WO2010024211A1 - 薄膜光電変換装置およびその製造方法 - Google Patents
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- WO2010024211A1 WO2010024211A1 PCT/JP2009/064697 JP2009064697W WO2010024211A1 WO 2010024211 A1 WO2010024211 A1 WO 2010024211A1 JP 2009064697 W JP2009064697 W JP 2009064697W WO 2010024211 A1 WO2010024211 A1 WO 2010024211A1
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- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier
- H01L31/075—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PIN type
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
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- H—ELECTRICITY
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- H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
- H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier
- H01L31/075—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by at least one potential-jump barrier or surface barrier the potential barriers being only of the PIN type
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
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- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic System
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Definitions
- the present invention relates to an improvement in a thin film photoelectric conversion device, and more particularly, to an improvement in utilization efficiency of long wavelength light using a crystalline germanium semiconductor.
- crystalline and “microcrystal” in the present specification are also used in the case of partially containing amorphous, as used in this technical field.
- photoelectric conversion devices that convert light into electricity using the photoelectric effect inside semiconductors have attracted attention and development has been vigorously conducted.
- silicon-based thin film photoelectric conversion devices are large at low temperatures. Since it can be formed on a glass substrate or a stainless steel substrate having an area, cost reduction can be expected.
- Such a silicon-based thin film photoelectric conversion device generally includes a transparent electrode layer, one or more photoelectric conversion units, and a back electrode layer that are sequentially stacked on a transparent insulating substrate.
- the photoelectric conversion unit generally has a p-type layer, an i-type layer, and an n-type layer laminated in this order or vice versa, and the i-type photoelectric conversion layer occupying the main part is amorphous. Is called an amorphous photoelectric conversion unit, and those having an i-type layer crystalline are called crystalline photoelectric conversion units.
- the photoelectric conversion layer is a layer that absorbs light and generates electron-hole pairs.
- an i-type layer of a pin junction is a photoelectric conversion layer.
- the i-type layer which is a photoelectric conversion layer occupies the main film thickness of the photoelectric conversion unit.
- the i-type layer is an intrinsic semiconductor layer that ideally does not contain conductivity-type determining impurities. However, even if a small amount of impurities is included, if the Fermi level is at the approximate center of the forbidden band, it functions as a pin junction i-type layer, which is substantially called an i-type layer. Generally, a substantially i-type layer is produced without adding a conductivity determining impurity to a source gas. In this case, a conductivity determining impurity may be included in an allowable range that functions as an i-type layer. Further, the substantially i-type layer may be formed by intentionally adding a small amount of conductivity-type determining impurities in order to remove the influence of impurities caused by the atmosphere or the underlayer on the Fermi level.
- a photoelectric conversion device employing a structure called a stacked type in which two or more photoelectric conversion units are stacked is known.
- a front photoelectric conversion unit including a photoelectric conversion layer having a large optical forbidden band width is disposed on the light incident side of the photoelectric conversion device, and subsequently has a small optical forbidden band width (for example, Si ⁇
- a rear photoelectric conversion unit including a photoelectric conversion layer such as a Ge alloy
- the wavelength of light that can be photoelectrically converted by i-type amorphous silicon (a-Si) is although it is up to about 700 nm on the long wavelength side, i-type crystalline silicon can photoelectrically convert light having a longer wavelength of about 1100 nm.
- a-Si i-type amorphous silicon
- a thickness of about 0.3 ⁇ m is sufficient for light absorption sufficient for photoelectric conversion.
- the crystalline silicon photoelectric conversion layer made of crystalline silicon having a small absorption coefficient preferably has a thickness of about 2 to 3 ⁇ m or more in order to sufficiently absorb long wavelength light. That is, the crystalline silicon photoelectric conversion layer usually needs to be about 10 times as thick as the amorphous silicon photoelectric conversion layer.
- the photoelectric conversion unit on the light incident side is referred to as the top cell
- the photoelectric conversion unit on the rear side is referred to as the bottom cell.
- a three-junction thin film photoelectric conversion device including three photoelectric conversion units is also used.
- the photoelectric conversion units of the three-junction thin film photoelectric conversion device are referred to as a top cell, a middle cell, and a bottom cell in order from the light incident side.
- the open-circuit voltage (Voc) is high
- the short-circuit current density (Jsc) is low
- the amorphous silicon photoelectric conversion layer of the top cell is lower than in the case of two junctions.
- the film thickness can be reduced. For this reason, the optical deterioration of the top cell can be suppressed.
- the band gap of the photoelectric conversion layer of the middle cell narrower than that of the top cell and wider than that of the bottom cell, incident light can be used more effectively.
- Thin film photoelectric conversion devices stacked in the order of photoelectric conversion units, or thin film photoelectric conversion devices stacked in the order of a-Si photoelectric conversion unit / a-SiGe photoelectric conversion unit / crystalline silicon photoelectric conversion unit can be given.
- the band gap of i-type a-SiGe in the photoelectric conversion layer of the middle cell can be controlled to a value between the top cell and the bottom cell.
- the Ge concentration of the bottom cell is set higher than that of the middle cell.
- a-SiGe which is an alloy layer
- a-SiGe which is an alloy layer
- a three-junction stacked thin-film photoelectric conversion device using a-SiGe as a middle-cell or bottom-cell photoelectric conversion layer is not sufficiently improved in efficiency as compared with a two-junction thin-film photoelectric conversion device.
- the photodegradation of a-SiGe is large, there is a problem that the photodegradation is not sufficiently suppressed even though a three-junction stacked thin film photoelectric conversion device is used.
- the wavelength of light that can be photoelectrically converted is up to about 900 nm on the long wavelength side, and when the crystalline silicon photoelectric conversion unit is used for the bottom cell, the wavelength of light that can be photoelectrically converted is long.
- the wavelength limit on the long wavelength side up to about 1100 nm on the wavelength side is not improved at the same wavelength as the two-junction thin film photoelectric conversion device, and the conversion efficiency of the three-junction thin film photoelectric conversion device is not sufficiently improved There is.
- Non-Patent Document 1 discloses a single-junction thin-film photoelectric conversion device using weak n-type microcrystalline germanium for a photoelectric conversion layer.
- the structure of the thin film photoelectric conversion device is stainless steel substrate / n-type amorphous silicon / i-type amorphous silicon / microcrystalline silicon germanium composition gradient layer / weak n-type microcrystalline germanium photoelectric conversion layer / microcrystalline silicon germanium composition. It is a structure in which an inclined layer / p-type microcrystalline silicon layer / ITO are sequentially laminated.
- the microcrystalline germanium photoelectric conversion layer is formed by an ECR remote plasma CVD method using microwave discharge.
- Non-Patent Document 2 discloses a single-junction thin-film photoelectric conversion device using microcrystalline silicon germanium having a Ge composition of 0% to a maximum of 35% for a photoelectric conversion layer.
- the structure of the thin film photoelectric conversion device is that a glass substrate / uneven ZnO / p-type microcrystalline silicon / i-type microcrystalline silicon germanium photoelectric conversion layer / n-type microcrystalline silicon layer / ZnO / Ag is sequentially laminated. This is the structure.
- the Ge composition in the film is increased to 20% or more, all of Voc, Jsc, and FF are lowered and Eff is lowered.
- the Ge concentration in the film is 30% or more, the FF is remarkably lowered.
- the FF is about 0.4 and the Eff is about 2%.
- the wavelength at which the quantum efficiency is 10% is about 1050 nm even when the Ge concentration is 35% at the maximum.
- the upper limit of the wavelength that can be used on the long wavelength side is 900.
- the wavelength that can be used on the long wavelength side is 900.
- ⁇ 1100 nm there is a problem that long wavelength light is not sufficiently utilized and conversion efficiency is not sufficiently improved.
- the thin film photoelectric conversion device using microcrystalline Ge for the photoelectric conversion layer has a problem that the FF is low and the conversion efficiency is low. Further, there is a problem that sufficient improvement cannot be obtained when the upper limit of the wavelength of the long-wavelength light capable of photoelectric conversion is about 1080 nm.
- the thin-film photoelectric conversion device using microcrystalline SiGe for the photoelectric conversion layer has a problem that when the Ge concentration in the film is increased to 20% or more, Voc, Jsc, and FF decrease, and Eff rapidly decreases.
- microcrystalline silicon germanium having a Ge concentration of up to 35% in the film there is a problem that the upper limit of the wavelength of long-wavelength light capable of photoelectric conversion is about 1050 nm and sufficient improvement cannot be obtained.
- an object of the present invention is to provide a thin film photoelectric conversion device having high characteristics that can use long wavelength light of 1100 nm or more.
- a thin film photoelectric conversion device is a thin film photoelectric conversion device including one or more photoelectric conversion units each including a photoelectric conversion layer between a p-type semiconductor layer and an n-type semiconductor layer, wherein the photoelectric conversion of at least one photoelectric conversion unit is performed.
- converting layer comprises a crystalline germanium semiconductor intrinsic or weak n-type, and the absorption coefficient of the infrared absorption peak of the crystalline germanium semiconductor of 935 ⁇ 5 cm -1 is equal to or less than 6000 cm -1 Solve the problem.
- the absorption coefficient of the infrared absorption peak at a wave number of 960 ⁇ 5 cm ⁇ 1 of the crystalline germanium semiconductor is preferably less than 3500 cm ⁇ 1 .
- the origin of the infrared absorption peak at 960 ⁇ 5 cm ⁇ 1 has not been identified, it is thought to be derived from polymer or clustered germanium hydride or germanium oxide as described above, and this infrared absorption peak should be kept small. It is considered that dense crystalline germanium is formed by the above, and the characteristics of the thin film photoelectric conversion device are improved.
- the crystalline germanium semiconductor preferably has an intensity ratio of (220) peak to (111) peak of 2 or more as measured by X-ray diffraction.
- (220) The crystalline germanium forms columnar crystals in the direction perpendicular to the substrate due to the strengthening of the (220) orientation, the crystal size in the film thickness direction increases, and the photoelectric conversion current easily flows, so that the thin film photoelectric conversion device Improved characteristics.
- the photoelectric conversion layer may have a structure in which a substantially genuine crystalline silicon semiconductor and the crystalline germanium semiconductor are stacked.
- a crystalline silicon semiconductor serves as a base layer, improves the crystallinity of the crystalline germanium semiconductor stacked thereon, and / or reduces defects at the interface between the conductive type layer and the crystalline germanium semiconductor, thereby reducing the thickness of the thin film.
- the characteristics of the photoelectric conversion device are improved.
- by forming a crystalline silicon semiconductor over a crystalline germanium semiconductor defects at the interface with the reverse conductivity type layer formed thereon are reduced, and the characteristics of the thin film photoelectric conversion device are improved.
- three photoelectric conversion units are provided, a first photoelectric conversion unit using an amorphous silicon semiconductor for the photoelectric conversion layer in order from the light incident side, a second photoelectric conversion unit using a crystalline silicon semiconductor for the photoelectric conversion layer, A three-junction stacked thin film photoelectric conversion device in which the third photoelectric conversion units including the crystalline germanium semiconductor are sequentially arranged in the photoelectric conversion layer may be formed. With such a configuration, it is possible to improve the characteristics of the thin film photoelectric conversion device by using sunlight in a wide wavelength range and realizing a high Voc.
- the thin film photoelectric conversion device of the present invention can be manufactured by forming a crystalline germanium semiconductor by a high frequency discharge plasma CVD method having a frequency of 10 to 100 MHz.
- the crystalline germanium semiconductor is desirably formed at a substrate temperature of 250 ° C. or higher.
- the crystalline germanium semiconductor is preferably formed with a high frequency power density of 550 mW / cm 2 or more.
- the high-frequency plasma CVD apparatus for forming a crystalline germanium semiconductor a plasma CVD apparatus including a substrate-side electrode on which a substrate is disposed and a high-frequency electrode can be used.
- the distance (ES) between the high frequency electrode and the substrate is desirably 12 mm or less.
- the high-frequency electrode is preferably a hollow cathode type electrode.
- the high-frequency plasma forming the crystalline germanium semiconductor does not detect a Ge atom emission peak having a peak at a wavelength of 265 nm ⁇ 2 nm and a Ge atom emission peak having a peak at 304 nm ⁇ 2 nm in the emission spectrum.
- the crystalline germanium semiconductor of the thin film photoelectric conversion device of the present invention preferably has a refractive index with respect to light having a wavelength of 600 nm of 4.0 or more, more preferably 4.7 or more, and even more preferably 4.9 or more.
- the crystalline germanium semiconductor has a refractive index with respect to a wavelength of 600 nm of 4.0 or more, preferably 4.7 or more, and more preferably 4.9 or more, so that dense crystalline germanium is formed and a thin film photoelectric conversion device is formed.
- the long wavelength light exceeding 1100 nm can be used, FF is improved, and the characteristics of the thin film photoelectric conversion device are improved.
- FIG. 1 is a schematic cross-sectional view of a single-junction thin-film photoelectric conversion device according to one embodiment of the present invention.
- the typical sectional view of the single junction thin film photoelectric conversion device concerning another embodiment of the present invention.
- the typical sectional view of the 3 junction thin film photoelectric conversion device concerning another embodiment of the present invention.
- Crystalline germanium photoelectric conversion layer wavenumber 755 cm -1 was measured by FTIR relative to a substrate temperature during film formation of, 860cm -1, 935cm -1, the absorption coefficient of the peak of 960 cm -1.
- the emission spectral spectrum at the time of forming the crystalline germanium photoelectric conversion layer of Examples 12, 13, and 14 of the present invention The emission spectral spectrum at the time of forming the crystalline germanium photoelectric conversion layer of Examples 12, 13, and 14 of the present invention.
- FIG. 27 shows a standard sunlight spectrum of air mass 1.5.
- the irradiation intensity of sunlight has a maximum value near the wavelength of 550 nm, and the intensity decreases as the wavelength increases. At that time, the irradiation intensity does not decrease monotonously, but a minimum value appears near wavelengths of 900 nm, 1100 nm, and 1400 nm due to the influence of oxygen and water vapor in the atmosphere.
- microcrystalline silicon germanium also referred to as ⁇ c-SiGe
- ⁇ c-SiGe increases the Ge concentration in the film and rapidly deteriorates the characteristics of the thin film photoelectric conversion device. This is presumably because defects increase with the Ge concentration in the ⁇ c-SiGe film.
- a 13.56 MHz high-frequency plasma CVD apparatus is used, SiH 4 and GeH 4 are used as a source gas, H 2 is used as a dilution gas, and a ⁇ c-SiGe semiconductor thin film and a crystalline germanium semiconductor thin film are formed on a glass substrate.
- H 2 dilution ratio H 2 / (SiH 4 + GeH 4 ) 2000 times constant, GeH 4 flow rate ratio GeH 4 / (GeH 4 + SiH 4 ) changed by 30% to 100% to produce semiconductor thin film on glass substrate Membrane was performed.
- FIG. 28 shows the Raman scattering spectrum.
- FIG. 29 shows the absorption coefficient at a wavelength of 1300 nm with respect to the GeH 4 gas ratio GeH 4 / (GeH 4 + SiH 4 ) of the ⁇ c-SiGe semiconductor thin film and the crystalline germanium semiconductor thin film of Reference Experimental Example 1.
- GeH 4 / (GeH 4 + SiH 4 ) 30 to 70%
- the absorption coefficient is almost constant despite increasing the proportion of Ge.
- crystalline germanium with GeH 4 / (GeH 4 + SiH 4 ) 100% shows a high absorption coefficient exceeding 6000 cm ⁇ 1 with an abrupt increase in absorption coefficient. This is due to the high crystallinity of crystalline germanium.
- the FF of the thin film photoelectric conversion device is as very low as 0.36, and the conversion efficiency is as low as 2.0%.
- the quantum efficiency is 10% at a wavelength of 1080 nm. At a wavelength of 1300 nm, the quantum efficiency is 0.5%, and the use of long wavelength light is not sufficient.
- the absorption coefficient of the infrared absorption peak of 935 ⁇ 5 cm -1 can be solved the problem by and less than 6000 cm -1 It was.
- the origin of the infrared absorption peak at 935 ⁇ 5 cm ⁇ 1 has not been identified, it is thought to be derived from polymer or cluster-like germanium hydride or germanium oxide. It is presumed that the quality of the thin film photoelectric conversion device is improved by the formation of porous germanium.
- the absorption coefficient of the infrared absorption peak at 960 ⁇ 5 cm ⁇ 1 is preferably less than 3500 cm ⁇ 1 .
- Non-Patent Document 3 G. Lucovsky, SSChao, J. Yang, JETylor, RCRoss and W. Czubatyj, “Chemical bonding of hydorogen and oxygen in glow-discharge-deposited thin films of a-Ge: H and a-Ge (H, O), Phys. Rev. B, vol.31, No.4, pp.2190-2197,1985) and are.
- Non-Patent Document 1 of Prior Example 1 there is no description of an infrared absorption peak of microcrystalline germanium.
- the microwave plasma CVD method is used for forming the microcrystalline germanium, and it is considered that oxygen is contained as an impurity in the film. It is well known to those skilled in the art that when the microwave plasma CVD method is used, oxygen easily enters an amorphous silicon or microcrystalline silicon film as an impurity. This is because the microwave plasma CVD method uses (1) a quartz tube for microwave introduction, and the quartz surface is exposed to plasma and etched, and oxygen derived from quartz tends to enter the film as impurities.
- Non-Patent Document 1 of Prior Example 1 has a description that “the microcrystalline germanium is n-type is presumed to be because oxygen is doped as an impurity in the microcrystalline germanium”.
- the microcrystalline germanium of the first example is considered to have a GeO bond formed by oxygen impurities, 935 ⁇ 5 cm, which is probably due to oxygen doping from residual gases in the reactor.
- absorption coefficient of the infrared absorption peak of -1 6000 cm -1 or more, the absorption coefficient of the infrared absorption peak of 960 ⁇ 5 cm -1 is estimated to be 3500 cm -1 or more.
- FIG. 1 is a schematic cross-sectional view of a single junction thin film photoelectric conversion device according to an example of an embodiment of the present invention.
- the transparent electrode layer 2 On the transparent substrate 1, the transparent electrode layer 2, the crystalline germanium photoelectric conversion unit 3, and the back electrode layer 6 are arranged in this order.
- a plate-like member or a sheet-like member made of glass, transparent resin or the like is used for the transparent substrate 1 used in a photoelectric conversion device of a type in which light enters from the substrate side.
- a glass plate it is preferable to use a glass plate as the transparent substrate 1 because it has a high transmittance and is inexpensive.
- the transparent substrate 1 since the transparent substrate 1 is located on the light incident side of the thin film photoelectric conversion device, it is preferable that the transparent substrate 1 be as transparent as possible so that more sunlight is transmitted and absorbed by the photoelectric conversion unit. From the same intention, it is preferable to provide a non-reflective coating on the light incident surface of the transparent substrate 1 in order to reduce the light reflection loss on the sunlight incident surface.
- the transparent electrode layer 2 is preferably made of a conductive metal oxide such as SnO 2 or ZnO, and is preferably formed using a method such as CVD, sputtering, or vapor deposition.
- the transparent electrode layer 2 desirably has the effect of increasing the scattering of incident light by having fine irregularities on its surface.
- the crystalline germanium photoelectric conversion unit 3 is formed by laminating, for example, a p-type layer, a photoelectric conversion layer, and an n-type layer in this order by a plasma CVD method. Specifically, for example, p-type microcrystalline silicon layer 31 doped with 0.01 atomic% or more of boron, substantially i-type or weak n-type crystalline germanium photoelectric conversion layer 32, and phosphorus is 0.01 An n-type microcrystalline silicon layer 33 doped with at least atomic percent is deposited in this order.
- the crystalline germanium photoelectric conversion layer 32 is an intrinsic type or a weak n-type.
- a gas containing a conductivity determining impurity element is not used.
- crystalline germanium may be weak n-type, and it can be said that crystalline germanium easily incorporates atmospheric impurities such as oxygen into the film.
- the carrier concentration of crystalline germanium obtained by Hall effect measurement is preferably 10 17 cm ⁇ 3 or less, and the mobility is preferably 1 cm 2 / (V ⁇ s) or more. If the carrier concentration is too high, the dark current of the photoelectric conversion device increases, the leakage current increases, and the FF of the photoelectric conversion device decreases.
- Crystalline germanium photoelectric conversion layer 32 it is important that the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 is less than 0 cm -1 or more 6000 cm -1, preferably less than 0 cm -1 or more 5000 cm -1 There, more preferably less than 10 cm -1 or more 2500 cm -1. Although the origin of the infrared absorption peak with a wave number of 935 ⁇ 5 cm ⁇ 1 has not been identified, it is thought to be derived from polymer or cluster-like germanium hydride or germanium oxide. It is estimated that crystalline germanium is formed and the characteristics of the thin film photoelectric conversion device are improved. As described in FIG.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 5000 cm -1, more preferable because Eff exceeds 3.5%.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 10 cm -1 or more 2500 cm -1, further preferably so Eff exceeds 4.5%.
- the absorption coefficient of the infrared absorption peak at a wave number of 935 ⁇ 5 cm ⁇ 1 is preferably 0 cm ⁇ 1 .
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 is preferably not less than 10 cm -1.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 960 ⁇ 5 cm -1 is less than 0 cm -1 or more 3500 cm -1, more preferably less than 0 cm -1 or more 3000 cm -1, 10 cm -1 or more More preferably, it is less than 1300 cm ⁇ 1 .
- the origin of the infrared absorption peak at 960 ⁇ 5 cm ⁇ 1 has not been identified, it is thought to be derived from polymer or clustered germanium hydride or germanium oxide as described above, and this infrared absorption peak should be kept small. Thus, it can be said that dense crystalline germanium is formed, and the characteristics of the thin film photoelectric conversion device are improved.
- the absorption coefficient of the infrared absorption peak at a wave number of 960 ⁇ 5 cm ⁇ 1 is less than 3500 cm ⁇ 1
- the short-circuit current density (Jsc) and the quantum efficiency at a wavelength of 1300 nm rapidly increase.
- Jsc shows a high value of 30 mA / cm 2 or more
- quantum efficiency shows a value of 5% or more.
- the conversion efficiency (Eff) is less than 1% when the absorption coefficient is 3500 cm ⁇ 1 or more, whereas when the absorption coefficient is less than 3500 cm ⁇ 1 , Eff increases rapidly and a high Eff of 3% or more. Indicates.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 3000 cm -1, more preferable because Eff exceeds 3.5%.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 1300 cm -1, more preferable because Eff exceeds 4.5%.
- the absorption coefficient of the infrared absorption peak at a wave number of 960 ⁇ 5 cm ⁇ 1 is preferably 0 cm ⁇ 1 .
- the absorption coefficient of the infrared absorption peak at a wavenumber of 960 ⁇ 5 cm -1 is preferably not less than 10 cm -1.
- the infrared absorption spectrum can be measured by FTIR (Fourier Transform Infrared Spectroscopy).
- FTIR Fastier Transform Infrared Spectroscopy
- an infrared absorption spectrum can be obtained by the following procedure. (1) A film is formed on a crystalline silicon substrate having a high resistance of 1 ⁇ ⁇ cm or more under the same film forming conditions as the photoelectric conversion layer, and an infrared transmission spectrum is measured. (2) Divide the transmittance of the sample by the transmittance of the crystalline silicon substrate without the film to obtain the transmission spectrum of only the crystalline germanium film. (3) Since the transmission spectrum obtained in (2) includes the influence of interference and offset, the base line is drawn by connecting non-absorption areas, and divided by the base line transmittance. (4) Finally, the absorption coefficient ⁇ is obtained by the following equation.
- d is the film thickness
- T s is the transmissivity of the crystalline silicon substrate
- ⁇ T is the transmissivity of the film obtained in the above (3). If an ATR crystal is used, an infrared absorption spectrum of a crystalline germanium film formed on a glass substrate, a transparent electrode layer, or a metal electrode layer can be obtained. If the transmission spectrum of the film on the crystalline silicon substrate and the calibration curve of the spectrum using the ATR crystal are obtained in advance, the infrared absorption coefficient can be obtained from the spectrum measured using the ATR crystal.
- the crystalline germanium photoelectric conversion layer 32 preferably has an intensity ratio of (220) peak to (111) peak measured by X-ray diffraction of 2 or more.
- (220) The crystalline germanium forms columnar crystals in the direction perpendicular to the substrate due to the strengthening of the (220) orientation, the crystal size in the film thickness direction increases, and the photoelectric conversion current easily flows, so that the thin film photoelectric conversion device Improved characteristics.
- the (220) / (111) peak intensity ratio is less than 2 and Eff is less than 1%
- the (220) / (111) peak intensity ratio is 2 or more. Eff increases rapidly and shows a high Eff of 4% or more.
- the (220) / (111) peak intensity ratio is desirably 70 or less.
- the germanium photoelectric conversion layer 32 desirably has a refractive index of 4.0 or more for light having a wavelength of 600 nm.
- the refractive index of the crystalline germanium photoelectric conversion layer is increased, the quantum efficiency ( ⁇ @ 1300) at a wavelength of 1300 nm and the short-circuit current density (Jsc) are increased, and the refractive index is increased to 4.0 or more.
- ⁇ @ 1300 increases to 5% or more, and long wavelength light up to 1100 nm can be used for power generation.
- a high value of 30 mA / cm 2 or more can be obtained as the short-circuit current density (Jsc).
- a refractive index of 4.9 or more is preferable because Jsc is 35 mA / cm 2 or more, which is even higher.
- the refractive index is 4.0 or more, dense crystalline germanium is formed, and it becomes possible to use long wavelength light exceeding 1100 nm.
- Eff becomes 3.0% or more when the refractive index is 4.0 or more.
- the refractive index is increased to 4.7, Eff increases abruptly, and Eff increases slowly with a refractive index higher than that. Therefore, it is more desirable to set the refractive index to 4.7 or more, and by making the refractive index 4.7 or more, Eff is stably increased. In this case, Eff of 5.7% or more is obtained.
- a crystalline germanium semiconductor has a characteristic peak of refractive index in the vicinity of a wavelength of 600 nm. Therefore, the difference in film characteristics can be determined with high sensitivity by using the refractive index of this wavelength.
- Figure 41 a single-junction using the crystalline germanium photoelectric conversion layer for Eff of the photoelectric conversion device, the absorption coefficient of 935cm -1 due to the FTIR of the crystalline germanium photoelectric conversion layer ( ⁇ @ 935cm -1), and the wavelength of 600nm
- the refractive index (n) with respect to light is shown.
- ⁇ @ 935 cm ⁇ 1 decreases with increasing Eff.
- alpha at Eff of about 3.7% or more @ 935cm -1 are variations, a clear correlation with the Eff eliminated at 0 ⁇ 3000 cm -1.
- the absorption coefficient at 960 cm ⁇ 1 has a similar tendency, and the Eff decreased to about 3.7%, and the variation became larger at Eff beyond that.
- the rough determination whether Eff is 3.7% or less is preferable to determine the absorption coefficient of 935cm -1 or 960 cm -1 by FTIR.
- the refractive index for light with a wavelength of 600 nm is 5.6 in the case of single crystal germanium.
- a refractive index of 5.6 or less is preferable because it is smaller than that of single crystal germanium, and it can be determined that impurity contamination of heavy elements such as heavy metals is suppressed.
- the refractive index for light with a wavelength of 600 nm can be measured by using spectroscopic ellipsometry.
- a crystalline germanium semiconductor under the same conditions as the photoelectric conversion device can be formed on a glass or crystalline silicon wafer, and the refractive index can be measured by spectroscopic ellipsometry.
- the photoelectric conversion device can be measured by spectroscopic ellipsometry after removing the back electrode by wet etching, plasma etching, or the like. In this case, it is desirable to further measure and measure with the crystalline germanium semiconductor exposed on the outermost surface in order to improve accuracy.
- the crystalline germanium photoelectric conversion layer is desirably formed by a high frequency plasma CVD method using, for example, GeH 4 or H 2 as a reactive gas.
- a high frequency plasma CVD method using, for example, GeH 4 or H 2 as a reactive gas.
- a capacitively coupled parallel plate electrode is used rather than a microwave frequency such as 2.45 GHz, and a frequency of 10 to 100 MHz. It is desirable to use In particular, it is preferable to use 13.56 MHz, 27.12 Mz, and 40 MHz that are approved for industrial use.
- the high frequency power density is desirably 200 mW / cm 2 or more in order to promote crystallization. Since the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 can be easily less than 6000 cm -1, the high-frequency power density may be more desirable to 550 mW / cm 2 or more.
- FIG. 30 shows a conceptual diagram of an example of a plasma CVD apparatus.
- the vacuum chamber 10 includes a high-frequency electrode 11 and a substrate-side power supply 12 that faces the high-frequency electrode 11, and generates a plasma 14 between the electrodes to form a film.
- the substrate-side electrode 12 on which the substrate 13 is disposed is preferably provided with a heater inside so that the substrate 13 can be heated.
- High-frequency power is applied to the high-frequency electrode 11 by a high-frequency power source 18 and a gas introduction pipe 15 that also serves as an electrical connection.
- the gas introduction pipe 15 is insulated from the wall surface of the vacuum chamber 10 by an insulating material 16. It is desirable that the high-frequency electrode 11 also serves as a so-called shower plate that uniformly supplies gas from a large number of holes opened like a shower. At this time, the distance (ES) between the high frequency electrode and the substrate is desirably 12 mm or less. By setting ES to 12 mm or less, as will be described later, the refractive index of the crystalline germanium semiconductor increases, a dense film is obtained, and the characteristics of the thin film photoelectric conversion device are improved. The gas in the vacuum chamber is exhausted through the exhaust pipe 14.
- the high-frequency electrode is preferably a hollow cathode type electrode.
- FIG. 31 shows a conceptual diagram of an example of a plasma CVD apparatus using a hollow cathode electrode 19 as a high-frequency electrode.
- the high-frequency electrode is a normal flat electrode, if ES is reduced to 12 mm or less, plasma is hardly generated between the electrodes, and in an extreme case, no film is attached to the substrate.
- the high-frequency electrode is a hollow cathode electrode, even if ES is 12 mm or less, plasma is stably generated between the electrodes, and a dense crystalline germanium semiconductor can be formed with good uniformity. .
- the refractive index of the crystalline germanium semiconductor is higher than that of the flat electrode, and a denser crystalline germanium semiconductor can be formed.
- the hollow cathode electrode is an electrode having a cylindrical or rectangular parallelepiped depression on the surface.
- the size of the recess is an aspect ratio in which the diameter (a) is 0.1 mm to 10 mm, the depth (b) is 0.1 mm to several tens of mm, and the ratio of depth to diameter (b / a). Is preferably 0.2 to 5, and more preferably 0.5 to 2.
- one side of the recess is 0.1 mm to 10 mm
- the depth (b) is 0.1 mm to several tens of mm
- the aspect ratio is the ratio of one side to the depth of 0.2 to 5.
- 0.5 to 2 is more desirable.
- the pit has a relatively large aspect ratio of 0.2 to 5, the electron density of the plasma is increased in the dent, and plasma is likely to be generated. The plasma is stable even when the ES is 12 mm or less. Occur between.
- the aspect ratio is more preferably 2 or less, and more preferably 0.5 or more in order to increase the electron density.
- a plurality of hollows of hollow cathode type electrodes are arranged uniformly over almost the entire surface of the high-frequency electrode facing the substrate.
- the hollow cathode electrode also serves as a shower plate
- there may be a gas supply hole in the hollow of the hollow cathode or there may be a gas supply hole at a position different from the hollow of the hollow cathode. . It is desirable to dispose the gas supply hole in the hollow of the hollow cathode because it is easy to process and the number of the recesses and gas supply holes per unit area can be increased.
- the high-frequency plasma forming the crystalline germanium semiconductor has a Ge atomic emission peak having a peak at a wavelength of 265 nm ⁇ 2 nm and a peak at 304 nm ⁇ 2 nm due to excited germanium atoms (Ge *) in its emission spectrum. Desirably none of the peaks are detected. It is considered that Ge atoms, which are active species having high reactivity, cause a chain reaction as shown in Formula (2) with GeH 4 as a source gas in plasma to generate a polymer or cluster containing a plurality of Ge atoms.
- FIG. 32 shows a conceptual diagram of an example of an apparatus for measuring an emission spectrum.
- a quartz glass window 20 is attached to the above-described plasma CVD apparatus, plasma emission is condensed by a quartz lens 21, guided to an optical fiber 22, and an emission spectrum is obtained by a spectrometer 23. Since the emission peak of Ge atoms is the wavelength of ultraviolet light, it is desirable that the window 20, the lens 21 and the optical fiber 22 are made of quartz so as to transmit ultraviolet light.
- a fiber multichannel spectroscope USB4000 manufactured by Ocean Optics was used as the spectroscope 23.
- the measurable wavelength range is 200 to 850 nm.
- FIG. 33 and 34 show emission spectra when a Ge atom emission peak is detected (Example 12 described later) and when a Ge atom emission peak is not detected (Examples 13 and 14 described later).
- FIG. 33 shows the spectrum of the entire wavelength region (200 to 850 nm) measured. In each of Examples 12, 13, and 14, a peak of H ⁇ due to a hydrogen atom is visible. In addition, many peaks due to hydrogen molecules are observed. Only in Example 12, a Ge atom emission peak is observed at a position indicated as Ge *.
- FIG. 34 shows a spectrum obtained by enlarging the wavelength near the Ge atomic emission peak and further subtracting the baseline. The base line used was a straight line connecting the wavelength 255 nm as the start point and 315 nm as the end point.
- Example 12 Ge atomic emission peaks are clearly recognized at wavelengths of 265 nm and 304 nm. In either case, the half width is about 2.5 nm. In contrast, in Examples 13 and 14, no Ge atomic emission peak was detected.
- the fact that the Ge atomic emission peak defined in the present application is not detected means that no signal other than the noise level is detected in the spectrum obtained by subtracting the baseline at any wavelength of 265 nm ⁇ 2 nm and 304 nm ⁇ 2 nm. .
- the present application indicates that only a peak having a half-value width of 1 nm or less is detected at any wavelength of 265 nm ⁇ 2 nm and 304 nm ⁇ 2 nm.
- the substrate temperature when forming the crystalline germanium photoelectric conversion layer is preferably 200 ° C. or higher in order to suppress the generation of powder during film formation. Since the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 can be easily less than 6000 cm -1, the substrate temperature may be more desirable than 250 ° C.. In order to suppress the diffusion of impurities from the conductive layer to the photoelectric conversion layer, the substrate temperature is desirably 500 ° C. or less, and more desirably 400 ° C. or less.
- the pressure at the time of forming the crystalline germanium photoelectric conversion layer is preferably 40 Pa or more and 2000 Pa or less because of good crystallinity. Moreover, 200 Pa or more and 1500 Pa or less are more preferable in order to improve the uniformity of a large area. Furthermore, 800 Pa or more and 1330 Pa or less is more preferable for achieving both crystallinity and a high film forming speed. As shown in FIGS. 37 and 38, which will be described later, it is preferable because Jsc of the photoelectric conversion device is a high value of 35 mA / cm 2 or more at 800 Pa or more. Since Eff shows a high value of 5.8% or more, 800 Pa or more and 1330 Pa or less is more preferable. Since Eff is 6% or more, 850 Pa or more and 1000 Pa or less is more preferable.
- the back electrode layer 6 it is preferable to form at least one metal layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr by sputtering or vapor deposition. Between the photoelectric conversion unit and the metal layer, ITO, may be formed a layer made of SnO 2, conductive oxides such as ZnO (not shown).
- FIG. 3 is a cross-sectional view schematically showing a three-junction thin film photoelectric conversion device according to another embodiment of the present invention.
- an amorphous silicon photoelectric conversion unit and a crystalline silicon photoelectric conversion unit are sequentially arranged between the transparent electrode layer 2 and the crystalline germanium photoelectric conversion unit 3 of the single junction thin film photoelectric conversion device of FIG. It has a structure. That is, in order from the light incident side, the amorphous silicon photoelectric conversion unit corresponds to the top cell, the crystalline silicon photoelectric conversion unit corresponds to the middle cell, and the crystalline germanium photoelectric conversion unit corresponds to the bottom cell.
- the substrate, the transparent electrode layer, the crystalline germanium photoelectric conversion unit as the bottom cell, and the back electrode layer can be formed by the same configuration and manufacturing method as in FIG.
- the amorphous silicon photoelectric conversion unit 4 which is a top cell is formed by laminating, for example, a p-type layer, an i-type layer, and an n-type layer in this order by a plasma CVD method. Specifically, p-type amorphous silicon carbide layer 41 doped with 0.01 atomic% or more of boron, photoelectric conversion layer 42 of substantially i-type amorphous silicon, and 0.01 atomic% of phosphorus. The n-type microcrystalline silicon layer 43 thus doped is deposited in this order.
- the crystalline silicon photoelectric conversion unit 5 which is a middle cell is formed by stacking, for example, a p-type layer, an i-type layer, and an n-type layer in this order by a plasma CVD method. Specifically, p-type microcrystalline silicon layer 51 doped with boron by 0.01 atomic% or more, substantially i-type crystalline silicon photoelectric conversion layer 52, and phosphorus doped by 0.01 atomic% or more. An n-type microcrystalline silicon layer 53 is deposited in this order.
- FIG. 3 shows a three-junction thin film photoelectric conversion device, if a crystalline germanium photoelectric conversion unit is arranged in the photoelectric conversion unit farthest from the light incident side, two or more junction photoelectric conversion units are stacked. Needless to say, the thin film photoelectric conversion device may be used.
- FIG. 1 shows a thin film photoelectric conversion device in which light is incident from the substrate side
- the present invention is also effective in a thin film photoelectric conversion device in which light is incident from the opposite side of the substrate.
- the substrate, the back electrode layer, the crystalline germanium photoelectric conversion unit, and the transparent electrode layer may be stacked in this order.
- the crystalline germanium photoelectric conversion unit is preferably laminated in the order of the n-type layer, the crystalline germanium photoelectric conversion layer, and the p-type layer.
- the present invention is also effective in an integrated thin film photoelectric conversion device in which a series connection structure is formed on the same substrate using laser patterning.
- laser patterning can be easily performed. Therefore, a structure in which light is incident from the substrate side as shown in FIG. 1 is desirable.
- Example 1 As Example 1, a single-junction thin-film photoelectric conversion device 7 having the structure shown in FIG. As the transparent substrate 1, a glass substrate having a thickness of 0.7 mm was used. On the transparent substrate 1, a SnO 2 film including minute pyramidal surface irregularities and having an average thickness of 700 nm was formed by a thermal CVD method. Further, an Al-doped ZnO film having a thickness of 20 nm was formed by sputtering to produce a transparent electrode layer 2 in which SnO 2 and ZnO were laminated. The sheet resistance of the obtained transparent electrode layer 2 was about 9 ⁇ / ⁇ . The haze ratio measured with a C light source was 12%, and the average height difference d of the surface irregularities was about 100 nm. The haze ratio was measured based on JISK7136.
- a crystalline germanium photoelectric conversion unit 3 was produced on the transparent electrode layer 2 using a capacitively coupled high-frequency plasma CVD apparatus having parallel plate electrodes having a frequency of 13.56 MHz, whose conceptual diagram is shown in FIG. .
- SiH 4 , H 2, and B 2 H 6 are introduced as reaction gases to form a p-type microcrystalline silicon layer 31 having a thickness of 10 nm
- GeH 4 and H 2 are introduced as reaction gases to form a crystalline germanium photoelectric conversion layer 32 having a thickness of 2.0 ⁇ m.
- the flow rate ratio of H 2 / GeH 4 was 2000 times, the substrate temperature was 300 ° C., the pressure was 800 Pa, and the high frequency power density was 300 mW / cm 2 .
- the electrode spacing (ES) was 12 mm. Thereafter, SiH 4 , H 2 and PH 3 were introduced as reaction gases to form an n-type microcrystalline silicon layer 53 having a thickness of 15 nm, thereby forming a crystalline germanium photoelectric conversion unit 3.
- a crystalline germanium layer was formed on the glass substrate under the same conditions as described above, and the absorption coefficient at a wavelength of 1300 nm measured from a transmission spectrum and a reflection spectrum was 8300 cm ⁇ 1 , indicating a high absorption coefficient for long-wavelength light. Further, an X-ray diffraction spectrum measured by the ⁇ -2 ⁇ method is shown in FIG. Sharp peaks of (111), (220), (311) orientation are observed and it can be seen that they are crystallized. The (220) peak intensity was the strongest, and the peak intensity ratio of (220) / (111) was 13. The crystal grain size determined from the (220) half width of the peak was 63 nm. The Raman scattering spectrum is shown in FIG.
- a sharp peak of the TO mode of crystalline Ge—Ge bond is observed in the vicinity of 300 cm ⁇ 1, indicating that it is crystallized.
- the Hall effect was measured, the crystalline germanium layer was weak n-type, the carrier density was 1.9 ⁇ 10 16 cm ⁇ 3 , and the mobility was 3.0 cm 2 / (V ⁇ s). .
- the refractive index with respect to light having a wavelength of 600 nm measured by spectroscopic ellipsometry was 4.62.
- FIG. 6 shows an infrared absorption spectrum measured by FTIR after forming a crystalline germanium layer on the crystalline silicon substrate under the same conditions as the above thin film photoelectric conversion device.
- 560cm -1, 755cm -1, 860cm -1 , 935cm -1 is observed peak or shoulder of absorption to 960cm -1.
- 560 cm -1 is Ge-H bonds
- 860 cm -1 is derived from (Ge-O-Ge) n bond.
- 755cm -1, 935cm -1 the absorption peak of 960 cm -1 has not been identified.
- 935cm -1 respective absorption coefficient absorption peak at 960 cm -1 is 2000 cm -1, it was 1250 cm -1.
- an Al-doped ZnO film having a thickness of 30 nm and an Ag film having a thickness of 300 nm were sequentially formed by a sputtering method.
- the film formed on the SnO 2 film 2 is partially removed by laser scribing and separated into a size of 1 cm 2 , and a single junction thin film photoelectric conversion device 7 (light receiving area) 1 cm 2 ) was produced.
- the output characteristics were measured by irradiating the single-junction thin-film photoelectric conversion device 7 (light-receiving area 1 cm 2 ) obtained as described above with light of AM 1.5 at a light amount of 100 mW / cm 2 , the implementation shown in Table 1 was performed.
- the open circuit voltage (Voc) is 0.270 V
- the short circuit current density (Jsc) is 34.4 mA / cm 2
- the fill factor (FF) is 0.58
- the conversion efficiency (Eff) is 5. 4%.
- the quantum efficiency at a wavelength of 1300 nm was 10%.
- Comparative Example 1 As Comparative Example 1, a single-junction thin film photoelectric conversion device similar to Example 1 was produced. Comparative Example 1 was produced in the same manner as Example 1 except that the crystalline germanium photoelectric conversion layer of FIG. 1 was formed at 200 ° C.
- the absorption coefficient at a wavelength of 1300 nm measured in the same manner as in Example 1 was 5000 cm ⁇ 1 , indicating a high absorption coefficient for long wavelength light. Further, an X-ray diffraction spectrum measured by the ⁇ -2 ⁇ method is shown in FIG. Peaks of (111), (220), and (311) orientations are observed, indicating that crystallization has occurred. In Comparative Example 1, the difference in intensity between the peaks was small, and the peak intensity ratio of (220) / (111) was 1.8. The crystal grain size determined from the (220) peak half width was 41 nm. The Raman scattering spectrum is shown in FIG.
- a sharp peak of the TO mode of crystalline Ge—Ge bond is observed in the vicinity of 300 cm ⁇ 1, indicating that it is crystallized.
- the crystalline germanium layer was weak n-type, the carrier density was 3.2 ⁇ 10 16 cm ⁇ 3 , and the mobility was 1.3 cm 2 / (V ⁇ s). .
- the refractive index for light having a wavelength of 600 nm measured by spectroscopic ellipsometry was 3.67.
- FIG. 7 shows an infrared absorption spectrum measured by FTIR after forming a crystalline germanium layer on the crystalline silicon substrate under the same conditions as the above thin film photoelectric conversion device.
- Wave number of 560cm -1, 755cm -1, 860cm -1 , 935cm -1 is observed peak of absorption to 960cm -1.
- Wavenumber 935cm -1 the absorption peak of each absorption coefficient of 960 cm -1 was 8400cm -1, 5130cm -1.
- Example 1 is improved in all parameters, and in particular, Jsc shows a large value exceeding 30 mA / cm 2 . Moreover, it is shown that the quantum efficiency with respect to 1300 nm long wavelength light of Example 1 reaches 10%, and the use of long wavelength light is possible.
- the crystalline germanium layers of Comparative Example 1 and Example 1 do not show a large difference in Raman scattering spectra. However, of the infrared absorption peaks, the peaks at 935 cm ⁇ 1 and 960 cm ⁇ 1 are smaller than half in Example 1 compared to Comparative Example 1.
- Example 1 has suppressed the generation of clusters, polymers, or germanium oxide, and the characteristics of the thin film photoelectric conversion device have been improved. Further, the X-ray diffraction spectrum of Example 1 shows a large value in which the (220) / (111) beak intensity ratio exceeds 10, and it can be said that large crystal grains have grown in the film thickness direction. It is considered that Jsc showed a high value exceeding 30 mA / cm 2 .
- Example 2 As Example 2, a single-junction thin film photoelectric conversion device similar to Example 1 was produced. Example 2 was produced in the same manner as in Example 1 except that the crystalline germanium photoelectric conversion layer of FIG. 1 was formed at 400 ° C.
- the absorption coefficient at a wavelength of 1300 nm measured in the same manner as in Example 1 was 16200 cm ⁇ 1 , indicating a high absorption coefficient for long wavelength light.
- An X-ray diffraction spectrum is shown in FIG. In the X-ray diffraction spectrum, a particularly strong peak was observed in the (220) orientation, indicating that it was crystallized. The peak intensity ratio of (220) / (111) was 91. The crystal grain size determined from the (220) peak half width was 51 nm.
- the Raman scattering spectrum is shown in FIG. A sharp peak of the TO mode of crystalline Ge—Ge bond is observed in the vicinity of 300 cm ⁇ 1, indicating that it is crystallized.
- Example 2 (Summary of Examples 1 and 2 and Comparative Example 1)
- the infrared absorption peaks of 935 cm ⁇ 1 and 960 cm ⁇ 1 were not observed, the long-wavelength quantum efficiency showed a high value exceeding 10%, and Jsc showed a high value exceeding 30 mA / cm 2 .
- the reason why Eff is slightly lower than that in Example 1 is considered to be that impurities are diffused between the p-type layer and the crystalline germanium layer due to a decrease in Voc and FF due to a high film-forming temperature.
- the Raman scattering spectra of the crystalline germanium layer are crystallized in Examples 1 and 2 and Comparative Example 1, and no significant difference is observed.
- Example 3 As Example 3, a single-junction thin film photoelectric conversion device similar to Example 1 was produced.
- the crystalline germanium photoelectric conversion layer of FIG. 1 was (1) formed at 200 ° C., (2) the H 2 / GeH 4 flow rate ratio was 500 times, and (3) high frequency power density was It was produced in the same manner as in Example 1 except for 3 points of 1100 mW / cm 2 .
- the absorption coefficient at a wavelength of 1300 nm measured in the same manner as in Example 1 was 8700 cm ⁇ 1 , indicating a high absorption coefficient for long wavelength light.
- peaks of (111), (220), and (311) orientation were observed, and it was found that crystallization occurred.
- the peak intensity ratio of (220) / (111) was 2.5.
- the crystal grain size determined from the (220) peak half width was 40 nm.
- a sharp peak of TO mode of crystalline Ge—Ge bond was observed near 300 cm ⁇ 1 , indicating that it was crystallized.
- Comparative Example 2 As Comparative Example 2, a single-junction thin-film photoelectric conversion device similar to Example 3 was produced. Comparative Example 2 was produced in the same manner as Example 3 except that the crystalline germanium photoelectric conversion layer in FIG. 1 was set to a high frequency power density of 300 mW / cm 2 .
- the absorption coefficient at a wavelength of 1300 nm measured in the same manner as in Example 1 was 640 cm ⁇ 1 , and the absorption coefficient of long wavelength light in Comparative Example 2 was lower by one digit or more than that in Example 3.
- the peaks (111), (220), and (311) were observed, indicating that the film was amorphous.
- the peak intensity ratio of (220) / (111) could not be measured.
- a gentle peak of the TO mode of amorphous Ge—Ge bond was observed in the vicinity of 280 cm ⁇ 1 , indicating that it was amorphous.
- Example 3 (Summary of Example 3 and Comparative Example 2)
- the absorption coefficient of the infrared absorption peak at a wave number of 935 cm ⁇ 1 was obtained by increasing the high frequency power density to 1100 mW / cm 2.
- the quantum efficiency at a wavelength of 1300 nm was 8.5%, which enabled the use of long wavelength light, and Jsc showed a high value exceeding 30 mA / cm 2 .
- Example 4 and 5 As Examples 4 and 5, single-junction thin film photoelectric conversion devices similar to Example 1 were produced.
- the crystalline germanium photoelectric conversion layer shown in FIG. 1 was prepared in the same manner as in Example 1 except that Example 4 was formed at 250 ° C. and Example 5 was formed at 350 ° C.
- the crystalline germanium layer was formed on the crystalline silicon substrate on the same conditions as the photoelectric converting layer of a thin film photoelectric conversion apparatus similarly to Example 1, and the infrared absorption spectrum was measured by FTIR.
- Example 1 shows the absorption coefficient of the infrared absorption peak with respect to the film formation temperature of the crystalline germanium photoelectric conversion layer and the characteristics of the photoelectric conversion device.
- the crystalline germanium photoelectric conversion layer wavenumber 755 cm -1 was measured by FTIR relative to a substrate temperature during film formation of, 860cm -1, 935cm -1, indicating the absorption coefficient of the peak of 960 cm -1.
- Wave number 755 cm -1 with increasing substrate temperature the absorption coefficient of the peak of 935cm -1, 960cm -1 monotonically decreases, less than 500 cm -1 at 350 ° C. or higher.
- the absorption coefficient of the peak of 935cm -1 becomes less than 6000 cm -1
- the absorption coefficient of the peak of 960 cm -1 becomes less than 4000 cm -1
- the absorption coefficient of the peak of 755 cm -1 is less than 1500 cm -1 It becomes.
- the absorption coefficient of the peak at 860 cm ⁇ 1 has a minimum value at 250 ° C., a maximum value at 300 ° C., and less than 500 cm ⁇ 1 at 350 ° C. or higher, as the substrate temperature increases.
- FIG. 12 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the substrate temperature when forming the crystalline germanium photoelectric conversion layer.
- Jsc and quantum efficiency increase rapidly from a substrate temperature of 200 ° C. to 250 ° C., and show a saturation tendency at a temperature higher than that.
- Jsc is 30 mA / cm 2 or more at a substrate temperature of 250 ° C. or higher, and the quantum efficiency at a wavelength of 1300 nm is a high value exceeding 5%.
- FIG. 13 shows the Eff of the thin film photoelectric conversion device with respect to the substrate temperature when forming the crystalline germanium photoelectric conversion layer. Eff shows a value of 3% or more at 250 ° C. or higher, and is maximum at 300 ° C.
- FIG. 14 shows the FF of the thin film photoelectric conversion device with respect to the substrate temperature when forming the crystalline germanium photoelectric conversion layer.
- the FF increases rapidly from the substrate temperature of 200 ° C. to 250 ° C., and shows a saturation tendency at a temperature higher than that.
- FIG. 15 shows Voc of the thin film photoelectric conversion device with respect to the substrate temperature at the time of forming the crystalline germanium photoelectric conversion layer. Voc becomes maximum at 300 ° C. with respect to the substrate temperature.
- the absorption coefficient of the infrared absorption peak at 935 cm ⁇ 1 at a substrate temperature of 250 ° C. or higher is less than 6000 cm ⁇ 1
- the Jsc is 30 mA / cm 2 or more
- the quantum efficiency at a wavelength of 1300 nm exceeds 5%. It can be seen that long-wavelength light can be used and the characteristics of the thin film photoelectric conversion device are improved.
- Example 6 As Examples 6, 7, and 8, single-junction thin film photoelectric conversion devices similar to Example 3 were produced.
- the crystalline germanium layer was formed on the crystalline silicon substrate on the same conditions as the photoelectric converting layer of a thin film photoelectric conversion apparatus similarly to Example 3, and the infrared absorption spectrum was measured by FTIR.
- Example 2 shows the absorption coefficient of the infrared absorption peak with respect to the high frequency power density of the crystalline germanium photoelectric conversion layer and the characteristics of the photoelectric conversion device.
- Figure 16 shows the absorption coefficient of the peak of the crystalline wavenumber 755 cm -1 was measured by FTIR the germanium photoelectric conversion layer relative to the RF power density during deposition, 860cm -1, 935cm -1, 960cm -1.
- the absorption coefficients of the peaks at wave numbers 755 cm ⁇ 1 , 935 cm ⁇ 1 , and 960 cm ⁇ 1 monotonously decrease as the high frequency power density increases.
- the absorption coefficient of the peak of 935cm -1 becomes less than 6000 cm -1
- the absorption coefficient of the peak of 960 cm -1 becomes less than 4000 cm -1
- the absorption coefficient of the peak of 755 cm -1 is 1500cm Less than -1 .
- the absorption coefficient of the peak at 860 cm ⁇ 1 has a maximum value at 550 mW / cm 2 with respect to the increase in high frequency power density.
- FIG. 17 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the high frequency power density when forming the crystalline germanium photoelectric conversion layer.
- the high-frequency power density increased from 300mW / cm 2 550mW / cm 2 increase Jsc and quantum efficiency abruptly when subjected, gradually increases at higher RF power density.
- a high frequency power density of 550 mW / cm 2 or higher indicates that Jsc is 30 mA / cm 2 or higher, and a quantum efficiency at a wavelength of 1300 nm exceeds 5%.
- FIG. 18 shows the Eff of the thin film photoelectric conversion device with respect to the high frequency power density when the crystalline germanium photoelectric conversion layer is formed. Eff shows a value of 3% or more at 550 mW / cm 2 or more, and becomes maximum at 1100 mW / cm 2 .
- FIG. 19 shows an FF of a thin film photoelectric conversion device with respect to a high frequency power density when a crystalline germanium photoelectric conversion layer is formed. FF increases rapidly over a high-frequency power density from 300 mW / cm 2 to 550 mW / cm 2, indicating a saturation tendency at higher RF power density.
- FIG. 20 shows Voc of the thin film photoelectric conversion device with respect to the high frequency power density at the time of forming the crystalline germanium photoelectric conversion layer. Voc is maximum at 1100 mW / cm 2 with respect to the high frequency power density.
- the absorption coefficient of the infrared absorption peak at 935 cm ⁇ 1 at a high frequency power density of 550 mW / cm 2 or less is less than 6000 cm ⁇ 1.
- the Jsc is 30 mA / cm 2 or more and the quantum efficiency at a wavelength of 1300 nm is 5% or more, so that long wavelength light can be used and the characteristics of the thin film photoelectric conversion device are improved.
- FIG. 21 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the absorption coefficient of the infrared absorption peak at a wave number of 935 cm ⁇ 1 .
- FIG. 22 shows the Eff of the thin film photoelectric conversion device with respect to the absorption coefficient of the infrared absorption peak at a wave number of 935 cm ⁇ 1 .
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 5000 cm -1, more preferable because Eff exceeds 3.5%.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 10 cm -1 or more 2500 cm -1, further preferably so Eff exceeds 4.5%.
- FIG. 23 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the absorption coefficient of the infrared absorption peak at a wave number of 960 cm ⁇ 1 .
- FIG. 24 shows the Eff of the thin film photoelectric conversion device with respect to the absorption coefficient of the infrared absorption peak at a wave number of 960 cm ⁇ 1 .
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 3000 cm -1, more preferable because Eff exceeds 3.5%.
- the absorption coefficient of the infrared absorption peak at a wavenumber of 935 ⁇ 5 cm -1 becomes less than 1300 cm -1, more preferable because Eff exceeds 4.5%.
- Examples 1 to 3 and Comparative Example 1 show photoelectric conversion characteristics of a thin film photoelectric conversion device with respect to a (220) / (111) peak intensity ratio measured by X-ray diffraction of a crystalline germanium photoelectric conversion layer.
- FIG. 25 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the (220) / (111) peak intensity ratio.
- the (220) / (111) peak intensity ratio is 2 or more
- Jsc shows a high value of 30 mA / cm 2 or more
- the quantum efficiency at a wavelength of 1300 nm shows a high value of 5% or more.
- FIG. 26 shows the Eff of the thin film photoelectric conversion device with respect to the (220) / (111) peak intensity ratio.
- the (220) / (111) peak intensity ratio is 2 or more, Eff shows a high value of 3% or more. It is more preferable that the (220) / (111) peak intensity ratio is 2.1 or more and 70 or less because Eff shows a high value of 4% or more.
- Example 9 As Example 9, a single-junction thin-film photoelectric conversion device 8 similar to Example 1 was produced.
- Example 9 is the same as Example 1 except that a substantially genuine crystalline silicon layer 34 is disposed between the p-type microcrystalline silicon layer 31 and the crystalline germanium photoelectric conversion layer 32 as shown in FIG. It produced similarly.
- the genuine crystalline silicon layer 34 was formed to a thickness of 100 nm by a high frequency plasma CVD method using SiH 4 and H 2 as reaction gases.
- Voc and FF are increased, and Eff is a high value of 6.0%. showed that. This is presumably because the crystallinity of the crystalline germanium photoelectric conversion layer was improved and / or defects at the interface between the p-type layer and the photoelectric conversion layer were reduced.
- Example 10 As Example 10, a single-junction thin film photoelectric conversion device similar to Example 9 was produced. Example 10 was produced in the same manner as Example 9 except that a substantially genuine crystalline silicon layer 35 was disposed between the crystalline germanium photoelectric conversion layer 32 and the n-type microcrystalline silicon layer 33. The genuine crystalline silicon layer 35 was formed to a thickness of 100 nm by a high frequency plasma CVD method using SiH 4 and H 2 as reaction gases.
- Example 11 As Example 11, a three-junction thin film photoelectric conversion device 9 shown in FIG. In Example 11, (1) an amorphous silicon photoelectric conversion unit 4 and a crystalline silicon photoelectric conversion unit 5 were sequentially disposed between the transparent electrode layer 2 and the crystalline germanium photoelectric conversion unit 3 of Example 1, ( 2) The crystalline germanium photoelectric conversion layer 32 was prepared in the same manner as in Example 1, except that the film thickness was 2.5 ⁇ m and (3) the transparent electrode layer 2 was composed of only SnO 2 . .
- An amorphous silicon photoelectric conversion unit 4 was produced on the transparent electrode layer 2 using a plasma CVD apparatus. SiH 4 , H 2 , CH 4 and B 2 H 6 are introduced as a reaction gas to form a p-type amorphous silicon carbide layer 41 having a thickness of 15 nm, and SiH 4 is introduced as a reaction gas to form an amorphous silicon photoelectric conversion layer 42.
- the amorphous silicon photoelectric conversion unit 3 was formed by forming 80 nm, and then introducing SiH 4 , H 2 and PH 3 as reaction gases to form an n-type microcrystalline silicon layer 43 having a thickness of 10 nm.
- SiH 4 , H 2 and B 2 H 6 are introduced as reaction gases to form a p-type microcrystalline silicon layer 51 having a thickness of 10 nm, and then SiH 4 and H 2 are introduced as reaction gases.
- the crystalline silicon photoelectric conversion layer 52 is formed to a thickness of 1.5 ⁇ m, and then SiH 4 , H 2 and PH 3 are introduced as reaction gases to form an n-type microcrystalline silicon layer 53 having a thickness of 15 nm. Formed.
- the crystalline germanium photoelectric conversion unit 3 and the back electrode layer 6 were sequentially formed.
- the open circuit voltage (Voc) was measured.
- the short circuit current density (Jsc) was 11.5 mA / cm 2
- the fill factor (FF) was 0.71
- the conversion efficiency (Eff) was 14.0%.
- the quantum efficiency at a wavelength of 1300 nm was 10.1%.
- Example 12 When the crystalline germanium photoelectric conversion layer of Example 12 was formed, an emission spectrum was measured with a measuring apparatus shown in FIG. 33 and 34 show the emission spectrum. Ge atomic emission peaks were clearly observed at wavelengths of 265 nm and 304 nm.
- Example 13 As Example 13, a single-junction thin film photoelectric conversion device similar to Example 12 was produced. Example 13 was produced in the same manner as Example 12 except that when the crystalline germanium photoelectric conversion layer was formed, the electrode spacing ES was 12 mm. Further, the infrared absorption coefficient and refractive index are shown in Table 3 as in Example 12.
- Example 13 emission spectral spectra measured in the same manner as in Example 12 are shown in FIGS.
- Example 13 unlike Example 12, only noise level peaks were measured at wavelengths of 265 nm and 304 nm, and no Ge atomic emission peak was detected.
- Example 14 emission spectral spectra measured in the same manner as in Example 12 are shown in FIGS.
- the emission spectroscopy is measured after changing ES to 15 mm.
- Example 14 unlike Example 12, only noise level peaks were measured at wavelengths of 265 nm and 304 nm, and no Ge atomic emission peak was detected.
- Example 12 (Summary of Examples 12, 13, and 14) In Example 12, a Ge atomic emission peak was detected, the quantum efficiency of long-wavelength light was 9.5%, and Jsc was 33.5 mA / cm 2 . In contrast, in Example 13, no Ge atomic emission peak was detected, the quantum efficiency of long-wavelength light was improved to 11%, and Jsc was improved to 34.9 mA / cm 2 . In Example 13, since the Ge atom emission peak was not detected, it can be seen that the density of highly reactive Ge atoms is low. Therefore, it can be said that the chain reaction as shown in Formula 2 hardly occurs and the generation of polymers and clusters is suppressed, and a dense crystalline germanium semiconductor is formed and the characteristics of the thin film photoelectric conversion device are improved.
- Example 14 The film forming conditions of Examples 12 and 13 are different for ES of 15 mm and 12 mm, respectively.
- Example 15 As Examples 15, 16, and 17, single junction thin film photoelectric conversion devices similar to Example 12 were produced.
- the crystalline germanium photoelectric conversion layer of FIG. 1 was formed in the same manner as in Example 12 except that the ES was 9 mm in Example 15, 7.5 mm in Example 16, and 6.5 mm in Example 17. It was prepared. Further, the infrared absorption coefficient, refractive index, and characteristics of the thin film photoelectric conversion device are shown in Table 3 as in Example 12.
- Table 3 shows the absorption coefficient of the infrared absorption peak with respect to ES of the crystalline germanium photoelectric conversion layer, the refractive index at a wavelength of 600 nm, and the characteristics of the photoelectric conversion device.
- FIG. 35 shows the Jsc of a thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to ES when a crystalline germanium photoelectric conversion layer is formed.
- ES is decreased from 15 mm to 6.5 mm, Jsc and quantum efficiency increase monotonously.
- ES is 12 mm or less, Jsc is about 35 mA / cm 2 or more, and the quantum efficiency at a wavelength of 1300 nm exceeds 10%.
- the quantum efficiency at a wavelength of 1300 nm increases rapidly.
- FIG. 36 shows Eff of the thin film photoelectric conversion device with respect to ES at the time of forming the crystalline germanium photoelectric conversion layer. Eff increases with decreasing ES, and Eff shows a value of 5.5% or more when ES is 12 m or less. Further, when ES is 7.5 mm or less, Eff further increases.
- Example 18 As Example 18, a single-junction thin film photoelectric conversion device similar to Example 16 was produced. Example 18 was produced in the same manner as in Example 16 except that a plasma CVD apparatus provided with a hollow cathode electrode shown in FIG. 31 was used when the crystalline germanium photoelectric conversion layer was formed.
- the hollow of the hollow cathode had a diameter of 3 mm ⁇ , a depth of 3 mm, and a plurality of depressions with a pitch of 5 mm.
- a gas introduction hole was provided at the center of the recess.
- the infrared absorption coefficient, refractive index, and characteristics of the thin film photoelectric conversion device are shown in Table 3 as in Example 12.
- Example 18 As shown in Table 3, the infrared absorption coefficient of Example 18 was not much different from that of Example 16. On the other hand, the refractive index of Example 18 is as high as 5.38 compared with 5.01 of Example 16. The uniformity of the film thickness distribution was ⁇ 7% in Example 16, whereas it was ⁇ 4% in Example 18.
- Example 19 to 23 As Examples 19 to 23, single-junction thin film photoelectric conversion devices similar to Example 16 were produced.
- the crystalline germanium photoelectric conversion layer of FIG. 1 was formed at a pressure of 670 Pa in Example 19, 850 Pa in Example 20, 930 Pa in Example 21, 1000 Pa in Example 22, and 1330 Pa in Example 23. Except for, it was produced in the same manner as in Example 16.
- Table 4 shows the infrared absorption coefficient, refractive index, and characteristics of the thin film photoelectric conversion device.
- FIG. 37 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency at a wavelength of 1300 nm with respect to the pressure at the time of forming the crystalline germanium photoelectric conversion layer.
- Jsc increases and is almost saturated at a pressure of 800 Pa or higher.
- the quantum efficiency also increases with increasing pressure and then saturates.
- Jsc is 35 mA / cm 2 or more at a pressure of 800 Pa, and the quantum efficiency at a wavelength of 1300 nm is more than 10%.
- FIG. 38 shows Eff of the thin film photoelectric conversion device with respect to the pressure at the time of forming the crystalline germanium photoelectric conversion layer. As the pressure increases, Eff increases, shows a maximum value at 850 Pa, and then gradually decreases. Eff shows a high value of 5.9% or more in a pressure range of 800 Pa to 1330 Pa, and Eff shows a high value of 6.1% at a pressure of 850 Pa.
- the pressure during film formation of the crystalline germanium photoelectric conversion layer is preferably 800 Pa or more from FIGS.
- the upper limit of the pressure is desirably 2000 Pa or less for increasing the crystallinity, more desirably 1500 Pa or less for increasing the uniformity, and more desirably 1330 Pa or less from FIGS.
- Example 24 As Example 24, a single-junction thin film photoelectric conversion device similar to Example 1 was produced, and the characteristics of the thin film photoelectric conversion device with respect to the refractive index at a wavelength of 600 nm were examined.
- the crystalline germanium photoelectric conversion layer shown in FIG. 1 is formed under the following conditions: substrate temperature 200 to 300 ° C., high frequency power density 300 to 1400 mW / cm 2 , H 2 / GeH 4 flow rate ratio 500 to 2000 times, ES
- a large number of thin-film photoelectric conversion devices having a thickness of 6.5 to 15 mm and a pressure of 670 to 1330 Pa were manufactured. Any of the photoelectric conversion device also infrared absorption coefficient of the peak of 935cm -1 is less than 6000 cm -1, infrared absorption coefficient of the peak of 960 cm -1 is less than 4000 cm -1.
- FIG. 39 shows the Jsc of the thin film photoelectric conversion device and the quantum efficiency of 1300 nm wavelength with respect to the refractive index of 600 nm wavelength of the crystalline germanium photoelectric conversion layer.
- the data of Comparative Examples 1 and 2 are also shown as comparative examples in the figure.
- the quantum efficiency of long-wavelength light which was 1% or less, is increased to 5% or more when the refractive index is 4.0 or more.
- Jsc also increases.
- Jsc shows a high value of 30 mA / cm 2 or higher.
- Jsc is 35 mA / cm 2 . An even higher value is shown.
- FIG. 40 shows the Eff of the thin film photoelectric conversion device with respect to the refractive index of the crystalline germanium photoelectric conversion layer having a wavelength of 600 nm.
- the data of Comparative Examples 1 and 2 are also shown as comparative examples in the figure.
- Eff increases.
- Eff shows a value of 3.0% or more.
- Eff shows a saturation tendency by setting the refractive index to 4.7 or more.
- Eff is stable and shows a high value of 5.5% or more.
- Figure 41 a single-junction using the crystalline germanium photoelectric conversion layer for Eff of the photoelectric conversion device, the absorption coefficient of 935cm -1 due to the FTIR of the crystalline germanium photoelectric conversion layer ( ⁇ @ 935cm -1), and the wavelength of 600nm
- the refractive index (n) with respect to light is shown.
- the infrared absorption spectrum has a large variation and it is difficult to judge the quality.
- the refractive index has a good correlation, and the quality of the crystalline germanium semiconductor is judged. It turns out that it is suitable as a parameter
- the refractive index is preferably 4.0 or more, more preferably 4.7 or more, and further preferably 4.9 or more. However, if the refractive index exceeds 5.6, the refractive index is higher than that of single crystal germanium, and there is a concern about impurity contamination by heavy metals. Therefore, the refractive index is preferably 5.6 or less.
Abstract
Description
非特許文献1に、光電変換層に弱n型微結晶ゲルマニウムを用いた単接合の薄膜光電変換装置が開示されている。薄膜光電変換装置の構造は、ステンレス基板/n型非晶質シリコン/i型非晶質シリコン/微結晶シリコンゲルマニウムの組成傾斜層/弱n型微結晶ゲルマニウム光電変換層/微結晶シリコンゲルマニウムの組成傾斜層/p型微結晶シリコン層/ITOを順次積層した構造である。薄膜光電変換装置の特性は開放電圧Voc=0.22V、短絡電流密度Jsc=25mA/cm2、曲線因子FF=0.36、変換効率Eff=2.0%、長波長側で量子効率が10%となる波長は約1080nm、量子効率が5%となる波長は1130nmである。微結晶ゲルマニウム光電変換層はマイクロ波放電を用いたECRリモートプラズマCVD法で形成している。
非特許文献2に、光電変換層にGe組成0%から最大35%までの微結晶シリコンゲルマニウムを用いた単接合の薄膜光電変換装置が開示されている。具体的には、薄膜光電変換装置の構造は、ガラス基板/凹凸ZnO/p型微結晶シリコン/i型微結晶シリコンゲルマニウムの光電変換層/n型微結晶シリコン層/ZnO/Agを順次積層したの構造である。薄膜光電変換装置の特性は、微結晶シリコンゲルマニウムの膜中Ge濃度20%でJsc、Effが最大となり、Voc=0.427V、Jsc=24.1mA/cm2、FF=0.616、Eff=6.33%を示す。膜中Ge組成を20%以上に増加するとVoc、Jsc、FFがいずれも低下してEffが低下する。特に膜中Ge濃度を30%以上にするとFFが著しく低下し、Ge濃度35%ではFFが約0.4となり、Effが約2%と低くなる。また、量子効率が10%となる波長はGe濃度が最大の35%の場合でも約1050nmである。
Ge2Hx+GeH4→Ge3Hy
Ge3Hy+GeH4→Ge4Hz
・・・式(2)
Ge原子発光ピークが検出されないと、反応性が高い活性種であるGe原子が少ないことがわかり、プラズマ中でのポリマーやクラスターの発生が抑制されて、緻密な結晶質ゲルマニウム半導体が形成されて光電変換装置の特性が向上する。
実施例1として、図1に示す構造の単接合の薄膜光電変換装置7を作製した。透明基板1は、厚さ0.7mmのガラス基板を用いた。透明基板1の上に、微小なピラミッド状の表面凹凸を含みかつ平均厚さ700nmのSnO2膜が熱CVD法にて形成された。さらにスパッタ法でAlドープされたZnO膜を20nm形成し、SnO2とZnOが積層した透明電極層2を作製した。得られた透明電極層2のシート抵抗は約9Ω/□であった。またC光源で測定したヘイズ率は12%であり、表面凹凸の平均高低差dは約100nmであった。ヘイズ率はJISK7136に基づき測定した。
比較例1として、実施例1に類似の単接合の薄膜光電変換装置を作製した。比較例1は、図1の結晶質ゲルマニウム光電変換層を200℃で形成したことを除いて、実施例1と同様に作製した。
比較例1に対して、実施例1はすべてのパラメータで向上しており、特にJscは30mA/cm2を超える大きな値を示している。また、実施例1の1300nmの長波長光に対する量子効率が10%に達し、長波長光の利用が可能であることが示されている。比較例1と実施例1の結晶質ゲルマニウム層は、ラマン散乱スペクトルに大きな差は見られない。しかし、赤外線吸収ピークのうち935cm-1と960cm-1のピークが、比較例1に比べて実施例1で半分以下に小さくなっている。このため、実施例1の結晶質ゲルマニウム光電変換層は、クラスターまたはポリマーあるいは酸化ゲルマニウムの発生が抑制されていると考えられ、薄膜光電変換装置の特性が向上したといえる。また、実施例1のX線回折スペクトルは(220)/(111)のビーク強度比が10を超える大きな値を示し、膜厚方向に柱状に大きな結晶粒が成長したといえ、発電電流が流れやすくなって、Jscが30mA/cm2を超える高い値を示したと考えられる。
実施例2として、実施例1に類似の単接合の薄膜光電変換装置を作製した。実施例2は、図1の結晶質ゲルマニウム光電変換層を400℃で形成したことを除いて、実施例1と同様に作製した。
実施例2は赤外線の935cm-1および960cm-1の吸収ピークが観察されず、長波長の量子効率は10%を超える高い値を示し、Jscは30mA/cm2を超える高い値を示した。実施例1よりEffがやや低いのはVoc、FFの減少により、高い製膜温度によってp型層と結晶質ゲルマニウム層との間で不純物の拡散が起こったためと考えられる。結晶質ゲルマニウム層のラマン散乱スペクトルは、実施例1、2、比較例1ともに結晶化しており、顕著な差は認められない。これに対して、935cm-1と960cm-1の赤外線吸収ピーク、X線回折の(220)/(111)ピーク強度比は顕著な差が見られ、結晶質ゲルマニウム半導体の良否の判定の指標として有効であることが見出された。また、結晶質ゲルマニウム半導体は形成温度が200℃である場合に比べて、300℃と400℃の場合に波数935cm-1と960cm-1の吸収係数が低くなり、薄膜光電変換装置の特性が高くなるといえる。
実施例3として、実施例1に類似の単接合の薄膜光電変換装置を作製した。実施例3は、図1の結晶質ゲルマニウム光電変換層を(1)200℃で形成したこと、(2)H2/GeH4の流量比を500倍としたこと、(3)高周波パワー密度を1100mW/cm2としたことの3点を除いて、実施例1と同様に作製した。
比較例2として、実施例3に類似の単接合の薄膜光電変換装置を作製した。比較例2は、図1の結晶質ゲルマニウム光電変換層を高周波パワー密度300mW/cm2としたことを除いて、実施例3と同様に作製した。
実施例3は、結晶質ゲルマニウムを200℃の低い基板温度で作製しているにもかかわらず、高周波パワー密度を1100mW/cm2と高くすることにより、波数935cm-1の赤外線吸収ピークの吸収係数が6000cm-1未満となり、薄膜光電変換装置の特性が高くなった。波長1300nmの量子効率は8.5%となり、長波長光の利用が可能となり、Jscは30mA/cm2を超える高い値を示した。
実施例4、5として、実施例1に類似の単接合の薄膜光電変換装置を作製した。図1の結晶質ゲルマニウム光電変換層を実施例4は250℃、実施例5は350℃で形成したことを除いて、実施例1と同様に作製した。また、実施例1と同様に薄膜光電変換装置の光電変換層と同一の条件で結晶シリコン基板上に結晶質ゲルマニウム層を形成し、FTIRにより赤外線吸収スペクトルを測定した。
実施例1、2、4、5、比較例1について、結晶質ゲルマニウム光電変換層の製膜温度に対する赤外吸収ピークの吸収係数および光電変換装置の特性を表1に示す。
実施例6、7、8として、実施例3に類似の単接合の薄膜光電変換装置を作製した。図1の結晶質ゲルマニウム光電変換層を製膜時の高周波パワー密度を実施例6は550mW/cm2、実施例7は850mW/cm2、実施例8は1400mW/cm2で形成したことを除いて、実施例3と同様に作製した。また、実施例3と同様に薄膜光電変換装置の光電変換層と同一の条件で結晶シリコン基板上に結晶質ゲルマニウム層を形成し、FTIRにより赤外線吸収スペクトルを測定した。
実施例3、6、7,8、比較例2について、結晶質ゲルマニウム光電変換層の高周波パワー密度に対する赤外吸収ピークの吸収係数および光電変換装置の特性を表2に示す。
実施例1~8、比較例1、2について、結晶質ゲルマニウム光電変換層の波数935cm-1の赤外吸収ピークの吸収係数に対する光電変換特性を示す。
実施例1~3、比較例1について、結晶質ゲルマニウム光電変換層のX線回折で測定した(220)/(111)ピーク強度比に対する薄膜光電変換装置の光電変換特性を示す。
実施例9として、実施例1に類似の単接合の薄膜光電変換装置8を作製した。実施例9は、図2に示すようにp型微結晶シリコン層31と結晶質ゲルマニウム光電変換層32の間に実質的に真正な結晶質シリコン層34を配置したことを除いて、実施例1と同様に作製した。真正な結晶質シリコン層34は反応ガスとしてSiH4、H2を用いて、高周波プラズマCVD法で膜厚100nm形成した。
実施例10として、実施例9に類似の単接合の薄膜光電変換装置を作製した。実施例10は、結晶質ゲルマニウム光電変換層32とn型微結晶シリコン層33の間に実質的に真正な結晶質シリコン層35を配置したことを除いて、実施例9と同様に作製した。真正な結晶質シリコン層35は反応ガスとしてSiH4、H2を用いて、高周波プラズマCVD法で膜厚100nm形成した。
実施例11として、図3に示す3接合の薄膜光電変換装置9を作製した。実施例11は、(1)実施例1の透明電極層2と結晶質ゲルマニウム光電変換ユニット3の間に非晶質シリコン光電変換ユニット4と結晶質シリコン光電変換ユニット5を順次配置したこと、(2)結晶質ゲルマニウム光電変換層32の膜厚を2.5μmとしたこと、(3)透明電極層2をSnO2だけから構成したことの3点を除いて、実施例1と同様に作製した。
実施例12として、実施例1に類似の単接合の薄膜光電変換装置を作製した。実施例12は、図1の結晶質ゲルマニウム光電変換層を(1)電極間隔ES=15mmで形成したこと、(2)高周波パワー密度を850mW/cm2としたことの2点を除いて、実施例1と同様に作製した。実施例1と同様に薄膜光電変換装置の光電変換層と同一の条件で結晶シリコン基板およびガラス基板上に結晶質ゲルマニウム層を形成し、FTIRにより赤外線吸収スペクトル、および分光エリプソメトリーによる屈折率を測定した。表3に波数935cm-1および960cm-1における赤外吸収ピークの吸収係数、および波長600nmにおける屈折率を示す。
実施例13として、実施例12に類似の単接合の薄膜光電変換装置を作製した。実施例13は、結晶質ゲルマニウム光電変換層を製膜する際、電極間隔ES=12mmで形成したことを除いて、実施例12と同様に作製した。また、赤外吸収係数、屈折率を実施例12と同様に表3に示す。
実施例14として、実施例12に類似の単接合の薄膜光電変換装置を作製した。実施例14は、結晶質ゲルマニウム光電変換層を製膜する際、電極間隔ES=12mmでプラズマを開始し、プラズマを切らずにES=15mmとしたことを除いて、実施例12と同様に作製した。また、赤外吸収係数、屈折率を実施例12と同様に表3に示す。
実施例12は、Ge原子発光ピークが検出され、長波長光の量子効率は9.5%、Jscは33.5mA/cm2であった。これに対して、実施例13はGe原子発光ピークが検出されず、長波長光の量子効率は11%、Jscは34.9mA/cm2と向上した。実施例13は、Ge原子発光ピークが検出されなかったことにより、反応性の高いGe原子の密度が低いことがわかる。従って、式2に示すような連鎖反応が起こりにくく、ポリマーやクラスターの発生が抑制されると考えられ、緻密な結晶質ゲルマニウム半導体が形成されて、薄膜光電変換装置の特性が向上したといえる。
実施例15、16、17として、実施例12に類似の単接合の薄膜光電変換装置を作製した。図1の結晶質ゲルマニウム光電変換層を製膜時のESを実施例15は9mm、実施例16は7.5mm、実施例17は6.5mmで形成したことを除いて、実施例12と同様に作製した。また、赤外吸収係数、屈折率、および薄膜光電変換装置の特性を実施例12と同様に表3に示す。
実施例12、13、15、16、17について、結晶質ゲルマニウム光電変換層のESに対する赤外吸収ピークの吸収係数、波長600nmの屈折率、および光電変換装置の特性を表3に示す。
実施例18として、実施例16に類似の単接合の薄膜光電変換装置を作製した。実施例18は、結晶質ゲルマニウム光電変換層を製膜する際、図31に示すホローカソード形電極を備えるプラズマCVD装置を用いたことを除いて、実施例16と同様に作製した。ホローカソードの窪みは、直径3mmφ、深さ3mmで、ピッチ5mmで複数の窪みを設けた。また、窪みの中心に、ガス導入穴を設けた。赤外吸収係数、屈折率および薄膜光電変換装置の特性を実施例12と同様に表3に示す。
実施例19~23として、実施例16に類似の単接合の薄膜光電変換装置を作製した。図1の結晶質ゲルマニウム光電変換層を製膜時の圧力を実施例19は670Pa、実施例20は850Pa、実施例21は930Pa、実施例22は1000Pa、実施例23は1330Pa、で形成したことを除いて、実施例16と同様に作製した。また、赤外吸収係数、屈折率、および薄膜光電変換装置の特性を表4に示す。
実施例24として、実施例1に類似の単接合の薄膜光電変換装置を作製し、波長600nmの屈折率に対する、薄膜光電変換装置の特性を調べた。図1の結晶質ゲルマニウム光電変換層を製膜時の条件を、基板温度200~300℃、高周波パワー密度300~1400mW/cm2、H2/GeH4の流量比を500~2000倍、ESを6.5~15mm、圧力670~1330Paと変化させた多数の薄膜光電変換装置を作製した。いずれの光電変換装置も、935cm-1のピークの赤外吸収係数が6000cm-1未満、960cm-1のピークの赤外吸収係数が4000cm-1未満であった。
2 透明電極層
3 結晶質ゲルマニウム光電変換ユニット
31 p型微結晶シリコン層
32 結晶質ゲルマニウム光電変換層
33 n型微結晶シリコン層
34 実質的に真性な結晶質シリコン層
35 実質的に真性な結晶質シリコン層
4 非晶質シリコン光電変換ユニット
41 p型非晶質炭化シリコン層
42 実質的に真性な非晶質シリコン光電変換層
43 n型微結晶シリコン層
5 結晶質シリコン光電変換ユニット
51 p型微結晶シリコン層
52 実質的に真性な結晶質シリコン層の光電変換層
53 n型微結晶シリコン層
6 裏面電極層
7 薄膜光電変換装置
8 薄膜光電変換装置
9 薄膜光電変換装置
10 真空チャンバ
11 高周波電極
12 基板側電極
13 基板
14 プラズマ
15 ガス導入管
16 絶縁材
17 排気管
18 高周波電源
19 ホローカソード形電極
20 窓
21 レンズ
22 光ファイバ
23 分光器
Claims (15)
- p形半導体層とn型半導体層の間に光電変換層を備えた光電変換ユニットを1以上含む薄膜光電変換装置であって、少なくとも1つの光電変換ユニットの光電変換層が真性または弱n形の結晶質ゲルマニウム半導体を含み、かつ前記結晶質ゲルマニウム半導体の波数935±5cm-1の赤外吸収ピークの吸収係数が6000cm-1未満であることを特徴とする薄膜光電変換装置。
- 請求項1に記載の薄膜光電変換装置において、前記結晶質ゲルマニウム半導体の波数960±5cm-1の赤外吸収ピークの吸収係数が3500cm-1未満であることを特徴とする薄膜光電変換装置。
- 請求項1または2に記載の薄膜光電変換装置において、前記結晶質ゲルマニウム半導体はX線回折で測定した(220)ピークと(111)ピークの強度比が2以上であることを特徴とする薄膜光電変換装置。
- 請求項1乃至3のいずれかに記載の薄膜光電変換装置であって、光電変換層が実質的に真正な結晶質シリコン半導体と前記結晶質ゲルマニウム半導体を積層した構造であることを特徴とする薄膜光電変換装置。
- 請求項1乃至4のいずれかに記載の薄膜光電変換装置であって、光電変換ユニットを3つ備え、光入射側から順に光電変換層に非晶質シリコン半導体を用いた第一光電変換ユニット、光電変換層に結晶質シリコン半導体を用いた第二光電変換ユニット、光電変換層に前記結晶質ゲルマニウム半導体を含む第三光電変換ユニットを順次配置したことを特徴とする薄膜光電変換装置。
- 請求項1乃至5のいずれかに記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を10~100MHzの周波数の高周波放電プラズマCVD法で形成することを特徴とする薄膜光電変換装置の製造方法。
- 請求項6に記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を基板温度250℃以上で形成することを特徴とする薄膜光電変換装置の製造方法。
- 請求項6または7に記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を高周波パワー密度550mW/cm2以上で形成することを特徴とする薄膜光電変換装置の製造方法。
- 請求項6乃至8のいずれかに記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を、基板を配置した基板側電極と高周波電極とを備えるプラズマCVD装置を用いて作製し、かつ高周波電極と基板間の距離(E/S)が、12mm以下であることを特徴とする薄膜光電変換装置の製造方法。
- 請求項6乃至9のいずれかに記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を、基板を配置した基板側電極と高周波電極とを備えるプラズマCVD装置を用いて作製し、かつ高周波電極がホローカソード形の電極であることを特徴とする薄膜光電変換装置の製造方法。
- 請求項6乃至10のいずれかに記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を作製するときの高周波放電プラズマの発光スペクトルに、波長265nm±2nmにピークを持つGe原子発光ピーク、および304nm±2nmにピークを持つGe原子発光ピークがいずれも検出されないことを特徴とする薄膜光電変換装置の製造方法。
- 請求項6乃至11のいずれかに記載の薄膜光電変換装置の製造方法であって、前記結晶質ゲルマニウム半導体を、製膜時の圧力が800Pa以上で作製することを特徴とする薄膜光電変換装置の製造方法。
- 請求項1乃至5のいずれかに記載の薄膜光電変換装置において、前記結晶質ゲルマニウム半導体の波長600nmの光に対する屈折率が4.0以上であることを特徴とする薄膜光電変換装置。
- 請求項1乃至5のいずれかに記載の薄膜光電変換装置において、前記結晶質ゲルマニウム半導体の波長600nmの光に対する屈折率が4.7以上であることを特徴とする薄膜光電変換装置。
- 請求項1乃至5のいずれかに記載の薄膜光電変換装置において、前記結晶質ゲルマニウム半導体の波長600nmの光に対する屈折率が4.9以上であることを特徴とする薄膜光電変換装置。
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CN200980133876.0A CN102138221B (zh) | 2008-08-29 | 2009-08-24 | 薄膜光电转换装置及其制造方法 |
US13/061,036 US8933327B2 (en) | 2008-08-29 | 2009-08-24 | Thin-film photoelectric converter and fabrication method therefor |
EP09809862A EP2330632A1 (en) | 2008-08-29 | 2009-08-24 | Thin-film photoelectric converter and fabrication method therefor |
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Cited By (5)
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WO2011055600A1 (ja) * | 2009-11-05 | 2011-05-12 | 三菱電機株式会社 | 光起電力装置およびその製造方法 |
WO2012160804A1 (ja) * | 2011-05-25 | 2012-11-29 | 株式会社クレブ | 発光分析装置 |
CN102832117A (zh) * | 2011-06-14 | 2012-12-19 | 国际商业机器公司 | 用于形成多结光生伏打结构的剥离方法和光生伏打器件 |
WO2013035686A1 (ja) | 2011-09-07 | 2013-03-14 | 株式会社カネカ | 薄膜光電変換装置およびその製造方法 |
US9121829B2 (en) | 2011-03-04 | 2015-09-01 | Joled Inc. | Crystallinity evaluation method, crystallinity evaluation device, and computer software thereof |
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FR2956208B1 (fr) * | 2010-02-05 | 2012-04-27 | Centre Nat Rech Scient | Methode de determination sans contact de caracteristiques d'un photoconvertisseur |
EP2541614A4 (en) * | 2010-02-24 | 2015-11-04 | Kaneka Corp | THIN-FILM PHOTOELECTRIC CONVERSION DEVICE AND METHOD FOR PRODUCING THE SAME |
US9653639B2 (en) * | 2012-02-07 | 2017-05-16 | Apic Corporation | Laser using locally strained germanium on silicon for opto-electronic applications |
JP6045250B2 (ja) * | 2012-08-10 | 2016-12-14 | オリンパス株式会社 | 固体撮像装置および撮像装置 |
CN108963015B (zh) * | 2017-05-17 | 2021-12-10 | 上海耕岩智能科技有限公司 | 一种光侦测薄膜、器件、显示装置、光敏二极管的制备方法 |
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WO2011055600A1 (ja) * | 2009-11-05 | 2011-05-12 | 三菱電機株式会社 | 光起電力装置およびその製造方法 |
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US9121829B2 (en) | 2011-03-04 | 2015-09-01 | Joled Inc. | Crystallinity evaluation method, crystallinity evaluation device, and computer software thereof |
WO2012160804A1 (ja) * | 2011-05-25 | 2012-11-29 | 株式会社クレブ | 発光分析装置 |
CN103562435A (zh) * | 2011-05-25 | 2014-02-05 | 株式会社Crev | 发光分析装置 |
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WO2013035686A1 (ja) | 2011-09-07 | 2013-03-14 | 株式会社カネカ | 薄膜光電変換装置およびその製造方法 |
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JP5379801B2 (ja) | 2013-12-25 |
US20110146756A1 (en) | 2011-06-23 |
CN102138221A (zh) | 2011-07-27 |
CN102138221B (zh) | 2015-03-04 |
US8933327B2 (en) | 2015-01-13 |
EP2330632A1 (en) | 2011-06-08 |
JPWO2010024211A1 (ja) | 2012-01-26 |
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