JPH09139514A - Solar cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a solar battery of low cost, by reducing semiconductor material cost and forming a PN junction by a simple method. SOLUTION: An N-type silicon coating film 3 is printed and formed on a glass board 1 and made fine. A P-type silicon coating film 4 is printed and formed on other glass board 2 and made fine. The glass boards 1, 2 on which the coating films 3, 4 are formed are so unified in a body that the P-type and the N-type silicon coating films face with each other. By pressing the unified structure simultaneously with heating, a PN junction is formed, and a solar battery 10 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell and a method for manufacturing the same, and more particularly to a method for producing a silicon solar cell which is stable over time and low in cost using a semiconductor powder.

[0002]

2. Description of the Related Art Solar cells make use of the photovoltaic effect of a semiconductor pn junction and are capable of converting sunlight into electric energy in a clean manner, and are often used to improve conversion efficiency and reduce manufacturing costs. Have been studied.

Various materials have been studied in the form of searching for a semiconductor material which improves the conversion efficiency by eliminating the reflection of sunlight energy and maximizing the light absorption.

On the other hand, the manufacturing cost is being studied from the viewpoint of both material cost and processing cost. For example, in the case of silicon semiconductor, single crystal to polycrystal, and bulk silicon to thin film silicon are used. Therefore, a method of manufacturing a solar cell in which a pn junction is formed by a simple method has been tried.

Despite these efforts, solar cells cannot compete with commercial power sources in terms of power generation cost and have not yet occupy a large position as an energy source in a broad sense.

When the solar cell is considered as a power supply source, the crystalline silicon solar cell is most used in terms of cost of power generation and reliability over time. So-called amorphous silicon thin-film solar cells have the most suitable structure for reducing power generation costs from the viewpoint of their materials and manufacturing methods, but because of their crystallographic instability and low conversion efficiency, they are used as power supply solar cells. Has not been widely put to practical use.

On the other hand, crystalline silicon solar cells have high conversion efficiency and high reliability over time, but it is difficult to reduce power generation cost because both the single crystal and polycrystalline silicon, which are the main constituent materials of solar cells, are expensive. There was a problem. For this reason, in crystalline silicon solar cells, reduction of material cost has become the most urgent issue for reduction of solar cell cost, and techniques for forming solar cells with less silicon materials have been developed.

However, in a solar cell composed of a semiconductor pn junction, conversion of sunlight into electric energy is performed in a very shallow region of the crystal surface. Therefore, the same conversion efficiency can be obtained if the physical constants of the semiconductor are the same in both thick bulk crystals and thin film crystals. In the actual bulk solar cell, most of the thick crystals only function as a base for supporting the energy conversion portion near the pn junction. Therefore, thinning the semiconductor material is the most effective factor in reducing the material cost. 20 μm ~
If a solar cell can be made of crystalline silicon with a thickness of 30 μm, the effect of lowering the material cost will be extremely large, but since there is no established technology to form a thick film or thin film of crystalline silicon, thick-film silicon solar cells are not available. Not not.

[0009]

One of the technical problems to be solved by the present invention is to reduce the material cost and to construct an inexpensive solar cell with less semiconductor material.

Another technical problem to be solved by the present invention is to provide a low-cost method for forming a pn junction in a solar cell. Formation of a pn junction in a conventional solar cell is performed by thermal diffusion of an impurity element, ion implantation, CVD.
And the like. These are the most common methods for forming pn junctions, but the execution thereof requires enormous equipment and working time, and the cost of solar cells is reflected in many cases.

[0011]

The present invention has been proposed to solve the above-mentioned problems, and a solar cell of the present invention has a p-type semiconductor between a pair of heat-resistant substrates, at least one of which is a glass substrate. It is characterized by comprising a pn junction formed by a sintered layer of crystal powder and a sintered layer of n-type semiconductor crystal powder. Further, in the manufacturing method thereof, a step of forming a coating film of p-type (or n-type) semiconductor powder on a heat-resistant glass substrate, a coating film of n-type (or p-type) semiconductor powder on the heat-resistant substrate A step of forming a p-type semiconductor powder coating film and a substrate on which an n-type semiconductor powder coating film is formed such that the substrates are integrated so that the coating surfaces face each other. The method is characterized by including a step of heating and pressing by hydrostatic pressing, hot pressing, or the like. In addition, a p-type (or n-type) is formed on a heat-resistant glass substrate or a metal substrate.
Type) semiconductor powder coating film is laminated, an n-type (or p-type) semiconductor powder coating film is laminated thereon, and a heat-resistant glass substrate or a metal plate is brought into contact therewith and heated and pressed. It is characterized by including a process.

The present invention makes it possible to form a pn junction at the same time as densifying the semiconductor powder by a simple method of high temperature pressure welding, and to make the inclination of the pn junction and the depth from the surface arbitrary. It has a feature that can be controlled. Although it is a powder semiconductor coating film, it can be formed into a thick film with a substantially true density by hot isostatic pressing, and a good pn junction can be formed. In the solar cell formed by the above structure, the thickness of the pn junction in the depth direction required for converting light energy into electric energy is secured, but the substrate supporting it is formed of glass or the like. There is. Therefore, compared with, for example, a bulk silicon solar cell, the silicon material used can be significantly reduced and the cost can be reduced.

Further, according to the present invention, the pn junction is formed at the same time as the density of the semiconductor powder such as silicon powder applied by heating and pressing is increased. This enables the formation of the pn junction more easily than the conventional method for forming the pn junction, and the manufacturing cost can be reduced.

In the present invention, crystalline silicon is sintered, but this is not amorphous silicon, so that it has a high energy conversion efficiency and is extremely stable over time.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, a method for producing high-purity silicon powder, which is a basic constituent element of the present invention, will be described. The starting material is preferably cast type silicon to which impurities have been added and which has been adjusted so as to give a predetermined conductivity type and specific resistance. This is placed in a ball mill pot made of high-purity polysilicon, and it is crushed by rotating for a certain period of time. After crushing, this is passed through a predetermined sieving mesh to obtain high-purity silicon powder with uniform particle size.

FIG. 3 shows an embodiment of the solar cell according to the present invention. The glass substrates 1 and 2 in FIGS. 1, 2 and 3 are highly heat resistant Pyrex glass having substantially the same linear expansion coefficient as that of silicon. For example, Corning 7052 glass can be used for this. A coating layer 3 of n-type silicon powder having a specific resistance of 1 Ω-cm having a thickness of 20 μ is formed on the glass substrate 1 in FIG.
m. The silicon powder can be applied onto the glass substrate by, for example, forming a paste of silicon powder with ethanol and applying the paste into a predetermined uniform thickness by a so-called doctor blade method.

The silicon coating film can be formed by other methods. That is, butyl acetate in which nitrocellulose is dissolved is added to silicon powder to form a paste, the viscosity is adjusted, and then the coating film can be formed by silk screen printing. After drying, the binder is sublimated by heating to 450 ° C. in vacuum. In addition, a dip method, a spray method, etc. can also be used.

When the silicon coating film thus formed has low density and insufficient adhesion to the glass substrate,
In order to improve this, densification is performed as follows. That is, a carbon electrode, which is a conductor having good heat resistance, is placed on a dried silicon powder coating film, and a glass substrate (−) and a carbon electrode (+) are applied at a temperature of 500 ° C. while applying a DC voltage of about 800 v. To heat. This treatment can be performed either in vacuum or in a nitrogen atmosphere. By this treatment, electrostatic attraction acts between the powder silicon coating film and the glass substrate, and the silicon coating film is densified and firmly adheres to the glass substrate. In addition to carbon, a semiconductor plate such as a silicon plate and a refractory metal such as tantalum, molybdenum, or dangsten can be used as an electrode as a conductor having good heat resistance. Cold isostatic pressing is also effective as another method of densification.

0.0 on the glass substrate 2 in FIG.
P-type silicon powder coating layer 4 having a resistivity of 05 Ω-cm 4
Is formed to a thickness of 5 μm by the same method as the substrate 1 and densified by the same method.

The two glass substrates having the p-type and n-type silicon coating layers are integrated so as to face each other on their silicon coating surfaces, leaving the electrode extraction portions. Further, the periphery of the facing surface of the silicon is covered with the frit glass powder 5 and melted by the subsequent heat treatment so that the airtightness is maintained.

In the solar cell according to the present invention, the pn junction is formed by simultaneously pressing the integrated structure while heating it by a hot press or a hot isostatic press (HIP). That is, HIP
Taking processing as an example, first, the integrated structure is installed in a HIP device, and heating is started while exhausting to a vacuum degree of about 10 ⁻³ mmHg. When the temperature of the structure rises to 800 ° C., the glass frit 5 around the facing surface is melted and sealed so as to keep the surrounding area of the facing surface airtight.

In such a state, next, 9
Pressurization with argon gas is started while the temperature is raised to 00 ° C. or more, for example, 1000 ° C., and finally hydrostatically pressurized to 1500 atm. As a result of being heated to 1000 ° C,
Both the glass substrates 1 and 2 are softened, and the pressure of the argon gas is effectively transmitted to the silicon coating film to the inside. By this treatment, the silicon powder coating film is densified to a value close to the true density of silicon, and a uniform pn junction 6 is formed over the entire facing surface. The temperature and pressure may be selected according to the semiconductor material, glass material, and the like. Further, in the case of hot pressing as well, the temperature, pressure and the like can be appropriately selected.

The solar potential 10 is constructed in this way,
Electric power generated by the photovoltaic effect of the incident sunlight can be extracted from the extraction electrode 7 exposed to the outside.

In the above-mentioned embodiment, an example in which crystalline silicon powder is used as the semiconductor material has been described, but the present invention is not limited to this, and other crystalline semiconductor materials such as SiGe powder, chalcopyrite (CuInS ₂ , CuInSe ₂ ) and other alloys. Powder can also be used by appropriately selecting the expansion coefficient of the substrate material.

Further, the coating film thickness of the semiconductor powder is not limited to the above and can be appropriately selected in consideration of efficiency and the like. In particular, the present invention provides a semiconductor powder coating film of several microns or less,
It is characterized in that it is formed in a so-called thick film of several tens of microns, and since the resistance value in the horizontal direction of the substrate is sufficiently low for this reason, an electrode layer such as ITO or a metal thin film is previously formed on the substrate. It is not necessary and is advantageous in cost. Furthermore, in order to increase the energy conversion efficiency, pn
It is also easy to optimize the depth and shape of the joint.

In the above embodiment, both heat resistant substrates are glass substrates, but one substrate, for example, the substrate on the side where light does not enter may be a metal plate. As the metal plate, it is necessary to match the expansion coefficient with the semiconductor material such as silicon as much as possible, and for example, there is a stainless plate whose composition is selected. The use of a metal plate is advantageous in strength and excellent in conductivity, so that the efficiency can be improved.

As a modified example of the present invention, a coating film of p-type (or n-type) semiconductor powder is formed in a thick film on a glass substrate or a metal plate, and a coating film of n-type (or p-type) semiconductor powder is formed thereon. Is laminated to form a thick film, and a separate glass substrate or metal plate (stainless steel, etc.) is brought into contact therewith, and heated by hot isostatic pressing or hot pressing to apply p-type,
You may form the pn junction which consists of an n-type sintered layer. This method is more cost-effective than the above-mentioned method because the process is simplified.

[0029]

According to the present invention, a pn junction can be formed with less semiconductor material and a simple method, and a low-cost solar cell can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one conductivity type silicon powder coating layer formed on a glass substrate of a solar cell according to the present invention.

FIG. 2 is a cross-sectional view showing another conductive type silicon powder coating layer similar to that of FIG.

FIG. 3 is a cross-sectional view of a solar cell according to the present invention.

[Explanation of symbols]

 1 glass substrate 2 glass substrate 3 n-type silicon coating film 4 p-type silicon coating film 5 frit glass 6 pn junction 7 extraction electrode 10 solar cell

Claims (7)

[Claims] 1. A pn junction formed by a sintered layer of p-type semiconductor crystal powder and a sintered layer of n-type semiconductor crystal powder is provided between a pair of heat-resistant substrates, at least one of which is a glass substrate. Solar cells. 2. A p-type (or n-type) on a heat-resistant glass substrate.
A step of forming a coating film of semiconductor powder, a step of forming a coating film of n-type (or p-type) semiconductor powder on a heat resistant substrate, a coating film of the p-type semiconductor powder and a coating of the n-type semiconductor powder A step of integrating the substrates on which the films are formed so as to face each other on the coating surface, and heating the integrated components,
A method of manufacturing a solar cell, which includes a step of applying pressure. 3. The method for manufacturing a solar cell according to claim 2, wherein after forming a coating film of p-type (or n-type) semiconductor powder, the coating film is densified. 4. The method for manufacturing a solar cell according to claim 2, wherein heating and pressing are performed by hot isostatic pressing or hot pressing. 5. The method for manufacturing a solar cell according to claim 2, wherein the semiconductor powder is crystalline silicon powder. 6. An electrode having good heat resistance is placed on the coating film,
The method for manufacturing a solar cell according to claim 3, wherein the coating film is densified by applying a high voltage so that the electrode becomes + and the substrate becomes − at a high temperature. 7. A coating film of p-type (or n-type) semiconductor powder is formed on a heat-resistant glass substrate or a metal substrate, and a coating film of n-type (or p-type) semiconductor powder is laminated and formed thereon.
A method of manufacturing a solar cell, which comprises a step of bringing a heat-resistant glass substrate or a metal plate into contact therewith, and heating and pressing.