KR20120051501A - Paste compisition for rear electrode of solar cell including the same, and solar sell - Google Patents

Abstract

PURPOSE: A paste composition is provided to form a backside electrode having high reflectivity. CONSTITUTION: A paste composition comprise: conductive powder containing spherical powder and non-spherical powder; an organic vehicle containing a solvent and a binder; and a glass frit. The binder comprises a first binder containing at least one of cellulose acetate butyrate and cellulose acetate propionate. The non-spherical powder comprises at least one selected from a group consisting of aluminum, nickel, gold, silver, palladium, platinum, and alloys thereof.

Description

Paste composition for back electrode of solar cell and solar cell {PASTE COMPISITION FOR REAR ELECTRODE OF SOLAR CELL INCLUDING THE SAME, AND SOLAR SELL}

The present substrate relates to a paste composition for a front electrode of a solar cell and a solar cell.

Recently, due to the depletion of fossil fuels, the importance of developing the next generation of clean energy is increasing. Among them, solar cells are expected to be an energy source that can solve future energy problems due to low pollution, infinite resources, and long-lasting life.

Such solar cells may include front and back electrodes formed on a silicon substrate. In order to improve efficiency and the like, an additional reflective layer for reflection may be further provided on the rear surface of the silicon substrate. However, separately forming such reflective layers has a problem of complicated process and increased manufacturing cost.

Embodiments provide a solar cell having a paste composition capable of forming a back electrode having high reflectivity and a back electrode prepared thereby.

Paste composition for a back electrode of a solar cell according to the embodiment, the conductive powder comprising a spherical powder and a non-spherical powder; An organic vehicle comprising a solvent and a binder; Glass frit. The binder includes a first binder including at least one of cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP).

The non-spherical powder may include at least one selected from the group consisting of aluminum, copper, nickel, gold, silver, palladium, platinum and alloys thereof.

The spherical powder may comprise aluminum.

The non-spherical powder may be included by 0.1 to 10% by weight based on the entire conductive powder. In this case, the non-spherical powder may be included by 0.1 to 5% by weight based on the entire conductive powder.

The organic vehicle may be included by 15 to 25% by weight based on the whole paste composition for the back electrode of the solar cell. The binder may be included in an amount of 5 to 15% by weight based on the entire organic vehicle.

The binder may comprise a second binder comprising ethyl cellulose. The first binder may be included by 50 to 70% by weight based on the entire binder.

An additive may be further included with respect to the entire front electrode paste composition of the solar cell. The conductive powder is 50 to 90% by weight, the organic vehicle is 10 to 50% by weight, the glass frit is 1 to 20% by weight, and the additive is 0.1 to 10% by weight based on the entire front electrode paste composition of the solar cell. As many as can be included.

The solar cell according to the embodiment includes a back electrode formed by using the paste composition for the back electrode described above.

According to this embodiment, the conductive powder comprises non-spherical powders and the binder includes CAB or CAP, so that when the paste composition is sintered, the CAB or CAP self-aligns the non-spherical powders to improve the reflectivity of the back electrode. can do. In particular, the light of the long wavelength region may be reflected from the rear surface without transmitting the light.

Accordingly, the overall photocurrent is increased and the recombination rate of the carrier is small, thereby improving efficiency.

In addition, since the reflectivity of the rear electrode itself can be improved, it is not necessary to form a separate reflective layer for improving reflection, so that the reflectivity can be improved without adding a manufacturing process and manufacturing cost.

1 is a cross-sectional view showing an embodiment of a solar cell.
2 is a graph showing the reflectivity of the solar cell including a back electrode prepared according to Examples 1 to 4, Comparative Example.

In the description of embodiments, each layer, region, pattern, or structure may be “on” or “under” the substrate, each layer, region, pad, or pattern. Substrate formed in ”includes all formed directly or through another layer. Criteria for the top / bottom or bottom / bottom of each layer will be described with reference to the drawings.

The thickness or the size of each layer (film), region, pattern or structure in the drawings may be modified for clarity and convenience of explanation, and thus does not entirely reflect the actual size.

Hereinafter, the paste composition for back electrodes ("paste composition") used for formation of the solar cell which concerns on this invention, and the back electrode of this solar cell is demonstrated in detail.

An example of a solar cell to which the paste composition of the present invention can be applied will be described with reference to FIG. 1. 1 is a cross-sectional view showing an embodiment of a solar cell.

Referring to FIG. 1, a solar cell includes a p-type silicon substrate 10 including an n-type semiconductor portion 11 on its front surface, a front electrode 12 and a p-type electrically connected to the n-type semiconductor portion 11. And a back electrode 13 electrically connected to the silicon substrate 10. An anti-reflection film 14 may be formed on the top surface of the n-type semiconductor unit 11 except for the front electrode 12. In addition, a back surface field (BSF) 15 may be formed on the silicon substrate 10 on which the back electrode 13 is formed.

The paste composition of the present invention can be used to form the back electrode 13 of such a solar cell. That is, the paste composition of the present invention may be applied to the silicon substrate 10, dried, and then fired to form the back electrode 13. In one example, the composition of the paste may be dried for 1 to 30 minutes at 80 ~ 200 ℃, it may be fired by rapid heat treatment at 700 ~ 900 ℃.

Such paste compositions may include conductive powders, organic vehicles, glass frits, and additives.

In the present embodiment, the conductive powder includes spherical powder and non-spherical powder. As the non-spherical powder may be used a powder having a plate, bell or flake shape. Aspherical powder is added to improve the reflectivity of the rear electrode 13, which will be described in more detail later.

As spherical powder, aluminum powder which forms the main component of the back electrode 13 can be used. As the non-spherical powder, aluminum, copper, nickel, gold, silver, palladium, platinum, an alloy containing the same, and the like having excellent reflectance may be used.

The average particle diameter of the conductive powder may be 0.1 ~ 30 ㎛. If the average particle diameter is less than 0.1 μm, there may be less space for organic matter to enter between the conductive powders, so that dispersion may not be smooth. And when the average particle diameter exceeds 30㎛, there are many voids between the conductive powder, so that the density can be lowered and the resistance can be increased. Considering the dispersing characteristics and the density, the average particle diameter of the conductive powder may be 0.1 ~ 10㎛. However, the present invention is not limited thereto, and of course, conductive powders having various particle diameters may be used.

Here, in the case of the spherical powder, the average particle diameter of the conductive powder may be obtained based on the particle size, and in the case of the non-spherical powder, based on the length of the long side.

As the conductive powder, single particles may be used, or particles having different particle diameters or the like may be mixed and used.

Such conductive powder may be included by 50 to 90% by weight based on the whole paste composition. If the conductive powder is included in excess of 90% by weight it may be difficult to form the composition in a paste state. When the conductive powder is included in less than 50% by weight, the amount of the conductive powder may be reduced, so that the electrical conductivity of the manufactured rear electrode 13 may be low.

And the non-spherical powder may be included by 0.1 to 10% by weight based on the entire conductive powder. Here, when the non-spherical powder is included in excess of 10% by weight, the overall viscosity of the paste composition may be high, and thus, it may be difficult to form the paste, thereby degrading printing characteristics. If the non-spherical powder is included in less than 0.1% by weight it may be difficult to fully implement the effect of improving the reflectivity of the rear electrode (13).

In consideration of printing characteristics, the non-spherical powder may be included in an amount of 0.1 to 5% by weight based on the entire conductive powder, and more preferably 0.1 to 2% by weight of the non-spherical powder.

 The organic vehicle may be one in which a binder is dissolved in a solvent, and may further include an antifoaming agent and a dispersant. As the solvent, organic solvents such as terpineol and carbitol can be used. As the binder, cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), or the like may be used as the first binder. Along with this CAB or / and CAP, an acrylic resin, a cellulose resin, an alkyd resin, or the like may further use a second binder. Since the first binder CAB, CAP, etc. may not have a hydroxyl group (OH), the viscosity may be low. Therefore, the paste composition may have a desired viscosity by adding a second binder such as ethyl cellulose (EC), which may have a hydroxyl group to increase the viscosity. Can have The second binder is not essential and can be added as necessary according to the desired viscosity or the like.

Here, the first binder of CAB and CAP serves to align the non-spherical powders by self-aligning the non-spherical powders by the functional groups present in the binder when the solvent is evaporated when the paste composition is sintered. Thereby, the reflectivity of the back electrode 13 can be improved. In particular, the reflectivity of the rear electrode 13 may be improved by improving the reflectivity of light in the long wavelength region.

The organic vehicle powder may be contained by 10 to 50% by weight based on the whole paste composition. Here, when the organic vehicle is included in excess of 50% by weight, the electrical conductivity of the rear electrode 13 may be lowered. When the organic vehicle is included in less than 10% by weight, the bonding property with the silicon substrate 10 may be degraded. At this time, in consideration of the electrical conductivity and bonding properties, the organic vehicle may be included by 15 to 25% by weight based on the whole paste composition.

The binder may be included in an amount of 5 to 15 wt% based on the entire organic vehicle. Here, when the binder is included in excess of 15% by weight, the binder may not be easily dissolved in the solvent. When the binder is included in less than 5% by weight, the bonding property with the silicon substrate 10 may be degraded.

When the second binder is included together with the first binder, the first binder may be included in an amount of 50 to 70 wt% based on the total binder. This is to optimize the paste composition viscosity while maximizing the effect of the first binder, such as CAB, CAP, self-aligning the non-spherical powder. However, the present invention is not limited thereto, and it is also possible to use only the first binder without the second binder.

Glass frits include PbO-SiO ₂ , PbO-SiO ₂ -B ₂ O ₃ , ZnO-SiO ₂ , ZnO-B ₂ O ₃ -SiO ₂ , Bi ₂ O ₃ -B ₂₃ -ZbO-SiO ₂ And the like can be used.

Glass frit may be included by 1 to 20% by weight based on the whole paste composition. The glass frit can improve the adhesive force, the sinterability, and the post-processing characteristics of the solar cell within the range of 1 to 20% by weight.

The additive may further include a thixotropic agent, a leveling agent, an antifoaming agent, and the like. The thixotropic agent may be a polymer / organic substance such as urea-based, amide-based, urethane-based or inorganic silica or the like.

The additive may be included by 0.1 to 10% by weight based on the whole paste composition. In this range, the conductive powder may be added in a sufficient amount to maintain the electrical conductivity at a high level, and may exert the effect by the additive. At this time, the additive is preferably contained by 0.2 to 5% by weight based on the whole paste composition.

Such a paste composition can be prepared by the following method.

The binder is dissolved in a solvent and then pre-mixed to form an organic vehicle. The conductive powder and the additive are added to the organic vehicle and aged for 1 to 12 hours. At this time, the glass frit may be added together. The aged mixture is mechanically mixed and dispersed through a 3 roll mill. The mixture is filtered and defoamed to prepare a paste composition. However, this method is only presented as an example and the present invention is not limited thereto.

The solar cell including the back electrode 13 formed by using the paste composition according to the present exemplary embodiment may have improved reflectivity to increase the overall photocurrent and decrease the recombination rate of the carrier, thereby improving efficiency.

In addition, since the reflectivity of the rear electrode 13 itself can be improved, it is not necessary to form a separate reflective layer for improving reflection, so that the reflectivity can be improved without adding a manufacturing process and manufacturing cost.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example  One

The organic vehicle was prepared by dissolving a binder in a solvent. A mixed solvent of diethylene glycol monobutyl ether acetate and α-terpineol was used as a solvent, and CAP was used as a binder.

The conductive vehicle, glass frit and additives were added to the organic vehicle and then mixed. It was aged for 12 hours and then mixed and dispersed in a second roll using a 3 roll mill. It was filtered and defoamed to form a paste composition.

At this time, the paste composition contained 20% by weight of organic vehicle [90% by weight of organic solvent, 10% by weight of binder], 75% by weight of conductive powder, and 5% by weight of glass frit. As the conductive powder, 70 wt% spherical aluminum powder and 5 wt% non-spherical aluminum powder were used with respect to the entire paste composition. Example 2

A rear electrode was manufactured in the same manner as in Example 1, except that a binder having a CAP of 50% by weight and an EC of 50% by weight was used.

Example  3

A back electrode was prepared in the same manner as in Example 1, except that CAB was used instead of CAP as a binder.

Example  4

A rear electrode was prepared in the same manner as in Example 3, except that a binder having a CAB of 70% by weight and an EC of 30% by weight was used.

Comparative example

A back electrode was prepared in the same manner as in Example 1, except that EC was used as the binder.

Table 1 shows the short-circuit current (I _SC ), the open circuit voltage (V _OC ), the fill factor, and the efficiency of the solar cell including the front electrode manufactured by Examples 1 to 4 and the comparative example. . And the reflectivity according to Examples 1 to 4, Comparative Example was measured and shown in FIG. Reflectance was measured by 0-vis reflection of light from 300nm to 1200nm using a UV-visible spectrophotometer (UV-visible spectrophotometer).

Short circuit current [A] Open voltage [V] Filling rate efficiency[%] Example 1 8.52 0.626 0.768 17.15 Example 2 8.49 0.628 0.764 17.01 Example 3 8.51 0.625 0.76 16.92 Example 4 8.52 0.624 0.761 16.93 Comparative example 8.51 0.625 0.739 16.43

Referring to Table 1, it can be seen that the solar cells according to Examples 1 to 4 have excellent filling rate and efficiency as compared with the comparative examples. And, referring to Figure 2, it can be seen that the solar cells according to Examples 1 to 4 have excellent reflectivity, especially at a wavelength of 1000nm or more than the comparative example.

The features, structures, effects and the like described in the foregoing embodiments are included in at least one embodiment of the present invention and are not necessarily limited to one embodiment. In addition, the features, structures, effects, and the like illustrated in the embodiments may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

In addition, the above description has been made with reference to the embodiments, which are merely examples and are not intended to limit the invention. It will be appreciated that various modifications and applications are possible. For example, each component specifically shown in the embodiments may be modified and implemented. It is to be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

Claims (11)

Conductive powders including spherical powders and non-spherical powders;
An organic vehicle comprising a solvent and a binder; And
Glass frit
Including,
The paste composition of claim 1, wherein the binder comprises a first binder including at least one of cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP). The method of claim 1,
The non-spherical powder is a paste composition for a back electrode of a solar cell comprising at least one selected from the group consisting of aluminum, copper, nickel, gold, silver, palladium, platinum and an alloy containing the same. The method of claim 1,
Paste composition for a back electrode of a solar cell, wherein the spherical powder comprises aluminum. The method of claim 1,
The aspherical powder is paste composition for a back electrode of a solar cell is contained by 0.1 to 10% by weight based on the entire conductive powder. The method of claim 4, wherein
The non-spherical powder is paste composition for a back electrode of a solar cell is contained by 0.1 to 5% by weight based on the entire conductive powder. The method of claim 1,
The organic vehicle is a paste composition for a back electrode of a solar cell is contained by 15 to 25% by weight relative to the entire back electrode paste composition of the solar cell. The method of claim 1,
The binder is a paste composition for a back electrode of a solar cell is contained by 5 to 15% by weight based on the entire organic vehicle. The method of claim 1,
Paste composition for a back electrode of a solar cell, wherein the binder comprises a second binder comprising ethyl cellulose. The method of claim 8,
Paste composition for a back electrode of a solar cell, wherein the first binder is included by 50 to 70% by weight based on the entire binder. The method of claim 1,
Further comprises an additive,
The conductive powder is 50 to 90% by weight, the organic vehicle is 10 to 50% by weight, the glass frit is 1 to 20% by weight, and the additive is 0.1 to 10% by weight based on the entire front electrode paste composition of the solar cell. Paste composition for a rear electrode is included as much. A solar cell comprising a back electrode formed using the paste composition for back electrode according to any one of claims 1 to 10.

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