JPS6332276B2

JPS6332276B2 -

Info

Publication number: JPS6332276B2
Application number: JP56125811A
Authority: JP
Inventors: Hajime Ichanagi; Tadashi Igarashi; Nobuhiko Fujita
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1981-08-10
Filing date: 1981-08-10
Publication date: 1988-06-29
Also published as: JPS5827376A

Description

[Detailed description of the invention]

本発明は太陽電池素子の製造方法に関する。従来より各種半導体および酸化物系透明導電膜
を使用した光起電力素子は存在する。近年モノシ
ラン（SiH₄）ガスをグロー放電分解することな
どにより得られるアモルフアスシリコン（以下ａ
−Siと称する）はそれまで不可能とされていた価
電子制御が可能であることが明らかにされた。そ
れ以来薄膜で光起電力素子が構成でき、大面積化
が容易であるなどの特徴が考えられ、太陽電池な
どへの応用が考えられている。太陽電池などに使用される、つまり価電子制御
が可能なａ−Si膜には多量の水素やフツ素が含ま
れている。また、ａ−Si作成時の基板温度の最適
値は約250℃である。このａ−Si膜上に酸化物系
透明導電膜を形成し、光起電力素子とするが、透
明導電膜の特性としては光の透過率が高いこと、
および面抵抗が小さいことがその必要条件とされ
る。透過率は85％以上、面抵抗は100Ω／□以下で
あることが望ましい。酸化インジウム、酸化錫な
どの酸化物系透明導電膜に於いては、85％以上の
透過率を得るためには1μｍ以下の厚みが好まし
く、また100Ω／□以下の面抵抗を得るためには
1000Å以上の厚みが好ましいため、透明導電膜の
厚みは3000Å程度のものがよく使用される。酸化
物系透明導電膜を真空蒸着等の手段で作成すると
きの基板温度が300℃以上でなければ光透過率の
良い、抵抗の小さい透明導電膜は得られない。と
ころがａ−Si膜を形成后、ａ−Siをその形成時の
温度（250℃）以上に加熱すると、ａ−Si中に含
まれていた水素やフツ素が離脱することなどによ
りａ−Siの特性、つまり太陽電池の特性が悪くな
る欠点を有していた。一方、反応性イオンプレーテイング法、反応性
スパツタ法などの方法で、プラズマをかいして酸
化物系透明導電膜を作成する場合、比較的低温で
光の透過率の良い導電膜が得られる。しかし、半
導体表面が活性化された酸素のため酸化等により
犯され、半導体と透明導電膜の界面状態が悪くな
り、太陽電池特性が悪くなる欠点を有していた。本発明は、半導体上に第１の透明導電膜を通常
の真空蒸着法で形成し、しかる後に第１の透明導
電膜上に第２の透明導電膜をプラズマ状態を経て
形成することにより、特性の良い、つまり光電変
換効率の高い光起電力素子を提供するものであ
る。以下、実施例について詳細に説明する。第１図は、従来法によるａ−Si半導体を使用し
た光起電力素子の構造を示す断面図であり、１は
ステンレス鋼基板、２はａ−Si半導体層、３は酸
化インジウム・錫（酸化錫が５〜10wt％）の透
明導電膜、４は太陽光線を示す。ａ−Si半導体層
２はホウ素(B)をドープしたＰ形のａ−Si層、不純
物をドープしないｉ形のａ−Si層、および燐
（Ｐ）をドープしたｎ形のａ−Si層から成立つて
おり、プラズマCVD法（グロー放電分解法）で
作成される。ステンレス鋼基板１上にａ−Si層２
を形成したものの上に酸化インジウム錫透明導電
膜３を従来法で形成した。従来法１酸化インジウム・錫透明導電膜を基板温度150
℃で真空蒸着法で形成した。真空度は10^-6Torr
台、膜成長速度は約１Å／secである。従来法透明導電膜を基板温度150℃で10^-4Torrの酸素
雰囲気で真空蒸着法で形成した。膜成長速度は約
１Å／secである。従来法透明導電膜を基板温度350℃で10^-4Torrの酸素
雰囲気で真空蒸着法で形成した。膜成長速度は約
１Å／secである。従来法酸化インジウム・錫透明導電膜を下に述べるイ
オンプレーテイング法で、基板温度150℃で形成
した。イオンプレーテイング法とは蒸発源と基板
との間に高周波または直流電圧を印加するイオン
化電極により、蒸発粒子あるいは／および雰囲気
ガスをイオン化し、成膜する方法である。本方法
では蒸発物と雰囲気ガスがイオン化し、活性化し
ているので、蒸発物質と雰囲気ガスとの反応性蒸
着が可能である。本従来法においては、蒸発源は酸化インジウ
ム・錫（酸化錫が５〜10wt％）をし、イオン化
電極には13.56MHzの高周波電力を200Wかけ、
10^-4Torrの酸素雰囲気とした。第２図は本発明の製造方法によるａ−Si半導体
を使用した太陽電池素子の構造を示す断面図であ
り、１１はステンレス鋼基板、１２はａ−Si半導
体層、１３は第１の酸化インジウム・錫（酸化錫
が５〜10wt％）の透明導電膜、１４は第２の酸
化インジウム錫（酸化錫が５〜10wt％）の透明
導電膜、１５は太陽光線である。ａ−Si半導体層１２は、第１図で示したａ−Si
半導体層２と同じである。実施例ステンレス基板１１上にａ−Si層１２を形成
し、その上に第１の透明導電膜１３を真空蒸着法
で、10^-4Torr台の酸素雰囲気で、基板温度150℃
で、膜厚100Å形成した。しかる后に第１の透明
導電膜１３上に前述のイオンプレーテイング法で
第２の透明導電膜１４を基板温度150℃で膜厚
2900Å形成した。イオンプレーテイング法は基板
に負電圧を印加することにより、イオン化した粒
子を通常の蒸着などより大きい運動オネルギで基
板に付着させ、密着性の良い膜を形成することも
可能である。本実施例においては、蒸発源は酸化インジウ
ム・錫（酸化錫が５〜10wt％）とし、イオン化
電極には13.56MHzの高周波電力を200Wかけ、
10^-4Torrの酸素雰囲気とした。酸素分圧はイオ
ン化を安定するために10^-2〜10^-5Torrが好まし
い。また、基板には直流負電圧を印加しなかつ
た。以上説明した従来法および本発明の実施例にお
いて、透明導電膜の厚みは3000Åとし、面積は９
mm²とした。また透明導電膜以外の製法、および構
造は全て同一とした。以上説明した従来法、および本発明の実施例で
試作した光起電力素子の太陽光（AM−１、100
ｍＷ／cm²）照射時の出力特性を表１に示す。 Jscは短絡光電流、Vocは周波端電圧、FFはカ
ーブフイルフアクタ、Effは光電変換効率である。 The present invention relates to a method for manufacturing a solar cell element. Photovoltaic elements using various semiconductor and oxide-based transparent conductive films have conventionally existed. In recent years, amorphous silicon (hereinafter referred to as a) obtained by glow discharge decomposition of monosilane (SiH ₄ ) gas
-Si) was found to be capable of controlling valence electrons, which was previously thought to be impossible. Since then, it has been considered that photovoltaic elements can be constructed from thin films and that it is easy to increase the area, and applications such as solar cells have been considered. A-Si films used in solar cells and the like, which are capable of controlling valence electrons, contain large amounts of hydrogen and fluorine. Further, the optimum value of the substrate temperature during a-Si production is about 250°C. An oxide-based transparent conductive film is formed on this a-Si film to form a photovoltaic device, but the characteristics of the transparent conductive film are that it has high light transmittance;
The necessary condition is that the sheet resistance is small. It is desirable that the transmittance is 85% or more and the sheet resistance is 100Ω/□ or less. For oxide-based transparent conductive films such as indium oxide and tin oxide, the thickness is preferably 1 μm or less in order to obtain a transmittance of 85% or more, and the thickness is preferably 1 μm or less in order to obtain a sheet resistance of 100 Ω/□ or less.
Since a thickness of 1000 Å or more is preferable, a transparent conductive film with a thickness of about 3000 Å is often used. A transparent conductive film with good light transmittance and low resistance cannot be obtained unless the substrate temperature is 300° C. or higher when forming an oxide-based transparent conductive film by means such as vacuum evaporation. However, after forming the a-Si film, if the a-Si is heated above the temperature at which it was formed (250°C), the hydrogen and fluorine contained in the a-Si will be released, causing the a-Si to deteriorate. It had the disadvantage that the characteristics, that is, the characteristics of the solar cell deteriorated. On the other hand, when creating an oxide-based transparent conductive film using plasma using a method such as reactive ion plating or reactive sputtering, a conductive film with good light transmittance can be obtained at a relatively low temperature. However, the surface of the semiconductor is damaged by oxidation due to the activated oxygen, resulting in poor interface conditions between the semiconductor and the transparent conductive film, resulting in poor solar cell characteristics. The present invention is characterized by forming a first transparent conductive film on a semiconductor using a normal vacuum evaporation method, and then forming a second transparent conductive film on the first transparent conductive film through a plasma state. In other words, the present invention provides a photovoltaic element with high photoelectric conversion efficiency. Examples will be described in detail below. FIG. 1 is a cross-sectional view showing the structure of a photovoltaic device using an a-Si semiconductor according to a conventional method. 1 is a stainless steel substrate, 2 is an a-Si semiconductor layer, and 3 is an indium oxide/tin oxide (oxide 4 represents sunlight. The a-Si semiconductor layer 2 consists of a P-type a-Si layer doped with boron (B), an i-type a-Si layer not doped with impurities, and an n-type a-Si layer doped with phosphorus (P). It is created using the plasma CVD method (glow discharge decomposition method). a-Si layer 2 on stainless steel substrate 1
An indium tin oxide transparent conductive film 3 was formed on the indium tin oxide transparent conductive film 3 by a conventional method. Conventional method 1 Indium oxide/tin transparent conductive film at substrate temperature 150
It was formed by vacuum evaporation method at ℃. Vacuum level is 10 ^-6 Torr
The film growth rate was approximately 1 Å/sec. Conventional method A transparent conductive film was formed by vacuum evaporation in an oxygen atmosphere of 10 ^-4 Torr at a substrate temperature of 150°C. The film growth rate is approximately 1 Å/sec. Conventional method A transparent conductive film was formed by vacuum evaporation in an oxygen atmosphere of 10 ^-4 Torr at a substrate temperature of 350°C. The film growth rate is approximately 1 Å/sec. Conventional method An indium oxide/tin transparent conductive film was formed using the ion plating method described below at a substrate temperature of 150°C. The ion plating method is a method of forming a film by ionizing evaporated particles and/or atmospheric gas using an ionization electrode that applies a high frequency or DC voltage between an evaporation source and a substrate. In this method, since the evaporated substance and the atmospheric gas are ionized and activated, reactive vapor deposition of the evaporated substance and the atmospheric gas is possible. In this conventional method, the evaporation source is indium tin oxide (5 to 10 wt% tin oxide), and 200 W of 13.56 MHz high frequency power is applied to the ionization electrode.
The oxygen atmosphere was 10 ^-4 Torr. FIG. 2 is a cross-sectional view showing the structure of a solar cell element using an a-Si semiconductor according to the manufacturing method of the present invention, in which 11 is a stainless steel substrate, 12 is an a-Si semiconductor layer, and 13 is a first indium oxide layer. - A transparent conductive film of tin (5 to 10 wt% tin oxide); 14 is a second transparent conductive film of indium tin oxide (5 to 10 wt% tin oxide); 15 is sunlight. The a-Si semiconductor layer 12 is the a-Si semiconductor layer 12 shown in FIG.
This is the same as the semiconductor layer 2. Example An a-Si layer 12 is formed on a stainless steel substrate 11, and a first transparent conductive film 13 is deposited thereon by a vacuum evaporation method at a substrate temperature of 150° C. in an oxygen atmosphere of about 10 ⁻⁴ Torr.
A film with a thickness of 100 Å was formed. After that, the second transparent conductive film 14 is formed on the first transparent conductive film 13 by the above-mentioned ion plating method at a substrate temperature of 150°C.
2900Å was formed. In the ion plating method, by applying a negative voltage to the substrate, ionized particles can be attached to the substrate with greater kinetic energy than in normal vapor deposition, and it is also possible to form a film with good adhesion. In this example, the evaporation source was indium tin oxide (5 to 10 wt% tin oxide), and 200 W of 13.56 MHz high frequency power was applied to the ionization electrode.
The oxygen atmosphere was 10 ^-4 Torr. The oxygen partial pressure is preferably 10 ^-2 to ^{10 -5} Torr in order to stabilize ionization. Further, no direct current negative voltage was applied to the substrate. In the conventional method and the embodiment of the present invention explained above, the thickness of the transparent conductive film is 3000 Å, and the area is 9
^mm2 . In addition, the manufacturing method and structure other than the transparent conductive film were all the same. The solar light (AM-1, 100
Table 1 shows the output characteristics during irradiation (mW/cm ² ). Jsc is the short-circuit photocurrent, Voc is the frequency edge voltage, FF is the curve foil factor, and Eff is the photoelectric conversion efficiency.

【表】表１に示すごとく、従来法に於いては透明導
電膜の光の透過率が悪いため、短絡光電流の値が
悪い。従来法に於いては、従来法に比べて透
明導電膜の光の透過率は若干改善されて短絡光電
流は増加しているものの充分ではない。従来法
に於いては透明導電膜の光の透過率は良くなつて
はいるが、透明導電膜形成時にａ−Si膜の形成さ
れた基板温度を350℃にも上げるため、ａ−Si膜
の特性が劣化し、従つて短絡光電流も伸びなやみ
他の特性も悪く、従つて光電変換効率も悪い。ま
た、従来法に於いては、透明導電膜の透光性は
改善されてはいるが、透明導電膜形成時の酸素イ
オンにより、半導体表面が犯され、半導体と透明
導電膜との界面状態が悪くなり、太陽電池特性は
良くない。一方、本発明の実施例に於いては、第１の透
明導電膜により、ａ−Si半導体表面が被覆されて
いるため、第２の透明導電膜をプラズマをかいし
て形成しても、半導体表面が犯されることなく、
従つて半導体と透明導電膜の界面状態も良い。ま
た、第１の透明導電膜の膜厚を適当に選ぶことに
より、基板温度が低くくても、透光性の良い透明
導電膜が得られる。従つて太陽電池特性として非
常に優れた特性を示す。プラズマを作る方法として電子線照射により酸
素や蒸発粒子をイオン化する方法などがあるが、
前述の高周波電界、あるいは直流電界によりイオ
ン化する方法が高透光性、低抵抗の透明導電膜を
得るのに好ましい。また、本実施例においては、蒸発源として酸化
インジウム・錫を利用した場合について述べた
が、蒸発源を金属インジウム・錫を使用し、反応
性蒸着を行つても同様の効果が得られる。透明導電膜として酸化インジウム・錫ほどの酸
化インジウム系の場合について述べたが、酸化
錫、酸化錫に酸化アンチモンを添加したものなど
の酸化錫系の透明導電膜でも同様の効果が得られ
る。他に透光性および導電性を有する酸化物があ
るが、酸化錫系および酸化インジウム系透明導電
膜が優れている。また、半導体として、ａ−Siの場合について述
べたが、250℃以上の高温にさらすと特性の悪く
なる半導体の場合も同様の効果が得られる。第１の透明導電膜の厚みは、第２の透明導電膜
形成時に、半導体表面が犯されなくするため、つ
まり膜として存在し、半導体表面がおおわれ得る
50Å以上でかつ基板温度が低くても充分な透光性
を有する1000Å以下が好ましい。以上詳細に説明したごとく、本発明によれば光
電変換効率の高い太陽電池が得られる。[Table] As shown in Table 1, in the conventional method, the light transmittance of the transparent conductive film is low, so the short-circuit photocurrent value is low. In the conventional method, although the light transmittance of the transparent conductive film is slightly improved and the short-circuit photocurrent is increased compared to the conventional method, it is not sufficient. In the conventional method, the light transmittance of the transparent conductive film has improved, but since the temperature of the substrate on which the a-Si film is formed is raised to 350°C during the formation of the transparent conductive film, the temperature of the a-Si film is The characteristics deteriorate, and therefore the short-circuit photocurrent does not increase, and other characteristics also deteriorate, and the photoelectric conversion efficiency also deteriorates. In addition, in the conventional method, although the light transmittance of the transparent conductive film is improved, the semiconductor surface is damaged by oxygen ions during the formation of the transparent conductive film, resulting in poor interface conditions between the semiconductor and the transparent conductive film. Therefore, the solar cell characteristics are not good. On the other hand, in the embodiment of the present invention, since the surface of the a-Si semiconductor is covered with the first transparent conductive film, even if the second transparent conductive film is formed using plasma, the semiconductor without the surface being violated;
Therefore, the state of the interface between the semiconductor and the transparent conductive film is also good. Furthermore, by appropriately selecting the thickness of the first transparent conductive film, a transparent conductive film with good light transmission properties can be obtained even when the substrate temperature is low. Therefore, it exhibits very excellent solar cell characteristics. There are methods to create plasma such as ionizing oxygen and evaporated particles using electron beam irradiation.
The above-mentioned method of ionization using a high frequency electric field or a direct current electric field is preferable for obtaining a transparent conductive film with high light transmittance and low resistance. Further, in this embodiment, a case has been described in which indium/tin oxide is used as an evaporation source, but similar effects can be obtained by using metallic indium/tin as an evaporation source and performing reactive vapor deposition. Although the case of an indium oxide-based transparent conductive film such as indium oxide/tin has been described, a similar effect can be obtained with a tin oxide-based transparent conductive film such as tin oxide or a film in which antimony oxide is added to tin oxide. Although there are other oxides that have translucency and conductivity, tin oxide-based and indium oxide-based transparent conductive films are excellent. Moreover, although the case of a-Si has been described as a semiconductor, the same effect can be obtained in the case of a semiconductor whose characteristics deteriorate when exposed to high temperatures of 250° C. or higher. The thickness of the first transparent conductive film is set so that the semiconductor surface is not damaged when the second transparent conductive film is formed, that is, it exists as a film and can cover the semiconductor surface.
The thickness is preferably 50 Å or more and 1000 Å or less, which provides sufficient light transmission even at low substrate temperatures. As explained in detail above, according to the present invention, a solar cell with high photoelectric conversion efficiency can be obtained.

[Brief explanation of the drawing]

第１図は従来の太陽電池の構造を示す断面図、
第２図は本発明の製法による太陽電池の構造を示
す断面図である。１，１１：ステンレス鋼基板、２，１２：ａ−
Si半導体層、３：透明導電膜、１３：第１の透明
導電膜、４，１５：太陽光線、１４：第２の透明
導電膜。 Figure 1 is a cross-sectional view showing the structure of a conventional solar cell.
FIG. 2 is a sectional view showing the structure of a solar cell produced by the manufacturing method of the present invention. 1, 11: stainless steel substrate, 2, 12: a-
Si semiconductor layer, 3: transparent conductive film, 13: first transparent conductive film, 4, 15: sunlight, 14: second transparent conductive film.

Claims

[Claims] 1. In a solar cell element comprising at least an oxide-based transparent conductive film and a semiconductor, a first transparent conductive film is formed on the semiconductor by a vacuum evaporation method; 1. A method for manufacturing a solar cell element, comprising forming a second transparent conductive film in a plasma state. 2. The method for manufacturing a solar cell element according to claim 1, wherein the means for generating plasma when forming the second transparent conductive film is a high frequency electric field and/or a direct current electric field. 3. The method of manufacturing a solar cell element according to claim 2, wherein the oxygen partial pressure of the atmosphere when forming the second transparent conductive film is 10 ^-2 to ^{10 -5} Torr. 4. Manufacturing a solar cell element according to claim 1, 2, or 3, wherein the first and second transparent conductive films are indium oxide-based or tin oxide-based transparent conductive films. Method. 5 Claims 1, 2, and 3 characterized in that the semiconductor is amorphous silicon.
The method for manufacturing a solar cell element according to item 1 or 4. 6. The method for manufacturing a solar cell element according to claims 1 to 5, wherein the first transparent conductive film has a thickness of 50 Å to 1000 Å.