JP2001053004A - Forming method of crystal silicon film and manufacturing method of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily form a crystal silicon film with a large crystal particle diameter on an inexpensive substrate by irradiating an amorphous silicon film where a silicon crystal particle is dispersed with an electromagnetic wave of a specific wavelength and by converting the amorphous silicon film to the crystal silicon film. SOLUTION: A silicon film is formed on a substrate 6. In the silicon film, an extremely small amount of silicon crystal particles 3 is dispersed in the region of amorphous silicon 4. Then, an electromagnetic wave 1 with wavelength of at least approximately 730 nm is applied to the silicon film, and the silicon film is crystallized again for forming the crystal silicon film, thus forming a crystal silicon film and hence increasing the temperature of the region of the amorphous silicon 4 near the crystal particle 3 by irradiating the electromagnetic wave 1, and hence crystallizing the region of the amorphous silicon 4 near the crystal particle 3 from the interface of the crystal particle 3 by thermal energy again. In this case of a recrystallization process, a small amount of the crystal particles 3 grow as a nucleus, and the region of the amorphous silicon 4 finally disappears.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a crystalline silicon film and a method for manufacturing a solar cell. More specifically, the present invention relates to a method for forming a crystalline silicon film that gives good photoelectric conversion efficiency when used in a solar cell.

[0002]

2. Description of the Related Art Conventionally, solar cells using silicon as a semiconductor material for forming a photoelectric conversion layer have been known. 2. Description of the Related Art There are known solar cells in which a pn junction is formed on a single-crystal or polycrystalline wafer, and in which a pin junction is formed by depositing an amorphous silicon film on a substrate. Among these solar cells, a solar cell using a single crystal or polycrystalline silicon wafer (hereinafter, referred to as a crystalline silicon wafer solar cell) is preferable from the viewpoint of converting light energy into electric energy. On the other hand, a solar cell in which an amorphous silicon film is deposited on an inexpensive substrate (hereinafter, referred to as an amorphous silicon film solar cell) is preferable from the viewpoint of increasing the area, reducing the process temperature, and reducing the cost.

However, the amorphous silicon film solar cell has a disadvantage that the photoelectric conversion efficiency is remarkably deteriorated from the early stage of production due to light irradiation. This defect is Stable
It has been found to occur due to a light-induced defect called the r-Wronski effect, but it has not been resolved despite years of intensive research. In addition, the optical absorption edge of amorphous silicon is about 1.7 eV.
The fact that near-infrared light cannot be used to convert electric energy is also a reason for the lower photoelectric conversion efficiency compared to crystalline silicon wafer solar cells. Therefore, in recent years, a solar cell having a crystalline silicon film deposited on a substrate for the purpose of obtaining a solar cell having a large area similar to that of an amorphous silicon film solar cell and a photoelectric conversion efficiency as high as that of a crystalline silicon wafer solar cell has been developed. A battery (hereinafter, referred to as a crystalline silicon film solar cell) is being studied.

[0004]

As compared with a polycrystalline silicon wafer, a crystalline silicon film contains many small crystal grains. Therefore, dangling bonds, impurities, and the like, which are considered to be localized at crystal grain boundaries, function as scatterers that hinder free carrier transport. Further, dangling bonds existing on the crystal grain surface and in the amorphous region function as recombination centers. Due to these actions, the collection efficiency of the photogenerated carriers is reduced. Therefore, in order to manufacture a highly efficient crystalline silicon film solar cell, it is important to increase the size of individual crystal grains. Hereinafter, the average size of the individual crystal grains contained in the film will be referred to as a crystal grain size.

The following methods are known as methods for producing a crystalline silicon film. (1) A method for thermally decomposing a silicon film production gas such as SiH ₄ or Si ₂ H ₆ under a low pressure on a high-temperature substrate surface to deposit a crystalline silicon film (LPCVD method). In this method, since the substrate temperature must be 600 ° C. or higher, an inexpensive substrate such as blue plate glass cannot be used, and it is difficult to reduce the cost. The crystal grain size obtained is about several hundred nm.

(2) Among the CVD methods, a method using high-frequency power (PECVD method), a method using microwaves (μ-wave PECVD method, ECRPECVD method), a method using ultraviolet light (photo CVD method), and a metal catalyst. In a method such as a method using applied heat (catalytic CVD method), a silicon film manufacturing gas such as SiH ₄ or Si ₂ H ₆ diluted with hydrogen or a rare gas by an externally applied energy is decomposed in a gas phase. Forming a crystalline silicon film by generating a precursor and depositing the precursor on a substrate.

In this method, the substrate temperature can be reduced to 550 ° C. or less, so that an inexpensive substrate such as blue plate glass can be used. However, the crystal grain size of the obtained crystalline silicon film is very small, about several tens of nm. Further, since the crystalline region and the amorphous region are mixed, the transport characteristics of free carriers of the obtained crystalline silicon film are very poor.

(3) Amorphous silicon is crystallized by irradiating a laser beam to the amorphous or polycrystalline silicon film deposited by the above method (1) or (2) and melting and recrystallizing instantaneously. A method of increasing the crystal grain size (laser annealing method). In this method, a crystalline silicon film having a large area can be generally obtained by scanning a linear pulsed laser beam generated by an excimer laser device in a substrate surface direction. However, stable melting and recrystallization using an excimer laser device is currently difficult, and the process cost is high. The obtained crystal grain size is about several μm in the film surface direction. However, since the energy of the laser beam reaches at most several tens of nm in the film thickness direction, recrystallization can be performed only in this range. Therefore, it is not suitable for a crystalline silicon film solar cell requiring a photoelectric conversion layer having a thickness of 1 to several microns.

(4) The amorphous film deposited by the above method (1) or (2) or a silicon film containing a mixture of crystal grains and amorphous components is heated together with the substrate to a temperature at which the amorphous film is not melted. A method of recrystallizing components (solid phase growth method). In this method, crystal nuclei are generated everywhere in the film in the amorphous region in the film, so that the crystal nucleus density becomes too high. Therefore, the crystal grain size of the obtained crystalline silicon film is about several hundred nm.

As a method similar to the above method, a method of heating after laminating an n-type silicon film and an i-type amorphous silicon film (T. Matsuyama, et al., Pr.
received of Mat. Res. Soc. Sy
mp. Proc. , 283 (1993) 727. )
A method of raising and lowering the temperature from 200 ° C. to 600 ° C. in steps of 100 ° C. from room temperature (R. Ruther, et a
l. , Thin Solid Films, 310 (19)
97) 67. ) Has been proposed, and a large crystal grain size of about several microns has been obtained. However, any of these methods is not practical because the crystallization processing time is very long, which is several hours.

(5) An amorphous silicon film deposited by the above method (1) or (2) and a catalytic metal layer such as Ni or Al are laminated and heated to recrystallize the amorphous silicon film. Method (metal element induced crystallization method). Compared with the above (4), this method can lower the recrystallization temperature to 550 ° C. However, since the catalytic metal is incorporated into the crystalline silicon film, the photoelectric conversion efficiency of the solar cell decreases. In addition, by patterning the catalyst metal layer in-plane and recrystallizing it in the lateral direction, the concentration of metal taken into the crystalline silicon film can be reduced. However, the recrystallization time is significantly longer than when a catalytic metal layer is laminated on the entire surface of the silicon film.

(6) A method of irradiating a lamp light to an amorphous silicon film deposited by the method (1) or (2) or the like and recrystallizing the film by using thermal energy generated as a result of light absorption of the film. (High-speed lamp annealing method). Unlike the above (4) solid phase growth method, this method uses light absorption of an amorphous silicon film as a heating principle. Therefore, only the amorphous silicon film can be heated without directly heating a transparent substrate that does not absorb lamp light or a metal substrate having high light reflectance. Therefore, an inexpensive substrate such as glass can be used. Further, the apparatus configuration is simple and low cost, and the process cost is lower than that of the laser annealing method (3). Further, the time required for recrystallization is as short as tens of seconds to several minutes.

A crystallization film forming technique utilizing this method is specifically disclosed in JP-A-6-140325. According to this publication, the amorphous carbon film inserted between the glass substrate and the silicon film is heated by utilizing the magnitude of the light absorption coefficient of the amorphous carbon film with respect to the lamp light, and the polycrystalline silicon film having a large crystal grain size is obtained. Is described. However, similar to the above method (4), in this method, since crystal nuclei occur everywhere in the amorphous silicon film, the crystal nucleus density becomes too high, and the crystal grain size of the obtained crystalline silicon film is about several hundred nm. And small. In view of the above problems, an object of the present invention is to provide a method for easily forming a crystalline silicon film having a large crystal grain size on an inexpensive substrate and a method for manufacturing a solar cell having high photoelectric conversion efficiency. It is in.

[0014]

Thus, according to the present invention, after forming an amorphous silicon film in which silicon crystal grains are dispersed on a substrate, the amorphous silicon film is formed on the substrate.
There is provided a method for forming a crystalline silicon film, which comprises converting an amorphous silicon film into a crystalline silicon film by irradiating an electromagnetic wave having a wavelength of 30 nm or more and growing a crystal with silicon crystal grains as nuclei. Further, according to the present invention, there is provided a method for manufacturing a solar cell comprising a first conductive type silicon film, a substantially intrinsic crystalline silicon film and a second conductive type silicon film on a substrate in this order. Further, there is provided a method for manufacturing a solar cell, comprising at least a crystalline silicon film formed by the above method.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, in the present invention, the following method is employed to increase the crystal grain size of a crystalline silicon film formed on a substrate. That is, first, the structure of a silicon film formed on a substrate is to use a structure in which fine silicon crystal grains are dispersed in an amorphous silicon region (in other words, a structure in which a plurality of crystal regions are mixed in an amorphous region). Is preferred. The average grain size is 1
It is preferably in the range of at least nm. Average particle size is 1n
When the diameter is smaller than m, the absorption coefficient of the fine crystal grains becomes smaller for light having a wavelength of 730 nm or more due to the size effect, which is not preferable.

The silicon film having a structure in which a plurality of crystal grains are mixed in the amorphous region as described above can be formed by, for example, a capacitively coupled parallel plate plasma CVD method. This CVD method includes SiH ₄ , Si ₂ H ₆ , SiH _x C
A gas for producing a silicon film, such as l _4-x (x = 0 to 3) or SiH _x F _4-x (x = 0 to 3), may be replaced with hydrogen, helium, argon, krypton, xenon, or the like, if necessary. A source gas diluted with a gas can be used. Also, by appropriately setting the film forming conditions (content ratio of silicon film production gas, reaction temperature, reaction chamber pressure, RF frequency, RF power density, etc.), the crystal grain size of silicon crystal grains, the amorphous region and the It is possible to change the volume ratio with the grains.

The silicon film is not only an i-type, but also a p-type and an n-type.
It may have a conductive type. When the silicon film is n-type, the source gas containing O, N, P, As, etc. as such or in the form of a compound is p-type.
A gas containing Al or the like as it is or in the form of a compound may be used together with the above raw materials.

Next, the silicon film is recrystallized by irradiating the silicon film with an electromagnetic wave having a wavelength of 730 nm or more to form a crystalline silicon film. The wavelength of the electromagnetic wave is more preferably in the range of 730 to 1130 nm. As a source of the electromagnetic wave, for example, a halogen lamp, an infrared lamp, or the like is used. It is preferable that the silicon film be irradiated with the electromagnetic wave through a filter having a transmittance of a wavelength of 730 nm or less that is almost 0%. The intensity spectrum of the electromagnetic wave is as shown in FIG. 2 (a), but by passing through a filter, it can be processed into an optimum spectrum as shown in FIG. 2 (b).

Further, when impurities such as oxygen, water, and carbon monoxide are present in the gas phase atmosphere in which the recrystallization treatment is performed, the impurities are mixed into the silicon film from the surface and chemically bonded at the crystal interface. Such impurities cause a reduction in free carrier transport characteristics of the crystalline silicon film. Therefore, in order to minimize the contamination of impurities, irradiation is not performed on silicon such as a high vacuum atmosphere (for example, 1 Torr or less) and rare gases such as hydrogen, nitrogen, helium, argon, krypton, and xenon. It is preferable to perform the reaction in an atmosphere of an active gas.

The silicon film may be irradiated with electromagnetic waves continuously, but the irradiation intensity may be changed with time in order to more easily maintain the temperature difference between the crystal grains and the amorphous region. Specifically, for example, there is a method of increasing or decreasing the irradiation intensity, or changing the irradiation intensity periodically or aperiodically.

That is, when the substrate is made of a material having a poor thermal conductivity such as glass, the speed at which heat generated in the amorphous region by electromagnetic wave irradiation or heat flowing in from the crystal grains flows to the substrate is reduced. . Therefore, the temperature of the amorphous region may rise to a temperature higher than the recrystallization temperature, and a new crystal nucleus may be generated in the amorphous region. If the electromagnetic wave intensity is reduced to prevent this, the temperature difference from the crystal grains is reduced, and the crystal growth rate is also reduced.
In addition, by optimizing the irradiation wavelength range of electromagnetic waves,
Although the generation of new crystal nuclei can be prevented, there is a disadvantage that, for optimization, the labor for replacing filters and examining the conditions is increased. In addition, to minimize power consumption for generating electromagnetic waves and reduce costs,
It is better to make the irradiation wavelength range as wide as possible. Therefore, the recrystallization conditions can be optimized by changing the irradiation intensity with time.

The silicon film before recrystallization has a structure in which a plurality of crystal grains are mixed in the above-described amorphous region, and then is recrystallized by irradiating an electromagnetic wave having a wavelength of 730 nm or more for the following reasons. Because.
First, as shown in FIG. 3, crystalline silicon and amorphous silicon have different electromagnetic wave absorption coefficients. Where 730
A wavelength of nm corresponds to an energy of 1.7 eV. 1.
The absorption coefficient for electromagnetic waves with energy higher than 7 eV is
Amorphous silicon is higher, and conversely, crystalline silicon has a higher absorption coefficient for electromagnetic waves of energy lower than 1.7 eV.

Therefore, when a film in which a plurality of crystal grains are mixed in the amorphous region is irradiated with an electromagnetic wave having an energy lower than 1.7 eV (electromagnetic wave having a wavelength of 730 nm or more), the crystal grains are slightly smaller than the surrounding amorphous region. High temperature. Since the crystal grains and the amorphous region are in close contact with each other, a heat flow is generated from the crystal particles to the amorphous region, and the temperature of the amorphous region near the crystal grains increases.

Therefore, most of the amorphous region can be kept at a temperature lower than the recrystallization temperature and the temperature of the crystal grains can be kept at a temperature higher than the recrystallization temperature of the amorphous silicon.
The amorphous region near the crystal grain is recrystallized from the crystal grain interface by thermal energy. The recrystallization process at this time grows with fine crystal grains dispersed before the electromagnetic wave irradiation as nuclei. In addition, since most of the amorphous regions are lower than the recrystallization temperature, no new crystal nuclei are generated in the amorphous regions.

Therefore, the crystal growth proceeds with only the fine crystal grains dispersed before the electromagnetic wave irradiation as nuclei, and finally, the amorphous region disappears and the crystalline silicon film composed of the crystal grains having a large diameter. Is obtained. In addition, heat is generated between the silicon film and the substrate when the electromagnetic wave is irradiated. When only the electromagnetic wave irradiation on the silicon film is the source of thermal energy and the irradiated electromagnetic wave is not absorbed by the substrate, only the silicon film is heated first, as in the high-speed lamp annealing method, and the heat flow from the silicon film to the substrate is reduced. Occurs. Since this heat flow plays a role in releasing a small amount of heat generated in the amorphous region to the substrate, it is possible to prevent the temperature of the amorphous region from rising above the recrystallization temperature of amorphous silicon. However, this heat flow also plays a role of flowing heat energy necessary for recrystallization of amorphous silicon near crystal grains to the substrate. Therefore, the desired recrystallization may not proceed. Therefore, in order to optimize the recrystallization conditions, as shown in FIG. 1, a heat source such as a heater 7 is installed at a position opposite to the electromagnetic wave irradiation side with the substrate 6 interposed therebetween, and the substrate is assisted at the time of electromagnetic wave irradiation. It may be heated.

The above method for forming a crystalline silicon film can be used for forming a photoelectric conversion layer of a silicon film solar cell. Silicon film The silicon film of a solar cell is usually a p-i-
an n-junction, and the film is a silicon film of a first conductivity type.
An i-type silicon film—a second conductivity type silicon film. Here, the first conductivity type means p or n-type, and the second conductivity type means n-type when the first conductivity type is p-type, and p-type when it is n-type. Specifically, the silicon film of the silicon film solar cell has a configuration in which a pin layer or an nip layer is formed in this order. Here, the i-layer is a substantially intrinsic semiconductor layer and functions as a photoelectric conversion layer, and the method for forming a silicon film can be suitably applied to the formation of the i-layer.

When an i-layer of a solar cell is formed by using the method for forming a crystalline silicon film of the present invention, a p-i (or n / i) layer is deposited and then recrystallized (irradiation of electromagnetic waves). ), And then depositing an n (or p) layer.

Here, when the recrystallization treatment is performed after all the three layers are deposited, both the n-type dopant and the p-type dopant diffuse into the i-layer due to the thermal energy due to the recrystallization, and the junction characteristics are deteriorated. Therefore, the photoelectric conversion efficiency of the solar cell may be reduced. However, when the recrystallization treatment is performed after the two-layer deposition, the dopant diffusing into the i-layer is n
(Or p) type only, and the concentration can be made low enough not to adversely affect the photoelectric conversion efficiency. If the third p (or n) layer is formed at a low temperature by, for example, a capacitively coupled parallel plate plasma CVD method, diffusion of the p (or n) dopant into the i-layer is minimized. Can be minimized.

FIG. 4 shows a specific structure of a solar cell in which the method of the present invention can be used. The solar cell of FIG.
A transparent conductive film 1 is placed on a substrate 10 such as a transparent glass substrate.
1, a p-type silicon film (p-layer) 12, an i-type crystalline silicon film (i-layer) 13, an n-type silicon film (n-layer) 14, a transparent conductive film 15, and an electrode 16 are laminated in this order. are doing. This solar cell can be manufactured as follows.

(Step A) The transparent conductive film 11 is formed on the substrate 10. (Step B) p-type silicon film 12 on the transparent conductive film 11
To form (Step C) On the p-type silicon film 12, an i-type silicon film in which fine silicon crystal grains are dispersed in an amorphous silicon phase is formed. (Step D) The crystalline silicon film 13 is irradiated by irradiating the i-type silicon film with an electromagnetic wave containing only a long wavelength component of 730 nm or more.
To form (Step E) An n-type silicon film 14 is formed on the crystalline silicon film 13. (Step F) A transparent conductive film 15 is formed on the n-type silicon film 14.
And the electrodes 16 are formed in this order.

The transparent conductive film deposited on the substrate in step A may be made of a material such as ITO, ZnO, SnO ₂ or the like. As a method for depositing the transparent conductive film, for example, a thermal CVD method, a sputtering method, an evaporation method, and the like can be given. The thickness of the transparent conductive film is suitably about 1 μm.

The surface of the transparent conductive film is 100 to 1000
It is desirable to have irregularities of about Å height. This is because light incident on the solar cell formed on such an uneven surface obliquely enters the silicon layer by passing through the uneven interface. For this reason, the optical path length becomes longer, and the light absorptivity of the i-type silicon layer serving as the photoelectric conversion layer is improved.
As a result, the short-circuit current value can be improved.

As a method for forming a p-type or n-type silicon film in the steps B and E, for example, a sputtering method, an RFPECVD method and the like can be mentioned. For example, RFP
Source gases for forming a silicon film using the ECVD method are SiH ₄ , Si ₂ H ₆ , and SiH _x Cl _4-x (x = 0 to 0).
3) A gas for producing a silicon film such as SiH _x F _4-x (x = 0 to 3) is optionally replaced with H ₂ , He, Ar, Kr, or Xe.
A gas diluted with such a gas can be used. Further, by optimizing the forming conditions such as temperature, pressure, high-frequency power, and source gas mixture ratio during the formation, the silicon film can be made into an amorphous phase or a crystalline / amorphous mixed phase.

When the p-type or n-type silicon film is n-type, a gas containing O, N, P, As, etc. as such or as a compound is used. The containing gas is used together with the raw material gas. The p and n layers may have any of an amorphous phase, a mixed phase of crystal and amorphous, and a crystalline phase. Further, the p and n layers may be silicon alloy layers such as SiC and SiGe. Such an alloy layer
It can be formed by mixing a gas such as CH ₄ , GeH ₄ or GeF _{4 with the} above-mentioned source gas. Step C
Can be formed as described in the method for forming a crystalline silicon film.

In the step D, for example, an apparatus having a configuration as shown in FIG. 1 is used. In FIG. 1, 1 indicates an electromagnetic wave, 2 indicates a filter, 3 indicates silicon crystal grains, 4 indicates an amorphous phase, 5 indicates an electrode, 6 indicates a substrate, and 7 indicates a heater. Irradiation conditions can be performed as described in the method for forming a crystalline silicon film. In FIG. 1, at the same time as the irradiation, the substrate is supplementarily heated by a heater installed at a position facing the filter with the substrate interposed therebetween.

As a material for forming the back electrode in the step F, aluminum, silver and the like can be mentioned. These materials are preferable because the reflectivity of light is high and the short-circuit current value can be improved by reflecting incident light reaching the back electrode from the silicon layer and re-entering the photoelectric conversion layer. In FIG. 4, a transparent conductive film made of ITO, ZnO, SnO ₂ or the like is laminated between the silicon layer and the back electrode. This transparent conductive film need not be formed. However, by forming this transparent conductive film, the reflectance of the back electrode of the laminated structure can be increased.
The short-circuit current value can be further improved. In addition, as a method for forming a metal film, a vapor deposition method / sputter method is used, and as a method for forming a transparent conductive film, a thermal CVD method / sputter method / vapor deposition method is used.

[0037]

EXAMPLES The method for manufacturing a crystalline silicon film solar cell according to the present invention will now be described in detail with reference to examples.

(Example 1) First, a transparent conductive film made of ZnO was formed on a substrate made of a transparent glass plate by sputtering. The thickness of the transparent conductive film was 1 μm, and the height of the surface irregularities was Rmax = 30 nm. Next, an n-type amorphous silicon film was formed on the transparent conductive film using an RFPECVD method. The film forming conditions were as follows: substrate temperature = 300 ° C., reaction chamber pressure = 1 Torr, SiH ₄ = 100 sccm, H ₂
= 200 sccm, PH ₃ (1000 based on H ₂₎
ppm) = 10 sccm, RF frequency =
13.56 MHz, RF power density = 0.2 W / c
m ² and the deposited film thickness were 250 °.

Next, an i-type silicon film was formed by using the RFPECVD method. The film formation conditions were as follows: substrate temperature = 300
° C, reaction chamber pressure = 0.2 Torr, SiH ₄ = 50 sc
cm, H ₂ = 200 sccm, RF frequency = 13.56
MHz, RF power density = 25 mW / cm ² , and deposited film thickness = 1 μm. The i-type silicon film obtained under these conditions had a structure in which fine crystal grains were dispersed in an amorphous phase. The average crystal grain size of the crystal grains = 10n
The volume fraction of crystal grains in the m, i-type silicon film was 10%.

Next, as shown in FIG. 1, the i-type silicon film was irradiated with an electromagnetic wave through a filter to form a crystalline silicon film. The source of electromagnetic waves was a halogen lamp, and the lamp was repeatedly turned on and off every 10 seconds. The filter has a transmittance of 0 to 730 nm or less for electromagnetic waves.
%, Average transmittance of electromagnetic waves at a wavelength of 730 nm or more 70%
Was used. Note that a heater was installed at a position facing the electromagnetic wave incident side with the substrate interposed therebetween, and the substrate was heated supplementarily. The irradiation step was performed under a nitrogen atmosphere at atmospheric pressure. The conditions were as follows: maximum value of electromagnetic wave irradiation intensity = 40 W / cm ² , substrate temperature = 350 ° C., nitrogen flow rate 100 L / min.

As a result, the average crystal grain in the crystalline silicon film
The diameter = 2 μm and the crystal volume fraction = 100%. next,
P-type amorphous silicon film using RFPECVD
Was formed. The formation conditions were as follows: substrate temperature = 230 ° C, reaction chamber
Pressure = 0.5 Torr, SiH_Four= 20sccm, H_Two=
200sccm, B_TwoH₆(Also diluted to 1000ppm
) = 2 sccm, RF frequency = 13.56 MHz, R
F power density = 30 mW / cm ^Two, And film thickness = 200Å
Was. Next, a transparent conductive material made of ZnO was formed by sputtering.
The film was formed on a p-type amorphous silicon film. Transparent
The thickness of the electrolytic film was set to 30 nm. Finally, use the sputtering method
Then, an Ag film was formed on the transparent conductive film. Ag film thickness
= 500 nm. According to the above steps, the solar cell of Example 1
Pond could be manufactured.

Comparative Example 1 First, a transparent conductive film made of ZnO was formed on a substrate made of a transparent glass plate by using a sputtering method. The thickness of the transparent conductive film was 1 μm, and the height of the surface irregularities was Rmax = 30 nm. Next, an n-type amorphous silicon film was formed on the transparent conductive film using an RFPECVD method. The film forming conditions were as follows: substrate temperature = 300 ° C., reaction chamber pressure = 1 Torr, SiH ₄ = 100 sccm, H ₂
= 200 sccm, PH ₃ (1000 based on H ₂₎
ppm) = 10 sccm, RF frequency =
13.56 MHz, RF power density = 0.2 W / c
m ² and the deposited film thickness were 250 °.

Next, an i-type silicon film was formed by RFPECVD. The film formation conditions were as follows: substrate temperature = 300
° C, reaction chamber pressure = 0.2 Torr, SiH ₄ = 20 sc
cm, H ₂ = 200 sccm, RF frequency = 13.56
MHz, RF power density = 50 mW / cm ² , and deposited film thickness = 1 μm. The i-type silicon film obtained under these conditions had a structure in which fine crystal grains were dispersed in an amorphous phase. The average crystal grain size of the crystal grains = 200 n
The volume fraction of crystal grains in the m, i-type silicon film was 80%.

Next, a p-type amorphous silicon is formed by using the RFPECVD method.
A rufus silicon film was formed. Formation conditions are substrate temperature
= 230 ° C., reaction chamber pressure = 0.5 Torr, SiH_Four=
20sccm, H_Two= 200sccm, B_TwoH₆(100
Diluted to 0 ppm) = 2 sccm, RF frequency =
13.56 MHz, RF power density = 30 mW / c
m ^Two, And film thickness = 200 °. Next, using the sputtering method
Transparent conductive film made of ZnO by p-type amorphous silicon
Formed on the film. The thickness of the transparent conductive film = 30 nm
Was.

Finally, an Ag film was formed on the transparent conductive film by using a sputtering method. The thickness of the Ag film was set to 500 nm. The solar cell of Comparative Example 1 was able to be manufactured by the above steps. With respect to the solar cells manufactured by the methods of Example 1 and Comparative Example 1, current-voltage characteristics under light irradiation were measured. The measurement conditions were irradiation light AM1.5 (100 m
W / cm ² ) and the measurement temperature was 25 ° C. Table 1 shows the measurement results.

[0046]

[Table 1]

Table 1 shows that the solar cell of Example 1 is superior to the solar cell of Comparative Example 1 in all of the open-circuit voltage, short-circuit current density, fill factor, and conversion efficiency.

[0048]

As described above, according to the present invention, a crystalline silicon film made of a crystal having a large average grain size can be formed. In addition, when a crystalline silicon film is used for a photoelectric conversion layer of a solar cell, a crystalline silicon film solar cell with high photoelectric conversion efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a method for forming a crystalline silicon film according to the present invention.

FIG. 2 is a diagram illustrating wavelength dispersion of electromagnetic wave intensity used in the first embodiment of the present invention.

FIG. 3 is a diagram showing energy dependence of absorption coefficients of amorphous silicon and crystalline silicon.

FIG. 4 is a conceptual diagram showing an example of a solar cell manufactured by the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electromagnetic wave 2 Filter 3 Silicon crystal grain 4 Amorphous silicon 5, 16 Electrode 6, 10 Substrate 7 Heater 11, 15 Transparent conductive film 12 p-type silicon film 13 i-type crystalline silicon film 14 n-type silicon film

Continued on the front page F term (reference) 5F051 AA03 AA05 CA15 CA32 CB01 CB24 CB29 DA04 GA03 5F052 AA13 AA24 CA04 DA01 DB03 JA09

Claims (5)

[Claims] An amorphous silicon film in which silicon crystal grains are dispersed is formed on a substrate, and the amorphous silicon film is irradiated with an electromagnetic wave having a wavelength of 730 nm or more to grow a crystal with the silicon crystal grains as nuclei. A method for forming a crystalline silicon film, comprising converting an amorphous silicon film to a crystalline silicon film. 2. The method according to claim 1, wherein the electromagnetic wave has a wavelength of 730 to 1130 nm. 3. The method according to claim 1, wherein the substrate is irradiated with an electromagnetic wave in a vacuum or in a gas atmosphere inert to silicon while heating the substrate. 4. The method according to claim 1, wherein the electromagnetic wave is irradiated while increasing or weakening the intensity with time or changing the intensity periodically or aperiodically so that the growth of the crystal centered on the silicon crystal grains proceeds. Item 4. The forming method according to any one of Items 1 to 3. 5. A silicon film of a first conductivity type on a substrate,
A method for manufacturing a solar cell comprising an intrinsic crystalline silicon film and a second conductive type silicon film in this order, wherein at least the crystalline silicon film is formed by the method according to any one of claims 1 to 4. A method for manufacturing a solar cell, characterized by being formed.