JP3069208B2 - 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 of manufacturing a thin film polycrystalline Si solar cell, and more particularly to a method of manufacturing a thin film polycrystalline Si solar cell having good energy conversion efficiency.

[0002]

2. Description of the Related Art Conventionally, a solar cell has been used as a driving energy source in various devices. A solar cell uses a pn junction in a device portion, and Si is generally used as a semiconductor forming the pn junction. In terms of the efficiency of converting light energy to electromotive force, single crystal Si
Is preferred, but amorphous Si is considered to be advantageous from the viewpoint of increasing the area and reducing the cost. In recent years, the use of polycrystalline Si has been studied for the purpose of obtaining low cost comparable to amorphous (amorphous) and high energy conversion efficiency comparable to single crystal Si. However, it has been difficult to reduce the thickness to 0.3 mm or less by using a plate-shaped body obtained by slicing a massive polycrystal in the conventionally proposed method. In this respect, the effective utilization of the material was 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 about several hundredths of a micron. 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 laser light to melt and recrystallize it, but cost reduction is not sufficient, and stable production is difficult.

[0004] 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 using a liquid phase method (exit, Hamamoto, Itagaki, Ishihara, Morikawa, Sasaki, Sato). , Namisaki; Proceedings of the 51st Fall Meeting of the Japan Society of Applied Physics, 29a-G-2p695).

[0005]

In the above-mentioned method, an SiO ₂ film is provided on the substrate surface in order to prevent impurities contained in the low-cost substrate from being taken into the grown Si crystal. At this time, in the liquid phase method using Sn as a solvent, Sn cannot be directly grown on SiO ₂ due to poor Sn leaking property.
It is necessary on the _two, not uniform film was obtained undergo aggregation when Si layer is thin, and the surface resistance unevenness intensified separate crystal grains grow when the Si layer is thicker become worse. This is because the liquid phase method is a growth under quasi-thermal equilibrium, and therefore the growth rate anisotropy greatly depends on the crystal plane orientation.
This is because the smaller the crystal grain size of the i-layer becomes, the more remarkable it becomes. 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.

An object of the present invention is to solve the problems of the prior art and to provide a method of manufacturing a thin-film polycrystalline Si solar cell having a large grain size and good quality. Another object of the present invention is to provide a method of manufacturing a thin-film polycrystalline Si solar cell capable of manufacturing an inexpensive solar cell by growing a large-crystalline polycrystalline semiconductor layer on a metal substrate which is a low-cost substrate. Is to do.

Still another object of the present invention is to form a large grain Si crystal layer on a small Si grain formed on an insulating film (eg, an SiO ₂ film) as a seed crystal, thereby forming An object of the present invention is to provide a method for manufacturing a thin-film polycrystalline Si solar cell capable of manufacturing a high-quality solar cell by eliminating contamination of impurities.

[0008]

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. An object of the present invention is to provide a method for manufacturing a thin-film polycrystalline Si solar cell. That is, the present invention is a method for manufacturing a polycrystalline Si solar cell. i) a step of depositing an insulating layer on a metal substrate; ii) a step of depositing a Si layer on the surface of the insulating layer;
Increasing the crystal grain size in the Si layer by introducing high concentration impurities into the layer and heating in an inert gas atmosphere; and iv) heating the Si crystal grains in an active gas atmosphere to reduce the Si crystal grains. Forming on the insulating layer; v)
Aggregation of the Si layer with a high degree of supersaturation by the liquid phase method
(Vi) heating the crystal in an active gas atmosphere to promote a solid-phase reaction between the Si crystal grains and the insulating layer by using the crystal grains as a seed crystal to grow the island-like single crystal; Contacting the surface of the metal substrate with the bottom surface of the Si crystal grains; and vii) growing the Si crystal grains further by a liquid phase method and covering the surface of the insulating layer with a Si layer. Is what you do.

[0009]

Principle techniques DETAILED DESCRIPTION OF THE INVENTION The present invention, as shown in FIG. 1, C on the SiO ₂ insulating layer deposited on the metal substrate
A Si layer is formed by a VD method or the like, a high concentration of impurities is introduced into the surface by thermal diffusion or the like, and annealing is performed in an inert atmosphere such as nitrogen to increase the grain size of the Si layer, and then annealing is performed in a hydrogen atmosphere. To aggregate the Si layer,
The i-grain is formed on a substrate, and the Si grain is used as a seed crystal to form a polycrystalline Si thin film layer having a large grain size by a liquid phase growth method.

At this time, during the liquid phase growth, S
When the i crystal grain is grown, annealing is performed in a hydrogen atmosphere to cause a solid phase reaction between the Si crystal and the SiO ₂ layer, thereby bringing 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 base is achieved. Thereafter, the Si crystal grains are further grown to finally obtain a continuous film.

The present inventors have 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 a SiO ₂ film as a seed crystal. I found In addition, the present inventors have further conducted experiments to obtain the Si
It has been found that the orientation of the Si crystal grown as a seed crystal using the agglomerated Si grains can be controlled by introducing impurities into the layer in advance and annealing in an inert atmosphere to increase the grain size.

Further, the present inventors conducted further experiments, and when the agglomerated Si grains were grown to some extent by liquid phase growth, the growth was suspended once, and the Si grains were annealed in an active gas atmosphere (for example, a hydrogen atmosphere). By causing a solid-phase reaction between the crystal and the insulating layer to bring 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 is achieved. Large grain polycrystalline Si
It was found that a continuous thin film was obtained, and the present invention was completed.

Hereinafter, an experiment 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 (insulating layer) was formed as a 0.1 μm SiO ₂ layer (insulating layer) on the surface of a 0.8 mm thick Mo substrate 201 as an insulating layer 202 by a normal atmospheric pressure CVD method. And then a normal L
The thermal decomposition of SiH ₄ at 630 ° C. by PCVD equipment
An i layer 203 was deposited to a thickness of 0.1 μm.

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 the Si layer on such a metal substrate,
P implanted by ion implantation at an acceleration voltage of 50 KV and a dose of 8 × 10 ¹⁵ / cm ² , and similarly in an inert atmosphere (N ₂ atmosphere) after implanting P
Three types, one that was annealed at 000 ° C. for 3 hours, were prepared.

When the change in crystal grain size was examined by a transmission electron microscope, the one immediately after ion implantation was amorphous, but the one annealed after ion implantation was expanded to a maximum of about 3 μm. Was. Furthermore, in the above, the impurity diameter was diffused by depositing phosphorus glass instead of ion implantation, and annealing at 1000 ° C. for 3 hours in an N ₂ atmosphere after removing the phosphorus glass also increased the crystal grain size. .

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.
Fine Si grains 204 having a size of about 1.5 μm were formed on the SiO ₂ layer. The density of the Si grains at this time is approximately 1 to 3 ×
It was 10 ⁷ pieces / cm ² .

(Experiment 2) Si crystal growth by liquid phase growth method Using the fine 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 grown by immersion in 95% ° C. saturated n-type Si having a specific resistance of 2Ω · cm in Sn solvent. Starting temperature 950 ° C, degree of supercooling 3
° C., gradually cooled at a cooling rate 0.5 ° C. / min, which was annealed in an N ₂ atmosphere after ion implantation is likewise growth start temperature 950 ° C., supercooling degree 30 ° C., cooling rate 0.5 ° C. / min And the crystal was grown. Growth time is 15 each
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. It was obtained (FIG. 2 (d)). However,
The density of the grown Si crystal was 2 to 5 × 10 ⁴ / cm ² , and it became clear that not all the fine Si grains formed by aggregation were crystal-grown.

Also, there is a large difference in the morphology of the Si crystal after the growth, and no priority was found in the crystal orientation for the non-ion-implanted and the ion-implanted only. The crystal annealed in the atmosphere had overwhelmingly many crystals with the (111) plane oriented in the direction perpendicular to the substrate surface, and the coverage of the substrate surface with Si crystals was the highest.

(Experiment 3) SiO_TwoSolid between layer and Si crystal
Phase reaction The (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
Cross-section of the substrate surface with high resolution scanning
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 can be achieved.

(Experiment 4) Formation of Continuous Film Subsequent to Experiment 3, crystal growth was further performed by a liquid phase method. The growth was performed at a growth start temperature of 950 ° C., a degree of supercooling of 3 ° C., a cooling rate of 0.5 / min, and a growth time of 80 minutes. After the growth was completed, the surface of the substrate was observed with an optical microscope and a scanning electron microscope in the same manner as in Experiment 2. As a result, adjacent Si crystals were completely in contact with each other, and the average grain size was about 50 μm.
It was confirmed that a large-diameter Si crystal thin film (continuous film) was obtained. At this time, the height of the continuous film is Si
It was about 40 μm from above the surface of the O ₂ layer.

(Experiment 5) Formation of Solar Cell B was implanted into the surface of the large-diameter Si crystal thin film on the Mo substrate obtained in Experiment 4 by ion implantation at 20 KeV and 1 × 10 ^15.
/ Cm ² and annealed at 800 ° C. for 30 minutes to form ap ⁺ layer. With respect to the solar cell having the large-diameter Si crystal thin film / SiO ₂ / Mo structure manufactured in this manner, the I− under the irradiation of AM1.5 (100 mW / cm ² ) light.
When the V characteristics were measured, the cell area was 0.16.
Open voltage 0.52 V, short circuit current 25 mA / c in cm ²
m ² and the fill factor were 0.72, and a conversion efficiency of 9.4% 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 that has good conductivity and preferably forms a compound such as Si and silicide is used,
Representative examples include W, Mo, Cr, Ni, Ti, and the like, but of course, other values may be used.
As an insulating layer, SiO ₂ is used because it causes a solid-phase reaction with Si.
Is used, and its thickness is not particularly specified,
It is appropriate that the thickness be in the range of 0.05 to 0.5 μm.

The Si layer deposited on the insulating layer may be crystalline or amorphous, or may be a mixture of crystalline and non-crystalline. LPCVD, plasma CV
Any method such as D method, vapor deposition method and sputtering method may be used.
The PCVD method is used. The thickness of the Si layer is approximately 0.1
A range of 0.5 μm is appropriate. Impurities are introduced into such a Si layer for the purpose of increasing the particle size. The method for introducing impurities is ion implantation or thermal diffusion, and P, As, and Sn for n-type impurities are used as impurities.
And B, Al and the like are selected for the p-type.

The amount of impurities to be introduced is appropriately determined depending on the thickness of the Si layer and the annealing conditions, but is generally 4 × 10 ²⁰ cm ⁻³ or more. The upper limit is 5 × 10
²¹ cm ^-3 is preferred. If it is less than 4 × 10 ²⁰ cm ⁻³ , remarkable enlargement of the grain size is not expected, and it is difficult to control the orientation of the grown Si crystal. In the method of the present invention, the temperature of the annealing of the Si layer in an inert gas for the purpose of increasing the particle size is preferably 900 ° C. or higher, although it depends on the processing time. , Ar, etc. are used.

In addition, S in the active gas performed after the particle size is increased
The temperature in the aggregation of the i-layer is approximately 950 to 11
The temperature is preferably in the range of 00 ° C., and the active gas is H
2 is used. 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. Further, the degree of supercooling is preferably set to about several tens of degrees Celsius in order to suppress the high-doped fine Si particles from melting back in the solvent when growing Si crystals from the fine Si particles. In the case where the growth is continued after the phase reaction, the temperature is preferably about several 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 50, respectively, due to the requirements on the characteristics of the solar cell and the constraints of the process.
0 μm is appropriate, preferably 30 to 500 μm each.
μm is desirable. A junction is formed by providing a p ⁺ or n ⁺ layer on the surface of the obtained Si crystal, and its thickness is preferably in the range of 0.05 to 1 μm, depending on the amount of impurities to be introduced. Suitable, preferably 0.1-0.5μ
m is desirable.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of forming a desired solar cell according to an embodiment of the method of manufacturing a thin-film polycrystalline Si solar cell according to the present invention will be described in more detail below. However, the present invention is not limited by these embodiments. Not something. (Example 1) As described above, a large grain Si crystal solar cell on a metal substrate was manufactured in the same manner as in Experiments 1 to 5. FIG.
(A) to (g) show the manufacturing process. Metal substrate 1
A Mo plate having a thickness of 0.8 mm was used for 01. An SiO ₂ layer was formed thereon by 0.08 μm using a normal pressure CVD apparatus (FIG. 1A), and then Si was formed using a normal LPCVD apparatus.
H ₄ was thermally decomposed at 630 ° C. to deposit 0.1 μm polycrystalline Si (FIG. 1B).

Next, phosphorus glass was deposited on the surface of the polycrystalline Si to diffuse impurities. Table 1 shows the deposition conditions of phosphorus glass. Immediately after phosphorus glass deposition
℃ leave to the drove 5 minutes in N ₂ atmosphere. HF: H2 O = 1: 10 HF after impurity diffusion is completed
Remove the phosphorus glass with an aqueous solution and then
Annealing was performed at 0 ° C. for 3 hours to increase the particle size. The maximum particle size obtained at this time was about 2.8 μm.

[0030]

[Table 1] Subsequently, annealing was performed in an H ₂ atmosphere at 1030 ° C. for 10 minutes to aggregate the Si layer to obtain fine Si grains on the SiO ₂ layer (FIG. 1C). At this time, the grain size of the Si grains 104 is 0.4 to 1.5 μm, and the density is 3 × 1.
0 ⁷ was / cm ^2.

Crystal growth was carried out using Sn as a solvent under the following continuous conditions by a conventional liquid phase growth apparatus by a slide boat method to obtain a continuous thin film of a large grain Si crystal. That is,
In a hydrogen atmosphere, growth start temperature 950 ° C, degree of supercooling 30
After the liquid phase growth at a temperature of 0.5 ° C., a cooling rate of 0.5 ° C./min, and a growth time of 10 minutes (island-like single crystal growth: FIG. 1D), the metal substrate was separated from the solvent and the temperature was raised to 1050 ° C. After holding for 20 minutes in a hydrogen atmosphere (continuity between the metal substrate and the island-shaped single crystal: FIG. 1 (e)), the temperature was returned to 950 ° C. again, this time with a degree of supercooling of 3 ° C., and a temperature drop rate of 0.5 ° C. Liquid phase growth was performed at a growth rate of 80 minutes / minute (FIG. 1 (f)).

The Si crystal thin film 10 thus obtained is
The particle size and film thickness of No. 5 were both about 50 μm. No priority was observed for the orientation of the Si crystal after growth when no impurity was introduced, but when annealing was performed in an N ₂ atmosphere after introducing the impurity with phosphorus glass, (1
11) Many crystals are oriented in a direction perpendicular to the substrate surface,
The proportion contained in all the grown Si crystals was about 50%.

B was implanted into 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. Finally, a current collecting electrode (Ti / Pd / Ag (0.04 μm / 0.02 μm) was deposited by EB (Electron Beam) evaporation.
md / 1 μm)) / An ITO transparent conductive film was formed on the p ⁺ layer.

[0034] were measured for the I-V characteristic at AM1.5 (100mW / cm ²⁾ under light irradiation on this way a large grain size Si crystal solar cell obtained, the open-circuit voltage in the cell area 0.25 cm ² 0.54V, short-circuit photocurrent 28
mA / cm ² , the fill factor was 0.72, and an energy conversion efficiency of 10.9% was obtained. Thus, a solar cell exhibiting good characteristics was produced using the large grain Si crystal layer grown on the metal substrate.

Example 2 An amorphous silicon carbide / polycrystalline Si hetero-contact solar cell was produced in the same manner as in Example 1. The metal substrate with Cr, 0.1 [mu] m the amorphous Si layer of SiO ₂ layer was 0.12μm deposited by atmospheric pressure CVD method thereon, further 550 ° C. by LPCVD thereon by the decomposition of SiH ₄ Deposited.

By ion implantation, As is 50 KeV,
Implanted into the surface of the Si layer under the condition of 6 × 10 ¹⁵ / cm ² ,
Annealing was performed at 1000 ° C. for 3 hours in an Ar atmosphere to increase the grain size of the Si layer. Subsequently, in an H ₂ atmosphere at 1000 ° C.
Annealing was performed under the conditions of × 20 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 was 0.3 to 1.2 μm, and the density was 5 × 1.
0 ⁷ was / 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 large grain Si crystal. That is, in a hydrogen atmosphere, a growth start temperature of 970 ° C., a degree of supercooling of 25 ° C.,
After a cooling rate of 0.3 ° C./minute and a growth time of 13 minutes, the substrate was separated from the solvent, the temperature was increased to 1030 ° C., the temperature was maintained for 30 minutes in a hydrogen atmosphere, and the temperature was returned to 970 ° C. The growth was performed at a cooling degree of 3 ° C., a temperature decreasing rate of 0.5 ° C./min, and a growth time of 70 minutes.

The grain size and thickness of the Si crystal thin film thus obtained were about 60 μm and about 45 μm, respectively.
No priority was observed in the orientation of the Si crystal after growth when no impurity was introduced, but when annealing was performed in an N ₂ atmosphere after introducing As by ion implantation, the (111) plane was observed. Many of the crystals were oriented in the direction perpendicular to the substrate surface, and the proportion contained in all grown Si crystals was about 55%.

FIGS. 4 (a) to 4 (g) show the 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 of p-type amorphous silicon carbide 407
Was formed on the Si crystal layer. The p-type amorphous silicon carbide layer 407 was deposited on the Si crystal surface at 0.02 μm under the conditions shown in Table 2 by a normal plasma CVD apparatus. At this time, the dark conductivity of the amorphous silicon carbide film was 10 ⁻² S · cm ⁻¹ , and the composition ratio of C and Si in the film was 2: 3.

[0040]

[Table 2] The transparent conductive film 408 is made of ITO of about 0.1 μm.
It is formed by electron beam evaporation, and a current collecting electrode (Cr (0.02 μm) / Ag (1 μm) / Cr (0.
004 μm)) was formed by vacuum evaporation.

The thus obtained amorphous silicon
Concarbite / Polycrystalline Si heterojunction solar cell A
Measurement of IV characteristics under M1.5 light irradiation
(Cell area 0.16cm2), open voltage 0.60V, short
Photocurrent 29.5 mA / cm ^Two , With a fill factor of 0.65
As a result, a high value of 11.5% was obtained. (Embodiment 3) As shown in FIG.
A large grain Si crystal solar cell was fabricated by the process. I mentioned earlier
On the Mo substrate_TwoForming a layer having a thickness of 0.1 μm;
SiO in PCVD equipment_Two0.1 polycrystalline Si layer on the layer surface
μm deposited, and then phosphorus glass is deposited on the surface under the conditions shown in Table 1.
Then, impurity diffusion was performed. Phosphorus glass with HF aqueous solution
After the removal, annealing was performed at 1050 ° C. for 3 hours.
And the particle size was increased.

Next, annealing was performed in an H ₂ atmosphere at 1040 ° C. for 8 minutes to aggregate the Si layer to obtain fine Si grains on the SiO ₂ layer. At this time, the particle size of the Si particles is 0.4 to 1.3 μm, and the density is 4 × 10 ⁷ / cm ^2.
Met. Crystal growth was performed 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-diameter Si crystal. That is, in a hydrogen atmosphere, a growth start temperature is 970 ° C., a degree of supercooling is 33 ° C., a temperature drop rate is 0.5 ° C./min, and after a growth time of 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 growth was performed at a supercooling degree of 2 ° C., at a temperature lowering rate of 0.7 ° C./min, and for a growth time of 60 minutes.

The grain size and thickness of the Si crystal thin film thus obtained were both about 50 μm. S after growth
No priority was found for the orientation of the i-crystal when no impurity was introduced, but (111) when annealing was performed in an N ₂ atmosphere after introducing the impurity with phosphorus glass.
Many of the crystals were oriented in the direction perpendicular to the substrate surface, and the proportion contained in all grown Si crystals was about 50%.

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 Theme) is deposited.
rmal 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.

After removing BSG with an aqueous HF solution, finally, a current collecting electrode (Ti / Pd / Ag (0.04
μm / 0.02 μm / 1 μm)) / Transparent conductive 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, the cell area was 0.25 cm ^2.
The open-circuit voltage is 0.53 V, the short-circuit photocurrent is 26 mA / cm ² ,
The fill factor was 0.74, and a conversion efficiency of 10.2% 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. On a Cr substrate, an SiO2 layer
2 μm, and SiH is formed thereon using an LPCVD apparatus.
₄ was thermally decomposed at 630 ° C. to deposit polycrystalline Si of 0.08 μm.

B is implanted on the surface of the polycrystalline Si under the conditions of an energy of 20 KeV and a dose of 7 × 10 ¹⁵ / cm ² , and the particles of the polycrystalline Si layer are annealed at 1000 ° C. for 4 hours in an N 2 atmosphere. The diameter was enlarged. Next, an annealing treatment is performed in an H ₂ atmosphere at 1050 ° C. for 5 minutes to aggregate the Si layer to reduce fine Si particles to SiO 2.
Obtained on _two layers. At this time, the particle size of the Si particles is 0.2 to 1.
The density was 1 μm and the density was 3 × 10 ⁷ pieces / cm 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 sliding 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 980 ° C., a degree of supercooling of 30 ° C.,
After a cooling rate of 0.2 ° C./minute and a growth time of 15 minutes, the substrate was separated from the solvent, the temperature was increased to 1040 ° C., the temperature was maintained for 30 minutes in a hydrogen atmosphere, and the temperature was returned to 980 ° C. The growth was performed at a cooling degree of 3 ° C., a temperature decreasing rate of 0.3 ° C./min, and a growth time of 130 minutes. S obtained in this way
The grain size and thickness of the i-crystal thin film are about 50 μm and about 40, respectively.
μm.

The orientation of the Si crystal after growth had no priority when impurities were not introduced, but when B was introduced by ion implantation and annealing was performed in an N ₂ atmosphere, Many of the crystals had the (111) plane oriented in a direction perpendicular to the surface of the substrate, and the ratio contained in all grown Si crystals was about 45%. Next, P was thermally diffused on the surface of the Si crystal layer using POCl ₃ as a diffusion source at a temperature of 900 ° C. 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 collecting electrode (Ti / P
d / Ag (0.04 μm / 0.02 μm / 1 μm) was deposited. Finally, on top of that, a transparent conductive film ITO
(0.082 μm) to complete the fabrication of the solar cell.

When the IV characteristics of the thin film crystal solar cell fabricated in this manner were examined under AM1.5 light irradiation,
With a cell area of 0.36 cm 2, the open voltage was 0.57 V, the short-circuit photocurrent was 28 mA / cm 2, the fill factor was 0.72, and a conversion efficiency of 11.5% was obtained. As described above, according to the present invention, 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 a Si layer as a seed crystal, and mass productivity can be improved by using this. Certain inexpensive solar cells have been shown to be manufactured.

[0051]

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

[Brief description of the drawings]

FIG. 1 is a process chart showing a manufacturing process of a thin-film solar cell according to an embodiment of a method of manufacturing a thin-film polycrystalline Si solar cell according to the present invention.

FIG. 2 is a process diagram illustrating a method of growing a Si crystal using fine Si particles formed by aggregation in the present invention.

FIG. 3 is a diagram showing a state where the bottom surface of the crystal and the surface of the substrate are brought into contact by a solid-phase reaction during the growth of the Si crystal in the present invention.

FIG. 4 is a process chart showing a manufacturing process of a heterojunction solar cell manufactured by the method of the present invention.

[Explanation of symbols]

101, 201, 301, 401 Metal substrate 102, 202, 302, 402 Insulating layer 103, 203, 403 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 amorphous silicon carbide 106,406 transparent conductive layer 108,408 current collecting electrode

Claims (6)

(57) [Claims] 1. A method for manufacturing a thin-film polycrystalline Si solar cell, comprising: a step of depositing an insulating layer on a metal substrate; a step of depositing a Si layer on a surface of the insulating layer; Introducing and heating in an inert gas atmosphere to increase the crystal grain size in the Si layer; and heating in an active gas atmosphere to agglomerate the Si layer to reduce the Si crystal grains to the insulating layer. Forming an Si single crystal in the form of an island using the Si crystal grain as a seed crystal with a high degree of supersaturation by a liquid phase method; and heating the Si crystal grain in an active gas atmosphere. A step of contacting the surface of the metal substrate and the bottom surface of the Si crystal grains by promoting a solid phase reaction with the insulating layer; and further growing the Si crystal grains by a liquid phase method to form a surface of the insulating layer. Covering with a Si layer. Thin film polycrystalline Si solar method for producing a battery, characterized in that. 2. The method according to claim 1, wherein the insulating layer is made of SiO ₂ . 3. The method according to claim 1, wherein the impurity is any one of P, As, and B. 4. The method according to claim 1, wherein the inert gas is any one of N ₂ , He, and Ar. 5. The method according to claim 1, wherein the active gas is H ₂ . 6. The method according to claim 1, wherein the solvent and the solute used in the liquid phase method are Sn and Si, respectively.