JPH07142749A - Solar cell and its manufacture - Google Patents

Abstract

PURPOSE:To make it possible to industrially realize solar cells having excellent conversion efficiency at a low cost by depositing a photovoltaic film on a supporting substrate and forming a plurality of semi-spherical projections with a particular height on the surface of the photovoltaic film. CONSTITUTION:This solar cell is produced by forming a polycrystalline silicon film 2 on a quartz glass substrate 3 as a supporting substrate and by forming almost semi-spherical projections 1 consisting of fine particles of silicon on the surface of the film. A solar cell having this kind of surface shape is almost perpendicular to the incident light near the apex of that shape, so that reflection loss of incident light can be considerably reduced compared with the conventional technology and thus the conversion efficiency can be further improved. Particularly, if the height of the semi-spherical projection is made equal to 0.1 to 10mum, the incident light can be efficiently taken into the solar cell and thus the height is optimum. Therefore, the solar cells having excellent conversion efficiency can be simply produced at a low cost.

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 in particular, the surface of the solar cell is roughened with fine particles to confine incident light and improve the conversion efficiency into electric power. , Providing a highly efficient solar cell.

[0002]

2. Description of the Related Art Solar cells are promising as clean energy and have already been partially put into practical use as elements for outdoor power generation. Solar cells are required to have high conversion efficiency to convert sunlight into electricity, stable and reliable power generation capability without deterioration over a long period of 20 years or more, low cost, etc. Therefore, these are important issues that are indispensable for the widespread use of solar cells.

Above all, it is important to improve the conversion efficiency, and the crystalline solar cells are superior to the amorphous solar cells, and the materials, structures, and manufacturing methods for the crystalline solar cells in order to further improve the efficiency. Development related to etc. is being actively conducted.

Various developments have been made on the structure of solar cells. For example, it is a well-known fact that the structure in which the surface of the solar cell is roughened makes it possible to effectively convert incident light into electric power and improve the conversion efficiency.

For example, FIG. 5 is a perspective sectional view in which the surface of a conventional single crystal silicon solar cell is roughened, and shows a typical example in which conversion efficiency is improved by a texture treatment.
(Advancements in Silicon Buried Contact Solar)
Cells; SR Wenham, F. Zhang, CMChong and MAG
reen; p.323-p.326). This single crystal silicon solar cell can obtain the highest conversion efficiency among various solar cells. In the roughening of the surface of the solar cell in this conventional technique, the single crystal silicon substrate 20 is anisotropically etched with an alkaline etching solution to form pyramidal protrusions 21 having a uniform shape.

In this conventional example, a conversion efficiency as high as 21% or more is obtained.

The peculiar surface shape capable of improving the conversion efficiency of the solar cell as shown in FIG. 5 can be formed when the orientation of the single crystal silicon substrate 20 which is the substrate matches the etching orientation selectivity of the etching solution. is there. That is, a single crystal silicon solar cell is expensive because a large single crystal substrate that is used in the semiconductor industry is inevitably required in order to have a surface shape that is uniform over a large area as a solar cell. It has become.

FIG. 6 is a perspective sectional view showing a roughened surface of a conventional polycrystalline silicon solar cell, which shows a typical example in which conversion efficiency is improved by a texture treatment (thin high-efficiency polycrystalline). Silicon solar cell; Tomohiro Machida, Ron Okamoto, Koji Okamoto, etc .; Sharp Technical Report; No. 50; 1991, 9
Month; p.15-p.19). Since the polycrystalline silicon substrate used for this polycrystalline silicon solar cell has a lower cost than the single crystal silicon substrate shown in the technical example of FIG. 5, a low cost solar cell can be provided. The roughening of the surface of the solar cell according to this conventional technique is performed by dicing the polycrystalline silicon substrate 10 to form the grooves 22 having an interval of 120 μm and a depth of 70 μm on the entire substrate. In this conventional example, a conversion efficiency of 16% or more is obtained.

In the conventional solar cell as shown in FIG. 6, since the polycrystalline silicon substrate is used, it is inevitably required to roughen the surface by machining such as dicing. The reason is that since the polycrystalline silicon substrate is an aggregate of a large number of crystal grains, in the etching shown in the technique of FIG. 5, the direction of the pyramid varies depending on the crystal grains, which makes control difficult. is there.

[0010]

In the solar cells of the prior art described above, since the roughened shape formed on the surface is a pyramid shape or a triangular roof shape, the incident light is reflected on the sloped portion of these shapes. The loss is also so large that it cannot be ignored, and some form improvement is necessary to achieve sufficient conversion efficiency.

Further, in the above-mentioned conventional technique, in the case of a single crystal silicon solar cell, although the highest conversion efficiency can be obtained, it becomes expensive. On the other hand, in the case of a polycrystalline silicon solar cell, an extra machining process such as dicing is required, which complicates the manufacturing process.

Therefore, according to the conventional technique, it is difficult to manufacture a solar cell having a high conversion efficiency, a simple manufacturing process and a low cost, and to widely disseminate it.

In view of such circumstances, it is an object of the present invention to industrially realize a solar cell with excellent conversion efficiency and low cost.

[0014]

In order to solve the above-mentioned problems and to achieve the object, the present invention relates to a photovoltaic film deposited on a supporting substrate or a photovoltaic substrate, Photovoltaic film or hemispherical or substantially hemispherical shape made of the composition material of the substrate has a height of 0.1 μm to 10 μm
The solar cell is characterized by arranging a plurality of protrusions.

The second invention is the step of forming a photovoltaic film on the supporting substrate, or the step of forming a photovoltaic substrate, and the photovoltaic film on the photovoltaic film or on the substrate. A step of arranging fine particles of a material, wherein the photovoltaic film or the substrate is heated to near the melting point of the fine particles at the same time as the fine particles are deposited, or the fine particles are heated to near the melting point of the fine particles. It is a method of manufacturing a solar cell.

A third aspect of the invention is to form a photovoltaic film on the supporting substrate, or to form a photovoltaic substrate, and to form a photovoltaic film on the photovoltaic film or on the substrate. A method of manufacturing a solar cell, which comprises the step of arranging fine particles of a material, and irradiating the surface of the photovoltaic film or the substrate with active hydrogen atoms simultaneously with the deposition of the fine particles.

A fourth aspect of the present invention is a step of producing fine particles of a photovoltaic material in an inert gas atmosphere or a hydrogen gas atmosphere, and a step of forming the fine particles on a photovoltaic film formed on the supporting substrate. Alternatively, it is a method for producing a solar cell, which comprises a step of arranging it on a photovoltaic substrate so as to have a surface roughness of 0.1 μm to 10 μm.

[0018]

According to the first invention, a solar cell having a surface shape in which the surface of the solar cell is hemispherical or substantially hemispherical is provided.
The reflection loss of the incident light can be significantly reduced as compared with the above-mentioned conventional technique because the light is nearly perpendicular to the incident light in the vicinity of the apexes of these shapes, and the conversion efficiency can be further improved.

In order to improve the conversion efficiency as described above, the height of the hemispherical or substantially hemispherical protrusion is set to 0.1.
It is preferable that the thickness is 10 μm to 10 μm because incident light is efficiently taken into the solar cell.

Further, the projection depends on the forming method,
For example, when it is formed separately from the photovoltaic film or the substrate on the photovoltaic film or the photovoltaic substrate,
Since atomic dangling bonds exist at the interface between the projection and the film or the substrate, which may adversely affect the characteristics of the solar cell, it is desirable to terminate the dangling bond with hydrogen or the like. Since hydrogen has the smallest atomic radius, hydrogen easily penetrates into the solid interface as described above. Further, especially for a silicon solar cell, silicon and hydrogen are likely to bond with each other. For these reasons, termination with hydrogen is preferred.

Next, according to the second aspect of the invention, when the solar cell of the first aspect of the invention is manufactured, at the same time as the deposition of the fine particles forming the surface shape of the solar cell, the film or the substrate is placed near the melting point of the fine particles. Since it is heated to the above, the crystal orientation of the fine particles deposited on the film or the substrate is easily aligned with the crystal orientation of the film or the substrate. That is, the interface between the film or the substrate and the fine particles that are the protrusions is eliminated, and it becomes possible to manufacture a solar cell with high conversion efficiency.

Next, according to the third invention, when the solar cell of the first invention is manufactured, active hydrogen atoms (atomic hydrogen,
Alternatively, hydrogen radicals) are applied to the surface of the film or the substrate. The active hydrogen atoms easily penetrate into the solid interface as described above, but for that purpose, it is required to heat the temperature of the film or the substrate to, for example, 300 ° C. or higher. In the present invention, such heating is unnecessary by irradiating the surface of the film or the substrate with active hydrogen atoms simultaneously with the deposition of the fine particles forming the protrusions.

Next, according to a fourth aspect of the invention, when the solar cell of the first aspect of the invention is manufactured, fine particles of the photovoltaic material generated in an inert gas atmosphere or in a hydrogen gas atmosphere are used in the atmosphere. In above, it is arranged on the photovoltaic film formed on the supporting substrate or on the photovoltaic substrate.

The fine particles produced by such a method are clean, and there are almost no impurities on the surface thereof which adversely affect the characteristics of the solar cell. Further, when fine particles are deposited on a film or a substrate in an inert gas atmosphere or a hydrogen gas atmosphere, impurities that adversely affect the characteristics of the solar cell may be present at the interface between the fine particles that are protrusions and the film or the substrate. Since there is almost no, a clean bonding surface can be formed. That is, it becomes possible to manufacture a solar cell with high conversion efficiency.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a structural example of a polycrystalline silicon solar cell in one embodiment of the first invention.

In the solar cell of this embodiment, a polycrystalline silicon film 2 is formed on a quartz glass substrate 3 which is a supporting substrate, and a substantially hemispherical projection 1 made of silicon fine particles is formed on the surface of the film.
Is formed.

The polycrystalline silicon film 2 is subjected to thermal CV using a mixed gas of Si ₂ H ₆ diluted with hydrogen gas and PCl ₃ as a raw material.
Formed in D. The formed film was N-type, the film thickness was 10 μm, and the average crystal grain size of each crystal was about 50 μm. A polycrystalline silicon film of such a size is satisfactory as a photovoltaic film for solar cells. Further, in order to form a PN junction, thermal diffusion of B ₂ H ₆ diluted with hydrogen gas was performed after the formation of the film.

The substantially hemispherical protrusion 1 formed on the polycrystalline silicon film 2 is manufactured according to the second invention. FIG. 2 shows a block diagram of a manufacturing apparatus for carrying out the second invention. In the figure, 4 is a decompression container, 5 is silicon fine powder, 6 is argon gas, 7 is RF plasma torch, 8 is thermal plasma, 9 is semi-molten silicon fine powder, and arrow A indicates the evacuation direction. The basis of the method of forming the substantially hemispherical protrusion 1 in this manufacturing apparatus is to optimize the spraying conditions by RF plasma spraying using silicon fine powder having an average particle diameter of 5 μm as a raw material.

As an example of thermal spraying conditions, the quartz glass substrate 3 on which the polycrystalline silicon film 2 is formed is placed in a decompression container 4, and an argon gas 6 as a plasma gas is introduced into the RF plasma torch 7 at a flow rate of 7 l / min. Then, the pressure in the decompression container 4 is set to 20000 Pa. Subsequently, when RF power having a frequency of 27 kHz and an output of 10 kW is applied to the RF plasma torch 7, the thermal plasma 8 of the argon gas 6 is generated. After that, when the silicon fine powder 5 is put into the RF plasma torch 7, the silicon fine powder 5 is heated by the thermal plasma 8 and becomes a semi-molten silicon fine powder 9. When such softened semi-molten silicon fine powder 9 is deposited on the polycrystalline silicon film 2, the substantially hemispherical projection 1 as shown in FIG. 1 is formed. The height of the substantially hemispherical protrusion 1 was 0.6 μm to 3.8 μm, and was formed almost on the front surface of the polycrystalline silicon film 2.

A 3 cm square polycrystalline silicon solar cell was produced by the above operation, and its characteristics were measured under the evaluation conditions of AM0. As a result, a conversion efficiency of 17.4% was obtained.

In the embodiment in which the protrusion is formed, RF is used.
If the RF power applied to the plasma torch 7 is too large or the flow rate of the plasma gas is too large, the projections will be too flat, or will be distorted, resulting in a good shape as a projection for a solar cell. It is easy to form things. This is because the silicon fine powder is heated too much, or the speed of the heated silicon fine powder becomes too high.

Next, FIG. 3 shows a block diagram of a manufacturing apparatus for carrying out the third invention. In the figure, 10 is a polycrystalline silicon substrate, 11
Is hydrogen gas, and the same members as those in FIG. 2 are denoted by the same reference numerals and the description thereof will be omitted.

In this example, a polycrystalline silicon substrate was used as the photovoltaic substrate, and the protrusions made of silicon were formed on the substrate.

The silicon protrusions were formed by RF plasma spraying containing active hydrogen atoms. As an example of thermal spraying conditions, the polycrystalline silicon substrate 10 is placed in a decompression container 4, and hydrogen gas 11 as a plasma gas in an RF plasma torch 7 at a flow rate of 5 l / min and an argon gas 6 at a flow rate of 3
1 / min and then the RF plasma torch 7
When RF power having a frequency of 27 kHz and an output of 10 kW is applied to the, a thermal plasma 8 of the mixed gas of hydrogen and argon is generated. After that, RF the silicon fine powder 5
When charged into the plasma torch 7, the silicon fine powder 5
Since it is heated by the thermal plasma 8, it becomes semi-molten silicon fine powder 9. When such softened semi-molten silicon fine powder 9 is deposited on the polycrystalline silicon substrate 10, a substantially hemispherical projection 1 as shown in FIG. 1 is formed.

In the present embodiment, the thermal plasma 8 containing hydrogen gas 11 is simultaneously formed on the polycrystalline silicon substrate 10 at the same time when the protrusions are formed.
Is irradiated. Since a large amount of active hydrogen atoms generated by dissociation of hydrogen gas 11 exist in this thermal plasma 8,
Even if a dangling bond is present at the interface between the protrusion and the substrate, active hydrogen atoms can be strongly terminated.

A 3 cm square polycrystalline silicon solar cell was produced by the above operation, and its characteristics were measured under the AM0 evaluation conditions. As a result, a conversion efficiency of 17.9% was obtained.

Next, FIG. 4 is a configuration diagram (a) of a manufacturing apparatus for carrying out the fourth invention and diagrams (b) and (c) showing an example of the structure of the manufactured polycrystalline silicon solar cell. In the figure, 12 is a substrate delivery chamber, 13 is a particle deposition chamber, 14 is a particle generation chamber, 15 is a silicon electrode, 16 is arc discharge, and 17 is a particle transfer tube. 18 is an annealing chamber, and 19 is a substrate take-out chamber. In addition, the same members as those in FIG. 2 and FIG.

In this example, a polycrystalline silicon substrate was used as the photovoltaic substrate, and the protrusions made of silicon were formed on the substrate. FIG. 4 (a) shows an outline of the generation of crystalline fine particles of silicon, the deposition of the fine particles on a polycrystalline silicon substrate, and the formation of silicon protrusions. Although not shown, the chamber of each process is evacuated by a vacuum pump.

From the substrate delivery chamber 12 to a polycrystalline silicon substrate
10 is transferred to the particle deposition chamber 13. The deposition process of the silicon fine particles 5 in the fine particle deposition chamber 13 will be described below. A pair of silicon electrodes 15, 15 are installed to face each other in the particle generation chamber 14 and are evacuated by a vacuum pump (not shown). Argon gas 6 is supplied to the particle generation chamber 14 to set a predetermined pressure. Then the silicon electrode
It was generated by applying AC power from an AC power supply (not shown) between 15 and 15 to generate arc discharge 16.

The silicon fine particles 5 are transferred to the fine particle transfer pipe 17 by the gas pressure difference between the fine particle generation chamber 14 and the fine particle deposition chamber 13.
It is transported inside and deposited spherically on the polycrystalline silicon substrate 10 as shown in FIG. 4 (b).

The polycrystalline silicon substrate 10 on which the silicon fine particles 5 are deposited is then transferred to the annealing chamber 18. In this example, the annealing method used was heating with high-temperature hydrogen plasma. That is, hydrogen gas is applied to the RF plasma torch 7.
11 is introduced to generate the thermal plasma 8 and the silicon fine particles 5 are heated by the heat of the thermal plasma 8.

This thermal plasma has a large amount of impurities, which does not pose a problem with impurities that adversely affect the characteristics of the solar cell, and has a large thermal energy. For that purpose polycrystalline silicon substrate
It is suitable for melting the silicon fine particles 5 deposited on the surface 10 to form a substantially hemispherical silicon protrusion 1 having a good shape for a solar cell as shown in FIG. 4 (c). Furthermore, since a large amount of active hydrogen atoms are present in the thermal plasma of hydrogen gas, dangling bonds that tend to remain at the interface between the formed protrusion and the substrate are terminated, and polycrystalline silicon having a high-quality protrusion is formed. A substrate can be manufactured.

An example of manufacturing conditions for manufacturing a polycrystalline silicon solar cell by selecting the conditions in each manufacturing step according to the above manufacturing steps, and the characteristics of the manufactured solar cell will be described below.

The silicon fine particles 5 are generated in the fine particle generation chamber.
The pressure of the argon gas 6 of 14 is 40 Torr, the silicon electrode 15,1
The arc voltage at 5 was set to 60 V, the current was set to 130 A, and the atmosphere in the particle deposition chamber 13 was set to 1 Torr by argon gas 6 flowing from the particle generation chamber 14. As a result, the generated silicon fine particles 5 have a particle size of about
The average particle size was about 1.6 μm with a distribution of 0.5 to 2.8 μm.

The conditions for generating the thermal plasma 8 of the hydrogen gas 11 in the annealing chamber 18 are as follows: the pressure of the annealing chamber 18 is 0.1 Torr, the flow rate of the hydrogen gas 11 is 2 l / min, and the generated power of the thermal plasma 8 is 5 Torr.
It was set to 0kW.

FIG. 4 (c) shows the resulting polycrystalline silicon substrate having protrusions formed on its surface. Further, after this film formation, the polycrystalline silicon substrate is made into a P-type or N-type semiconductor thin film in a subsequent step such as an ion doping method or a thermal diffusion method.

A 3 cm square polycrystalline silicon solar cell was produced by the above operation, and its characteristics were measured under the evaluation condition of AM0. As a result, a conversion efficiency of 17.5% was obtained.

[0048]

As described above, according to the present invention, a projection having a good shape for a solar cell can be formed on a polycrystalline thin film and a polycrystalline substrate, which has excellent conversion efficiency and low cost. Moreover, a solar cell having a simple manufacturing process is provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a structural example of a polycrystalline silicon solar cell in one example of the first invention of the present invention.

FIG. 2 is a configuration diagram of a manufacturing apparatus for carrying out a second invention of the present invention.

FIG. 3 is a configuration diagram of a manufacturing apparatus for carrying out a third invention of the present invention.

FIG. 4 is a configuration diagram of a manufacturing apparatus for carrying out a fourth invention of the present invention and a diagram showing a structural example of a polycrystalline silicon solar cell.

FIG. 5 is a perspective cross-sectional view in which the surface of a conventional single crystal silicon solar cell is roughened.

FIG. 6 is a perspective cross-sectional view in which the surface of a conventional polycrystalline silicon solar cell is roughened.

[Explanation of symbols]

1 ... Approximately hemispherical protrusion, 2 ... Polycrystalline silicon film, 3
... quartz glass substrate, 4 ... decompression container, 5 ... silicon fine powder, 8 ... thermal plasma, 9 ... semi-molten state silicon fine powder, 10 ... polycrystalline silicon substrate, 11 ... hydrogen gas,
12 ... Substrate delivery chamber, 13 ... Fine particle deposition chamber, 14 ... Fine particle generation chamber, 15 ... Silicon electrode, 16 ... Arc discharge,
17 ... Particle transfer tube, 18 ... Annealing room, 19 ... Substrate removal room.

Claims (6)

[Claims] 1. A hemispherical shape or a substantially hemispherical shape made of the composition material of the photovoltaic film or the substrate on the photovoltaic film deposited on the supporting substrate or on the photovoltaic substrate has a height of 0.1. A solar cell having a plurality of projections of μm to 10 μm. 2. The solar cell according to claim 1, wherein the hemispherical or substantially hemispherical projections are formed of fine particles of a photovoltaic material. 3. A projection formed by fine particles formed on the photovoltaic film deposited on the supporting substrate or on the photovoltaic substrate, and atoms at the interface between the photovoltaic film and the substrate. The solar cell according to claim 1, wherein the dangling bond is terminated with hydrogen. 4. A step of forming a photovoltaic film on the supporting substrate, or a step of forming a photovoltaic substrate, and disposing fine particles of a photovoltaic material on the photovoltaic film or on the substrate. And a step of heating the photovoltaic film or the substrate to a temperature near the melting point of the particles, or heating the particles to a temperature near the melting point of the particles. . 5. A step of forming a photovoltaic film on the support substrate, or a step of forming a photovoltaic substrate, and disposing fine particles of a photovoltaic material on the photovoltaic film or on the substrate. A method for manufacturing a solar cell, comprising the steps of: irradiating the surface of the photovoltaic film or the substrate with active hydrogen atoms simultaneously with the deposition of the fine particles. 6. A step of producing fine particles of a photovoltaic material in an inert gas atmosphere or a hydrogen gas atmosphere, and on a photovoltaic film on which the fine particles are formed on the supporting substrate, or a photovoltaic substrate. A method for manufacturing a solar cell, which comprises a step of disposing the surface layer on the surface of the solar cell so as to have a surface roughness of 0.1 μm to 10 μm.