JPH07297428A - Thin film solar battery and its manufacture - Google Patents

Abstract

PURPOSE:To take out even such a carrier that is generated in an amorphous phase by forming at least one of semiconductor thin films in a mixed phase of an amorphous phase and crystalline phase, with the crystal phase containing a columnar or conic phase nearly perpendicular to the main surface of a substrate. CONSTITUTION:After forming an n-type microcrystalline silicon film 3 on a metallic substrate 2, the crystallinity of the film 3 is improved by irradiating the filnt 3 with X rays and a semiconductor thin film 4 is formed on the filnt 3 by using the plasma CVD method. Then the thin film 4 is irradiated with X rays by using a mask for X rays having openings at 3-mum intervals in both the longitudinal and transversal directions. As a result, n-type crystal areas 43 having diameters of <=1mumphi are formed in the amorphous area 41 which is substantially formed in i-type of the thin film 4 at the positions corresponding to the pattern of the mask. Carriers generated in the amorphous phase 41 having a high carrier generating rate can be run by selectively guiding the carriers to the crystalline phase 43 having a good carrier running property by forming an electric field between the amorphous phase 41 and crystalline phase 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell which is one of photoelectric conversion elements and a method for manufacturing the same, and more particularly to a thin film solar cell having high efficiency and low cost comparable to a single crystal silicon solar cell and a method for manufacturing the same. Regarding the method.

[0002]

2. Description of the Related Art Generally, a single crystal silicon solar cell has a high photoelectric conversion efficiency, but it requires a high temperature process, and since it has a small absorption coefficient, it requires a thickness of about 100 μm and is relatively expensive. On the other hand, it is known that an amorphous solar cell does not require a high temperature process, and since it has a large absorption coefficient, it only requires a thickness of about 1 μm or less and is relatively inexpensive. However, in an amorphous solar cell, the minority carrier lifetime in the p and n layers is extremely short, and the dopant layer cannot be used as a carrier generation layer at all.
As one of the methods for solving such a problem, a solar cell having a mixed phase of a polycrystalline phase and an amorphous phase has been proposed.
-58193.

[0003]

However, a high-efficiency solar cell cannot be obtained by merely having a mixed phase of a polycrystalline phase and an amorphous phase as described above. One of the reasons for this is that if the crystal phase is intrinsic, good carrier mobility cannot be obtained, and if only the film forming method is devised, a good crystalline portion and an amorphous portion are simultaneously formed. There are things that you cannot do.

An object of the present invention is to solve the problems of the prior art and to provide a high efficiency and low cost thin film solar cell comparable to a single crystal silicon solar cell and a manufacturing method thereof. .

[0005]

The above object is to provide a thin-film solar cell comprising a semiconductor thin film containing silicon as a main component and an electrode on at least the main surface of a substrate, and at least one layer of the semiconductor thin film is substantially formed. A mixed layer consisting of an intrinsic amorphous phase and an n-type or p-type crystal phase, and the crystal phase includes a columnar or pyramidal phase substantially perpendicular to the main surface of the substrate. And a thin film formed by irradiating the amorphous layer or the microcrystalline layer with X-rays in whole or in part in the formation of the above mixed layer. This can be achieved by using a method for manufacturing a solar cell. That is, according to the present invention, a semiconductor thin film is formed in an amorphous state, and then, a columnar or conical pyramid or n-type polycrystalline or single crystal silicon having good carrier mobility is produced. Is the main point.

[0006]

The operation of the present invention will be described with reference to FIGS. A conventional multi-phase thin film solar cell is, as shown in FIG.
The power generation layer 4 was sandwiched between two different types of doping layers 3 and 5, and the power generation layer 4 consisted of an intrinsic amorphous phase 41 and an intrinsic crystalline phase 42. However, in this structure, the electric field is formed by the upper and lower doping layers 3 and 5, and the carriers are extracted essentially through each of the amorphous phase 41 and the crystalline phase 42. Therefore, the carriers generated in the amorphous phase 41, which has a poor carrier running property, cannot be sufficiently taken out. To improve this, as shown in FIG. 1, the intrinsic crystal phase 42 may be replaced with a doped crystal phase 43. As a result, an electric field is formed between the amorphous phase 41 and the crystalline phase 43, and the carriers generated in the amorphous phase 41 with a good carrier generation rate are selectively induced to the crystalline phase 43 with a good carrier running property. Can be run.

Conventionally, as a method of forming a mixed phase thin film silicon, a method of forming it at a high temperature of 500 ° C. or higher and then improving the quality of an amorphous phase by plasma treatment, and a relatively low temperature of about 300 ° C. The method of forming by the plasma CVD method has been known, but in the former, the quality of the amorphous phase is not good, and in the latter, the crystalline phase is not polycrystalline and the crystal grain size is smaller (5 to 5). (15 nm) only fine crystals can be formed,
In this part, the traveling performance of minority carriers was extremely poor, which was a problem. Especially for amorphous silicon,
YL can cause significant quality deterioration in heat treatment at 300 ° C or higher.
aaziz, A.Bennouna and ELAmeziane, “The Effect of
Annealing on the Optical and Electrical Properties
of a‐Si: H Sputtered Films ”: Solar Energy Mate
rials and Solar Cells, 31 (1993) pp.23-32, it is not practical to use a heat treatment step of 300 ° C or higher. On the other hand, in the present invention, by performing low-temperature crystallization of the amorphous phase by X-ray irradiation, not a fine crystal but a polycrystalline phase having a larger crystal grain size can be used as a high-quality intrinsic amorphous phase. To form in. This has made it possible to form highly efficient mixed-phase thin-film solar cells.

[0008]

EXAMPLES The constitution of the present invention will be specifically described below with reference to examples.

<Embodiment 1> An embodiment of the present invention will be described with reference to FIG. First, by the plasma CVD method,
An n-type microcrystalline silicon 3 having a thickness of 30 nm was formed on the metal substrate 2. For film formation, monosilane and phosphine diluted with hydrogen as an n-type doping gas were used. Next, X-ray irradiation was performed at 400 ° C. for 7 minutes to improve the crystallinity of the microcrystalline silicon. The X-ray is a continuous X-ray having a peak of intensity distribution at about 3 keV. The number of photons irradiated on the sample surface was 1 × 10 ¹⁷ / cm ² near the peak energy. Crystallographic evaluation of this sample was conducted by Raman spectroscopy, and it was confirmed that only a peak peculiar to the crystal due to the Si-Si bond was observed and that crystallization proceeded. The crystal grain size of the thin film at this time is 100 nm on average, and the conductivity is 0.5.
It was (Ωcm) ^-1 .

Next, a semiconductor thin film 4 having a thickness of 300 nm was formed by the plasma CVD method. For film formation, monosilane and 100 ppm phosphine (diluted with hydrogen) as a doping gas were used. At this time, the gas flow rate was set so that Si: P in the gas was 1: 2 × 10 ⁻⁶ . Next, X-ray irradiation was carried out at 300 ° C. for 5 minutes using an X-ray mask having 0.3 μmφ openings at 3 μm intervals in the vertical and horizontal directions. After the irradiation,
Mapping measurement by microscopic Raman spectroscopy confirmed that a crystalline region 43 of 1 μmφ or less was formed in the amorphous region 41 at a position according to the mask pattern. At this time, the crystalline region 43 was n-type and the amorphous region 41 was substantially i-type. That is, a thin film having the properties of n-type crystal in the vertical direction and i-type amorphous in the horizontal direction was obtained.
From the evaluation of the electrical conductivity in the vertical and horizontal directions, the crystalline region 43 was 0.3 (Ωc
It is estimated that m) ⁻¹ and the amorphous region 41 have a conductivity of about 2 × 10 ⁻¹⁰ (Ωcm) ⁻¹ .

Next, a p-type amorphous silicon carbide 5 having a thickness of 20 nm was formed by the plasma CVD method. For the film formation, monosilane, methane, and diborane diluted with hydrogen as a p-type doping gas were used. Then, In ₂ O ₃ + SnO ₂ (hereinafter referred to as ITO) is formed as the transparent electrode layer 6 by the vapor deposition method.
Of 80 nm and aluminum of 800 nm as the collecting electrode 7 were formed.

The obtained sample was irradiated with sunlight 1 and the solar cell characteristics of a short circuit current of 19 mA / cm ² , an open end voltage of 0.75 V and a fill factor of 0.71 were confirmed. Further, even after irradiation of sunlight for one month, the short-circuit current and the reduction of the fill factor were 8% or less, and it was confirmed that the deterioration was less than that of a normal amorphous solar cell. The relatively large short-circuit current in the device characteristics is considered to be due to the generation of carriers in the crystal phase having a small band gap in the mixed layer. This is supported by the fact that the open circuit voltage is slightly low.

Example 2 The n layer was formed in the same manner as in Example 1, and then the semiconductor thin film 4 was formed to 300 nm by the plasma CVD method. Only monosilane was used for film formation. Next, make 0.5μmφ opening 5
Using an X-ray mask having an interval of μm, phosphorus ions were implanted at a peak position of 10 ¹⁷ / cm ^3, and then,
X-ray irradiation was performed at 300 ° C. for 5 minutes. At this time, hydrogen gas was introduced. This improved the film quality. After irradiation,
Mapping measurement by microscopic Raman spectroscopy confirmed that a crystal region 43 of 1 μmφ or less was formed at a position according to the mask pattern. Then, a p-layer was formed in the same manner as in Example 1. Finally, ITO was formed to a thickness of 80 nm as the transparent electrode layer 6 and aluminum was formed to a thickness of 800 nm as the collector electrode 7 by the vapor deposition method. For the samples obtained as described above, the fill factor was further improved.

<Embodiment 3> Still another embodiment of the present invention will be described with reference to FIG. On a glass substrate 8 having a metal layer partially as a collector electrode (not shown), Sb-doped SnO ₂ was used as a transparent electrode 9 by a chemical vapor deposition method.
Of 1 μm was formed. As a result, a surface shape having irregularities on the order of submicrons was obtained.

Next, an n-type polycrystalline silicon 10 having a thickness of 20 nm was formed by the thermal CVD method. For film formation, monosilane and phosphine diluted with hydrogen as an n-type doping gas were used.
Next, a semiconductor thin film 11 having a thickness of 300 nm was formed by the plasma CVD method. For film formation, monosilane and 10 ppm diborane (diluted with hydrogen) as a doping gas were used. At this time, the gas flow rate was set so that Si: B in the gas was 1: 7 × 10 ⁻⁶ . Next, the entire surface was irradiated with X-rays at 250 ° C. for 5 minutes. At this time, hydrogen gas was introduced and plasma treatment was performed under a pressure of 1 Torr. As a result, the grain boundaries were passivated and the film quality was greatly improved. Mapping measurement by microscopic Raman spectroscopy after the above X-ray irradiation revealed that crystalline regions 111 of 1 μmφ or less were formed selectively in the protrusions of the SnO ₂ crystal in the amorphous region 110 at submicron intervals. It was confirmed. At this time, the crystalline region 111 was p-type and the non-crystalline region 110 was substantially i-type. Next, p-type polycrystalline silicon 12 was formed to a thickness of 10 nm by the thermal CVD method. At this time, monosilane and diborane diluted with hydrogen were used as a p-type doping gas for the film formation. Finally, the back electrode 13 is made of Al by vacuum deposition.
Was formed to a thickness of 1 μm.

The sample thus obtained has a remarkable light confinement effect due to the uneven shape, and the short circuit current 22
The solar cell characteristics of mA / cm ² , open-ended voltage 0.72V and fill factor 0.70 were confirmed.

<Embodiment 4> Still another embodiment of the present invention will be described with reference to FIG. 30 nm of n-type microcrystalline silicon 15 was formed on the metal substrate 14 by the plasma CVD method. The formation method was exactly the same as in forming the n-layer of Example 1. Next, the semiconductor thin film 16 is deposited to 900n by plasma CVD.
m formed. For film formation, monosilane and 10 ppm phosphine (diluted with hydrogen) as a doping gas were used. At this time, the gas flow rate was set so that Si: P was 1: 2 × 10 ⁻⁶ . Next, make a 0.5 μmφ opening 10
X-ray irradiation is performed at 300 ° C using an X-ray mask with μm intervals.
For 5 minutes. Furthermore, the above X-ray mask is moved by 5 μm in both the X and Y axes from the opening during the previous X-ray irradiation,
Boron ions were implanted so that the maximum concentration was 10 ¹⁷ / cm ^3, and then X-ray irradiation was performed at 300 ° C. for 5 minutes. After irradiation, a mapping measurement was performed by microscopic Raman spectroscopy. As a result, the n-type crystal region 16 of 1 μmφ or less was formed in the amorphous region 161.
It was confirmed that 2 and the p-type crystal region 163 were formed at the positions according to the mask pattern. That is, it was confirmed that the thin film has properties as a pin junction not only in the vertical direction but also in the horizontal direction.

Next, a p-type amorphous silicon carbide 17 having a thickness of 20 nm was formed by the plasma CVD method. For film formation,
Monosilane, methane, and diborane diluted with hydrogen were used as a p-type doping gas. After that, ITO was formed to a thickness of 80 nm as the transparent electrode 18 and aluminum was formed to a thickness of 1 μm as the collector electrode 19 by the vacuum deposition method.

The obtained sample was irradiated with sunlight 1 to obtain almost the same solar cell characteristics as in Example 1. Also, 1
It was confirmed that the deterioration in photoelectric conversion efficiency after 5 months of solar irradiation was 5% or less, and the deterioration was extremely small. It is considered that this is attributed to the fact that the pn junction is formed in the lateral direction.

<Embodiment 5> Still another embodiment of the present invention will be described with reference to FIG. An n-type microcrystal 21 having a thickness of 30 nm was formed on the metal substrate 20 by the plasma CVD method. The formation method was exactly the same as in forming the n-layer of Example 1. Next, a semiconductor thin film 22 having a thickness of 900 nm was formed by the plasma CVD method. For film formation, monosilane and a doping gas of 10
ppm phosphine (diluted with hydrogen) was used. At this time, the gas flow rate was set so that Si: P in the gas was 1: 2 × 10 ⁻⁶ . Further, during the film formation, the introduction of the doping gas was stopped at the time of forming the film with a thickness of 500 nm, and then the film was formed only with monosilane. Next, using a mask having 0.5 μmφ openings vertically and horizontally at intervals of 10 μm, boron ions are implanted at a maximum concentration of 10 ¹⁷ / cm ³ , and the implantation region is n-type microcrystalline silicon.
I went so as not to reach 21. After that, using a mask having 0.5 μmφ openings at 5 μm intervals vertically and horizontally,
X-ray irradiation was performed at 200 ° C. for 3 minutes. After the above-mentioned irradiation, mapping measurement was performed by microscopic Raman spectroscopy. As a result, it was found that an n-type crystal region 222 and a p-type crystal region 223 having a diameter of 1 μmφ or less were formed in the amorphous region 221 at the positions according to the mask pattern. confirmed. That is, it has been known that the thin film has a property as a pin junction not only in the vertical direction but also in the horizontal direction.

Next, a p-type amorphous silicon carbide 23 having a thickness of 20 nm was formed by the plasma CVD method. For film formation,
Monosilane, methane, and diborane diluted with hydrogen were used as a p-type doping gas. After that, ITO was formed to a thickness of 80 nm as a transparent electrode and aluminum was formed to a thickness of 1 μm as a collector electrode 25 by a vacuum evaporation method.

When the sample obtained as described above was irradiated with sunlight 1, the solar cell characteristics were the same as in Example 1 in terms of short-circuit current, but the open-ended voltage and fill factor were improved. , 0.82V and 0.77 were obtained.

As the crystal phase in the mixed phase region,
Not only the ones described in the above embodiments, but may be changed from the submicron region to about 100 μm depending on the film quality, or the crystal phase may be increased to about 5 μmφ, and further, the p-type phase may be used. Needless to say, the n-type phase may be randomly dispersed in places. In the above example, only an amorphous Si type is shown as an example of a thin film solar cell, but an alloy type mainly containing silicon, such as S
It may be iC or SiGe. Further, it is needless to say that the present invention can be applied not only to the single-junction type, but also to the tandem type and the multi-junction type, and is effective even if formed on a crystalline silicon solar cell, for example.

[0024]

As described above, the thin film solar cell and the method for producing the same are used as the solar cell having the constitution of the present invention and the method for producing the same, thereby solving the problems of the prior art, and thereby producing a single crystal. It was possible to provide a high-efficiency, low-cost thin-film solar cell comparable to a silicon solar cell and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of the thin film solar cell of the present invention.

FIG. 2 is a cross-sectional view showing a schematic configuration of a conventional thin film solar cell.

FIG. 3 is a sectional view showing a schematic configuration of another embodiment of the thin film solar cell of the present invention.

FIG. 4 is a sectional view showing a schematic configuration of still another embodiment of the thin film solar cell of the present invention.

FIG. 5 is a sectional view showing a schematic configuration of still another embodiment of the thin film solar cell of the present invention.

[Explanation of symbols]

1 ... Sunlight irradiation, 2 ... Metal substrate, 3 ... Microcrystalline silicon,
4 ... Semiconductor thin film, 5 ... Amorphous silicon carbide, 6 ...
Transparent electrode layer, 7 ... Current collecting electrode, 8 ... Glass substrate, 9 ... Transparent electrode, 10 ... N-type polycrystalline silicon, 11 ... Semiconductor thin film, 12 ...
p-type polycrystalline silicon, 13 ... back electrode, 14 ... metal substrate, 15
... microcrystalline silicon, 16 ... semiconductor thin film, 17 ... amorphous silicon carbide, 18 ... transparent electrode layer, 19 ... collector electrode, 20 ... metal substrate, 21 ... microcrystalline silicon, 22 ... semiconductor thin film, 23 ... amorphous Silicon carbide, 24 ... Transparent electrode layer, 25 ... Current collecting electrode, 41 ... Amorphous region, 42 ... Crystal region, 43 ... Crystal region, 11
0 ... Amorphous region, 111 ... Crystal region, 161 ... Amorphous region, 162
... n-type crystal region, 163 ... p-type crystal region, 221 ... amorphous region, 222 ... n-type crystal region, 223 ... p-type crystal region.

Claims (10)

[Claims] 1. A thin-film solar cell comprising a semiconductor thin film containing silicon as a main component and an electrode on at least a main surface of a substrate, wherein at least one layer of the semiconductor thin film is substantially intrinsic amorphous. A thin-film solar cell, which is a mixed layer of a phase and an n-type or p-type crystal phase, and the crystal phase includes a columnar or pyramidal phase substantially perpendicular to the main surface of the substrate. 2. An n-type or p-type polycrystalline or microcrystalline semiconductor layer containing silicon as a main component, the above-mentioned mixed layer, and p-type or n type containing silicon as a main component on at least the main surface of the substrate. 2. A thin-film solar cell comprising a polycrystalline or microcrystalline semiconductor layer of 1. 3. The thin film solar cell according to claim 1, wherein an electrode layer made of a metal thin film or a conductive oxide having an uneven surface is formed on at least one of the semiconductor thin films in contact with the semiconductor thin film. . 4. The thin-film solar cell according to claim 1, wherein the mixed layer in the semiconductor thin film is a mixed layer in which an n-type or p-type dopant is partially introduced in the in-plane direction. 5. The thin film solar cell according to claim 1, wherein the mixed layer in the semiconductor thin film is a layer having both n-type and p-type crystal phases. 6. The mixed layer in a semiconductor thin film is a layer having both n-type and p-type crystal phases, in which a substantially lateral pn or pin junction is formed. The thin film solar cell according to claim 1, wherein 7. A method of manufacturing a thin film solar cell, wherein the mixed layer according to claim 1 is formed by irradiating an amorphous layer or a microcrystalline layer with X-rays in whole or in part. Method. 8. The method of manufacturing a thin-film solar cell according to claim 7, wherein the X-ray irradiation is performed while the substrate is kept at 300 ° C. or lower. 9. The thin-film sun according to claim 7, wherein the X-ray irradiation is performed while introducing any one of hydrogen gas, helium gas, halogen gas, halogen hydride or a mixture thereof. Battery manufacturing method. 10. The method for manufacturing a thin-film solar cell according to claim 9, wherein the X-ray irradiation performed while introducing the gas is irradiation performed while plasma-discharging the introduced gas.