KR20120053289A - Solar cell and method of fabricating the same - Google Patents

Abstract

PURPOSE: A solar cell and a manufacturing method thereof are provided to improve the efficiency of a solar cell by efficiently absorbing external light through an uneven part on the surface of a transparent electrode. CONSTITUTION: A micro lens layer(120) is formed on an insulation substrate(101). The micro lens layer is made of light transmitting materials. A first electrode(130) made of carbon nano tubes is formed on the micro lens. A p-n junction semiconductor layer(140) is formed on the first electrode. A second electrode(150) is formed on the semiconductor layer.

Description

Solar cell and its manufacturing method {Solar cell and method of fabricating the same}

The present invention relates to a solar cell, and in particular, to provide a solar cell that can maximize the efficiency of the solar cell.

Recently, as interest in environmental problems and energy depletion has increased, there is a growing interest in solar cells as an alternative energy with abundant energy resources, no problems with environmental pollution, and high energy efficiency.

Solar cells can be divided into solar cells that generate steam required to rotate turbines using solar heat and solar cells that convert sunlight into electrical energy using the properties of semiconductors.

Among them, researches on photovoltaic cells (hereinafter, referred to as solar cells) in which electrons of p-type semiconductors generated by absorbing light and holes of n-type semiconductors are converted into electrical energy have been actively conducted.

1 is a schematic diagram illustrating a concept of driving a typical solar cell, and FIGS. 2A to 2B are enlarged views of a surface of a transparent electrode of a solar cell.

As shown in FIG. 1, the solar cell 10 has a structure of a pn junction semiconductor layer composed of a p-type semiconductor layer 15 and an n-type semiconductor layer 17 between electrodes 11 and 13 facing each other. ought.

When a light bulb is connected to the electrodes 11 and 13 of the solar cell 10 as a light emitting unit and the solar cell 10 is exposed to a light source such as sunlight, the n-type semiconductor layer 17 and the p-type semiconductor layer 15 The electromotive force is generated by the photovoltaic effect through which current flows across

As such, a light bulb electrically connected to the solar cell 10 may be turned on by electromotive force generated by the photovoltaic effect.

On the other hand, in such a solar cell 10, in order to more efficiently receive light from the external light source into the pn junction semiconductor layers 15 and 17, the electrode 11 positioned in the direction toward the light source is transparent in an uneven shape. It is made of material.

Here, the uneven shape of the transparent electrode 11 may be formed through chemical vapor deposition (CVD). The uneven shape of the transparent electrode 11 formed through chemical vapor deposition is illustrated in FIG. 2A. In the process of forming a pn junction semiconductor layer on the transparent electrode 11, which is formed in a pointed mountain shape as described above, a track of the pn junction semiconductor layer 15 is generated.

In addition, such a chemical vapor deposition method is an expensive process, there is a problem that is not suitable for mass production.

Therefore, in recent years, a separate facility is not required, and an uneven shape is formed on the transparent electrode 11 through a wet etching process that is easy to manage in mass production and has high productivity.

In the wet etching method, the substrate (not shown) on which the transparent electrode 11 is formed is dipped into a bath (not shown) containing an etchant (not shown) that reacts with the transparent conductive oxide, or the transparent electrode 11 Unevenness may be formed on the surface of the transparent electrode 11 by performing an etching process such as spraying an etchant (not shown) on the surface.

In this case, by appropriately adjusting the exposure time to the etchant (not shown), convex and convexities are formed on the surface by not being completely etched but partly being etched and partly not being etched.

However, the concave-convex shape of the transparent electrode 11 thus formed is convex in the direction in which external light is incident as shown in FIG. 2B, and its size is irregularly formed.

That is, the surface uneven shape formed by the conventional etching process is very difficult to precisely control the shape and size of the uneven shape by depending on the etching chemical (not shown) and the corrosion chemical reaction rate of the transparent electrode 11.

As a result, scattering of light incident through the substrate (not shown) is not effectively performed, which causes a problem of reducing the efficiency of the solar cell 10.

The present invention is to solve the above problems, by forming a concave-convex shape having a uniform size and uniform shape on the surface of the transparent electrode, to more effectively absorb the external light to improve the efficiency of the solar cell The purpose.

In order to achieve the above object, the present invention provides an insulating substrate; A micro-lens layer formed on the insulating substrate and having an uneven surface; A first electrode formed on the microlens layer and made of carbon nanotubes (CNTs); A p-n junction semiconductor layer formed on the first electrode; It provides a solar cell including a second electrode formed on the semiconductor layer.

In this case, the microlens layer is made of a light transmissive material, and the semiconductor layer is composed of an n-type semiconductor layer, a pure amorphous silicon layer, and a p-type semiconductor layer.

The second electrode is made of one selected from silver (Ag), aluminum (Al), and aluminum alloy (Al alloy), and the surface of each of the second electrode and the semiconductor layer is uneven.

Light having a long wavelength (650 to 1100 nm) is diffracted toward the semiconductor layer through the microlens layer, and light having a short wavelength (350 to 650 nm) is diffracted toward the semiconductor layer through the first electrode.

In addition, the present invention comprises the steps of depositing a layer of a transparent material on one side of the insulating substrate; Patterning the light transmissive material layer into a convex lens shaped microlens layer using a concave lens shaped mold substrate; Forming a first electrode made of carbon nanotubes on the microlens layer; Forming a p-n junction semiconductor layer on the first electrode; It provides a method of manufacturing a solar cell comprising the step of forming a second electrode on the p-n junction semiconductor layer.

The forming of the first electrode may include coating a solvent in which carbon nanotubes are dispersed on the microlens layer; Annealing the solvent in which the carbon nanotubes are dispersed, and removing only the solvent, and forming the pn junction semiconductor layer comprises: forming a p-type semiconductor layer on the first electrode Making a step; And forming an n-type semiconductor layer on the p-type semiconductor layer.

The method may further include forming a pure amorphous silicon layer between the p-type semiconductor layer and the n-type semiconductor layer.

As described above, according to the present invention by forming a microlens layer having a concave-convex shape on the insulating substrate, the first electrode is formed of carbon nanotubes, thereby increasing the optical path of the light incident into the solar cell And, the surface of the semiconductor layer and the second electrode through the microlens layer also has an uneven shape, thereby improving the light trapping ability of the solar cell, and finally has the effect of improving the efficiency of the solar cell.

In addition, the light of various wavelength bands (long wavelength, short wavelength) can be diffracted into the solar cell, thereby increasing the amount of light incident on the semiconductor layer. Therefore, there is an effect which can improve the efficiency of a solar cell more.

1 is a schematic diagram illustrating a concept of driving a general solar cell.
2a to 2b are enlarged views of the surface of the transparent electrode of the solar cell.
3 is a cross-sectional view schematically showing the structure of a solar cell according to an embodiment of the present invention.
Figure 4 is a schematic diagram showing a principle of improving the light efficiency of the solar cell according to an embodiment of the present invention.
5a to 5b are experimental graphs measuring the transmittance and haze characteristics of a general transparent electrode.
6a to 6b are experimental graphs of the transmittance and haze characteristics of a first electrode including a microlens layer and carbon nanotubes according to an embodiment of the present invention.
Figure 7a to 7f is a cross-sectional view of the manufacturing step of the solar cell according to the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.

3 is a cross-sectional view schematically showing the structure of a solar cell according to an embodiment of the present invention, Figure 4 is a schematic diagram showing a principle of improving the light efficiency of the solar cell according to an embodiment of the present invention.

As shown, the solar cell 100 of the present invention is composed of an insulating substrate 101, a semiconductor layer 140 and the first and second electrodes 130, 150, in particular, the insulating substrate 101 and The microlens layer 120 is further positioned between the first electrodes 130, and the first electrode 130 is formed of carbon nanotubes (CNTs).

In detail, the solar cell 100 defines a transparent insulating substrate 101 and one surface on which light such as solar light is incident as an upper surface of the insulating substrate 101, and is formed on the lower surface of the insulating substrate 101. A micro-lens layer 120 is formed.

In order to increase the photovoltaic effect, the microlens layer 120 has an uneven surface. The microlens layer 120 is made of a light transmissive material. For example, the microlens layer 120 may be a polymer compound such as glass or a polymer.

That is, the optical path of the light incident into the solar cell 100 is increased by the microlens layer 130 having an irregular shape. Through this, the light collected and collected into the solar cell 100 is allowed to stay in the solar cell 100 for a long time.

This improves the light trapping capability of the solar cell 100, thereby improving the light trapping ability of the solar cell 100, thereby finally improving the efficiency of the solar cell 100.

In the solar cell 100 of the present invention, the first electrode 130, the semiconductor layer 140, and the second electrode 150 are sequentially formed on the microlens layer 120, and the microlens layer 120 As the concave-convex shape is formed, the surfaces of the first and second electrodes 130 and 150 and the semiconductor layer 140 formed on the microlens layer 120 to form the concave-convex shape by the microlens layer 120 are formed. do.

Therefore, the light trapping ability of the solar cell 100 can be further improved, and the efficiency of the solar cell 100 is further improved.

The first electrode 130 is formed on the microlens layer 120, and the first electrode 130 is formed of carbon nanotubes (CNTs).

In addition to the role of the electrode, the first electrode 130 made of carbon nanotubes forms contact characteristics between the first electrode 130 and the microlens layer 120 by forming the first electrode 130 as carbon nanotubes. In addition, the contact characteristics between the first electrode 130 and the semiconductor layer 140 may be improved.

And, it serves to further increase the path of the light incident into the solar cell 100.

In particular, in the solar cell 100, light having various wavelength bands (long wavelength and short wavelength) is diffracted by the first electrode 130 made of carbon nanotubes, thereby increasing the amount of light incident on the semiconductor layer 140.

Therefore, the efficiency of the solar cell 100 can be further improved.

At this time, the first electrode 130 made of carbon nanotubes is formed on the surface of the microlens layer 120 along the concave-convex shape.

In addition, the semiconductor layer 140 is positioned on the first electrode 130 made of carbon nanotubes, and the semiconductor layer 140 includes an n-type semiconductor layer 140a including n + -type impurities and a p + -type impurity. As the p-type semiconductor layer 140b, a pure amorphous silicon layer 140c is formed between the n-type semiconductor layer 140a and the p-type semiconductor layer 140b.

At this time, electrons in the semiconductor layer 140 should be present asymmetrically. That is, in the semiconductor layer 140, the n-type semiconductor layer 140a has a large electron density and a small hole density, and the p-type semiconductor layer 140b has a small electron density and a large hole density. Have

At this time, the semiconductor layer 140 is also formed along the uneven shape of the microlens layer 120 by the first electrode 130 formed on the surface thereof so as to form the uneven surface along the uneven shape of the microlens layer 120. do.

On the semiconductor layer 140, a second electrode 150, which is called a back electrode, formed of silver (Ag), aluminum (Al), and aluminum alloy (Al alloy) having excellent reflection characteristics is formed.

Here, the second electrode 150 is formed in one surface contacting the semiconductor layer 140 is concave in the direction in which the external light is incident along the uneven shape of the semiconductor layer 140, it can reflect a large amount of light To further improve the photovoltaic effect of the solar cell 100.

This further improves the efficiency of the solar cell (100).

That is, when the solar cell 100 is exposed to light such as sunlight, electromotive force is generated by a photovoltaic effect in which current flows across the p-type semiconductor layer 140a and the n-type semiconductor layer 140b. This happens.

The generated electromotive force generates a potential difference between the first electrode 130 and the second electrode 150 made of carbon nanotubes, thereby charging the solar cell 100.

At this time, the light incident on the solar cell 100 and passing through the semiconductor layer 140 is reflected by the second electrode 150 having an uneven shape and re-entered into the semiconductor layer 140 so that the electromotive force becomes larger. do.

As such, when the electromotive force is improved, the efficiency of the solar cell 100 is substantially improved.

Referring to this in more detail with reference to Figure 4, the solar cell 100 of the present invention is to increase the optical path of the light incident into the solar cell 100 by the microlens layer 120 is formed in a concave-convex shape.

Through this, the light that is collected and incident inside the solar cell 100 is allowed to stay in the solar cell 100 for a long time.

In addition, the total amount of light incident on the semiconductor layer 140 may be increased by preventing total reflection and expanding light scattering more efficiently when the light is incident.

This is to improve the light trapping ability of the solar cell 100, thereby increasing the amount of light incident on the solar cell 100, thereby improving the light trapping ability, thereby improving the efficiency of the solar cell 100.

In particular, in the solar cell 100 of the present invention, since the first electrode 130 is made of carbon nanotubes, the path of light incident into the solar cell 100 may be further increased, and in particular, the inside of the solar cell 100. This allows the diffraction of light in various wavelength bands (long wavelength, short wavelength).

Therefore, it is possible to diffract a wider range of sunlight, the amount of light incident on the semiconductor layer 140 can be increased, and the efficiency of the solar cell 100 can be further improved.

In addition, the reflectance of the light may be further increased through the second electrode 150 concave in the direction in which the external light is incident, thereby further improving the amount of light inside the solar cell 100.

Here, the operation principle of the solar cell 100 will be described in more detail.

As described above, electrons in the semiconductor layer 140 are asymmetrically present, but in the semiconductor layer 140 formed by the junction of the p-type semiconductor layer 140a and the n-type semiconductor layer 140b in a thermal equilibrium state. Dispersion of charges due to diffusion due to the concentration gradient of carriers results in the formation of an electric field.

Accordingly, light having an energy greater than the band gap energy, which is an energy difference between a conduction band and a valence band of a material forming the semiconductor layer 140, into the semiconductor layer 140. When irradiated, electrons that receive light energy are excited at the conduction band to the conduction band, and the electrons excited at the conduction band can move freely.

In the valence band, holes are generated where electrons escape.

The generated free electrons and holes are called excess carriers, and the excess carriers are diffused by concentration differences in the conduction band or the valence band.

At this time, the excess carriers, that is, electrons excited in the p-type semiconductor layer 140a and holes made in the n-type semiconductor layer 140b are defined as respective minority carriers, and are p-type or n-type before conventional bonding. The carriers (ie, p-type holes and n-type electrons) in the semiconductor layers 140a and 140b are defined as majority carriers.

At this time, the plurality of carriers are interrupted by the flow due to the energy barrier (energy barrier) due to the electric field, but electrons that are a minority carrier of the p-type semiconductor layer 140a can move to the n-type semiconductor layer 140b.

Therefore, a potential difference is generated in the semiconductor layer 140 due to diffusion of the minority carriers, and the first electrode 130 and the second electrode 130 made of carbon nanotubes located at both sides of the semiconductor layer 140 ( By using the electromotive force by connecting the 150 to an external circuit, these semiconductor layers 140 are used as a battery.

At this time, by forming the concave-convex microlens layer 120 on the insulating substrate 101, the path of light incident into the solar cell 100 is improved, thereby increasing the light absorption of the solar cell 100. Improve the energy conversion efficiency.

As a result, the potential difference in the semiconductor layer 140 becomes greater, thereby improving the efficiency of the solar cell 100.

In particular, in the solar cell 100 of the present invention, as the second electrode 150 is concave in the direction in which the external light is incident, a greater amount of light is reflected, so that the solar cell 100 is incident again into the semiconductor layer 140. By doing so, the light absorption of the solar cell 100 is further increased.

In addition, according to the solar cell 100 of the present invention, as the first electrode 130 is formed of carbon nanotubes, the light path of the light incident into the solar cell 100 is further increased, whereby It will further improve the light trapping ability.

Therefore, the efficiency of the solar cell 100 is improved.

In addition, by diffracting light having a short wavelength into the solar cell 100 through the first electrode 130 made of carbon nanotubes of the present invention, the solar cell 100 is formed through the uneven shape of the microlens layer 120. The light having a long wavelength is diffracted into the solar cell 100, and the light having a short wavelength is diffracted into the solar cell 100 through the first electrode 130 made of carbon nanotubes, thereby entering the semiconductor layer 140. It is possible to increase the amount of light.

Therefore, the light path of the light incident into the solar cell 100 is increased, thereby improving the efficiency of the solar cell 100.

Here, the uneven shape of the microlens layer 120 diffracts light in a long wavelength region of about 650 to 1100 nm, and the first electrode 130 made of carbon nanotubes diffracts light in a short wavelength region of about 350 to 650 nm.

5A and 5B are results of measuring transmittance and haze characteristics of a general transparent electrode, and FIGS. 6A and 6B illustrate transmittance and haze characteristics of a first electrode including a microlens layer and carbon nanotubes according to an embodiment of the present invention. One result.

Prior to the description, the horizontal axes of FIGS. 5A and 6A represent wavelength bands of light, the vertical axes represent transmittance, the horizontal axes of FIGS. 5B and 6B represent wavelength bands of light, and the vertical axes represent haze values.

6A to 6B, the first electrode made of the microlens layer and the carbon nanotube according to the embodiment of the present invention exhibits a transmittance of about 78% and a haze value of 12.6% in the wavelength range of 550 nm. have.

In contrast, referring to FIGS. 5A to 5B, a typical transparent electrode in the wavelength range of 550 nm has a transmittance of about 73%, and a haze value of 10.5%, and includes a microlens layer and carbon nanotubes according to an embodiment of the present invention. It can be confirmed that the transmittance and haze value are lower than those of one electrode.

Thus, the high transmittance of the present invention indicates that a large amount of light is incident on the semiconductor layer through external light such as solar light through a first electrode made of a microlens layer and carbon nanotubes. A lot of light diffusion of incident light occurs, indicating that the optical path is increased.

That is, the solar cell of the present invention increases the amount of light incident on the solar cell 100 by the first electrode made of a microlens layer and carbon nanotubes, and increases the amount of light incident on the solar cell 100. It can be seen that the path can be increased further.

Through this, it can be seen that the efficiency of the solar cell is improved.

7A to 7F are cross-sectional views of steps in manufacturing a solar cell according to the present invention.

First, as shown in FIG. 7A, a light-transmitting material layer 120a having a flat surface is formed on a transparent insulating substrate 101, for example, a glass substrate or a plastic substrate.

The light transmissive material layer 120a is made of a polymer compound such as glass or polymer.

Next, as shown in FIG. 7B, a mold substrate 200 having a predetermined intaglio 210 formed on a surface of the light transmissive material layer 120a is prepared.

The mold substrate 200 may pattern the light transmissive material layer 120a formed on the upper surface of the insulating substrate 101.

Here, a soft mold made of polydimethylsiloxsane (PDMS) is used as the mold substrate 200. Since the PDMS mold is an elastic body, the PDMS mold may be in uniform contact with the surface of the light transmissive material layer 120a to be patterned, and the surface energy is small so that the PDMS mold is easily separated from the light transmissive material layer 120a after patterning.

Thus, as shown in FIG. 7C, the mold substrate (200 of FIG. 7B) is formed with a concave lens-shaped intaglio (210 of FIG. 7B) to form a light-transmissive material layer formed on the upper surface of the insulating substrate 101 (FIG. 120a of 7b has a convex-convex concave-convex shape formed convexly.

Next, the convex lens-shaped concave-convex light-transmitting material layer (120a of FIG. 7B) is formed through the curing process to form the microlens layer 120.

The optical path of light incident into the solar cell (100 of FIG. 3) is increased by the microlens layer 120 formed in the uneven shape. Through this, the light incident and collected by the solar cell (100 of FIG. 3) is allowed to stay inside the solar cell (100 of FIG. 3) for a long time.

Next, as shown in FIG. 7D, a solvent (not shown) in which carbon nanotubes are dispersed is coated on the microlens layer 120. Thereafter, a solvent (not shown) in which carbon nanotubes are dispersed is annealed.

Through this, the solvent (not shown) is removed so that only carbon nanotubes are present on the microlens layer 120, thereby forming a first electrode 130 made of carbon nanotubes.

In this case, the first electrode 130 made of carbon nanotubes is formed along the surface of the microlens layer 120 formed in an uneven shape.

Therefore, the path of the light incident into the solar cell 100 of FIG. 3 is further increased, thereby improving the efficiency of the solar cell 100 of FIG. 3.

In particular, the light of various wavelength bands (long wavelength, short wavelength) is diffracted into the solar cell 100 of FIG. 3, thereby increasing the amount of light incident on the semiconductor layer 140 of FIG. 3.

Next, as illustrated in FIG. 7E, a semiconductor material including p-type impurities is deposited on the first electrode 130 made of carbon nanotubes to form the p-type semiconductor layer 140a on the entire surface of the insulating substrate 101. And sequentially depositing a pure amorphous silicon layer 140c and a semiconductor material including n-type impurities on the p-type semiconductor layer 140a to form a pure amorphous silicon layer 140c and an n-type semiconductor layer 140b. do.

As a result, the p-n junction semiconductor layer 140 is formed on the first electrode 130 made of carbon nanotubes. In this case, the p-n junction semiconductor layer 140 may delete the pure amorphous silicon layer 140c between the p-type semiconductor layer 140a and the n-type semiconductor layer 140b.

In this case, the pn junction semiconductor layer 140 is formed along a step of the microlens layer 120 having an uneven shape, and thus, the pn junction semiconductor layer 140 is formed in the same uneven shape as the microlens layer 120. .

Subsequently, as shown in FIG. 7F, a metal material, in particular, silver (Ag), aluminum (Al), or an aluminum alloy (Al alloy) having excellent reflection characteristics is deposited on the pn junction semiconductor layer 140 and patterned thereon. The solar cell 100 according to the present invention can be completed by forming the second electrode 150 on the entire surface of the insulating substrate 101.

As described above, the solar cell 100 of the present invention forms a microlens layer 120 having an uneven shape on the insulating substrate 101 to increase the optical path of the light incident into the solar cell 100. And, the surface of the semiconductor layer 140 and the second electrode 150 through the microlens layer 120 also has a concave-convex shape, thereby improving the light trapping ability of the solar cell 100, finally the solar cell ( 100) to improve the efficiency.

In addition, by forming the first electrode 130 with carbon nanotubes, it is possible to further increase the path of the light incident into the solar cell 100, in particular of various wavelengths (long wavelength, short wavelength) into the solar cell 100 The light may be diffracted, thereby increasing the amount of light incident on the semiconductor layer 140. Therefore, the efficiency of the solar cell 100 can be further improved.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

100: solar cell
101: insulation board
120: microlens layer
130: first electrode
140: semiconductor layer (140a: p-type semiconductor layer, 140b: n-type semiconductor layer, 140c: amorphous silicon layer)
150: second electrode

Claims (10)

An insulating substrate;
A micro-lens layer formed on the insulating substrate and having an uneven surface;
A first electrode formed on the microlens layer and made of carbon nanotubes (CNTs);
A pn junction semiconductor layer formed on the first electrode;
A second electrode formed on the semiconductor layer
Solar cell comprising a.
The method of claim 1,
The microlens layer is a solar cell made of a light transmissive material.
The method of claim 1,
The semiconductor layer is a solar cell consisting of an n-type semiconductor layer, a pure amorphous silicon layer and a p-type semiconductor layer.
The method of claim 1,
The second electrode is made of one selected from silver (Ag), aluminum (Al), aluminum alloy (Al alloy).
The method of claim 1,
Each of the second electrode and the semiconductor layer has a concave-convex surface.
The method of claim 1,
The long wavelength (650 ~ 1100nm) light is diffracted toward the semiconductor layer through the microlens layer, the light of short wavelength (350 ~ 650nm) is diffracted toward the semiconductor layer through the first electrode.
Depositing a layer of transparent material on one side of the insulating substrate;
Patterning the light transmissive material layer into a convex lens shaped microlens layer using a concave lens shaped mold substrate;
Forming a first electrode made of carbon nanotubes on the microlens layer;
Forming a pn junction semiconductor layer on the first electrode;
Forming a second electrode on the pn junction semiconductor layer
Method for manufacturing a solar cell comprising a.
The method of claim 7, wherein
Forming the first electrode,
Coating a solvent in which carbon nanotubes are dispersed on the microlens layer;
Annealing the solvent in which the carbon nanotubes are dispersed to remove only the solvent.
The method of claim 1,
Forming the pn junction semiconductor layer,
Forming a p-type semiconductor layer over the first electrode;
Forming an n-type semiconductor layer on the p-type semiconductor layer
≪ / RTI >
The method of claim 9,
Forming a pure amorphous silicon layer between the p-type semiconductor layer and the n-type semiconductor layer.

Images