JP6207331B2 - Solar cell and method for producing carbon electrode thereof - Google Patents

Solar cell and method for producing carbon electrode thereof Download PDF

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JP6207331B2
JP6207331B2 JP2013207735A JP2013207735A JP6207331B2 JP 6207331 B2 JP6207331 B2 JP 6207331B2 JP 2013207735 A JP2013207735 A JP 2013207735A JP 2013207735 A JP2013207735 A JP 2013207735A JP 6207331 B2 JP6207331 B2 JP 6207331B2
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cdte
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JP2015073006A (en
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土居　真
真 土居
保 岡本
保 岡本
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JFE Engineering Corp
Institute of National Colleges of Technologies Japan
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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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/543—Solar cells from Group II-VI materials
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Description

本発明は、太陽電池及びそのカーボン電極の製造方法に係り、特に、硫化カドミウムＣｄＳ／テルル化カドミウムＣｄＴｅ系太陽電池のＣｄＴｅ半導体膜層及びそのカーボン電極の製造方法に関する。   The present invention relates to a solar cell and a method for manufacturing the carbon electrode thereof, and more particularly to a CdTe semiconductor film layer of a cadmium sulfide CdS / cadmium telluride CdTe solar cell and a method for manufacturing the carbon electrode.

ＣｄＴｅ太陽電池は、ＣｄＴｅ光吸収層が約１．５ｅＶと太陽電池として最適な禁制帯幅を有している。又、エネルギーバンド構造が直接遷移型であるため、光吸収係数はＳｉなどの間接遷移型半導体に比べて大きく、薄膜化が可能である。又、イオン性が強い結晶であるため、多結晶構造でも比較的長い少数キャリヤの拡散長が得られる。このように、ＣｄＴｅは多結晶薄膜太陽電池用材料として優れた特性を有している。更に、ＣｄＴｅは高品質で大面積の多結晶膜を簡単なプロセスで高速に製膜することができるため、低コスト化が可能である。以上のことから、ＣｄＴｅ多結晶薄膜太陽電池は低コストで高効率な薄膜太陽電池として着目されている。   The CdTe solar cell has a CdTe light absorption layer of about 1.5 eV, which is an optimum band gap as a solar cell. In addition, since the energy band structure is a direct transition type, the light absorption coefficient is larger than that of an indirect transition type semiconductor such as Si, and the thickness can be reduced. In addition, since the crystal has strong ionicity, a relatively long minority carrier diffusion length can be obtained even in a polycrystalline structure. Thus, CdTe has excellent characteristics as a polycrystalline thin film solar cell material. Furthermore, CdTe can produce a high-quality and large-area polycrystalline film at a high speed by a simple process, so that the cost can be reduced. From the above, CdTe polycrystalline thin-film solar cells are attracting attention as low-cost and high-efficiency thin-film solar cells.

このＣｄＴｅ太陽電池に関して、発明者の一人は、特許文献１で、図１に示すような、透光性耐熱性基板２１と、透光性導電膜２２と、例えば硫化カドミウムＣｄＳ半導体膜でなる金属硫化物層２３と、テルル化カドミウムＣｄＴｅ半導体膜でなるＣｄＴｅ層２４と、該ＣｄＴｅ層２４にオーミック接触させたカーボン電極２５と、金属電極（集電極）２６とを有する太陽電池２０を提案している。   As for the CdTe solar cell, one of the inventors in Patent Document 1 discloses a metal made of a translucent heat-resistant substrate 21, a translucent conductive film 22, and, for example, a cadmium sulfide CdS semiconductor film as shown in FIG. Proposing a solar cell 20 having a sulfide layer 23, a CdTe layer 24 made of a cadmium telluride CdTe semiconductor film, a carbon electrode 25 in ohmic contact with the CdTe layer 24, and a metal electrode (collector electrode) 26 Yes.

このようなＣｄＳ半導体膜（２３）とＣｄＴｅ半導体膜（２４）より構成されるｐｎ接合を持つ太陽電池２０において、−側電極としては、透光性導電膜２２上に形成した金属電極（例えばＡｇＩｎ電極）２６が、また＋側電極としては、ＣｄＴｅ層２４に形成したカーボン電極２５が用いられる。これらの電極には、電極自体の抵抗が低いことはもちろん、電極の半導体膜との接触面近傍の抵抗および電極と半導体膜との接触抵抗が低いことが要求されている。ＣｄＴｅ層２４側の電極材料としては、ＣｄＴｅとのオーミック接触を形成するため電子親和力が約５ｅＶと大きいカーボン材料、特に、電極自体の抵抗を低くするために有効なグラファイト（黒鉛）が用いられていたが、この場合には前記接触面近傍の抵抗および接触抵抗が高くなることが問題視されていた。この抵抗が高くなる原因の一つは、グラファイトが層状構造を有するので、面方向の導電性は良好であるが、層間方向の電気抵抗が大きい特質を持っていることにある。即ち、カーボン電極２５は通常、ＣｄＴｅ層２４上にカーボンペーストを塗布し、乾燥、焼成して形成されるが、この電極膜中のグラファイト粒子は、前記接触面の近傍では接触面に沿って層方向に配置されている。そのため、前記接触面近傍の電極の面抵抗は小さいが、接触面に垂直な方向の抵抗はグラファイトの層間抵抗に依存して大きくなる。抵抗が高くなる原因のもう一つは、グラファイト粒子が５〜２０μｍ長さの比較的大きな扁平形状をしているため、凹凸のあるＣｄＴｅ膜表面への前記積層は両者が点接触となり接触抵抗が大きくなることである。   In the solar cell 20 having a pn junction composed of such a CdS semiconductor film (23) and a CdTe semiconductor film (24), the negative electrode is a metal electrode (for example, AgIn) formed on the translucent conductive film 22. Electrode) 26, and the carbon electrode 25 formed on the CdTe layer 24 is used as the + side electrode. These electrodes are required not only to have a low resistance of the electrode itself, but also to have a low resistance near the contact surface of the electrode with the semiconductor film and a low contact resistance between the electrode and the semiconductor film. As the electrode material on the CdTe layer 24 side, a carbon material having a large electron affinity of about 5 eV to form an ohmic contact with CdTe, particularly graphite (graphite) effective for reducing the resistance of the electrode itself is used. However, in this case, it has been regarded as a problem that the resistance in the vicinity of the contact surface and the contact resistance increase. One of the causes for the high resistance is that graphite has a layered structure, so that the electrical conductivity in the plane direction is good, but the electrical resistance in the interlayer direction is large. That is, the carbon electrode 25 is usually formed by applying a carbon paste on the CdTe layer 24, drying and firing, and the graphite particles in the electrode film are layered along the contact surface in the vicinity of the contact surface. Arranged in the direction. Therefore, although the surface resistance of the electrode near the contact surface is small, the resistance in the direction perpendicular to the contact surface increases depending on the interlayer resistance of graphite. Another reason for the increased resistance is that the graphite particles have a relatively large flat shape with a length of 5 to 20 μm, so that the lamination on the surface of the uneven CdTe film becomes point contact with each other, resulting in contact resistance. Is to grow.

これを改善するために、図２（Ａ）及び（Ｂ）に示すように、グラファイト（黒鉛）２５Ａとカーボンブラック（ＣＢ）２５Ｂを混合して電極材料として用いることが提案されている。この方法は、電気抵抗的に異方性が少ないカーボンブラック２５Ｂを混合することにより、前記接触面とその近傍の抵抗を低減し、更に、グラファイトに比較して粒径がサブミクロンオーダーと小さく、かつ球形に近い形状のカーボンブラック粒子が、前記接触面もしくはその近傍においてグラファイト粒子相互間、およびグラファイト粒子とＣｄＴｅ層２４との界面の空隙を埋めることにより、カーボン電極２５のＣｄＴｅ膜接触面近傍の抵抗およびカーボン電極２５とＣｄＴｅ層２４との接触抵抗を低減することを期待したものである。   In order to improve this, as shown in FIGS. 2A and 2B, it has been proposed that graphite (graphite) 25A and carbon black (CB) 25B are mixed and used as an electrode material. In this method, by mixing carbon black 25B having little anisotropy in electrical resistance, the resistance of the contact surface and the vicinity thereof is reduced, and the particle size is smaller on the order of submicron than graphite, The carbon black particles having a spherical shape fill the gaps between the graphite particles and the interface between the graphite particles and the CdTe layer 24 at or near the contact surface, so that the carbon black particles near the CdTe film contact surface of the carbon electrode 25 are filled. This is expected to reduce the resistance and contact resistance between the carbon electrode 25 and the CdTe layer 24.

しかし、この方法では、図２（Ａ）のようにＣＢが少ないと、前記接触面もしくはその近傍に期待通りにカーボンブラック２５Ｂを十分に存在させることができず、僅かな効果が得られるに過ぎなかった。これを改善するため図２（Ｂ）のように多量のカーボンブラックを混合した場合には、界面の接触抵抗が低減されるものの、粒子間抵抗が大きいカーボンブラックが過剰に存在するため、電極自体の抵抗が増大する問題があった。   However, in this method, if the CB is small as shown in FIG. 2A, the carbon black 25B cannot be sufficiently present as expected on or near the contact surface, and only a slight effect is obtained. There wasn't. In order to improve this, when a large amount of carbon black is mixed as shown in FIG. 2 (B), although the contact resistance at the interface is reduced, the carbon black having a large interparticle resistance exists excessively, so that the electrode itself There is a problem that the resistance increases.

このような問題を解決するべく、特許文献２には、図２（Ａ）及び（Ｂ）に示すような粒状黒鉛２５Ａと、カーボンブラック（ＣＢ）２５Ｂを含むカーボン電極２５内のカーボンブラック比率を、例えば遠心分離や超音波振動により、図２（Ｃ）に示すように、ＣｄＴｅ層２４との界面部で高めてカーボンブラック（ＣＢ）２５Ｂを堆積（２５Ｃ）させ、密着性を高め、界面抵抗を減少させ、光電変換効率を改善することが記載されている。   In order to solve such a problem, Patent Document 2 discloses the ratio of carbon black in the carbon electrode 25 including granular graphite 25A and carbon black (CB) 25B as shown in FIGS. 2 (A) and 2 (B). For example, by centrifugal separation or ultrasonic vibration, as shown in FIG. 2C, carbon black (CB) 25B is deposited (25C) at the interface with the CdTe layer 24 to increase adhesion, and interface resistance is increased. Is described, and photoelectric conversion efficiency is improved.

又、特許文献３には、ガラス基板上にＣｄＳ膜、ＣｄＴｅ膜およびカーボン膜を順次積層形成した後、光透過性で熱硬化性の樹脂を含むＡｇ・Ｉｎ膜を、ＣｄＳ膜およびカーボン膜上に形成し、この樹脂を硬化以前に、加圧によりＣｄＴｅ膜およびＣｄＳ膜中に浸透させることにより、短絡光電流密度と開放電圧を増大させ、光電変換効率を向上させることが記載されている。   In Patent Document 3, a CdS film, a CdTe film, and a carbon film are sequentially laminated on a glass substrate, and then an Ag / In film containing a light-transmitting and thermosetting resin is formed on the CdS film and the carbon film. It is described that the short circuit photocurrent density and the open circuit voltage are increased and the photoelectric conversion efficiency is improved by allowing the resin to penetrate into the CdTe film and the CdS film by pressurization before curing.

又、特許文献４には、カーボンペーストに、ＣｄＴｅ膜中のキャリヤ濃度を高める金属の化合物（銅又は金の有機化合物など）や、密着性を確保するためのカップリング剤（ヘキサメチルジシラザン）や、電極の抵抗増加を抑制するための導電フィラーを調合して、光電変換効率と信頼性を向上することが記載されている。   Patent Document 4 discloses a carbon paste, a metal compound (such as an organic compound of copper or gold) that increases the carrier concentration in the CdTe film, and a coupling agent (hexamethyldisilazane) for ensuring adhesion. In addition, it is described that a conductive filler for suppressing an increase in electrode resistance is prepared to improve photoelectric conversion efficiency and reliability.

又、特許文献５には、ＣｄＴｅ層とカーボン電極の間に亜鉛化合物層を介在させることで、各構成膜の密着性、電気的接合性および均一製膜性を向上させ、高変換効率、高信頼性を得ることが記載されている。   Patent Document 5 discloses that a zinc compound layer is interposed between the CdTe layer and the carbon electrode, thereby improving the adhesion, electrical bondability, and uniform film forming property of each constituent film, and high conversion efficiency, high It is described to obtain reliability.

ＷＯ２０１２／１１４８０３号公報WO2012 / 114803 Publication 特開平１１−３３０５０６号公報JP-A-11-330506 特開平０６−２８３７４５号公報Japanese Patent Laid-Open No. 06-283745 特開平１１−１３５８１６号公報JP-A-11-135816 特開２０００−３１５１３号公報JP 2000-31513 A

数十ｎｍサイズのカーボンブラックは、数十μｍサイズの黒鉛間に充填され、密着性を上げることができるが、逆に黒鉛表面の高抵抗層となるため、特許文献２に記載されているように、遠心分離や超音波振動処理が必要となる。しかしながら、カーボンペースト塗布後の大面積ガラス基板へ遠心分離や超音波振動を与えて、ペースト内のカーボンブラックを移動させることは、実用的には困難であり、処理時間やコスト面で採算が取れないという問題点を有していた。   Carbon black with a size of several tens of nm is filled between graphites with a size of several tens of μm and can improve adhesion, but conversely becomes a high resistance layer on the surface of graphite, so that it is described in Patent Document 2 In addition, centrifugation and ultrasonic vibration treatment are required. However, it is practically difficult to move the carbon black in the paste by applying centrifugal separation or ultrasonic vibration to the large area glass substrate after applying the carbon paste, and it is profitable in terms of processing time and cost. Had the problem of not.

又、特許文献３〜５に記載の技術も、処理時間やコスト面で十分とは言えなかった。   In addition, the techniques described in Patent Documents 3 to 5 are not sufficient in terms of processing time and cost.

本発明は、前記従来の問題点を解消するべくなされたもので、遠心分離や超音波振動処理など特別な処理を行うことなく、カーボン電極において高い太陽電池性能を得ることを課題とする。   The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to obtain high solar cell performance in a carbon electrode without performing special treatment such as centrifugation or ultrasonic vibration treatment.

本発明は、金属硫化物層、テルル化カドミウム層、およびテルル化カドミウム層側のカーボン電極を具備し、前記カーボン電極がグラファイトとカーボンナノチューブを含み、前記カーボン電極のカーボンナノチューブ含有量が、２〜２０．２重量％であることを特徴とする太陽電池により、前記課題を解決したものである。 The present invention, metal sulfide layer, cadmium telluride layer, and comprising a carbon electrode for the cadmium telluride layer side, the carbon electrode is viewed contains graphite and carbon nanotubes, carbon nanotube content of the carbon electrode, 2 The above-mentioned problem is solved by a solar cell characterized by being -20.2% by weight .

本発明は、又、金属硫化物層とテルル化カドミウム層を備えた太陽電池のテルル化カドミウム層側のカーボン電極の製造方法であって、グラファイトとカーボンナノチューブを含み、カーボンナノチューブ含有量が、０．９９〜９．１０重量％であるペーストを前記テルル化カドミウム層の上面に塗布した後、焼成することを特徴とする太陽電池のカーボン電極の製造方法により、同じく前記課題を解決したものである。 The present invention also relates to a method for manufacturing a cadmium telluride layer side of the carbon electrode of a solar cell having a metal sulfide layer and the cadmium telluride layer, viewed contains graphite and carbon nanotubes, the amount of carbon nanotubes containing, The above-mentioned problem is also solved by a method for producing a carbon electrode of a solar cell, wherein a paste of 0.99 to 9.10% by weight is applied to the upper surface of the cadmium telluride layer and then fired. is there.

本発明によれば、図３に示す如く、カーボンナノチューブ（ＣＮＴ）２５Ｄが、高抵抗の黒鉛堆積方向（図の上下方向）にＣｄＴｅ層２４表面と黒鉛２５Ａ間を接続するので、遠心分離や超音波振動処理など特別な処理を行うことなく、カーボン電極２５において高い太陽電池性能を得ることができる。   According to the present invention, as shown in FIG. 3, the carbon nanotube (CNT) 25D connects the surface of the CdTe layer 24 and the graphite 25A in the high resistance graphite deposition direction (vertical direction in the figure). High solar cell performance can be obtained in the carbon electrode 25 without performing special treatment such as sonic vibration treatment.

発明者の一人が特許文献１で提案した太陽電池の構成を示す概略断面図Schematic sectional view showing the configuration of a solar cell proposed by one of the inventors in Patent Document 1 特許文献２に記載された技術の原理を示す断面図Sectional drawing which shows the principle of the technique described in patent document 2 本発明に係るカーボン電極の要部構成を示す断面図Sectional drawing which shows the principal part structure of the carbon electrode which concerns on this invention 本発明に係るカーボン電極を含む太陽電池の製造方法の一例の手順を示すフローチャートThe flowchart which shows the procedure of an example of the manufacturing method of the solar cell containing the carbon electrode which concerns on this invention 従来例と本発明の実施例の太陽電池性能を比較して示す図The figure which compares and shows the solar cell performance of the example of a conventional example and this invention. 同じく太陽電池直列抵抗を測定した結果を比較して示す図The figure which compares and shows the result which measured the solar cell series resistance similarly

以下、図面を参照して、本発明を好適に実施するための形態（以下、実施形態という）につき、詳細に説明する。尚、本発明は以下の実施形態および実施例に記載した内容により限定されるものではない。又、以下に記載した実施形態および実施例における構成要件には、当業者が容易に想定できるもの、実質的に同一のもの、いわゆる均等の範囲のものが含まれる。更に、以下に記載した実施形態および実施例で開示した構成要素は適宜組み合わせてもよいし、適宜選択して用いてもよい。   DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings. In addition, this invention is not limited by the content described in the following embodiment and an Example. The constituent elements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that are so-called equivalent ranges. Furthermore, the constituent elements disclosed in the embodiments and examples described below may be appropriately combined or may be appropriately selected and used.

本実施形態は、図１に示した従来と同様の太陽電池２０において、そのカーボン電極２５に、図３に要部構成を示した如く、ＣＮＴ２５Ｄを含めたものである。   In the present embodiment, in the solar cell 20 similar to the conventional one shown in FIG. 1, the carbon electrode 25 includes the CNT 25D as shown in FIG.

これにより、遠心分離や超音波振動処理を行うことなく、カーボン電極において高い太陽電池性能を達成することができる。   Thereby, high solar cell performance can be achieved in the carbon electrode without performing centrifugation or ultrasonic vibration treatment.

前記太陽電池２０は、図１に示した如く、透光性耐熱性基板２１と、透光性導電膜２２と、金属硫化物層２３と、ＣｄＴｅ層２４と、カーボン電極２５と、金属電極（集電極）２６とを有する。   As shown in FIG. 1, the solar cell 20 includes a translucent heat-resistant substrate 21, a translucent conductive film 22, a metal sulfide layer 23, a CdTe layer 24, a carbon electrode 25, a metal electrode ( Current collector 26).

透光性耐熱性基板２１は、半導体層で光電変換に寄与し得る波長の光を透過させる性質を有する。透光性耐熱性基板２１としては、透光性と強度を有するものが用いられ、例えば、ホウ珪酸ガラス、ソーダライムガラスなどが挙げられる。   The translucent heat-resistant substrate 21 has a property of transmitting light having a wavelength that can contribute to photoelectric conversion in the semiconductor layer. As the translucent heat-resistant substrate 21, a substrate having translucency and strength is used, and examples thereof include borosilicate glass and soda lime glass.

透光性導電膜２２は、透光性耐熱性基板２１上に設けられている。透光性導電膜２２としては、例えば、酸化スズ膜、酸化インジウムスズ膜などのスズ酸化物からなる膜、酸化亜鉛膜などが挙げられる。これらの中でも、特に、酸化スズ膜が好ましい。透光性導電膜２２の膜厚は、光の透過率と導電性との両立を図る観点から、例えば、１００ｎｍ以上１０００ｎｍ以下であることが好ましい。   The translucent conductive film 22 is provided on the translucent heat-resistant substrate 21. Examples of the light-transmitting conductive film 22 include a film made of a tin oxide such as a tin oxide film and an indium tin oxide film, and a zinc oxide film. Among these, a tin oxide film is particularly preferable. The film thickness of the translucent conductive film 22 is preferably, for example, 100 nm or more and 1000 nm or less from the viewpoint of achieving both light transmittance and conductivity.

金属硫化物層２３は、透光性導電膜２２の上に積層される。金属硫化物層２３は金属硫化物を含む層であり、ｎ型半導体層として機能する。金属硫化物としては、例えば、硫化カドミウム、硫化亜鉛などが挙げられる。これらは単独で用いてもよく、組み合わせて用いてもよい。これらのうちでは、硫化カドミウム、硫化カドミウムと硫化亜鉛との混合物が好ましい。金属硫化物層２３の膜厚は、例えば、５０ｎｍ以上５００ｎｍ以下であることが好ましい。   The metal sulfide layer 23 is laminated on the translucent conductive film 22. The metal sulfide layer 23 is a layer containing a metal sulfide and functions as an n-type semiconductor layer. Examples of the metal sulfide include cadmium sulfide and zinc sulfide. These may be used alone or in combination. Of these, cadmium sulfide and a mixture of cadmium sulfide and zinc sulfide are preferable. The film thickness of the metal sulfide layer 23 is preferably 50 nm or more and 500 nm or less, for example.

ＣｄＴｅ層２４は、金属硫化物層２３の上に積層される。ＣｄＴｅ層２４はＣｄＴｅ膜を用いて形成され、ｐ型半導体層として機能する。ＣｄＴｅ層２４の膜厚は、光の吸収効率と導電性との両立を図る観点から、例えば、１μｍ以上１０μｍ以下であることが好ましい。   The CdTe layer 24 is stacked on the metal sulfide layer 23. The CdTe layer 24 is formed using a CdTe film and functions as a p-type semiconductor layer. The thickness of the CdTe layer 24 is preferably, for example, 1 μm or more and 10 μm or less from the viewpoint of achieving both light absorption efficiency and conductivity.

本発明に係るカーボン電極２５は、ＣｄＴｅ層２４上に設けられ、ＣｄＴｅ層２４にオーミック接触させた電極である。このカーボン電極２５は、図３に示した如く、グラファイト２５ＡとＣＮＴ２５Ｄを含んで構成される。   The carbon electrode 25 according to the present invention is an electrode provided on the CdTe layer 24 and in ohmic contact with the CdTe layer 24. The carbon electrode 25 includes graphite 25A and CNT 25D as shown in FIG.

金属電極２６は、カーボン電極２５上および露出させた透光性導電膜２２上に設けられている。金属電極２６は、例えば、アルミニウム（Ａｌ）、銀（Ａｇ）、インジウム（Ｉｎ）の１つ以上を含む混合物などで形成される。   The metal electrode 26 is provided on the carbon electrode 25 and the exposed translucent conductive film 22. The metal electrode 26 is formed of, for example, a mixture containing one or more of aluminum (Al), silver (Ag), and indium (In).

以下、図４を参照して、太陽電池２０の作製方法の一例について説明する。まず、透光性耐熱性基板２１を所定の寸法（例えば、１００ｍｍ×１００ｍｍ×１ｍｍ）にした後、この透光性耐熱性基板２１上に所定の膜厚（例えば、６００ｎｍ）の透光性導電膜２２を形成する（ステップ１００）。   Hereinafter, an example of a method for manufacturing the solar cell 20 will be described with reference to FIG. First, the translucent heat-resistant substrate 21 is set to a predetermined dimension (for example, 100 mm × 100 mm × 1 mm), and then the translucent conductive film having a predetermined film thickness (for example, 600 nm) is formed on the translucent heat-resistant substrate 21. A film 22 is formed (step 100).

この透光性導電膜２２上にジメチルジチオカルバミン酸カドミウムを２８０℃程度に加熱して発生するガスを６０秒間誘導することによって透光性導電膜２２上に所定の膜厚（例えば、５０ｎｍ）の金属硫化物層２３を形成する（ステップ１１０）。   A metal having a predetermined film thickness (for example, 50 nm) is formed on the translucent conductive film 22 by inducing a gas generated by heating cadmium dimethyldithiocarbamate to about 280 ° C. on the translucent conductive film 22 for 60 seconds. A sulfide layer 23 is formed (step 110).

金属硫化物層２３上に所定の膜厚（例えば、５μｍ）のＣｄＴｅ層２４を、主として近接昇華（Ｃlosed Ｓpaced Ｓublimation：ＣＣＳ）法あるいは気相輸送堆積（Ｖapor Ｔransport Ｄeposition：ＶＤＴ）法を用いて形成する（ステップ１２０）。   A CdTe layer 24 having a predetermined film thickness (for example, 5 μm) is formed on the metal sulfide layer 23 mainly by using a closed sublimation (CCS) method or a vapor transport deposition (VDT) method. (Step 120).

ＣｄＴｅ層２４上に、例えばＣＮＴの分散溶媒であるイソプロピルアルコール（ＩＰＡ）を用いてＣＮＴの分散性とペーストの粘性を調整した、黒鉛２５ＡとＣＮＴ２５Ｄを含むカーボンペーストを塗布し、焼成してカーボン電極２５を形成する（ステップ１３０）。その後、受光面となる部分の周囲の金属硫化物層２３とＣｄＴｅ層２４を、例えば、レーザースクライブ（波長１．０５μｍ）やメカニカルスクライブを用いて剥離し、透光性導電膜２２を露出させる（ステップ１４０）。最後に、カーボン電極２５上および露出させた透光性導電膜２２上に金属電極２６を各々形成する（ステップ１５０）。これにより、太陽電池２０が得られる。なお、ステップ１３０とステップ１４０の順序は逆でも良い。   On the CdTe layer 24, for example, a carbon paste containing graphite 25A and CNT 25D in which the dispersibility of the CNT and the viscosity of the paste are adjusted using isopropyl alcohol (IPA), which is a dispersion solvent of CNT, is applied and baked to obtain a carbon electrode. 25 is formed (step 130). Thereafter, the metal sulfide layer 23 and the CdTe layer 24 around the portion that becomes the light receiving surface are peeled off by using, for example, laser scribe (wavelength 1.05 μm) or mechanical scribe to expose the translucent conductive film 22 ( Step 140). Finally, metal electrodes 26 are formed on the carbon electrode 25 and the exposed transparent conductive film 22 (step 150). Thereby, the solar cell 20 is obtained. Note that the order of step 130 and step 140 may be reversed.

本実施形態では、ＣｄＴｅ層２４は１層構造としているが、多層構造としてもよい。ＣｄＴｅ層製膜後にＣｄＴｅ層の高品質化のために塩化カドミウム（ＣｄＣｌ2）処理を行う。これは、ＣｄＣｌ2溶液を表面にコーティングした後に、４００℃程度で熱処理を施すものであり、これにより太陽電池特性が向上する。また、カーボンペーストには微粉Ｃｕ、ＣｕＯ、ナフテン酸銅などを１０〜２００ｐｐｍ添加し、３００〜４００℃の焼成時にＣｄＴｅ層へＣｕを拡散させるドーピングにより、ＣｄＴｅ層のアクセプタ濃度を上げ太陽電池特性を向上させることができる。 In this embodiment, the CdTe layer 24 has a single layer structure, but may have a multilayer structure. After forming the CdTe layer, a cadmium chloride (CdCl 2 ) treatment is performed to improve the quality of the CdTe layer. In this method, after the surface is coated with a CdCl 2 solution, heat treatment is performed at about 400 ° C., thereby improving the solar cell characteristics. Also, fine powder Cu, CuO, copper naphthenate, etc. is added to the carbon paste in an amount of 10 to 200 ppm, and the doping concentration for diffusing Cu into the CdTe layer during baking at 300 to 400 ° C. increases the acceptor concentration of the CdTe layer and improves the solar cell characteristics. Can be improved.

元のカーボンペーストの黒鉛は、導電性の高い燐片状の天然黒鉛が良いが、高導電性の人造黒鉛でも良い。溶剤（粘結剤）としてはブチルカルビトール（ジエチレングリコールモノブチルエーテル）やテルピネオールなどが用いられ、バインダーは接着用として低融点のガラスフリットやエポキシ樹脂が用いられ、また、増粘剤のポリビニルブチラールなどの樹脂を添加しても良い。   The graphite of the original carbon paste is preferably flaky natural graphite having high conductivity, but may be artificial graphite having high conductivity. As the solvent (binding agent), butyl carbitol (diethylene glycol monobutyl ether) or terpineol is used, and as the binder, a low-melting glass frit or an epoxy resin is used for bonding, and a thickener such as polyvinyl butyral is used. A resin may be added.

図５に、２３重量％の外径がおよそ５〜１０μｍの燐片天然黒鉛と７重量％のカーボンブラックと５重量％の鉛ガラスフリットと溶剤としてブチルカルビトールを用いたペーストを使用した従来例（▲）、さらに５重量％のカーボンブラックを添加したペーストを使用した従来例（●）と、本発明に係る４種類のペーストＡ〜Ｄを使用した実施例（▼、△、□、▽）、及びペーストＥを使用した参考例（○）における太陽電池特性の光電変換効率Ｅｆｆ、曲線因子（Ｆill Ｆactor）Ｆ．Ｆ．、短絡光電流密度Ｊsc、開放電圧Ｖocを比較して示す。金属硫化物層２３としてはＣｄＳ半導体膜を用いた。ここで、示差熱・熱重量同時測定ＴＧ／ＤＴＡから推定されるペーストＡ〜Ｅにおける焼成後の電極中のＣＮＴ含有量推定値は、表１の通りである。 FIG. 5 shows a conventional example using 23 wt% of a flake natural graphite having an outer diameter of about 5 to 10 μm, 7 wt% of carbon black, 5 wt% of lead glass frit, and a paste using butyl carbitol as a solvent. (▲) In addition, a conventional example (●) using a paste added with 5% by weight of carbon black and an example using the four types of pastes A to D according to the present invention (▼, Δ, □, ▽ ) , And the photoelectric conversion efficiency Eff of the solar cell characteristics in the reference example ( ◯) using the paste E, fill factor F.F. F. The short-circuit photocurrent density J sc and the open circuit voltage V oc are compared and shown. As the metal sulfide layer 23, a CdS semiconductor film was used. Here, the estimated value of the CNT content in the electrode after firing in pastes A to E estimated from the simultaneous differential heat / thermogravimetric measurement TG / DTA is shown in Table 1.

ここでは、塗布のし易さやＣＮＴの混合を良くするためのペーストの粘性調整剤としてイソプロピルアルコール（ＩＰＡ）を用いた。ペーストＡとＢでＩＰＡの添加量を変えているのは、ペーストの粘性を変えるためである。また、すべてＣｕドーピングのためナフテン酸銅を５０ｐｐｍ前後ペーストへ添加している。   Here, isopropyl alcohol (IPA) was used as a viscosity modifier for the paste to improve the ease of application and mixing of CNTs. The reason why the amount of IPA added is changed between pastes A and B is to change the viscosity of the paste. Moreover, copper naphthenate is added to the paste around 50 ppm for all Cu doping.

焼成は、特許文献１に記載されたものと同様の方法で行い、焼成条件は３２０〜３５０℃、窒素＋酸素２０００ｐｐｍ、１５分、ＩＰＡ密度は０．７８０８４ｇ／ｃｍ3であり、示差熱・熱重量同時測定ＴＧ／ＤＴＡ結果より、焼成後は３０％カーボン＋６％バインダー（焼成残量：３６重量％）と推定される。 Firing is performed by the same method as that described in Patent Document 1, firing conditions are 320 to 350 ° C., nitrogen + oxygen 2000 ppm, 15 minutes, IPA density is 0.78084 g / cm 3 , differential heat / heat From the results of simultaneous weight measurement TG / DTA, it is estimated that 30% carbon + 6% binder (remaining firing amount: 36% by weight) after firing.

図５から、本発明の実施例において、従来のカーボン電極以上の太陽電池性能が得られていることが明らかである。これは図６に示すように直列抵抗ＲsがＣＮＴの添加により減少しているＣＮＴ濃度範囲で性能が向上していることから、ＣＮＴによりＣｄＴｅ層との界面接触抵抗及び黒鉛積層方向の抵抗が低減し、性能が向上していると考えられる。 From FIG. 5, it is clear that the solar cell performance higher than that of the conventional carbon electrode is obtained in the example of the present invention. As shown in FIG. 6, since the performance is improved in the CNT concentration range where the series resistance R s is decreased by the addition of CNT, the interface contact resistance with the CdTe layer and the resistance in the graphite lamination direction are increased by the CNT. It is considered that the performance is improved.

参考例のペーストＥで逆に太陽電池性能が低下している要因は、高濃度に添加したＣＮＴのペースト内での分散が悪かったことによるものである。 On the contrary, the reason why the solar cell performance is lowered in the paste E of the reference example is that the dispersion of the CNT added at a high concentration in the paste was bad.

なお、実施例では金属硫化物層２３としてＣｄＳ半導体膜を用いていたが、金属硫化物層２３はこれに限定されず、硫化亜鉛ＣｄＺｎや、ＣｄＺｎとＣｄＳの混合物を用いることもできる。   In the embodiment, a CdS semiconductor film is used as the metal sulfide layer 23. However, the metal sulfide layer 23 is not limited to this, and zinc sulfide CdZn or a mixture of CdZn and CdS can also be used.

また、実施例では密着性向上のためカーボンブラックを少量添加しているが、このカーボンブラックとしては、ケッチェンブラック、チャネルブラック、サーマルブラックや同粒径（数〜数百ｎｍ）のカーボン系微粒子を用いることができる。   In the examples, a small amount of carbon black is added to improve adhesion, but as this carbon black, ketjen black, channel black, thermal black, and carbon-based fine particles having the same particle size (several to several hundred nm) are used. Can be used.

２０…太陽電池
２１…透光性耐熱性基板
２４…ＣｄＴｅ層
２５…カーボン電極
２５Ａ…グラファイト（黒鉛）
２５Ｄ…カーボンナノチューブ（ＣＮＴ）
２６…金属電極 DESCRIPTION OF SYMBOLS 20 ... Solar cell 21 ... Translucent heat-resistant substrate 24 ... CdTe layer 25 ... Carbon electrode 25A ... Graphite (graphite)
25D ... Carbon nanotube (CNT)
26 ... Metal electrode

Claims (2)

金属硫化物層、テルル化カドミウム層、およびテルル化カドミウム層側のカーボン電極を具備し、
前記カーボン電極がグラファイトとカーボンナノチューブを含み、
前記カーボン電極のカーボンナノチューブ含有量が、２〜２０．２重量％であることを特徴とする太陽電池。 A metal sulfide layer, a cadmium telluride layer, and a carbon electrode on the cadmium telluride layer side;
The carbon electrode is viewed contains graphite and carbon nanotubes,
The carbon electrode has a carbon nanotube content of 2 to 20.2% by weight . 金属硫化物層とテルル化カドミウム層を備えた太陽電池のテルル化カドミウム層側のカーボン電極の製造方法であって、
グラファイトとカーボンナノチューブを含み、カーボンナノチューブ含有量が、０．９９〜９．１０重量％であるペーストを前記テルル化カドミウム層の上面に塗布した後、焼成することを特徴とする太陽電池のカーボン電極の製造方法。 A method for producing a carbon electrode on a cadmium telluride layer side of a solar cell having a metal sulfide layer and a cadmium telluride layer,
See contains graphite and carbon nanotubes, the amount of contained carbon nanotube, after the paste is from 0.99 to 9.10 wt% was applied to the upper surface of the cadmium telluride layer, carbon of a solar cell and firing Electrode manufacturing method.
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