【発明の詳細な説明】[Detailed description of the invention]
本発明はアモルフアスシリコン（以下ａ―Siと
称する）を用いた太陽電池等の光起電力素子に関
する。
従来より、各種半導体材料を使用した光起電力
素子が存在する。この中でシラン（SiH4）ガス等
のシリコン化合物をグロー放電分解することなど
により得られるａ―Si半導体は結晶半導体に比べ
て低温工程で製造でき、大面積化が比較的容易で
不純物のドーピングが容易に行なえ、しかも薄膜
で光起電力素子を形成し得るなどの特徴があり、
代替エネルギ源開発の要請に応える材料として着
目されている。
しかし、現在のところａ―Si光起電力素子は他
の単結晶（例えばGaAS、Si）半導体材料を使用
した光起電力素子に比べて光を電気エネルギに変
換する効率が低く、従つて製造コストが高いた
め、一般のエネルギ源としては普及されるまでに
至つていない。
第１図は従来のａ―Si光起電力素子の構造を示
す断面図であり、１はガラス等の透明基板、２は
酸化インジウム系、酸化錫系などの透明導電膜、
３はａ―Si半導体層で、ｐ型ａ―Si層４、ｉ型ａ
―Si層５、ｎ型ａ―Si層６を積層したものであ
り、７はアルミニウムなどの電極、８は太陽光線
である。透明導電膜２は公知の真空蒸着法、イオ
ンプレーテイング法、スパツタ法、CVD法ある
いはスプレー法などによつて得られ、その厚みは
500〜5000Å程度である。ａ―Si層３は公知のグ
ロー放電分解法、反応性スパツタ法などによつて
得られ、ｐ型ａ―Si層４はホウ素（Ｂ）などをド
ープし、ｉ型ａ―Si層５は不純物をドープせず、
ｎ型ａ―Si層６は燐（Ｐ）などをドープしてお
り、各々の厚みはｐ型ａ―Si層４が50〜200Å、
ｉ型ａ―Si層５が約5000Å、ｎ型ａ―Si層６が約
500Åである。電極７はアルミニウムなどを真空
蒸着することによつて作成され、その厚みは0.5
μｍ〜１μｍ程度である。
このような構造のａ―Si光起電力素子において
その面積が小さい時（0.1cm2程度以下）、および大
きい時（１cm2程度以上）の光電変換効率を、透明
導電膜が酸化錫系（酸化錫に酸化アンチモンなど
をドープすることもあるので酸化錫系と呼ぶ）と
酸化インジウム系（酸化インジウムに酸化錫など
をドープすることもあるので酸化インジウム系と
呼ぶ）である場合について第１表に示す。
透明導電膜のシート抵抗値および550nm（ナノ
メーター）の波長の光に対するガラス基板を含め
た透過率もあわせて第１表に示す。
The present invention relates to a photovoltaic element such as a solar cell using amorphous silicon (hereinafter referred to as a-Si). Photovoltaic elements using various semiconductor materials have conventionally existed. Among these, a-Si semiconductors, which are obtained by glow discharge decomposition of silicon compounds such as silane (SiH 4 ) gas, can be manufactured in a lower temperature process compared to crystalline semiconductors, are relatively easy to increase in area, and are not doped with impurities. It has the characteristics of being easy to perform and also being able to form photovoltaic elements with thin films.
It is attracting attention as a material that can meet the demands of developing alternative energy sources. However, at present, a-Si photovoltaic devices are less efficient at converting light into electrical energy than photovoltaic devices using other single-crystal (e.g., GaAS, Si) semiconductor materials, and therefore have lower manufacturing costs. Due to its high energy consumption, it has not yet become widespread as a general energy source. FIG. 1 is a cross-sectional view showing the structure of a conventional a-Si photovoltaic device, in which 1 is a transparent substrate such as glass, 2 is a transparent conductive film such as indium oxide, tin oxide, etc.
3 is an a-Si semiconductor layer, p-type a-Si layer 4, i-type a
-Si layer 5 and n-type a-Si layer 6 are laminated, 7 is an electrode such as aluminum, and 8 is sunlight. The transparent conductive film 2 is obtained by a known vacuum deposition method, ion plating method, sputtering method, CVD method, spray method, etc., and its thickness is
It is about 500 to 5000 Å. The a-Si layer 3 is obtained by a known glow discharge decomposition method, reactive sputtering method, etc., the p-type a-Si layer 4 is doped with boron (B), etc., and the i-type a-Si layer 5 is doped with impurities. without doping,
The n-type a-Si layer 6 is doped with phosphorus (P), etc., and each thickness is 50 to 200 Å for the p-type a-Si layer 4,
The i-type a-Si layer 5 has a thickness of approximately 5000 Å, and the n-type a-Si layer 6 has a thickness of approximately 5000 Å.
It is 500Å. The electrode 7 is made by vacuum evaporating aluminum or the like, and its thickness is 0.5
It is about μm to 1 μm. In an a-Si photovoltaic element with such a structure, the photoelectric conversion efficiency when the area is small (about 0.1 cm 2 or less) and when it is large (about 1 cm 2 or more) is Table 1 shows the cases where tin is sometimes doped with antimony oxide, so it is called a tin oxide type) and indium oxide type (indium oxide is sometimes doped with tin oxide, so it is called an indium oxide type). show. Table 1 also shows the sheet resistance value of the transparent conductive film and the transmittance including the glass substrate for light with a wavelength of 550 nm (nanometers).
【表】
第１表に示すごとく、光起電力素子の面積が小
さい時には酸化錫系透明導電膜の方が酸化インジ
ウム系透明導電膜より、シート抵抗が大きいにも
かかわらず、変換効率が高い。一方、光起電力素
子の面積が大きい時には酸化インジウム系の透明
導電膜の方が変換効率が高い。
そこで発明者らはこの現象を次のように解釈し
た。つまり、酸化物透明導電膜は半導体であり、
フエルミレベルも仕事関数も材質によつて異な
り、また他の半導体との界面には材質によつて界
面準位を作ることがある。透明導電膜とａ―Si層
とを接合した光起電力素子に於いては本質的に透
明導電膜として酸化インジウム系より酸化錫系透
明導電膜の方がその特性として良いので透明導電
膜のシート抵抗値が問題にならない小面積の光起
電力素子に於いては酸化錫系透明導電膜の方が光
電変換効率が高くなる。ところが光起電力素子の
面積が大きくなると、発生する電流が多くなるの
でシート抵抗が問題となり、シート抵抗値の大き
い酸化錫系の透明導電膜を使用した方が、シート
抵抗値の小さい酸化インジウム系の透明導電膜を
使用するより光起電力素子としての光電変換効率
が悪くなる。
ところが、酸化錫系透明導電膜はシート抵抗値
を小さく、しかも光の透過率を高くすることは困
難である。そこで上記解釈を基に発明者らは、
種々検討した結果、少なくとも透明導電層とａ―
Si半導体層とを備えた光起電力素子において透明
導電層が、酸化インジウム系と酸化錫系透明導電
層の２層とからなり酸化錫系透明導電層とａ―Si
層が接合している光起電力素子にすれば透明導電
層のシート抵抗も小さくなるため比較的大きい面
積の光起電力素子でも高い光電変換効率を得るこ
とが出来ることを見い出した。従つて本発明の目
的は、比較的面積が大きくとも、高い光電変換効
率を有する、ａ―Si光起電力素子を提供すること
にある。以下実施例について詳細に説明する。
第２図は本発明によるａ―Si太陽電池の１実施
例の構造を示す断面図であり、１０はガラスなど
の透明基板、１１は酸化インジウム系透明導電
膜、１２は酸化錫系透明導電膜、１３はａ―Si半
導体層で基板側から順次ｐ型ａ―Si層１４、ｉ型
ａ―Si層１５、ｎ型ａ―Si層１６の接合構造でな
りたつており、１７はアルミニウムなどの電極、
１８は太陽光線を示す。この構造のａ―Si光起電
力素子を素子Ａと呼ぶ。
素子Ａと基本構造的には同じで、ステンレス鋼
などの金属基板上にｎ型、ｉ型、ｐ型のａ―Si
層、酸化錫系透明導電膜、および酸化インジウム
系透明導電膜を順次形成した構造の光起電力素子
を素子Ｂと呼ぶ。この構造の場合、光は基板の反
対側から入射される。
第３図は本発明によるａ―Si光起電力素子の他
の実施例の構造を示す断面図であり、２０はガラ
スなどの透明基板、２１は酸化インジウム系透明
導電膜、２２は酸化錫系透明導電膜、２３はａ―
Si半導体層で基板側から順次ｎ型ａ―Si層２４、
ｉ型ａ―Si層２５、ｐ型ａ―Si層２６の接合構造
でなりたつており、２７はアルミニウムなどの電
極、２８は太陽光線を示す。この構造のａ―Si光
起電力素子を素子Ｃと呼ぶ。
素子Ｃと基本構造的には同じで、ステンレス鋼
などの金属基板上にｐ型、ｉ型、ｎ型のａ―Si層
酸化錫系透明導電膜、および酸化インジウム系透
明導電膜を順次形成した構造の光起電力素子を素
子Ｄと呼ぶ。この構造の場合、光は基板の反対側
から入射される。
第４図は本発明によるａ―Si光起電力素子の他
の実施例の構造を示す断面図であり、３０はガラ
スなどの透明基板、３１は酸化インジウム系透明
導電膜、３２は酸化錫系透明導電膜、３３はａ―
Si半導体層で基板側から順次ｉ型ａ―Si層３５、
ｎ型ａ―Si層３６の接合構造でなりたつており、
３７はアルミニウムなどの電極、３８は太陽光線
を示す。この構造のａ―Si光起電力素子を素子Ｅ
と呼ぶ。
素子Ａ，Ｂ，Ｃ，ＤおよびＥにおいて酸化錫系
および酸化インジウム系透明導電膜１１，１２，
２１，２２，３１および３２は公知の真空蒸着
法、スパツタ法、イオンレーテイング法、CVD
法あるいはスプレー法などによつて得られ、酸化
錫系透明導電膜１２，２２および３２は酸化アン
チモンを約５重量％ドープしたもので、その厚み
は50〜1500Åとし、酸化インジウム系透明導電膜
１１，２１および３１は酸化錫を約５重量％ドー
プしたもので、その厚みは100Å〜4000Åとし
た。ａ―Si層１３，２３，３３は公知のグロー放
電分解法、反応性スパツタ法などによつて得ら
れ、ｐ型ａ―Si層１４、２６はホウ素（Ｂ）など
をドープし、その厚みは50〜300Åで、ｉ型ａ―
Si層１５，２５，３５は不純物をドープせず、そ
の厚みは3000〜8000Åで、ｎ型ａ―Si層１６，２
４，３６は燐（Ｐ）などをドープし、その厚みは
100〜1000Åである。電極１７，２７，３７はア
ルミニウムなどを公知の真空蒸着法などで作成さ
れ、その厚みは0.3〜１μｍ程度である。
このような構造の本発明によるａ―Si光起電力
素子Ａ，Ｂ，Ｃ，Ｄ，Ｅおよびこれら各々の素子
と同じ構造で透明導電膜が酸化インジウム系のみ
である従来の素子Ｆ，Ｇ，Ｈ，Ｉ，Ｊの面積が
各々２cm2の光電変換効率を第２表に示す。透明導
電膜のシート抵抗値および550nmの波長の光に対
するガラス基板を含めた透過率は全て同じものを
使用し、各々シート抵抗が12Ω／□、透過率が85
％である。第２表には、各々の構造の素子につい
て、本発明による光電変換効率が従来のものに比
べて増加した割合も合せて示す。[Table] As shown in Table 1, when the area of the photovoltaic element is small, the conversion efficiency of the tin oxide-based transparent conductive film is higher than that of the indium oxide-based transparent conductive film despite having a higher sheet resistance. On the other hand, when the area of the photovoltaic element is large, an indium oxide-based transparent conductive film has higher conversion efficiency. Therefore, the inventors interpreted this phenomenon as follows. In other words, the oxide transparent conductive film is a semiconductor,
The Fermi level and work function vary depending on the material, and depending on the material, interface states may be created at the interface with other semiconductors. In a photovoltaic device in which a transparent conductive film and an a-Si layer are bonded, a tin oxide-based transparent conductive film has better characteristics than an indium oxide-based transparent conductive film, so a transparent conductive film sheet is used. In small-area photovoltaic elements where resistance is not a problem, tin oxide-based transparent conductive films have higher photoelectric conversion efficiency. However, as the area of the photovoltaic element increases, the generated current increases, so sheet resistance becomes a problem, and it is better to use a tin oxide-based transparent conductive film, which has a higher sheet resistance value, than an indium oxide-based film, which has a lower sheet resistance value. The photoelectric conversion efficiency as a photovoltaic element becomes worse than using a transparent conductive film. However, it is difficult for tin oxide-based transparent conductive films to have a low sheet resistance value and high light transmittance. Therefore, based on the above interpretation, the inventors
As a result of various studies, at least the transparent conductive layer and a-
In a photovoltaic element equipped with a Si semiconductor layer, the transparent conductive layer is composed of two layers, an indium oxide-based transparent conductive layer and a tin oxide-based transparent conductive layer, and a tin oxide-based transparent conductive layer and an a-Si semiconductor layer.
It has been found that if the photovoltaic elements are made of bonded layers, the sheet resistance of the transparent conductive layer will be reduced, so even a photovoltaic element with a relatively large area can achieve high photoelectric conversion efficiency. Accordingly, an object of the present invention is to provide an a-Si photovoltaic device that has a relatively large area but has high photoelectric conversion efficiency. Examples will be described in detail below. FIG. 2 is a cross-sectional view showing the structure of one embodiment of the a-Si solar cell according to the present invention, in which 10 is a transparent substrate such as glass, 11 is an indium oxide-based transparent conductive film, and 12 is a tin oxide-based transparent conductive film. , 13 is an a-Si semiconductor layer consisting of a p-type a-Si layer 14, an i-type a-Si layer 15, and an n-type a-Si layer 16 in order from the substrate side, and 17 is an electrode made of aluminum or the like. ,
18 indicates the sun's rays. The a-Si photovoltaic device having this structure is called device A. The basic structure is the same as element A, with n-type, i-type, and p-type a-Si on a metal substrate such as stainless steel.
A photovoltaic element having a structure in which a layer, a tin oxide-based transparent conductive film, and an indium oxide-based transparent conductive film are sequentially formed is referred to as element B. In this structure, light is incident from the opposite side of the substrate. FIG. 3 is a sectional view showing the structure of another embodiment of the a-Si photovoltaic device according to the present invention, in which 20 is a transparent substrate such as glass, 21 is an indium oxide-based transparent conductive film, and 22 is a tin oxide-based transparent conductive film. Transparent conductive film, 23 is a-
An n-type a-Si layer 24 in Si semiconductor layer from the substrate side,
It consists of a junction structure of an i-type a-Si layer 25 and a p-type a-Si layer 26, 27 represents an electrode such as aluminum, and 28 represents sunlight. The a-Si photovoltaic device having this structure is called device C. The basic structure is the same as that of element C, in which p-type, i-type, and n-type a-Si layer tin oxide-based transparent conductive films and indium oxide-based transparent conductive films were sequentially formed on a metal substrate such as stainless steel. The photovoltaic device having this structure is called device D. In this structure, light is incident from the opposite side of the substrate. FIG. 4 is a sectional view showing the structure of another embodiment of the a-Si photovoltaic device according to the present invention, in which 30 is a transparent substrate such as glass, 31 is an indium oxide-based transparent conductive film, and 32 is a tin oxide-based transparent conductive film. Transparent conductive film, 33 is a-
I-type a-Si layer 35 in Si semiconductor layer from the substrate side,
It consists of a junction structure of n-type a-Si layer 36,
Reference numeral 37 indicates an electrode such as aluminum, and reference numeral 38 indicates sunlight. An a-Si photovoltaic device with this structure is used as device E.
It is called. In elements A, B, C, D and E, tin oxide-based and indium oxide-based transparent conductive films 11, 12,
21, 22, 31 and 32 are known vacuum evaporation methods, sputtering methods, ion rating methods, CVD
The tin oxide-based transparent conductive films 12, 22, and 32 are doped with about 5% by weight of antimony oxide, and have a thickness of 50 to 1500 Å. , 21 and 31 were doped with about 5% by weight of tin oxide, and had a thickness of 100 Å to 4000 Å. The a-Si layers 13, 23, 33 are obtained by a known glow discharge decomposition method, reactive sputtering method, etc., and the p-type a-Si layers 14, 26 are doped with boron (B), etc., and have a thickness of 50 to 300 Å, type i a-
The Si layers 15, 25, 35 are not doped with impurities and have a thickness of 3000 to 8000 Å, and the n-type a-Si layers 16, 2
4,36 is doped with phosphorus (P), etc., and its thickness is
It is 100 to 1000 Å. The electrodes 17, 27, and 37 are made of aluminum or the like by a known vacuum deposition method, and have a thickness of about 0.3 to 1 μm. The a-Si photovoltaic devices A, B, C, D, and E according to the present invention having such a structure, and the conventional devices F, G, and F, which have the same structure as each of these devices and have only an indium oxide-based transparent conductive film. Table 2 shows the photoelectric conversion efficiency when the areas of H, I, and J are each 2 cm 2 . The sheet resistance value of the transparent conductive film and the transmittance including the glass substrate for light with a wavelength of 550 nm are all the same, and the sheet resistance is 12Ω/□ and the transmittance is 85.
%. Table 2 also shows the percentage increase in photoelectric conversion efficiency according to the present invention compared to the conventional one for elements of each structure.
【表】
第２表に示すごとく、本発明によれば、透明導
電層とａ―Si半導体層とを備えた光起電力素子に
おいて、透明導電層が、酸化インジウム系透明導
電層と、酸化錫系透明導電層の積層でなり、酸化
錫系透明導電層とａ―Si半導体層が接合した構造
にすることにより光電変換効率が大巾に増加す
る。しかもａ―Si半導体層がｐ―ｉ―ｎ構造の場
合その効果が大きくなり、透明導電膜とｐ型ａ―
Si層とが接合した構造の場合、さらにその効果が
大きい。
ａ―Si半導体層は上述の水素添加ａ―Siの他、
微結晶アモルフアスSi、あるいは他の元素例えば
弗素、炭素、窒素、ゲルマニウム、錫、酸素、等
を添加したａ―Si半導体であつてもよい。
以上の説明は酸化錫系透明導電膜が酸化アンチ
モンを酸化インジウム系透明導電膜が酸化錫を
各々ドープしたものについて述べたが、各々他の
物質をドープしても、あるいは不純物をドープし
なくとも良い。
また、透明導電膜の厚みは限定されるものでは
ないが、可視域での光の透過率は80％以上、シー
ト抵抗値は50Ω／□以下が好ましい。
ａ―Si層と接合する酸化錫系透明導電膜の厚み
は膜として存在し得る50A゜以上で、酸化インジ
ウム系透明導電膜の厚みはシート低抗値が50Ω／
□以下になる100A゜以上で各々、光の透過率が
極端に減少しない厚みが好ましい。また光源のス
ペペクトル分布およびａ―Si光起電力素子の分光
感度特性から得られる有効波長範囲で光起電力素
子に入射する光の反射率が小さくなるように透明
電導層の厚みを設定することにより光起電力素子
の光電変換効率が向上することは云うまでもな
い。
以上詳細に説明したごとく本発明によれば、比
較的面積が大きくとも、光電変換効率の高いａ―
Si光起電力素子が得られる。
光電変換効率は基板の表面状態、ａ―Siの成膜
条件にもよるが光起電力素子の短絡電流、開放電
圧、曲線因子（Fill Factor）の少なくとも一つ
の特性が向上することにより高くなる。また、酸
化インジウム系透明導電層単層を使用した光起電
力素子に比べ、酸化錫系と酸化インジウム系の二
層の透明導電層を使用した方が透明導電層の表面
状態の影響を受けにくく特性が安定している。[Table] As shown in Table 2, according to the present invention, in a photovoltaic element comprising a transparent conductive layer and an a-Si semiconductor layer, the transparent conductive layer is composed of an indium oxide-based transparent conductive layer and a tin oxide-based transparent conductive layer. By forming a structure in which a tin oxide based transparent conductive layer and an a-Si semiconductor layer are bonded, the photoelectric conversion efficiency is greatly increased. Moreover, when the a-Si semiconductor layer has a p-i-n structure, the effect becomes greater, and the transparent conductive film and p-type a-
In the case of a structure in which the Si layer is bonded, the effect is even greater. The a-Si semiconductor layer is made of the above-mentioned hydrogenated a-Si,
It may be microcrystalline amorphous Si or an a-Si semiconductor to which other elements such as fluorine, carbon, nitrogen, germanium, tin, oxygen, etc. are added. In the above explanation, the tin oxide-based transparent conductive film is doped with antimony oxide, and the indium oxide-based transparent conductive film is doped with tin oxide, but they can also be doped with other substances or without impurities. good. Further, the thickness of the transparent conductive film is not limited, but it is preferable that the light transmittance in the visible range is 80% or more and the sheet resistance value is 50Ω/□ or less. The thickness of the tin oxide-based transparent conductive film bonded to the a-Si layer is 50A° or more, which can exist as a film, and the thickness of the indium oxide-based transparent conductive film is such that the sheet resistance value is 50Ω/
It is preferable that the thickness be such that the light transmittance does not decrease significantly at 100 A° or more, which is less than □. In addition, by setting the thickness of the transparent conductive layer so that the reflectance of light incident on the photovoltaic element is small in the effective wavelength range obtained from the spectral distribution of the light source and the spectral sensitivity characteristics of the a-Si photovoltaic element. It goes without saying that the photoelectric conversion efficiency of the photovoltaic element is improved. As explained in detail above, according to the present invention, even if the area is relatively large, the a-
A Si photovoltaic device is obtained. Although the photoelectric conversion efficiency depends on the surface condition of the substrate and the conditions for forming the a-Si film, it can be increased by improving at least one of the short circuit current, open circuit voltage, and fill factor of the photovoltaic element. In addition, compared to a photovoltaic element that uses a single layer of indium oxide-based transparent conductive layer, using a two-layer transparent conductive layer of tin oxide and indium oxide is less affected by the surface condition of the transparent conductive layer. Characteristics are stable.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は従来のａ―Si光起電力素子の構造を示
す断面図であり、第２図、第３図および第４図は
本発明のａ―Si光起電力素子の構造を示す断面図
である。
１，１０，２０，３０：ガラス基板、２，１
１，１２，２２，３１，３２：透明導電膜、３，
１３，２３，３３：ａ―Si層、７，１７，２７，
３７：電極、８，１８，２８，３８：太陽光線。
FIG. 1 is a cross-sectional view showing the structure of a conventional a-Si photovoltaic device, and FIGS. 2, 3, and 4 are cross-sectional views showing the structure of the a-Si photovoltaic device of the present invention. It is. 1, 10, 20, 30: glass substrate, 2, 1
1, 12, 22, 31, 32: transparent conductive film, 3,
13, 23, 33: a-Si layer, 7, 17, 27,
37: Electrode, 8, 18, 28, 38: Sunlight.