JP2000357660A - Substrate provided with polycrystalline silicon film, method for forming the same, and solar cell using the film - Google Patents

Abstract

[PROBLEMS] To provide a substrate provided with a polycrystalline silicon film which does not require a complicated processing step and has a reduced defect density at a grain boundary. SOLUTION: By forming a polycrystalline silicon film on a metal substrate having a biaxial orientation by an epitaxial growth method, it is possible to form a polycrystalline silicon film in which a single crystal constituting the film has a uniform crystal orientation. Therefore, the above problem can be solved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate provided with a polycrystalline silicon film, a method for forming the same, and a solar cell using the substrate. More specifically, the present invention relates to a substrate provided with a polycrystalline silicon film having a low defect density, a method for forming the same, and a solar cell using the substrate and having good photoelectric conversion efficiency.

[0002]

2. Description of the Related Art Fossil fuels such as petroleum have a problem that supply and demand in the future are concerned and carbon dioxide which causes global warming is emitted. Solar cells have attracted attention as an alternative energy source for such fossil fuels.

[0003] A solar cell uses a pn junction for a photoelectric conversion layer for converting light energy into electric power, and silicon is generally most often used as a semiconductor constituting the pn junction. As silicon, single crystal silicon is preferably used in terms of photoelectric conversion efficiency. However, it is difficult to supply a raw material and increase the area, and thus there is a problem that the cost is high.

On the other hand, an amorphous silicon solar cell using amorphous silicon has been put to practical use as a material for a photoelectric conversion layer which is advantageous for realizing a large area and a low cost. However, its photoelectric conversion efficiency is inferior to single-crystal silicon solar cells. Further, it is known that a phenomenon called the Staebler-Wronski effect occurs in amorphous silicon in which the defect density in a film increases as light is irradiated. Therefore, the amorphous silicon solar cell has a problem that the photoelectric conversion efficiency deteriorates with time.

[0005] In recent years, in order to realize a solar cell having both high and stable photoelectric conversion efficiency at the level of a single-crystal silicon solar cell and large area and low cost at the level of an amorphous silicon solar cell, polycrystalline silicon has been developed. Use for a photoelectric conversion layer is being studied. In particular, a polycrystalline silicon solar cell using polycrystalline silicon as a photoelectric conversion layer by using a thin film forming technique by chemical vapor deposition (CVD) similar to the case of amorphous silicon has attracted attention.

[0006] However, the photoelectric conversion efficiency of the polycrystalline silicon solar cell manufactured by the above method is only at the same level as that of the amorphous silicon solar cell. The major factors that lower the photoelectric conversion efficiency are as follows: (1) Since the individual crystal grains of polycrystalline silicon have various orientations that are not related to each other, the bonding state of silicon atoms at crystal grain boundaries is extremely disturbed. And (2) the crystal grain boundary area is large because the crystal grain size is as small as several tens of nm.

In general, dangling bonds, which are dangling bonds of atoms in a semiconductor layer, form defect levels in a forbidden band. Therefore, the characteristics of a semiconductor device are closely related to the defect density of the semiconductor layer. In particular, in a crystal grain boundary in a polycrystalline semiconductor, the bonding state of atoms is disturbed and a dangling bond density is extremely high. Therefore, in order to improve the characteristics of a polycrystalline semiconductor device, the area of the crystal grain boundary is reduced. That is, it is considered effective to increase the crystal grain size. Attempts to obtain a polycrystalline silicon film having a large crystal grain size have been made by various techniques.

For example, a so-called laser annealing method is known in which an amorphous silicon film formed on a substrate by a CVD method or the like is irradiated with laser light to melt the film and then solidify to obtain a polycrystalline silicon film. Have been. Further, a so-called partial doping method is known in which crystallization by solid phase growth is selectively started by doping a part of an amorphous silicon film with phosphorus, boron, or the like.

However, the crystal grain size obtained by the above-mentioned method is at most about several μm. This particle size is at a level sufficient for a device such as a thin film transistor (TFT) having an element size of about several μm. However, in solar cells required to be formed in a large area, those having a larger particle size are desired. However, when trying to further increase the particle size by the above-described method, there have been problems such as deterioration of film properties and heat treatment time of several tens of hours. Therefore, it has been difficult to obtain a polycrystalline silicon film having a larger crystal grain size.

On the other hand, in a polycrystalline silicon semiconductor, it is known that if the crystal orientations of the crystal grains constituting the semiconductor are aligned as much as possible, the disorder of the bonding state of atoms at the crystal grain boundaries is reduced. By reducing the disorder of the coupling state, improvement in device characteristics is expected.

As a method of aligning crystal orientations, a method described in Japanese Patent No. 272271 is known, and this method is performed as follows. First, after a single-crystal silicon film having a uniform crystal orientation is arranged on a metal substrate at intervals, heating is performed to form a metal-silicon intermediate layer between the metal substrate and the single-crystal silicon film. Next, the exposed surface of the metal substrate is oxidized. Next, a polycrystalline silicon film is formed by selective epitaxial growth using single crystal silicon as a seed crystal for crystal growth. It is described that the obtained polycrystalline silicon film has a uniform crystal orientation of a single crystal as a constituent element, so that the defect density at a grain boundary is reduced.

[0012]

The above-mentioned Patent No. 272
In the method described in Japanese Patent No. 1271, a single crystal silicon film is arranged on a metal substrate by the following method. That is, first, an insulating layer is formed on a silicon wafer, and a fine opening is provided in a part of the insulating layer. Thereafter, a single crystal silicon film is formed by a selective epitaxial growth method, and the single crystal silicon film is separated from the silicon wafer by ultrasonic vibration. Next, the separated single crystal silicon film is provided over a metal substrate. As described above, the method described in the above publication includes complicated processing steps, and it has been difficult to stably and inexpensively manufacture a polycrystalline silicon film.

An object of the present invention is to provide a polycrystalline silicon film having a reduced defect density at a crystal grain boundary without a complicated processing step, a method of forming the same, and a high-quality and inexpensive solar cell using the film. It is to provide a battery.

[0014]

Thus, according to the present invention, there is provided a biaxially oriented metal substrate formed by a rolling process, and a biaxially oriented metal substrate formed on the biaxially oriented metal substrate by an epitaxial growth or an amorphous silicon film or a microcrystalline silicon film. A polycrystalline silicon film formed by applying a polycrystalline silicon film, wherein the polycrystalline silicon film is made of an individual single crystal having a crystal orientation tightly oriented to the metal substrate. A provided substrate is provided.

Further, according to the present invention, a biaxially oriented metal substrate is obtained by rolling, and energy is applied to the metal substrate by an epitaxial growth method or by applying energy to an amorphous silicon film or a microcrystalline silicon film. ,
A method for forming a substrate having a polycrystalline silicon film, characterized by forming a polycrystalline silicon film composed of individual single crystals having a crystal orientation closely related to the orientation of a metal substrate, is provided. Further, according to the present invention, there is provided a solar cell including the polycrystalline silicon film as a photoelectric conversion layer and a metal substrate as an electrode.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. In the present invention, a biaxially oriented metal substrate formed by rolling is used. The material forming the metal substrate preferably contains at least one metal of aluminum, copper, nickel, silver, iron, chromium, and titanium. Also, alloys of these metals (for example, iron-nickel alloys) may be used, and alloys with silicon (for example, iron-silicon alloys)
It may be. These materials may have a face-centered cubic lattice or a body-centered cubic lattice.

The metal substrate has a (100) surface and a rolling direction of [001] or a surface of (110) and a rolling direction of [-11].
It consists of a face-centered cubic lattice having a crystal orientation biaxially oriented in the [2] direction, or the surface has a (110) plane and the rolling direction is [00].
It is preferable to be composed of a body-centered cubic lattice having a crystal orientation biaxially oriented in the 1] direction. Here, the crystal orientation is 100
It is preferable that the metal substrate is oriented in a predetermined direction. However, since it is generally difficult to achieve 100%, it is only necessary to recognize that the metal substrate as a whole is biaxially oriented.

In the above description, the surface means a surface parallel to the rolling direction and having the largest surface area. Specifically, it means a surface that comes into contact with rolling means (for example, a roller) during rolling.

Further, it is preferable that the interstitial distance between crystals on the metal substrate surface on which the polycrystalline silicon film is formed is as close as possible to the interstitial distance between crystalline silicon. In particular, when a polycrystalline silicon film is epitaxially grown on a metal substrate,
It is preferable that the difference between the two lattice distances is 15% (absolute value) or less. The metal substrate can be formed, for example, by rolling the above material in the form of a slab. Rolling can be performed hot and / or cold.

The rolled metal substrate is made of polycrystal. For this reason, in a general rolling process, the crystal orientations of single-crystal bodies, which are polycrystalline constituents, are random with respect to each other. Grain boundaries in polycrystals having random orientations have no continuity of the crystal lattice.

However, by appropriately setting the processing conditions such as the rolling reduction and the temperature during the rolling process and the heat treatment conditions, the crystal orientation of the single crystal as a constituent unit of the polycrystal has a specific biaxial direction (for example, (A direction perpendicular to the surface of the metal substrate and a direction in which rolling is performed).
By performing biaxial orientation, continuity of a crystal lattice at a crystal grain boundary can be maintained.

The rolling process is described in Patent No. 26268.
No. 45, JP-A-63-255911, JP-A-1-201447, U.S. Pat. No. 5,741,377, and the like can all be employed.
Next, a polycrystalline silicon film is formed on the metal substrate.

Here, in polycrystalline silicon, if the continuity of the crystal lattice is maintained, the defect density at the crystal grain boundary is greatly reduced. Therefore, it is desired to maintain the continuity of the crystal lattice. Therefore, if a polycrystalline silicon film is formed on a metal substrate having a biaxial orientation as described above, a polycrystalline silicon film composed of individual single crystals having a uniform crystal orientation with a tight orientation of the metal substrate is obtained. be able to.

As a method for forming the polycrystalline silicon film, there can be mentioned a method capable of epitaxial growth such as a sputtering method, an electron beam evaporation method and a plasma CVD method. Further, there is also a method of forming an amorphous silicon film or a microcrystalline silicon film on a metal substrate and then crystallizing the film by applying energy such as heat or electromagnetic waves.

Further, the conductivity type of the polycrystalline silicon film is not limited to the intrinsic type (i-type), but may be p-type or n-type by including an element such as boron or phosphorus in the silicon film. Is also possible.

The above-mentioned polycrystalline silicon film having a uniform crystal orientation can be particularly preferably used as a photoelectric conversion layer of a solar cell having high photoelectric conversion efficiency.

When used for the photoelectric conversion layer, any known structure can be applied to the structure.
, Pin type, nip type, MIS structure Schottky cell type and the like. The metal substrate plays a role as a back electrode.

When the photoelectric conversion layer is of a pin type (or nip type), the thickness of each layer may be 5 to 50 nm for the p layer, 300 to 30000 nm for the i layer, and 5 to 50 nm for the n layer. preferable.

In the case of a solar cell, a transparent conductive material made of a material such as SnO ₂ , ITO, or ZnO is provided between the back electrode and the photoelectric conversion layer of the silicon film in order to improve the photoelectric conversion efficiency, particularly the short-circuit current. Often a membrane is inserted. The refractive index of these materials is about 2 to 3, which is smaller than the refractive index of silicon (about 4), and can function as a light reflection layer on the back surface of the solar cell. Therefore, it is very useful for improving the photoelectric conversion efficiency of the solar cell.

In this case, since the conductive film is formed by laminating a silicon film having a predetermined orientation on the substrate, the conductive film also needs to have a high orientation on the substrate. Such a condition satisfies any of the materials for the conductive film specifically described above.

Therefore, in order to further improve the photoelectric conversion efficiency, when forming a transparent conductive film, (1) a conductive film is formed on a metal substrate by sputtering, electron beam evaporation, CV
It must be made of a material that can be epitaxially grown by a method such as the D method, and (2) the conductive film must be made of a material on which a polycrystalline silicon film can be epitaxially grown. The above-mentioned materials satisfy such conditions. The thickness of the transparent conductive film is generally from 10 to 1000 °. Further, a surface transparent conductive film is usually formed on the photoelectric conversion layer opposite to the metal substrate, and a surface current collecting electrode is formed thereon. The same material as the above-mentioned conductive film can be used for this surface transparent conductive film. The electrodes are made of, for example, a metal such as aluminum or silver. Its thickness is 1000-50
It is about 000Å.

[0032]

Embodiments of the present invention will be described below. Note that the method and conditions for forming the polycrystalline silicon film are not limited to the present embodiment, and can be appropriately set according to the materials, the desired orientation, and the like of the metal substrate and the transparent conductive film. <Formation of polycrystalline silicon film>

Example 1 A metal substrate was formed according to the method described in JP-A-63-255911 or JP-A-1-201447. That is, an aluminum plate (thickness: 50 mm) having a purity of 99.9% by weight or more is approximately 450
The sample was hot-rolled at 10 ° C. to 10 mm, then cold-rolled to about 0.3 mm, and further heat-treated (annealed) at about 500 ° C. The obtained metal substrate had a (100) plane surface and a rolling direction in the [001] direction, and had a biaxially oriented structure with a uniform crystal orientation. Note that such biaxial orientation is generally called a cube orientation.

The thus obtained gold having a thickness of about 0.3 mm
Undoped crystalline silicon on a metal substrate by plasma CVD
A film was formed to have a thickness of about 1 μm. Formation condition is SiH
_Four/ H _TwoFlow ratio 1/20, metal substrate temperature 200 ° C, power density 0.5W
/cm^TwoAnd the pressure was 0.3 Torr.

The crystalline silicon film obtained under the above conditions was a polycrystalline silicon film. The single crystal, which is a component of polycrystalline silicon, is made of aluminum (10%) so as to inherit the crystal orientation of the underlying aluminum metal substrate.
The (0) plane is parallel to the (100) plane of the crystalline silicon, and
It was confirmed by the X-ray pole figure method, which is a kind of X-ray diffraction method, that the layers were stacked so that the [001] direction of aluminum and the [001] direction of crystalline silicon were parallel.

The (100) plane of aluminum and the crystal silicon
Fig. 1 shows a schematic diagram of each atomic arrangement on the (100) plane.
(A) and (b). The difference between the interstitial distance in the [001] direction of aluminum and the interstitial distance in the [001] direction of crystalline silicon is only (3.84−4.05) /4.05×100=−5.19% and is generally known. This satisfies the condition that the difference in the interstitial distance is 15% or less, which is the condition that enables epitaxial growth.

The metal material that takes the cube orientation by rolling and heat treatment is not limited to aluminum, but applies to metals having a face-centered cubic lattice and the entire alloy system thereof. For example, US Pat. No. 5,741,377
The publication describes a method of obtaining a cube orientation in the case of nickel by performing rolling and heat treatment. The difference between the interstitial distance of nickel in the [100] direction and the interstitial distance of crystalline silicon in the [100] direction is (3.84-3.52) /
3.52 × 100 = + 9.09%. Therefore, it is possible to epitaxially grow polycrystalline silicon on a nickel plate. Therefore, the metal substrate and the method for manufacturing the same described in U.S. Pat. No. 5,741,377 can be used in the present invention.

Example 2 A metal substrate was formed according to the method described in Japanese Patent No. 2626845. That is, an aluminum plate having a purity of 99.9% by weight or more (having a thickness of 5
0 mm) was hot rolled to about 10 mm at about 450 ° C. and then cold rolled to about 0.3 mm. The obtained metal substrate had a surface of the (110) plane and a rolling direction in the [-112] direction, and had a biaxially oriented structure with a uniform crystal orientation. An undoped crystalline silicon film was formed on the thus obtained metal substrate having a thickness of about 0.3 mm under the same conditions as in Example 1.

The crystalline silicon film obtained under the above conditions was a polycrystalline silicon film. The single crystal body, which is a component of polycrystalline silicon, is made of aluminum (11) so as to inherit the crystal orientation of the underlying aluminum metal substrate.
The (0) plane is parallel to the (110) plane of crystalline silicon, and
Lamination was performed so that the [-110] direction of aluminum and the [001] direction of crystalline silicon were parallel.

(110) plane of aluminum, crystalline silicon
Fig. 2 shows a schematic diagram of each atomic arrangement on the (110) plane.
(A) and (b). The difference between the interstitial distance of aluminum in the [-110] direction and the interstitial distance of crystalline silicon in the [001] direction is only (5.43-5.72) /5.72×100=−5.07%. Also, the difference between the [001] interstitial distance of aluminum and the [1-10] interstitial distance of crystalline silicon is
(3.84−4.05) /4.05×100=−5.19%. In this orientation relationship, the difference in interstitial distance is 15%, which is a condition that enables generally known epitaxial growth.
The following conditions were satisfied.

Example 3 An iron-silicon alloy plate (thickness: 200 mm) containing about several percent by weight of silicon was hot-rolled to about 3 mm at about 900 ° C.
It was cold-rolled to 5 mm and heat-treated (annealed) at about 1200 ° C. The obtained metal substrate has a surface of (110) plane and [001]
Direction, and had a biaxially oriented structure with a uniform crystal orientation. Such biaxial orientation is called Goss orientation. On this iron-silicon alloy substrate having a thickness of about 0.5 mm, an undoped crystalline silicon film was formed under the same conditions as in Example 1.

The crystalline silicon film obtained under the above conditions was a polycrystalline silicon film. The single crystal, which is a component of the polycrystalline silicon, is a direction perpendicular to the surface of the iron-silicon alloy plate, that is, the (110) plane of the iron-silicon alloy, so as to inherit the crystal orientation of the underlying iron-silicon alloy. Laminated so that the (110) plane of the crystalline silicon is parallel and the rolling direction of the iron-silicon alloy plate, that is, the [001] direction of the iron-silicon alloy and the [001] direction of the crystalline silicon are parallel. Was.

FIGS. 3A and 3B are schematic diagrams showing the atomic arrangements of the (110) plane of the iron-silicon alloy and the (110) plane of crystalline silicon. Iron-silicon alloy [001]
The difference between the interstitial distance in the direction and the interstitial distance in the [001] direction of crystalline silicon is (5.43−5.74) /5.74×100=−5.40%
It's just The difference between the [1-10] interstitial distance of the iron-silicon alloy and the [1-10] interstitial distance of crystalline silicon is (3.84−4.06) /4.06×100=−5.42%. Not just. In this orientation relation, the condition that the difference in the interstitial distance is 15% or less, which is a generally known condition for enabling epitaxial growth, is satisfied.

[0044] The <Production of solar cell> [Comparative Example] sputtering on a metal substrate 41 made of aluminum random orientation and going on a thickness of about 1 mm, the SnO ₂ is about 6000Å thick as a transparent conductive film 42 Formed as follows. The formation conditions are pressure 0.005 Torr, O ₂ / Ar ratio 0.02
3. The metal substrate temperature was set to 200 ° C. On this metal substrate, n was formed by a plasma CVD method using a plasma excitation frequency of 81.56 MHz.
A type polycrystalline silicon film 43, an i-type polycrystalline silicon film 44, and a p-type polycrystalline silicon film 45 were formed in this order to form a photoelectric conversion layer.
Table 1 shows the forming conditions.

[0045]

[Table 1]

Next, ZnO was formed as a surface transparent conductive film 46 by sputtering so as to have a thickness of about 700 °. Further, an Al electrode is formed as a surface current collecting electrode 47 by an electron beam evaporation method so as to have a thickness of about 6000 mm.
A solar cell having the structure shown in FIG.

The current-voltage characteristics of the pin-type polycrystalline silicon solar cell obtained as described above under AM1.5 (100 mW / cm ² ) irradiation conditions were measured. As a result, the cell area is 1 cm ²
As a result, values of 0.448 V for open circuit, 18.23 mA / cm ^{2 for} short-circuit current, 0.54 for fill factor, and 4.41% for photoelectric conversion efficiency were obtained.

Example 4 FIG. 4 shows the same method and conditions as those of the comparative example on an aluminum metal substrate having a thickness of about 1 mm which was biaxially oriented so as to have the cube orientation shown in Example 1. A polycrystalline silicon solar cell having a structure was fabricated.

The SnO ₂ obtained under these conditions is polycrystalline, but the single crystal of SnO ₂ as a constituent element is oriented in a direction perpendicular to the surface of the aluminum plate so as to inherit the crystal orientation of aluminum as a base. That is, aluminum (10
0) plane and the (100) plane of SnO ₂ are parallel, and the rolling direction of the aluminum plate, ie, [001] of aluminum
The layers were stacked such that the direction was parallel to the [001] direction of SnO ₂ .

Further, the crystalline silicon film obtained under these conditions was a polycrystalline silicon film. The single crystal of crystalline silicon, which is a component of the polycrystalline silicon film, has the (100) plane of SnO _{2 and} the (100) plane of crystalline silicon parallel to inherit the crystal orientation of the underlying SnO ₂ , And SnO ₂
The layers were stacked such that the [001] direction and the [001] direction of the crystalline silicon were parallel.

(100) plane of aluminum, (100) plane of SnO ₂ ,
FIGS. 5A to 5C show schematic diagrams of the respective atomic arrangements on the (100) plane of crystalline silicon. Here, the atomic arrangement of SnO ₂ is represented by the atomic position of Sn.

The difference between the lattice spacing in the [001] direction of aluminum and the lattice spacing in the [001] direction of SnO ₂ is (3.80−4.0).
5) /4.05×100=−6.17%, which satisfies the condition that the difference in interstitial distance is 15% or less, which is a generally known condition for enabling epitaxial growth.

Since the lattice spacing in the [011] direction of silicon is 3.84 °, the difference from the lattice spacing in the [100] direction of SnO ₂ is (3.84−3.80) /3.80×100=+1.05. %, Which also satisfies the condition for enabling epitaxial growth.

The current-voltage characteristics of the pin-type polycrystalline silicon solar cell obtained as described above under AM1.5 (100 mW / cm ² ) irradiation conditions were measured, and the cell area was 1 cm ^2.
, An open-circuit voltage of 0.512 V, a short-circuit current of 20.84 mA / cm ² , a fill factor of 0.62, and a photoelectric conversion efficiency of 6.62% were obtained. The polycrystalline silicon solar cell of the present invention had higher characteristics than the polycrystalline silicon solar cell having the random orientation in the comparative example.

[0055]

According to the present invention, a polycrystalline silicon film having a low defect density at a crystal grain boundary can be formed by using a metal substrate subjected to a biaxial orientation treatment. When this polycrystalline silicon film is used as a photoelectric conversion layer, a high photoelectric conversion rate is exhibited, and since this film can be manufactured at low cost, the manufacturing cost of a solar cell can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing aluminum (10) in Example 1 of the present invention.
FIG. 2 is a schematic view of an atomic arrangement in a (0) plane and a (100) plane of crystalline silicon.

FIG. 2 is a graph showing aluminum (11) in Example 2 of the present invention.
FIG. 3 is a schematic view of an atomic arrangement in a (0) plane and a (110) plane of crystalline silicon.

FIG. 3 shows an iron-silicon alloy in Example 3 of the present invention.
FIG. 3 is a schematic view of an atomic arrangement in a (110) plane and a (110) plane of crystalline silicon.

FIG. 4 is a schematic view of an element structure of a solar cell in a comparative example and Example 4 of the present invention.

FIG. 5 shows (10) of aluminum in Example 4 of the present invention.
FIG. 2 is a schematic view of the atomic arrangement in the (0) plane, the (100) plane of SnO _{2, and} the (100) plane of crystalline silicon.

[Explanation of symbols]

 41 metal substrate 42 transparent conductive film 43 n-type polycrystalline silicon film 44 i-type polycrystalline silicon film 45 p-type polycrystalline silicon film 46 surface transparent conductive film 47 surface current collecting electrode

Claims (7)

[Claims] 1. A biaxially oriented metal substrate formed by rolling and a polycrystalline silicon film formed thereon by epitaxial growth or by applying energy to an amorphous silicon film or a microcrystalline silicon film. A substrate comprising a polycrystalline silicon film, wherein the polycrystalline silicon film is made of an individual single crystal having a crystal orientation that closely follows the orientation of the metal substrate. 2. The substrate according to claim 1, wherein a conductive film is provided between the metal substrate and the polycrystalline silicon film. 3. The method according to claim 1, wherein the metal substrate is aluminum, nickel,
3. The substrate according to claim 1, comprising a metal or an alloy selected from copper, silver, iron, chromium, and titanium, and having a crystal structure of a face-centered cubic lattice or a body-centered cubic lattice. 4. The metal substrate has a surface (100) plane and a rolling direction of [001] or a surface (110) plane and a rolling direction of [-].
It consists of a face-centered cubic lattice having a crystal orientation that is biaxially oriented in the 112] direction, or the surface is (110) plane and the rolling direction is
4. The substrate according to claim 1, comprising a body-centered cubic lattice having a crystal orientation biaxially oriented in the [001] direction. 5. A biaxially oriented metal substrate is obtained by rolling, and the orientation of the metal substrate is changed by an epitaxial growth method or by applying energy to an amorphous silicon film or a microcrystalline silicon film. A method for forming a substrate having a polycrystalline silicon film, comprising forming a polycrystalline silicon film composed of individual single crystals having a sharp crystal orientation. 6. The method according to claim 5, wherein after forming a conductive film on the metal substrate by an epitaxial growth method, a polycrystalline silicon film is formed on the conductive film. 7. A solar cell comprising the polycrystalline silicon film according to claim 2 as a photoelectric conversion layer and a metal substrate as an electrode.