JPH05102502A - Amorphous solar cell - Google Patents

Abstract

(57) [Abstract] [Object] The present invention provides a conductive thin film having crystallinity in an ultrathin film state, low absorption of visible light, and high performance in order to improve the performance of an amorphous solar cell. Apply a semiconductor thin film with high carrier density to improve open-circuit voltage, short-circuit photocurrent and photoelectric conversion efficiency. [Structure] A p-layer or an n-layer of an amorphous solar cell forms a thin film while irradiating the growth surface with ions generated by discharge of a mixed gas of a hydrocarbon compound or an organosilicon compound and a non-depositing gas The crystalline semiconductor thin film is characterized by repeating the process and the process of performing only ion irradiation, and the thickness of the thin film formed in each repetition is 1 to 100Å and the total film thickness is 300Å or less. Amorphous solar cell. [Effect] According to the present invention, it is possible to form a crystalline semiconductor thin film having a film thickness of 300 Å or less, a low absorption of visible light, and a high carrier density, which was impossible with the conventional technique. The photoelectric conversion efficiency can be remarkably improved by applying it to the p layer or the n layer of the solar cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the performance of an amorphous solar cell, and more particularly, to a crystalline semiconductor thin film having low absorption of visible light, low resistance and high carrier density in an extremely thin film state. Related to forming technology.

[0002]

2. Description of the Related Art Amorphous solar cells have already been put to practical use as a low-output energy supply source for driving calculators and watches. However, it cannot be said that the performance and stability are sufficient as an energy supply source with a large output of 0.1 W or more, such as solar power generation applications, and various studies have been carried out with the aim of improving performance. There is. Then, the photoelectric conversion efficiency of the solar cell is the open circuit voltage,
It is represented by the product of short circuit photocurrent and fill factor. As a result of various studies, regarding the short-circuit photocurrent and the fill factor, the currently achieved values have come close to the theoretically expected values,
That is, the open-circuit voltage has not been sufficiently improved.

In order to improve the reliability of solar cells, a pin type amorphous solar cell having a p-layer on the light incident side has been studied in recent years. In order to improve the open-circuit voltage in this amorphous solar cell, the photoelectric characteristics of the p-type semiconductor thin film must be improved, and in particular, the optical bandgap and the electrical conductivity must be increased at the same time. Where it didn't happen, there was technical difficulty.

A microcrystalline thin film has been proposed as a material satisfying these requirements. However, the conventional technique such as the plasma CVD method is used to form the p-type microcrystalline thin film on the transparent electrode under the film forming conditions. Even if the formation is attempted, the open circuit voltage of the amorphous solar cell is not improved as a result. The reason for this is pi
50-300 Å necessary and sufficient for p-layer of n-type amorphous solar cell
It has been reported that it is difficult to form a p-type microcrystalline thin film on a transparent electrode with a film thickness of 1 μm (see, for example, Bee Goldstein et al. Type SiC: H Microcrystalline Thin Film Properties, Applied Physics Letters, 53, 2672-2674,
Published in 1988 (B. Goldstein et al., "Properties of p + mi
crocrystalline films of SiC: H deposited by convent
ional rfglow discharge ", Applied Physics letters,
53, p2672-2674 (1988)). That is, in the film thickness of 50 to 300 Å, it does not crystallize and has a high resistance, the fill factor is low, and the improvement of the open circuit voltage cannot be obtained. On the other hand, ECR (Elec
tron CyclotronResonance) plasma CVD method
When a layer is formed, improvement in open-circuit voltage and improvement in photoelectric conversion efficiency have been reported. However, this method causes severe damage to the underlying material due to ion bombardment, and the p-type microcrystalline thin film obtained by this method At present, the characteristics have not been fully exploited (eg, Yutaka Hattori et al., "High-efficiency amorphous heterojunction solar cell using p-type microcrystalline SiC film formed by ECR-CVD" Technical Digest of
International PVSEC-3, pp. 171-174, published in 1987 (Y. Hattori et al., "High Efficiency Amorphous He
terojunction Solar cell Employing ECR-CVD Produced
p-Type Microcrystalline SiC Film ", Technical Dige
st of the International PVSEC-3, p.171-174 (198
7)). In recent years, it has been reported that a microcrystalline thin film can be obtained by repeating treatment with atomic hydrogen generated by microwave plasma or high frequency plasma after film formation. It is not mentioned whether microcrystallization is possible even when the value is less than 300Å (for example,
A. Asano "Effect of hydrogen atoms on the network structure of hydrogenated amorphous silicon and microcrystalline silicon thin films",
Applied Physics Letter, Volume 56, 533-535
Page, published in 1990 (A. Asano, "Effects of hydrogen atom
s on the network structure of hydrogenated amorpho
us and microcrystalline silicon thin films ", Appli
ed Physics letters, 56, p.533-535 (1990)), Isamu. Shimizu et al. “Chemical reaction control for growth of crystalline silicon at low substrate temperature”, Material Research Society Symposium Proceedings, 164, 195
~ 204 pages, published in 1990 (I. Shimizu et al., "CONTROL OF
CHEMICAL REACTIONS FOR GROWTH OF CRYSTALLINE Si A
T LOW SUBSTRATE TEMPERATURE ", Materials Research S
ociety Symposium Proceeding Vol.164, p.195〜204
(1990))). It has also been reported that a microcrystalline thin film can be obtained by treating with an ion beam after forming a 900-1000Å silicon thin film, but in these cases, keV
It is necessary to irradiate high-energy ions in the order of ~ MeV (for example, JS Im et al., "Crystal Nucleation by Ion Irradiation in Amorphous Silicon Thin Films", Applied Physics Letters, 57, 1766-1768).
Page, published in 1990 (JSImet al., "Ion irradiation enh
anced crystal nucleation in amorphous Si thin film
s ", Applied Physics letters, 57, p.1766 ~ 1768 (19
90)), Sea. Spinella et al. "Grain Growth Mechanism of Ion Beam Irradiation on Amorphous Silicon by Chemical Vapor Deposition" Applied Physics Letters, 57, 554-
556, published in 1990 (C. Spinella et al., "Grain growt
h kinetics during ion beam irradiation of chemical
vapor deposited amorphous silicon ", AppliedPhysic
s letters, 57, p. 554 to 556 (1990)), damage to the base material, and the device being extremely large and expensive, which is not practical.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have crystallinity in an extremely thin film state (300 Å or less), which has hitherto been impossible,
Moreover, they have found that a crystalline semiconductor thin film having low absorption of visible light, low resistance, and high carrier density can be formed. Therefore, an object of the present invention is to achieve extremely high open circuit voltage and photoelectric conversion efficiency by applying the crystalline semiconductor thin film to the p layer and / or the n layer of an amorphous solar cell having a pin or nip structure. It is in the field.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors have introduced a gas containing a gas of a hydrocarbon compound or an organosilicon compound into an ion generator to grow the surface. After forming an ultrathin film of 100 Å or less while irradiating low energy ions of preferably 1 keV or less, crystallization of the film is promoted by continuing ion irradiation, and by repeating the process, a film of 300 Å or less can be obtained. It has been found that it is possible to form a semiconductor thin film having crystallinity even with a thick thickness, low absorption of visible light, low resistance, and high carrier density. The inventors have found that by applying the semiconductor thin film to the p-layer and / or the n-layer of an amorphous solar cell, the cell characteristics, especially the open-circuit voltage can be greatly improved, and the present invention has been completed.

According to the present invention, on a substrate, a first electrode, a first conductive thin film, a substantially intrinsic thin film, a second conductive thin film,
In an amorphous solar cell in which a second electrode is formed in this order, the first conductive thin film and / or the second conductive thin film is a mixed gas of a hydrocarbon compound or an organosilicon compound and a non-depositing gas. Of forming a silicon-based thin film by supplying a silicon-based thin film forming raw material in an atmosphere containing charged particles obtained by discharging (hereinafter, abbreviated as film forming step)
And stopping the supply of the silicon-based thin film forming raw material, and exposing the thin film forming surface to an atmosphere containing charged particles obtained by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas. A crystalline semiconductor thin film with a total thickness of 300 Å or less, in which the thickness of the thin film formed by repeating the process (hereinafter abbreviated as "reforming process") is 1 to 100 Å. The subject is an amorphous solar cell, which is characterized by being present.

FIG. 1 shows an example of the layer structure of an amorphous solar cell, which is the object of the present invention.

In forming the conductive thin film, the first conductive thin film and the second conductive thin film have different conductivity types. For example, if the first conductivity type is p-type, the second conductivity type is n-type. It goes without saying that the opposite case is also possible. The present invention is characterized in that the crystalline semiconductor thin film described in the claims is applied to the first conductive thin film and / or the second conductive thin film.

First, the details of the method for forming a crystalline semiconductor thin film, which is the greatest feature of the present invention, will be described. In the formation of the semiconductor thin film of the present invention, the film forming step is performed at the maximum by performing the thin film growth in an atmosphere containing charged particles generated by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas. Has the characteristics of
The means for supplying the thin film forming raw material, and thus the film forming means itself, are not particularly limited. Specifically, it is carried out by a physical film forming method such as vacuum deposition, sputtering or ion plating, or a chemical vapor deposition (CVD) method such as photo CVD or plasma CVD. The atmosphere containing charged particles is an atmosphere containing a cation or anion of a hydrocarbon or organic silicon compound and / or a non-depositing gas, which is generated by discharging a non-depositing gas. is there. In the present invention, this is guided (collision) to the surface of the thin film formed on the substrate by means such as applying a bias voltage to the substrate.

On the other hand, in the reforming step, the supply of the thin film forming raw material in the film forming step is stopped, and charged particles produced by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas are generated. In this step, only the atmosphere containing is continued to guide (expose) to the surface of the thin film formed on the substrate to modify the properties of the semiconductor thin film formed in the film forming step. In addition,
At this time, even if the decomposition product species of the hydrocarbon compound or the organosilicon compound covers the surface of the thin film, the effect of the present invention is not impeded. Further, of course, the hydrocarbon compound and the organosilicon compound may be used together.

An effective physical film forming method will be described below. As described above, the generation of the atmosphere containing the charged particles generated by discharging the mixed gas of the hydrocarbon compound or the organic silicon compound and the non-depositing gas in the film forming step is caused by the physical film forming method or the physical film forming method described below. Although it is performed together with the chemical vapor deposition method, it can be controlled independently. However, since this is the same generation method as the generation method of the atmosphere containing the charged particles generated by discharging the mixed gas of the hydrocarbon compound or the organic silicon compound and the non-depositing gas in the reforming step, The effective generation method and the like will be described in the specific section of the reforming step described later.

Silicon as a starting material for film formation,
Elements, compounds and alloys such as silicon carbide, silicon nitride, silicon-germanium alloy or composite powder, silicon-tin alloy or composite powder can be effectively used. The film forming condition is not particularly limited except that it is exposed to an atmosphere containing charged particles during thin film growth, and rare gases such as argon, xenon, helium, neon, krypton, hydrogen, hydrocarbons, fluorine and nitrogen are used. The film can be formed in an atmosphere such as oxygen gas. As specific conditions, the gas flow rate is 0.1 to 100 sccm, and the reaction pressure is 0.0001 mtorr.
It is in the range of ~ 100 mtorr. Further, the film forming conditions such as the flow rate, the pressure and the electric power are appropriately selected according to the film forming rate.

The film formation temperature is controlled by controlling the substrate temperature. The temperature range is not basically limited, but it is preferable to set the temperature in conformity with the reforming process. Specifically, it is selected in the temperature range of 500 ° C or lower.

Next, a concrete example of an effective chemical vapor deposition method will be shown. As a source gas for film formation, the general formula Si _n H
_{2n + 2} (n is a natural number) monolane, disilane,
Silane compounds such as trisilane and tetrasilane, fluorinated silanes, organic silanes, hydrocarbons, germane compounds and the like are used. Further, gases such as hydrogen, deuterium, fluorine, chlorine, helium, argon, neon, xenon, krypton and nitrogen may be introduced together with the source gas. When using these gases, 0.01 to 100 relative to the source gas
% (Volume ratio) is effective, and is appropriately selected in consideration of the film formation rate and film characteristics. Similar to the physical film forming method, the film forming conditions are not particularly limited except that the film formation is performed in an atmosphere containing charged particles during thin film growth. The specific conditions are disclosed below.

In photo-CVD, a raw material gas is decomposed by using an ultraviolet light source having a wavelength of 350 nm or less, such as a low pressure mercury lamp, a deuterium lamp or a rare gas lamp, to form a film. As film formation conditions, consider gas flow rate of 1 to 100 sccm, reaction pressure of 15 mtorr to atmospheric pressure, substrate temperature of 200 to 600 ° C, heat resistance of substrate, film formation time considered from film formation speed, temperature of reforming process, etc. Then, more preferably, it is appropriately selected in the range of 300 to 500 ° C.

The plasma CVD will be specifically described below. As the discharge method, high frequency discharge, direct current discharge, microwave discharge, ECR discharge or the like can be effectively used. A raw material gas flow rate of 1 to 900 sccm, a reaction pressure of 0.001 mtorr to atmospheric pressure, and an electric power of 1 mW / cm ² to 10 W / cm ² are sufficient. These film forming conditions are appropriately changed depending on the film forming rate and the discharging method. Substrate temperature is 200
To 600 ° C, and more preferably 300 to 500 ° C.

In the present invention, the atmosphere containing charged particles obtained by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas in the reforming step and the film forming step means a hydrocarbon. Discharge using a mixed gas of a compound or an organosilicon compound and a non-depositing gas to generate charged particles composed of cations or anions of a hydrocarbon or organosilicon and / or a non-depositing gas,
The atmosphere exposed to the growth surface. The presence of non-ionized substances in the atmosphere does not hinder the effect of the present invention. Exposure to this discharge atmosphere and application of a bias voltage to the substrate to effectively guide the ionized components onto the substrate is a more preferable modification method. Therefore, as a method of generating discharge, high frequency discharge, direct current discharge, microwave discharge, ECR discharge, etc. can be effectively utilized. It is also a useful method in the present invention to effectively generate ions by an ion generator and guide the ions to the substrate surface. Specifically, various ion generators such as a Kauffman type ion gun and an ECR ion gun are used.

In the present invention, the gas of a hydrocarbon compound or an organic silicon compound is a saturated hydrocarbon compound such as methane or ethane, an unsaturated hydrocarbon compound such as ethylene or acetylene, methylsilane, dimethylsilane, disilylmethane, dimethyldisilane, etc. Organic silane compounds, etc., and if necessary, hydrogen gas, deuterium gas, fluorine gas, hydrogen fluoride gas, nitrogen trifluoride,
Mixing non-depositing gases such as carbon tetrafluoride, argon gas, neon gas, helium gas, xenon gas, krypton gas is not a hindrance to the present invention, but is a more preferred embodiment. The mixing ratio of the gas of the hydrocarbon compound or the organosilicon compound and the gas other than that is appropriately determined in accordance with the absorption coefficient, conductivity, and carrier density of the desired thin film.
It is selected, but usually 100 ppm to 100%, more preferably
It is mixed in the range of 1% to 50%. If this mixing ratio is too low, the absorption coefficient will be high, and if this mixing ratio is too high, crystallization will be hindered, the carrier density will decrease, and a high resistance film will be formed. As already mentioned, the hydrocarbon compound and the organosilicon compound may be used in combination. In this case, the mixing ratio should be within the above range in total.

Next, specific conditions for the reforming process will be disclosed. When using discharge, discharge power 1 to 500 W, flow rate of gas containing hydrocarbon compound or organic silicon compound 5 to 5
It is generated and maintained in the range of 00 sccm and pressure of 0.001 mtorr to atmospheric pressure. When using an ion gun, flow rate of gas containing hydrocarbon compound or organosilicon compound 0.1 to 50 scc
m 2, pressure 0.0001 mtorr to 100 mtorr, a pressure range with ion generation as well as sufficient lifetime is used. The ion energy is sufficient in the range of 10 to 1000 eV, preferably 100 to 600 eV. If the energy of ions is increased beyond this range, the damage due to ions and the sputtering phenomenon will be more severe than the effect of modification, which is not effective. The temperature condition in the reforming process is controlled by the temperature of the substrate. This substrate temperature is the same as or lower than the substrate temperature in the film forming process, and is from room temperature to 600 ° C.
C., preferably 200 to 500.degree. In one film forming step, the film is formed to a film thickness of 1 to 100Å, preferably 3 to 50Å. When the film thickness exceeds 100Å, the effect of the present invention is reduced. Further, if the film thickness is less than 1 Å, the number of repetitions of film formation and modification increases from the viewpoint of practicality, which is not preferable. The time required for one cycle is not particularly limited, but is 1000 seconds or less.

In order to apply the thin film of the present invention to the first conductive thin film and / or the second conductive thin film of an amorphous solar cell, as a matter of course, when the conductive thin film is formed, In addition to the gases shown above, a gas imparting p-type or a gas imparting n-type is introduced. Gases imparting p-type are boron hydrides such as diborane, boron halides such as boron trifluoride, organoboron compounds such as trimethylboron, aluminum halides such as aluminum trichloride, organoaluminum compounds such as trimethylaluminum. And so on. On the other hand, the gas imparting n-type is a phosphorus hydride such as phosphine, a phosphorus halide such as phosphorus trifluoride, an organic phosphorus compound such as trimethyl phosphorus, an arsenic hydride such as arsine, an organic arsenic compound such as trimethylarsenic. Gas such as is used. If necessary, mix these gases with hydrogen gas, deuterium gas, hydrogen fluoride gas, fluorine gas, nitrogen trifluoride, carbon tetrafluoride, argon gas, neon gas, helium gas, xenon gas, krypton gas, etc. Doing so is not a hindrance to the present invention, but is a more preferable embodiment. The mixing ratio of the gas that imparts p-type or n-type and the other gas is appropriately selected in accordance with the desired conductivity and carrier density of the thin film, but is usually 10 ppm to 20%, more preferably, It is mixed in the range of 200 ppm to 5%. If the mixing ratio is too low, a gas having a high carrier density cannot be obtained because of a shortage of gas imparting p-type or n-type, and a high-resistance film is obtained. If this mixing ratio is too high, crystallization is hindered, and only a film having a low carrier density can be obtained,
It becomes a high resistance film. Needless to say, when the first conductive thin film is of p-type, the second conductive thin film is of n-type, and conversely, the first conductive thin film is of n-type. In the case of the conductivity type, the second conductive thin film has the p-type conductivity.

Next, the substantially intrinsic thin film will be described. In the present invention, the substantially intrinsic thin film is a silicon hydride thin film, a silicon hydride germanium thin film, a silicon hydride carbon thin film, or the like, and forms a photoactive region of an amorphous solar cell. These substantially intrinsic thin films are compounds having silicon in the molecule such as silane and disilane, compounds having germanium in the molecule such as germane, organic silane compounds such as methylsilane, or a combination of these compounds and hydrocarbon gas. It is easily formed by applying a film forming means such as a plasma CVD method or an optical CVD method to a raw material gas appropriately selected from a mixed gas or the like according to a target semiconductor thin film. Diluting the source gas with hydrogen, deuterium, helium, argon, xenon, neon, krypton or the like does not hinder the effect of the present invention. As specific forming conditions, the temperature is 150 to 500 ° C., preferably 175 to 350 ° C., and the pressure is 0.01 to 5 Torr, preferably 0.03 to 1.5 Torr. The thickness of the substantially intrinsic thin film is not a limiting condition of the present invention, but 300 to 10000Å is usually sufficient.

The material of the substrate and electrodes used in the present invention is not particularly limited, and conventionally used substances can be effectively used. For example, the substrate may have any of insulating, conductive, transparent, and opaque properties. Basically, a film- or plate-shaped material formed of a substance such as glass, alumina, silicon, stainless steel, aluminum, molybdenum, chromium, and heat-resistant polymer can be effectively used. As the electrode material, either the first electrode or the second electrode is always on the light incident side, and of course, a transparent or transparent material must be used on the light incident side. There is no. A metal such as aluminum, silver, chromium or titanium or a metal oxide such as tin oxide or zinc oxide can be appropriately selected and used.

A schematic view of an example of a preferable apparatus for forming the amorphous solar cell of the present invention is shown in FIG. Here, 1 is a substrate insertion chamber, 2 is a first conductive thin film forming chamber, 3
Is a substantially intrinsic thin film forming chamber, 4 is a second conductive thin film forming chamber, 5 is a second electrode forming chamber, 6 is a substrate extracting chamber, 7 is a substrate, 8 is an RF electrode, 9 is a substrate heating electrode, 10 is a metal mask, 11 is a second electrode evaporation source, 12 is a vacuum exhaust line, 13
Is a source gas introduction line, 14 is a silicon evaporation source, 15 is an ion generator, and 16 is a gate valve. In FIG. 2, the first conductive thin film forming chamber 2 is a silicon evaporation source 1
4. The ion generator 15 is provided, in which the step of forming the first conductive thin film and the modification step thereof are performed. In addition,
The details are as described in Japanese Patent Application No. 3-248861.

[0025]

EXAMPLES Example 1 The apparatus shown in FIG. 2 was used. As described above, this is composed of the substrate insertion chamber, the first conductive thin film forming chamber, the substantially intrinsic thin film forming chamber, the second conductive thin film forming chamber, and the second electrode forming chamber. The conductive thin film forming chamber has an electron beam vapor deposition device for depositing silicon and an ion generating device for generating ions. The glass substrate on which tin oxide was previously formed as the first electrode was heated in a vacuum in the substrate insertion chamber and transferred to the first conductive thin film forming chamber. For the first conductive thin film, high-purity silicon was set as a starting material in a crucible, and an electron beam was incident thereon to be evaporated. 10 hydrogen in the ion generator
sccm, 2% diborane / hydrogen 0.5sccm, methane gas 0.2sccm as a hydrocarbon compound were introduced, the pressure was adjusted to 1 × 10 ^-3 Torr, an ion beam voltage of 300V and an acceleration voltage of 50V were applied to generate an ion beam, The shutter of the ion beam was opened and the substrate surface was irradiated with the ion beam. At the same time, open the shutter of the electron beam evaporation system for 20 seconds and set 20Å on the substrate.
A silicon thin film was deposited (film forming step). Next, the shutter of the electron beam vapor deposition apparatus was closed and only ion beam irradiation was performed for 10 seconds (reforming step). In this way, opening and closing of the shutter of the electron beam vapor deposition apparatus was repeated at each time interval. A p-type crystalline silicon thin film having a thickness of about 200Å was formed by repeating 10 times. Next, the substrate is transferred to a substantially intrinsic thin film forming chamber, 10 sccm of monosilane is introduced, and an amorphous silicon thin film is formed to a thickness of about 6000 Å by the plasma CVD method at a pressure of 0.05 Torr and a temperature of 250 ° C. did. The plasma CVD method used 13.56MHz RF discharge, and the RF power at this time was 5W. After forming the substantially intrinsic thin film, the substrate was transferred to the second conductive thin film forming chamber. In order to impart n-type conductivity to the second conductive thin film, monosilane / phosphine / hydrogen was introduced at a ratio of 10 / 0.01 / 100 as a raw material gas, pressure 0.2 Torr, temperature 25
An n-type microcrystalline silicon film having a thickness of about 500Å was formed at 0 ° C and RF power of 80W. Then, it was transferred to the second electrode forming chamber and an aluminum film was formed as a second electrode by vacuum vapor deposition.

The photoelectric conversion characteristics of the thus-obtained amorphous solar cell are AM-1.5, and the light of 100 mW / cm ² is solar simulator.
The measurement was performed by irradiating with a laser. As a result, the open circuit voltage is 0.
A very high value of 980V was obtained. The short-circuit photocurrent and fill factor were high at 18.15 mA / cm ² and 0.730, respectively, and as a result, the photoelectric conversion efficiency was 13.0%, which was an extremely excellent performance. When only the thin film formed under the same conditions as the first conductive thin film was measured by Raman scattering spectrum, a Raman scattering spectrum of 520 cm ^-1 peculiar to crystalline silicon was obtained.

Example 2 In Example 1, only the vapor deposition thickness and the reforming time per time in the case of forming the first conductive thin film were changed to about 4Å and 6 seconds, respectively. The vapor deposition thickness was changed by changing the opening time of the shutter of the electron beam vapor deposition apparatus. In Example 1, the deposition rate by electron beam evaporation was found to be about 1 Å / sec. Therefore, in this Example, the film formation time was set to 4 seconds. A p-type crystalline thin film of about 200 Å was formed by repeating the vapor deposition step-reforming step 50 times. As a result of measuring the photoelectric conversion characteristics in the same manner as in Example 1, the open end voltage was 0.970 V, and the short circuit photocurrent was 18.01 mA / c.
High value of m ² , fill factor of 0.733, and photoelectric conversion efficiency of 1
It was an excellent value of 2.8%.

Example 3 In Example 1, only the vapor deposition thickness and the reforming time per time in the case of forming the first conductive thin film were changed to about 80Å and 10 seconds, respectively. The vapor deposition thickness was changed by changing the opening time of the shutter of the electron beam vapor deposition apparatus. In Example 1, the deposition rate by electron beam evaporation was found to be about 1 Å / sec. Therefore, in this example, the deposition time for one time was set to 80 seconds. A p-type crystalline thin film of about 240 Å was formed by repeating the vapor deposition process and the modification process three times. As a result of measuring the photoelectric conversion characteristics in the same manner as in Example 1, the open circuit voltage was 0.973 V, the short circuit photocurrent was 18.12 mA / cm ² ,
High fill factor of 0.732, photoelectric conversion efficiency of 12.9%
And was an excellent value.

Comparative Example 1 In Example 1, in the case of forming the first conductive thin film,
A p-type crystalline thin film was formed to a thickness of 200 Å without undergoing a modification process using only ion irradiation. That is, the shutters of the ion beam vapor deposition apparatus and the electron beam vapor deposition apparatus were simultaneously opened, and in Example 1, it was found that the vapor deposition rate by electron beam vapor deposition was about 1Å / sec. The formation of the crystalline thin film was completed. This sample was also measured for photoelectric conversion characteristics similar to those of the example, and the open-circuit voltage was 0.880 V, the short-circuit photocurrent was 16.70 mA / cm ² ,
The fill factor was 0.675 and the photoelectric conversion efficiency was 9.92%, which was lower than that of the example. When only the thin film formed under the same conditions as the formation conditions of the first conductive thin film was measured by the Raman scattering spectrum, the Raman scattering spectrum of 520 cm ^-1 peculiar to crystalline silicon was not observed, and the reason for the low performance was It was revealed that this was due to the presence or absence of crystallization. This comparative example shows that in order to apply a crystalline thin film to a conductive thin film, it is essential to repeat film formation and modification by ion irradiation.

Comparative Example 2 In Example 1, in the case of forming the first conductive thin film,
After forming a Si thin film to a thickness of 200Å, only ion irradiation was continued. The time only for irradiation was 1000 seconds. The photoelectric conversion characteristics of the device obtained under these conditions have an open circuit voltage of 0.88.
The performance was low at 2 V, short-circuit photocurrent 16.65 mA / cm ² , fill factor 0.690, and photoelectric conversion efficiency 10.1%. The thin film produced under the same conditions as the formation conditions of the first conductive thin film was not crystallized, and therefore, improvement in open circuit voltage and short circuit photocurrent was not obtained. This comparative example shows that, in applying a crystalline thin film to a conductive thin film, there is an upper limit to the film thickness per repetition of the film forming-reforming process.

Comparative Example 3 In Example 1, in the case of forming the first conductive thin film,
A film was formed without performing ion irradiation in the film forming process. That is, open the shutter of the electron beam evaporation system for 20 seconds,
After depositing a 20Å silicon thin film on the substrate, the shutter of the electron beam evaporation system was closed and the ion beam shutter was opened, and the ion beam irradiation was performed for 10 seconds. next,
The shutter for the ion beam is closed and the shutter for the electron beam evaporation system is opened again to form a film. By repeating this film formation and reforming 10 times, about 2
A p-type microcrystalline thin film of 00Å was formed. The photoelectric conversion characteristics of the device obtained under these conditions are: open circuit voltage 0.876 V, short circuit photocurrent 16.37 mA / cm ² , fill factor 0.695, photoelectric conversion efficiency 9.97.
It had a low performance of%. The thin film produced under the same conditions as the formation conditions of the first conductive thin film was not crystallized, and therefore, improvement in open circuit voltage and short circuit photocurrent was not obtained.
That is, this comparative example shows that ion irradiation is necessary also in the film forming step in applying the crystalline thin film to the conductive thin film.

[0032]

As is clear from the above examples and comparative examples, the semiconductor thin film produced by this method is
Even if the film thickness is less than Å, it has crystallinity, which makes it possible to apply the microcrystalline semiconductor thin film to the p-layer and / or n-layer of an amorphous solar cell, which has been difficult in the past. ,
This has led to significant improvements in open circuit voltage and short circuit photocurrent. Therefore, the present invention can provide a technology that enables high conversion efficiency and high reliability required for a solar cell for electric power, and it must be said that the present invention is an extremely useful invention for the energy industry.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of the configuration of an amorphous solar cell obtained by the present invention.

FIG. 2 is a schematic view showing an example of a preferable apparatus for forming the element of the present invention.

[Explanation of symbols]

 1 Substrate insertion chamber 2 First conductive thin film forming chamber 3 Substantially intrinsic thin film forming chamber 4 Second conductive thin film forming chamber 5 Second electrode forming chamber 6 Substrate take-out chamber 7 Substrate 8 RF electrode 9 Substrate heating Electrode 10 Metal mask 11 Second electrode evaporation source 12 Vacuum exhaust line 13 Raw material gas introduction line 14 Silicon evaporation source 15 Ion generator 16 Gate valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyuki Yanagawa 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. An amorphous solar cell in which a first electrode, a first conductive thin film, a substantially intrinsic thin film, a second conductive thin film, and a second electrode are formed in this order on a substrate. In an atmosphere containing charged particles obtained by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas, wherein the first conductive thin film and / or the second conductive thin film is silicon. A step of supplying a silicon-based thin film forming raw material to form a silicon-based thin film, and stopping the supply of the silicon-based thin film forming raw material to discharge a mixed gas of a hydrocarbon compound or an organosilicon compound and a non-depositing gas. The step of exposing the thin film forming surface to the atmosphere containing the obtained charged particles is repeated, and the thickness of the silicon-based thin film formed in one cycle is 1 to 100Å and the total film thickness is 300Å
An amorphous solar cell comprising the following crystalline semiconductor thin film. 2. A mixture gas of a hydrocarbon compound or an organic silicon compound and a non-depositing gas is introduced into an ion generator to irradiate a thin film having a thickness of 1 to 100 Å with low energy ions. The amorphous solar cell according to claim 1, wherein the step of forming the amorphous solar cell and the step of stopping the supply of the silicon-based thin film forming raw material and continuing the ion irradiation are repeated. 3. The amorphous solar cell according to claim 2, wherein the low-energy ions irradiated to the thin film growth surface are 1 KeV or less.