KR101523272B1 - Method for texturing a solar cell using ion implantation - Google Patents

Abstract

The present invention relates to a solar cell and, more particularly, to a method for manufacturing a solar cell by injecting hydrogen into a silicon wafer with a hydrogen ion implantation, performing a thermal treatment, and texturing the solar cell according to a crack on the silicon wafer. The purpose of the present invention is to provide a solar cell texturing method capable of texturing the solar cell using an ion implantation.

Description

TECHNICAL FIELD The present invention relates to a method of texturing a solar cell using ion implantation,

The present invention relates to a solar cell, and more particularly, to a method of manufacturing a solar cell by texturing a solar cell according to a crack propagated on a silicon wafer by injecting hydrogen into a silicon wafer by hydrogen ion implantation and performing heat treatment It is about.

With the recent depletion of existing energy resources such as oil and coal, interest in alternative energy to replace them is increasing. Among them, solar energy has attracted particular attention because it has abundant energy resources and there is no problem about environmental pollution. The use of solar energy includes solar energy that generates the steam needed to rotate the turbine using solar heat and solar energy that converts photons to electrical energy using the properties of semiconductors, Refers to a photovoltaic cell (hereinafter, referred to as a "solar cell").

The basic structure of a solar cell is a p-type semiconductor such as a diode and an n-

When a light is incident on a solar cell, the electrons and electrons that are charged (-) escape (+) due to the interaction between the light and the material constituting the semiconductor of the solar cell So that the current flows as they move. The p-type (101) and n-type semiconductors constituting the solar cell are attracted toward the n-type semiconductor and the holes are attracted toward the p-type semiconductor to form n-type semiconductors And the p-type semiconductor 102. When these electrodes are connected to each other by electric wires, electric power can be obtained because electricity flows.

On the other hand, the solar cell can be manufactured by forming a conductive layer of a conductive type different from that of the silicon substrate and forming an antireflection film (not shown) and a front electrode (not shown) and a rear electrode (not shown). However, before such a process is performed, a silicon substrate is subjected to a process of slicing a silicon ingot to remove damaged layers generated on the substrate surface, and to reduce the reflectance of the silicon substrate, a texturing process is performed.

The texturing process is a process that makes irregularities on the surface of the substrate to make it possible to absorb more light incident on the substrate.

Generally, the etching speed depends on the crystal orientation of silicon. Only the crystal orientation in which the etching rate is the slowest is left, and the substrate is textured and appears as a pyramid.

In the general texturing process, irregularities are formed on the entire surface of the silicon substrate by anisotropic etching using an etchant solution obtained by mixing an alkaline solution (for example, KOH and NaOH) with IPA (isopropyl alcohol) A wet method for performing texturing, or the like is used.

However, there is a difficulty in controlling the size of the pyramid in the case of texturing using such a wet method. That is, when the height of the texturing is increased, the paste may not uniformly exist due to the texturing height in the screen printing process.

In addition, the resistance is increased due to such unevenness, which may cause a loss.

1. Korean Published Patent No. 10-2009-0102508 2. Korean Patent Publication No. 10-2012-0070314 3. Korean Patent Publication No. 1020110005520

It is an object of the present invention to provide a solar cell texturing method for performing texturing of a solar cell using ion implantation.

The present invention provides a solar cell texturing method for performing texturing of a solar cell using ion implantation in order to achieve the above-described object.

The solar cell texturing method includes:

A solar cell texturing method in a solar cell manufacturing process,

Preparing a semiconductor substrate;

Implanting ions into a prepared semiconductor substrate;

Annealing the semiconductor substrate on which the ions are implanted;

Forming a plurality of bubbles in the semiconductor substrate by the heat treatment;

Propagating microcracks in a specific direction from the plurality of generated bubbles; And

And forming a pyramid shape on the upper surface of the semiconductor substrate by the propagated micro cracks.

At this time, the ion implantation may be characterized in that the pattern size of the implantation is determined according to the texturing height.

In addition, the ion may be a hydrogen ion.

The ion implantation direction may be perpendicular to the upper surface of the semiconductor substrate.

(여기서, y는 텍스쳐링 높이이고, x는 텍스쳐링 너비를 나타낸다)으로 정해지는 것을 특징으로 할 수 있다.Further, the pattern interval of the implantation is expressed by the following equation

(Where y is the texturing height and x is the texturing width).

Further, the crack propagates along the silicon surface of the semiconductor substrate.

In addition, the crack propagation may occur in a case where the bonding energy among the silicon planes of the semiconductor substrate is smaller.

The semiconductor substrate may be a substrate having a dot pattern.

In addition, the ion implantation may be characterized by a point shape rather than a continuous shape.

According to the present invention, since the texturing is performed using the hand ion implantation, the height of the texturing can be freely adjusted.

Another advantage of the present invention is that since the height of the texturing is uniformly maintained, the resistance after the doping can be kept constant, thereby reducing the loss.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a phenomenon in which bubbles generated by injected hydrogen are generally diffused in a lateral direction in a silicon. FIG.
FIG. 2 is a diagram illustrating a phenomenon in which bubbles generated by injected hydrogen generally diffuse in a longitudinal direction through a weak spot inside the silicon. FIG.
3 is a flowchart illustrating a process of performing texturing using ion implantation according to an embodiment of the present invention.
4 is a conceptual diagram according to the hydrogen implantation step (S320) shown in FIG.
5 is a conceptual diagram showing an arrangement of bubbles generated by the hydrogen implantation shown in FIG.
FIG. 6 is a conceptual diagram showing the propagation direction of micro cracks due to the bubbles generated by the hydrogen implantation shown in FIG. 3. FIG.
FIG. 7 is a conceptual view showing texturing according to the propagation of micro cracks shown in FIG. 3. FIG.
FIG. 8 is a conceptual diagram showing a texturing state according to the pyramid shape generation step (S340) shown in FIG.
9 is a conceptual diagram showing the size of an implantation pattern according to a general height.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for similar elements in describing each drawing.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. The term "and / or" includes any combination of a plurality of related listed items or any of a plurality of related listed items.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be construed as ideal or overly formal in meaning unless explicitly defined in the present application Should not.

Hereinafter, a method of texturing a solar cell using ion implantation according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In general, a solar cell is a device that converts solar energy into electrical energy. It has a junction form of a p-type semiconductor and an n-type semiconductor, and the basic structure is the same as a diode.

Most of the solar cells consist of large-area pn junction diodes. The basic requirement for the photovoltaic energy conversion of the solar cell is that the p-type semiconductor region has a small electron density and a large hole density hole density, and the n-type semiconductor region has a large electron density and a small hole density, electrons must exist asymmetrically within the semiconductor structure.

Therefore, in a diode formed of a junction of a p-type semiconductor and an n-type semiconductor in a thermal equilibrium state, a charge imbalance occurs due to a diffusion due to a concentration gradient of a carrier and an electric field is thereby formed So that diffusion of abnormal carriers does not occur.

When light above a band gap energy, which is an energy difference between a conduction band and a valence band of the material, is applied to the above-described pn junction diode, electrons, which receive light energy, . ≪ / RTI > At this time, the electrons excited by the conduction band are allowed to move freely, and electrons are generated in the valence band. This is referred to as an excess carrier, and the excess carrier is diffused by a concentration difference in a conduction band or a valence band.

At this time, the electrons excited in the p-type semiconductor and the holes formed in the n-type semiconductor are called minority carriers, and carriers in the p-type semiconductor or the n-type semiconductor before the junction (that is, holes in the p- Type semiconductor is referred to as a majority carrier by distinguishing it from a minority carrier. The majority carriers are subject to flow interruption due to the energy barrier created by the electric field, but electrons, which are minority carriers of the p-type semiconductor, can migrate toward the n-type semiconductor.

The diffusion of the minority carriers causes a potential drop in the pn junction diode, and when the electromotive force generated at the positive terminal of the pn junction diode is connected to an external circuit, it acts as a solar cell.

A texturing process according to an embodiment of the present invention in the process of manufacturing such a solar cell will be described with reference to FIGS. 1 to 9. FIG.

FIG. 1 is a view for explaining a phenomenon in which bubbles generated by injected hydrogen are diffused in the lateral direction in the inside of silicon, and FIG. 2 is a view for explaining a phenomenon in which bubbles generated by injected hydrogen are weak inside a silicon ) And spread in the longitudinal direction. In addition, in the case of FIG. 1, the bubbles are diffused in both directions in the silicon of the semiconductor substrate. In Fig. 2, both ends of the bubble are diffused into a weak spot in the silicon of the semiconductor substrate.

Generally, the semiconductor substrate is composed of a backside electrode layer (not shown), a backside front layer (not shown), a base layer (not shown), an emitter layer (not shown), and an insulation layer (not shown).

In addition, the emitter layers, which are the second impurity portions, are provided above and below the base layer, which is the first impurity, respectively. The emitter layer is located at the top of the base layer located on the side where the light is incident.

An insulating layer may be disposed on the emitter layer, and the insulating layer may be an antireflection film layer, a passivation layer, a dielectric, or the like.

A back surface field (BSF) is sequentially formed on the lower layer of the base layer, which is a first impurity located on a surface opposite to the front surface (hereinafter, referred to as a 'rear surface' Layer, a rear electrode layer, and the like.

The base layer is located on a semiconductor substrate of a first conductivity type, for example, p-type conductivity type silicon, and contains a first impurity of the first conductivity type. At this time, the base layer may contain an impurity of a trivalent element such as boron (B), gallium (Ga), indium (In) or the like.

Silicon is crystalline silicon such as single crystal silicon or polycrystalline silicon or amorphous silicon. Alternatively, the semiconductor substrate may be of the n-type conductivity type, in which case the base layer may contain impurities of pentavalent elements such as phosphorus (P), arsenic (As), antimony (Sb)

Further, in another embodiment, the semiconductor substrate may be made of a semiconductor material other than silicon.

3 is a flowchart illustrating a process of performing texturing using ion implantation according to an embodiment of the present invention. Referring to FIG. 3, the method includes preparing a semiconductor substrate (S310), implanting ions into a prepared semiconductor substrate (S320), heat treating the semiconductor substrate with ions implanted (S330) A plurality of bubbles are generated inside the semiconductor substrate, and a micro crack propagates in a specific direction from the generated bubbles (S340). A pyramid shape is formed on the upper surface of the semiconductor substrate by the propagated micro cracks, (S360).

4 is a conceptual diagram according to the hydrogen implantation step (S320) shown in FIG. Referring to FIG. 4, hydrogen ion implantation is performed on the semiconductor substrate 410. The implantation direction 420 is perpendicular to the top surface of the semiconductor substrate 410. In addition, the implantation is not a continuous form but a point form.

Hydrogen bubbles having a certain pattern are formed in the silicon of the semiconductor substrate 410 by the hydrogen ion implantation in the point shape and the constant pattern, and when the hydrogen bubble crack propagates, the silicon is separated along a specific plane inside the silicon I'm going.

5 is a conceptual diagram showing an arrangement of bubbles generated by the hydrogen implantation shown in FIG. Referring to FIG. 5, after the hydrogen ion implantation is performed, heat treatment is performed to generate a plurality of bubbles 501.

FIG. 6 is a conceptual diagram showing the propagation direction of micro cracks due to the bubbles generated by the hydrogen implantation shown in FIG. 3. FIG. Referring to FIG. 6, the first silicon surface direction 610, the second silicon surface direction 611, and the third silicon surface direction 613 (see FIG. 3) from the bubble 501 as heat treatment progresses in the heat treatment step The crack propagates.

This crack propagation is caused because the bonding energy of the silicon surface in the second silicon surface direction 611 and the third silicon surface direction 613 is smaller than the bonding energy of the silicon surface in the first silicon surface direction 610 to be. That is, cracks are generated in the second silicon face direction 611 and the silicon face direction in the third silicon face direction 613 where the binding energy is small, and the generated crack propagates.

Particularly, when the semiconductor substrate has a point pattern, cracks are mutually encountered, so that a substrate having pyramid shapes arranged at regular intervals can be obtained.

The bonding energy along the silicon surface direction is smaller in the second silicon surface direction 611 and the third silicon surface direction 613 than in the first silicon surface direction 610, Crack propagation occurs on the surface of the third silicon surface direction 613.

If defects exist in the shape of a dot, the crack propagation due to the defect will follow the second silicon face direction 611 and the third silicon face direction 613 having small energy. If there is a dot pattern of the same size, the second silicon planar direction 611 and the third silicon planar direction 613 are propagated and the generated pattern is uniformly emitted.

FIG. 7 is a conceptual view showing texturing according to the propagation of micro cracks shown in FIG. 3. FIG. Referring to Fig. 7, this is an example showing the propagation of micro cracks. That is, when the cracked radio wave 710 is generated from the plurality of bubbles 501, the silicon at the overlapping portion of the cracked radio wave 710 is separated. FIG. 8 shows a pyramid shape generated through this process.

FIG. 8 is a conceptual diagram showing a texturing state according to the pyramid shape generation step (S340) shown in FIG. Referring to FIG. 8, a recess 810 is repeatedly formed on the upper surface of the semiconductor substrate 410 to form a pyramid shape. That is, the front surface of the semiconductor substrate 410 is textured to have a textured surface which is an uneven surface.

8, only the edge portion of the semiconductor substrate 410 is shown as a texturing surface. However, the entire front surface of the semiconductor substrate 410 substantially has a texturing surface, so that the insulating layer (also referred to as an antireflection film or the like) located on the front surface of the semiconductor substrate 410 also has an uneven surface. Alternatively, the semiconductor substrate 410 may have a texturing surface on the front side as well as on the back side.

Due to the texturing surface, the surface area of the semiconductor substrate 410 increases to increase the incidence area of the light and the amount of light reflected by the semiconductor substrate 410 decreases, thereby increasing the amount of incident light.

9 is a conceptual diagram showing the size of an implantation pattern according to a general height. Referring to FIG. 9, the size of the implantation pattern is defined by the following equation.

Where y is the texturing height and x is the texturing width. The texturing width is equal to the implantation interval.

Also, an angle of about 54.7 degrees is the angle between the silicon planes, as follows:

Here, (h ₁ k- ₁ l ₁ ) and (h ₂ k ₂ l ₂ ) represent the silicon surface, and the used silicon surface is the surface of the first silicon surface direction 610, the second silicon surface direction 611, Is the surface of the third silicon surface direction 613.

Therefore, the size of the implantation pattern according to the required height is shown in the following table.

x (탆) y (m) y (m) x (탆) One 1.752841 One 0.570502 2 3.505682 2 1.141005 3 5.258524 3 1.711507 4 7.011365 4 2.282009 5 8.764206 5 2.852512 6 10.51705 6 3.423014 7 12.26989 7 3.993516 8 14.02273 8 4.564019 9 15.77557 9 5.134521 10 17.52841 10 5.705023

410: semiconductor substrate
420: direction of hydrogen ion implantation
610, 611, 613, 710: direction of crack propagation
501: Bubble
810: Groove

Claims (9)

A solar cell texturing method in a solar cell manufacturing process,
Preparing a semiconductor substrate;
Implanting ions into a prepared semiconductor substrate;
Annealing the semiconductor substrate on which the ions are implanted;
Forming a plurality of bubbles in the semiconductor substrate by the heat treatment;
Propagating microcracks in a specific direction from the plurality of generated bubbles; And
Generating a pyramid shape on the upper surface of the semiconductor substrate by propagated micro cracks;
≪ / RTI >
The method according to claim 1,
Wherein the ion implantation determines the pattern size of the implantation according to the texturing height.
The method according to claim 1,
Wherein the ions are hydrogen ions.
The method according to claim 1,
Wherein the implantation direction of the ions is perpendicular to the top surface of the semiconductor substrate.
3. The method of claim 2,
The pattern size of the implant can be expressed as:

(Where y is the texturing height and x is the texturing width).
The method according to claim 1,
Wherein the crack propagates along the silicon surface of the semiconductor substrate.
The method according to claim 1,
Wherein the crack propagation occurs at a lower bonding energy among the silicon planes of the semiconductor substrate.
The method according to claim 1,
Wherein the semiconductor substrate is a substrate having a dot pattern.
The method according to claim 1,
Wherein the implantation is performed in a point shape rather than a continuous shape.

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