JP3107425B2 - Amorphous 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 an improvement in the performance of an amorphous solar cell, and in particular, to a crystalline semiconductor thin film having a low absorption of visible light, a low resistance and a high carrier density in an extremely thin state. Related to forming technology.

[0002]

2. Description of the Related Art Amorphous solar cells have already been put into practical use as energy sources with a small output for driving calculators and watches. However, as an energy source with a large output of 0.1 W or more, such as for photovoltaic power generation, its performance and stability are not sufficient, and various studies have been conducted with the aim of improving performance. I have. Therefore, the photoelectric conversion efficiency of the solar cell is the open-circuit voltage,
It is expressed by the product of the short-circuit photocurrent and the fill factor. As a result of various studies, with regard to the short-circuit photocurrent and fill factor, the current achieved value has approached the theoretically expected value.
That is, the open-circuit voltage has not been sufficiently improved.

In order to improve the reliability of the solar cell, a pin type amorphous solar cell provided with a p-layer on the light incident side has recently been studied. In this amorphous solar cell, in order to improve the open-circuit voltage, the photoelectric characteristics of the p-type semiconductor thin film must be improved. In particular, it is necessary to simultaneously increase the optical band gap and improve the electrical conductivity. Where it wasn't, there was technical difficulty.

[0004] A microcrystalline thin film has been proposed as a material that satisfies these requirements. However, using a conventional technique such as a plasma CVD method, a thin film of a p-type microcrystalline thin film is formed on a 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. For this reason, pi
50-300Å 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 at a film thickness of, for example, B. Goldstein et al. Characteristics of Type SiC: H Microcrystalline Thin Films ", Applied Physics Letter, 53, pp. 2672 to 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)). In other words, at a film thickness of 50 to 300 °, crystallization does not occur, the resistance is increased, the fill factor is low, and the improvement of the open-circuit voltage cannot be obtained. Meanwhile, ECR (Elec
tron Cyclotron Resonance)
When a layer is formed, improvement of the open-circuit voltage and improvement of the photoelectric conversion efficiency have been reported. However, in this method, damage to the underlying material due to ion bombardment is severe, and the p-type microcrystalline thin film obtained by this method is At present, the characteristics have not been fully exploited (for example, Yutaka Hattori et al., “Highly Efficient Amorphous Heterojunction Solar Cell Using p-type Microcrystalline SiC Film Formed by ECR-CVD” Technical Digest of
International PVSEC-3, pages 171 to 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 the treatment with atomic hydrogen generated by microwave plasma or high-frequency plasma after film formation. It is not mentioned whether microcrystallization is possible even at 300 mm or less (for example,
A. Asano, "Effect of hydrogen atoms on the network structure of hydrogenated amorphous silicon and microcrystalline silicon thin films",
Applied Physics Letter, 56, 533-535
Page, 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 Crystalline Silicon Growth at Low Substrate Temperature," Material Research Society Symposium Proceeding, 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))). In addition, it has been reported that a microcrystalline thin film can be obtained by forming a silicon thin film of 900 to 1000 mm and then treating it with an ion beam.
It must be irradiated with high-energy ions of the order of ~ MeV (for example, J. S. Im et al., "Crystal nucleation by ion irradiation in amorphous silicon thin film", Applied Physics Letter, vol. 57, pp. 1766-1768)
Page, 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 Amorphous Silicon by Chemical Vapor Deposition under Ion Beam Irradiation," Applied Physics Letter, 57, 554-
556 pages, 1990 (C. Spinella et al., "Grain growt
h kinetics during ion beam irradiation of chemical
vapor deposited amorphous silicon ", AppliedPhysic
s letters, 57, p. 554-556 (1990)), causing damage to the underlying material and making the device extremely large and expensive, making it impractical.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have crystallinity in an extremely thin film state (300 ° or less), which has been impossible in the past,
Further, they have found that a crystalline semiconductor thin film having characteristics of low absorption, low resistance and high carrier density with respect to visible light can be formed. 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 a p-layer and / or an n-layer of an amorphous solar cell having a pin or nip configuration. I'm in it.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, introduced a gas containing a hydrocarbon compound or an organic silicon compound gas into the ion generator, and grown the growth surface. After forming an ultra-thin film of 100 mm or less while irradiating low-energy ions of preferably 1 keV or less, crystallization of the film is promoted by further continuing ion irradiation. It has been found that it is possible to form a semiconductor thin film which has crystallinity even at a large thickness, has low absorption for visible light, low resistance and high carrier density. By applying the present semiconductor thin film to a p-layer and / or an n-layer of an amorphous solar cell, it has been found that cell characteristics, particularly open-circuit voltage, can be greatly improved, and the present invention has been completed.

According to the present invention, a first electrode, a first conductive thin film, a substantially intrinsic thin film, a second conductive thin film,
In the amorphous solar cell formed in the order of the second electrode, the first conductive thin film and / or the second conductive thin film is a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-deposited 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 the silicon (hereinafter, abbreviated as a film forming step)
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-deposition gas. (Hereinafter abbreviated as a reforming step) and a crystalline semiconductor thin film having a total thickness of 300 mm or less, wherein the thickness of the thin film formed in each repetition of both steps is 1 to 100 mm. The present invention provides an amorphous solar cell, which is characterized in that it has a certain feature.

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

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 reverse 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 method of forming a crystalline semiconductor thin film, which is the most significant feature of the present invention, will be described in detail. In the formation of the semiconductor thin film of the present invention, the film formation step is performed 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-depositable gas. With the characteristics of
The means for supplying the raw material for forming a thin film, and the film forming means itself, are not particularly limited. Specifically, it is performed by a physical film forming method such as vacuum evaporation, sputtering, or ion plating, or a chemical vapor deposition (CVD) method such as optical CVD or plasma CVD. The atmosphere containing charged particles is an atmosphere containing hydrocarbons, organic silicon, and / or cations or anions of non-deposited gas generated by discharging a non-deposited gas with a hydrocarbon compound or an organic silicon compound. is there. In the present invention, this is guided (collides) with 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, the reforming step is to stop supplying the thin film forming raw material in the film forming step and discharge the mixed gas of the hydrocarbon compound or the organosilicon compound and the non-deposited gas to generate charged particles. In this step, only the atmosphere containing the thin film is continued (exposed) to the surface on which the thin film formed on the substrate is formed, and the properties of the semiconductor thin film formed in the film forming step are modified. In addition,
At this time, the effect of the present invention is not impeded even if the hydrocarbons or the species produced by decomposition of the organic silicon compound cover the surface of the thin film. Of course, the hydrocarbon compound and the organic silicon compound may be used in combination.

Hereinafter, an effective physical film forming method will be described. As described above, the generation of an atmosphere containing charged particles generated by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-deposition gas in the film forming step is performed by a physical film forming method to be described below. It is performed in conjunction with the chemical vapor deposition method, but can be controlled independently. Thus, this is the same generation method as the generation method of the atmosphere including the charged particles generated by discharging the mixed gas of the hydrocarbon compound or the organic silicon compound and the non-depositable gas in the reforming step, An effective generation method and the like will be described in a specific section of the reforming step described later.

As starting materials for film formation, silicon,
Elements, compounds and alloys such as silicon carbide, silicon nitride, silicon-germanium alloy or composite powder, silicon-tin alloy or composite powder can be used effectively. The film forming conditions are not particularly limited except that the film is exposed to an atmosphere containing charged particles during the growth of the thin film, and rare gases such as argon, xenon, helium, neon, and krypton, hydrogen, hydrocarbon, 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 ~ 100mtorr. In addition, film forming conditions such as a flow rate, a pressure, and an electric power are appropriately selected according to a film forming speed.

The film formation temperature is controlled by controlling the substrate temperature. Although the temperature range is not basically limited, it is preferable to set the temperature in accordance with the reforming step. Specifically, it is selected in a temperature range of 500 ° C. or less.

Next, a specific example of an effective chemical vapor deposition method will be described. As a source gas for film formation, a general formula Si _n H
Monolan, disilane, represented by _{2n + 2} (n is a natural number)
A silane compound such as trisilane or tetrasilane, a fluorinated silane, an organic silane, a hydrocarbon, a germane compound, or the like is used. Further, a gas such as hydrogen, deuterium, fluorine, chlorine, helium, argon, neon, xenon, krypton, or nitrogen may be introduced together with the source gas. When using these gases, 0.01 to 100
% (Volume ratio) is effective, and is appropriately selected in consideration of the film forming speed and film characteristics. Like the physical film forming method, the film forming conditions are not particularly limited, except that the film is formed in an atmosphere containing charged particles during the growth of the thin film. Specific conditions are disclosed below.

In the photo CVD, a source 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. Conditions for film formation include 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 a discharge method, a method such as a high-frequency discharge, a DC discharge, a microwave discharge, and an ECR discharge can be effectively used. A flow rate of the raw material gas of 1 to 900 sccm, a reaction pressure of 0.001 mtorr to atmospheric pressure, and a power of 1 mW / cm ² to 10 W / cm ² are sufficient. These film forming conditions are appropriately changed according to the film forming speed and the discharge method. Substrate temperature is 200
To 600 ° C, more preferably 300 to 500 ° C.

In the present invention, the atmosphere containing these charged particles obtained by discharging a mixed gas of a hydrocarbon compound or an organic silicon compound and a non-deposition gas in the reforming step and the film forming step is defined as A discharge using a mixed gas of a compound or an organic silicon compound and a non-depositable gas generates charged particles composed of cations or anions of hydrocarbons and organic silicon and / or a non-depositable gas,
An atmosphere exposed to the growth surface. The presence of non-ionized substances in the atmosphere does not hinder the effects of the present invention. Exposure to the discharge atmosphere and application of a bias voltage to the substrate to effectively guide ionized components onto the substrate are more preferable means as a modification method. As a method of generating a discharge, a high-frequency discharge, a DC discharge, a microwave discharge, an ECR discharge, or the like can be effectively used. 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 ion gun and an ECR ion gun are used.

In the present invention, the hydrocarbon compound or organic silicon compound gas includes saturated hydrocarbon compounds such as methane and ethane, unsaturated hydrocarbon compounds such as ethylene and acetylene, methylsilane, dimethylsilane, disilylmethane, dimethyldisilane and the like. Of these gases, if necessary, hydrogen gas, deuterium gas, fluorine gas, hydrogen fluoride gas, nitrogen trifluoride,
Mixing a non-deposition gas such as carbon tetrafluoride, argon gas, neon gas, helium gas, xenon gas, and krypton gas does not hinder the present invention and is a more preferable embodiment. The mixing ratio between the hydrocarbon compound or the organic silicon compound gas and the other gas is appropriately adjusted according to the absorption coefficient, conductivity, and carrier density of the desired thin film.
Selected, but is usually 100 ppm to 100%, more preferably,
It is mixed in the range of 1% to 50%. If the mixing ratio is too low, the absorption coefficient will be high. If the mixing ratio is too high, crystallization will be inhibited, the carrier density will be reduced, and the film will have high resistance. As described above, the hydrocarbon compound and the organic silicon compound may be used in combination. In this case, the mixing ratio is set in the above range in total of both.

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

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 the amorphous solar cell, it is needless to say that when forming the conductive thin film, In addition to the above gases, a gas for imparting p-type or a gas for imparting n-type is introduced. The gas that imparts p-type includes boron hydrides such as diborane, boron halides such as boron trifluoride, organic boron compounds such as trimethyl boron, aluminum halides such as aluminum trichloride, and organic aluminum compounds such as trimethyl aluminum. And so on. On the other hand, the gas imparting n-type includes phosphorus hydrides such as phosphine, phosphorus halides such as phosphorus trifluoride, organic phosphorus compounds such as trimethyl phosphorus, arsenic hydrides such as arsine, and organic arsenic compounds such as trimethyl arsenic. Gases such as are 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 does not hinder the present invention, but rather is a more preferred embodiment. The mixing ratio between the gas imparting p-type or n-type and the other gas is appropriately selected according to the conductivity of the desired thin film and the carrier density, but is usually 10 ppm to 20%, and more preferably, It is mixed in the range of 200 ppm to 5%. If the mixing ratio is too low, a film having a high carrier density cannot be obtained due to a shortage of a gas for imparting p-type or n-type, and a high-resistance film is obtained. On the other hand, if the 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 conductivity, the second conductive thin film is of n-type conductivity, and conversely, the first conductive thin film is of n-type conductivity. In this case, the second conductive thin film has a p-type conductivity.

Next, a substantially intrinsic thin film will be described. In the present invention, the substantially intrinsic thin film is a silicon hydride thin film, a silicon germanium hydride thin film, a silicon hydride thin film, or the like, which forms a photoactive region of an amorphous solar cell. These substantially intrinsic thin films are formed of a compound having silicon in a molecule such as silane or disilane, a compound having germanium in a molecule such as germane, an organic silane compound such as methylsilane, or a mixture of these compounds and a 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 source 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 effects 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. Although the thickness of the substantially intrinsic thin film is not a limiting condition of the present invention, usually 300 to 10000 ° is sufficient.

The materials of the substrate and the electrodes used in the present invention are not particularly limited, and conventionally used substances are effectively used. For example, the substrate may have any of insulating or conductive, transparent, and opaque properties. Basically, a film or plate-like material formed of a substance such as glass, alumina, silicon, stainless steel, aluminum, molybdenum, chromium, or a heat-resistant polymer can be effectively used. As the electrode material, either the first 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, but other substantial restrictions There is no. It can be appropriately selected from metals such as aluminum, silver, chromium, and titanium, and metal oxides such as tin oxide and zinc oxide.

FIG. 2 is a schematic view showing an example of a preferred apparatus for forming the amorphous solar cell of the present invention. 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 a substrate taking-out 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
Denotes a source gas introduction line, 14 denotes a silicon evaporation source, 15 denotes an ion generator, and 16 denotes a gate valve. In FIG. 2, a first conductive thin film forming chamber 2 includes a silicon evaporation source 1.
4. An ion generator 15 is provided, where a first conductive thin film forming step and a reforming step thereof are performed. In addition,
The details are as described in Japanese Patent Application No. 3-248861.

[0025]

EXAMPLE 1 The apparatus shown in FIG. 2 was used. This comprises a substrate insertion chamber, a first conductive thin film forming chamber, a substantially intrinsic thin film forming chamber, a second conductive thin film forming chamber, and a second electrode forming chamber, as described above. The conductive thin film forming chamber has an electron beam evaporation apparatus for depositing silicon and an ion generator 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, as a starting material, high-purity silicon was set in a crucible, and an electron beam was incident thereon to evaporate. Hydrogen 10 in the ion generator
sccm, 2% diborane / hydrogen 0.5 sccm, methane gas 0.2 sccm as a hydrocarbon compound were introduced, the pressure was adjusted to 1 × 10 ⁻³ Torr, and an ion beam voltage of 300 V and an acceleration voltage of 50 V were applied to generate ion beams. The shutter of the ion beam was opened, and the surface of the substrate was irradiated with the ion beam. At the same time, open the shutter of the electron beam evaporation system for 20 seconds,
A silicon thin film was deposited (film formation step). Next, the shutter of the electron beam evaporation apparatus was closed, and only ion beam irradiation was performed for 10 seconds (reforming step). Thus, opening and closing of the shutter of the electron beam evaporation apparatus were repeated at each time interval. By repeating 10 times, a p-type crystalline silicon thin film having a thickness of about 200 ° was formed. Next, the substrate is transferred to a substantially intrinsic thin film forming chamber, monosilane is introduced at 10 sccm, and an amorphous silicon thin film is formed to a thickness of about 6000 mm by a plasma CVD method at a pressure of 0.05 Torr and a temperature of 250 ° C. did. The plasma CVD method used 13.56 MHz RF discharge, and the RF power at this time was 5 W. After forming the substantially intrinsic thin film, the substrate was transferred to a second conductive thin film forming chamber. 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 source gas at a pressure of 0.2 Torr and a temperature of 25/25.
An n-type microcrystalline silicon film having a thickness of about 500 ° was formed at 0 ° C. and an RF power of 80 W. Next, the aluminum film was transferred to a second electrode formation chamber, and an aluminum film was formed as a second electrode by vacuum evaporation.

The photovoltaic conversion characteristics of the amorphous solar cell thus obtained were AM-1.5, and light of 100 mW / cm ^{2 was} measured by a solar schiller.
Irradiation was carried out using a tar. As a result, the open-circuit voltage is 0.
I got a very high value of 980V. Both the short-circuit photocurrent and the fill factor maintained a high value of 18.15 mA / cm ² and 0.730, respectively, and as a result, the photoelectric conversion efficiency was 13.0%, which was extremely excellent. When only a thin film formed under the same conditions as those for forming the first conductive thin film was measured by Raman scattering spectrum, a Raman scattering spectrum of 520 cm ⁻¹ characteristic of crystalline silicon was obtained.

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

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

Comparative Example 1 In Example 1, when forming the first conductive thin film,
A p-type crystalline thin film was formed to a thickness of 200 mm without going through a modification step using only ion irradiation. That is, the shutters of the ion beam evaporation apparatus and the electron beam evaporation apparatus were simultaneously opened, and in Example 1, the deposition rate by the electron beam evaporation was found to be about 1 mm / sec. The formation of the crystalline thin film was completed. This sample was also measured for the same photoelectric conversion characteristics as in the example.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 performance than the examples. When only the thin film formed under the same conditions as the formation conditions of the first conductive thin film were measured by Raman scattering spectrum, the Raman scattering spectrum of 520 cm ^-1 specific to crystalline silicon was not recognized, and the cause of low performance was It turned out that it was due to the presence or absence of this 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, when forming the first conductive thin film,
After forming a Si thin film to a thickness of 200 mm, only ion irradiation was continued. The time of irradiation only was 1000 seconds. The photoelectric conversion characteristic of the device obtained under these conditions is 0.88
The performance was as low as 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 those for forming the first conductive thin film is not crystallized, and therefore, the open-circuit voltage and the short-circuit photocurrent have not been improved. This comparative example shows that there is an upper limit to the film thickness per repetition of the film formation-modification step when applying a crystalline thin film to the conductive thin film.

Comparative Example 3 In Example 1, when forming the first conductive thin film,
Film formation was performed without performing ion irradiation in the film forming process. That is, open the shutter of the electron beam evaporation apparatus for 20 seconds,
After depositing a 20 ° silicon thin film on the substrate, the shutter of the electron beam evaporation apparatus was closed, the shutter of the ion beam was opened, and ion beam irradiation was performed for 10 seconds. next,
While the shutter of the ion beam is closed, the shutter of the electron beam evaporation apparatus is opened again to form a film. By repeating this film formation and modification 10 times, about 2
A p-type microcrystalline thin film of 00 ° 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
% Performance was low. The thin film produced under the same conditions as those for forming the first conductive thin film is not crystallized, and therefore, the open-circuit voltage and the short-circuit photocurrent have not been improved.
That is, the present 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 has a thickness of 300
Å It has crystallinity even at the following film thickness, which makes it possible to apply a microcrystalline semiconductor thin film to the p-layer and / or the 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 power solar cell, and must be said to be an extremely useful invention for the energy industry.

[Brief description of the drawings]

FIG. 1 is a schematic cross-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 preferred apparatus for forming an element of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate insertion room 2 First conductive thin film formation room 3 Substantially intrinsic thin film formation room 4 Second conductive thin film formation room 5 Second electrode formation room 6 Substrate removal room 7 Substrate 8 RF electrode 9 Substrate heating Electrode 10 Metal mask 11 Second electrode evaporation source 12 Vacuum exhaust line 13 Source gas introduction line 14 Silicon evaporation source 15 Ion generator 16 Gate valve

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-32018 (JP, A) JP-A-3-217014 (JP, A) JP-A-2-177375 (JP, A) JP-A-57- 36873 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 31/04-31/078 H01L 21/205

Claims (3)

(57) [Claims] 1. An amorphous solar cell having a first electrode, a first conductive thin film, a substantially genuine thin film, a second conductive thin film, and a second electrode formed in this order on a substrate. Wherein the first conductive thin film and / or the second conductive thin film are p
A silicon-based thin film forming raw material is supplied in an atmosphere containing charged particles obtained by discharging a mixed gas of a gas for providing a layer or an n-layer, a hydrocarbon compound or an organosilicon compound, and a non-deposition gas. a step of forming a thin film, by stopping the supply of the silicon-based thin film forming raw material, p layer or n layer
Exposing the thin film-forming surface to an atmosphere containing charged particles obtained by discharging a mixed gas of a gas imparting a hydrocarbon compound or an organosilicon compound and a non-depositing gas, and once The total thickness of the silicon-based thin film formed in the repetition of
A method for producing an amorphous solar cell, comprising a crystalline semiconductor thin film having a thickness of not more than 00 °. 2. A mixed gas of a gas for imparting a p-layer or an n-layer, a hydrocarbon compound or an organosilicon compound and a non-depositable gas is introduced into the ion generator, and a thin film of 1 to 100 ° is formed. 2. The amorphous solar cell according to claim 1, wherein the step of irradiating the formation surface with low-energy ions and the step of stopping supply of the silicon-based thin film forming raw material and further continuing the ion irradiation are repeated. Production method. 3. The method for producing an amorphous solar cell according to claim 2, wherein the low energy ions irradiated to the thin film growth surface are 1 KeV or less.