KR20120080904A - Solar cell and manufacturing method thereof - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to reduce resistance by increasing a cross section of an electrode unit. CONSTITUTION: A substrate has a first conductive type. An emitter unit(120) is arranged on one surface of a substrate and has a second conductive type which is opposite to the first conductive type. An antireflection layer(130) is arranged on the emitter unit. The electrode unit is electrically and physically connected to the emitter unit. The electrode unit is made of the first conductive paste.

Description

Solar cell and its manufacturing method {SOLAR CELL AND MANUFACTURING METHOD THEREOF}

The present invention relates to a solar cell and a method of manufacturing the same.

With the recent prediction of the depletion of existing energy resources such as oil and coal, the interest in renewable energy to replace them is increasing, and solar cells producing electric energy from solar energy are attracting attention.

A typical solar cell includes a substrate and an emitter layer, each of which is composed of semiconductors of different conductive types, such as p-type and n-type, and electrodes connected to the substrate and the emitter, respectively. At this time, a p-n junction is formed at the interface between the substrate and the emitter portion.

When light is incident on a solar cell having such a configuration, electrons in the semiconductor become free electrons (hereinafter referred to as 'electrons') by a photoelectric effect, and electrons and holes according to the principle of pn junction. Moves toward the n-type semiconductor and the p-type semiconductor, respectively, for example toward the emitter portion and the substrate. The moved electrons and holes are collected by respective electrodes electrically connected to the substrate and the emitter portion.

The technical problem to be achieved by the present invention is to provide a high efficiency solar cell.

Another technical problem to be achieved by the present invention is to provide a method of manufacturing a solar cell for manufacturing a high efficiency solar cell.

According to an embodiment of the present invention, a solar cell includes a substrate of a first conductivity type; An emitter portion of a second conductivity type located on one side of the substrate and having a conductivity type opposite to the first conductivity type; An antireflection film positioned on the emitter portion; And an electrode portion electrically and physically connected to the emitter portion, wherein the electrode portion is formed of a first conductive paste and is formed of a lower layer in contact with the emitter portion and a second conductive paste and is disposed on the lower layer. The upper width of the upper layer is 0.8 times or more than the lower width of the lower layer.

The lower layer is formed to the first thickness, the upper layer is formed to the second thickness, and the first thickness and the second thickness are formed differently. For example, the second thickness is formed larger than the first thickness.

The first conductive paste and the second conductive paste may have the same composition or may have different compositions.

The first conductive paste and the second conductive paste may each include a glass frit.

In a solar cell having such a configuration, in a method of manufacturing a solar cell in which an electrode portion including a lower film and an upper film is formed on a substrate of a solar cell, a first conductive paste is formed by using a first screen mask having a hole pattern having a first line width. Forming a lower layer formed of the lower layer; And forming an upper layer formed of the second conductive paste on the lower layer by using a second mask having a hole pattern having a second line width larger than the first line width, on the lower layer.

In this case, the first line width of the first screen mask is 60% to 80% of the second line width of the second mask. The upper layer is formed thicker than the lower layer, and the upper width of the upper layer is 0.8 times or more than the lower width of the lower layer.

Before forming the lower layer, forming an emitter portion of a second conductivity type on one side of the substrate having a first conductivity type; And forming an anti-reflection film on the emitter portion.

Forming the lower layer includes printing a first conductive paste to form a lower layer pattern and drying the lower layer pattern to increase the line width and decrease the thickness of the lower layer pattern, wherein forming the upper layer Printing the second conductive paste to form an upper layer pattern and drying the upper layer pattern.

The lower film pattern and the upper film pattern can be fired at the same time.

According to this feature, even if the electrode portion is formed by performing the screen printing method twice, the difference between the upper width and the lower width of the electrode portion is suppressed. That is, the electrode portion is formed in a shape having a wider lower width than the upper width, for example, a cross-sectional shape of a substantially quadrangular shape instead of a cross section of a hat-shaped shape.

Therefore, it is possible to form a high aspect ratio electrode portion while minimizing the amount of conductive paste used.

In addition, due to the increase in the cross-sectional area of the electrode portion, the resistance decreases, the fill factor of the solar cell is improved, and the reduction of the light receiving area is suppressed, thereby reducing the short circuit current density.

As a result, the efficiency of the solar cell is improved.

1 is a perspective view of an essential part of a solar cell according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view of "II-II" of FIG. 1.
FIG. 3 is a plan view of a first screen mask and a second screen mask used when forming the electrode part of FIG. 1. Shown on the right side of 3 is a plan view of the second screen mask used when forming the upper film.
4 is a flowchart sequentially illustrating a method of manufacturing a solar cell using the first and second screen masks of FIG. 3.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In order to clearly illustrate the present invention in the drawings, portions not related to the description are omitted, and like reference numerals are given to similar portions throughout the specification.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. When a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the case directly above another portion but also the case where there is another portion in between. Conversely, when a part is "directly over" another part, it means that there is no other part in the middle.

Next, a solar cell and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a perspective view of an essential part of a solar cell according to an exemplary embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of "II-II" of FIG. 1.

As shown, the solar cell includes a substrate 110, an emitter portion 120 positioned on one surface of the substrate 110, for example, a front surface, and an anti-reflection film disposed on the emitter portion 120 ( 130, a first electrode 140 positioned on the emitter portion 120 in the region where the anti-reflection film 130 is not located, and a back electric field located on the back surface of the substrate 110. surface field (BSF) unit 150, and a second electrode 160 positioned on the rear surface of the rear electric field unit 150.

The substrate 110 is made of a silicon wafer of a first conductivity type, for example an n-type conductivity type. In this case, the silicon may be monocrystalline silicon, a polycrystalline silicon substrate, or amorphous silicon.

Since the substrate 110 has an n-type conductivity type, the substrate 110 contains impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb).

Alternatively, the substrate 110 may be of a p-type conductivity type and may be made of a semiconductor material other than silicon.

When the substrate 110 has a p-type conductivity type, the substrate 110 may contain impurities of trivalent elements such as boron (B), gallium, and indium.

The substrate 110 may be formed of a texturing surface on which at least one surface of the surface is textured.

The emitter portion 120 positioned on the front surface of the substrate 110 is an impurity portion having a second conductivity type, for example, a p-type conductivity type, which is opposite to the conductivity type of the substrate 110. Pn junction with (110).

Due to the built-in potential difference due to this pn junction, the electron-hole pair, the charge generated by the light incident on the substrate 110, is separated into electrons and holes, and the electrons move toward the n-type The hole moves towards the p-type.

Therefore, when the substrate 110 is n-type and the emitter portion 120 is p-type, the separated electrons move toward the substrate 110 and the separated holes move toward the emitter portion 120. Therefore, electrons are the majority carriers in the substrate 110, and holes are the majority carriers in the emitter part 120.

When the emitter section 120 has a p-type conductivity type, the emitter section 120 is formed by doping an impurity of a trivalent element such as boron (B), gallium (Ga), indium (In) .

On the contrary, when the substrate 110 has a p-type conductivity type, the emitter portion 120 has an n-type conductivity type. In this case, the separated holes move toward the substrate 110 and the separated electrons move toward the emitter part 120.

When the emitter part 120 has an n-type conductivity type, impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb) may be formed by doping the substrate 110.

The anti-reflection film 130 formed on the emitter portion 120 of the front surface of the substrate 110 reduces reflectivity of light incident through the front surface of the substrate 110 and increases selectivity of a specific wavelength region. Increase the efficiency of the solar cell.

The anti-reflection film 130 having such a function may have a thickness of about 70 nm to 80 nm, and may include at least one of a silicon oxide film, a silicon nitride film, a titanium dioxide film, and an aluminum oxide film.

The first electrode 140 is formed on the emitter portion 120 and is electrically connected to the emitter portion 120.

The first electrode 140 includes a plurality of front electrodes extending side by side in one direction and a plurality of front electrode current collectors positioned in a direction crossing the front electrodes and having a larger line width than the front electrodes.

Each front electrode collects charges, for example, electrons, which are moved toward the emitter part 120, and transfers them to the current collector for the front electrode.

The first electrode 140 including the front electrode and the current collector for the front electrode is formed of a double layer of the lower layer 142 and the upper layer 144.

The lower layer 142 is formed of the first conductive paste and is in contact with the emitter portion 120. The upper layer 144 is formed of a second conductive paste and is positioned on the lower layer 142.

The first conductive paste and the second conductive paste may be the same composition, or may be different compositions.

The first conductive paste and the second conductive paste may be made of silver (Ag) paste including glass frit.

In this case, the content of the silver particles contained in the first conductive paste and the silver particles contained in the second conductive paste may be different from each other or may be the same.

The first electrode 140 having such a configuration applies a conductive paste, that is, silver (Ag) paste, onto the antireflection film 130 using a screen printing process, and calcinates the substrate 110 at a temperature of about 750 ° C to 800 ° C. In the firing process, the emitter unit 120 may be electrically connected to the emitter unit 120.

In this case, the above-described electrical connection is performed as the etching component included in the silver (Ag) paste is etched from the anti-reflection film 130 so that the silver particles come into contact with the emitter portion 120.

The upper layer 144 of the first electrode 140 is formed to have substantially the same width as the lower layer 142. That is, in the present embodiment, the upper width W2 of the upper layer 144 is formed in a range of 0.8 to 1.0 times the lower width W1 of the lower layer 142. Therefore, the first electrode 140 has a quadrangular cross-sectional shape as a whole.

When the lower film is formed by the screen printing method, the conductive paste spreads due to the influence of the organic material contained in the paste material during the drying process of the conductive paste, thereby increasing the line width of the lower film than the line width of the first printed lower film pattern.

For example, when the width of the first printed lower layer pattern is 100 μm, the lower layer pattern after the drying process is formed to have a width of about 120 μm to 130 μm due to the spreading phenomenon. That is, the lower layer pattern after the drying process has a width that is increased by about 20% to 30% than the first printed lower layer pattern.

In addition, due to the spreading phenomenon, the thickness of the lower layer is reduced than that of the originally printed lower layer pattern.

However, when the conductive paste is printed on the lower layer by screen printing again to form the upper layer, the organic substance contained in the conductive paste material is absorbed by the lower layer, and the spreading phenomenon is significantly reduced.

Therefore, when the first electrode composed of the lower film and the upper film is formed by a conventional double printing method, the first electrode has a cross-sectional shape of a hat-shaped shape in which the width of the upper film is 0.8 times or less than the width of the lower film.

However, in the first electrode 140 of the present embodiment, the upper width W2 of the upper layer 144 is 0.8 times or more larger than the lower width W1 of the lower layer 142, preferably 0.8 to 1.0 times. It is formed in the size of (0.8W1≤W2≤W1).

As described above, since the upper width W2 of the first electrode 140 of the present exemplary embodiment is formed to be 0.8 times or more larger than the lower width W1, the first electrode 140 has a high aspect ratio. Here, the aspect ratio refers to the ratio of the width and the thickness of the first electrode 140.

The lower layer 142 is formed to have a first thickness T1, and the upper layer 144 is formed to have a second thickness T2 greater than the first thickness T1.

Although the variation is severe depending on the composition of the conductive paste, when the total thickness (T1 + T2) of the first electrode 140 is 30 μm to 45 μm, the first thickness T1 of the lower layer 142 is approximately 10. It is formed to about 15 to 15 ㎛ ㎛, the second thickness (T2) of the upper film 144 is formed of about 20 to 30 ㎛.

The back surface field part 150 is a region in which impurities of the same conductivity type as the substrate 110 are doped at a higher concentration than the substrate 110, for example, a p + region.

The back surface field part 150 forms a potential barrier due to a difference in impurity concentration with the substrate 110, thereby preventing hole movement toward the back surface of the substrate 110. As a result, electrons and holes are recombined and disappeared near the surface of the substrate 110.

The second electrode 160 positioned on the rear side of the rear electric field unit 150 may include a plurality of rear electrodes 162 for collecting charges, for example, electrons, which move toward the substrate 110, and a current collector 164 for the rear electrodes. It includes.

The back electrode 162 includes aluminum (A), nickel (Ni), copper (Cu), silver (Ag), tin (Sn), zinc (Zn), indium (In), titanium (Ti), and gold (Au). And at least one conductive material selected from the group consisting of a combination thereof.

The rear electrode current collector 164 may be positioned in a direction parallel to the front electrode current collector. The current collector for the rear electrode outputs the charge collected from the rear electrode to the outside.

The operation of the solar cell having such a structure is as follows.

When light irradiated to the solar cell is incident on the substrate 110 through the emitter unit 120, electron-hole pairs are generated by the light energy incident on the substrate 110.

At this time, when the front surface of the substrate 110 is formed as a texturing surface, the light reflectivity at the front surface of the substrate 110 is reduced, and the absorption rate of the light is increased to improve the efficiency of the solar cell.

In addition, the reflection loss of light incident on the substrate 110 by the anti-reflection film 130 is reduced, so that the amount of light incident on the substrate 110 is further increased.

These electron-hole pairs are separated from each other by the pn junction of the substrate 110 and the emitter portion 120, and the electrons move toward the substrate 110 having an n-type conductivity type, and the holes form a p-type conductivity type. It moves to the emitter portion 120 having a.

As such, the electrons moved toward the substrate 110 move to the second electrode 160 through the rear electric field part 150, and the holes moved toward the emitter part 120 move to the first electrode 140.

Therefore, when the first electrode 140 of one solar cell and the second electrode 160 of the solar cell adjacent to each other are connected with a conductor such as an interconnector, a current flows, which is used as power from the outside.

Hereinafter, a method of manufacturing a solar cell according to an embodiment of the present invention will be described with reference to FIGS. 3 and 4.

FIG. 3 is a plan view of a first screen mask and a second screen mask used when forming the electrode part of FIG. 1, and a plan view of the first screen mask used when the lower film is formed on the left side of FIG. Shown on the right side of 3 is a plan view of the second screen mask used when forming the upper film.

4 is a process diagram sequentially illustrating a method of manufacturing a solar cell using the first and second screen masks of FIG. 3.

First, the emitter portion 120 is formed on one surface, for example, the front surface of the substrate 110 having the first conductivity type, and the anti-reflection film 130 is formed on the emitter portion 120.

When the substrate 110 has an n-type conductivity type, the emitter portion 120 is formed by doping the substrate 110 with impurities of trivalent elements such as boron (B), gallium (Ga), and indium (In). can do.

On the contrary, when the substrate 110 has a p-type conductivity type, the emitter unit 120 may include impurities of pentavalent elements such as phosphorus (P), arsenic (As), and antimony (Sb) on the substrate 110. Can be formed by doping.

Before forming the emitter unit 120, one surface of the substrate 110 may be textured to form a plurality of irregularities on the entire surface of the substrate 110.

Texturing generally consists of soaking the substrate 110 for a period of time in a bath containing an alkaline solution.

For example, the texturing operation may be performed in an alkaline solution at a temperature of about 80 ° C. for about 20 to 40 minutes. When the texturing operation is performed, the front surface of the substrate 110 is etched to form irregularities having an irregular pyramid structure.

As the alkaline solution, approximately 2% by weight (wt%) to 5% by weight of potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution may be used, and an ammonium hydroxide (NH 4 OH) solution may be used.

At this time, the height of the irregularities formed, that is, the height of each pyramid structure may be about 1㎛ to 10㎛.

After the emitter portion 120 is formed, the anti-reflection film 130 is formed using chemical vapor deposition or sputtering such as PECVD.

The anti-reflection film 130 may be one of a silicon nitride film, a silicon oxide film, an aluminum oxide film, a silicon oxynitride film, or a titanium dioxide film.

The anti-reflection film 130 may include two films having different physical properties. In this case, the lower layer may be formed of a material having a high refractive index, and the upper layer may be formed of a material having a lower refractive index than the lower layer.

After the anti-reflection film 130 is formed, the rear electrode 162 and the rear electric field unit 150 are formed on the other side of the substrate 110, for example, the rear side.

The back electrode 162 may be formed by depositing aluminum, and the back electric field unit 150 may be formed by heat-treating the substrate 110 on which aluminum is deposited.

After the rear electric field unit 150 is formed, a portion of the rear electrode 162 may be removed to form the current collector 164 for the rear electrode.

Subsequently, the first conductive paste is screen printed on the antireflection film 130 to form a lower film pattern 142A. When forming the lower layer pattern 142A, the first screen mask 210 illustrated on the left side of FIG. 3 is used.

The first screen mask 210 has hole patterns HP1 and HP2 having the first line widths W3-1 and W3-2, and the hole pattern HP1 having the first line width W3-1 has a front electrode. The hole pattern HP2 having the first line width W3-2 is for forming a current collector for the front electrode.

When the first conductive paste is printed using the first screen mask 210, the first printed lower layer pattern 142A has the same first line width W3 as the hole patterns HP1 and HP2 of the first screen mask 210. -1, W3-2).

However, when the printed lower layer pattern 142A is dried, the lower layer pattern 142A is changed due to the influence of the organic material contained in the paste material.

That is, the line width of the lower layer pattern 142A is increased than the first line widths W3-1 and W3-2 of the first screen mask 210, and the thickness is reduced.

Therefore, when the drying process is completed, the lower layer pattern 142A is formed to have a line width and a thickness as shown in FIG. 1.

In the drying process of the lower layer pattern 142A, a paste spread phenomenon occurs as described above.

Therefore, in order to form the line widths of the lower layer pattern 142A and the upper layer pattern 144A in the same or similar manner, the first line widths W3- of the hole patterns HP1 and HP2 provided in the first screen mask 210 are formed. 1 and W3-2 are 60% to 80% of the second line widths W4-1 and W4-2 of the hole patterns HP3 and HP4 provided in the second screen mask 220 to be described later. It is narrowly formed {(0.6W4-1) ≤W3-1≤ (0.8W4-1), (0.6W4-2) ≤W3-2≤ (0.8W4-2)}.

After the lower layer pattern 142A is dried, an upper layer pattern 144A is formed on the lower layer pattern 142A.

The upper film pattern 144A is formed by screen printing the second conductive paste using the second screen mask 220.

In this case, the second conductive paste may have the same composition as the first conductive paste or may be different from each other.

The second screen mask 220 has hole patterns HP3 and HP4 having second line widths W4-1 and W4-2. The second line width W4-1 of the hole pattern HP3 is greater than the first line width W3-1 of the hole pattern HP1 formed in the first screen mask 210, and the second line width of the hole pattern HP4 is formed. W4-2 is greater than the first line width W3-2 of the hole pattern HP2 formed in the first screen mask 210.

In this case, the second line widths W4-1 and W4-2 of the hole patterns HP3 and HP4 provided in the second screen mask 220 are the same as the line widths of the lower layer pattern 142A after the drying is completed. It is desirable to form similarly.

On the other hand, since the second line widths W4-1 and W4-2 of the hole patterns HP3 and HP4 are larger than the first line widths W3-1 and W3-2 of the hole patterns HP1 and HP2, the second screen is larger. When the upper layer pattern 144A is formed using the mask 220, the first thickness T1 of the upper layer pattern 144A is larger than the second thickness T2 of the lower layer pattern 142A.

After printing the upper film pattern 144A, the upper film pattern 144A is dried. When the upper film pattern 144A is dried, the organic component contained in the second conductive paste material is absorbed by the lower film 142A.

Therefore, the upper layer pattern 144A hardly increases compared to the second line widths W4-1 and W4-2 of the hole patterns HP3 and HP4 provided in the second screen mask 220, and the thickness is also substantially reduced. I never do that.

Thereafter, the lower layer pattern 142A and the upper layer pattern 144A are simultaneously baked to form the first electrode 140 including the lower layer 142 and the upper layer 144.

After forming the first electrode 140, a current collector 164 for the rear electrode of the second electrode 160 may be formed.

In this case, the current collector 164 for the rear electrode may also be formed by the same double printing method as the first electrode 140.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

110: substrate 120 emitter part
130: antireflection film 140: first electrode
142: underlayer 142A: underlayer pattern
144: top film 144A: top film pattern
150: rear electric field unit 160: second electrode

Claims (13)

A substrate of a first conductivity type;
An emitter portion of a second conductivity type located on one side of the substrate and having a conductivity type opposite to the first conductivity type;
An anti-reflection film positioned on the emitter portion; And
Electrode portion electrically and physically connected to the emitter portion
Including,
The electrode portion may include a lower layer formed of a first conductive paste and in contact with the emitter portion, and an upper layer formed of a second conductive paste and positioned on the lower layer, and the upper width of the upper layer may be lower than the lower width of the lower layer. Solar cells are formed more than 0.8 times. In claim 1,
The lower layer is formed of a first thickness, the upper layer is formed of a second thickness, the first thickness and the second thickness of the solar cell. In claim 2,
And the second thickness is greater than the first thickness. 4. The method according to any one of claims 1 to 3,
A solar cell having the same composition as the first conductive paste and the second conductive paste. 4. The method according to any one of claims 1 to 3,
A solar cell having a different composition of the first conductive paste and the second conductive paste. 4. The method according to any one of claims 1 to 3,
The first conductive paste and the second conductive paste each comprise a glass frit. In the solar cell manufacturing method of forming an electrode portion including a lower film and an upper film on a substrate of a solar cell,
Forming a lower layer made of a first conductive paste using a first screen mask having a hole pattern having a first line width; And
Forming an upper layer made of a second conductive paste on the lower layer by using a second mask having a hole pattern having a second line width larger than the first line width;
Method for manufacturing a solar cell comprising a. In claim 7,
And forming a first line width of the first screen mask to 60% to 80% of a second line width of the second mask. In claim 7 or 8,
The solar cell manufacturing method of forming the upper layer thicker than the lower layer. The method of claim 9,
A method of manufacturing a solar cell, wherein the upper width of the upper layer is formed to be 0.8 times or more than the lower width of the lower layer. 11. The method of claim 10,
Before forming the lower layer,
Forming an emitter portion of a second conductivity type on one side of the substrate having a first conductivity type; And
Forming an anti-reflection film on the emitter portion
Method for manufacturing a solar cell further comprising. 12. The method of claim 11,
The forming of the lower layer may include printing the first conductive paste to form a lower layer pattern, and drying the lower layer pattern to increase the line width and reduce the thickness of the lower layer pattern. Way. The method of claim 12,
The forming of the upper layer may include printing the second conductive paste to form an upper layer pattern and drying the upper layer pattern.
A method of manufacturing a solar cell which simultaneously fires the lower layer pattern and the upper layer pattern.

Images