KR20050100806A - Silicon thin film solar cell and method of fabricating the same - Google Patents

Abstract

The silicon thin film solar cell of the present invention and a method of manufacturing the same are used to improve the light efficiency by growing the grain in the horizontal direction to form a horizontal pn junction (junction) to apply to the solar cell, alternately in the horizontal direction on the substrate A formed p + type semiconductor layer, p type semiconductor layer and n + type semiconductor layer; And an emitter electrode formed on the n + type semiconductor layer and a base electrode formed on the p + type semiconductor layer.

Description

Silicon Thin Film Solar Cell and Manufacturing Method Thereof {SILICON THIN FILM SOLAR CELL AND METHOD OF FABRICATING THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon thin film solar cell and a method for manufacturing the same, and more particularly, to a silicon thin film solar cell in which an active layer is crystallized using horizontal crystallization and a method of manufacturing the same.

In general, a solar cell is a semiconductor device that converts solar energy into electrical energy, and has a junction type of a p-type semiconductor and an n-type semiconductor.

Most ordinary solar cells consist of large area pn junction diodes, and the basic requirement for solar cells for photovoltaic energy conversion is that the electrons are asymmetric in the semiconductor structure. It should be. That is, the n-type semiconductor region has a large electron density and a small hole density, and the p-type semiconductor region is formed in the opposite direction. Therefore, in the thermal equilibrium diode, which is a junction of a p-type semiconductor and an n-type semiconductor, an imbalance of charge occurs due to diffusion due to a concentration gradient of carriers, and thus an electric field is formed. Carrier diffusion no longer occurs. In this case, when light is applied to the pn junction diode above a band gap energy, which is an energy difference between a conduction band and a valence band of the material, the electrons subjected to the light energy are in the valence band. Excite as the evangelism. At this time, the electrons excited by the conduction band can move freely, and holes are generated in the valence band where electrons escape. This is called an excess carrier, and the excess carriers diffuse by concentration differences in the conduction band or the valence band.

At this time, electrons excited in the p-type semiconductor and holes made in the n-type semiconductor are called respective minority carriers, and carriers in the p-type or n-type semiconductor (ie, p-type holes and n-type semiconductors) before conventional bonding are formed. The former is called a majority carrier. At this time, the majority carriers are disturbed by the flow due to the energy barrier due to the electric field, but electrons, which are p-type minority carriers, can move toward the n-type. The diffusion of the minority carrier causes a potential drop in the pn junction diode, and when the electromotive force generated at the anode terminal of the pn junction diode is connected to an external circuit, it acts as a solar cell.

On the other hand, thin film solar cells using silicon are largely divided into single crystal and polycrystalline materials and are basically used for solar cells as pn homojunctions. Single crystal is a high quality material with high purity and low crystal defect density, which can achieve high efficiency, but is expensive, and polycrystalline material can manufacture a battery having an efficiency that can be commercialized at a relatively low cost.

Hereinafter, a general silicon thin film solar cell will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view schematically illustrating a structure of a general solar cell, and illustrates a polycrystalline silicon thin film solar cell using polycrystalline silicon as an active layer.

As shown in the figure, a p-type polycrystalline silicon thin film 20 having a predetermined thickness is formed on the substrate 10, and an n-type silicon layer 30 is formed on the p-type silicon layer 20.

At this time, a silicon wafer (wafer) is mainly used as the substrate 10, and the p-type silicon layer 20 forms a seed layer (not shown) on the substrate 10 and then forms a liquid phase growth method (Liquid). The p-type semiconductor layer 20 in the form of crystalline silicon is formed by growing by Phase Epitaxy (LPE) or Chemical Vapor Deposition (CVD).

In this case, the seed layer is formed by depositing an amorphous silicon thin film on the silicon wafer and heat treatment at a high temperature, the p-type semiconductor layer 20 is formed to a thickness of several to several tens of ㎛.

Since the n-type semiconductor layer is formed on the p-type semiconductor layer 20 formed as described above, a pn junction having a vertical structure is formed. In the case of the conventional polycrystalline silicon thin film solar cell, the grain size is small to within a few μm, and thus the electrons of minority carriers are moved. There is a disadvantage that is hampered by this many grain boundaries.

On the other hand, when the thickness of the p-type semiconductor layer 20 is formed to increase the electron collection probability as described above, an aluminum layer is used as a lower electrode (not shown) to collect electrons generated on the rear surface. By using the electrical property called Back Surface Field (BSF), charges are collected on the surface without dying, increasing efficiency.

However, since the active layer is formed of thick silicon as described above, not only the manufacturing cost increases, but also the charges are transferred to the electrodes due to the thick active layer, so that the dies occur in the middle due to the BSF effect. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a polycrystalline silicon thin film solar cell and a method of manufacturing the same, which improve light efficiency by improving a pn junction structure.

Other objects and features of the present invention will be described in the configuration and claims of the invention described below.

In order to achieve the above object, the thin film solar cell of the present invention comprises a p + type semiconductor layer, a p type semiconductor layer and an n + type semiconductor layer alternately formed in the horizontal direction on the substrate; And an emitter electrode formed on the n + type semiconductor layer and a base electrode formed on the p + type semiconductor layer.

In this case, the semiconductor layer may be composed of a polycrystalline silicon thin film, and the polycrystalline silicon thin film may be composed of grain grown horizontally using a horizontal crystallization method such as sequential horizontal crystallization.

In addition, the substrate may be formed of an insulating substrate such as glass, and the n + type semiconductor layer may be formed in the grain boundary region of the p type semiconductor layer.

On the other hand, it may further include a protective film formed on the substrate to prevent the reflection of the incident light.

In addition, the manufacturing method of the thin film solar cell of the present invention comprises the steps of forming a p-type semiconductor layer on the substrate; Alternately forming n + type semiconductor layers and p + type semiconductor layers in predetermined regions of the p-type semiconductor layer; Forming a first electrode connected to the n + type semiconductor layer on the substrate and forming a second electrode electrically connected to the p + type semiconductor layer; And forming a protective film on the substrate.

In this case, the method may further include forming a buffer layer on the substrate before forming the p-type semiconductor layer on the substrate.

The forming of the p-type semiconductor layer may include forming a p-type amorphous silicon layer on the substrate; And forming a polycrystalline silicon layer having grains grown in a horizontal direction by using horizontal crystallization in the amorphous silicon.

In this case, the p-type amorphous silicon layer may be formed to a thickness of about 500 ~ 5000Å, it is possible to form a polycrystalline silicon layer having a grain grown by 1㎛ or more in the horizontal direction using the sequential horizontal crystallization in the amorphous silicon.

In addition, n + type silicon layers and p + type silicon layers may be formed by alternately implanting high concentrations of n-type impurity ions and p-type impurity ions into the grain boundary regions of the p-type polycrystalline silicon layer.

Meanwhile, an n + type semiconductor layer and a p + type semiconductor layer may be formed on both sides of the p type semiconductor layer to form a pn junction diode having a sandwich structure.

In addition, the first electrode may be formed of a conductive metal such as aluminum, and the second electrode may be formed of a conductive metal such as titanium, palladium, nickel, copper, and silver.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of a thin film solar cell and a method for manufacturing the same.

2 is a cross-sectional view schematically showing a part of a thin film solar cell according to an embodiment of the present invention, showing an example of using a polycrystalline silicon thin film as an active layer.

As shown in the figure, a buffer layer 111 is formed on a substrate 110 made of a transparent insulating material, and a p + type silicon is disposed on the buffer layer 111 with a p type silicon layer 120 interposed therebetween. The layer 125 and the n-type silicon layer 130 are alternately formed.

In this case, the silicon layers 120, 125, and 130 are made of a polycrystalline silicon thin film having grains grown in a horizontal direction by using a horizontal crystallization method such as sequential lateral crystallization (SLS). The n-type and n-type semiconductor layers form a pn junction diode in a sandwich structure.

Meanwhile, an emitter electrode 140 made of a conductive metal such as aluminum is formed on the n-type silicon layer 140 which is an emitter layer, and titanium is formed on the p + type silicon layer 125 which is a base layer. A base electrode 150 made of a conductive metal such as titanium (Ti), palladium (Pd), nickel (Ni), or the like is formed.

At this time, an entire surface of the substrate 110 on which the emitter electrode 140 and the base electrode 150 are formed is formed of an insulating material such as silicon oxide film (SiO ₂ ) and an anti-reflection layer (in anti-reflection layer) for suppressing reflection of light ( 160 is formed.

As described above, the thin film solar cell of the present embodiment has a horizontal pn junction structure, and the p-type silicon layer as the active layer has grains grown in the horizontal direction by horizontal crystallization, and when using sequential horizontal crystallization, grains of 1 μm or more are used. As it grows, the flow of electrons by grain boundaries is not disturbed. As a result, it is possible to reduce the loss of electrons to improve the light efficiency, which will be described in detail through the manufacturing process of the following solar cell.

3A to 3F are cross-sectional views sequentially illustrating a manufacturing process of the solar cell illustrated in FIG. 2, and FIGS. 4A to 4D are plan views sequentially illustrating a manufacturing process of the solar cell illustrated in FIG. 2.

First, as shown in FIG. 3A, a buffer layer 111 made of a silicon oxide film is formed on a substrate 110 made of a transparent insulating material. In this case, a glass substrate may be used as the substrate 110, and the buffer layer 110 serves to block impurities such as sodium (Narium) present in the glass substrate 110 from penetrating into the upper layer during the process. do.

In this embodiment, by using the sequential horizontal crystallization it is possible to use the glass substrate 110, which is significantly lower than the melting point of the wafer and the quartz (quartz) substrate, it is possible to obtain the effect of reducing the manufacturing cost.

In this case, the sequential horizontal crystallization takes advantage of the fact that the grain grows in a direction perpendicular to the interface at the interface between the liquid phase silicon and the solid phase silicon, the size of the laser energy and the irradiation range of the laser beam It is a crystallization method which can improve the size of a silicon grain by laterally growing grain by predetermined length by adjusting suitably.

Next, the p-type amorphous silicon layer 120 'to be used as the active layer is formed on the buffer layer 110. The amorphous silicon layer 120' may be deposited in various ways, and the amorphous silicon layer may be formed. Representative methods include Low Pressure Chemical Vapor Deposition (LPCVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD).

In this case, the p-type silicon layer 120 'is a semiconductor layer in which p-type impurities such as boron (B) and gallium (Ga) are injected at low concentrations, and generally have a thickness of several μm or more. By using the horizontal pn junction structure of the silicon layer 120 'can be formed to a thin thickness of about 500 ~ 5000Å.

Subsequently, after the dehydrogenation process for removing hydrogen atoms present in the amorphous silicon layer 120 ′ and horizontal crystallization, the grains are grown horizontally as shown in FIGS. 3B and 4A. The polycrystalline silicon layer 120 having the same will be formed.

In this case, the polycrystalline silicon layer 120 has a grain grown by 1 μm or more in a horizontal direction that is the movement direction of the electrons, and the grain boundary 121 formed perpendicular to the movement direction of the electrons is, for example, as shown. One or more electrons are formed in the movement path of the electrons so that they hardly interfere with the movement of the electrons.

In this embodiment, the sequential horizontal crystallization method is used as the horizontal crystallization. However, the present invention is not limited thereto, and other horizontal crystallization methods may be used as long as the grains grow in the horizontal direction to form a horizontal pn junction diode having a sandwich structure. (For example, SELAX (Selectively Enlarging Laser Crystallization), Metal Induced Lateral Crystallization (MILC), etc.) may be used.

In addition, even during sequential horizontal crystallization, a two-shot process may be performed for mass production, and the size of grain may be increased by overlapping shots.

Hereinafter, the sequential horizontal crystallization method used in this embodiment will be briefly described.

First, the amorphous silicon layer is completely melted by irradiating a laser having an energy density or more at which the amorphous silicon layer is completely melted.

At this time, immediately after the irradiation of the laser energy, the amorphous silicon is cooled through both sides, i.e., the non-irradiation region where the laser is not irradiated. This is because the solid-state amorphous silicon layer on the side has a greater thermal conductivity than the buffer layer or glass substrate under the amorphous silicon layer.

Therefore, the liquid amorphous silicon layer reaches the nucleation temperature preferentially at the interface between the solid phase and the liquid phase on both sides rather than the central portion, and crystal nuclei are formed at the portion. After the nuclei are formed, the horizontal growth of grain occurs from the lower side to the higher side.

In this method, the crystal particles can be grown in the horizontal direction along the irradiation direction of the laser by irradiating the amorphous silicon thin film at intervals substantially equal to the distance at which the lateral growth by single melting can be achieved. In particular, considering the maximum size of grain that can be grown by sequential horizontal crystallization, if sequential horizontal crystallization is performed on both sides, grains have crystal grains having a larger grain size with only one grain boundary.

Next, as shown in FIGS. 3C and 4B, a high concentration of n-type impurity ions is implanted into a predetermined region using a mask to form an n + -type silicon layer 130. In this case, since the silicon thin film solar cell requires a silicon layer having a predetermined thickness in order to electrically convert light, n-type doping is performed in consideration of the grain size of the p-type polycrystalline silicon layer 120 formed by horizontal crystallization. It is perpendicular to the pn junction surface is formed perpendicular to the surface of the glass substrate 110.

That is, when the pn junction is formed in the sandwich structure as described above, a thin crystalline silicon layer can be applied to the solar cell.

Meanwhile, the n + silicon layer 130 may be formed in the grain boundary 121 region so as not to affect the movement of charge as the emitter layer.

Next, by implanting high concentration of p-type impurity ions into a predetermined region of the substrate 110 on which the p-type silicon layer 120 and the n + -type silicon layer 130 are formed, as shown in FIGS. 3D and 4C. Likewise, the p + type silicon layer 125 is formed on both sides of the pn junction diode around the n + type silicon layer 130.

Thereafter, as shown in FIGS. 3E and 4D. An emitter electrode 140 is formed on the n + type silicon layer 130 and a base electrode 150 is formed on the p + type silicon layer 130.

At this time, the emitter electrode 140 may be formed of aluminum to effectively collect the generated electrons, the aluminum layer is not only good conductivity but also can obtain the electrical properties of the BSF as a trivalent element, Good affinity and good bonding.

In addition, the base electrode 150 may be a conductive metal material such as titanium, palladium, nickel, cup (Cu), silver (argentum; Ag), and the like, and the base electrode 150 may be p + type silicon. It is configured to contact the layer 125, so that the contact resistance is lower than when directly contacting the p-type silicon layer.

Next, as shown in FIG. 3F, a protective film 160 made of a silicon oxide film or a silicon nitride film is formed on the entire surface of the substrate 110 on which the emitter electrode 140 and the base electrode 150 are formed.

In this case, when the protective layer 160 is formed by controlling the thickness, an antireflection effect of suppressing reflection of incident light can be obtained.

As described above, when the metal contact is formed on the pn junction diode, electrons which are minority carriers formed in the p-type silicon layer are collected. Since the electrons formed by the light move parallel to the horizontal grain, the loss due to the grain boundary region can be minimized. To improve the light efficiency.

In addition, the crystallization using the sequential horizontal crystallization method as in the present embodiment has the advantage of forming a solar cell on an insulating substrate having a low melting point such as a glass substrate. That is, all processes including the crystallization process can be performed at a low temperature, so that low-cost and large-area substrates can be used like glass substrates.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, the silicon thin film solar cell and the method of manufacturing the same according to the present invention form a sandwiched pn junction using a polycrystalline silicon layer grown horizontally, thereby minimizing electron loss due to grain boundaries and improving light efficiency. to provide.

In addition, the present invention is to crystallize the silicon layer used as the active layer at a low temperature in a sequential horizontal crystallization method to produce a solar cell using a low-cost glass substrate provides an effect of lowering the unit cost of the product.

1 is a cross-sectional view schematically showing the structure of a typical solar cell.

2 is a schematic cross-sectional view of a portion of a silicon thin film solar cell according to an embodiment of the present invention.

3A to 3F are cross-sectional views sequentially illustrating a manufacturing process of the solar cell shown in FIG. 2.

4A to 4D are plan views sequentially illustrating a manufacturing process of the solar cell illustrated in FIG. 2.

** Explanation of symbols for main parts of drawings **

110: insulating substrate 111: buffer layer

120: p-type silicon layer 125: p + type silicon layer

130: n-type silicon layer 140,150: contact electrode

160: protective layer

Claims (14)

A p + type semiconductor layer, a p type semiconductor layer and an n + type semiconductor layer formed alternately on the substrate in a horizontal direction; And A thin film solar cell comprising an emitter electrode formed on the n + type semiconductor layer and a base electrode formed on the p + type semiconductor layer. The thin film solar cell of claim 1, wherein the semiconductor layer comprises a polycrystalline silicon thin film. The thin film solar cell of claim 1, wherein the polycrystalline silicon thin film comprises grains grown horizontally by using a horizontal crystallization method such as sequential horizontal crystallization. The thin film solar cell of claim 1, wherein the substrate is made of an insulating substrate such as glass. The thin film solar cell of claim 1, wherein the n + type semiconductor layer is formed at a grain boundary region of a p type semiconductor layer. The thin film solar cell of claim 1, further comprising a passivation layer formed on the substrate to prevent reflection of incident light. Forming a p-type semiconductor layer on the substrate; Alternately forming n + type semiconductor layers and p + type semiconductor layers in predetermined regions of the p-type semiconductor layer; Forming a first electrode connected to the n + type semiconductor layer on the substrate and forming a second electrode electrically connected to the p + type semiconductor layer; And A method of manufacturing a thin film solar cell comprising forming a protective film on the substrate. The method of claim 7, further comprising forming a buffer layer on the substrate before forming the p-type semiconductor layer on the substrate. 8. The method of claim 7, wherein forming the p-type semiconductor layer comprises: forming a p-type amorphous silicon layer on the substrate; And forming a polycrystalline silicon layer having grains grown in a horizontal direction on the amorphous silicon using horizontal crystallization. The method of claim 9, wherein the p-type amorphous silicon layer is formed to a thickness of about 500 to 5000 GPa. 10. The method of claim 9, wherein a polycrystalline silicon layer having grains grown in the horizontal direction by 1 µm or more is formed on the amorphous silicon using sequential horizontal crystallization. 10. The thin film according to claim 9, wherein a high concentration of n-type impurity ions and p-type impurity ions is injected into the grain boundary region of the p-type polycrystalline silicon layer to form an n + type silicon layer and a p + type silicon layer. Manufacturing method of solar cell. 8. The method of claim 7, wherein an n + type semiconductor layer and a p + type semiconductor layer are formed on both sides of the p type semiconductor layer to form a pn junction diode having a sandwich structure. The method of claim 7, wherein the first electrode is formed of a conductive metal such as aluminum, and the second electrode is formed of a conductive metal such as titanium, palladium, nickel, copper, and silver. .