JP2005050983A

JP2005050983A - Solar battery cell and its manufacturing method

Info

Publication number: JP2005050983A
Application number: JP2003205207A
Authority: JP
Inventors: Noriyasu Kawakita; 典保河北; Yuko Fukawa; 祐子府川; Shuichi Fujii; 修一藤井
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2003-07-31
Filing date: 2003-07-31
Publication date: 2005-02-24
Anticipated expiration: 2023-07-31
Also published as: JP4439213B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery cell that is inexpensive and can realize the same output characteristic as in conventionals without applying an acid treatment and a covering solder layer on the surface of the electrodes after baking the electrodes on a reflection preventing film and hardly generates degradation of long-term reliability. <P>SOLUTION: The solar battery cell is provided with a reverse conductive diffusion layer on the surface side of a semiconductor substrate showing a single conductivity, a reflection prevention film and a surface electrode formed thereon and a rear side electrode formed on its rear side. The surface side electrode and/or the rear side electrode is made mainly of silver and contains at least one kind or plural kinds of Ti, Co, Mg, Bi, Zn, Zr, Fe, and Cr or their compound at 0.05-5 weight part to 100 weight part of the silver in terms of metal as well as 0.1-10 weight part of a halogenated compound. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は太陽電池素子に関し、特に半導体基板に電極を有する太陽電池素子に関する。
【０００２】
【従来の技術】
従来の太陽電池素子の断面図を図２に示す。１は例えばｐ型シリコンの半導体基板、２は半導体基板１の表面部分にリン（Ｐ）などを拡散して形成された拡散層、３は窒化シリコン膜や酸化シリコン膜などから成る反射防止膜である。また、半導体基板１の裏面側には例えばアルミニウムなどを拡散して形成された高濃度ｐ型のＢＳＦ層４を有する。
【０００３】
さらに、半導体基板１の表裏両面にはそれぞれ出力を取り出すための表面電極５および裏面電極６が形成される。その形成法としては一般的に低コスト化のため、スクリーン印刷法が用いられ、銀粉末と有機ビヒクルおよびガラスフリットを含むペーストを半導体基板１の表面に印刷し、６００〜８００℃で１〜３０分程度焼成することによって焼き付けられる。つまり、電極ペースト中にガラスフリットを添加して、電極ペースト中の金属成分の焼結を促進させるとともに、基板材料のシリコンと共融状態を作って密着強度を向上させるものである。この表面電極５を形成する際、前記反射防止膜３の電極形成部を除去して、この部分に表面電極５を焼き付けて形成する場合と、反射防止膜の電極形成部の除去を行わずに、反射防止膜の上から直接表面電極５を焼き付けて形成する場合とがある。
この後、金属ペースト中のバインダーあるいはガラスフリットなどを取り除いて、電気伝導性を向上させるために酸処理を行い、そして表面電極５および裏面電極６の表面を、後工程で太陽電池素子同士を接続するためにインナーリード（不図示）と接続しやすくするため、また太陽電池素子の長期信頼性を確保するために半田層７で被覆されている。（例えば特許文献１参照）従来、このような半田層７としては、Ｓｎ−Ｐｂの共晶半田が用いられていた。
【０００４】
【特許文献１】
特開２００２−１１１０１６号公報
【０００５】
【特許文献２】
特開２００１−３１３４００号公報
【０００６】
【特許文献３】
特開１９９７−２１３９７９号公報
【０００７】
【特許文献４】
特開２０００−３３２２７１号公報
【０００８】
【発明が解決しようとする課題】
この従来の太陽電池素子では、反射防止膜の電極形成部を除去して、この部分に電極を焼き付けて形成する場合、工程が多いため作業が煩雑となり、たとえば反射防止膜の電極形成部にペースト状の電極材料を印刷する際には、厳密な位置合わせが必要となり、位置ずれなどが生じると歩留まりを低下させる要因になる。
【０００９】
一方、反射防止膜の上から直接電極材料を焼き付ける場合、焼成による高温状態で反射防止膜材料を溶融させて、電極材料とシリコン基板とを接触させるため、安定したオーミック接触が得られなかった。
【００１０】
また、表面電極５と裏面電極６を焼き付けた後に酸処理を行うことから、電気伝導性が向上して素子の特性が著しく向上するようになるが、酸が電極中に残存した場合、電極が腐食し、長期信頼性の低下を起こす恐れがあり、そのため半田層を被覆する必要があった。
【００１１】
また、近年環境問題が重要視される中、Ｓｎ−Ｐｂの共晶半田に含まれる鉛が問題となってきており、鉛フリー半田の開発が進められている。しかしながら、その使用温度や長期信頼性および高コスト化の観点から、従来のＳｎ−Ｐｎ共晶半田に勝る太陽電池素子に適した鉛フリー半田は未だ開発されていない。
【００１２】
また、この従来の太陽電池素子では、表面電極５および裏面電極６を焼き付けた後に酸処理、半田被覆工程を行うことで高コストとなり、また太陽電池素子の製造工程が煩雑であるという問題もある。
【００１３】
特許文献２（特開２００１−３１３４００号公報）には、Ｔｉ、Ｂｉ、Ｃｏ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒ、成分のうちいずれか一種または複数種を含有する太陽電池の電極材料であって、この電極材料を反射防止膜の上から塗布して焼き付けることで、安定的なオーミック接触と引っ張り強度の強い太陽電池素子が得られることが開示されている。ところが、電極材料を焼き付けた後、酸処理を行う必要があり、また半田層を被覆しない場合において長期信頼性の低下を起こすという問題があった。
【００１４】
特許文献３（特開１９９７−２１３９７９号公報）には、電極の上に半田層を被覆しない太陽電池素子の製造方法であって、焼成して形成した電極を酸で化学処理することで高出力の太陽電池素子が得られることが開示されている。ところが、酸が電極中に残存した場合、電極を腐食し、長期信頼性の低下を起こすという問題があった。
【００１５】
特許文献４（特開２０００−３３２２７１号公報）には、表面電極および／または裏面電極に金属フッ化物を含有させることで、酸処理工程を行うことなく電気伝導性が得られ電極強度が向上することが開示されている。ところが、金属添加物を添加すると良好な電極強度が得られるが、半田層を被覆しない場合において長期信頼性が十分に得られなかった。
【００１６】
本発明はこのような従来技術の問題点に鑑みてなされたものであり、電極を反射防止膜の上から焼き付けた後、酸処理工程と電極表面に半田層の被覆を行わずに、従来と同様の出力特性を得て、さらに長期信頼性の低下を起こすことのない低コストな太陽電池素子を提供することを目的とする。
【００１７】
【課題を解決するための手段】
上記目的を達成するために、請求項１に係る太陽電池素子では、一導電型を呈する半導体基板の表面側に逆導電型の拡散層を有し、その上に反射防止膜と表面電極を設けると共に、裏面側に裏面電極を設けた太陽電池素子において、前記表面電極および／または裏面電極が銀を主成分とし、Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物のうちいずれか一種または複数種を前記銀１００重量部に対して金属換算で０．０５〜５重量部含有すると共にハロゲン化合物を０．１〜１０重量部含有することを特徴とする。
【００１８】
また、上記太陽電池素子では、前記表面電極または裏面電極に第Ｖ族元素化合物を含有させたほうが好ましい。
【００１９】
また、上記太陽電池素子の製造方法では、一導電型を呈する半導体基板の表面側に逆導電型の拡散層を形成すると共に、この半導体基板の表面側に反射防止膜を形成し、この反射防止膜と前記半導体基板の裏面側に銀、有機ビヒクル、ガラスフリットを含む電極材料を焼き付けることによって表面電極と裏面電極を形成する太陽電池素子の製造方法において、前記電極材料にＴｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物のうちいずれか一種または複数種を前記銀１００重量部に対して金属換算で０．０５〜５重量部含有すると共にハロゲン化合物を０．１〜１０重量部含有することを特徴とする。
【００２０】
また、上記太陽電池素子の形成方法では、前記電極材料に第Ｖ族元素化合物も含有させたほうが好ましい。
【００２１】
【発明の実施の形態】
以下、本発明の実施形態を添付図面に基づき詳細に説明する。
【００２２】
図１は本発明に係る太陽電池素子の一実施形態を示す断面図である。図１において、１は半導体基板、２は拡散層、３は反射防止膜、４はＢＳＦ層、５は表面電極、６は裏面電極を示す。
【００２３】
本発明では、一導電型の半導体基板１の表面側に逆導電型の拡散層２と反射防止膜３を形成した太陽電池素子において、前記反射防止膜３の上に形成した表面電極５と前記半導体基板１の裏面側に形成した裏面電極６が銀を主成分としＴｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物のいずれか一種または複数種を銀１００重量部に対して金属換算で０．０５〜５重量部の範囲で含有すると共にハロゲン化合物を０．１〜１０重量部の範囲で含有することを特徴とする。このようにすることにより、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、また長期信頼性も得ることができる。
【００２４】
ここでいう初期特性とは、電極形成後にソーラーシュミレーターを用いて、２５℃、Ａｍ−１．５の条件で測定したときにおける出力特性、特に曲線因子ＦＦのことであり、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子のＦＦ値に対して初期特性が９９％未満の場合、従来と同様の初期特性が得られたとはいえない。また、長期信頼性の評価にはＪＩＳＣ８９１７に基づき温湿度サイクル試験を行い、試験後のＦＦ値が試験前のＦＦ値の９２％未満の場合、電極の出力特性が著しく低下することから、長期信頼性に問題があるといえる。
【００２５】
電極中に前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物は銀１００重量部に対して金属換算で０．０５〜５重量部の範囲で含有させることにより、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子を得ることができる。しかし、前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物の含有量が銀１００重量部に対して金属換算で０．０５重量部以下の含有であれば、長期信頼性を確保することができない。また、金属換算で５重量部以上の含有であれば、不純物の混入により電極の線抵抗が増大し、初期特性におけるＦＦ値の低下が生じる。
【００２６】
電極中に前記ハロゲン化合物は銀１００重量部に対して０．１〜１０重量部の範囲で含有させることにより、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子を得ることができる。しかし、前記ハロゲン化合物の含有量が銀１００重量部に対して０．１重量部以下の含有であれば、長期信頼性を確保することができない。また、１０重量部以上の含有であれば、不純物の混入により電極の線抵抗が増大し、初期特性においてＦＦ値の低下が生じる。
【００２７】
また、上記太陽電池素子において、前記表面電極５または前記裏面電極６に第Ｖ族元素化合物を含有させたほうが好ましい。ただし、第Ｖ族元素化合物は前記半導体基板１がｐ型の半導体基板であり、前記拡散層がｎ型である場合は前記表面電極５に、また前記半導体基板１がｎ型の半導体基板であり、前記拡散層がｐ型である場合は前記裏面電極６に含有させる。第Ｖ族元素化合物を含有させることにより、表面電極５または裏面電極６と前記半導体基板１との接触抵抗を小さくすることができ、初期特性において高いＦＦ値を得ることができる。
【００２８】
次に、上記太陽電池素子の製造工程を説明する。まず、半導体基板１を用意する。この半導体基板１は、単結晶または多結晶シリコンなどからなる。この半導体基板１は、ボロン（Ｂ）などの一導電型半導体不純物を１×１０^１６〜１×１０^１８ａｔｏｍｓ／ｃｍ^３程度含有し、比抵抗１．０〜２．０Ω・ｃｍ程度の基板である。単結晶シリコン基板の場合は引き上げ法などによって形成され、多結晶シリコン基板の場合は鋳造法などによって形成される。多結晶シリコン基板は、大量生産が可能であり、製造コスト面で単結晶シリコン基板よりも有利である。引き上げ法や鋳造法によって形成されたインゴットを３００〜５００μｍ程度の厚みにスライスして、１０ｃｍ×１０ｃｍもしくは１５ｃｍ×１５ｃｍ程度の大きさに切断して半導体基板１とする。
【００２９】
次に、半導体基板１を拡散炉中に配置して，オキシ塩化リン（ＰＯＣｌ_３）など不純物元素を含むガス中で熱処理を行って不純物を拡散させる方法や、不純物元素を含む薬液を基板表面に塗布した後、熱処理を行うことにより形成する方法によって、半導体基板１の表面部分にリン原子などの不純物元素を１×１０^１６〜１×１０^１８ａｔｏｍｓ／ｃｍ^３程度拡散させて拡散層２を形成する。この拡散層２は０．２〜０．５μｍ程度の深さに、またシート抵抗が４０Ω／□以上になるように形成される。次に、半導体基板１の表面側に反射防止膜３を形成する。この反射防止膜３は半導体基板１内に光が有効に取り込むための膜であり、その厚みが５００〜１０００Å、屈折率が１．９〜２．３程度になるようにプラズマＣＶＤ法などで形成される。この反射防止膜の材料としては窒化シリコン膜の他に、一酸化シリコン（ＳｉＯ）、二酸化シリコン（ＳｉＯ２）、二酸化チタン（ＴｉＯ２）などがある。
【００３０】
裏面側に電極材料を塗布するとともに、前記反射防止膜３の上に直接電極材料を塗布して焼成するいわゆるファイヤースルー法により表面電極５と裏面電極６が形成される。
【００３１】
電極材料としては銀粉末と有機ビヒクルにガラスフリットを銀１００重量部に対してそれぞれ１０〜３０重量部、０．１〜０．５重量部を添加してペースト状にした電極ペーストなどが用いられ、電極ペーストをスクリーン印刷法で印刷して６５０〜９００℃で１〜３０分程度焼成することにより焼き付けられる。
【００３２】
本発明において、電極材料にＴｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒの金属粉末、酸化物粉末あるいは焼成によってこれらを析出し得る有機金属化合物のいずれか１つ、または２つ以上を銀１００重量部に対して金属換算で０．０５〜５重量部を含有し、かつ例えばフッ化銀、塩化銀、フッ化クロム、塩化コバルトなどのハロゲン化合物を銀１００重量部に対して０．１〜１０重量部を含有させることによって、表面電極５と裏面電極６中に前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒ成分と前記ハロゲン成分を含有させる。
【００３３】
前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒ成分が焼成中に、ガラスフリットに作用してその一部が溶け込むことによって、反射防止膜に作用し、コンタクト性および接着強度が向上する。さらに、ハロゲン成分がすべての元素と強い化学反応をおこす性質をもつことから、ハロゲン化合物を添加した電極材料を太陽電池素子の電極として印刷、乾燥、焼成すると電気伝導性を得ることができ、従来の酸処理工程が不要となる。よって、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、また電極材料に上記添加物を含有させることで長期信頼性も確保することができる。
【００３４】
電極材料中に前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物は銀１００重量部に対して金属換算で０．０５〜５重量部の範囲で含有させることにより、ファイヤースルー法による十分なコンタクト性および接着強度を持ち、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子を得ることができる。しかし、前記Ｔｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物の含有量が銀１００重量部に対して金属換算で０．０５重量部以下の含有であれば、十分なコンタクト性および接着強度が得らないためＦＦ値が低く、また長期信頼性を確保することができない。また、５重量部以上の含有であれば、不純物の混入により電極の線抵抗が増大し、初期特性におけるＦＦ値の低下が生じる。
【００３５】
電極材料中に前記ハロゲン化合物は銀１００重量部に対して０．１〜１０重量部の範囲で含有することにより、電極に酸処理を行うと共に電極表面に半田層を被覆した従来の太陽電池素子と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子を得ることができる。前記ハロゲン化合物の含有量が銀１００重量部に対して０．１重量部以下の含有であれば、接触抵抗が大きくなるためＦＦ値が低下し、また長期信頼性を確保することができない。また、１０重量部以上の含有であれば、電極ペースト中の金属成分の焼結が十分促進されず、また不純物の混入により電極の線抵抗が増大し、初期特性におけるＦＦ値の低下が生じる。
【００３６】
また、上記太陽電池素子において、前記表面電極５または前記裏面電極６を形成するのに電極材料中に第Ｖ族元素化合物を含有させたほうが好ましい。ただし、前記電極材料は前記半導体基板１がｐ型の半導体基板であり、前記拡散層がｎ型である場合は前記表面電極５に、また前記半導体基板１がｎ型の半導体基板であり、前記拡散層がｐ型である場合は前記裏面電極６を形成するのために用いる。第Ｖ族元素化合物を含有する電極材料を用いることにより、表面電極５または裏面電極６と前記半導体基板１との接触抵抗を小さくすることができ、高いＦＦ値を得ることができる。第Ｖ族元素化合物としては、たとえばＰ_２Ｏ_５、Ｓｂ_２Ｏ_３、Ａｓ_２Ｏ_３などがある。
【００３７】
【実施例１】
以下、本発明の実施例を説明する。１５ｃｍ×１５ｃｍで比抵抗１．５Ω・ｃｍの多結晶半導体基板１表面のダメージ層をアルカリでエッチングして洗浄した。次に、半導体基板１を拡散炉中に配置して、オキシ塩化リン（ＰＯＣｌ_３）の中で加熱することによって、半導体基板１の表面にリン原子を拡散させて拡散層２を形成した。このときのシート抵抗は６０Ω／□であった。次に、半導体基板１の表面側にプラズマＣＶＤ法によって反射防止膜３となる厚み８５０Åの窒化シリコン膜を形成した後、裏面にアルミニウムペーストを塗布して８５０℃で焼き付けることによってＢＳＦ層を形成した。その後表面に残った余剰なアルミニウムを除去した後、銀粉末と有機ビヒクルにガラスフリットを銀１００重量部に対して０．１〜５重量部添加し、酸化チタン粉末を銀１００重量部に対して金属換算で０．０４〜５．５重量部と、フッ化銀を銀１００重量部に対して０．０９〜１０．５重量部を含有した電極ペースト（条件Ｎｏ．９〜１３、１５〜１９、２１〜２５、２７〜３１、３３〜３７）を表裏面にスクリーン印刷法によって各１０枚塗布し、８００℃で１０分間焼き付けて太陽電池素子を形成した。電極に酸処理を行わないと共に電極表面に半田層を被覆せずに、ソーラーシュミレーターを用いて２５℃、Ａｍ−１．５の条件で初期特性の測定を行うとともに、ＪＩＳＣ８９１７に基づき温湿度サイクル試験を行って長期信頼性の評価を行った。比較例として、上記添加物を含まない電極ペーストで印刷・焼成した電極に、酸処理、半田層の被覆を行った太陽電池素子（条件Ｎｏ．１）、と、酸化チタン粉末および／またはフッ化銀を含まない電極ペーストで印刷・焼成した電極について、酸処理、半田層の被覆を行わない太陽電池素子（条件Ｎｏ．２〜８、１４、２０、２６、３２）についても同様の測定を行った。これらの結果を表１に示す。
【００３８】
【表１】

【００３９】
表１に示すように、条件Ｎｏ．２の酸化チタンとフッ化銀を含有しない電極に酸処理を行わないと共に電極表面に半田層を被覆しない太陽電池素子においては、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する条件Ｎｏ．２の初期特性がＰｍ、ＦＦ値は８４．５％、８７．１％と大きく下回り、ＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も７６．５％、７８．４％と大きく低下している。また、条件Ｎｏ．３、８、９などのように電極中の酸化チタンの含有量が０もしくは０．０４重量部の条件、またはフッ化銀の含有量が０もしくは０．０９重量部の条件では温湿度サイクル試験後の出力特性の低下が大きく、長期信頼性に問題がある。また、条件Ｎｏ．３１、３６、３７などのように電極中の酸化チタンの含有量が５．５重量％の条件、またはフッ化銀の含有量が１０．５重量部の条件では、温湿度サイクル試験後の出力特性の低下は小さいものの初期の出力特性が低い。
【００４０】
しかしながら、条件Ｎｏ．１６〜１８、２２〜２４、２８〜３０の酸化チタンの含有量が０．０５〜５重量部とフッ化銀の含有量が０．１〜１０重量部の条件では、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する各条件の初期特性がＰｍ、ＦＦ値とも９９％を超える値を得ることができる。また、ＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も９２％を超える条件となり、表面電極と裏面電極に酸処理を行わないと共に電極表面に半田層を被覆しなくても、電極に酸処理を行うと共に電極表面に半田層を被覆した場合と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子が得られた。
【００４１】
【実施例２】
実施例１の形成プロセスに従って、銀粉末と有機ビヒクルにガラスフリットを銀１００重量部に対して０．１〜５重量部添加し、酸化コバルト粉末を銀１００重量部に対して金属換算で０．０４〜５．５重量部と、フッ化銀を銀１００重量部に対して０．０９〜１０．５重量部を含有した電極ペースト（条件Ｎｏ．３９〜４３、４５〜４９、５１〜５５、５７〜６１、６３〜６７）を表裏面にスクリーン印刷法によって各１０枚塗布し、８００℃で１０分間焼き付けて太陽電池素子を形成し、初期特性と長期信頼性を調査した。比較例として条件Ｎｏ．１と、酸化コバルト粉末および／またはフッ化銀を含まない電極ペーストで印刷・焼成した電極について、酸処理、半田層の被覆を行わない太陽電池素子（条件Ｎｏ．２〜８、４４、５０、５６、６２）についても同様の測定を行った。これらの結果を表２に示す。
【００４２】
【表２】

【００４３】
表２に示すように、条件Ｎｏ．３、３８、３９などのように電極中の酸化コバルトの含有量が０もしくは０．０４重量部の条件、またはフッ化銀の含有量が０もしくは０．０９重量％の条件では温湿度サイクル試験後の出力特性の低下が大きく、長期信頼性に問題がある。また、条件Ｎｏ．６１、６６、６７などのように電極中の酸化コバルトの含有量が５．５重量％の条件、またはフッ化銀の含有量が１０．５重量部の条件では、温湿度サイクル試験後の出力特性の低下は小さいものの初期の出力特性が低い。
【００４４】
しかしながら、条件Ｎｏ．４６〜４８、５２〜５４、５８〜６０の酸化コバルトの含有量が０．０５〜５重量部とフッ化銀の含有量が０．１〜１０重量部の条件では、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する各条件の初期特性がＰｍ、ＦＦ値とも９９％を超える値を得ることができる。また、ＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も９２％を超える条件となり、表面電極と裏面電極に酸処理を行わないと共に電極表面に半田層を被覆しなくても、電極に酸処理を行うと共に電極表面に半田層を被覆した場合と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子が得られた。
【００４５】
【実施例３】
実施例１の形成プロセスに従って、銀粉末と有機ビヒクルにガラスフリットを銀１００重量部に対して０．１〜５重量部添加し、酸化マグネシウム粉末を銀１００重量部に対して金属換算で０．０４〜５．５重量部と、フッ化銀を銀１００重量部に対して０．０９〜１０．５重量部を含有した電極ペースト（条件Ｎｏ．６９〜７３、７５〜７９、８１〜８５、８７〜９１、９３〜９７）を表裏面にスクリーン印刷法によって各１０枚塗布し、８００℃で１０分間焼き付けて太陽電池素子を形成し、初期特性と長期信頼性を調査した。比較例として条件Ｎｏ．１と、酸化マグネシウム粉末および／またはフッ化銀を含まない電極ペーストで印刷・焼成した電極について、酸処理、半田層の被覆を行わない太陽電池素子（条件Ｎｏ．２〜８、７４、８０、８６、９２）についても同様の測定を行った。これらの結果を表３に示す。
【００４６】
【表３】

【００４７】
表３に示すように、条件Ｎｏ．３、６８、６９などのように電極中の酸化マグネシウムの含有量が０もしくは０．０４重量部の条件、またはフッ化銀の含有量が０もしくは０．０９重量部の条件では温湿度サイクル試験後の出力特性の低下が大きく、長期信頼性に問題がある。また、条件Ｎｏ．９１、９６、９７などのように電極中の酸化マグネシウムの含有量が５．５重量部の条件、またはフッ化銀の含有量が１０．５重量部の条件では、温湿度サイクル試験後の出力特性の低下は小さいものの初期の出力特性が低い。
【００４８】
しかしながら、条件Ｎｏ．７６〜７８、８２〜８４、８８〜９０の酸化マグネシウムの含有量が０．０５〜５重量部とフッ化銀の含有量が０．１〜１０重量部の条件では、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する各条件の初期特性がＰｍ、ＦＦ値とも９９％を超える値を得ることができる。また、ＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も９２％を超える条件となり、表面電極と裏面電極に酸処理を行わないと共に電極表面に半田層を被覆しなくても、電極に酸処理を行うと共に電極表面に半田層を被覆した場合と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子が得られた。
【００４９】
なお、酸化チタン、酸化コバルト、酸化マグネシウムに代えて酸化ビスマス、酸化亜鉛酸化ジルコニア、酸化鉄、酸化クロムを使用した場合であっても、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する各条件の初期特性がＰｍ、ＦＦ値とも９９％を超える値を得ることができ、またＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も９２％を超える条件となり、表面電極と裏面電極に酸処理を行わないと共に電極表面に半田層を被覆しなくても、電極に酸処理を行うと共に電極表面に半田層を被覆した場合と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子が得られた。
【００５０】
【実施例４】
実施例１の形成プロセスに従って銀粉末と有機ビヒクルにガラスフリットを銀１００重量部に対して０．１〜５重量部添加し、酸化チタン粉末を銀１００重量部に対して金属換算で０．０４〜５．５重量部と、フッ化銀を銀１００重量部に対して０．０９〜１０．５重量部と第Ｖ元素化合物である五酸化二リンを銀１００重量部に対して０．５重量部を含有した電極ペースト（条件Ｎｏ．１０５〜１０９、１１１〜１１５、１１７〜１２１、１２３〜１２７、１２９〜１３３）を表面に、五酸化二リンを含有しない上記電極ペーストを裏面にスクリーン印刷法によって各１０枚塗布し、８００℃で１０分間焼き付けて太陽電池素子を形成し、初期特性と長期信頼性を調査した。比較例として条件Ｎｏ．１と、酸化チタン粉末および／またはフッ化銀を含まない電極ペーストで印刷・焼成した電極について、酸処理、半田層の被覆を行わない太陽電池素子（条件Ｎｏ．８８〜１０４、１１０、１１６、１２２、１２８）についても同様の測定を行った。これらの結果を表４に示す。
【００５１】
【表４】

【００５２】
表４に示すように、条件Ｎｏ．９９、１０４、１０５などのように電極中の酸化マグネシウムの含有量が０もしくは０．０４重量部の条件、またはフッ化銀の含有量が０もしくは０．０９重量部の条件では温湿度サイクル試験後の出力特性の低下が大きく、長期信頼性に問題がある。また、条件Ｎｏ．１２７、１３２、１３３などのように電極中の酸化マグネシウムの含有量が５．５重量部の条件、またはフッ化銀の含有量が１０．５重量部の条件では、温湿度サイクル試験後の出力特性の低下は小さいものの初期の出力特性が低い。
【００５３】
しかしながら、条件Ｎｏ．１１２〜１１４、１１８〜１２０、１２４〜１２６の酸化チタンの含有量が０．０５〜５重量部とフッ化銀の含有量が０．１〜１０重量部の条件では、条件Ｎｏ．１の上記添加物を含有しない電極に酸処理を行うと共に電極表面に半田層を被覆した太陽電池素子の初期特性に対する各条件の初期特性がＰｍ、ＦＦ値とも９９％を超える値を得ることができる。また、第Ｖ元素化合物を含有しない条件Ｎｏ．１６〜１８、２２〜２４、２８〜３０に比べて、電極中に第Ｖ元素化合物を含有することで電極と半導体基板との接触抵抗を小さくすることができ、Ｐｍ、ＦＦ値とも約１％向上する。また、ＪＩＳＣ８９１７の温湿度サイクル試験前に対する試験後のＰｍ、ＦＦ値の比率も９２％を超える条件となり、表面電極と裏面電極に酸処理を行わないと共に電極表面に半田層を被覆しなくても、電極に酸処理を行うと共に電極表面に半田層を被覆した場合と同様の初期特性が得られ、長期信頼性を確保できる太陽電池素子が得られた。
【００５４】
【発明の効果】
以上説明したように、本発明に係る太陽電池素子によれば、表面電極および／または裏面電極にＴｉ、Ｃｏ、Ｍｇ、Ｂｉ、Ｚｎ、Ｚｒ、Ｆｅ、Ｃｒもしくはその化合物のうちいずれか一種または複数種を銀１００重量部に対して金属換算で０．０５〜５重量部含有すると共にハロゲン化合物を０．１〜１０重量部含有させることから、この反射防止膜上に直接電極材料を塗布して焼成するいわゆるファイヤースルー法によっても半導体基板と電極との安定したオーミック接触が得られ、さらに酸処理を行うことなく電気伝導性を得ることができるために従来と同様の出力特性が得られる。また、電極に半田層を被覆しなくても太陽電池素子の長期信頼性を確保することができる。そのため、酸処理工程、半田被覆工程を行う必要がなく、製造工程を簡略化できる。
【００５５】
また、上記太陽電池素子では、前記表面電極または裏面電極に第Ｖ族元素化合物を含有することで、電極と半導体基板との接触抵抗を小さくすることができ、高いＦＦ値を得ることができる。
【図面の簡単な説明】
【図１】本発明に係る太陽電池素子を示す断面図である。
【図２】従来の太陽電池素子を示す断面図である。
【符号の説明】
１・・・半導体基板
２・・・拡散層
３・・・反射防止膜
４・・・ＢＳＦ層
５・・・表面電極
６・・・裏面電極
７・・・半田層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar cell element, and more particularly to a solar cell element having an electrode on a semiconductor substrate.
[0002]
[Prior art]
A sectional view of a conventional solar cell element is shown in FIG. Reference numeral 1 denotes, for example, a p-type silicon semiconductor substrate, 2 a diffusion layer formed by diffusing phosphorus (P) or the like on the surface portion of the semiconductor substrate 1, and 3 an antireflection film made of a silicon nitride film or a silicon oxide film. is there. Further, a high-concentration p-type BSF layer 4 formed by diffusing aluminum or the like, for example, is provided on the back side of the semiconductor substrate 1.
[0003]
Further, a front surface electrode 5 and a back surface electrode 6 for taking out outputs are formed on both the front and back surfaces of the semiconductor substrate 1. As a forming method thereof, a screen printing method is generally used for cost reduction, and a paste containing silver powder, an organic vehicle, and glass frit is printed on the surface of the semiconductor substrate 1, and 1-30 at 600 to 800 ° C. It is baked by baking for about minutes. In other words, glass frit is added to the electrode paste to promote the sintering of the metal component in the electrode paste and to improve the adhesion strength by creating a eutectic state with silicon of the substrate material. When the surface electrode 5 is formed, the electrode forming portion of the antireflection film 3 is removed and the surface electrode 5 is baked on the portion, and the electrode forming portion of the antireflection film is not removed. In some cases, the surface electrode 5 is formed by baking directly from above the antireflection film.
Thereafter, the binder or glass frit in the metal paste is removed, acid treatment is performed to improve electrical conductivity, and the surface of the front electrode 5 and the back electrode 6 is connected to the solar cell elements in a later step. Therefore, in order to facilitate connection with an inner lead (not shown), and to ensure long-term reliability of the solar cell element, it is covered with a solder layer 7. Conventionally, for example, Sn—Pb eutectic solder has been used as such a solder layer 7.
[0004]
[Patent Document 1]
JP 2002-1111016 A
[0005]
[Patent Document 2]
JP 2001-313400 A
[0006]
[Patent Document 3]
JP 1997-213979 A
[0007]
[Patent Document 4]
JP 2000-332271 A
[0008]
[Problems to be solved by the invention]
In this conventional solar cell element, when the electrode forming portion of the antireflection film is removed and the electrode is baked and formed on this portion, the work is complicated because there are many steps. For example, the paste is applied to the electrode forming portion of the antireflection film. When printing the electrode material, a precise alignment is required. If a positional deviation occurs, it causes a decrease in yield.
[0009]
On the other hand, when the electrode material is baked directly from above the antireflection film, the antireflection film material is melted at a high temperature by firing to bring the electrode material into contact with the silicon substrate, so that stable ohmic contact cannot be obtained.
[0010]
In addition, since the acid treatment is performed after the front electrode 5 and the back electrode 6 are baked, the electrical conductivity is improved and the characteristics of the device are remarkably improved. However, when the acid remains in the electrode, the electrode Corrosion and long-term reliability may be deteriorated, so it was necessary to coat the solder layer.
[0011]
Further, in recent years, environmental issues have been regarded as important, and lead contained in Sn—Pb eutectic solder has become a problem, and development of lead-free solder is being promoted. However, a lead-free solder suitable for a solar cell element superior to the conventional Sn-Pn eutectic solder has not been developed yet from the viewpoint of its use temperature, long-term reliability, and high cost.
[0012]
In addition, in this conventional solar cell element, there is a problem that an acid treatment and a solder coating process are performed after the front electrode 5 and the back electrode 6 are baked, and the manufacturing process of the solar cell element is complicated. .
[0013]
Patent Document 2 (Japanese Patent Application Laid-Open No. 2001-313400) discloses an electrode material for a solar cell containing any one or more of Ti, Bi, Co, Zn, Zr, Fe, Cr and components, It is disclosed that a solar cell element having stable ohmic contact and high tensile strength can be obtained by applying and baking this electrode material on the antireflection film. However, after baking the electrode material, it is necessary to perform an acid treatment, and there is a problem that long-term reliability is deteriorated when the solder layer is not coated.
[0014]
Patent Document 3 (Japanese Patent Application Laid-Open No. 1997-213979) discloses a method of manufacturing a solar cell element in which a solder layer is not coated on an electrode, and a high output is obtained by chemically treating an electrode formed by firing with an acid. It is disclosed that a solar cell element can be obtained. However, when the acid remains in the electrode, there is a problem that the electrode is corroded and long-term reliability is lowered.
[0015]
In Patent Document 4 (Japanese Patent Application Laid-Open No. 2000-332271), by including a metal fluoride in the front electrode and / or the back electrode, electrical conductivity is obtained without performing an acid treatment step, and the electrode strength is improved. It is disclosed. However, when a metal additive is added, good electrode strength can be obtained, but long-term reliability is not sufficiently obtained when the solder layer is not coated.
[0016]
The present invention has been made in view of such problems of the prior art, and after baking the electrode from above the antireflection film, without performing an acid treatment step and coating the solder surface on the electrode surface, An object of the present invention is to provide a low-cost solar cell element that obtains similar output characteristics and does not cause deterioration in long-term reliability.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the solar cell element according to claim 1 has a diffusion layer of reverse conductivity type on the surface side of a semiconductor substrate exhibiting one conductivity type, and an antireflection film and a surface electrode are provided thereon. In addition, in the solar cell element in which the back electrode is provided on the back side, the front electrode and / or the back electrode is mainly composed of silver, and Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr, or a compound thereof Any one or more kinds are contained in an amount of 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of the silver and 0.1 to 10 parts by weight of a halogen compound.
[0018]
Moreover, in the said solar cell element, it is more preferable to contain the group V element compound in the said surface electrode or a back surface electrode.
[0019]
Further, in the above method for manufacturing a solar cell element, a diffusion layer of reverse conductivity type is formed on the surface side of a semiconductor substrate exhibiting one conductivity type, and an antireflection film is formed on the surface side of the semiconductor substrate. In the method for manufacturing a solar cell element in which a surface electrode and a back electrode are formed by baking an electrode material containing silver, an organic vehicle, and a glass frit on the back side of the film and the semiconductor substrate, Ti, Co, Mg, One or more of Bi, Zn, Zr, Fe, Cr or a compound thereof is contained in an amount of 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of silver and 0.1 to 10 halogen compounds. It is characterized by containing parts by weight.
[0020]
In the method for forming a solar cell element, it is preferable that the electrode material contains a Group V element compound.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[0022]
FIG. 1 is a cross-sectional view showing one embodiment of a solar cell element according to the present invention. In FIG. 1, 1 is a semiconductor substrate, 2 is a diffusion layer, 3 is an antireflection film, 4 is a BSF layer, 5 is a front electrode, and 6 is a back electrode.
[0023]
In the present invention, in the solar cell element in which the reverse conductivity type diffusion layer 2 and the antireflection film 3 are formed on the surface side of the one conductivity type semiconductor substrate 1, the surface electrode 5 formed on the antireflection film 3 and the above-mentioned The back surface electrode 6 formed on the back surface side of the semiconductor substrate 1 is mainly composed of silver, and Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr, or one or more kinds thereof are added to 100 parts by weight of silver. In addition, it contains 0.05 to 5 parts by weight in terms of metal and contains a halogen compound in the range of 0.1 to 10 parts by weight. By doing in this way, the initial characteristic similar to the conventional solar cell element which performed the acid treatment to the electrode and coat | covered the solder layer on the electrode surface is acquired, and long-term reliability can also be acquired.
[0024]
The initial characteristics here are output characteristics when measured under conditions of 25 ° C. and Am-1.5 using a solar simulator after electrode formation, in particular, the fill factor FF, and the electrode is subjected to acid treatment. At the same time, when the initial characteristic is less than 99% with respect to the FF value of the conventional solar cell element in which the electrode surface is coated with the solder layer, it cannot be said that the initial characteristic similar to the conventional one is obtained. For long-term reliability evaluation, a temperature and humidity cycle test is performed based on JIS C8917. If the FF value after the test is less than 92% of the FF value before the test, the output characteristics of the electrode are significantly reduced. It can be said that there is a problem with reliability.
[0025]
In the electrode, the Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof is contained in the range of 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of silver. An initial characteristic similar to that of a conventional solar cell element in which an acid treatment is performed and a solder layer is coated on the electrode surface is obtained, and a solar cell element that can ensure long-term reliability can be obtained. However, if the content of Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof is 0.05 parts by weight or less in terms of metal with respect to 100 parts by weight of silver, long-term reliability Can not be secured. Moreover, if it contains 5 weight part or more in conversion of a metal, the line resistance of an electrode will increase by mixing of an impurity, and the fall of FF value in an initial characteristic will arise.
[0026]
A conventional solar cell element in which the halogen compound is contained in an electrode in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of silver, whereby the electrode is acid-treated and the electrode surface is coated with a solder layer; Similar initial characteristics can be obtained, and a solar cell element that can ensure long-term reliability can be obtained. However, if the content of the halogen compound is 0.1 parts by weight or less with respect to 100 parts by weight of silver, long-term reliability cannot be ensured. Further, if the content is 10 parts by weight or more, the line resistance of the electrode increases due to the mixing of impurities, and the FF value decreases in the initial characteristics.
[0027]
In the solar cell element, it is preferable that the front electrode 5 or the back electrode 6 contains a group V element compound. However, as for the group V element compound, the semiconductor substrate 1 is a p-type semiconductor substrate, and when the diffusion layer is n-type, the surface electrode 5 is used, and the semiconductor substrate 1 is an n-type semiconductor substrate. When the diffusion layer is p-type, it is contained in the back electrode 6. By containing the Group V element compound, the contact resistance between the front electrode 5 or the back electrode 6 and the semiconductor substrate 1 can be reduced, and a high FF value can be obtained in the initial characteristics.
[0028]
Next, the manufacturing process of the said solar cell element is demonstrated. First, the semiconductor substrate 1 is prepared. The semiconductor substrate 1 is made of single crystal or polycrystalline silicon. The semiconductor substrate 1 is made of 1 × 10 1 semiconductor impurity such as boron (B). ¹⁶ ~ 1x10 ¹⁸ atoms / cm ³ It is a substrate having a specific resistance of about 1.0 to 2.0 Ω · cm. A single crystal silicon substrate is formed by a pulling method or the like, and a polycrystalline silicon substrate is formed by a casting method or the like. The polycrystalline silicon substrate can be mass-produced and is more advantageous than the single crystal silicon substrate in terms of manufacturing cost. An ingot formed by a pulling method or a casting method is sliced to a thickness of about 300 to 500 μm and cut into a size of about 10 cm × 10 cm or 15 cm × 15 cm to obtain a semiconductor substrate 1.
[0029]
Next, the semiconductor substrate 1 is placed in a diffusion furnace, and phosphorus oxychloride (POCl) is placed. ₃ ) Or the like in a gas containing an impurity element to diffuse the impurities, or a method in which a chemical solution containing an impurity element is applied to the substrate surface and then formed by performing a heat treatment on the surface portion of the semiconductor substrate 1. Impurity elements such as phosphorus atoms are 1 × 10 ¹⁶ ~ 1x10 ¹⁸ atoms / cm ³ The diffusion layer 2 is formed by diffusing to some extent. The diffusion layer 2 is formed to a depth of about 0.2 to 0.5 μm and a sheet resistance of 40Ω / □ or more. Next, an antireflection film 3 is formed on the surface side of the semiconductor substrate 1. This antireflection film 3 is a film for effectively taking light into the semiconductor substrate 1, and is formed by plasma CVD or the like so that its thickness is 500 to 1000 mm and its refractive index is about 1.9 to 2.3. Is done. In addition to the silicon nitride film, the material for the antireflection film includes silicon monoxide (SiO), silicon dioxide (SiO2), titanium dioxide (TiO2), and the like.
[0030]
The surface electrode 5 and the back electrode 6 are formed by a so-called fire-through method in which an electrode material is applied on the back surface side and the electrode material is directly applied on the antireflection film 3 and baked.
[0031]
As an electrode material, an electrode paste or the like made by adding 10 to 30 parts by weight and 0.1 to 0.5 parts by weight of glass frit to 100 parts by weight of silver and silver powder and an organic vehicle, respectively, is used. The electrode paste is printed by screen printing and baked at 650 to 900 ° C. for about 1 to 30 minutes.
[0032]
In the present invention, the electrode material is any one of Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr metal powder, oxide powder, or an organometallic compound that can be deposited by firing, or two or more thereof. Containing 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of silver, and for example, halogen compounds such as silver fluoride, silver chloride, chromium fluoride and cobalt chloride are added to 0 parts by weight of silver. By containing 1 to 10 parts by weight, the Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr component and the halogen component are contained in the front electrode 5 and the back electrode 6.
[0033]
The Ti, Co, Mg, Bi, Zn, Zr, Fe, and Cr components act on the glass frit and partially dissolve during firing, thereby acting on the antireflection film and improving the contact property and adhesive strength. To do. Furthermore, since the halogen component has the property of causing a strong chemical reaction with all elements, it is possible to obtain electrical conductivity by printing, drying and firing the electrode material to which the halogen compound is added as the electrode of the solar cell element. No acid treatment step is required. Therefore, it is possible to obtain the same initial characteristics as those of the conventional solar cell element in which the electrode is subjected to acid treatment and the electrode surface is coated with a solder layer, and long-term reliability is ensured by including the above-mentioned additives in the electrode material. Can do.
[0034]
By containing the Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof in the electrode material in a range of 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of silver, A solar cell that has sufficient contact properties and adhesive strength by the through method, has the same initial characteristics as a conventional solar cell element in which the electrode is acid-treated and a solder layer is coated on the electrode surface, and long-term reliability can be ensured An element can be obtained. However, if the content of Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof is 0.05 parts by weight or less in terms of metal with respect to 100 parts by weight of silver, sufficient contact is obtained. Therefore, the FF value is low and long-term reliability cannot be ensured. Moreover, if it contains 5 weight part or more, the line resistance of an electrode will increase by mixing of an impurity, and the FF value in initial characteristics will fall.
[0035]
A conventional solar cell element in which the halogen compound is contained in an electrode material in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of silver, whereby the electrode is subjected to acid treatment and the electrode surface is coated with a solder layer. The solar cell element which can obtain the initial characteristics similar to those and can ensure long-term reliability can be obtained. If the content of the halogen compound is 0.1 parts by weight or less with respect to 100 parts by weight of silver, the contact resistance increases, so the FF value decreases and long-term reliability cannot be ensured. If the content is 10 parts by weight or more, the sintering of the metal component in the electrode paste is not sufficiently promoted, and the line resistance of the electrode increases due to the mixing of impurities, resulting in a decrease in the FF value in the initial characteristics.
[0036]
Moreover, in the said solar cell element, it is preferable to contain a group V element compound in an electrode material in order to form the said surface electrode 5 or the said back surface electrode 6. FIG. However, the electrode material is that the semiconductor substrate 1 is a p-type semiconductor substrate, the surface electrode 5 when the diffusion layer is n-type, and the semiconductor substrate 1 is an n-type semiconductor substrate, When the diffusion layer is p-type, it is used for forming the back electrode 6. By using an electrode material containing a Group V element compound, the contact resistance between the surface electrode 5 or the back electrode 6 and the semiconductor substrate 1 can be reduced, and a high FF value can be obtained. Examples of Group V element compounds include P ₂ O ₅ , Sb ₂ O ₃ , As ₂ O ₃ and so on.
[0037]
[Example 1]
Examples of the present invention will be described below. The damaged layer on the surface of the polycrystalline semiconductor substrate 1 having a specific resistance of 1.5 Ω · cm at 15 cm × 15 cm was cleaned by etching with alkali. Next, the semiconductor substrate 1 is placed in a diffusion furnace, and phosphorus oxychloride (POCl) is placed. ₃ ) To diffuse phosphorus atoms on the surface of the semiconductor substrate 1 to form a diffusion layer 2. The sheet resistance at this time was 60Ω / □. Next, after forming a silicon nitride film having a thickness of 850 mm to be the antireflection film 3 on the surface side of the semiconductor substrate 1 by plasma CVD, an aluminum paste was applied to the back surface and baked at 850 ° C. to form a BSF layer. . Then, after removing excess aluminum remaining on the surface, 0.1 to 5 parts by weight of glass frit is added to silver powder and organic vehicle with respect to 100 parts by weight of silver, and titanium oxide powder is added to 100 parts by weight of silver. Electrode paste containing 0.04 to 5.5 parts by weight in terms of metal and 0.09 to 10.5 parts by weight of silver fluoride with respect to 100 parts by weight of silver (Condition Nos. 9 to 13, 15 to 19) Ten to twenty-five, twenty-five to twenty-five, twenty-seven to thirty-one, and thirty-seven to thirty-seventh 37) were applied to the front and back surfaces by screen printing and baked at 800 ° C. for 10 minutes to form solar cell elements. The electrode is not treated with acid and the surface of the electrode is not coated with a solder layer. Using a solar simulator, the initial characteristics are measured at 25 ° C. and Am-1.5, and the temperature and humidity cycle is based on JIS C8917. Tests were performed to evaluate long-term reliability. As a comparative example, a solar cell element (condition No. 1) in which an electrode printed and baked with an electrode paste containing no additive is subjected to acid treatment and solder layer coating, titanium oxide powder and / or fluoride. The same measurement was performed for solar cell elements (conditions No. 2 to 8, 14, 20, 26, and 32) that were not subjected to acid treatment or solder layer coating on electrodes printed and fired with an electrode paste that did not contain silver. It was. These results are shown in Table 1.
[0038]
[Table 1]

[0039]
As shown in Table 1, condition no. In the solar cell element in which the electrode containing no titanium oxide and silver fluoride of 2 is not subjected to acid treatment and the electrode surface is not covered with the solder layer, the condition No. No. 1 for the initial characteristics of the solar cell element in which the electrode containing no additive was subjected to acid treatment and the electrode surface was coated with a solder layer. The initial characteristics of Pm and FF values are significantly lower than 84.5% and 87.1%, respectively, and the ratios of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 are also 76.5% and 78.4%. % Has fallen significantly. In addition, Condition No. Temperature / humidity cycle test under conditions where the content of titanium oxide in the electrode is 0 or 0.04 parts by weight, such as 3, 8, 9 or the like, or when the content of silver fluoride is 0 or 0.09 parts by weight There is a problem in long-term reliability because the output characteristics are greatly lowered later. In addition, Condition No. When the content of titanium oxide in the electrode is 5.5% by weight, such as 31, 36, 37, or the condition that the content of silver fluoride is 10.5 parts by weight, the output after the temperature and humidity cycle test Although the deterioration of the characteristic is small, the initial output characteristic is low.
[0040]
However, condition no. In the conditions that the content of titanium oxide of 16 to 18, 22 to 24, and 28 to 30 is 0.05 to 5 parts by weight and the content of silver fluoride is 0.1 to 10 parts by weight, Condition No. The initial characteristics of each condition with respect to the initial characteristics of the solar cell element in which the electrode containing no additive is subjected to acid treatment and the surface of the electrode is coated with a solder layer, both Pm and FF values exceed 99%. it can. In addition, the ratio of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 exceeds 92%, and the surface electrode and the back electrode are not subjected to acid treatment, and the electrode surface is not coated with a solder layer. In addition, an initial characteristic similar to that obtained when the electrode was subjected to acid treatment and the electrode surface was coated with a solder layer was obtained, and a solar cell element capable of ensuring long-term reliability was obtained.
[0041]
[Example 2]
According to the formation process of Example 1, 0.1 to 5 parts by weight of glass frit is added to silver powder and organic vehicle with respect to 100 parts by weight of silver, and cobalt oxide powder is added to 100 parts by weight of silver in terms of metal. 04 to 5.5 parts by weight, and electrode paste containing 0.09 to 10.5 parts by weight of silver fluoride with respect to 100 parts by weight of silver (Condition Nos. 39 to 43, 45 to 49, 51 to 55, 57 to 61, 63 to 67) were applied to the front and back surfaces by screen printing, and baked at 800 ° C. for 10 minutes to form solar cell elements. The initial characteristics and long-term reliability were investigated. As a comparative example, Condition No. 1 and an electrode printed and baked with an electrode paste not containing cobalt oxide powder and / or silver fluoride, a solar cell element not subjected to acid treatment or solder layer coating (conditions No. 2 to 8, 44, 50, The same measurement was performed for 56 and 62). These results are shown in Table 2.
[0042]
[Table 2]

[0043]
As shown in Table 2, condition no. Temperature and humidity cycle test under conditions where the cobalt oxide content in the electrode is 0 or 0.04 parts by weight, such as 3, 38, 39, etc., or where the silver fluoride content is 0 or 0.09% by weight There is a problem in long-term reliability because the output characteristics are greatly lowered later. In addition, Condition No. When the content of cobalt oxide in the electrode is 5.5% by weight, such as 61, 66, 67, or the condition that the content of silver fluoride is 10.5 parts by weight, the output after the temperature and humidity cycle test Although the deterioration of the characteristic is small, the initial output characteristic is low.
[0044]
However, condition no. 46 to 48, 52 to 54, and 58 to 60, the content of cobalt oxide is 0.05 to 5 parts by weight and the content of silver fluoride is 0.1 to 10 parts by weight. The initial characteristics of each condition with respect to the initial characteristics of the solar cell element in which the electrode containing no additive is subjected to acid treatment and the surface of the electrode is coated with a solder layer, both Pm and FF values exceed 99%. it can. In addition, the ratio of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 exceeds 92%, and the surface electrode and the back electrode are not subjected to acid treatment, and the electrode surface is not coated with a solder layer. In addition, an initial characteristic similar to that obtained when the electrode was subjected to acid treatment and the electrode surface was coated with a solder layer was obtained, and a solar cell element capable of ensuring long-term reliability was obtained.
[0045]
[Example 3]
According to the formation process of Example 1, 0.1 to 5 parts by weight of glass frit is added to silver powder and organic vehicle with respect to 100 parts by weight of silver, and magnesium oxide powder is added in an amount of 0. 04 to 5.5 parts by weight, and electrode paste containing 0.09 to 10.5 parts by weight of silver fluoride with respect to 100 parts by weight of silver (Condition Nos. 69 to 73, 75 to 79, 81 to 85, 87 to 91 and 93 to 97) were applied to the front and back surfaces by screen printing, and baked at 800 ° C. for 10 minutes to form solar cell elements. The initial characteristics and long-term reliability were investigated. As a comparative example, Condition No. 1 and an electrode printed and baked with an electrode paste containing no magnesium oxide powder and / or silver fluoride, a solar cell element (conditions Nos. 2 to 8, 74, 80, 86, 92), the same measurement was performed. These results are shown in Table 3.
[0046]
[Table 3]

[0047]
As shown in Table 3, condition no. Temperature / humidity cycle test under the condition that the magnesium oxide content in the electrode is 0 or 0.04 parts by weight, such as 3, 68, 69, or the condition that the silver fluoride content is 0 or 0.09 parts by weight. There is a problem in long-term reliability because the output characteristics are greatly lowered later. In addition, Condition No. When the magnesium oxide content in the electrode is 5.5 parts by weight or the silver fluoride content is 10.5 parts by weight, such as 91, 96, 97, etc., the output after the temperature and humidity cycle test Although the deterioration of the characteristic is small, the initial output characteristic is low.
[0048]
However, condition no. No. 76-78, 82-84, 88-90 magnesium oxide content of 0.05-5 parts by weight and silver fluoride content of 0.1-10 parts by weight. The initial characteristics of each condition with respect to the initial characteristics of the solar cell element in which the electrode containing no additive is subjected to acid treatment and the surface of the electrode is coated with a solder layer, both Pm and FF values exceed 99%. it can. In addition, the ratio of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 exceeds 92%, and the surface electrode and the back electrode are not subjected to acid treatment, and the electrode surface is not coated with a solder layer. In addition, an initial characteristic similar to that obtained when the electrode was subjected to acid treatment and the electrode surface was coated with a solder layer was obtained, and a solar cell element capable of ensuring long-term reliability was obtained.
[0049]
Even when bismuth oxide, zinc oxide zirconia oxide, iron oxide, and chromium oxide are used instead of titanium oxide, cobalt oxide, and magnesium oxide, the condition no. The initial characteristics of each condition with respect to the initial characteristics of the solar cell element in which the electrode containing no additive is subjected to acid treatment and the surface of the electrode is coated with a solder layer, both Pm and FF values exceed 99%. In addition, the ratio of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 exceeds 92%, and the surface electrode and the back electrode are not subjected to acid treatment, and the electrode surface is not coated with a solder layer. However, the same initial characteristics as when the electrode was acid-treated and the electrode surface was coated with a solder layer were obtained, and a solar cell element capable of ensuring long-term reliability was obtained.
[0050]
[Example 4]
According to the formation process of Example 1, 0.1 to 5 parts by weight of glass frit is added to 100 parts by weight of silver to silver powder and an organic vehicle, and titanium oxide powder is added to 0.04 by metal in terms of 100 parts by weight of silver. 5.5 parts by weight, 0.09 to 10.5 parts by weight of silver fluoride with respect to 100 parts by weight of silver, and 0.5 phosphorus with respect to 100 parts by weight of diphosphorus pentoxide which is a V element compound. Screen printing of the electrode paste containing parts by weight (conditions No. 105 to 109, 111 to 115, 117 to 121, 123 to 127, 129 to 133) on the front surface and the above electrode paste not containing diphosphorus pentoxide on the back surface Ten sheets of each were applied by the method and baked at 800 ° C. for 10 minutes to form a solar cell element, and the initial characteristics and long-term reliability were investigated. As a comparative example, Condition No. 1 and an electrode printed and baked with an electrode paste containing no titanium oxide powder and / or silver fluoride, a solar cell element (conditions No. 88 to 104, 110, 116, 122, 128) were also measured in the same manner. These results are shown in Table 4.
[0051]
[Table 4]

[0052]
As shown in Table 4, condition no. Temperature and humidity cycle test under the condition that the magnesium oxide content in the electrode is 0 or 0.04 parts by weight, such as 99, 104, 105, etc., or the silver fluoride content is 0 or 0.09 parts by weight There is a problem in long-term reliability because the output characteristics are greatly lowered later. In addition, Condition No. When the content of magnesium oxide in the electrode is 5.5 parts by weight, such as 127, 132, 133, or the condition that the content of silver fluoride is 10.5 parts by weight, the output after the temperature and humidity cycle test Although the deterioration of the characteristic is small, the initial output characteristic is low.
[0053]
However, condition no. Nos. 112 to 114, 118 to 120, and 124 to 126 had a titanium oxide content of 0.05 to 5 parts by weight and a silver fluoride content of 0.1 to 10 parts by weight. The initial characteristics of each condition with respect to the initial characteristics of the solar cell element in which the electrode containing no additive is subjected to acid treatment and the surface of the electrode is coated with a solder layer, both Pm and FF values exceed 99%. it can. In addition, the condition No. containing no V element compound. Compared with 16-18, 22-24, 28-30, the contact resistance between the electrode and the semiconductor substrate can be reduced by containing the V element compound in the electrode, and both Pm and FF values are about 1%. improves. In addition, the ratio of Pm and FF values after the test to the temperature / humidity cycle test of JIS C8917 exceeds 92%, and the surface electrode and the back electrode are not subjected to acid treatment, and the electrode surface is not coated with a solder layer. In addition, an initial characteristic similar to that obtained when the electrode was subjected to acid treatment and the electrode surface was coated with a solder layer was obtained, and a solar cell element capable of ensuring long-term reliability was obtained.
[0054]
【The invention's effect】
As described above, according to the solar cell element of the present invention, one or more of Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof is used for the front electrode and / or the back electrode. Since the seed is contained in an amount of 0.05 to 5 parts by weight in terms of metal with respect to 100 parts by weight of silver and the halogen compound is contained in an amount of 0.1 to 10 parts by weight, an electrode material is directly applied on the antireflection film. The so-called fire-through method of firing also provides stable ohmic contact between the semiconductor substrate and the electrode, and furthermore, electrical conductivity can be obtained without performing acid treatment, so that output characteristics similar to those of the prior art can be obtained. Further, long-term reliability of the solar cell element can be ensured without covering the electrodes with a solder layer. Therefore, it is not necessary to perform an acid treatment process and a solder coating process, and the manufacturing process can be simplified.
[0055]
Moreover, in the said solar cell element, the contact resistance of an electrode and a semiconductor substrate can be made small by containing a V group element compound in the said surface electrode or a back surface electrode, and a high FF value can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a solar cell element according to the present invention.
FIG. 2 is a cross-sectional view showing a conventional solar cell element.
[Explanation of symbols]
1 ... Semiconductor substrate
2 ... Diffusion layer
3 ... Antireflection film
4 ... BSF layer
5 ... Surface electrode
6 ... Back electrode
7 ... Solder layer

Claims

In a solar cell element having a reverse conductivity type diffusion layer on the surface side of a semiconductor substrate exhibiting one conductivity type, an antireflection film and a surface electrode on the diffusion layer, and a back electrode on the back side, the surface electrode And / or the back electrode is mainly composed of silver, and one or more of Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or a compound thereof is converted into metal with respect to 100 parts by weight of silver. A solar cell element containing 0.05 to 5 parts by weight and 0.1 to 10 parts by weight of a halogen compound.

The solar cell element according to claim 1, wherein the front electrode or the back electrode contains a group V element compound.

A diffusion layer of the reverse conductivity type is formed on the surface side of the semiconductor substrate exhibiting one conductivity type, and an antireflection film is formed on the surface side of the semiconductor substrate, and silver is formed on the antireflection film and the back surface side of the semiconductor substrate. In a method for manufacturing a solar cell element in which an electrode material including an organic vehicle and glass frit is baked to form a front electrode and a back electrode, the electrode material may be Ti, Co, Mg, Bi, Zn, Zr, Fe, Cr or the like A solar cell comprising 0.05 to 5 parts by weight of a compound in terms of metal with respect to 100 parts by weight of silver and 0.1 to 10 parts by weight of a halogen compound. Device manufacturing method.

The method for manufacturing a solar cell element according to claim 3, wherein the electrode material contains a Group V element compound.