JP3968000B2 - Method for forming solar cell element - Google Patents

Method for forming solar cell element Download PDF

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JP3968000B2
JP3968000B2 JP2002342880A JP2002342880A JP3968000B2 JP 3968000 B2 JP3968000 B2 JP 3968000B2 JP 2002342880 A JP2002342880 A JP 2002342880A JP 2002342880 A JP2002342880 A JP 2002342880A JP 3968000 B2 JP3968000 B2 JP 3968000B2
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metal
semiconductor substrate
solar cell
cell element
paste
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JP2004179336A (en
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祐子 府川
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Kyocera Corp
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Kyocera Corp
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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
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    • Y02E10/50—Photovoltaic [PV] energy

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Description

【０００１】
【発明の属する技術分野】
本発明は太陽電池素子の形成方法に関し、特に金属ペーストを焼き付けて表面電極と裏面電極を形成する太陽電池素子の形成方法に関する。
【０００２】
【従来の技術および発明が解決しようとする課題】
従来の太陽電池素子を図１に示す。例えばＰ型半導体基板１の表面近傍の全面に一定の深さまでＮ型不純物を拡散させてＮ型を呈する拡散層２を設け、半導体基板１の表面に窒化シリコン膜などから成る反射防止膜３を設け、表面に表面電極４を設けるとともに、裏面にアルミニウムなどから成る集電部５と銀などから成る出力取出部６とで構成される裏面電極５、６を設けている。また半導体基板１の裏面には高濃度のＰ型拡散層７が形成される。
【０００３】
これらの太陽電池素子の表面電極４および裏面電極５、６を形成するには、アルミニウムからなる第二の金属を主成分とするペーストを半導体基板１の裏面の一部を除いた大部分に塗布して乾燥した後、この第二の金属を主成分とするペーストを塗布しなかった部分とその周縁部を覆うように銀からなる第三の金属を主成分とするペーストを塗布して乾燥し、最後に半導体基板１の表面に銀からなる第一の金属を主成分とするペーストを塗布して乾燥して、第一の金属を主成分とするペーストと第二の金属を主成分とするペーストと第三の金属を主成分とするペーストとを同時に焼成する方法、すなわち同時焼成法が従来用いられてきた（例えば特許文献１参照。）。
【０００４】
また、図２に示すように銀からなる第三の金属を主成分とするペーストを塗布して乾燥し、この第三の金属を主成分とするペーストを塗布しなかった部分とその周縁部を覆うようにアルミニウムからなる第二の金属を主成分とするペーストを半導体基板１の裏面の一部を除いた大部分に塗布して１回目の焼成を行った後、半導体基板１の表面に銀からなる第一の金属を主成分とするペーストを塗布して乾燥して２回目の焼成を行う方法もある（例えば特許文献２参照。）。
【０００５】
さらに、銀からなる第三の金属を主成分とするペーストを塗布して１回目の焼成を行った後、この第三の金属を主成分とするペーストを塗布しなかった部分とその周縁部を覆うようにアルミニウムからなる第二の金属を主成分とするペーストを半導体基板１の裏面の一部を除いた大部分に塗布して乾燥し、半導体基板１の表面に銀からなる第一の金属を主成分とするペーストを塗布して乾燥して２回目の焼成を行う方法もある（例えば特許文献２参照。）。
【０００６】
これによって半導体基板１の裏面には、集電部５とはんだ濡れ性の良好な出力取出部６が形成されるとともに、集電部５の下の半導体基板１には高濃度のＰ型拡散層７が形成される。
【０００７】
その後、表面電極４および裏面電極の出力取出部６上にはんだ（不図示）を被着して、太陽電池素子を直列もしくは並列に接続するインナーリードを接続する。
【０００８】
ところが、この従来の太陽電池素子の形成方法では、焼成の際に集電部５のアルミニウムと出力取出部６の銀との重なり部、つまり熱膨張係数の異なる半導体基板１とアルミニウムと銀との重なり部に応力が発生し、半導体基板１の割れの原因になるという問題があった。
【０００９】
また、アルミニウムを焼成してから表裏面に銀を塗布して焼成する方法によれば、上記問題は解決されるもののアルミニウムを主成分とする金属ペーストを塗布して焼成することによって、半導体基板１の裏面にアルミニウムの凝集等による凹凸が形成されることがあり、その凹凸によって表面電極４を形成するためのペーストをスクリーン印刷で塗布する際に半導体基板１に割れが発生するという問題があった。
【００１０】
またこれらの方法によると、表面電極４が形成時もしくはそれ以降に剥離するという問題が発生することがあった。すなわち、図３および図４からわかるように表面電極４や出力取出部６の面積に比べ、集電部５の面積が広く使用するペースト量も多く、これらのペーストは金属の他に溶剤とエチルセルロース等のバインダーを混合して構成されるため、集電部５を焼成する際に揮発する溶剤やバインダーの成分が飛散し、半導体基板１の表面を汚染したり表面電極４の焼結を阻害するためにこの剥離の問題は発生するものと思われる。なお、図3は一般的な太陽電池素子の表面電極の構造を示し、図4は裏面電極の構造を示す。
【００１１】
この問題を解決する方法としては裏面電極の集電部５を形成した後に、半導体基板１の表面を洗浄して、その後表面電極４を形成する方法が考えられる。しかし、この方法を行うと工程数が増加してしまい製造上不適である。
【００１２】
さらに半導体基板１の表面に銀からなる第一の金属を主成分とするペーストを塗布して１回目の焼成を行い、アルミニウムからなる第二の金属を主成分とするペーストを半導体基板１の裏面の一部を除いた大部分に塗布して２回目の焼成を行った後、この第二の金属を主成分とするペーストを塗布しなかった部分とその周縁部を覆うように銀からなる第三の金属を主成分とするペーストを塗布して３回目の焼成を行う方法もある（例えば特許文献３参照。）。この方法によれば、集電部５を形成する前に表面電極４を形成してしまうため、上記のような剥離の問題は発生しない。
【００１３】
しかしこの方法によれば、表面電極４を形成した後、集電部５を形成し、更にその後に出力取出部６を形成するため、３回の高温焼成を繰り返すことになり、太陽電池素子の出力特性の低下の問題が発生したりすることがあった。そしてこの問題を回避するため、焼成温度を下げたり時間を短くしたりすると、裏面電極の集電部５と出力取出部６の間で剥離が発生してしまうという問題が発生することもあった。
【００１４】
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、電極の剥離の発生を防止するとともに、半導体基板の割れを防止できる太陽電池素子の形成方法を提供することを目的とする。
【００１５】
【特許文献１】
特開平１０−３３５２６７号公報
【特許文献２】
特開平１０−１４４９４３号公報
【特許文献３】
特開２０００−１８８４０９号公報
【００１６】
【課題を解決するための手段】
上記目的を達成するために、本発明に係る太陽電池素子の形成方法では、一導電型を呈する半導体基板の一主面側に逆導電型半導体不純物を拡散するとともに、第一の金属を主成分とする表面電極を形成し、他の主面側に第二の金属を主成分とする集電部とこの第二の金属よりも半田濡れ性のよい第三の金属を主成分とする出力取出部とから成る裏面電極を形成する太陽電池素子の形成方法において、前記半導体基板の一主面側に前記表面電極となる第一の金属を主成分とするペーストを塗布するとともに、他の主面側に前記裏面電極の出力取出部となる第三の金属を主成分とするペーストを塗布して１回目の焼成を行った後、他の主面側に前記裏面電極の集電部となる第二の金属を主成分とするペーストを塗布して２回目の焼成を行うことを特徴とする。
【００１７】
上記太陽電池素子の形成方法では、前記第一の金属と前記第三の金属は銀からなることが望ましい。
【００１８】
また上記太陽電池素子の形成方法では、前記半導体基板がシリコンからなり、前記第三の金属を主成分とするペーストにアルミニウムを含有することが望ましい。
【００１９】
また上記太陽電池素子の形成方法では、前記第二の金属がアルミニウムからなることが望ましい。
【００２０】
【発明の実施の形態】
以下、本発明の実施形態を詳細に説明する。
本発明に係る太陽電池素子の構造も基本的には従来の太陽電池素子と同様である。すなわち、例えばＰ型半導体基板１の表面近傍全面に一定の深さまでＮ型不純物を拡散させてＮ型を呈する拡散層２を設け、半導体基板１の表面に窒化シリコン膜などから成る反射防止膜３を設け、表面に表面電極４を設けるとともに、裏面にはアルミニウムなどから成る集電部５と銀などから成る出力取出部６とで構成される裏面電極を設けている。また半導体基板１の裏面には高濃度のＰ型拡散層７が形成される。
【００２１】
このような太陽電池素子は、例えばＰ型半導体基板１をＮ型不純物雰囲気中で熱処理などして、表面領域の全面に一定の深さまでＮ型不純物を拡散させてＮ型を呈する拡散層２を形成し、ＣＶＤ法などで反射防止膜３を形成して拡散層２を分離した後、表面電極４および集電部５と電極取出部６とから成る裏面電極が形成されるとともに、集電部５の下の半導体基板１に高濃度のＰ型拡散層７が形成される。
【００２２】
上記表面電極４、集電部５、および電極取出部６は、以下のように形成される。すなわち、半導体基板１の表面に表面電極４となる例えば銀からなる第一の金属を主成分とするペーストを塗布するとともに、半導体基板１の裏面に出力取出部６となる例えば銀からなる第三の金属を主成分とするペーストを塗布し、約７００〜８００℃で１〜３０分程度の１回目の焼成を行う。このときの焼成温度が７００℃以下であったり、焼成時間が１分以下であったりすると、表面電極４の半導体基板１との接触抵抗を十分に低下させることができず太陽電池素子の特性低下を招くおそれがある。また、焼成温度が８００℃以上であったり、焼成時間が３０分以上であったりすると、拡散層２の不純物が再度拡散されることによって接合が深くなったり、表面電極４が拡散層２の接合を破壊するなどの問題が発生するおそれがある。
【００２３】
次に、半導体基板１の裏面に集電部５となるアルミニウムからなる第二の金属を主成分とするペーストを塗布し、約６５０〜７８０℃で０．５〜２０分程度の２回目の焼成を行う。このときの焼成温度が６５０℃以下であったり、焼成時間が０．５分以下であったりすると、アルミニウムが十分に半導体基板１に拡散されず、出力特性が低下するなどの問題が発生するおそれがある。反対に焼成温度が７８０℃以上であったり、焼成時間が２０分以上であったりすると、上記と同様に拡散層２の不純物が再度拡散されることによって接合が深くなったり、表面電極４が拡散層２の接合を破壊するなどの問題が発生するおそれがある。
【００２４】
この方法によれば、表面電極４の銀からなる第一の金属は１回目の焼成によって焼結する。したがって、その後半導体基板の裏面の大部分にアルミニウムからなる第二の金属を塗布し焼成しても、そのときに揮発するバインダーや溶剤によって表面電極の下の半導体基板表面が汚染されたり、第一の金属の焼結が阻害されるといった問題は発生せず、表面電極の剥離の問題を有効に回避できる。
【００２５】
また出力取出部６の銀からなる第三の金属も１回目の焼成によって焼結する。したがって、その後その上に集電部５となるアルミニウムからなる第二の金属を主成分とするペーストを塗布して２回目の焼成を行っても、銀はすでに焼結しているので、アルミニウムとは合金化しにくい。これによって熱膨張係数の異なる半導体基板１とアルミニウムと銀との重なり部での応力が緩和され、従来問題であったこの重なり部での応力に起因する半導体基板１の割れを低減できる。
【００２６】
また、集電部５のアルミニウムからなる第二の金属を主成分とするペーストを焼成する前に銀からなる第一の金属を主成分とするペーストを塗布するため、アルミニウムの表面に焼成によって凹凸が形成されても、基板割れの原因とはならない。
【００２７】
また、出力取出部６として塗布される銀からなる第三の金属を主成分とするペーストにはアルミニウムを含有することが望ましい。半導体基板１に使用するシリコンへの拡散係数の大きなアルミニウムを銀に含有させることにより、１回目の焼成で出力取出部６のシリコンとの接着強度を確保することができるからである。
【００２８】
このような金属を主成分とするペーストは、他にガラスフリット、溶剤とエチルセルロース等のバインダーを混合して構成される。
【００２９】
なお、本発明は上記実施形態に限定されるものではなく、本発明の範囲内で多くの修正および変更を加えることができる。例えば１回目の焼成によって形成される表面電極４の銀からなる第一の金属を主成分とするペーストと出力取出部６の銀からなる第三の金属を主成分とするペーストとを塗布する順番はどちらが先でも構わない。また、ペーストを塗布した後の乾燥は、次のペーストを塗布するときに印刷機の作業テーブルやスクリーンに前のペーストが付着するといった問題がなければ省略してもよい。
【００３０】
第１および第３の金属としては金や白金を用いてもよい。
【００３１】
【発明の効果】
以上のように、本発明に係る太陽電池素子の形成方法によれば、半導体基板の一主面側に表面電極となる第一の金属を主成分とするペーストを塗布するとともに、他の主面側に裏面電極の出力取出部となる第三の金属を主成分とするペーストを塗布して１回目の焼成を行った後、他の主面側に裏面電極の集電部となる第二の金属を主成分とするペーストを塗布して２回目の焼成を行うことから、熱膨張係数の異なる半導体基板と第二の金属と第三の金属との重なり部での応力が緩和され、この重なり部での応力に起因する太陽電池素子の割れを低減できる。また、第二の金属にアルミニウムを使用してもアルミニウムを焼成する前に表面電極となる第一の金属を主成分とするペーストを塗布するため、焼成によってアルミニウムの表面に凹凸が形成されても基板割れは起こりにくくなる。さらに集電部の焼成時に揮発するバインダーや溶剤によって表面電極の下の半導体基板１表面が汚染されたり、第一の金属の焼結が阻害されるといった問題は発生せず、表面電極の剥離の問題を有効に回避できる。
【００３２】
本発明の形成方法によって得られる太陽電池素子は、特に印刷の際に強い圧力を必要とする微細な表面電極を形成した太陽電池素子と、平面度を要求される大型の太陽電池モジュールや、表裏面に硬質の部材を使用した太陽電池モジュールに使用すれば更にその効果を有効に発揮する。
【図面の簡単な説明】
【図１】太陽電池素子の構造を説明する図である。
【図２】太陽電池素子の構造を説明する図である。
【図３】太陽電池素子の表面電極構造を説明する図である。
【図４】太陽電池素子の裏面電極構造を説明する図である。
【符号の説明】
１・・・半導体基板、２・・・拡散層、３・・・反射防止膜、４・・・表面電極、５・・・集電部、６・・・出力取出部、７・・・高濃度Ｐ型拡散層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a solar cell element, and more particularly to a method for forming a solar cell element in which a metal paste is baked to form a front electrode and a back electrode.
[0002]
[Background Art and Problems to be Solved by the Invention]
A conventional solar cell element is shown in FIG. For example, an N-type diffusion layer 2 is formed by diffusing N-type impurities to a certain depth over the entire surface near the surface of the P-type semiconductor substrate 1, and an antireflection film 3 made of a silicon nitride film or the like is formed on the surface of the semiconductor substrate 1. In addition, the front surface electrode 4 is provided on the front surface, and the back surface electrodes 5 and 6 including the current collecting portion 5 made of aluminum or the like and the output extraction portion 6 made of silver or the like are provided on the back surface. A high concentration P-type diffusion layer 7 is formed on the back surface of the semiconductor substrate 1.
[0003]
In order to form the surface electrode 4 and the back electrodes 5 and 6 of these solar cell elements, a paste mainly composed of a second metal made of aluminum is applied to most of the semiconductor substrate 1 except for a part of the back surface. After drying, apply a paste mainly composed of a third metal made of silver so as to cover the portion where the paste composed mainly of the second metal is not applied and the peripheral portion thereof, and then dry. Finally, a paste mainly composed of a first metal made of silver is applied to the surface of the semiconductor substrate 1 and dried, so that the paste mainly composed of the first metal and the second metal are mainly composed. A method of simultaneously firing a paste and a paste containing a third metal as a main component, that is, a simultaneous firing method has been conventionally used (see, for example, Patent Document 1).
[0004]
Further, as shown in FIG. 2, a paste mainly composed of a third metal made of silver is applied and dried, and a portion where the paste mainly composed of the third metal is not applied and its peripheral portion are formed. A paste mainly composed of a second metal made of aluminum is applied so as to cover most of the back surface of the semiconductor substrate 1 except for a part of the back surface, and after firing for the first time, silver is applied to the surface of the semiconductor substrate 1. There is also a method in which a paste containing the first metal as a main component is applied and dried and then fired for the second time (see, for example, Patent Document 2).
[0005]
Furthermore, after applying a paste composed mainly of a third metal made of silver and firing it for the first time, the portion not coated with the paste composed mainly of the third metal and its peripheral portion A first metal composed of silver is applied to the surface of the semiconductor substrate 1 by applying a paste composed mainly of a second metal composed of aluminum so as to cover the surface of the semiconductor substrate 1 except for a part of the back surface and drying the paste. There is also a method of applying a paste containing as a main component, drying, and performing a second baking (see, for example, Patent Document 2).
[0006]
As a result, a current collector 5 and an output extraction portion 6 with good solder wettability are formed on the back surface of the semiconductor substrate 1, and a high-concentration P-type diffusion layer is formed on the semiconductor substrate 1 below the current collector 5. 7 is formed.
[0007]
Thereafter, solder (not shown) is deposited on the output extraction portions 6 of the front electrode 4 and the back electrode, and inner leads for connecting the solar cell elements in series or in parallel are connected.
[0008]
However, in this conventional method for forming a solar cell element, during the firing, the overlapping portion of the aluminum of the current collector 5 and the silver of the output extraction portion 6, that is, the semiconductor substrate 1 having a different thermal expansion coefficient, aluminum and silver There is a problem in that stress is generated in the overlapping portion, causing the semiconductor substrate 1 to crack.
[0009]
Further, according to the method of firing aluminum and then applying silver on the front and back surfaces, the above problem can be solved, but by applying and firing a metal paste mainly composed of aluminum, the semiconductor substrate 1 There is a case where unevenness due to aggregation of aluminum or the like is formed on the back surface of the semiconductor substrate, and there is a problem that the semiconductor substrate 1 is cracked when the paste for forming the surface electrode 4 is applied by screen printing. .
[0010]
Further, according to these methods, there is a problem that the surface electrode 4 is peeled off at the time of formation or after that. That is, as can be seen from FIGS. 3 and 4, compared to the area of the surface electrode 4 and the output extraction part 6, the area of the current collecting part 5 is large and the amount of paste used is large. Since the binder and the like are mixed, the solvent and binder components that volatilize when the current collector 5 is fired scatters, contaminates the surface of the semiconductor substrate 1 and inhibits the sintering of the surface electrode 4. Therefore, this peeling problem seems to occur. FIG. 3 shows the structure of a surface electrode of a general solar cell element, and FIG. 4 shows the structure of a back electrode.
[0011]
As a method for solving this problem, a method in which the surface of the semiconductor substrate 1 is cleaned after the current collector portion 5 of the back electrode is formed and then the surface electrode 4 is formed can be considered. However, when this method is performed, the number of steps increases, which is not suitable for production.
[0012]
Furthermore, the paste which has the 1st metal which consists of silver as a main component on the surface of the semiconductor substrate 1 is baked for the first time, The paste which has the 2nd metal which consists of aluminum as a main component is the back surface of the semiconductor substrate 1 After the second baking is performed after applying to the most part except for a part of the first part, the second part made of silver is formed so as to cover the part where the paste mainly composed of the second metal is not applied and the peripheral part. There is also a method in which a paste containing a third metal as a main component is applied and firing is performed for the third time (see, for example, Patent Document 3). According to this method, since the surface electrode 4 is formed before the current collector 5 is formed, the above problem of peeling does not occur.
[0013]
However, according to this method, after the surface electrode 4 is formed, the current collecting portion 5 is formed, and then the output extraction portion 6 is formed, so that the high temperature firing is repeated three times. In some cases, the output characteristics may be degraded. In order to avoid this problem, if the firing temperature is lowered or the time is shortened, there may be a problem that peeling occurs between the current collecting part 5 and the output extracting part 6 of the back electrode. .
[0014]
The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a method for forming a solar cell element capable of preventing the occurrence of electrode peeling and cracking of a semiconductor substrate. And
[0015]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-335267 [Patent Document 2]
Japanese Patent Laid-Open No. 10-144543 [Patent Document 3]
JP 2000-188409 A [0016]
[Means for Solving the Problems]
In order to achieve the above object, in the method for forming a solar cell element according to the present invention, a reverse conductivity type semiconductor impurity is diffused on one main surface side of a semiconductor substrate exhibiting one conductivity type, and the first metal is a main component. A current collector with a second metal as the main component on the other main surface side and an output with a third metal as the main component, which has better solder wettability than this second metal In the method of forming a solar cell element for forming a back electrode comprising a portion, a paste mainly composed of a first metal to be the surface electrode is applied to one main surface side of the semiconductor substrate, and another main surface After applying a paste mainly composed of a third metal to be the output extraction portion of the back electrode on the side and performing the first firing, the other main surface side is to be the current collector of the back electrode. Apply a paste mainly composed of two metals and perform the second firing And features.
[0017]
In the method for forming a solar cell element, the first metal and the third metal are preferably made of silver.
[0018]
In the method for forming a solar cell element, it is preferable that the semiconductor substrate is made of silicon, and the paste containing the third metal as a main component contains aluminum.
[0019]
In the method for forming a solar cell element, it is preferable that the second metal is made of aluminum.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
The structure of the solar cell element according to the present invention is basically the same as that of a conventional solar cell element. That is, for example, an N-type diffusion layer 2 is formed by diffusing N-type impurities to a certain depth over the entire surface near the surface of the P-type semiconductor substrate 1, and the antireflection film 3 made of a silicon nitride film or the like is provided on the surface of the semiconductor substrate 1. The front surface electrode 4 is provided on the front surface, and the back surface electrode is provided on the back surface, which includes a current collecting portion 5 made of aluminum or the like and an output extraction portion 6 made of silver or the like. A high concentration P-type diffusion layer 7 is formed on the back surface of the semiconductor substrate 1.
[0021]
In such a solar cell element, for example, a P-type semiconductor substrate 1 is heat-treated in an N-type impurity atmosphere to diffuse an N-type impurity to a certain depth over the entire surface region to form an N-type diffusion layer 2. After forming the antireflection film 3 by CVD or the like and separating the diffusion layer 2, the back electrode composed of the front electrode 4, the current collector 5 and the electrode extraction part 6 is formed, and the current collector A high-concentration P-type diffusion layer 7 is formed in the semiconductor substrate 1 below the substrate 5.
[0022]
The surface electrode 4, the current collector 5 and the electrode take-out part 6 are formed as follows. That is, a paste mainly composed of a first metal made of, for example, silver, which becomes the surface electrode 4, is applied to the surface of the semiconductor substrate 1, and a third, for example, made of silver, which becomes the output extraction portion 6, on the back surface of the semiconductor substrate 1. A paste containing the above metal as a main component is applied, and the first baking is performed at about 700 to 800 ° C. for about 1 to 30 minutes. If the firing temperature at this time is 700 ° C. or less or the firing time is 1 minute or less, the contact resistance of the surface electrode 4 with the semiconductor substrate 1 cannot be sufficiently lowered, and the characteristics of the solar cell element deteriorate. May be incurred. Further, if the firing temperature is 800 ° C. or higher or the firing time is 30 minutes or longer, the impurities in the diffusion layer 2 are diffused again, resulting in deeper bonding, or the surface electrode 4 is bonded to the diffusion layer 2. May cause problems such as destroying.
[0023]
Next, a paste mainly composed of a second metal made of aluminum to be the current collector 5 is applied to the back surface of the semiconductor substrate 1, and the second baking is performed at about 650 to 780 ° C. for about 0.5 to 20 minutes. I do. If the firing temperature at this time is 650 ° C. or lower or the firing time is 0.5 minutes or shorter, aluminum may not be sufficiently diffused into the semiconductor substrate 1, and problems such as degradation of output characteristics may occur. There is. On the contrary, if the firing temperature is 780 ° C. or higher or the firing time is 20 minutes or longer, the impurities in the diffusion layer 2 are diffused again in the same manner as described above, and the junction becomes deeper or the surface electrode 4 diffuses. There is a possibility that problems such as breaking the bonding of the layer 2 may occur.
[0024]
According to this method, the first metal made of silver of the surface electrode 4 is sintered by the first firing. Therefore, even if a second metal made of aluminum is applied to the majority of the back surface of the semiconductor substrate and then fired, the surface of the semiconductor substrate under the surface electrode is contaminated by the binder or solvent that volatilizes at that time. The problem that the sintering of the metal is hindered does not occur, and the problem of peeling of the surface electrode can be effectively avoided.
[0025]
The third metal made of silver in the output extraction portion 6 is also sintered by the first firing. Therefore, even after applying a paste mainly composed of a second metal made of aluminum to be the current collector 5 and firing the second time thereon, the silver is already sintered. Is difficult to alloy. As a result, the stress at the overlapping portion of the semiconductor substrate 1 and the aluminum and silver having different thermal expansion coefficients is relaxed, and the cracking of the semiconductor substrate 1 due to the stress at the overlapping portion, which has been a problem in the past, can be reduced.
[0026]
Moreover, since the paste which has the 1st metal which consists of silver as a main component before baking the paste which has the 2nd metal which consists of aluminum of the current collection part 5 as a main component, it is uneven | corrugated by baking on the surface of aluminum. Even if formed, it does not cause the substrate to crack.
[0027]
Moreover, it is desirable that the paste mainly composed of the third metal made of silver applied as the output extraction portion 6 contains aluminum. This is because the aluminum having a large diffusion coefficient to silicon used for the semiconductor substrate 1 is contained in silver, so that the adhesive strength between the output extraction portion 6 and silicon can be ensured by the first firing.
[0028]
Such a paste containing a metal as a main component is composed of glass frit, a solvent and a binder such as ethyl cellulose.
[0029]
In addition, this invention is not limited to the said embodiment, Many corrections and changes can be added within the scope of the present invention. For example, the order of applying the paste mainly composed of the first metal made of silver of the surface electrode 4 and the paste mainly composed of the third metal made of silver of the output extraction portion 6 formed by the first baking. Whichever is first. The drying after applying the paste may be omitted if there is no problem that the previous paste adheres to the work table or screen of the printing machine when the next paste is applied.
[0030]
Gold and platinum may be used as the first and third metals.
[0031]
【The invention's effect】
As described above, according to the method for forming a solar cell element according to the present invention, the paste mainly composed of the first metal serving as the surface electrode is applied to one main surface side of the semiconductor substrate and the other main surface. After applying a paste mainly composed of a third metal to be the output extraction part of the back electrode on the side and performing the first firing, the second main part to be the current collecting part of the back electrode on the other main surface side Since the paste containing metal as a main component is applied and firing is performed for the second time, the stress at the overlapping portion of the semiconductor substrate, the second metal, and the third metal having different coefficients of thermal expansion is relieved. The crack of the solar cell element resulting from the stress in a part can be reduced. Even if aluminum is used for the second metal, a paste mainly composed of the first metal that becomes the surface electrode is applied before baking the aluminum, so that unevenness is formed on the surface of the aluminum by baking. Substrate cracking is less likely to occur. Furthermore, there is no problem that the surface of the semiconductor substrate 1 under the surface electrode is contaminated by the binder or solvent that volatilizes during the firing of the current collector, or that the sintering of the first metal is hindered. The problem can be effectively avoided.
[0032]
The solar cell element obtained by the forming method of the present invention includes a solar cell element in which a fine surface electrode that requires a strong pressure particularly during printing, a large-sized solar cell module that requires flatness, If it is used for a solar cell module using a hard member on the back surface, the effect is further effectively exhibited.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a structure of a solar cell element.
FIG. 2 is a diagram illustrating the structure of a solar cell element.
FIG. 3 is a diagram illustrating a surface electrode structure of a solar cell element.
FIG. 4 is a diagram illustrating a back electrode structure of a solar cell element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Diffusion layer, 3 ... Antireflection film, 4 ... Surface electrode, 5 ... Current collection part, 6 ... Output extraction part, 7 ... High P-type diffusion layer

Claims (2)

一導電型を呈する半導体基板の一主面側に逆導電型半導体不純物を拡散するとともに、第一の金属を主成分とする表面電極を形成し、他の主面側に第二の金属を主成分とする集電部とこの第二の金属よりも半田濡れ性のよい第三の金属を主成分とする出力取出部とから成る裏面電極を形成する太陽電池素子の形成方法において、シリコンからなる前記半導体基板の一主面側に前記表面電極となる第一の金属として銀を主成分とするペーストを塗布するとともに、他の主面側に前記裏面電極の出力取出部となる第三の金属として銀を主成分とするペーストを塗布して１回目の焼成を行った後、他の主面側に前記裏面電極の集電部となる第二の金属としてアルミニウムを主成分とするペーストを塗布して２回目の焼成を行うことを特徴とする太陽電池素子の形成方法。A reverse conductivity type semiconductor impurity is diffused on one main surface side of a semiconductor substrate exhibiting one conductivity type, a surface electrode mainly composed of a first metal is formed, and a second metal is mainly formed on the other main surface side. In the method of forming a solar cell element for forming a back electrode comprising a current collecting portion as a component and an output extraction portion mainly composed of a third metal having better solder wettability than the second metal, the solar cell element is made of silicon. A paste mainly composed of silver is applied as a first metal to be the surface electrode on one main surface side of the semiconductor substrate, and a third metal to be an output extraction portion of the back electrode on the other main surface side After applying a paste containing silver as a main component and firing it for the first time, a paste containing aluminum as a main component is applied to the other main surface side as the second metal that becomes the current collector of the back electrode. And the second firing A method of forming a Motoko Ike. 前記第三の金属を主成分とするペーストにアルミニウムを含有することを特徴とする請求項１に記載の太陽電池素子の形成方法。The method for forming a solar cell element according to claim 1, wherein the paste containing the third metal as a main component contains aluminum.
JP2002342880A 2002-11-26 2002-11-26 Method for forming solar cell element Expired - Fee Related JP3968000B2 (en)

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JPWO2007060742A1 (en) 2005-11-28 2009-05-07 三菱電機株式会社 Printing mask and solar cell
JP4425917B2 (en) 2005-11-28 2010-03-03 三菱電機株式会社 Solar cell and manufacturing method thereof
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