KR20090123275A - Solar cell and method for making thereof - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to form an antireflective film of uniform dielectric constant and thickness by circularly forming an edge and a vertex of a substrate surface of a solar cell surface-treated by a thermal process. CONSTITUTION: A hydrogen thermal process for annealing a surface-treated solar cell substrate(90) at a fixed temperature with a hydrogen atmosphere is performed. A doping film(120) for forming an emitter through dopant is formed on the hydrogen-annealed solar cell substrate(100). The doping film is formed by a selective emitter. An antireflective film(130) is coated on the doping film.

Description

SOLAR CELL AND MANUFACTURING METHOD THEREOF {SOLAR CELL AND METHOD FOR MAKING THEREOF}

The present invention relates to a solar cell, and more particularly, to a method for manufacturing a solar cell having improved efficiency by using a hydrogen heat treatment process.

A solar cell is an energy conversion device that converts light energy of the sun into electrical energy by applying a photovoltaic effect phenomenon. In the solar cell, when light is incident on the surface of the substrate, electrons and holes are generated inside, and as the generated charges move to the P and N poles, a potential difference, or photovoltaic power, is generated between the P and N poles. Connect the load to the current.

The efficiency of the solar cell depends on how efficiently it can absorb the light incident on the substrate surface.

In general, when the surface of the substrate of the solar cell is flat, part of the incident light is absorbed and refracted, and the other part is reflected, so that the light absorption phenomenon of the solar cell appears to be inefficient.

Therefore, as shown in FIG. 1, the substrate of the solar cell is configured in the form of a pyramid or an inverted pyramid, so as to reduce the reflectance of light incident on the surface layer, and to increase the length of light passing through the solar cell to increase absorption efficiency. The surface treatment method is used to increase the

That is, FIG. 1 shows the substrate surface of the solar cell 10 before the surface treatment and the substrate surface of the surface treated solar cell 20 in cross section. For reference, FIG. 2 shows a perspective view of the substrate surface of the solar cell in the surface-treated state only.

Referring to FIG. 1, when the surface of the solar cell 10 before the surface treatment as shown in (a) of FIG. 1 is wet or dry, the surface of the solar cell substrate is flat As shown in Fig. 1B, the substrate surface is formed in a pyramid shape. This state is the solar cell 20 surface-treated.

In this case, since the light incident on the substrate surface of the solar cell 20 is reflected back to the substrate surface of the solar cell 20, the reflection amount of the light is reduced and the absorption efficiency is improved.

However, a solar cell having a substrate surface formed in a pyramid shape has the following problems.

First, when the substrate surface of the solar cell 20 is formed in a pyramid shape or an inverted pyramid shape, a problem arises in that a dopant is not uniformly uniformly doped on the substrate surface of the solar cell 20 in the pn junction formation process. . That is, the doping may be formed non-uniformly at the vertices or corners of the pyramid shape.

In addition, when the doping process is completed, a process of coating the anti-reflection film is performed, wherein an anti-reflection film may be formed in which the thickness on the surface of the substrate is not constant and the dielectric constant is not the same as a whole.

These problems result in a direct decrease in the efficiency of the solar cell.

Therefore, an object of the present invention is to solve the above problems, to form a different surface shape of the substrate of the solar cell to improve the efficiency of the solar cell.

Another object of the present invention is to be able to absorb relatively more light in the substrate of the solar cell.

Yet another object of the present invention is to minimize crystal defects and impurities in the solar cell substrate.

According to a feature of the present invention for achieving the above object, a hydrogen heat treatment step of performing a heat treatment for a surface-treated solar cell substrate at a predetermined temperature in a hydrogen atmosphere; A doping film forming step of forming an emitter with a dopant on the hydrogen-treated solar cell substrate; And forming an anti-reflection film over the doped film.

The solar cell substrate may further include an impurity offset step of offsetting impurities at a temperature range different from that of the hydrogen heat treatment.

The impurity offset step may be performed before the hydrogen heat treatment is performed, or may be performed after the hydrogen heat treatment is performed.

When the hydrogen heat treatment is performed, the vertices and corners of the pyramid shape formed on the surface-treated solar cell substrate are formed in a rounded shape, and the doped film and the anti-reflection film are formed along the rounded surface.

When the surface of the solar cell substrate surface-treated by the hydrogen heat treatment is formed in a rounded form, impurities of the solar cell substrate may be removed at the same time.

The hydrogen heat treatment may be performed at 800 ° C. to 1100 ° C., and the impurity offset may be performed at a temperature range different from the hydrogen heat treatment temperature, that is, 400 ° C. to 800 ° C. or 1100 ° C. to 1250 ° C. When the impurity offset process is performed at 400 ° C. to 800 ° C., after the hydrogen heat treatment is performed, before or after the hydrogen heat treatment is performed when the impurity offset process is performed at 1100 ° C. to 1250 ° C. It can be carried out.

Hydrogen partial pressure during the hydrogen heat treatment is carried out in several hundred mill torr to atmospheric pressure.

The antireflection film is formed by a plasma chemical vapor deposition method, a sputtering method, an evaporator deposition method, or the like.

According to another feature of the invention, the solar cell substrate is subjected to the hydrogen heat treatment for the surface-treated solar cell substrate surface; A doped film in which an emitter is formed of a dopant on a surface of the hydrogen-treated solar cell substrate; There is provided a solar cell including an anti-reflection film formed on the doped film.

The solar cell is a solar cell subjected to a process of canceling impurities in order to reduce crystal defects and impurities of the solar cell substrate after the hydrogen heat treatment.

The temperature during the hydrogen heat treatment is 800 ℃ to 1100 ℃, the step of canceling the impurity has a temperature range different from the hydrogen heat treatment temperature, the temperature during the process of canceling the impurities is the It may be provided in a temperature range of less than the temperature of 400 ℃ to 800 ℃, and a temperature range higher than the temperature of the hydrogen heat treatment 1100 ℃ to 1250 ℃.

According to the solar cell of the present invention having the above-described configuration and a method of manufacturing the same, the following effects are obtained.

First, the hydrogenated heat treatment process is further performed on the surface-treated solar cell substrate to shape the pyramid-shaped vertices and corners formed in the solar cell substrate in a rounded shape, thereby uniformly doping the dopant throughout the substrate surface in the pn bonding process. In addition, the dielectric constant and thickness of the antireflection film can be uniformly coated to improve the efficiency of the solar cell.

In addition, since the vertices and corners of the pyramid shape are rounded, the cross-sectional area is increased compared to the conventional pyramid shape, so that light can be absorbed relatively more.

In addition, since the impurity offset process is performed in the hydrogen heat treatment process, crystal defects in the solar cell substrate can be reduced, thereby improving the carrier life time of the solar cell substrate, thereby producing a highly efficient solar cell. can do.

Hereinafter, a solar cell and a method of manufacturing the same according to the present invention will be described in detail with reference to the preferred embodiment shown in the accompanying drawings.

In the solar cell according to the embodiment of the present invention, the surface of the substrate is pyramid-shaped to perform the surface treatment to reduce the amount of light reflection as much as possible. Here, the solar cell in this state will be referred to as "solar cell before heat treatment."

3 is a process diagram showing a process of manufacturing a solar cell according to a preferred embodiment of the present invention.

First, as shown in FIG. 3 (a), the above-described 'solar cell before heat treatment' 90 is mounted inside a container having a hydrogen gas atmosphere. The container having a hydrogen gas atmosphere (hereinafter, referred to as a "hydrogen atmosphere") should be a condition in which the inside thereof is vacuum and a heat treatment process can be performed at a high temperature.

In such a hydrogen atmosphere, the 'solar cell before heat treatment' 90 is subjected to a heat treatment process for several minutes to several ten minutes at a high temperature of approximately 800 ° C to 1100 ° C. And when performing the heat treatment of the hydrogen atmosphere, the partial pressure of hydrogen may be provided up to several hundred mill Torr (Torr) to atmospheric pressure.

While the heat treatment process is performed, the 'solar cell before heat treatment' 90 having a surface energy unstable state causes silicon atoms to move to stabilize the surface energy. In such a case, the 'solar cell before heat treatment' 90 has the vertex portion A and the corner portion B of the pyramid into rounded shapes A 'and B'.

The rounding process will be described with reference to the state diagram of FIG. 4. 4 is not a pyramid but has a right-angled shape, but the principle is the same.

Referring to FIG. 4, when the heat treatment is performed at a high temperature in a hydrogen atmosphere for the 'solar cell before heat treatment', the silicon atoms 200 move as shown in FIGS. 4A and 4B, and FIG. ), The corners will be rounded.

In the present embodiment, a solar cell having a rounded corner shape as described above will be referred to as a 'solar cell after heat treatment' 100.

This will be described again with reference to FIG. 3.

When the high temperature heat treatment process is completed in a hydrogen atmosphere, the 'solar cell after heat treatment' 100 is formed as shown in FIG.

Then, a doping process is performed to form an emitter with impurities on the substrate surface 110 of the solar cell 100. The doping film 120 formed by the doping process is uniformly formed along the curvature of the substrate surface 110. This is possible. This state is shown in Fig. 3C. In this case, the doped film may be formed of a selective emitter that forms only a part of the emitter instead of forming all of the emitters on the substrate surface 110.

Then, as shown in Figure 3 (d) is formed an anti-reflection film 130 to prevent the reflection of the sunlight incident on the solar cell 100 to the maximum. The anti-reflection film 130 may also be formed to have a uniform thickness along the curvature of the substrate surface 110, in detail, the curvature of the doped film 120. That the thickness of the anti-reflection film 130 can be formed uniformly can provide a uniform dielectric property, thus bringing a uniform reflection detection effect of light in the entire area of the solar cell (100). The anti-reflection film 130 may be formed using various methods such as a plasma chemical vapor deposition method, a sputtering method, an evaporator deposition method, and the like.

On the other hand, it can be seen that the 'solar cell after heat treatment' 100 shown in (b) of FIG. 3 has an increased cross-sectional area to a certain ratio than the 'solar cell before heat treatment' 90 of FIG. . As the cross-sectional area is increased, the 'solar cell after heat treatment' 100 can absorb more sunlight than 'solar cell before heat treatment' 90, thereby improving light absorption efficiency.

Meanwhile, as described above, after the hydrogen heat treatment process is completed, a process of offsetting impurities in the substrate of the solar cell may be performed.

The impurity offset process is a process of offsetting impurities by inserting hydrogen (H) atoms into the substrate surface 110 of the solar cell 100 at a temperature range different from that of the hydrogen heat treatment process, which is a solar cell 100. Can reduce crystal defects.

In this case, the impurity offset temperature may be provided at a temperature lower or higher than the temperature of the hydrogen heat treatment process such as 400 ° C. to 800 ° C. and 1100 ° C. to 1250 ° C., and the impurity offset process is performed in this temperature range. do.

Specifically, the hydrogen heat treatment is performed at 800 ° C. to 1100 ° C., wherein the impurity offset process is performed at 400 ° C. to 800 ° C. before the hydrogen heat treatment is performed, and before the hydrogen heat treatment is performed. Or if it is carried out later it is preferably carried out at 1100 ℃ to 1250 ℃.

In addition, the temperature range at the time of the impurity cancellation is a temperature range in which impurities are most efficiently removed. This temperature range is the value produced by several experiments. If the impurity offset process is performed in a temperature range outside the impurity offset temperature, impurities in the substrate of the solar cell 100 may not be effectively removed. However, it should be noted that such a temperature range may vary depending on various characteristics such as the material of the solar cell 100.

As such, when the crystal defect is reduced, the carrier life-time of the solar cell 100 is improved. The charge life is a time taken for electrons moving along the surface of the semiconductor to recombine with the holes or for the holes to recombine with the electrons and die out. The charge life is closely related to crystal defects and impurity concentrations of the semiconductor. If it is above, a highly efficient solar cell can be produced.

On the other hand, it is described that the impurity offset step is performed after the hydrogen heat treatment step is performed, but it is not necessary to do so. That is, the impurity offset process may be first performed on the 'solar cell before heat treatment' 90 before the hydrogen heat treatment process is performed, and then the hydrogen heat treatment process may be performed.

In this embodiment, the hydrogen heat treatment is performed only on the front surface of the solar cell 100, but the hydrogen heat treatment may be simultaneously performed on the front and rear surfaces of the solar cell 100.

In addition, when the surface of the solar cell substrate surface-treated by the hydrogen heat treatment is formed in a rounded shape, impurities of the solar cell substrate may be removed at the same time.

Although not shown in the drawing, if a bracket for fixing the solar cell substrate in the longitudinal direction is installed in a container having a hydrogen gas atmosphere, and the hydrogen heat treatment process described above is performed in that state, the front and rear surfaces are formed. The vertices and corners of the pyramid can be rounded.

As such, when the front and rear surfaces of the solar cell substrate are subjected to hydrogen heat treatment, and then the doping process and the anti-reflective coating process are performed, the solar cell can absorb sunlight from both sides. The light absorption efficiency can be improved. This structure of the solar cell can be applied to a solar system that can absorb light from both sides.

Although described with reference to the illustrated embodiment of the present invention as described above, this is merely exemplary, those skilled in the art to which the present invention pertains various modifications without departing from the spirit and scope of the present invention. It will be apparent that other embodiments may be modified and equivalent. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a structural diagram of a solar cell substrate and a surface treated solar cell substrate before surface treatment;

Figure 2 is a perspective view of the surface of the solar cell substrate only surface treatment.

Figure 3 is a process diagram for manufacturing a solar cell according to a preferred embodiment of the present invention.

Figure 4 is an exemplary state diagram for explaining the movement state of silicon atoms in the solar cell manufacturing process of the present invention.

Claims (10)

A hydrogen heat treatment step of performing heat treatment on the surface-treated solar cell substrate at a predetermined temperature in a hydrogen atmosphere; A doping film forming step of forming an emitter with a dopant on the hydrogen-treated solar cell substrate; And, The solar cell manufacturing method comprising the step of forming an anti-reflection coating on the doping film. The method of claim 1, And an impurity canceling step for canceling crystal defects and impurities in the substrate in a temperature range different from that of the hydrogen heat treatment with respect to the solar cell substrate. The method of claim 2, The impurity offset step may be performed after the hydrogen heat treatment is carried out. The method of claim 3, When the hydrogen heat treatment is performed, the vertices and corners of the pyramidal shape formed on the surface of the solar cell substrate are formed in a rounded shape. The doped film and the anti-reflection film is a solar cell manufacturing method, characterized in that formed along the rounded surface. The method of claim 4, wherein When the surface of the solar cell substrate surface-treated by the hydrogen heat treatment to form a rounded form, the solar cell manufacturing method characterized in that to remove the impurities in the solar cell substrate at the same time. The method of claim 2, The hydrogen heat treatment is carried out at 800 ℃ to 1100 ℃, When the impurity offset process is carried out after the hydrogen heat treatment, it is carried out at 400 ℃ to 800 ℃, if the hydrogen heat treatment is carried out before or after is characterized in that it is carried out at 1100 ℃ to 1250 ℃ Solar cell manufacturing method. The method according to claim 1 or 2, Hydrogen partial pressure during the hydrogen heat treatment is characterized in that the solar cell manufacturing method characterized in that carried out within several hundred mill torr (torr) to atmospheric pressure. A solar cell substrate on which a hydrogen heat treatment is performed on the surface of the substrate of the surface treated solar cell; A doped film in which an emitter is formed of a dopant on a substrate surface of the hydrogen heat-treated solar cell; And, A solar cell comprising an anti-reflection film formed over the doped film. The method of claim 8, The solar cell is a solar cell, characterized in that configured to perform a process to cancel impurities to reduce the crystal defects of the solar cell substrate before or after the hydrogen heat treatment. The method of claim 9, The temperature during the hydrogen heat treatment is 800 ℃ to 1100 ℃, The temperature range during the process of canceling the impurities is characterized in that the temperature range of 400 ℃ to 800 ℃ which is smaller than the temperature of the hydrogen heat treatment, and 1100 ℃ to 1250 ℃ temperature range higher than the temperature of the hydrogen heat treatment Solar cell.

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