on the total weight of the paste composition.

In the paste composition for the back electrode of a solar cell according to an exemplary embodiment of the present invention, the aluminum conductive powder may have an average particle diameter of from 2 μm to 10 μm.

In a paste composition for a back electrode of a solar cell according to an exemplary embodiment of the present invention, an organic carrier may be obtained by dissolving an organic binder in a solvent, the organic binder comprising a cellulose selected from the group consisting of cellulose One or more of the group consisting of a resin, an acrylic resin, and a polyethylene resin.

Further, in another general aspect, a solar cell having a conventional structure or a passivated emitter and a back electrode (PERC) type structure is provided, which is formed using the paste composition as described above.

The paste composition for a back electrode of a solar cell according to the present invention can be excellent in waterproof stability, and can improve adhesion to an electrode, thereby achieving high conversion efficiency and high open circuit voltage.

Further, the present invention can provide a solar cell capable of having excellent stability and reliability and achieving high energy conversion efficiency by using the paste composition as described above.

Hereinafter, a paste composition for a back electrode of a solar cell according to the present invention, and a solar cell formed using the paste composition will be described in detail. The invention will be more fully understood from the following description of exemplary embodiments of the invention, which are not intended to limit the scope of the invention as defined by the appended claims. Here, unless otherwise defined by technical terms and scientific terms used herein, such terms have the meaning commonly understood by those skilled in the art to which the invention pertains.

The present invention is applicable to a solar cell having a conventional structure or a passivated emitter and a back electrode (PERC) type structure. Among them, the solar cells exemplified below are passivation emitters and back electrode type solar cells, but the present invention is not limited to passivation emitters and back electrode type solar cells.

The passivated emitter and back electrode type solar cells have a passivation at the back surface, so that the light absorption rate in the longer wavelength region can be improved, and the recombination of electrons and holes can be reduced to increase the short circuit current (Isc) and Open circuit voltage (Voc), thereby improving the efficiency of the solar cell. However, due to the presence of the passivation, it is necessary to form a partial back surface field layer. However, when an aluminum paste is applied, voids may occur due to a difference in diffusion speed between aluminum and tantalum. In addition, this reduces the adhesion to the electrodes, thereby reducing conversion efficiency and making it difficult to ensure the reliability of the module.

Accordingly, the inventors have conceived a paste composition for a back electrode of a solar cell, and completed the present invention, the paste composition including a combination of specific components, thereby suppressing the occurrence of the above-mentioned voids, so that the solar cell Maximizes efficiency while improving the traditional physical properties of aluminum pastes that are susceptible to water-resistant stability.

In the present invention, the paste composition for the back electrode of the solar cell is suitable It is applied to conventional solar cells, and passivated emitter and back electrode (PERC) type solar cells including a passivation layer, and is not limited to various operations including germanium semiconductor devices (generally referred to as solar cells). Further, the paste composition according to the present invention can effectively form a partial back surface field (BSF) layer having excellent reactivity between the tantalum and the aluminum interface, and can prevent contamination due to the passivation layer.

A paste composition for a back electrode of a solar cell according to a first aspect of the present invention may comprise: (a) an aluminum conductive powder, (b) a layer containing SiO ₂ , ZnO, Bi ₂ O ₃ , and B ₂ O ₃ a glass frit, and (c) an organic carrier.

The frit is free of lead, and each of the components of the frit serves as a major factor in waterproof stability and adhesion to the electrode, and these components can be combined with other components in the paste composition To achieve synergy.

In the glass frit according to the first aspect of the present invention, the content of each component of the glass frit may be controlled within the range in which the object of the present invention is achieved. Preferably, the glass frit may include 5% by weight to 30% by weight of SiO ₂ , 1% by weight to 20% by weight of ZnO, 10% by weight to 60% by weight of Bi ₂ O ₃ , and 5% by weight to 20% by weight. % of B ₂ O ₃ . Here, the insufficient content of the total weight of each component may be supplemented by further including one or more other oxides. As a specific example, any one or more selected from the group consisting of P ₂ O ₅ , Na ₂ O, K ₂ O, and Sb ₂ O ₃ may be included. In the glass frit, any one selected from the group consisting of P ₂ O ₅ , Na ₂ O, and K ₂ O may have a content of 0.1% by weight to 3% by weight, preferably 0.5% by weight to 2% by weight. Further, in the glass frit, Sb ₂ O ₃ may have a content of from 5% by weight to 20% by weight, preferably from 10% by weight to 16% by weight. When the above range is satisfied, excellent waterproof stability and adhesion to the electrode can be attained, and this is preferable in view of the improvement in the efficiency of the solar cell.

In addition to the first aspect of the invention as described above, the paste composition for a back electrode of a solar cell according to the present invention may further comprise any one of PbO and Al ₂ O ₃ as a glass frit component. In this case, the performance of the solar cell may be slightly deteriorated, but it is preferable in view of ensuring waterproof stability and improving adhesion to the electrode.

Further, the present invention provides a paste composition for a back electrode of a solar cell according to a second aspect of the present invention, which is capable of achieving water stability and stability without deteriorating solar cell performance Improvement of the adhesion of the electrodes.

The paste composition for a back electrode of a solar cell according to a second aspect of the present invention may comprise: (a) an aluminum conductive powder, (b ' ) containing SiO ₂ , ZnO, Bi ₂ O ₃ , B ₂ O ₃ , a glass frit of PbO, and Al ₂ O ₃ , and (c) an organic carrier.

The glass frit contains lead, and the waterproof stability and the adhesion to the electrode can be improved according to the combination of the components of the glass frit and the combination with other components in the paste composition, and more preferably, the quality can be maintained stably. Sex and reliability to enhance durability.

In the glass frit according to the second aspect of the present invention, the content of each component of the glass frit may be controlled within a range to attain the object of the present invention. Preferably, the glass frit may include 5 wt% to 30 wt% SiO ₂ , 1 wt% to 20 wt% ZnO, 10 wt% to 35 wt% Bi ₂ O ₃ , 5 wt% to 20 wt% B ₂ O ₃ , 5 wt% to 50 wt% PbO, and 1 wt% to 20 wt% Al ₂ O ₃ . Here, when the glass frit component satisfies the above range, the solar cell performance is more effectively improved, and good durability can be modified by reinforcing the adhesion to the electrode.

In the second aspect of the paste composition according to the present invention, more preferably, the paste composition includes a combination of PbO and Al ₂ O ₃ because this can ensure excellent solar energy in terms of conversion efficiency or open circuit voltage characteristics. The battery efficiency can be improved with physical properties such as adhesion to an electrode as compared with the case where the paste composition includes any one of PbO and Al ₂ O ₃ .

Here, the respective contents of PbO and Al ₂ O _{3 in} the glass frit may be controlled within a range that would achieve the object of the present invention. Preferably, the content of PbO is in the range of 5% by weight to 50% by weight, and the content of Al ₂ O ₃ is from 1% by weight to 20% by weight in view of durability, adhesion to electrodes, or resistance to bubble formation. The range of %.

As described above, the paste composition for the back electrode of the solar cell according to the present invention can be implemented in various aspects depending on the combination of the components of the glass frit.

In the paste composition for the back electrode of the solar cell according to the present invention, as a specific example, the glass frit may be SiO ₂ , ZnO, Bi ₂ O ₃ , B ₂ O ₃ , P ₂ O ₅ , Na ₂ O, K. ₂ O, and Sb ₂ O ₃ constitute, and as another specific example, the glass frit may be SiO ₂ , ZnO, Bi ₂ O ₃ , B ₂ O ₃ , PbO, Al ₂ O ₃ , Na ₂ O, SrO, K ₂ O and Sb ₂ O _{3 are} formed.

Here, the glass frit may preferably include 5% by weight to 30% by weight of SiO ₂ , 1% by weight to 20% by weight of ZnO, 10% by weight to 60% by weight of Bi ₂ O ₃ , and 5% by weight to 20% by weight. B ₂ O ₃ , 0% by weight to 50% by weight of PbO, and 0% by weight to 20% by weight of Al ₂ O ₃ . When the above range is satisfied, the viscosity of the paste is appropriately maintained, and specifically, the difference in diffusion speed between aluminum and tantalum is remarkably lowered, thereby preventing voids from being formed at the interface and improving the adhesion to the electrodes. Thereby, the conversion efficiency and the open circuit voltage are excellent and the efficiency of the solar cell is maximized by combining other components.

Specifically, SiO ₂ may have a content of from 5% by weight to 30% by weight, more preferably from 7% by weight to 21% by weight, based on the total weight of the glass frit. Further, ZnO may have a content of from 1% by weight to 20% by weight, more preferably from 5% by weight to 16% by weight, based on the total weight of the glass frit.

Further, Bi ₂ O ₃ may have a content of 10% by weight to 60% by weight, more preferably 12% by weight to 45% by weight, based on the total weight of the glass frit. In addition, when lead is included in the glass frit and Bi ₂ O _{3 is} used together with a combination of PbO and Al ₂ O ₃ , more preferably, in view of solar cell performance, Bi ₂ O ₃ is 10% by weight to 35% by weight. Preferably, the content is from 15% by weight to 30% by weight. For example, when Bi ₂ O ₃ is used together with PbO in a glass frit, when the content of Bi ₂ O ₃ is more than 35% by weight, the conversion efficiency and the open circuit voltage are deteriorated.

Further, B ₂ O ₃ may have a content of from 5% by weight to 20% by weight, more preferably from 10% by weight to 15% by weight, based on the total weight of the glass frit.

The frit may further comprise any one or more selected from the group consisting of PbO and Al ₂ O ₃ . Here, the PbO may have a content of from 5% by weight to 50% by weight, more preferably from 17% by weight to 43% by weight, based on the total weight of the glass frit. Further, Al ₂ O ₃ may have a content of from 1% by weight to 20% by weight, more preferably from 4% by weight to 8% by weight, based on the total weight of the glass frit.

When the components in the glass frit meet the respective content ranges, the present invention is better achieved according to the combination with other components in the glass frit and according to the combination of the aluminum conductive powder and the organic carrier in the paste composition. The desired efficacy of the invention.

When any one or more of the components of the glass frit are outside the above range, it is difficult to predict synergistic effects according to the combination of the components, and the solar cell performance may be poor, or the adhesion to the electrode may be weakened, And the waterproof stability can be reduced.

In the present invention, the conductive powder (a) includes aluminum as a main metal component. As the aluminum conductive powder, a single particle may be used, or particles having different characteristics may be mixed for use. In addition, the aluminum conductive powder may have a core-shell structure.

The aluminum conductive powder preferably has a spherical shape and may have a sheet type, a plate type, an amorphous type, or a combination thereof as the mechanical properties required.

The aluminum conductive powder may have an average particle diameter of from 0.5 μm to 10 μm, preferably from 1 μm to 9 μm. More preferably, the aluminum conductive powder may have an average particle diameter of from 1 micrometer to 7 micrometers. When satisfied In the above range, dispersibility and tightness are ensured, and it is advantageous to optimize the electrical performance of the solar cell. Further, it is preferred to mix and use conductive powders having different average particle diameters.

Further, the conductive powder may have a BET value of from 0.2 square meters / gram to 3.0 square meters / gram, preferably from 0.4 square meters / gram to 2.0 square meters / gram. When the above range is satisfied, it is advantageous to improve the electrical properties of the solar cell.

The conductive powder may include a conductive metal other than aluminum, and the conductive metal is not significantly limited. As an example, a suitable amount of a metal other than aluminum (for example, silver, copper, nickel, palladium, platinum, chromium, cobalt, tin, zinc, iron, ruthenium, osmium, tungsten, molybdenum, or magnesium) may be included, or The content of the alloy of the metal.

The aluminum conductive powder may have a content of 60% by weight to 95% by weight, preferably 65% by weight to 85% by weight, based on the total weight of the paste composition. When the above content is satisfied, phase separation can be suppressed, and printability is excellent due to good viscosity.

In the present invention, the glass frit includes the specific components exemplified in the first aspect, the second aspect, the third aspect, and the fourth aspect, and forms a paste with the organic carrier, and specifically When applied to a passivated emitter and a back electrode type solar cell, the reactivity at the back surface with the passivation layer can be improved and the adhesion to the electrode can be improved, thereby maximizing the efficiency of the solar cell and ensuring waterproof stability.

In the present invention, in the total content of the paste composition for the back electrode of the solar cell according to the present invention, the glass frit may preferably have from 0.1% by weight to 5.0% by weight, and more preferably from 0.5% by weight to 2.0% by weight. The content range. When the content range is satisfied, the reactivity at the interface can be good, and the adhesion to the electrode can be excellent, which can lower the contact resistance, and the efficiency of the solar cell can be maximized.

The glass frit may have a glass transition temperature (Tg) of from 300 ° C to 600 ° C, preferably from 300 ° C to 500 ° C. Further, the glass frit (b) of the present invention may have a softening point (Ts) of from 350 ° C to 750 ° C, preferably from 400 ° C to 650 ° C. When the above range of glass transition temperature and softening point is satisfied, it is advantageous to achieve desired physical properties.

Further, the glass frit may preferably have an average particle diameter of from 0.5 μm to 5.0 μm and preferably from 1.0 μm to 3.0 μm. It is preferable that the average particle diameter of the glass frit satisfies the above range, so that pinhole defects can be prevented from occurring when the electrode is formed.

For example, a frit is produced by melting the components together under atmospheric pressure and performing a cooling process to have overall glass properties. By the melting process, the corresponding components of the frit lose their properties as metal oxides due to bond breaks between the molecules, and the corresponding components in a molten state are homogeneously mixed and cooled to a glass. Here, the temperature and time of the melting process are not significantly limited, but preferably, the melting process may be performed at a melting temperature of 800 ° C to 1500 ° C for 10 minutes to 1 hour.

In the present invention, the organic vehicle (c) imparts viscosity and rheological properties to the composition by physically mixing the inorganic components of the paste for the back electrode to improve printability.

As the organic vehicle, an organic vehicle generally used for an electrode paste of a solar cell can be used. As an example, the organic vehicle can be a mixture of a polymer and a solvent. Preferably, the organic vehicle can be obtained by selecting a cellulose-based resin (for example, ethyl cellulose, methyl cellulose, nitrocellulose, cellulose ester, etc.), an acrylic resin (for example). At least one of a resin of rosin or alcohol polymethacrylate, acrylate or the like and a polyethylene resin (for example, polyvinyl alcohol, polyvinyl butyral, etc.) is added to at least one solvent selected from the group consisting of trimethyl Trimethyl pentanyl diisobutylate (TXIB), dibasic ester, Butyl carbitol (BC), butyl carbitol acetate, butyl carbitol, butyl cellosolve, butyl cellosolve acetate, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, Dimethyl dicarboxylate, dimethyl glutarate, propylene glycol monomethyl ether propionate, diethyl ether propionate, terpineol, propylene glycol monomethyl ether acetate, dimethylamino formaldehyde, methyl ethyl ketone, γ - Butyrolactone, ethyl lactate, and Texanol. More preferably, a solvent obtained by mixing butyl carbitol acetate, texasol, and terpineol is used.

The organic vehicle may have a content of from 10% by weight to 40% by weight, preferably from 15% by weight to 30% by weight, based on the total weight of the paste composition. When the organic carrier satisfies the above range, the conductive powder can be easily dispersed, and the conversion efficiency of the solar cell can be prevented from being deteriorated due to an increase in electric resistance due to residual carbon after firing.

In addition to the above components, the paste composition for the back electrode of a solar cell according to the present invention may further include general additives to improve flow properties, process properties, and stability. Examples of the additive may include a dispersant, a thickener, a thixotropic agent, a leveling agent, a plasticizer, a viscosity stabilizer, an antifoaming agent, a pigment, a UV stabilizer, an antioxidant, a coupling agent, etc., but the additive is not limited to This is the case.

Examples of the dispersing agent may include SOLSPERSE (LUBRISOL), DISPERBYK-180, 110, 996, and 997 (BYK), etc., but the dispersing agent is not limited thereto. Examples of the thickener may include BYK-410, 411, 420 (BYK Corporation, etc.), but the thickener is not limited thereto. Examples of the thixotropic agent may include THIXATROL MAX (ELEMENTIS), ANTI-TERRA-203, 204, 205 (BYK), etc., but the thixotropic agent is not limited thereto. Examples of the leveling agent may include BYK-3932 P, BYK-378, BYK-306, BYK-3440 (BYK), etc., but the leveling agent is not limited thereto. The organic additive may have about 1% by weight to about 100% by weight of the total paste composition for the back electrode 20% by weight.

Further, the present invention provides a solar cell having a conventional structure or a passivated emitter and a back electrode (PERC) type structure formed by including a paste composition for a back electrode as described above.

According to an exemplary embodiment of the present invention, the passivated emitter and back electrode type solar cell includes: a first conductive type substrate; a second conductive type emitter layer formed on the substrate; an anti-reflection a coating layer formed on the emitter layer; a front electrode penetrating the anti-reflective coating layer to be connected to the emitter layer; a passivation layer and a back surface electrode on the back surface of the substrate.

The first conductive type substrate is selected from the group consisting of a P type and an N type, and the second conductive type emitter layer is selected to have a conductivity type opposite to that of the substrate. To form a P+ layer, a group III element is doped as a dopant, and to form an N+ layer, a group V element is doped as a dopant. For example, to form a P+ layer, doping may be performed using B, Ga, and In, and to form an N+ layer, doping may be performed using P, As, and Sb. A P-N junction is formed at the interface between the substrate and the emitter layer, here a portion of the current that is generated according to the photovoltaic effect when sunlight is received. The electrons and holes generated by the photovoltaic effect can be attracted to the P layer and the N layer, respectively, and moved to a plurality of electrodes, and then, electricity can be generated by applying a load to the electrodes, and the electrodes are respectively connected to the substrate. The lower part and the upper part of the emitter layer.

The anti-reflective coating reduces the reflectivity of sunlight incident on the front side of the solar cell. When the reflectance of sunlight is lowered, the amount of light reaching the P-N junction increases, so that the short-circuit current of the solar cell is increased and the conversion efficiency of the solar cell is improved. As an example, the anti-reflective coating layer may have any single layer selected from the group consisting of a tantalum nitride film, a tantalum nitride film including hydrogen, a tantalum oxide film, and a hafnium oxynitride film, or a combination of two or more of the foregoing. Multi-layered knot However, the present invention is not limited to this.

The front electrode is formed by screen printing using a paste for a front electrode and then performing heat treatment. The front electrode penetrates the anti-reflective coating and is in contact with the emitter layer by a punch through phenomenon.

The passivation layer is formed on the back surface of the substrate and may be made of aluminum oxide (Al ₂ O ₃ ) and may be made of yttrium oxide (SiO ₂ ) or tantalum nitride (SiN). The passivation layer may have a thickness of from 1 nm to 50 nm. The passivation layer may be deposited by atomic layer deposition (ALD) or plasma enhanced chemical vapor deposition (PECVD).

The back electrode can be formed by screen printing on the back side of the passivation layer. The back electrode is formed using the paste composition for the back electrode of the solar cell according to the present invention. The back electrode is formed by first applying a paste composition, followed by drying and baking by a heat treatment process. The back electrode collects a hole (which is a charge that is moved from the substrate) and outputs the hole to an external device.

Hereinafter, although an embodiment of a paste composition for a back electrode of a solar cell according to the present invention is disclosed for the purpose of illustration, the present invention is not limited to the following examples.

(Examples 1 to 6 and Comparative Examples 1 to 6)

The components of the glass frit were placed in a reactor according to the composition shown in Table 1 and mixed, and melted at 1100 ° C for 30 minutes, and rapidly cooled by quenching with pure water (H ₂ O). . The rapidly cooled glass melt was ground into a powder by a ball-mill to prepare a glass frit having an average particle diameter of 2 μm.

Using the prepared glass frit to prepare a solar cell according to the present invention The paste composition of the back electrode.

Aluminum powder was used as the conductive powder. The aluminum powder had an average particle diameter of 5.0 μm and was used in an amount of 74.0% by weight. Further, the prepared glass frit was used at a content of 1.0% by weight, and an ethyl cellulose resin (ECN-50 of AQUALON) having a content of 2.0% by weight was used as a binder. As the solvent, 10.0% by weight of butyl carbitol acetate, 5.5% by weight of Texano, and 5.5% by weight of terpineol were used. 1.0% by weight of a thixotropic modifier (THIXATROL MAX from Haigens) and 1.0% by weight of an additive (oleic acid) were added as additives.

(Example 7)

Example 7 was carried out in the same manner as in Example 1 except that the content of the glass frit was changed to 0.5% by weight and the content of terpineol was changed to 6.0% by weight.

(Example 8)

Example 8 was carried out in the same manner as in Example 7, except that the content of the glass frit was changed to 1.5% by weight and the content of terpineol was changed to 5.0% by weight.

(Example 9)

Example 9 was carried out in the same manner as in Example 7, except that the content of the glass frit was changed to 2.0% by weight and the content of terpineol was changed to 4.5% by weight.

(Embodiment 10)

Example 10 was carried out in the same manner as in Example 7 except that the content of the frit was changed to 2.5% by weight and the content of terpineol was changed to 4.0% by weight.

(Manufacture of solar cells)

An emitter layer having a sheet resistance of 80 ohms/square was formed by performing phosphorus (P) doping by a diffusion process using a 156 mm crystalline germanium wafer in a tube furnace (850 ° C) using POCl ₃ . An anti-reflective coating was formed by depositing a tantalum nitride film having a thickness of 70 nm on the emitter layer by plasma enhanced chemical vapor deposition (PECVD) using precursors SiH ₄ and NH ₃ . DPS-1900V7 paste (Daewoo Co., Ltd.) was applied to the upper surface of the anti-reflective coating and dried. Subsequently, 1.3 g of the previously prepared paste composition for the back electrode was applied to the back surface of the crucible substrate, and dried at 250 ° C for 2 minutes. Here, the step of applying the front electrode and the back electrode is performed by screen printing (using a printer manufactured by ASYS) in a predetermined pattern.

In screen printing, a stainless steel wire 250 mesh having a frame of 450 mm x 450 mm is used. The film dried after screen printing had a thickness of 23 microns with a drying temperature of 250 °C. The obtained solar cell tantalum substrate was co-fired in a belt-type calciner at a maximum temperature of about 780 ° C for about 1 minute in an IN-OUT manner, thereby producing a desired solar cell.

The electrical properties (I-V properties) of the manufactured solar cells were tested using a solar simulator (SOL3A) manufactured by ORIEL. Ten sheet samples were made for each paste, and the properties of the fabricated solar cells were shown in Table 2 below for each of the ten sheet samples.

(assessment)

(1) Solar cell efficiency (conversion efficiency and open circuit voltage)

In the corresponding fabricated electrodes, the solar cell efficiency (Eff, %) and open circuit voltage (Voc, V) were measured using a measuring device for solar cell efficiency (PASNA, CT-801). ). Here, the respective measured values of the conversion efficiency and the open circuit voltage are It is calculated in a relative comparison manner by determining the result value according to Comparative Example 1 as a reference value (i.e., 100), and converting the measured value with the reference values.

(2) adhesion to the electrode

The tape (Tape, 3M Company, 810-ROK) was cut to a size of about 5 cm and completely adhered to the surface of the aluminum electrode of the fired solar cell, and the adhesive tape was quickly removed at an angle of 180 degrees. In Table 1, the case where the electrode is not adhered to the tape is marked as ○, and the case where the electrode is slightly adhered to the tape is marked as Δ (20% or less), and the electrode thereof is greater than 20%. The case of being attached is marked as ×.

(3) Time when bubbles appear

The calcined solar cell was immersed in deionized water at 75 ± 5 ° C to confirm and record the start time of the occurrence of bubbles on the surface of the aluminum electrode. The case where bubbles appeared after 15 minutes was marked as ◎. When bubbles begin to appear rapidly, the waterproof stability is low, and the reliability of the solar cell module is deteriorated.

As shown in Table 1, it was confirmed that Examples 1 to 3 corresponding to the paste composition including the lead-free glass frit according to the present invention have a conversion efficiency of up to 102.22% and an open circuit voltage of 100.89%, thereby making the solar cell It has excellent efficiency and meets the bonding force with the electrode and the time when the bubble appears. Further, it was confirmed that Examples 4 to 6 corresponding to the paste composition including the glass frit containing PbO and Al ₂ O ₃ according to the present invention have effects in solar cell efficiency, adhesion to electrodes, and prevention of bubble generation. . On the contrary, Comparative Examples 1 to 5 differed from the present invention in the composition of the glass frit, and therefore, there were problems in that the conversion efficiency and the open circuit voltage were remarkably lowered, the adhesion to the electrode was weakened, and bubbles or the like appeared.

Further, Examples 7 to 9 in which the content of the glass frit in the paste was changed according to the present invention exhibited excellent conversion efficiency and open circuit voltage as well as good adhesion to the electrode and resistance to bubble generation. Example 10 has a high content of frit, and therefore, conversion efficiency and open circuit voltage performance are slightly reduced.

In the above, the present invention has been described by way of specific exemplary embodiments, which are intended to provide a complete understanding of the invention. Accordingly, the invention is not limited to the exemplary embodiments. Various modifications and changes can be made by those skilled in the art in light of this disclosure.

Therefore, the spirit of the present invention should not be limited to the above-described exemplary embodiments, but the scope of the claims and the equivalents or equivalents of the scope of the claims are intended to be Within the spirit.

Claims (9)

A paste composition for a back electrode of a solar cell, comprising: (a) an aluminum conductive powder, (b) a glass frit comprising 5% by weight to 30% by weight of SiO ₂ , and 1% by weight to 20% by weight of ZnO, 10% to 60% by weight of Bi ₂ O ₃ , and 5% by weight to 20% by weight of B ₂ O ₃ , and (c) an organic vehicle. A paste composition for a back electrode of a solar cell, comprising: (a) an aluminum conductive powder, (b ' ) a glass frit, comprising 5% by weight to 30% by weight of SiO ₂ , and 1% by weight to 20% by weight ZnO, 10% by weight to 60% by weight of Bi ₂ O ₃ , 5% by weight to 20% by weight of B ₂ O ₃ , 5% by weight to 50% by weight of PbO, and 1% by weight to 20% by weight of Al ₂ O ₃ , and (c) an organic carrier. A paste composition for a back electrode of a solar cell according to claim 1, wherein the glass frit has an average particle diameter of from 0.5 μm to 5.0 μm. A paste composition for a back electrode of a solar cell according to claim 2, wherein the glass frit has an average particle diameter of from 0.5 μm to 5.0 μm. The paste composition for a back electrode of a solar cell according to claim 1, wherein the glass frit has a content of 0.1% by weight to 5.0% by weight based on the total weight of the paste composition. The paste composition for a back electrode of a solar cell according to claim 2, wherein the glass frit has a content of 0.1% by weight to 5.0% by weight based on the total weight of the paste composition. A paste composition for a back electrode of a solar cell according to claim 1, wherein the aluminum The conductive powder has an average particle diameter of from 0.5 μm to 10 μm. A paste composition for a back electrode of a solar cell according to claim 2, wherein the aluminum conductive powder has an average particle diameter of from 0.5 μm to 10 μm. A solar cell, which has a conventional structure or a passivated emitter and rear cell (PERC) type structure, and which utilizes the paste composition according to any one of claims 1 to 8. And formed.