KR20140099571A - Method of preparing front electrode of solar cell and solar cell using the method - Google Patents

Abstract

The present invention relates to a method of producing a front electrode of a solar cell, the front electrode produced by the method, and the solar cell having the same. More specifically, the present invention can minimize the risk of damage to a substrate, reduce amount of wasted ink material, produce continuously, and provide a usage range of the size and viscosity of a printing electrode material as compared to a printing device such as other inkjet or aerosols by using the method of manufacturing the front electrode of the solar cell which comprises a step of non-contacting typed electrohydrodynamics electro-hydraulic printing of a conductive layer for forming the front electrode of the solar cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for manufacturing a solar cell electrode,

The present invention relates to a method of manufacturing a solar cell electrode, and more particularly, to a method of manufacturing a solar cell electrode including a step of printing the conductive layer by a non-contact type electrohydrodynamic printing method in forming an electrode of a solar cell A manufacturing method thereof, an electrode manufactured using the above method, and a solar cell having the electrode.

Recently, as existing energy resources such as oil and coal are expected to be depleted, interest in alternative energy that can replace them is increasing. Among them, solar cells are attracting attention as next-generation batteries using semiconductor devices that convert solar energy directly into electric energy.

Solar cells are divided into silicon solar cell, compound semiconductor solar cell and tandem solar cell. Among them, silicon solar cells are mainstream.

Such a solar cell generally includes a semiconductor substrate and a semiconductor emitter layer made of semiconductors having different conductive types such as a p-type and an n-type, a reflective layer formed on a semiconductor emitter layer, A conductive electrode layer formed on the antireflection film, a front electrode formed on the conductive electrode layer, and a rear electrode formed on the semiconductor substrate. Therefore, a p-n junction is formed at the interface between the semiconductor substrate and the semiconductor emitter layer.

In the production of conventional silicon solar cells, in addition to the cost ratio of wafers, the electrode materials consumed for forming the conductive pattern also account for the high cost portion, and it is necessary to increase cost competitiveness by reducing material cost. In the process of forming an existing crystalline silicon solar cell electrode, a screen printing method in which a pressure is applied has been used, but an increase in the breakage rate due to the thinning of the crystalline silicon wafer becomes a problem.

The inkjet printing method is a technology maximizing utilization of materials compared with other existing technologies and is a digital printing method which does not require consumable parts such as screen plate. Accordingly, not only can the consumed amount of the electrode material composed of the expensive silver be significantly reduced, but also the cost of consuming the screen plate and the like can be reduced. However, in the inkjet printing method, it is impossible to eject ink having a size larger than that of the nozzle size. When ink having a high viscosity is applied, there is a risk that the nozzle sticks to the side surface of the discharge nozzle to clog the nozzle.

The conductive transparent electrode layer on the front electrode of the silicon solar cell is formed through an interfacial reaction between the metal paste and the antireflection film. The silver contained in the metal paste becomes a liquid at a high temperature and then recrystallized into a solid phase, And contact with the emitter layer through a punch through phenomenon through the antireflection film through a glass frit. The glass frit powder causes an interfacial reaction with the antireflection film to etch the antireflection film, which is an oxidation-reduction reaction, in which some elements are reduced to form byproducts. Therefore, the conventional process of performing the screen printing with the silver-containing paste includes Glass frit for forming the antireflection film when the front electrode is formed. However, it contains glass frit, which adversely affects the electric conductivity and disadvantageously deteriorates dispersion stability of the metal paste.

Therefore, in manufacturing the front electrode of the solar cell, it is necessary to increase the adhesion of the emitter layer and the conductive transparent electrode layer, and to solve problems such as the electric conductivity of the solar cell and the dispersion stability of the metal paste for forming the conductive layer It is necessary to develop a manufacturing method.

The present invention relates to a solar cell electrode which can minimize physical damage to a substrate, reduce the amount of wasted material, increase the adhesion between the emitter layer and the conductive transparent electrode layer by eliminating the need to form an electrode by applying pressure to the silicon substrate And an electrode of a solar cell using the same.

It is another object of the present invention to provide a method for manufacturing a front electrode of a solar cell which does not affect the dispersion stability of the ink composition for forming a conductive transparent electrode layer and the electric conductivity of the solar cell and an electrode of the solar cell using the same.

It is a further object of the present invention to form a conductive layer of a thin layer utilizing a low viscosity ink and to form a conductive layer having a high aspect ratio by utilizing a high viscosity ink, And an electrode of a solar cell using the same.

According to an aspect of the present invention, there is provided an electrode of a solar cell including a substrate, an emitter layer, an antireflection film, and a conductive layer, wherein the conductive layer is formed by an opening of an anti- And is in direct contact with the emitter layer, and the conductive layer does not include glass frit.

Another embodiment of the present invention is a method of manufacturing an electrode of a solar cell including a substrate, an emitter layer, an antireflection film, and a conductive layer, wherein an emitter layer formed on the substrate includes an anti-reflective coating (ARC ); Removing a portion of the anti-reflection film to form an opening; And forming a conductive layer by printing an electroconductive composition on an opening of the antireflection film by an electrohydrodynamics (EHD) printing method.

Preferably, the conductive layer may comprise two or more layers including a first conductive layer and a second conductive layer.

The front electrode of the solar cell and the method of manufacturing the same according to the present invention can minimize the physical damage to the substrate because there is no need to form an electrode by applying pressure to the silicon substrate, and the amount of wasted material is small, Can be increased. In addition, the present invention can form a conductive layer having a thin layer by utilizing a low viscosity ink, and can form a conductive layer having a high aspect ratio by utilizing a high viscosity ink, The electrodes can be formed utilizing the electrode material in the viscosity range.

In addition, the present invention can be applied to a non-contact printing process capable of minimizing physical impact on a thin silicon substrate to form an electrode pattern of a silicon solar cell, thereby simplifying the process and improving the productivity. It is economical to use the direct printing method to reduce the production cost.

1 is a schematic view illustrating a structure of a solar cell according to an embodiment of the present invention.
2 is a schematic diagram of a solar cell manufacturing process according to the first embodiment of the present invention.
3 is a schematic view of an electrohydrodynamic printing process, which is a non-contact printing method according to an embodiment of the present invention.
4 is a graph showing the sheet resistance of the nickel ink composition according to Example 1 of the present invention, according to the sintering temperature after printing.
5 is a TEM-EDX analysis result of a nickel electroconductive layer produced by baking the nickel ink composition according to Example 1 of the present invention at a baking temperature of 700 占 폚.
6A and 6B are photographs of electrodes after electrohydrodynamic printing according to Example 1. Fig.
7A and 7B are photographs of electrodes after electrohydrodynamic printing according to Comparative Example 2. Fig.
FIG. 8 shows an electroluminescence (EL) image of a solar cell having front electrodes according to Example 1 and Comparative Example 2. FIG.

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

One embodiment of the present invention is an electrode of a solar cell including a substrate, an emitter layer, an antireflection film and a conductive layer, wherein the conductive layer is formed in an opening of an anti-reflective coating (ARC) And the conductive layer contains glass frit in an amount of 1 wt% or less.

According to an embodiment of the present invention, an anti-reflective coating (ARC) is formed on an emitter layer formed on a substrate. Removing a portion of the anti-reflection film to form an opening; And printing the ink composition for forming a conductive layer on the opening of the antireflection film by an electrohydraulic printing method to form a conductive layer.

The electrode and the method of manufacturing the electrode will be described in detail.

The electrode of the solar cell includes a substrate, an emitter layer, an antireflection film, and a conductive layer. Preferably, the conductive layer is an electrode of a solar cell. Preferably, the conductive layer includes a first conductive layer and a second conductive layer And may comprise more than one layer. The first conductive layer is formed by printing on the opening of the antireflection film by an electrohydrodynamic printing method, so that the first conductive layer is formed in direct contact with the emitter layer without intervening layers.

The step of forming an anti-reflective coating (ARC) on the emitter layer formed on the substrate may be performed by a conventional electrode manufacturing process. Further, the substrate may be doped with a P-type impurity and the emitter layer may be doped with an N-type impurity, but is not particularly limited.

The antireflection film may be a single film selected from the group consisting of silicon nitride, silicon nitride including hydrogen, silicon oxide, MgF ₂ , ZnS, TiO ₂ , CeO _2, and mixtures thereof, or a multilayer film formed by combining two or more films.

As a step of removing an area of the anti-reflection film to form an opening, a photolithography method, a laser etching method, or an etching paste method may be used. Preferably, an electrohydrodynamic printing method using an etching paste or a screen printing method using an etching paste may be used, and more preferably, an electrohydrodynamic printing method using an etching paste. The formation of the openings using the photolithography method and the laser etching method may be performed according to a commonly known method and is not particularly limited.

In the case of forming the openings using the etching paste, for example, an etching paste is printed on the antireflection film and then immersed in an aqueous alkaline solution such as KOH 0.1% solution to remove the antireflection film using ultrasonic waves .

The size and shape of the opening region of the antireflection film should correspond to the size and shape of the conductive layer. In the present invention, the conductive layer is formed in the opening of the anti-reflective coating (ARC) to directly contact the emitter layer to form the silacide compound. For example, the shape of the opening corresponds to the shape of the electrode, and can be removed with a line width of the electrode, for example, a line width of 60 micrometers.

A conductive layer is formed by printing a composition for forming a conductive layer on the opening of the antireflection film by an electrohydraulic printing method so that a conductive layer is formed in the opening of the antireflection film to directly contact the emitter layer to form a silaceide compound, The contact resistance can be reduced.

The conductive layer may be formed by a non-contact direct printing method, and preferably by an electrohydrodynamic printing method. The electrohydraulic printing method is a technique for discharging droplets using an electric field. When a constant voltage is applied between the injection nozzle and the substrate, an electric field is generated, and at the same time, charges are concentrated on the surface of the fluid near the nozzle. In this case, when the pressure of the nozzle is larger than the surface tension of the fluid due to the electric charge and the electric field generated on the surface of the fluid, the spherical surface deforms into the shape of Taylor Cone, resulting in a much smaller particle size or spray than the size of the nozzle. Due to the formation of Taylor Cone by the electric field, it is possible to generate two or more droplets with a size of several tens of micrometers to several hundreds of micrometers to several hundreds of micrometers from a large nozzle of several hundred micrometers. In addition, it is possible to improve the straightness of the ejected droplet by optimizing the electric field.

Electrohydrodynamic printing does not require the formation of electrodes by applying pressure to the silicon substrate, such as screen printing, thus minimizing physical damage to the substrate, reducing the amount of wasted material, The electrode can be formed by utilizing the electrode material having a wide viscosity range. As a result, in the case of a nickel layer to which a thin layer electrode is to be applied, a thin layer can be formed by printing using a low viscosity ink, and in the case of an Ag electrode having a high aspect ratio, . This solves the limitations of inkjet and screen printing.

Wherein the conductive layer includes a first conductive layer in contact with the emitter layer and a second conductive layer formed on the first conductive layer, the first conductive layer prints the ink composition by electrohydrodynamic printing, Other plating methods such as screen printing, inkjet printing, dispensing, silver light induced plating (LIP), and electroless plating may be used, preferably by electrohydrodynamic printing.

The ink composition for forming a conductive layer according to the present invention includes conductive metal particles, a solvent, a binder and a dispersing agent, but may not include or contain a glass frit. For example, the glass frit content may be 1% by weight or less.

When the conductive layer is formed of two or more layers, the first conductive layer in contact with the emitter layer does not include glass frit, and the second conductive layer formed thereon does not include the first glass frit or contains a small amount For example, the glass frit content may be 0 to 1.0 wt% based on the total weight of the total ink composition. Or the second conductive layer may comprise glass frit in a content of less than or equal to 1%, more preferably less than or equal to 0.5%, based on the total weight of the ink composition. The particle diameter of the glass frit is not particularly limited, but may be, for example, 50 nm to 5 micrometers.

According to a conventional method of manufacturing a solar cell electrode, a conductive electrode layer is formed on an antireflection film without forming an opening corresponding to the conductive layer. At this time, the silver contained in the metal paste or ink becomes a liquid state at a high temperature And is recrystallized as a solid phase, and comes into contact with the emitter layer through a punch through phenomenon penetrating through the antireflection film through a glass frit. The glass frit powder contained in the metal paste causes an interfacial reaction with the antireflection film to etch the antireflection film. Therefore, existing processes for screen printing with silver-containing pastes have a certain amount of glass frit in order to penetrate the antireflection film, which may adversely affect the electrical conductivity of the electrode and the dispersion stability of the ink. It goes crazy.

Therefore, the composition for forming a conductive layer of the present invention has an advantage that the content of the glass frit is within a certain range, and therefore, it does not affect the electrical conductivity reduction by the glass frit or the dispersion stability of the ink composition. Therefore, even when the glass frit is optionally included in the composition for forming a conductive layer to be applied to the present invention, there is no particular limitation with respect to the particle diameter of the glass frit.

There is no particular limitation on the particle size or content of the metal particles to be used in the composition because the composition for forming a conductive layer of the present invention hardly affects the dispersion stability due to glass frit. The particle size of the metal particles that can be included in the composition for forming a conductive layer according to the present invention may be 50 nm to 5 micrometers, and the content may be 20 to 85% by weight based on the total weight of the total ink composition, but is not limited thereto .

The metal particles applicable to the composition for forming a conductive layer may include any conductive metal particles capable of forming a silicate compound with the emitter layer, without any particular limitation. For example, when the conductive layer includes a first conductive layer in contact with the emitter layer and a second conductive layer formed on the first conductive layer, the first conductive layer may include Ni, Ti, Co, Pt, Pd, Cu, W, and alloys thereof, and is preferably nickel. The second conductive layer may include metal particles selected from the group consisting of Ag, Au, Al, Ni, Pt, Cu, and alloys thereof, preferably silver. According to an embodiment of the present invention, the metal particles of the second conductive layer may be included in the first conductive layer in an amount of 10 parts by weight based on 100 parts by weight of the metal of the first conductive layer. In this case, There is an advantage that adhesion between layers can be increased.

The ink composition for forming a conductive layer may contain 20 to 60% by weight of the metal particles based on the total weight of the ink composition. When the content of the metal particles is less than 20% by weight, the ink composition is too thin to obtain sufficient conductivity, If the content exceeds the above range, the dispersion stability of the ink is deteriorated.

The composition for forming a conductive layer according to the present invention includes, in addition to metal particles, a solvent, a binder and a dispersant, and commonly used components and contents can be applied to the present invention.

The binder usable in the conductive ink composition of the present invention is used as a binder of components before firing of the electrode pattern, and is preferably prepared by suspension polymerization for uniformity. As such a binder, a polymer surface which can be dissolved in the main solvent can be used, and specifically, a resin containing a carboxyl group, specifically, a carboxyl group-containing photosensitive resin having an ethylenically unsaturated double bond itself and an ethylenically unsaturated double bond Containing resin having no carboxyl group. Examples of the binder include: i) a carboxyl group-containing photosensitive resin obtained by copolymerization of a compound having an unsaturated carboxylic acid and an unsaturated double bond, ii) a copolymer of an unsaturated carboxylic acid and a compound having an unsaturated double bond, , Iii) a carboxyl group-containing photosensitive resin obtained by reacting a copolymer of an acid anhydride having an unsaturated double bond and a compound having an unsaturated double bond with a compound having a hydroxyl group and an unsaturated double bond, But are not limited thereto, and one or more of them can be used. Preferred examples of the binder include an alkylphenol-formaldehyde copolymer (e.g., Tackirol manufactured by Taoka Chemical Co.), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), ethyl cellulose and the like.

If the content of the binder is less than 0.5% by weight, the distribution of the binder in the electrode pattern to be formed may be uneven, and the selective exposure and development The patterning by the organic residue after carbonization (Carbon ash) can increase the resistance of the electrode due to the pattern collapse when the electrode is fired.

The dispersing agent may be contained in an amount of 0.5 to 5% by weight of the total conductive composition. The dispersant may be a copolymer having an acid value of 50 mg KOH / g or more and an amine value of 100 mg KOH / g or less. As an example of the dispersant, BYK102 (acid value: 101 mg KOH / g, amine value: 0 mg KOH / g) and BYK 110 (acid value: 53 mg KOH / g, commercially available product BYK Chemie) (Acid value: 53 mg KOH / g), BYK145 (acid value: 76 mg KOH / g, amine value: 71 mg KOH / g), BYK 180 (acid value: 94 mg KOH / g, Amine value: 0 mg KOH / g), BYK996 (acid value: 71 mg KOH / g, and amine value: 0 mg KOH / g).

The solvent that can be used in the composition for forming a conductive layer can be applied to all of the present invention, as long as it can dissolve the binder and can be mixed well with other additives, Can be used by mixing a low boiling point solvent and a low boiling point solvent as main solvents.

The low boiling point solvent which is the main solvent may be a low boiling point glycol ether having a hydroxyl group at the terminal group and a boiling point of 130 캜 to 210 캜, preferably 170 to 210 캜. If the boiling point of the low boiling point solvent is less than 130 캜, the jetting property deteriorates. If the boiling point of the low boiling point solvent is more than 210 캜, the drying speed after jetting is low.

The low boiling point solvent is preferably contained in an amount of 30 to 70% by weight based on the total weight of the ink composition. If the content of the solvent is less than 30% by weight, it may be difficult to uniformly coat the ink, whereas if it exceeds 70% by weight, sufficient conductivity of the electrode pattern can not be obtained, .

Examples of preferred lower boiling solvents are diethylene glycol monomethyl ether (DMG), diethylene glycol monoethyl ether (ethyl carbitol), diethylene glycol monobutyl ether (Diethylene glycol monobutyl ether) Diethyleneglycol monoalkyl ethers such as ethy (butyl carbitol)); Or ethylene glycol ethyl ether (ethyl cellosolve), ethylene glycol propyl ether (propyl cellosolve), ethylene glycol n-butyl ether (n-butyl cellosolve) ) And the like, and the alkyl is a linear or branched alkyl group having 1 to 6 carbon atoms.

The high boiling point solvent is a solvent having a hydroxyl group at the terminal group and a boiling point of 240 to 300 캜, preferably 240 to 270 캜. Examples of the solvent include diethylene glycol, glycerol, But is not limited to, tripropyleneglycolmethylether.

The content of the high boiling point solvent may be 3 to 10% by weight based on the total ink composition. If the content is less than 3% by weight, the jetting property deteriorates. If the content is more than 10% by weight, The phenomenon becomes serious.

The ink composition for forming the front electrode according to the present invention may further comprise at least one additive selected from the group consisting of a thickener, a thixotropic agent, a leveling agent, and the like. 1 to 20 parts by weight.

The electroconductive ink composition according to the present invention may be manufactured by a ball milling process or a milling process. The milling process may be used to produce glass frit nanoparticles, It can be used by removing the particles which are aggregated or out of the particle diameter range through fixing. But it is not limited thereto, and can be produced through a process such as flame spray pyrolysis or plasma treatment.

The conductive ink composition may be used for forming a front electrode of a silicon solar cell. Nickel silicide may be formed by the combination of nickel and silicon to reduce the contact resistance between the silicon substrate and the electrode.

After the conductive layer is formed, firing may be performed to produce an electrode. The firing process may be performed at a temperature of 400 to 980 캜 for 0.1 to 20 minutes . In the case where the conductive layer includes the first conductive layer and the second conductive layer, the firing may be performed by performing a sintering step after formation of the individual conductive layers of the first conductive layer and the second conductive layer, After all, the firing step can be carried out together.

In another embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: printing a silicon-based semiconductor substrate of a crystalline silicon solar cell, an emitter layer formed on the substrate, an antireflection film formed on the emitter layer, And a second conductive layer formed on the first conductive layer.

The high Rs cell according to the present invention has a sheet resistance of 60 to 120 Ω / sq, which is higher than that of the emitter layer of a conventional crystalline solar cell having a sheet resistance of 40 to 50 Ω / sq. Do. That is, a high-efficiency solar cell reduces the portion of the emitter layer formed on the entire surface of the solar cell layer where a dead layer (a region where generated electrons are disturbed by the extra semiconductor impurity concentration) is formed, . Further, since the conductive layer does not contain or contains a very small amount of glass frit, the electrical conductivity of the electrode is not deteriorated.

In the case where the first conductive layer and the second conductive layer are formed on the electrode of the solar cell according to the present invention, the second conductive layer may contain 0 to 1.0% by weight of the glass frit based on the total weight of the composition for forming a conductive layer . The present invention also relates to a solar cell having a solar cell front electrode including a first conductive layer formed by printing the conductive ink composition and a second conductive layer formed on the first conductive layer. Each layer of the solar cell is as described above.

The solar cell front electrode according to the present invention is characterized in that it comprises the conductive ink composition. The front electrode of the solar cell is formed by patterning a silicon semiconductor substrate 1, an emitter layer 2 on the substrate, an antireflection film 3 formed on the emitter layer, and a first conductive layer 4 on the antireflection film A second conductive layer 5 formed on the entire upper surface of the first conductive layer, and a rear electrode 6.

According to another embodiment of the present invention, there is provided a semiconductor device comprising: a silicon semiconductor substrate; An emitter layer formed on the substrate; An antireflection film formed on the emitter layer; A front electrode including a first conductive layer and a second conductive layer which are connected to the emitter layer through the antireflection film from an upper portion of the antireflection film; And a rear electrode formed on a lower portion of the substrate, wherein the first conductive layer of the front electrode is formed using the ink composition described above.

Hereinafter, a solar cell according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 is a schematic view illustrating a structure of a solar cell according to an embodiment of the present invention. 1, a solar cell according to the present invention includes a silicon semiconductor substrate 1 (hereinafter referred to as a substrate), an emitter layer 2 formed on the substrate 1, an emitter layer 2 formed on the emitter layer 2 And a front electrode including a first conductive layer 4 and a second conductive layer 5 which are connected to the emitter layer 2 through the antireflection film 3 and the antireflection film 3, And a backside electrode 6 connected to the backside of the substrate 1.

The substrate 1 may be doped with an impurity such as B, Ga, or In, which is a Group 3 element, as the P-type impurity, and P, As, Sb or the like as a Group 5 element as an impurity in the emitter layer 2, Lt; / RTI > P-N junctions are formed at the interface between the substrate 1 and the emitter layer 2 when the substrate 1 and the emitter layer 2 are doped with impurities of the opposite conductivity type.

The antireflection film 3 immobilizes defects existing in the surface or bulk of the emitter layer 2 and reduces the reflectance of sunlight incident on the front surface of the substrate 1. [ When defects present in the emitter layer 2 are passivated, the recombination sites of the minority carriers are removed and the open-circuit voltage Voc of the solar cell increases. When the reflectance of sunlight is reduced, the amount of light reaching the P-N junction is increased and the short circuit current Isc of the solar cell is increased. As the open-circuit voltage and the short-circuit current of the solar cell are increased by the antireflection film 3, the conversion efficiency of the solar cell is improved accordingly.

On the other hand, as can be seen from FIG. 1, the front electrode is positioned at the top of the solar cell to cover the sunlight. Therefore, it is important to minimize the area of the front electrode without deteriorating the function of the front electrode.

Also, the rear electrode 6 may include aluminum, but is not limited thereto. For example, the rear electrode 6 may be formed by printing ink on the rear surface of the substrate 1 to which aluminum, quartz silica, binder, or the like is added, and then performing heat treatment. Aluminum may be diffused through the back surface of the substrate 1 during the heat treatment of the back electrode 6 so that a back surface field layer may be formed on the interface between the back electrode 6 and the substrate 1 . When the rear layer is formed, the carrier can be prevented from moving to the rear surface of the substrate 1 and recombining. When the recombination of the carriers is prevented, the open voltage is increased and the efficiency of the solar cell is improved.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the following examples serve to illustrate the present invention, and the scope of the present invention is not limited thereto.

< Example  1>

Phosphorus (P) was doped through a diffusion process using POCL ₃ at 880 ° C. in a tube furnace using a 156 mm polysilicon wafer to form an emitter layer having a sheet resistance of 80 Ω / sq.

A silicon nitride film was deposited on the emitter layer by Plasma-enhanced Chemical Vapor Deposition (PECVD) to have a thickness of 80 nm to form an antireflection film.

The antireflection film was printed with an etching paste (product of Merck Co., Ltd., SolarEtch BES) with a line width of 60 μm by electrohydrodynamic printing, and the wafer was immersed in a bath containing 0.1% KOH solution and etched with ultrasonic waves The antireflection film on which the paste was printed was removed and dried to form openings.

The nickel ink composition for the conductive layer was prepared by mixing 40 wt% of nickel particles having a particle size of about 50 nm, 50 wt% of ethyl cellosolve as a main solvent, 7 wt% of tripropyleneglycolmethylether as a high boiling solvent, 1% by weight of a co-polymer and 2% by weight of BYK996 as a dispersant were mixed, and the mixture was mixed with a ball mill for 2 hours to prepare an ink composition. The Ni ink composition thus prepared was subjected to electrohydrodynamic printing to form a nickel layer and dried at 60 ° C.

In order to produce Ag ink containing 0.5 wt% of glass frit on the nickel layer formed, 0.5 wt% of glass frit of SiO2-PbO-B2O3, 10 wt% of butyl carbitol acetate, 10 wt% of ethyl cellulose resin 5% by weight of Dow Co., Ltd .; Standard 100) and 84.1% by weight of Dowa (Dowa) having an average particle size (D50) of 3.21 탆. The mixed dispersion was dispersed by 3-roll milling to prepare an Ag ink composition. An Ag electrode was formed on the nickel layer by an electrohydraulic printing method with an Ag ink composition and dried at 270 캜.

Thereafter, the aluminum paste (ALSOLAR T company) was printed on the rear surface and the drying process was performed at 200 ° C. The dried wafer was fired in a belt firing at 900 ° C to form electrodes. The fired finger width was about 80 탆, and the thickness of the fired front electrode was about 23 탆.

In the electrohydraulic (EHD) process conditions, the printing experiment was mainly performed with an interval between the wafer and the nozzle of 400 to 600 μm, an applied voltage of about 1 to 1.5 kV, and a printing speed of 100 mm / s.

< Comparative Example  1>

A solar cell was fabricated in the same manner as in Example 1, except that a nickel layer was not formed, but a silver layer was prepared by contacting an emitter layer having openings formed therein. In Example 1, a nickel layer was present between the emitter layer and the silver layer, and after the heat treatment, NiSi was formed so that contact was made between the silicon and the electrode without glass frit, and the efficiency of the cell was observed. And to compare the characteristics of a solar cell having only an Ag electrode layer without a layer.

Specifically, phosphorus (P) was doped through a diffusion process using POCL ₃ at 880 ° C. in a tube furnace using a 156 mm polycrystalline silicon wafer to form an emitter layer having a sheet resistance of 80 Ω / sq.

A silicon nitride film was deposited on the emitter layer by Plasma-enhanced Chemical Vapor Deposition (PECVD) to have a thickness of 80 nm to form an antireflection film.

The antireflection film was printed with an etching paste (product of Merck Co., Ltd., SolarEtch BES) using an electrohydraulic printing method with a line width of 60 um, and then the wafer was immersed in a bath containing 0.1% KOH solution and etched using an ultrasonic wave The antireflection film on which the paste was printed was removed and dried to form openings.

To prepare an Ag ink containing 0.5 wt% of glass frit, 0.5 wt% of glass frit of SiO2-PbO-B2O3, 10 wt% of butyl carbitol acetate, 10 wt% of a binder 5% by weight of Ethyl Cellouse resin, trade name Ethocel, Dow, Standard 100), and an average particle size (D50) of 3.21 μm (Dowa) were mixed and dispersed in 84.5% by weight of powder. The mixed dispersion was dispersed by 3-roll milling to prepare an Ag ink composition. The Ag ink composition was subjected to electrohydrodynamic printing to form an Ag electrode and dried at 270 캜.

Thereafter, the aluminum paste (ALSOLAR T company) was printed on the rear surface and the drying process was performed at 200 ° C. The dried wafer was fired in a belt firing at 900 ° C to form electrodes. The fired finger width was about 80 탆, and the thickness of the fired front electrode was about 23 탆.

< Comparative Example  2>

Phosphorus (P) was doped through a diffusion process using POCL ₃ at 880 ° C. in a tube furnace using a 156 mm polysilicon wafer to form an emitter layer having a sheet resistance of 80 Ω / sq. A silicon nitride film was deposited on the emitter layer by Plasma-enhanced Chemical Vapor Deposition (PECVD) to have a thickness of 80 nm to form an antireflection film.

A silver conductive layer was formed on the antireflection film by screen printing with a commercial Heraeus silver paste. Thereafter, a solar cell was manufactured in substantially the same manner as in the process of Example 1 for the formation of the rear electrode and the baking process. The above process is generally manufactured by a method used for printing on a solar cell electrode.

< Comparative Example  3>

A solar cell was fabricated in the same manner as in Example 1, except that the nickel electroconductive layer was formed by a screen printing method instead of the electrohydraulic method.

In order to apply the screen printing method, the nickel content contained in the conductive nickel ink composition was increased to 60% by weight. To prepare the nickel ink composition, 60 wt% of nickel particles having a particle size of about 50 nm, 30 wt% of ethyl cellosolve as a main solvent, 7 wt% of tripropyleneglycolmethylether as a high boiling solvent, 1 wt% of an alkylphenol- formaldehyde copolymer as a binder, 2 wt% BYK996 were mixed and the mixture was dispersed by 3-roll milling.

<Experimental Example>

1) Surface Resistance Measurement

A pure polycrystalline silicon wafer was used and a wafer having a sheet resistance of 80 Ω / sq was doped with phosphorus (P) through a diffusion process using POCL ₃ at 900 ° C. in a tube furnace. Thereafter, the nickel ink composition prepared in Example 1 was printed on a silicon wafer and then subjected to RTP (Unitemp's Rapid Thermal Process) equipment at sintering temperatures of 300 ° C, 500 ° C, 700 ° C and 900 ° C under a nitrogen atmosphere And baked for 20 seconds to prepare a sample for sheet resistance measurement.

The sheet resistance of the sintered wafer was measured using a 4-probe meter, and the measurement results are shown in FIG. Referring to FIG. 4, it can be seen that the sheet resistance becomes lower as the temperature increases. It can be confirmed that nickel silicide is formed due to the diffusion of nickel from the interface of the silicon wafer by forming an electrode including nickel particles on the emitter layer, thereby exhibiting a low sheet resistance.

2) TEM-EDX analysis

Among the samples for measuring the sheet resistance, components of the wafer cross-section subjected to heat treatment at 700 ° C were analyzed by TEM-EDX to confirm whether or not NiSi was formed. The analysis results are shown in FIG.

As shown in the graph of FIG. 5, Ni and Si components were measured at a ratio of about 1: 1 at the 009-point portion of the TEM-EDX data, thereby confirming whether or not NiSi was formed. It was confirmed that the electrode contained a nickel layer and lowered sheet resistance due to the formation of nickel suicide. As a result, it was confirmed that the contact resistance was low.

3) Electrode pictures

The electrode photograph of the manufactured solar cell was measured using an OLYMPUS Confocal Laser Scanning Microscope.

The electrode obtained in Example 1, in which the nickel electroconductive layer was produced using the electrohydraulic printing method, is shown in Figs. 6A and 6B, and the electrode obtained in Comparative Example 3 in which the nickel electroconductive layer was produced by using the screen printing method, 7B. 7A is an image showing a two-dimensional image of the electrode viewed from above, which is taken in a 3D format of FIG.

As shown in FIGS. 6A and 6B and FIGS. 7A and 7B, in the electrodes of Example 1 and Comparative Example 3, 6A and 6B in which the electrohydrodynamic printing method was applied according to Example 1, the spread was small and the line shape was well formed. However, in FIGS. 7A and 7B for electrodes printed by screen printing according to Comparative Example 3, there is spread and the line height due to screen mesh traces is not constant. This part has a bad influence on the electrical characteristics due to the light shielding due to electrode spreading and the bending of the electrode.

4) Electroluminescence image of solar cell (Electro luminance image)

A solar cell was fabricated using the fabrication process described in Example 1 and Comparative Example 2, and an electro luminescent image of the solar cell was measured using a K3300 ELX instrument of Mac Science Inc., in FIG. The present invention relates to an image inspection method for determining an internal defect in a solar cell, comprising: power supply means for applying a forward voltage or current having a predetermined period and waveform and being electrically connected to both ends of the electrode of the solar cell; Detecting the electro-luminescence image generated in the solar cell with an image detecting means for detecting using a camera, and extracting internal defect information of the solar cell.

The electroluminescent images show brighter light with better cell characteristics in the cell characteristic part of the solar cell when the same voltage or current is applied, and the part with the shorted line becomes black. Example 1 exhibited brighter electroluminescence than Comparative Example 2 using a commercially available nickel ink composition, which is excellent in electrical characteristics such as contact resistance portion and series resistance portion, .

5) Measurement of solar cell efficiency

The electric efficiencies of the solar cells obtained in Example 1 and Comparative Examples 1, 2 and 3 were measured with a solar cell dedicated simulator. To measure the electrical efficiency, we used a solar simulator from ABET Technologies with a 150 Watt Xenon arc Lamp Source. The measurement results are shown in Table 1 below.

Where Jsc means the short circuit current density measured at the zero output voltage and Voc means the open circuit voltage measured at zero output current. FF [%] means fill factor, Eta [%] means efficiency.

As shown in the above Table 1, when the nickel layer is introduced, the contact resistance is lowered as a result of the above data. As a result, the fill factor is increased and the efficiency of the solar cell is increased.

division Jsc [mA / cm2] Voc [V] FF [%] Eta [%] Example 1 34.712 0.618 77.4 16.6 Comparative Example 1 25.61 0.592 28.6 4.3 Comparative Example 4 34.29 0.608 77 16.1 Comparative Example 3 34.15 0.603 56.5 11.6

1: Silicon semiconductor substrate
2: Emitter layer
3: antireflection film
4: the first conductive layer of the front electrode
5: the second conductive layer of the front electrode
6: Rear electrode

Claims (17)

Forming an anti-reflective coating (ARC) on an emitter layer formed on a substrate;
Removing a portion of the anti-reflection film to form an opening;
And forming a first conductive layer by printing an electroconductive composition on an opening of the antireflection film by an electrohydrodynamics (EHD) printing method. The method of manufacturing an electrode of a solar cell according to claim 1, wherein the opening region of the antireflection film corresponds to a region of the conductive layer. The method of manufacturing an electrode of a solar cell according to claim 1, wherein the step of forming the opening is performed by a method using a photolithography method, a laser etching method, or an etching paste. 4. The method according to claim 3, wherein the method using the etching paste is performed by removing the antireflection film of the printing portion corresponding to the opening after printing the etching paste by an electrohydraulic printing method or an inkjet printing method A method of manufacturing an electrode of a battery. The method of claim 1, further comprising forming a second conductive layer on the first conductive layer. [6] The method of claim 5, wherein the second conductive layer comprises 0 to 1.0% by weight based on the total weight of the composition for forming a conductive layer. The method for manufacturing an electrode of a solar cell according to claim 1, wherein the first conductive layer comprises metal particles selected from the group consisting of Ni, Ti, Co, Pt, Pd, Mo, Cr, Cu, W, . 6. The method of claim 5, wherein the second conductive layer comprises metal particles selected from the group consisting of Ag, Au, Al, Ni, Pt, Cu, and alloys thereof. The method of claim 5, wherein the second conductive layer is formed by an electrohydraulic printing method, a screen printing method, an inkjet printing method, a dispensing printing method, or a plating method. The method according to claim 1, wherein the manufacturing method comprises a step of firing at a temperature of 400 ° C to 980 ° C for 0.1 minute to 20 minutes after the first conductive layer forming step. 6. The method according to claim 5, wherein the conductive layer of the solar cell forms a first conductive layer, forms a second conductive layer on the first conductive layer, and then is baked at a temperature of 400 DEG C to 980 DEG C for 0.1 minute to 20 minutes Wherein the method comprises the steps of: The method of claim 1, wherein the substrate is doped with a P-type impurity and the emitter layer is doped with an N-type impurity. An electrode of a solar cell comprising a substrate, an emitter layer, an antireflection film and a conductive layer, wherein the conductive layer is formed in an opening of an anti-reflective coating (ARC) and is in direct contact with the emitter layer, The electrode of the solar cell having the sheet resistance of. The method of claim 13, wherein the anti-reflective coating is silicon nitride, silicon nitride, silicon oxide containing hydrogen, MgF _2, ZnS, TiO _2, CeO _2, and a single membrane selected from the group consisting of a mixture or two or more membranes in combination Electrode of a solar cell. 14. The electrode of a solar cell according to claim 13, wherein the conductive layer comprises a first conductive layer in contact with the emitter layer and a second conductive layer formed thereon. The electrode of a solar cell according to claim 13 or 15, wherein the first conductive layer or the second conductive layer contains glass frit in an amount of 0 to less than 1.0% by weight based on the total weight. The method of claim 15, wherein the first conductive layer comprises metal particles selected from the group consisting of Ni, Ti, Co, Pt, Pd, Mo, Cr, Cu, W, and alloys thereof, Wherein the electrode comprises metal particles selected from the group consisting of Ag, Au, Al, Ni, Pt, Cu, and alloys thereof.

Images