JP3067459B2 - Method for manufacturing thin-film polycrystalline Si solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solar cell, and more particularly to a thin film polycrystalline S having a good energy conversion efficiency.
i. A method for manufacturing a solar cell.

[0002]

2. Description of the Related Art In various devices, a solar cell is used as a driving energy source.

[0003] A solar cell uses a pn junction for a functional part, and a semiconductor composing the pn junction is generally Si.
Is used. It is preferable to use single crystal Si from the viewpoint of the efficiency of converting light energy into electric power, but from the viewpoint of increasing the area and reducing the cost, use amorphous.
Si is considered advantageous. In recent years, studies have been made to use polycrystalline Si for the purpose of obtaining low cost comparable to amorphous Si and high energy conversion efficiency comparable to single crystal Si. However, in the conventionally proposed method, a lump-shaped polycrystal is sliced into a plate-like body, and it is difficult to reduce the thickness to 0.3 mm or less because of using this.
Therefore, the thickness is greater than the thickness required to sufficiently absorb the light quantity, and in this regard, the effective use of the material is not sufficient.
That is, it is necessary to reduce the thickness sufficiently in order to reduce the cost.

Attempts have been made to form a thin film of polycrystalline Si using a thin film forming technique such as chemical vapor deposition (CVD). However, the crystal grain size is only several hundredths of a micron at most. Also, the energy conversion efficiency is lower than that of the bulk polycrystalline Si slice method. Attempts have been made to increase the crystal grain size by irradiating a polycrystalline Si thin film with a laser beam and melting and recrystallizing the film, but cost reduction is not sufficient and stable production is difficult.

[0005] Such a situation is a common problem not only in Si but also in compound semiconductors.

Therefore, there has been proposed a method of forming a crystalline Si film having a thickness sufficient to absorb sunlight on a low-cost substrate by using a liquid phase method (exit, Hamamoto, Itagaki, Ishihara, Morikawa, Sasaki, Sato, Namisaki; Proceedings of the 51st Autumn Meeting of the Japan Society of Applied Physics 29a-G-2p6
95).

[0007]

In the above-mentioned method, an SiO ₂ film is provided on the surface of a low-cost substrate in order to prevent impurities contained in the substrate from being taken into the growing Si crystal. At this time, in the liquid phase method using Sn as a solvent, S
Since n has poor wettability, Si cannot be grown directly on SiO ₂ . For this reason, Si, which is a growth
Although a layer is required on SiO ₂ , if the Si layer is thin, agglomeration occurs and a uniform film cannot be obtained, and if the Si layer is thick, independent crystal grains grow and irregularities become severe. The surface properties deteriorate. This is because the liquid phase method grows under quasi-thermal equilibrium, and the anisotropy of the growth rate depends on the crystal plane orientation, which becomes more pronounced as the crystal grain size of the Si layer becomes smaller. Therefore, in the above-described method, the Si layer is heated by a lamp and melted and recrystallized to increase the particle size. As a result, there is a problem that the selection of the substrate is restricted.

The present invention solves the above-mentioned problems of the prior art and provides a method of manufacturing a polycrystalline Si solar cell having a large grain size and high quality.

An object of the present invention is to provide an inexpensive solar cell by growing a large grain polycrystalline semiconductor layer on a metal substrate which is a low cost substrate.

[0010] Another object of the present invention is to provide a method in which fine Si grains formed on a SiO ₂ layer are used as seed crystals and a large grain size S
It is an object of the present invention to provide a high-quality solar cell by forming an i-crystal layer to eliminate impurities from a substrate.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and has been completed as a result of intensive studies by the present inventor to achieve the above object. The present invention relates to a method for manufacturing a thin polycrystalline solar cell.

That is, in the method for manufacturing a solar cell according to the present invention, in the method for manufacturing a polycrystalline Si solar cell, 1) a step of depositing an insulating layer on a metal substrate, and 2) an amorphous layer on the surface of the insulating layer. Depositing a Si layer, 3) heating the amorphous Si layer in an inert gas atmosphere and performing solid phase growth to form a crystalline Si layer, 4) heating in an active gas atmosphere, Aggregating the Si layer to form Si crystal grains on the insulating layer; 5) performing crystal growth using the Si crystal grains as a seed crystal by a liquid phase method; and 6) heating in an active gas atmosphere. Promoting a solid phase reaction between the Si crystal grains and the insulating layer to bring the surface of the metal substrate into contact with the bottom surface of the Si crystal grains; and 7) further crystallizing the Si crystal grains by a liquid phase method. Growing and covering the insulating layer surface with a Si layer. It is a manufacturing method of a thin film polycrystalline Si solar cell to fine.

[0013]

Principle techniques [action and example embodiment of the present invention, as shown for example in FIG. 1, (a), CVD method or the like on the insulation green layer of SiO ₂ deposited in (b) a metal substrate (C) annealing in an inert atmosphere such as nitrogen to cause solid phase growth to change the amorphous Si layer into a crystalline Si layer, followed by annealing in a hydrogen atmosphere Aggregate the crystalline Si layer with to form fine Si grains on the substrate,
(D) A polycrystalline Si thin film layer having a large grain size is formed by liquid phase growth using the Si grains as seed crystals.

(E) At the time of liquid phase growth, annealing is carried out in a hydrogen atmosphere when Si crystal grains have been grown to some extent.
A solid phase reaction is caused between the crystal and the SiO ₂ layer to bring the surface of the metal substrate into contact with the bottom surface of the Si crystal grain. Thereby, conduction between the Si crystal and the substrate is achieved. (F) Then, the Si crystal grains are further grown, and finally a continuous film can be obtained.

The present inventor has conducted a number of experiments to find that a Si crystal can be grown by a liquid phase growth method using fine Si grains obtained by aggregating a Si layer deposited on an SiO ₂ film as a seed crystal. I found

Further, the present inventor has further conducted experiments to introduce impurities into the Si layer to be aggregated in advance,
It has been found that by annealing in an inert atmosphere and expanding the particle size, the orientation of the Si crystal grown using the agglomerated Si particles as a seed crystal can be controlled.

According to another experiment, the present inventor used fine Si grains obtained by annealing an amorphous Si layer in an inert atmosphere and aggregating a crystalline Si layer grown in a solid phase. It has been found that the orientation controllability of the grown Si crystal is greatly improved as compared with the case where the impurity is introduced.

Further, the present inventor further conducted an experiment. When the agglomerated Si grains were grown to some extent by liquid phase growth, the growth was suspended once, and the Si grains and the SiO ₂ layer were annealed by annealing in a hydrogen atmosphere. Between the solid phase reaction,
It has been found that by bringing the surface of the metal substrate into contact with the bottom surface of the Si crystal grains, conduction between the Si crystal and the substrate can be achieved, and further growth is continued to obtain a continuous thin film of large grain polycrystalline Si. Thus, the present invention has been completed.

Hereinafter, the experiments performed by the present inventors will be described in detail.

(Experiment 1) Aggregation of Si Layer As shown in FIG. 2, an SiO ₂ layer as an insulating layer 202 is formed on a surface of a 0.8 mm thick Mo substrate 201 by ordinary normal pressure CVD.
The SiH ₄ was thermally decomposed at 630 ° C. by an ordinary LPCVD apparatus to deposit a 0.1 μm thick Si layer 203 (FIG. 2B). .
When the Si layer at this time was examined by X-ray diffraction, it was found to be polycrystalline Si having a crystal grain size of about 8 nm. For such a Si layer on a metal substrate, (1) as it is, (2)
P obtained by implanting P at an acceleration voltage of 50 kV and a dose of 8 × 10 ¹⁵ / cm ² by ion implantation, and (3) similarly obtained by implanting P and then annealing at 1000 ° C. for 3 hours in an N ₂ atmosphere. Available in different types. When the change in crystal grain size was measured by a transmission electron microscope,
The one immediately after ion implantation was amorphized, but the one annealed after ion implantation had a maximum crystal grain size of about 3
It expanded to μm.

Further, in the above, the impurity diffusion is performed by depositing phosphorus glass instead of ion implantation, and annealing is performed at 1000 ° C. for 3 hours in an N ₂ atmosphere after removing the phosphorus glass to similarly increase the crystal grain size. I was able to.

Next, these three types of substrates were placed in a hydrogen atmosphere for 1 hour.
After annealing at 050 ° C. for 5 minutes, the state of the surface was observed with an optical microscope and a scanning electron microscope.
Small 1.5 μm Si grains 204 were formed on the SiO ₂ layer (FIG. 2C). At this time, the density of the Si grains was approximately 1 to 3 × 10 ⁷ particles / cm ² .

(Experiment 2) Si crystal growth by liquid phase growth method Using the small Si grains on the metal substrate obtained in Experiment 1 as a seed crystal, an attempt was made to grow a Si crystal by the liquid phase growth method. Of the above three types of substrates, those not ion-implanted and those only ion-implanted are immersed in a Sn solvent saturated with n-type Si having a specific resistance of 2Ω · cm at 953 ° C. Growth start temperature 950 ℃, degree of supercooling 3
The temperature was gradually cooled at a rate of 0.5 ° C./min. In the same manner, the material which had been annealed in an N ₂ atmosphere after the ion implantation was gradually cooled at a growth start temperature of 940 ° C., a supercooling degree of 13 ° C., and a cooling rate of 0.5 ° C./min. The growth time was 15 minutes each.

After completion of the growth, the state of the surface was observed with an optical microscope and a scanning electron microscope. In each case, it was confirmed that the crystal had grown, and the Si crystal 205 having a particle size of several μm to several tens μm was obtained. Was obtained (FIG. 2D). However,
The density of the grown Si crystal is 2 × 10 ⁴ to 4 × 10 ⁵ / c
m ² , and it became clear that not all of the fine Si particles formed by aggregation grow crystals. Further, a large difference was observed in the form of Si crystals after growth, for those only implantation and ion shall not the ion implantation is was observed preference of the crystal orientation, the ion implantation was then N ₂ atmosphere Annealed in (11)
1) Many crystals whose planes were oriented in the direction perpendicular to the substrate surface were observed, and the coverage of the substrate surface with Si crystals was the highest.
At this time, the ratio of the crystal in which the (111) plane was oriented in a direction perpendicular to the substrate surface in all the crystals after growth was about 50%.

(Experiment 3) SiO_TwoSolid phase between layer and Si crystal
Reaction (111) plane obtained in Experiment 2 is perpendicular to the substrate surface
In a hydrogen atmosphere
Anneal at 1050 ° C. for 30 minutes, _TwoLayer-S
The solid-state reaction between i-crystals was promoted. Exactly the same process
High resolution scanning of the cross section of the substrate surface for another substrate that has passed
When observed with a scanning electron microscope, as shown in FIG.
The bottom of the i-crystal is SiO_TwoThrough the layer and the surface of the metal substrate
I was in contact. This allows conduction between the Si crystal and the metal substrate.
It turned out that communication was possible.

(Experiment 4) Aggregation and Crystal Growth of Solid Phase-Grown Si Layer In the same manner as in Experiment 1, aggregation of the crystal Si layer grown by solid phase and crystal growth by the liquid phase method were performed.

As in Experiment 1, an SiO ₂ layer was formed on the surface of a 0.8 mm thick Mo substrate 201 as an insulating layer 202 to a thickness of 0.1 μm by a normal atmospheric pressure CVD method.
SiH ₄ was thermally decomposed at 550 ° C. by a CVD apparatus to deposit an amorphous Si layer 203 having a thickness of 0.1 μm. Next, Si is accelerated to the amorphous Si layer by ion implantation at an accelerating voltage of 8.
The implantation was performed at 0 kV and a dose of 7.5 × 10 ¹⁴ / cm ² . Thereafter, annealing was performed in an N ₂ atmosphere at 600 ° C. for 50 hours, and the amorphous Si layer was crystallized by solid phase growth. When the change in crystal grain size was examined by a transmission electron microscope, the one immediately after ion implantation was completely amorphous, but the one after annealing showed dendritic crystal growth, and the 100% crystal Had been transformed. The crystal grain size was expanded up to about 5 μm. In addition, it was found from the diffraction image of the electron beam that such a resin-like crystal had almost the (111) plane oriented in a direction perpendicular to the substrate surface.

Next, the substrate is placed in a hydrogen atmosphere at 1050.
After annealing at 5 [deg.] C. for 5 minutes, the state of the surface was observed with an optical microscope and a scanning electron microscope. As a result, the Si layer was agglomerated on the substrate.
The i-grain 204 was formed on the SiO ₂ layer. At this time, the density of the Si grains was approximately 3 to 4 × 10 ⁷ / cm ² .

Using the obtained fine Si grains on the metal substrate as seed crystals, Si crystals were grown by a liquid phase growth method. Sn
Immerse in a solvent saturated with n-type Si having a specific resistance of 2 Ω · cm at 953 ° C., and start growing at a temperature of 950 ° C. and a degree of supercooling of 3
The crystal was grown by slowly cooling at a temperature of 0.5 ° C./min. The growth time was 15 minutes.

After completion of the growth, the state of the surface was observed with an optical microscope and a scanning electron microscope. In each case, it was confirmed that crystals had grown, and a Si crystal 205 having a particle size of several μm to several tens μm was obtained. Was obtained (FIG. 2D). The density of the grown Si crystal was 1.4 × 10 ⁵ / cm ² .
As for the form of the Si crystal after growth, a crystal in which the (111) plane is oriented in a direction perpendicular to the substrate surface is often observed, and the crystal in which the (111) plane is oriented in a direction perpendicular to the substrate surface in all the grown crystals. Was about 81%. As described above, the use of the amorphous Si solid-phase growth film greatly improves the controllability of the orientation of the grown crystal as compared with the case where the grain size is increased by implanting P as described in Experiment 1. Became clear.

(Experiment 5) Formation of Continuous Film Following Experiment 4, crystal growth was further performed by a liquid phase method.
Was. 1050 ° C. in a hydrogen atmosphere in the same manner as in Experiment 3.
Annealed for 30 minutes to achieve conduction between Si crystal and substrate
After that, the growth start temperature is 950 ° C, the degree of supercooling is 3 ° C, and the cooling rate is
The growth was performed at 0.5 ° C./min for a growth time of 80 minutes.
After the growth was completed, the substrate surface was examined with an optical microscope and the same as in Experiment 2.
When observed with a scanning electron microscope, the Si crystals
Are completely in contact with each other and have an average particle size of about 50μ.
m large-diameter Si crystal thin film (continuous film) must be obtained
Was confirmed. The height of the continuous film at this time is S
iO _TwoIt was about 40 μm from above the layer. Also, surface irregularities
The thickness of the film is determined when the particle size is increased by introducing P as described above.
± 60% of the case where the solid-phase grown film was used.
In this case, it was improved to ± 30%.

(Experiment 6) Formation of solar cell B was 20 keV and 1 × 10 ¹⁵ by ion implantation on the surface of the large grain Si crystal thin film on the Mo substrate obtained in Experiment 5.
/ Cm ² and annealed at 800 ° C. for 30 minutes to form ap ⁺ layer. The large-diameter Si crystal thin film / SiO ₂ / Mo solar cell fabricated in this manner was subjected to AM 1.5 (100 mW / cm ² ) light irradiation.
The measurement of the -V characteristic showed that the cell area was 0.1
Open voltage 0.54 V, short circuit current 27 mA / c at 6 cm ²
m ² and the fill factor were 0.73, and a conversion efficiency of 10.6% was obtained.

As described above, it has been shown that a large-diameter Si thin film can be formed on a metal substrate by using fine Si particles obtained by aggregation, whereby a solar cell having good characteristics can be formed.

As the metal substrate material used in the solar cell of the present invention, any metal which has good conductivity and preferably forms a compound such as silicide with Si is used. Examples thereof include Cr, Ni, and Ti, but of course other values are also possible. As the insulating layer, SiO ₂ is used because it causes a solid-phase reaction with Si, and its thickness is not particularly specified.
It is appropriate to set it in the range of 0.5 μm.

The method of depositing the amorphous Si layer may be any method such as LPCVD, plasma CVD, vapor deposition, sputtering and the like. The thickness of the amorphous Si layer is approximately 0.
A range of 01 to 0.5 μm is appropriate. Impurities may be introduced for the purpose of increasing the growth rate during crystallization of such an amorphous Si layer by solid-phase growth, and the method of introducing the impurities is to mix them in the raw material Si in advance. Or by ion implantation, and impurities such as P,
As, Sn, B, etc. are selected. The amount of impurities to be introduced is appropriately determined depending on the thickness of the amorphous Si layer and the conditions for the solid phase growth treatment, but is generally 5 × 10 ¹⁹ cm ⁻³ or more.

In the method of the present invention, the temperature for agglomeration of the crystallized Si layer in the active gas after the solid phase growth is preferably in the range of approximately 950 to 1100 ° C.
H ₂ is preferably used as the active gas.

The range of the growth temperature in the liquid phase growth method used in the method of the present invention depends on the type of the solvent.
It is desirable to control as follows. The degree of supercooling is preferably set to about 0 to several tens of degrees Celsius for the purpose of suppressing the melt back of the fine Si particles in the solvent, and after the solid-phase reaction between the grown Si crystal and the underlying SiO ₂ layer. In the case where the growth is performed subsequently, the temperature is preferably about 0 to several tens of degrees Celsius. It is preferable that the temperature decreasing rate is controlled in the range of 0.1 to 5 ° C./min.

The final grain size and film thickness of the Si crystal thin film obtained by the liquid phase growth method are 20 to 500, respectively, due to the requirements on the characteristics of the solar cell and the constraints of the process.
μm is appropriate, preferably 30 to 500 μm each.
m is desirable. P ⁺ or n ^{+ is} added to the surface of the obtained Si crystal.
The junction is formed by providing a layer, and its thickness is suitably in the range of 0.01 to 1 μm, preferably 0.1 to 0. 5 μm
It is desirable that

[0039]

Hereinafter, the formation of a desired solar cell by carrying out the method of the present invention will be described in more detail, but the present invention is not limited to these examples.

Example 1 As described above, Experiments 1 to 6
A large grain Si crystal solar cell on a metal substrate was produced in the same manner as in Example 1. 1A to 1G show a manufacturing process thereof.

The metal substrate 101 has a thickness of 0.8 mm of Mo.
A plate was used. After forming an SiO ₂ layer 102 thereon by a normal pressure CVD apparatus at 0.08 μm (FIG. 1A), Si ₂ H ₆ was thermally decomposed at 550 ° C. using an ordinary LPCVD apparatus to form a 0.1 μm layer. An amorphous Si layer 103 was deposited (FIG. 1B).

Next, the amorphous Si layer is annealed in an N ₂ atmosphere at 600 ° C. for 45 hours.
Solid phase growth was performed. The crystal grain size obtained at this time was up to about 4.5 μm. Subsequently, 1040 in an H ₂ atmosphere.
Annealing was performed at 8 ° C. for 8 minutes to aggregate the Si layer to obtain fine Si grains 104 on the SiO ₂ layer. At this time, the particle size of the Si particles was 0.4 to 1.2 μm, and the density was 3.7 × 10 ⁷ / cm ² (FIG. 1C).

Crystal growth was carried out under the following continuous conditions using Sn as a solvent by a liquid phase growth apparatus based on a conventional slide boat method, to obtain a continuous thin film 105 of large grain Si crystal (FIG. 1 (d)). ).

In a hydrogen atmosphere, a growth start temperature is 950 ° C., a degree of supercooling is 0.5 ° C., a temperature drop rate is 0.5 ° C./min, and a growth time is 10 minutes.
After a minute, the substrate is separated from the solvent, the temperature is raised to 1050 ° C., the temperature is maintained for 20 minutes in a hydrogen atmosphere, and the temperature is returned to 950 ° C. again, this time with a degree of supercooling of 3 ° C. and a cooling rate of 0.
The growth was performed at 5 ° C./min for a growth time of 80 minutes. The grain size and thickness of the Si crystal thin film thus obtained are both about 50.
μm (FIGS. 1 (e) and 1 (f)).

B was implanted on the surface of the Si layer by ion implantation under the conditions of ²⁰ keV and 1 × 10 ¹⁵ / cm ^2.
Annealing was performed at 00 ° C. for 30 minutes to form ap ⁺ layer 107. Finally, a current-collecting electrode (Ti / Pd / Ag (0.04 μm /) was deposited by EB (E1 electron Beam) evaporation.
0.02 μm / 1 μm) 108 / ITO transparent conductive film 10
6 was formed on the p ⁺ layer (FIG. 1 (g)).

[0046] This way, a large grain size Si crystal solar cell obtained, AM1.5 (100mW / cm ²⁾ was measured for the I-V characteristic under light irradiation, open in cell area 0.25 cm ² Voltage 0.55V, short-circuit photocurrent 2
9 mA / cm ² and a fill factor of 0.74 were obtained, and an energy conversion efficiency of 11.8% was obtained.

As described above, a solar cell exhibiting good characteristics was manufactured using the large grain Si crystal layer grown on the metal substrate.

(Example 2) p ⁺ μ
A c-Si / polycrystalline Si heterojunction solar cell was produced. The metal substrate with Cr, an SiO ₂ layer was 0.12μm deposited by atmospheric pressure CVD method thereon, further LP thereon
An amorphous Si layer was deposited to a thickness of 0.1 μm by decomposition of Si ₂ H ₆ at 550 ° C. by a CVD method. At this time, a slight amount of PH ₃ is previously mixed into Si ₂ H ₆ gas (PH ₃ / Si ₂ H ₆ = 2.0
× 10 ^-3 ), P was introduced into the amorphous Si layer. Anneal at 600 ° C for 40 hours in Ar atmosphere to perform solid phase growth,
The amorphous Si layer was crystallized.

Subsequently, in an H ₂ atmosphere at 1030 ° C., 20
The annealing treatment was performed under the conditions of minutes, and the Si layer was aggregated to obtain fine Si particles on the SiO ₂ layer. At this time, the grain size of the Si grains is 0.3 to 1.2 μm, and the density is 2.5 × 10
^{It was 7} pieces / cm ² .

Crystal growth was carried out under the following continuous conditions using Sn as a solvent by a liquid phase growth apparatus based on an ordinary slide boat method to obtain a continuous thin film of a large grain Si crystal. That is, in a hydrogen atmosphere, after the growth start temperature is 970 ° C., the degree of supercooling is 2 ° C., the cooling rate is 0.3 ° C./min, and the growth time is 15 minutes, the substrate is separated from the solvent and the temperature is raised to 1030 ° C. The temperature was returned to 970 ° C. again, and then the supercooling degree was 3 ° C., the cooling rate was 0.5 ° C./min, and the growth time was 70 minutes.
Grow in minutes. The grain size and thickness of the Si crystal thin film thus obtained were about 60 μm and about 45 μm, respectively.

FIGS. 4 (a) to 4 (g) show a process of the fabricated hetero solar cell. Is almost same as that of FIG. 1 shown in Example 1, p ⁺ layer 107 in (g)
Instead, a p-type μc-Si 407 is formed on the Si crystal layer. The p-type μc-Si layer 407 is a normal plasma CV
D apparatus was used on the surface of the Si crystal under the conditions shown in Table 1 for 0.1.
Deposited 02 μm. At this time, the dark conductivity of the μc-Si film was Ｓ10 S · cm ⁻¹ .

[0052]

[Table 1] Further, as the transparent conductive film 406, about 0.1 μm of ITO was used.
It is formed by electron beam evaporation, and a current collecting electrode 4 is further formed thereon.
08 (Ti / Pd / Ag (0.04 μm / 0.02 μm
/ 1 µm)) was formed by vacuum evaporation.

The p ⁺ μc-Si /
When the IV characteristics of a polycrystalline Si heterojunction solar cell under AM1.5 light irradiation were measured (cell area 0.1
6cm ² ), open voltage 0.59V, short-circuit photocurrent 30.5
mA / cm ² , fill factor 0.71 and conversion efficiency 1
Values as high as 2.8% were obtained.

Example 3 A large-grain Si crystal solar cell was manufactured by the process shown in FIG. As described above, the SiO ₂ layer is formed on the Mo substrate by 0.1%.
μm, and an amorphous Si layer was formed on the surface of the SiO ₂ layer by EB vapor deposition of high-purity Si using a normal vacuum vapor deposition apparatus.
μm was deposited. Next, annealing was performed in an N ₂ atmosphere at 600 ° C. for 50 hours to perform solid phase growth.

Annealing is performed in an H ₂ atmosphere at 1040 ° C. for 8 minutes to aggregate the Si layer to form fine Si
Grains were obtained on the SiO ₂ layer. At this time, the grain size of the Si grains is 0.4 to 1.3 μm, and the density is 3.4 × 10 ⁷ / c.
m ² .

Crystal growth was carried out under the following continuous conditions using Sn as a solvent by an ordinary liquid phase growth apparatus based on a slide boat method to obtain a continuous thin film of a large grain Si crystal. That is, in a hydrogen atmosphere, a growth start temperature of 970 ° C. and a degree of supercooling of 0.5
After the substrate was separated from the solvent, the temperature was raised to 1030 ° C., the temperature was maintained for 30 minutes in a hydrogen atmosphere, and the temperature was returned to 970 ° C. This time, the supercooling degree is 2 ° C, the cooling rate is 0.7 ° C / min,
The growth was performed for a growth time of 60 minutes. Both the particle size and the film thickness of the Si crystal thin film thus obtained were about 50 μm.

In order to form the p ⁺ layer, BSG (Boro
n Silicate Glass is deposited on the surface of the Si crystal by a normal pressure CVD apparatus, and RTA (Rapid Th) is used.
thermal annealing) treatment. The film thickness of the deposited BSG was about 0.6 μm, and the conditions of the RTA treatment were performed at 1050 ° C. for 60 seconds. At this time, the junction depth was about 0.2 μm.

BSG was removed with an aqueous HF solution, and finally EB was added.
A current collecting electrode (Ti / Pd / Ag (0.04 μm
/0.02 μm / 1 μm)) / Transparent conductive film ITO (0.
082 μm) was formed on the p ⁺ layer.

When the IV characteristics of the thin-film crystal solar cell thus manufactured under AM1.5 light irradiation were examined,
When the cell area is 0.25 cm ² , the open circuit voltage is 0.55 V, the short-circuit photocurrent is 28 mA / cm ² , and the fill factor is 0.73.
A conversion efficiency of 1.2% was obtained.

Example 4 A thin-film crystal solar cell was manufactured in the same manner as in Examples 1 and 3 by the process shown in FIG. An SiO ₂ layer is formed on a Cr substrate with a normal pressure CVD device at 0.1
2 μm, and SiH is formed thereon using an LPCVD apparatus.
₄ was thermally decomposed at 550 ° C. to deposit 0.08 μm of amorphous Si.

B is implanted on the surface of the amorphous Si under the conditions of an energy of 30 keV and a dose of 5 × 10 ¹⁵ / cm ² , and the amorphous Si is annealed in an N ₂ atmosphere at 600 ° C. for 50 hours. Solid phase growth of the layers was performed.

Next, annealing was performed in an H ₂ atmosphere at 1050 ° C. for 5 minutes to coagulate the Si layer to obtain fine Si particles on the SiO ₂ layer. At this time, the particle size of the Si particles is 0.2 to 1.1 μm, and the density is 4 × 10 ⁷ / c.
m ² .

Crystal growth was carried out under the following continuous conditions using Sn as a solvent by a conventional liquid phase growth apparatus based on a sliding boat method to obtain a continuous thin film of large grain Si crystal. That is, in a hydrogen atmosphere, after the growth start temperature is 980 ° C., the degree of supercooling is 2 ° C., the cooling rate is 0.2 ° C./min, and the growth time is 15 minutes, the substrate is separated from the solvent and the temperature is raised to 1040 ° C. For 30 minutes, and the temperature was returned to 980 ° C again.
This time, the growth was performed at a supercooling degree of 3 ° C., a temperature decreasing rate of 0.3 ° C./min, and a growth time of 130 minutes. The Si thus obtained
The grain size and thickness of the crystalline thin film are about 50 μm and about 40 μm, respectively.
m.

Next, P was thermally diffused on the surface of the Si crystal layer at 900 ° C. using P と し て Cl ₃ as a diffusion source to form an n ⁺ layer, and a junction depth of about 0.5 μm was obtained. The dead layer on the surface of the formed n ⁺ layer was removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.
Furthermore, the surface of the Si crystal layer is thinly oxidized by dry oxidation (up to 0.01 μm), the oxide film is etched into a fine grid shape using a photolithography method, and a current collector electrode (Ti / Pd / Ag (0.
04 μm / 0.02 μm / 1 μm)). Further, finally, a transparent conductive film ITO (0.082 μm) is formed thereon.
m) was formed to complete the fabrication of the solar cell.

The IV characteristics of the thin-film crystal solar cell thus manufactured under AM1.5 light irradiation were examined.
When the cell area was 0.36 cm ² , the open voltage was 0.58 V, the short-circuit photocurrent was 30 mA / cm ² , and the fill factor was 0.74. Thus, a conversion efficiency of 12.9% was obtained.

As described above, according to the present invention, Si
It has been shown that a large-diameter Si layer can be formed on a metal substrate by a liquid phase method using fine Si grains obtained by agglomeration of the layers as seed crystals, and a mass-productive and inexpensive solar cell can be manufactured using this. Was.

[0067]

As described above, according to the present invention, it is possible to form a thin film crystal solar cell having good characteristics on a metal substrate. As a result, mass-produced inexpensive and high-quality thin solar cells can be provided to the market.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a manufacturing process of a thin-film solar cell of the present invention.

FIG. 2 is a diagram illustrating a method of growing a Si crystal using aggregated fine Si particles.

FIG. 3 shows S by solid-phase reaction during the growth of a Si crystal.
FIG. 9 is a diagram showing a state in which the bottom surface of an i-crystal is brought into contact with the surface of a substrate.

FIG. 4 is a diagram illustrating an example of a manufacturing process of the heterojunction solar cell of the present invention.

[Explanation of symbols]

101, 201, 301, 401 metal substrate, 102, 202, 302, 402 insulating layer, 103, 203, 403 amorphous Si layer, 104, 204, 404 fine Si grain, 105, 205, 303, 405 Si crystal ( Growth layer), 107 p ⁺ layer or n ⁺ layer, 407 p-type microcrystallized silicon layer, 106,406 transparent conductive layer, 108,408 current collecting electrode.

Claims (7)

(57) [Claims] 1. A method for manufacturing a polycrystalline Si solar cell, comprising: 1) depositing an insulating layer on a metal substrate; 2) depositing an amorphous Si layer on the surface of the insulating layer; Heating the amorphous Si layer in an inert gas atmosphere and subjecting it to solid phase growth to form a crystalline Si layer; 4) heating in an active gas atmosphere to agglomerate the crystalline Si layer to form Si crystal grains. Forming a crystal on the insulating layer; 5) performing crystal growth using the Si crystal grain as a seed crystal by a liquid phase method; and 6) heating the Si crystal grain and the insulating layer in an active gas atmosphere. Contacting the surface of the metal substrate with the bottom surface of the Si crystal grains by accelerating the solid phase reaction between them; and 7) further growing the Si crystal grains by a liquid phase method to make the surface of the insulating layer Si. Covering with a layer, comprising: Method of manufacturing a pond. 2. The method according to claim 1, wherein the insulating layer is made of SiO ₂ . 3. The method for manufacturing a thin-film polycrystalline Si solar cell according to claim 1, wherein the amorphous Si layer contains impurities. 4. The method according to claim 3, wherein the impurity is one of P, As, Sn, and B. 5. The thin-film polycrystalline Si solar cell according to claim 1, wherein the inert gas is one of N ₂ , He, and Ar. Manufacturing method. 6. The method for manufacturing a thin-film polycrystalline Si solar cell according to claim 1, wherein the active gas is H ₂ . 7. The method for manufacturing a thin-film polycrystalline Si solar cell according to claim 1, wherein the solvent used in the liquid phase method is Sn, and the solute is Si. .