WO2013080803A1 - 光起電力装置 - Google Patents

光起電力装置 Download PDF

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Publication number
WO2013080803A1
WO2013080803A1 PCT/JP2012/079618 JP2012079618W WO2013080803A1 WO 2013080803 A1 WO2013080803 A1 WO 2013080803A1 JP 2012079618 W JP2012079618 W JP 2012079618W WO 2013080803 A1 WO2013080803 A1 WO 2013080803A1
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photovoltaic device
layer
circuit voltage
unit
transparent conductive
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French (fr)
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松本　光弘
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三洋電機株式会社
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    • H01L31/02—Details
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    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/02168—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells the coatings being antireflective or having enhancing optical properties for the solar cells
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    • H01L31/0224—Electrodes
    • H01L31/022466—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers
    • H01L31/022475—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of indium tin oxide [ITO]
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    • H01L31/022483—Electrodes made of transparent conductive layers, e.g. TCO, ITO layers composed of zinc oxide [ZnO]
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Definitions

  • the present invention relates to a photovoltaic device.
  • Solar cells using polycrystalline, microcrystalline, or amorphous silicon as a photoelectric conversion layer are known.
  • photovoltaic devices having a structure in which thin films of microcrystalline or amorphous silicon are stacked are attracting attention from the viewpoints of resource consumption, cost reduction, and efficiency.
  • a photovoltaic device is formed by sequentially laminating a first electrode, a photoelectric conversion cell made of a semiconductor thin film, and a second electrode on a substrate having an insulating surface.
  • the photoelectric conversion cell is configured by stacking a p-type layer, an i-type layer, and an n-type layer from the light incident side.
  • As a method for improving the conversion efficiency of a photovoltaic device it is known to stack two or more types of photoelectric conversion cells in the light incident direction.
  • a first photoelectric conversion unit including a photoelectric conversion layer having a wide band gap is disposed on the light incident side of the photovoltaic device, and then a photoelectric conversion having a narrower band gap than the first photoelectric conversion unit.
  • a second photoelectric conversion unit including a layer is disposed.
  • photoelectric conversion can be performed over a wide wavelength range of incident light, and the conversion efficiency of the entire apparatus can be improved.
  • a-Si unit an amorphous silicon photoelectric conversion unit
  • ⁇ c-Si unit microcrystalline silicon photoelectric conversion unit
  • the distribution tends to increase in the film thickness and characteristics of the transparent conductive film and the semiconductor layer in the substrate surface.
  • the doping amount, film thickness, and transparency of the p-type layer of the a-Si unit are usually set so that the open circuit voltage Voc at the initial stage of manufacture is not too low in the region where the open circuit voltage Voc is the lowest.
  • the unevenness of the texture of the conductive film is controlled.
  • One aspect of the present invention is a photovoltaic device having a power generation layer of amorphous silicon or a compound thereof formed on a transparent conductive layer, and a region in which an open-circuit voltage decreases after light irradiation in a substrate surface, And a region in which an open circuit voltage is improved after light irradiation.
  • the present invention it is possible to improve the efficiency of the photovoltaic device after the influence of light deterioration is stabilized.
  • FIG. 1 is a cross-sectional view showing the structure of a photovoltaic device 100 according to an embodiment of the present invention.
  • the photovoltaic device 100 includes an amorphous silicon photoelectric conversion unit (a-Si unit) having a transparent insulating substrate 10 as a light incident side, a transparent conductive film 12 from the light incident side, and a wide band gap as a top cell. ) 102, the intermediate layer 14, the microcrystalline silicon photoelectric conversion unit ( ⁇ c-Si unit) 104 having a narrower band gap than the a-Si unit 102 as the bottom cell, the first back electrode layer 16, the second back electrode layer 18, and the filler 20 And the protective film 22 is laminated.
  • each of the a-Si unit 102 and the ⁇ c-Si unit 104 functions as a power generation layer of the photovoltaic device 100 in the embodiment of the present invention.
  • a material having transparency in at least a visible light wavelength region such as a glass substrate or a plastic substrate can be applied.
  • a transparent conductive film 12 is formed on the transparent insulating substrate 10.
  • the transparent conductive film 12 is doped with tin oxide (SnO 2 ), zinc oxide (ZnO), indium tin oxide (ITO), etc. with tin (Sn), antimony (Sb), fluorine (F), aluminum (Al), etc. It is preferable to use at least one or a combination of a plurality of transparent conductive oxides (TCO).
  • zinc oxide (ZnO) is excellent in that it has high translucency, low resistivity, excellent plasma resistance, and can easily realize a suitable texture structure described later.
  • the transparent conductive film 12 can be formed by sputtering, for example.
  • the film thickness of the transparent conductive film 12 is preferably in the range of 0.5 ⁇ m to 5 ⁇ m.
  • the film quality of the transparent conductive film 12 will be described later.
  • an a-Si unit 102 is formed by sequentially laminating a silicon-based thin film of a p-type layer 40, an i-type layer 42, and an n-type layer 44.
  • the a-Si unit 102 includes silicon-containing gas such as silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiH 2 Cl 2 ), carbon-containing gas such as methane (CH 4 ), diborane (B 2 H 6 ) etc., formed by plasma CVD in which a mixed gas obtained by mixing a p-type dopant containing gas such as phosphine (PH 3 ) and a diluted gas such as phosphine (PH 3 ) and a diluent gas such as hydrogen (H 2 ) is formed into a plasma.
  • silicon-containing gas such as silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiH 2 Cl 2 ), carbon-containing gas such as methane (CH 4 ), diborane (B 2 H 6 ) etc.
  • plasma CVD in which a mixed gas obtained by mixing a p-type dopant containing
  • the RF plasma CVD can be a parallel plate type. It is good also as a structure which provided the gas shower hole for supplying the mixed gas of a raw material in the side which does not arrange
  • the plasma input power density is preferably 5 mW / cm 2 or more and 100 mW / cm 2 or less.
  • the p-type layer 40, the i-type layer 42, and the n-type layer 44 are formed in separate film formation chambers.
  • the film forming chamber can be evacuated by a vacuum pump and has an electrode for RF plasma CVD.
  • a transfer device for the transparent insulating substrate 10, a power source and matching device for RF plasma CVD, piping for gas supply, and the like are attached.
  • the p-type layer 40 is formed on the transparent conductive film 12.
  • the p-type layer 40 is a p-type amorphous silicon layer (p-type a-Si: H) doped with a p-type dopant (boron or the like).
  • the film quality of the p-type layer 40 can be changed by adjusting the mixing ratio of the silicon-containing gas, the carbon-containing gas, the p-type dopant-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation.
  • the film thickness of the p-type layer 40 will be described later.
  • the i-type layer 42 is an undoped amorphous silicon film formed on the p-type layer 40 and having a thickness of 50 nm to 500 nm.
  • the film quality of the i-type layer 42 can be changed by adjusting the mixing ratio of the silicon-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation. Further, the i-type layer 42 becomes a power generation layer of the a-Si unit 102.
  • the n-type layer 44 is an n-type amorphous silicon layer (n-type a-Si: H) having a thickness of 10 nm to 100 nm doped with an n-type dopant (such as phosphorus) formed on the i-type layer 42 or an n-type fine layer.
  • n-type dopant such as phosphorus
  • a crystalline silicon layer (n-type ⁇ c-Si: H) is used.
  • the film quality of the n-type layer 44 can be changed by adjusting the mixing ratio of the silicon-containing gas, the carbon-containing gas, the n-type dopant-containing gas and the dilution gas, the pressure, and the high-frequency power for plasma generation.
  • the intermediate layer 14 is formed on the a-Si unit 102.
  • the intermediate layer 14 is preferably made of a transparent conductive oxide (TCO) such as zinc oxide (ZnO) or silicon oxide (SiOx).
  • TCO transparent conductive oxide
  • ZnO zinc oxide
  • SiOx silicon oxide
  • Mg magnesium
  • the intermediate layer 14 can be formed by, for example, sputtering.
  • the film thickness of the intermediate layer 14 is preferably in the range of 10 nm to 200 nm. The intermediate layer 14 need not be provided.
  • a ⁇ c-Si unit 104 in which a p-type layer, an i-type layer, and an n-type layer are sequentially laminated is formed.
  • the ⁇ c-Si unit 104 includes a silicon-containing gas such as silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiH 2 Cl 2 ), a carbon-containing gas such as methane (CH 4 ), diborane (B 2 H 6 ) etc., formed by plasma CVD in which a mixed gas obtained by mixing a p-type dopant containing gas such as phosphine (PH 3 ) and a diluted gas such as phosphine (PH 3 ) and a diluent gas such as hydrogen (H 2 ) is formed into a plasma.
  • a silicon-containing gas such as silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiH 2 Cl 2 ),
  • RF plasma CVD for example, RF plasma CVD or VHF plasma CVD is preferably applied.
  • RF plasma CVD and VHF plasma CVD can be parallel plate types. It is good also as a structure which provided the gas shower hole for supplying the mixed gas of a raw material in the side which does not arrange
  • Input power density of the plasma is preferably set to 5 mW / cm 2 or more 1000 mW / cm 2 or less.
  • the p-type layer is formed on the intermediate layer 14 or the n-type layer 44 of the a-Si unit 102.
  • the p-type layer is a p-type microcrystalline silicon layer (p-type ⁇ c-Si: H) doped with a p-type dopant (boron or the like) and having a thickness of 5 nm to 50 nm.
  • the film quality of the p-type layer can be changed by adjusting the mixing ratio of the silicon-containing gas, the carbon-containing gas, the p-type dopant-containing gas and the dilution gas, the pressure, and the high frequency power for plasma generation.
  • the i-type layer is an undoped microcrystalline silicon film formed on the p-type layer and having a thickness of 0.5 ⁇ m to 5 ⁇ m. Details of the i-type layer will be described later.
  • the n-type layer is formed on the i-type layer.
  • the n-type layer is an n-type microcrystalline silicon layer (n-type ⁇ c-Si: H) doped with an n-type dopant (such as phosphorus) and having a thickness of 5 nm to 50 nm.
  • the ⁇ c-Si unit 104 is not limited to this, and any unit that uses an i-type microcrystalline silicon layer (i-type ⁇ c-Si: H) described below as a power generation layer may be used.
  • a laminated structure of a reflective metal and a transparent conductive oxide (TCO) is formed on the ⁇ c-Si unit 104 as the first back electrode layer 16 and the second back electrode layer 18.
  • a transparent conductive oxide (TCO) such as tin oxide (SnO 2 ), zinc oxide (ZnO), indium tin oxide (ITO), or the like is used.
  • the TCO can be formed by, for example, sputtering.
  • metals such as silver (Ag) and aluminum (Al), can be used.
  • the first back electrode layer 16 and the second back electrode layer 18 are preferably about 1 ⁇ m in total. It is preferable that at least one of the first back electrode layer 16 and the second back electrode layer 18 is provided with unevenness for enhancing the light confinement effect.
  • the surface of the second back electrode layer 18 is covered with the protective film 22 with the filler 20.
  • the filler 20 and the protective film 22 can be made of a resin material such as EVA or polyimide. As a result, it is possible to prevent moisture from entering the power generation layer of the photovoltaic device 100.
  • FIG. 1 YAG laser
  • the photovoltaic device 100 according to the present embodiment can be formed.
  • the haze ratio of the transparent conductive film 12 is preferably 20% or more.
  • the haze ratio is represented by (diffuse transmittance / total light transmittance) ⁇ 100 [%] (JIS K7136).
  • JIS K7136 Joint Photographic Experts Group
  • the p-type layer 40 of the a-Si unit 102 includes a region A having a film thickness where the open circuit voltage Voc is improved after photodegradation and a region B having a film thickness where the open circuit voltage Voc is decreased after photodegradation.
  • the film thickness of the p-type layer 40 of the a-Si unit 102 is such that the open circuit voltage Voc of the photovoltaic device 100 that has not undergone photodegradation intersects the open circuit voltage Voc of the photovoltaic device 100 after photodegradation.
  • the film thickness range X includes the thickness Tx.
  • the vicinity of the in-plane area of the photovoltaic device 100 is a region A having a film thickness that increases the open-circuit voltage Voc after light degradation, and the vicinity of the center of the photovoltaic apparatus 100 is after light degradation
  • the region B has a film thickness at which the open circuit voltage Voc decreases.
  • the film thickness does not need to be uniform in both the region A and the region B, and the film thickness may be continuously changed from the center to the periphery of the photovoltaic device 100.
  • tandem structure of the a-Si unit 102 and the ⁇ c-Si unit 104 has been described as an example.
  • the present invention is not limited to this, and any structure including the a-Si unit 102 may be used. Good.
  • Zinc oxide (ZnO) was formed as the transparent conductive film 12 on the 550 mm ⁇ 650 mm transparent insulating substrate 10 by low pressure chemical vapor deposition (LPCVD).
  • LPCVD low pressure chemical vapor deposition
  • the film forming conditions were as shown in Table 1.
  • the haze ratio of the transparent conductive film 12 was 21% on the average in the plane.
  • the p-type layer 40 of the a-Si unit 102 was formed on the transparent conductive film 12.
  • the p-type layer 40 has a tendency to increase the open-circuit voltage Voc after photodegradation as the doping amount is small.
  • the low-doped layer hardly forms an ohmic junction with the transparent conductive film 12, the p-type layer 40 is highly converted.
  • a laminated structure of a highly doped region / a lightly doped region was formed from the side close to the transparent conductive film 12.
  • the film formation conditions shown in Table 2 were used, but the B 2 H 6 / SiH 4 ratio was 0.4% or less in the low-doped region, and the B 2 H 6 / SiH 4 ratio was 0 in the high-doped region. 0.5% or more. Further, a non-doped buffer layer made of ⁇ c-SiC was formed. The film thickness of the p-type layer 40 was ⁇ 10% in the in-plane distribution. Thereafter, the i-type layer 42 and the n-type layer 44 were formed to a thickness of 300 nm and 20 nm, respectively, to form a single type photovoltaic device having only the a-Si unit 102.
  • a single type photovoltaic device in which tin oxide (SnO 2 ) was formed as a transparent conductive film 12 by an atmospheric pressure vapor phase growth method was formed. Except the transparent conductive film 12, it formed similarly to the said Example. At this time, the haze ratio of the transparent conductive film 12 was 10% in an in-plane average.
  • Table 3 shows the measurement results of characteristics in Examples and Comparative Examples. Here, an average value of the in-plane characteristics of the transparent insulating substrate 10 is measured, and each standardized value is shown as 1 in the comparative example.
  • the photovoltaic apparatus of a present Example and the comparative example was measured with the spectrum of AM1.5, and the illuminance of 1 sun (100 mW / cm ⁇ 2 >) using the solar simulator.
  • the light irradiation at the time of the light deterioration before and after light irradiation was performed on the conditions of 1 sun, 50 degreeC, and 1000 hours using the solar simulator.
  • the light irradiation conditions are not limited to these conditions, and may be any conditions that cause light deterioration of the amorphous silicon-based photovoltaic device. Light irradiation is performed with an intensity higher than 1 sun to accelerate the light deterioration phenomenon. Accelerated deterioration conditions may be used.
  • “before light irradiation” is usually a time point when the characteristics of the photovoltaic device are evaluated after manufacturing, but not limited to this, evaluation before and after light deterioration irradiation is performed at a certain time point after light irradiation treatment before light irradiation. May be performed.
  • monitoring cells may be formed on the entire surface of some samples and evaluated.
  • FIG. 4 is a graph showing the relationship between the total film thickness of the p-type layer 40 and the buffer layer and the open circuit voltage Voc in the photovoltaic device 100.
  • the thick solid line indicates the open circuit voltage Voc of the photovoltaic device 100 in the initial stage of manufacture that has not undergone photodegradation in the embodiment
  • the thick broken line indicates the open circuit voltage of the photovoltaic device 100 after photodegradation in the embodiment. Voc is shown.
  • the thin solid line indicates the open circuit voltage Voc of the photovoltaic device 100 in the initial stage of manufacture that has not undergone photodegradation in the comparative example
  • the thin broken line indicates the open circuit voltage Voc of the photovoltaic device 100 after photodegradation in the comparative example. Indicates.
  • the efficiency of the entire photovoltaic device 100 could be increased. That is, even if the p-type layer 40 has a film thickness distribution within the film thickness range X in the plane of the transparent insulating substrate 10, light irradiation is performed at the film thickness of the p-type layer 40 at which the initial open circuit voltage Voc is low.
  • the open-circuit voltage Voc is improved later, and the open-circuit voltage Voc after light irradiation decreases at the film thickness of the p-type layer 40 where the initial open-circuit voltage Voc increases.
  • the open circuit voltage Voc is made uniform in the plane of the transparent insulating substrate 10, and the efficiency of the entire photovoltaic device 100 is improved.
  • the film thickness at which the open circuit voltage Voc improves after light irradiation is around 16 nm to 17 nm as compared with the initial open circuit voltage Voc, and the initial open circuit voltage Voc is extremely low in this film thickness region. Therefore, even if the film thickness range of the p-type layer 40 includes this region and the open circuit voltage Voc is made uniform in the plane of the transparent insulating substrate 10, the conversion efficiency of the entire photovoltaic device 100 can be improved. Can not.
  • the open circuit voltage Voc decreases in all regions after light irradiation, and the open circuit voltage Voc cannot be made uniform in the plane of the transparent insulating substrate 10. Therefore, the conversion efficiency of the entire photovoltaic device 100 cannot be improved.
  • the power generation layer is not limited to amorphous silicon, but an amorphous silicon compound (amorphous silicon carbide: a-SiCx, amorphous silicon oxide: a-SiOx, amorphous silicon nitride: a-SiNx) Etc.
  • it may be a stack cell having three or more layers including an a-Si unit, or a stack cell of an a-Si unit and bulk crystalline silicon.
  • the structure in which the units are connected in series has been described as an example.
  • the electrical connection between the units is not limited to this, and may be, for example, a parallel junction or a four-terminal cell. A combination of series and parallel junctions may be used.
  • SYMBOLS 10 Transparent insulating substrate, 12 Transparent electrically conductive film, 14 Intermediate layer, 16 1st back surface electrode layer, 18 2nd back surface electrode layer, 20 Filler, 22 Protective film, 40 p-type layer, 42 i-type layer, 44 n-type layer , 100 Photovoltaic device, 102 Amorphous silicon photoelectric conversion unit (a-Si unit), 104 Microcrystalline silicon photoelectric conversion unit ( ⁇ c-Si unit).

Abstract

　透明導電層上に形成されたアモルファスシリコン又はその化合物の発電層を有する光起電力装置であって、基板面内において、光照射後に開放電圧が低下する領域Ａと、光照射後に開放電圧が向上する領域Ｂと、を含む光起電力装置とする。

Description

光起電力装置
　本発明は、光起電力装置に関する。
　多結晶、微結晶またはアモルファスシリコンを光電変換層として用いた太陽電池が知られている。特に、微結晶またはアモルファスシリコンの薄膜を積層した構造を有する光起電力装置は、資源消費の観点、コストの低下の観点および効率化の観点から注目されている。
　一般的に、光起電力装置は、表面が絶縁性の基板上に第１電極、半導体薄膜からなる光電変換セル及び第２電極を順に積層して形成される。光電変換セルは、光入射側からｐ型層、ｉ型層及びｎ型層を積層して構成される。光起電力装置の変換効率を向上させる方法として、２種以上の光電変換セルを光入射方向に積層することが知られている。この場合、例えば、光起電力装置の光入射側にはバンドギャップが広い光電変換層を含む第１の光電変換ユニットを配置し、その後に第１の光電変換ユニットよりもバンドギャップの狭い光電変換層を含む第２の光電変換ユニットを配置する。これにより、入射光の広い波長範囲に亘って光電変換を可能にし、装置全体として変換効率の向上を図ることができる。例えば、アモルファスシリコン光電変換ユニット（ａ－Ｓｉユニット）をトップセルとし、微結晶シリコン光電変換ユニット（μｃ－Ｓｉユニット）をボトムセルとした構成が知られている。
　アモルファスシリコンを発電層とするａ－Ｓｉユニットは、光照射と共に劣化し、開放電圧Ｖｏｃが低下することが知られている（特許文献１参照）。
特開２００７－０１２８３３号公報
　ところで、光起電力装置が大面積化すると共に、基板面内において透明導電膜や半導体層の膜厚や特性に分布が大きくなる傾向がある。このような面内分布がある場合、通常は最も開放電圧Ｖｏｃが低くなる領域において製造初期の開放電圧Ｖｏｃが低くなり過ぎないようにａ－Ｓｉユニットのｐ型層のドープ量や膜厚、透明導電膜のテクスチャの凹凸を制御している。
　しかしながら、このような方法で各層の成膜条件を最適化した場合、製造初期の開放電圧Ｖｏｃが高くなる領域における光劣化が顕著となり、光劣化による影響が安定した後の光起電力装置全体としての効率が低下する。
　本発明の１つの態様は、透明導電層上に形成されたアモルファスシリコン又はその化合物の発電層を有する光起電力装置であって、基板面内において、光照射後に開放電圧が低下する領域と、光照射後に開放電圧が向上する領域と、を含む、光起電力装置である。
　本発明によれば、光劣化による影響が安定した後の光起電力装置における効率を向上させることができる。
本発明の実施の形態における光起電力装置の構成を示す断面図である。 本発明の実施の形態における光起電力装置の構成を示す拡大断面図である。 本発明の実施の形態におけるａ－Ｓｉユニットのｐ型層の膜厚の面内分布例を示す図である。 本発明の実施の形態におけるａ－Ｓｉユニットのｐ型層及びバッファー層の合計膜厚と開放電圧との関係を示す図である。
　図１は、本発明の実施の形態における光起電力装置１００の構造を示す断面図である。本実施の形態における光起電力装置１００は、透明絶縁基板１０を光入射側として、光入射側から、透明導電膜１２、トップセルとして広いバンドギャップを有するアモルファスシリコン光電変換ユニット（ａ－Ｓｉユニット）１０２、中間層１４、ボトムセルとしてａ－Ｓｉユニット１０２よりバンドギャップの狭い微結晶シリコン光電変換ユニット（μｃ－Ｓｉユニット）１０４、第１裏面電極層１６、第２裏面電極層１８、充填材２０及び保護膜２２を積層した構造を有している。ここで、ａ－Ｓｉユニット１０２及びμｃ－Ｓｉユニット１０４は、それぞれ、本発明の実施の形態における光起電力装置１００の発電層として機能する。
　透明絶縁基板１０は、例えば、ガラス基板、プラスチック基板等の少なくとも可視光波長領域において透過性を有する材料を適用することができる。
　透明絶縁基板１０上に透明導電膜１２が形成される。透明導電膜１２は、酸化錫（ＳｎＯ２）、酸化亜鉛（ＺｎＯ）、インジウム錫酸化物（ＩＴＯ）等に錫（Ｓｎ）、アンチモン（Ｓｂ）、フッ素（Ｆ）、アルミニウム（Ａｌ）等をドープした透明導電性酸化物（ＴＣＯ）のうち少なくとも一種類又は複数種を組み合わせて用いることが好適である。特に、酸化亜鉛（ＺｎＯ）は、透光性が高く、抵抗率が低く、耐プラズマ特性にも優れており、後述する好適なテクスチャ構造を容易に実現できる点で優れている。
　透明導電膜１２は、例えば、スパッタリング等により形成することができる。透明導電膜１２の膜厚は０．５μｍ以上５μｍ以下の範囲とすることが好適である。透明導電膜１２の膜質については後述する。
　透明導電膜１２上に、図２の拡大断面図に示すように、ｐ型層４０、ｉ型層４２、ｎ型層４４のシリコン系薄膜を順に積層してａ－Ｓｉユニット１０２を形成する。ａ－Ｓｉユニット１０２は、シラン（ＳｉＨ４）、ジシラン（Ｓｉ２Ｈ６）、ジクロルシラン（ＳｉＨ２Ｃｌ２）等のシリコン含有ガス、メタン（ＣＨ４）等の炭素含有ガス、ジボラン（Ｂ２Ｈ６）等のｐ型ドーパント含有ガス、フォスフィン（ＰＨ３）等のｎ型ドーパント含有ガス及び水素（Ｈ２）等の希釈ガスを混合した混合ガスをプラズマ化して成膜を行うプラズマＣＶＤにより形成することができる。
　プラズマＣＶＤは、例えば、１３．５６ＭＨｚのＲＦプラズマＣＶＤを適用することが好適である。ＲＦプラズマＣＶＤは平行平板型とすることができる。平行平板型の電極のうち透明絶縁基板１０を配しない側には原料の混合ガスを供給するためのガスシャワー孔を設けた構成としてもよい。プラズマの投入電力密度は、５ｍＷ／ｃｍ２以上１００ｍＷ／ｃｍ２以下とすることが好ましい。
　一般的に、ｐ型層４０、ｉ型層４２、ｎ型層４４はそれぞれ別の成膜室において成膜される。成膜室は、真空ポンプによって真空排気可能であり、ＲＦプラズマＣＶＤのための電極が内蔵される。また、透明絶縁基板１０の搬送装置、ＲＦプラズマＣＶＤのための電源及びマッチング装置、ガス供給用の配管等が付設される。
　ｐ型層４０は、透明導電膜１２上に形成される。ｐ型層４０は、ｐ型ドーパント（ボロン等）をドープしたｐ型アモルファスシリコン層（ｐ型ａ－Ｓｉ：Ｈ）とする。ｐ型層４０の膜質は、シリコン含有ガス、炭素含有ガス、ｐ型ドーパント含有ガス及び希釈ガスの混合比、圧力及びプラズマ発生用高周波パワーを調整することによって変化させることができる。ｐ型層４０の膜厚については後述する。
　ｉ型層４２は、ｐ型層４０上に形成されたドープされていない膜厚５０ｎｍ以上５００ｎｍ以下のアモルファスシリコン膜とする。ｉ型層４２の膜質は、シリコン含有ガス及び希釈ガスの混合比、圧力及びプラズマ発生用高周波パワーを調整することによって変化させることができる。また、ｉ型層４２は、ａ－Ｓｉユニット１０２の発電層となる。
　ｎ型層４４は、ｉ型層４２上に形成されたｎ型ドーパント（リン等）をドープした膜厚１０ｎｍ以上１００ｎｍ以下のｎ型アモルファスシリコン層（ｎ型ａ－Ｓｉ：Ｈ）又はｎ型微結晶シリコン層（ｎ型μｃ－Ｓｉ：Ｈ）とする。ｎ型層４４の膜質は、シリコン含有ガス、炭素含有ガス、ｎ型ドーパント含有ガス及び希釈ガスの混合比、圧力及びプラズマ発生用高周波パワーを調整することによって変化させることができる。
　ａ－Ｓｉユニット１０２上に、中間層１４を形成する。中間層１４は、酸化亜鉛（ＺｎＯ）、酸化シリコン（ＳｉＯｘ）等の透明導電性酸化物（ＴＣＯ）を用いることが好適である。特に、マグネシウム（Ｍｇ）がドープされた酸化亜鉛（ＺｎＯ）や酸化シリコン（ＳｉＯｘ）を用いることが好適である。中間層１４は、例えば、スパッタリング等により形成することができる。中間層１４の膜厚は１０ｎｍ以上２００ｎｍ以下の範囲とすることが好適である。なお、中間層１４は、設けなくてもよい。
　中間層１４上に、図１に示すように、ｐ型層、ｉ型層、ｎ型層を順に積層したμｃ－Ｓｉユニット１０４を形成する。μｃ－Ｓｉユニット１０４は、シラン（ＳｉＨ４）、ジシラン（Ｓｉ２Ｈ６）、ジクロルシラン（ＳｉＨ２Ｃｌ２）等のシリコン含有ガス、メタン（ＣＨ４）等の炭素含有ガス、ジボラン（Ｂ２Ｈ６）等のｐ型ドーパント含有ガス、フォスフィン（ＰＨ３）等のｎ型ドーパント含有ガス及び水素（Ｈ２）等の希釈ガスを混合した混合ガスをプラズマ化して成膜を行うプラズマＣＶＤにより形成することができる。
　プラズマＣＶＤは、例えば、ＲＦプラズマＣＶＤ又はＶＨＦプラズマＣＶＤを適用することが好適である。ＲＦプラズマＣＶＤ及びＶＨＦプラズマＣＶＤは平行平板型とすることができる。平行平板型の電極のうち透明絶縁基板１０を配しない側には原料の混合ガスを供給するためのガスシャワー孔を設けた構成としてもよい。プラズマの投入電力密度は、５ｍＷ／ｃｍ２以上１０００ｍＷ／ｃｍ２以下とすることが好ましい。
　ｐ型層は、中間層１４又はａ－Ｓｉユニット１０２のｎ型層４４上に形成される。ｐ型層は、ｐ型ドーパント（ボロン等）をドープした膜厚５ｎｍ以上５０ｎｍ以下のｐ型微結晶シリコン層（ｐ型μｃ－Ｓｉ：Ｈ）とする。ｐ型層の膜質は、シリコン含有ガス、炭素含有ガス、ｐ型ドーパント含有ガス及び希釈ガスの混合比、圧力及びプラズマ発生用高周波パワーを調整することによって変化させることができる。ｉ型層は、ｐ型層上に形成されたドープされていない膜厚０．５μｍ以上５μｍ以下の微結晶シリコン膜とする。ｉ型層の詳細については後述する。ｎ型層は、ｉ型層上に形成される。ｎ型層は、ｎ型ドーパント（リン等）をドープした膜厚５ｎｍ以上５０ｎｍ以下ｎ型微結晶シリコン層（ｎ型μｃ－Ｓｉ：Ｈ）とする。ただし、μｃ－Ｓｉユニット１０４はこれに限定されるものではなく、発電層として以下に説明するｉ型微結晶シリコン層（ｉ型μｃ－Ｓｉ：Ｈ）が用いられるものであればよい。
　μｃ－Ｓｉユニット１０４上に、第１裏面電極層１６及び第２裏面電極層１８として反射性金属と透明導電性酸化物（ＴＣＯ）との積層構造を形成する。第１裏面電極層１６としては、酸化錫（ＳｎＯ２）、酸化亜鉛（ＺｎＯ）、インジウム錫酸化物（ＩＴＯ）等の透明導電性酸化物（ＴＣＯ）が用いられる。ＴＣＯは、例えば、スパッタリング等により形成することができる。また、第２裏面電極層１８としては、銀（Ａｇ）、アルミニウム（Ａｌ）等の金属が使用できる。第１裏面電極層１６及び第２裏面電極層１８は、合わせて１μｍ程度の膜厚とすることが好適である。第１裏面電極層１６及び第２裏面電極層１８の少なくとも一方には、光閉じ込め効果を高めるための凹凸を設けることが好適である。
　さらに、充填材２０によって第２裏面電極層１８の表面を保護膜２２で被う。充填材２０及び保護膜２２は、ＥＶＡ、ポリイミド等の樹脂材料とすることができる。これによって、光起電力装置１００の発電層への水分の浸入等を防ぐことができる。
　なお、ＹＡＧレーザ（基本波１０６４ｎｍ、２倍高調波５３２ｎｍ）を用いて、透明導電膜１２、ａ－Ｓｉユニット１０２、中間層１４、μｃ－Ｓｉユニット１０４、第１裏面電極層１６、第２裏面電極層１８の分離加工を行うことによって、複数のセルを直列に接続した構成にしてもよい。
　このようにして、本実施の形態における光起電力装置１００を形成することができる。
　ここで、透明導電膜１２のヘイズ率は２０％以上とすることが好適である。透明導電膜１２のヘイズ率を２０％以上とすることによって、光劣化による影響が安定した後の光起電力装置における効率を向上させることができる。なお、ヘイズ率とは、（拡散透過率／全光線透過率）×１００［％］で表されるものである（ＪＩＳ Ｋ７１３６）。ヘイズ率の簡易評価方法としては、Ｄ６５光源もしくはＣ光源を用いたヘイズメータによる測定が一般的に用いられる。
　さらに、ａ－Ｓｉユニット１０２のｐ型層４０は、光劣化後に開放電圧Ｖｏｃが向上する膜厚を有する領域Ａと、光劣化後に開放電圧Ｖｏｃが低下する膜厚を有する領域Ｂと、を含むものとする。すなわち、ａ－Ｓｉユニット１０２のｐ型層４０の膜厚は、光劣化を受けていない光起電力装置１００の開放電圧Ｖｏｃと光劣化後の光起電力装置１００の開放電圧Ｖｏｃが交差する膜厚Ｔｘを含む膜厚範囲Ｘを有するものとする。
　例えば、図３の平面図に示すように、光起電力装置１００の面内の周辺付近は光劣化後に開放電圧Ｖｏｃが向上する膜厚を有する領域Ａとし、面内の中心付近は光劣化後に開放電圧Ｖｏｃが低下する膜厚を有する領域Ｂとする。もちろん、領域Ａ及び領域Ｂのいずれにおいても膜厚は均一である必要はなく、光起電力装置１００の中心から周辺へ向けて連続的に膜厚が変化するものであってもよい。
　なお、本実施の形態では、ａ－Ｓｉユニット１０２とμｃ－Ｓｉユニット１０４とのタンデム構造を例に説明したが、これに限定されるものではなく、ａ－Ｓｉユニット１０２を含む構造であればよい。
　以下、本実施の形態の実施例について説明する。５５０ｍｍ×６５０ｍｍの透明絶縁基板１０上に、透明導電膜１２として酸化亜鉛（ＺｎＯ）を低圧化学気相成長法（ＬＰＣＶＤ）によって形成した。成膜条件は、表１の通りとした。この透明導電膜１２のヘイズ率は、面内平均で２１％であった。
Figure JPOXMLDOC01-appb-T000001
　次に、透明導電膜１２上にａ－Ｓｉユニット１０２のｐ型層４０を形成した。ｐ型層４０は、上記のようにドープ量が少ないほど光劣化後に開放電圧Ｖｏｃが向上する傾向を示しやすいが、低ドープ層は透明導電膜１２とのオーミック接合が形成され難いので、高い変換効率を得るために透明導電膜１２に近い側から高ドープ領域／低ドープ領域の積層構造とした。具体的には、表２に示す成膜条件としたが、低ドープ領域ではＢ２Ｈ６／ＳｉＨ４比を０．４％以下とし、高ドープ領域ではＢ２Ｈ６／ＳｉＨ４比を０．５％以上とした。また、さらにμｃ－ＳｉＣからなるノンドープのバッファー層を形成した。ｐ型層４０の膜厚は、面内分布において±１０％であった。その後、ｉ型層４２、ｎ型層４４をそれぞれ膜厚３００ｎｍ及び２０ｎｍで成膜し、ａ－Ｓｉユニット１０２のみを有するシングル型光起電力装置を形成した。
Figure JPOXMLDOC01-appb-T000002
　比較例として、透明導電膜１２として酸化錫（ＳｎＯ２）を大気圧気相成長法により成膜したシングル型光起電力装置を形成した。透明導電膜１２以外は、上記実施例と同様に形成した。このとき、透明導電膜１２のヘイズ率は、面内平均で１０％であった。
　表３は、実施例及び比較例における特性の測定結果を示す。ここでは、透明絶縁基板１０の面内の特性の平均値を測定し、比較例における各測定値を１として規格化した値を示す。
　なお、本実施例及び比較例の光起電力装置は、ソーラーシミュレータを用いてＡＭ１．５のスペクトル、１ｓｕｎ（１００ｍＷ／ｃｍ２）の照度で測定した。また、光照射前後の光劣化時の光照射は、ソーラーシミュレータを用いて１ｓｕｎ、５０℃及び１０００時間の条件で行った。光照射条件は、この条件に限定されるものではなく、アモルファスシリコン系の光起電力装置の光劣化を引き起こす条件であればよく、１ｓｕｎより高い強度で光照射を行い、光劣化現象を加速させる加速劣化条件でもよい。なお、光照射前とは、通常は製造後に光起電力装置の特性を評価した時点であるが、それに限ることなく、何らかの光照射処理後のある時点を光照射前として光劣化照射前後の評価を行ってもよい。
　また、光起電力装置の面内分布を評価する際は、モジュールを分割し、それぞれのミニモジュール又はミニセルの光照射時のＩ－Ｖ測定を行った。また、量産ラインでの特性チェック方法として、一部のサンプルにモニター用のセルを全面に形成し、それを評価してもよい。
Figure JPOXMLDOC01-appb-T000003
　表３に示すように、実施例では、比較例に対して開放電圧Ｖｏｃ及び短絡電流Ｉｓｃが増加し、その結果として光劣化後の効率ηが比較例に対して１．０４倍まで向上した。
　図４は、光起電力装置１００におけるｐ型層４０とバッファー層の合計膜厚と開放電圧Ｖｏｃとの関係を示すグラフである。ここで、太実線は、実施例において光劣化を受けていない製造初期の光起電力装置１００の開放電圧Ｖｏｃを示し、太破線は、実施例において光劣化後の光起電力装置１００の開放電圧Ｖｏｃを示す。また、細実線は、比較例において光劣化を受けていない製造初期の光起電力装置１００の開放電圧Ｖｏｃを示し、細破線は、比較例において光劣化後の光起電力装置１００の開放電圧Ｖｏｃを示す。
　実施例では、光照射による影響が安定化した後において光起電力装置１００全体としての効率を高めることができた。すなわち、透明絶縁基板１０の面内においてｐ型層４０が膜厚範囲Ｘ内において膜厚分布を有していたとしても、初期の開放電圧Ｖｏｃが低くなるｐ型層４０の膜厚では光照射後に開放電圧Ｖｏｃが向上し、初期の開放電圧Ｖｏｃが高くなるｐ型層４０の膜厚では光照射後の開放電圧Ｖｏｃが低下する。したがって、光照射による影響が安定化した後は、透明絶縁基板１０の面内において開放電圧Ｖｏｃは均一化され、光起電力装置１００全体としての効率が高められる。一方、比較例では、初期の開放電圧Ｖｏｃに比べて光照射後に開放電圧Ｖｏｃが向上する膜厚は１６ｎｍ～１７ｎｍ付近であり、この膜厚領域では初期の開放電圧Ｖｏｃが極めて低い。したがって、ｐ型層４０の膜厚範囲をこの領域を含むものとし、透明絶縁基板１０の面内において開放電圧Ｖｏｃを均一化させたとしても、光起電力装置１００全体の変換効率を向上させることができない。一方、初期の開放電圧Ｖｏｃが高い膜厚領域とした場合、光照射後には全ての領域において開放電圧Ｖｏｃが低下し、透明絶縁基板１０の面内において開放電圧Ｖｏｃを均一化させることができない。したがって、光起電力装置１００全体の変換効率を向上させることができない。
　以上のように、実施例における透明導電膜１２のテクスチャ構造を持たせることによって、光劣化による影響が安定化した後の光起電力装置１００全体としての特性を向上させることができた。
　なお、本実施の形態では、ａ－Ｓｉユニットとμｃ－Ｓｉユニットを積層させたタンデムセルについて説明したが、ａ－Ｓｉユニットのみのシングルセルであっても同様の効果を得ることができる。また、ａ－Ｓｉユニットは、発電層がアモルファスシリコンに限定されるものではなく、アモルファスシリコンの化合物（アモルファス炭化シリコン：ａ－ＳｉＣｘ、アモルファス酸化シリコン：ａ－ＳｉＯｘ、アモルファス窒化シリコン：ａ－ＳｉＮｘ）等としてもよい。
　また、ａ－Ｓｉユニットを含む３層又はそれ以上のスタックセルでもよく、ａ－Ｓｉユニットとバルク結晶シリコンとのスタックセルでもよい。また、本実施の形態では、ユニット同士が直列に接続されている構造を例に説明したが、ユニット同士の電気的接続はこれに限定されるものではなく、例えば並列接合や４端子セルでもよく、直列接合や並列接合の組み合わせでもよい。
　１０　透明絶縁基板、１２　透明導電膜、１４　中間層、１６　第１裏面電極層、１８　第２裏面電極層、２０　充填材、２２　保護膜、４０　ｐ型層、４２　ｉ型層、４４　ｎ型層、１００　光起電力装置、１０２　アモルファスシリコン光電変換ユニット（ａ－Ｓｉユニット）、１０４　微結晶シリコン光電変換ユニット（μｃ－Ｓｉユニット）。
 

Claims (4)

  1. 　透明導電層上に形成されたアモルファスシリコン又はその化合物の発電層を有する光起電力装置であって、
    　基板面内において、光照射後に開放電圧が低下する領域と、光照射後に開放電圧が向上する領域と、を含むことを特徴とする光起電力装置。
  2. 　請求項１に記載の光起電力装置であって、
    　前記透明導電層は、波長が５５０ｎｍの光に対して、ヘイズ率が２０％以上であることを特徴とする光起電力装置。
  3. 　請求項１に記載の光起電力装置であって、
    　前記透明導電層は、酸化亜鉛を含んで構成されることを特徴とする光起電力装置。
  4. 　請求項２に記載の光起電力装置であって、
    　前記透明導電層は、酸化亜鉛を含んで構成されることを特徴とする光起電力装置。
     
PCT/JP2012/079618 2011-11-30 2012-11-15 光起電力装置 WO2013080803A1 (ja)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011066213A (ja) * 2009-09-17 2011-03-31 Mitsubishi Heavy Ind Ltd 光電変換装置及びその製造方法
JP2011077220A (ja) * 2009-09-30 2011-04-14 Sanyo Electric Co Ltd 太陽電池
JP2011135053A (ja) * 2009-11-30 2011-07-07 Sanyo Electric Co Ltd 光電変換装置及びその製造方法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011066213A (ja) * 2009-09-17 2011-03-31 Mitsubishi Heavy Ind Ltd 光電変換装置及びその製造方法
JP2011077220A (ja) * 2009-09-30 2011-04-14 Sanyo Electric Co Ltd 太陽電池
JP2011135053A (ja) * 2009-11-30 2011-07-07 Sanyo Electric Co Ltd 光電変換装置及びその製造方法

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