KR101323199B1 - Electrode paste for solar cell and manufacturing method of solar cell using the same - Google Patents

Abstract

PURPOSE: An electrode paste for a solar cell and a method for manufacturing the solar cell using the same are provided to prevent the generation of Kirkendall voids by forming a back electrode using the powder of a core shell structure. CONSTITUTION: A substrate is prepared (S10). An emitter layer is formed on the front surface of the substrate (S20). An anti-reflection layer is formed on the upper part of an emitter layer (S30). A passivation layer is formed on the back surface of the substrate (S40). A front electrode is formed on the upper part of the anti-reflection layer (S70). [Reference numerals] (AA) Start; (BB) End; (S10) Substrate preparation step; (S20) Emitter layer forming step; (S30) Anti-reflection layer forming step; (S40) Passivation layer forming step; (S50) Barrier film forming step; (S60) Contact area forming step; (S70) Front electrode forming step; (S80) Back electrode forming step

Description

Electrode paste for solar cell and solar cell manufacturing method using same {Electrode Paste for Solar Cell and Manufacturing Method of Solar Cell using the same}

The present invention relates to a solar cell electrode paste and a solar cell manufacturing method using the same.

Solar cells are classified into crystal systems, amorphous systems, compound systems and the like depending on the kind of materials used, and crystal silicon solar cells are classified into monocrystalline type and polycrystalline type.

Single crystal silicon solar cell is easy to high efficiency because the quality of the substrate is good, but there is a disadvantage that the manufacturing cost of the substrate is large. On the other hand, polycrystalline silicon solar cells have a disadvantage in that high efficiency is difficult because the quality of the substrate is relatively poor compared to single crystal silicon solar cells.

In addition, the passivation effect is very important in terms of life and efficiency of the solar cell. The crystalline silicon solar cell first forms an emitter and then deposits an Al ₂ O ₃ film before or after the anti-reflective coating process, or deposits a SiO ₂ film before the anti-reflective coating to form a passivation film. Next, after Al paste is applied to the back of the solar cell, the Al paste penetrates the Al ₂ O ₃ film, which is a passivation film, to be in electrical contact with the back of the silicon substrate, or forms a via hole for electrode contact, and Al on the back of the passivation film. The paste is applied to form the back electrode. Alternatively, after the barrier layer is formed on the rear surface of the passivation layer, a via hole for the rear electrode contact is formed and an Al paste is applied on the rear surface of the barrier layer to form the rear electrode.

However, since the back electrode is formed of Al paste, the Si-Al intermetallic compound is formed at the junction interface with the substrate formed of Si, and the Kirkendall void is formed so that the electrical contact is not good. The electrical resistance is increased and there is a problem of lowering the efficiency of the solar cell.

The present invention provides an electrode paste for a solar cell and a method of manufacturing a solar cell using the same, which can reduce contact resistance by improving contact between a rear electrode and a substrate.

The electrode paste for a solar cell of the present invention is characterized in that it comprises a core-shell electrode powder, a binder and a solvent in which a silicon powder and a glass frit are coated on a surface of an aluminum powder. In this case, the silicon powder may be included in 1 to 15wt% relative to the total weight of the aluminum powder. In addition, the silicon powder may be formed of nanoparticles smaller in size than the aluminum powder.

In addition, the glass frit may be formed of nano particles having a smaller size than the aluminum powder.

In addition, the solar cell manufacturing method using the electrode paste of the present invention is a substrate preparation step of preparing a substrate of the first conductivity type, and an Emmy to form an emitter layer of the second conductivity type located on the front surface of the substrate A layer forming step, an antireflection film forming step of forming an antireflection film on top of the emitter layer, a passivation film forming step of forming a passivation film on the rear surface of the substrate, and an upper part of the antireflection film formed on the antireflection film and electrically Forming a front electrode connected to the front surface; and forming a rear electrode electrically connected to a rear surface of the substrate by applying an electrode paste to a rear surface of the passivation layer, wherein the electrode paste includes: Core formed by coating silicon powder and glass frit on the surface of aluminum powder (Core-shell) characterized by comprising the electrode powder, binder and solvent in the structure.

In addition, the forming of the rear electrode may be performed by first applying the electrode paste to the rear surface of the passivation layer, and then applying a general electrode paste.

In addition, the passivation film may be formed of an Al ₂ O ₃ film, a SiO 2 film or a SiN film.

In addition, the solar cell manufacturing method using the electrode paste of the present invention is a barrier film forming step of forming a silicon-based barrier film on the back surface of the passivation film, and removing the passivation film and a portion of the barrier film to remove the contact region on the back surface of the substrate And exposing a contact region, wherein the electrode paste is applied to a rear surface of the barrier layer to be in contact with a contact region of a rear surface of the substrate.

According to the solar cell electrode paste of the present invention and a solar cell manufacturing method using the same, Si is formed at a junction interface between the rear electrode and the substrate because the rear electrode is formed by using a core-shell powder coated with silicon powder on the surface of aluminum particles. It is possible to prevent the formation of kekendal voids in the -Al intermetallic compound to improve the contact between the back electrode and the substrate, reduce the contact resistance between the back electrode and the substrate, and increase the efficiency of the solar cell.

According to the electrode paste for a solar cell of the present invention and a solar cell manufacturing method using the same, the aluminum paste is manufactured by using a core shell structure powder coated with silicon particles having a relatively small size on the surface of the aluminum powder. It is mixed uniformly as a whole, silicon is uniformly distributed in the rear electrode, and the contact between the rear electrode and the substrate is improved uniformly as a whole.

1 is a flow chart of a solar cell manufacturing method according to an embodiment of the present invention.
2 is a partial perspective view of a solar cell manufactured by a solar cell manufacturing method according to an embodiment of the present invention.

Hereinafter, a solar cell electrode paste and a solar cell manufacturing method using the same will be described with reference to the accompanying drawings.

1 is a flow chart of a solar cell manufacturing method according to an embodiment of the present invention. 2 is a partial perspective view of a solar cell manufactured by a solar cell manufacturing method according to an embodiment of the present invention. 3 is a horizontal cross-sectional view showing the core shell structure of the electrode powder constituting the electrode paste according to the embodiment of the present invention.

In the solar cell manufacturing method according to an embodiment of the present invention, referring to Figures 1 and 2, the substrate preparation step (S10), the emitter layer forming step (S20), the passivation film forming step (S40), and the back electrode forming step It includes (S80). The solar cell manufacturing method may further include an anti-reflection film forming step (S30), a barrier film forming step (S50), a contact region forming step (S60), and a front electrode forming step (S70).

Meanwhile, hereinafter, the solar cell manufacturing method according to an embodiment of the present invention will be described with reference to the case of applying to a p-type solar cell, but of course can also be applied to the production of n-type solar cell. In addition, when the solar cell manufacturing method is applied to the manufacture of n-type solar cells, it is possible to deposit on both sides of the n-type substrate by atomic layer deposition.

The substrate preparing step (S10) is a step of preparing a substrate 10 forming a base of the solar cell. The substrate 10 is a semiconductor substrate made of silicon of a first conductivity type, for example a p-type conductivity. When the substrate 10 has a p-type conductivity type, it contains impurities of trivalent elements such as boron (B), gallium, indium, and the like.

The front surface and the rear surface of the substrate 10 may have a fine texturing structure or a concave-convex structure (not shown) through wet etching, such as acid etching, to reduce reflectance. Here, the front surface means an upper surface on which the front electrode is formed in FIG.

Meanwhile, the substrate 10 may be an n-type conductivity type. When the substrate 10 has an n-type conductivity type, the substrate 10 may contain impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb).

The emitter layer forming step S20 may include an impurity portion having a second conductivity type, for example, an n-type conductivity type, opposite to the conductivity type of the substrate 10 on the entire surface where light is incident from the substrate 10. Forming the emitter layer 20 as a step. The emitter layer 20 may be formed by a general method used in manufacturing a solar cell. For example, the emitter layer 20 forms a texturing surface on the front surface of the substrate 10 and diffuses impurities into the substrate 10 to form an emitter layer 20 having a predetermined thickness. Thereafter, the emitter layer 20 having an impurity concentration of solid solubility or higher is etched to form a textured surface. In order to increase the amount of charge transfer, the emitter layer 20 may remove a predetermined region having an impurity concentration above solid solubility as described above.

The emitter layer 20 forms a p-n junction with the substrate 10. Due to the built-in potential difference caused by the pn junction, the electron-hole pairs, which are charges generated by light incident on the substrate 10, are separated into electrons and holes, and electrons move toward the n-type The hole moves to the p-type side. Therefore, when the substrate 10 is p-type and the emitter layer 20 is n-type, the separated holes move toward the substrate 10, and the separated electrons move toward the emitter layer 20.

In addition, when the substrate 10 has an n-type conductivity type, the emitter layer 20 has a p-type conductivity type. In this case, the separated electrons move toward the substrate 10, and the separated holes move toward the emitter layer 20. When the emitter layer 20 has an n-type conductivity type, the emitter layer 20 doped the substrate 10 with impurities of pentavalent elements such as phosphorus (P), arsenic (As), antimony (Sb), and the like. Can be formed. In contrast, when the emitter layer 20 has a p-type conductivity type, the emitter layer 20 includes impurities of trivalent elements such as boron (B), gallium (Ga), and indium (In) on the substrate 10. Can be formed by doping.

The anti-reflection film forming step (S30) is a step of forming the anti-reflection film 30 on the emitter layer 20. The anti-reflection film 30 may be formed of an anti-reflection film formed on a general solar cell. For example, the anti-reflection film 30 may be formed of an insulating film such as SiN _x . In addition, the anti-reflection film 30 may be made of a material such as TiO ₂ , MgO, ITO, SnO ₂ , ZnO, or the like. The anti-reflection film 30 may be formed by plasma enhanced chemical vapor deposition (PECVD). Meanwhile, the anti-reflection film 30 may play a role of a passivation layer together with a role of an anti-reflection layer. In addition, the anti-reflection film 30 may be formed after a separate passivation film (not shown) is formed on the emitter layer 20.

The passivation film forming step (S40) is a step of forming the passivation film 40 on the rear surface of the substrate 10. The passivation film 40 is formed of an Al ₂ O ₃ film, and may be formed of an SiO 2 film or a SiN film. The passivation film 40 may be formed to a thickness of 5 ~ 50nm. The passivation film 40 is formed by deposition by atomic layer deposition (ALD) or plasma enhanced CVD (PECVD). The passivation film forming step (S40) uses Al (OC ₂ H ₅ ) ₃ (Tri Methyl Aluminum; TMA) as a source and uses water vapor (H ₂ O) or ozone (O ₃ ) as an oxygen source, and a process It may proceed at a temperature of 100 ℃ to 450 ℃. Meanwhile, when the passivation film 40 is formed by the atomic film deposition method, the passivation film 40 may be formed on the front surface of the emitter layer 20 as well as the back surface of the substrate 10.

On the other hand, the passivation film forming step (S40) may be performed before the anti-reflective film forming step (S30).

The barrier film forming step (S50) is a step of forming a silicon barrier film 50 on the back surface of the passivation film (40). The barrier film 50 may be formed of a SiNx film or a SiON film. The barrier layer 50 may be formed by atomic layer deposition (ALD) or plasma enhanced CVD (PECVD). When the barrier film 50 is formed of a SiON film, film formation is performed while supplying N ₂ O gas together with a source gas for forming a SiN x film.

The barrier layer 50 may be omitted according to the characteristics of the passivation layer 40.

The contact region exposing step S60 is a step of exposing the contact region 10a on the rear surface of the substrate 10 by removing a portion of the passivation layer 40 and the barrier layer 50 formed on the rear surface of the substrate 10. . Here, the contact region 10a refers to a region in which the back electrode 70 directly contacts the substrate 10. The contact region exposing step S60 may be performed by an etching process generally used in a semiconductor process, and a detailed description thereof will be omitted.

In the contact area exposing step S60, first, a lower via hole 50a is formed to penetrate the barrier layer 50 to expose the rear surface of the passivation layer 40, and is further connected to the lower via hole 50a and the passivation layer ( An upper via hole 40a penetrating through 40 is formed. The upper via hole 50a exposes the contact region 10a on the rear surface of the substrate 10.

Meanwhile, the contact region exposing step S60 may be omitted when only the passivation layer 40 is formed on the rear surface of the substrate.

The front electrode forming step (S70) is a step of forming the front electrode 60 electrically connected to the emitter layer 20 and formed on the upper surface of the anti-reflection film 30. The front electrode 60 may be formed by printing the front electrode paste on the upper portion of the anti-reflection film 50 on the emitter layer 20 and drying and firing. The front electrode paste passes through the anti-reflection film 50 to form a front electrode 60 in contact with the emitter layer 20 during the firing process. The conductive paste may be made of a material containing silver (Ag) or aluminum (Al). In addition, the front electrode 60 may be formed using a conductive paste capable of low temperature baking. When the front electrode 60 is formed of a conductive paste capable of low temperature baking, the front electrode 60 exhibits excellent electrical conductivity compared to the case of forming a conductive paste that is baked at high temperature, thereby improving charge collection efficiency.

Meanwhile, the front electrode 60 may be formed in a region where the anti-reflection film 50 is not formed or in an area where the anti-reflection film 50 is etched and removed to be electrically connected to the emitter layer 20. For example, when the front electrode 60 is formed of copper (Cu), the front electrode 60 is formed by a plating process on a pattern formed on the anti-reflection film 50.

The front electrode 60 may be formed of a plurality of electrodes extending side by side in a predetermined direction. The front electrode 60 may be formed of a general electrode used for a solar cell. The front electrode 60 collects charge, for example electrons, which have migrated toward the emitter layer 20. Although not shown, a plurality of current collectors may be positioned on the front electrode 60 in a direction crossing the front electrode 60, and the current collector and the front electrode 60 may be electrically and physically connected to each other.

Meanwhile, the front electrode forming step S60 may be performed after the rear electrode forming step S70.

The back electrode forming step (S80) is a step of forming a back electrode on the back of the substrate.

The rear electrode 70 is formed by applying an electrode paste having a core shell structure containing aluminum (Al) to the rear surface of the passivation layer 40 in the same manner as screen printing. In addition, the rear electrode 70 is an electrode After the paste is dried, it is calcined and formed through a thermal calcining process. The rear electrode 70 is electrically connected to the rear surface of the substrate 10 in point contact form.

On the other hand, the back electrode forming step (S80) may be carried out in two steps to apply the electrode paste of the core shell structure to the back of the passivation film 40, and to further apply a general electrode paste. Here, the general electrode paste includes aluminum powder, and means a general paste used for forming the back electrode, and a detailed description thereof will be omitted.

In addition, when the barrier layer 50 is formed on the rear surface of the passivation layer 40, the rear electrode 70 is formed in the via hole 50a and the passivation layer 40 formed in the barrier layer 50. It is electrically connected to the rear surface of the substrate 10 through the upper via hole 40a.

The back electrode 70 collects electric charges moving from the substrate 10 side, for example, holes and outputs them to an external device.

Hereinafter, an electrode paste having a core shell structure according to an embodiment of the present invention will be described in more detail.

The electrode paste is formed including an electrode powder, a binder and a solvent. In addition, the electrode paste may be formed by further including a dispersant.

Referring to FIG. 3, the electrode powder has a core-shell structure in which silicon (Si) powder and glass frit are coated on a surface of an aluminum (Al) powder forming the rear electrode 70. Is formed. In addition, the electrode powder may be formed by further comprising additives (additives) coated on the surface of the aluminum powder. The electrode powder is formed entirely of nano-sized powder.

The aluminum powder is a powder having a diameter in nano (nm) units, preferably formed of a spherical powder. In addition, the aluminum powder may be formed of a powder of a vinyl flake shape.

The silicon powder is a powder having a diameter in nano (nm) unit, is formed in a smaller size than the aluminum powder, preferably is formed at least 10 times smaller than the aluminum powder. The silicon powder is entirely coated on the surface of the aluminum powder. The silicon powder moves to the bonding interface between the back electrode 70 and the substrate 10 during the firing process, and prevents the generation of Kirkendall voids in the intermetallic compound of Si-Al formed at the bonding interface. do. The silicon powder is included in 1 to 15wt% relative to the total weight of the aluminum powder. When the content of the silicon powder is less than 1wt%, it is insufficient to prevent the generation of kirkendall voids in the intermetallic compound of Si-Al. In addition, when the content of the silicon powder is more than 15wt% there is no effect of increasing the silicon content.

The glass frit may be made of any one or more combinations selected from PbO-SiO 2, PbO-SiO 2 -B 2 O 3, ZnO-B 2 O 3 -SiO 2, and Bi 2 O 3 -B 2 O 3 -ZnO-SiO 2. The glass frit serves as an inorganic binder and allows the electrode paste to be bonded to the substrate 10 while firing.

The glass frit is formed of nano-sized particles and formed of a powder smaller in size than aluminum powder. Thus, the glass frit is coated on the surface of the aluminum powder. The glass frit is added in an amount of 1 to 3 wt% based on the total weight of the aluminum powder. When the amount of the glass frit is small, the coupling force between the rear electrode 70 and the substrate 10 is not sufficient. In addition, when the amount of the glass frit increases, the glass component is eluted to the surface of the rear electrode 70 during the firing process of the rear electrode 70, thereby affecting the connection process and connection strength with an external lead connected to the rear electrode. Will be given.

The additive may be various additives for adjusting the properties required in the electrode paste. For example, the additive may be an additive such as a thickener, a stabilizer, a dispersant, a viscosity modifier. The additive may be added in a predetermined amount for adjusting the properties of the electrode paste according to the properties of the additive, it may be added in an appropriate amount by those skilled in the art.

The binder may be a general binder used in the preparation of the electrode paste. In addition, the binder may be composed of any one or more selected from pine oil, ethylene glycol monobutyl ethyryr monoacetate, polymethacrylate, and ethyl cellulose terpineol. The binder may be included in 5 to 30% of the total weight of the electrode paste.

The solvent is butyl carbitol acetate, butyl carbitol, butyl shellusolve, butyl shellusolve acetate, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether propionate, ethyl ether pro Cationate, terpineol, propylene glycol monomethyl ether acetate, dimethylamino formaldehyde, methyl ether ketone, gamma butyrolactone, ethyl lactate and texanol. The solvent may be added in a predetermined content in a range necessary for forming the electrode paste.

The dispersant may be a general dispersant used in the preparation of the electrode paste. The dispersant allows the electrode powder to be uniformly dispersed in the electrode paste.

What has been described above is just one embodiment for carrying out the solar cell electrode paste according to the present invention and a solar cell manufacturing method using the same, the present invention is not limited to the above embodiment, it is claimed in the claims below As will be apparent to those skilled in the art to which the present invention pertains without departing from the gist of the present invention, the technical spirit of the present invention will be described to the extent that various modifications can be made.

10-Substrate 20-Emitter Layer
30-antireflection layer 40-passivation film
50-barrier layer 60-front electrode
70-back electrode

Claims (8)

An electrode paste for a solar cell, comprising a core-shell electrode powder, a binder, and a solvent in which a silicon powder and a glass frit are coated on a surface of an aluminum powder. The method of claim 1,
The silicon powder is a solar cell electrode paste, characterized in that 1 to 15wt% relative to the total weight of the aluminum powder. The method of claim 1,
The silicon powder is an electrode paste for a solar cell, characterized in that formed of nanoparticles smaller in size than the aluminum powder. The method of claim 1,
The glass frit is formed of nanoparticles having a smaller size than the aluminum powder electrode paste for solar cells. A substrate preparation step of preparing a substrate of a first conductivity type,
An emitter layer forming step of forming an emitter layer of a second conductivity type located on a front surface of the substrate;
An anti-reflection film forming step of forming an anti-reflection film on the emitter layer;
A passivation film forming step of forming a passivation film on a rear surface of the substrate;
Forming a front electrode formed on the anti-reflection film and electrically connected to the emitter layer;
Forming a back electrode by applying an electrode paste on a back surface of the passivation film to form a back electrode electrically connected to the back surface of the substrate,
The electrode paste is a solar cell manufacturing method, characterized in that formed with the electrode paste according to any one of claims 1 to 4. The method of claim 5, wherein
The forming of the back electrode may include applying the electrode paste to the rear surface of the passivation layer first, and then applying general electrode paste. The method of claim 5, wherein
The passivation film is a solar cell manufacturing method, characterized in that formed of Al ₂ O ₃ film, SiO 2 film or SiN film. The method of claim 5, wherein
Forming a barrier layer on a back surface of the passivation layer;
Removing a portion of the passivation layer and the barrier layer to form a contact region for exposing a contact region on a rear surface of the substrate;
The electrode paste is applied to the back of the barrier film is a solar cell manufacturing method, characterized in that formed in contact with the contact area of the back of the substrate.

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