KR20050087249A - A solar cell having an electrode formed by using nanosized paste and fabrication method thereof - Google Patents

Abstract

In order to manufacture the electrode of the solar cell by the screen printing method, it is to provide a solar cell with improved contact efficiency, lower the firing temperature, and lower the contact resistance between the electrode and the substrate. To this end, in the present invention, in forming an electrode by screen printing, an electrode of a solar cell is formed by using a paste including conductive particles having a nanometer size having a particle diameter of 100 nm or less. A solar cell according to the present invention includes a semiconductor layer of a first conductive type; A second conductive semiconductor layer formed on one surface of the first conductive semiconductor layer and having an opposite conductivity type; Formed by screen printing a paste containing conductive particles having contact with at least a portion of the second conductive semiconductor layer and having a particle diameter of 100 nm or less, occupying 5% or less of the total area of the second conductive semiconductor layer. Front electrode; And a back electrode in contact with at least a portion of the first conductive semiconductor layer.

Description

A solar cell having an electrode formed by using nanosized paste and fabrication method

The present invention relates to a solar cell and a method for manufacturing the same, and more particularly, to a method of forming an electrode of a solar cell by a screen printing method using a paste of nanoparticles.

Electrode formation of a solar cell is largely used by evaporation and screen printing. Among them, the evaporation method can maximize the efficiency of the solar cell, but prior to this, the photolithography and the wet process must be performed, thereby increasing the number of processes and increasing the price.

Therefore, in the case of commercially available solar cells, the front electrode and the rear electrode are formed by screen printing. However, the screen printing method has a problem of high contact resistance between the silicon substrate and the electrode metal.

Due to this increase in contact resistance, 80% of solar cells formed electrodes by the evaporation method on the diode fill factor of solar cells. 5% lower results.

In the conventional screen printing method, a silver paste containing an organic solvent, a binder, a glass frit, and the like, in addition to a silver powder having a particle size of 10 to 100 μm is applied to an electrode formation site, Fire.

After firing, the organic solvent and binder are evaporated away, but the glass frit remains with the silver powder to aid in contact between the silver powder and between silver and silicon. However, excessive glass frit between the silicon substrate and the silver metal increases the contact resistance between them, which in turn lowers the efficiency of the solar cell.

In the case of using a paste without glass frit, there is a problem in that the silver electrode is easily peeled off due to poor adhesion between the electrode and the substrate, and high temperature and long time firing are required for sufficient contact formation.

The present invention is to solve the problems as described above, the purpose is to produce the electrode of the solar cell by the screen printing method, to lower the contact resistance between the electrode and the substrate and to lower the firing temperature.

Another object of the present invention is to provide a solar cell having improved efficiency by manufacturing an electrode by a screen printing method.

In order to achieve the above object, in the present invention, in forming an electrode by screen printing, the electrode of the solar cell is formed by using a paste containing conductive particles of nanometer size having a particle diameter of 100nm or less.

That is, the solar cell according to the present invention, the first conductive semiconductor layer; A second conductive semiconductor layer formed on one surface of the first conductive semiconductor layer and having an opposite conductivity type; Formed by screen printing a paste containing conductive particles having contact with at least a portion of the second conductive semiconductor layer and having a particle diameter of 100 nm or less, occupying 5% or less of the total area of the second conductive semiconductor layer. Front electrode; And a back electrode in contact with at least a portion of the first conductive semiconductor layer.

In this case, the resistivity of the front electrode may be 3 μΩcm or less.

In addition, the rear electrode may be formed by screen printing a metal paste including conductive particles having a particle diameter of 100 nm or less on the other surface of the first conductive semiconductor layer, so that a specific resistance thereof may be 3 μΩcm or less.

The conductive particles may be any one of Ag, Cu, Au, Ti, W, Ni, Cr, Mo, Pb, Pd, and Pt.

The paste may contain 50-90% by weight of conductive particles, 9-40% by weight of an organic solvent which is one of water and alcohol, and 1-10% by weight of a binder.

In order to manufacture the solar cell as described above, the present invention comprises the steps of preparing a semiconductor layer having a first conductivity type; Forming a second conductive semiconductor layer having an opposite conductivity type on one surface of the first conductive semiconductor layer; Forming a front electrode to be connected to at least a portion of the second conductive semiconductor layer, and screen printing a paste including conductive particles having a particle diameter of 100 nm or less; It provides a method of manufacturing a solar cell comprising the step of forming a back electrode to be connected to at least a portion of the first conductive semiconductor layer.

In the forming of the back electrode, the metal paste including the conductive particles having a particle diameter of 100 nm or less may be screen printed on the other surface of the first conductive semiconductor layer.

After screen printing, heat treatment may be performed for 5 minutes or less at a temperature of 300-700 ° C., and heat treatment is preferably performed by an infrared lamp.

Hereinafter, with reference to the accompanying drawings for the present invention will be described in detail.

1 is a cross-sectional view showing the structure of a solar cell according to a first embodiment of the present invention. In the solar cell according to the first embodiment of the present invention, as shown in FIG. 1, an n layer 11 is formed on the front surface of the p-type silicon substrate 10, and is electrically connected to the n layer 11. The front electrode 12 is formed on a portion of the n layer, and the rear electrode 13 is formed on the rear surface of the p-type silicon substrate 10. The antireflection film 14 is formed on the n layer 11 except for the front electrode 12.

Here, the front electrode 12 is formed by screen printing a paste containing conductive particles having contact with at least a portion of the n layer 11 and having a particle diameter of 100 nm or less, so as to cover the entire area of the top surface of the n layer 11. Accounted for less than 5%. At this time, conductive particles having a particle size of 100 nm or less are referred to as nanoparticles.

The composition of the screen printing paste in the present invention is 50-90% by weight of the conductive particles, 9-40% by weight of an organic solvent which is one of water and alcohol, and 1-10% by weight of the binder, and the glass frit is It is characterized by the absence.

At this time, the conductive particles are any one of Ag, Cu, Au, Ti, W, Ni, Cr, Mo, Pb, Pd, Pt, the particle size is 100nm or less, the smaller the particle diameter is advantageous, the lower the minimum particle diameter Since it is limited by the particle diameter, there is no reason to limit it to the numerical value. Preferably, the conductive particles may have a particle diameter of 10-100 nm.

As described above, in the present invention, by reducing the size of the conductive particles contained in the conventional paste to the nanometer scale, it is possible to obtain the effect of reducing the contact resistance, the specific resistance of the electrode, and the reduction of the firing temperature. But you can get high efficiency.

An example of the paste used in the present invention is a silver paste containing 10 nm silver powder.

As described above, the paste used in the present invention has no glass frit, and thus, the firing temperature and time for forming a contact can be lowered compared to the case of using the conventional paste.

In the present invention, the paste may be heat-treated for a time of 5 minutes or less at a temperature of 300-700 ° C. after screen printing, and a heating method using an infrared lamp may be used during heat-treatment.

In addition, the conventional paste has a resistivity of about 5 μΩcm (manufactured by the manufacturer), but the paste used in the present invention has a resistivity of 3 μΩcm or less, so that the resistivity of the front electrode formed by screen printing such paste also has a value of 3 μΩcm or less. This has the advantage of reducing the line width of the front electrode.

2 is a cross-sectional view showing the structure of a solar cell according to a second embodiment of the present invention. The second embodiment of the present invention is distinguished from the first embodiment in that the front electrode as well as the rear electrode are formed by screen printing a paysheet having nanoparticles.

In the solar cell according to the second embodiment of the present invention, as shown in FIG. 2, an n layer 21 is formed on the front surface of the p-type silicon substrate 20 and electrically connected to the n layer 21. The front electrode 22 is formed on a portion of the n-layer 11, and the back electrode 23 electrically connected to the p-type silicon substrate 20 is formed on a portion of the back surface of the p-type silicon substrate.

An anti-reflection film 24 is formed on the n layer 21 except for the front electrode 22, and a back passivation layer 25 is formed on the back surface of the p-type silicon substrate 20 except for the back electrode 23.

When the front electrode 22 and the rear electrode 23 are formed, the same method as described in the first embodiment is applied. However, since the rear surface of the p-type semiconductor substrate 20 is not a light receiving surface, absorption of sunlight is not blocked by the area of the rear electrode 23. However, when the rear electrode is formed in the local electrode structure, there is an advantage that can prevent the recombination loss.

Hereinafter, a method of manufacturing the solar cell according to the present invention as described above will be described in detail.

First, a semiconductor layer having a first conductivity type is prepared. At this time, a semiconductor substrate of the first conductive type may be prepared, or a semiconductor layer of the first conductive type may be formed on the substrate.

Next, after forming the second conductive semiconductor layer having the opposite conductivity type on one surface of the first conductive semiconductor layer, the front electrode is formed to be connected to at least a portion of the second conductive semiconductor layer, The paste containing the electroconductive particle which has a particle diameter is screen-printed.

At this time, the front electrode is preferably screen printed to occupy 5% or less of the total area of the second conductive semiconductor layer, and the conductive particles and paste used in the screen printing are as described above.

Next, a rear electrode is formed to be connected to at least a portion of the first conductive semiconductor layer. In this case, the rear electrode may be formed on the entire rear surface of the first conductive semiconductor layer, or may be locally formed by screen printing using the same paste as the front electrode.

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

Experimental Example 1 Density Observation

In Experimental Example 1, the packing density after firing of the general-purpose paste used in the screen printing method for forming the electrode of the conventional solar cell and the paste proposed by the present invention was observed.

After the general purpose paste and the paste of the present invention were screen-printed and fired on a silicon substrate, a cross section of a 150 μm branched electrode was observed with a scanning electron microscope (SEM).

3A and 3B are scanning electron micrographs of 2000 and 5000 magnifications for the case of using the general-purpose paste, respectively, and FIGS. 4A and 4B are scanning electron micrographs of 2000 and 5000 magnifications for the case of the paste of the present invention, respectively. to be.

From these drawings, it was confirmed that the density of the paste was higher when the present invention was used, and from this it could be expected that the specific resistance of the electrode was lower.

Experimental Example 2 Observation of Adhesion According to Firing Conditions

In the case of the general purpose paste, the glass frit serves to bond the conductive particles to the substrate after firing. Therefore, in the case of paste without glass frit, there is a problem in adhesion to the substrate.

In Experimental Example 2, after screen printing using the paste proposed in the present invention, the adhesion with the substrate was observed for the case where the firing conditions were different.

In other words, the paste of the present invention was evaluated using heating by an infrared lamp using a convection oven, a hot plate, and a belt furnace to evaluate adhesion to a silicon substrate. As an evaluation method, 3M (3M) tape was attached on the formed electrode, and then peeled off. The results are shown in Table 1 below.

Firing conditions  result Convection oven 300 ℃, 30 minutes × 400 ° C., 30 minutes × Hot plate 200 ° C, 30 minutes × 300 ℃, 30 minutes △ 400 ° C., 30 minutes △ 200 ° C, 2 minutes × Belt Furnace (Infrared Lamp) 300 ℃, 2 minutes ○ 400 ° C., 2 minutes ○ 400 ° C., 1 minute ○ 400 ° C., 0.5 minutes ○ 500 ° C., 0.25 minutes ○ 700 ° C, 0.25 minutes ○

As shown in Table 1, the convection oven and hot place did not show good adhesion under the suggested firing conditions, but there was no problem with adhesion above 300 ° C. when heated by an infrared lamp using a belt furnace.

Experimental Example 3 Manufacture of Solar Cells

In Experimental Example 3, a solar cell was manufactured using a silver paste containing silver nanopowders. The solar cell process using the nano silver paste of the present invention as a front electrode is not much different from the conventional screen printing process, and the detailed manufacturing process is as follows.

First, an N layer was formed by doping phosphorus on a P-type substrate, and then the doping layer on the side of the substrate was removed.

Next, an aluminum paste was printed on the entire back surface of the substrate by the screen printing method and baked at 600 ° C. or higher to form a back electrode.

Next, the silver nano paste was printed on the N layer by the screen printing method, and baked at 400 ° C. for 1 minute by a heating method by an infrared lamp to form a front electrode.

Next, on the N layer except for the front electrode, a silicon nitride film was deposited by PECVD to form an antireflection film having a refractive index of 2.0 to 2.1 and a thickness of 700 to 950 nm.

Next, the silicon nitride film was heat-treated and hydrogen passivated to complete the manufacture of the solar cell.

As described above, according to the present invention, the advantages obtained when the nano paste including the nano conductive particles having a particle diameter of 100 nm or less is applied to the front electrode (or even the rear electrode) of the solar cell are as follows.

First, contact resistance is reduced. Conventional pastes contain a glass frit to improve adhesion, which is a factor that increases the contact resistance between the silicon substrate and the metal electrode. However, the nanopaste of the present invention does not include a glass frit and has excellent adhesion even without the glass frit, thereby reducing contact resistance.

Second, shading loss is reduced. Since the solar cell uses sunlight incident through the front surface, the larger the electrode area formed on the front surface, the smaller the amount of incident light. This is called shading loss, and reducing it increases the efficiency of the solar cell.

However, the front electrode should be secured to the extent that the generated current can flow without loss. In case of paste, loss of shading loss usually occurs 7 ~ 8%. However, the lower the specific resistance of the electrode can be reduced.

While the resistivity of the conventional paste is 5 μΩcm, the resistivity of the nano pastes of the present invention is 3 μΩcm, so the shading loss can be lowered to 5% or less in the present invention.

Third, lead-free products can be produced. Since no glass frit containing lead oxide is used, trade restrictions on heavy metals can be avoided.

As described above, in the present invention, since the electrode is formed using the paste without the glass frit, there is an effect of reducing the contact resistance of the electrode.

In addition, in the present invention, since the electrode is formed by using a paste having a lower resistivity, the resistivity of the electrode may be lowered, thereby reducing the line width of the electrode, thus reducing the shading loss.

And since the present invention does not use a glass frit containing lead has the effect of producing a lead-free (lead-free) product.

1 is a cross-sectional view showing the structure of a solar cell according to a first embodiment of the present invention,

2 is a cross-sectional view showing the structure of a solar cell according to a second embodiment of the present invention,

3A and 3B are scanning electron micrographs of 2000 magnification and 5000 magnification for the case of using the general purpose paste, respectively.

4A and 4B are scanning electron micrographs of 2000 magnification and 5000 magnification for the case of using the paste of the present invention, respectively.

Claims (12)

A first conductive semiconductor layer; A second conductive semiconductor layer formed on one surface of the first conductive semiconductor layer and having an opposite conductivity type; Formed by screen printing a paste containing conductive particles in contact with at least a portion of the second conductive semiconductor layer and having a particle diameter of 100 nm or less, wherein the total area of the second conductive semiconductor layer is 5% or less. A front electrode occupying; A back electrode in contact with at least a portion of the first conductive semiconductor layer Solar cell comprising a. The method of claim 1, A solar cell having a specific resistance of the front electrode of 3 μΩcm or less. The method of claim 1, The rear electrode is formed by screen printing a metal paste containing conductive particles having a particle diameter of 100 nm or less on the other surface of the first conductive semiconductor layer, and has a specific resistance of 3 μΩcm or less. The method according to claim 1 or 3, The conductive particles are any one of Ag, Cu, Au, Ti, W, Ni, Cr, Mo, Pb, Pd, Pt. The method according to claim 1 or 3, The paste includes 50-90% by weight of conductive particles, 9-40% by weight of an organic solvent which is one of water and alcohol, and 1-10% by weight of a binder. Preparing a semiconductor layer having a first conductivity type; Forming a second conductive semiconductor layer having an opposite conductivity type on one surface of the first conductive semiconductor layer; Forming a front electrode to be connected to at least a portion of the second conductive semiconductor layer, and screen printing a paste including conductive particles having a particle diameter of 100 nm or less; Forming a rear electrode to be connected to at least a portion of the first conductive semiconductor layer Method for manufacturing a solar cell comprising a. The method of claim 6, The front electrode is formed to occupy 5% or less of the total area of the second conductive semiconductor layer. The method of claim 6, In the forming of the back electrode, a method of manufacturing a solar cell for screen printing a metal paste including conductive particles having a particle diameter of 100nm or less on the other surface of the first conductive semiconductor layer. The method of claim 6 or 8, After the screen printing method of manufacturing a solar cell heat treatment at a temperature of 300-700 ℃ for 5 minutes or less. The method of claim 9, The heat treatment is a manufacturing method of a solar cell using a heating method by an infrared lamp. The method of claim 6 or 8, The conductive particles are any one of Ag, Cu, Au, Ti, W, Ni, Cr, Mo, Pb, Pd, Pt. The method of claim 6 or 8, The paste includes 50-90% by weight of conductive particles, 9-40% by weight of an organic solvent which is one of water and alcohol, and 1-10% by weight of a binder.