JP2007266488A - Method for manufacturing solar cell - Google Patents

Method for manufacturing solar cell Download PDF

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JP2007266488A
JP2007266488A JP2006092015A JP2006092015A JP2007266488A JP 2007266488 A JP2007266488 A JP 2007266488A JP 2006092015 A JP2006092015 A JP 2006092015A JP 2006092015 A JP2006092015 A JP 2006092015A JP 2007266488 A JP2007266488 A JP 2007266488A
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layer
substrate
solar cell
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JP4957042B2 (en
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Akira Yamada
朗 山田
Kiyoshi Saito
清 斎藤
Ayumi Nozaki
歩 野崎
Shigeru Matsuno
繁 松野
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Mitsubishi Electric Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a solar cell for suppressing the generation of the bending of a substrate, and for forming a BSF (Back Surface Field) layer whose thickness is effective even when the thickness of the substrate is thin. <P>SOLUTION: This method for manufacturing a solar cell includes a process for forming a start point layer on the surface at the opposite side of the light receiving surface of the substrate of the solar cell; a process for forming a main configuring layer as an electrode on the surface of the start point layer; and a thermal treatment process for forming an alloy layer of the start point layer and the surface of the substrate, and for diffusing a portion of the main configuring layer to the alloy layer and the substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

この発明は、多結晶シリコンなどの基板を用いた太陽電池における、ＢＳＦ（Ｂａｃｋ Ｓｕｒｆａｃｅ Ｆｉｅｌｄ）層を備えた太陽電池の製造方法に関するものである。   The present invention relates to a method for manufacturing a solar cell having a BSF (Back Surface Field) layer in a solar cell using a substrate such as polycrystalline silicon.

太陽電池においては、光の入射によって発生したキャリアを効率よく捕獲するために、太陽電池の裏面（受光面に対して反対側の基板面）にＢＳＦ層が形成されている。すなわち、太陽電池の基板の裏面には、発生したキャリアがその表面で再結合によって消失することを防ぐために、表面近傍に逆電界領域が形成されており、この逆電界領域で裏面に移動してきたキャリアを追い返す機能が付与されている。この逆電界領域がＢＳＦ層と呼ばれるもので、このようなＢＳＦ層（逆電界領域）の形成のためには、裏面電極の作製時に、ｐ型の太陽電池の基板に対してｐ＋型の導電型を有する領域が同時に形成されるような方法が取られている。このＢＳＦ層の形成を含めた裏面電極の作製方法としては、多結晶シリコン型の太陽電池の場合には、多結晶シリコン基板の裏面にアルミニウムペーストをスクリーン印刷により形成し、焼成時にアルミニウムペーストから基板内部へのアルミニウムの拡散によってｐ＋型の導電層（ＢＳＦ層）の形成と、アルミニウムによる裏面電極の作製とを同時に行う方法が低コストな作製方法として用いられている。また、他のＢＳＦ層の形成を含めた裏面電極の作製方法として、ｐ型のシリコン基板上にｐ＋型の微結晶シリコンを形成し、この上にアルミニウムを蒸着することによって裏面電極を作製する方法が開示されている（例えば、特許文献１参照）。   In the solar cell, a BSF layer is formed on the back surface (substrate surface opposite to the light receiving surface) of the solar cell in order to efficiently capture carriers generated by the incidence of light. That is, a reverse electric field region is formed on the back surface of the solar cell substrate in the vicinity of the surface in order to prevent the generated carriers from disappearing due to recombination on the surface, and the reverse electric field region has moved to the back surface. The ability to turn the carrier back is given. This reverse electric field region is called a BSF layer. In order to form such a BSF layer (reverse electric field region), a p + type conductivity type is used with respect to the substrate of the p type solar cell when the back electrode is formed. A method is employed in which regions having the same are formed simultaneously. In the case of a polycrystalline silicon type solar cell, an aluminum paste is formed on the back surface of the polycrystalline silicon substrate by screen printing, and the substrate is made from the aluminum paste during firing. A method of simultaneously forming a p + type conductive layer (BSF layer) by the diffusion of aluminum into the interior and the back electrode using aluminum is used as a low cost manufacturing method. Further, as a method for manufacturing a back electrode including formation of other BSF layers, a method of forming a back electrode by forming p + type microcrystalline silicon on a p type silicon substrate and depositing aluminum on the p + type microcrystalline silicon. Is disclosed (for example, see Patent Document 1).

特開平１０−２１４８８２号公報（４頁、図１、図２）JP-A-10-214882 (page 4, FIGS. 1 and 2)

従来のスクリーン印刷による裏面電極の作製方法では、粒径が約５μｍのアルミニウム粒子を主成分としたスクリーン印刷ペーストを基板の裏面に印刷し、これを焼成して裏面電極が形成されている。焼成過程中に印刷ペースト中のアルミニウム粒子は、シリコン基板の境界面でシリコン基板と低融点の合金層を形成し、この合金層を介して、基板中にアルミニウムが拡散して、ｐ＋導電層、すなわちＢＳＦ層が形成されている。   In a conventional method for producing a back electrode by screen printing, a screen printing paste mainly composed of aluminum particles having a particle size of about 5 μm is printed on the back surface of a substrate, and this is baked to form a back electrode. During the firing process, the aluminum particles in the printing paste form a low melting point alloy layer with the silicon substrate at the interface of the silicon substrate, and through this alloy layer, aluminum diffuses into the substrate, and the p + conductive layer, That is, a BSF layer is formed.

しかしながら、従来のスクリーン印刷を用いた裏面電極の製造方法では、焼成工程中に印刷ペーストの収縮によって応力が発生する。この応力によって、多結晶シリコン基板に反りが発生する。太陽電池においては、低コスト化のために多結晶シリコン基板の厚さを極力薄くすることが試みられており、基板が薄くなるにしたがって印刷ペーストの収縮によって発生する応力のためにさらに顕著な反りが発生し、最悪の場合は基板の割れも発生する。このため、薄い多結晶シリコン基板用いた場合、生産歩留まりの低下がさらに顕著になるという問題があった。   However, in the conventional method for manufacturing a back electrode using screen printing, stress is generated due to shrinkage of the printing paste during the firing process. This stress causes warpage in the polycrystalline silicon substrate. In solar cells, attempts have been made to reduce the thickness of the polycrystalline silicon substrate as much as possible in order to reduce the cost, and as the substrate becomes thinner, a more remarkable warpage is caused by the stress generated by the shrinkage of the printing paste. Occurs, and in the worst case, the substrate cracks. For this reason, when a thin polycrystalline silicon substrate is used, there is a problem that the production yield is further reduced.

また、発生応力による反りを抑制するためにアルミニウムを蒸着して裏面電極を形成する従来の方法では、基板の反りが発生しない程度の膜厚で裏面電極を形成することはできるが、裏面電極が薄いために、基板と電極との境界で形成される合金層が酸化などの影響で不均一となって必要な厚さのＢＳＦ層が形成されず、キャリアを追い返す効果が十分に発揮できないという問題があった。   In addition, in the conventional method of forming the back electrode by vapor deposition of aluminum in order to suppress the warpage due to the generated stress, the back electrode can be formed with a film thickness that does not cause the warpage of the substrate. The problem is that the alloy layer formed at the boundary between the substrate and the electrode is non-uniform due to oxidation and the like, and the BSF layer with the required thickness is not formed due to the thinness, so that the effect of repelling carriers cannot be fully exhibited. was there.

この発明は、上述のような問題点を解決するためになされたもので、基板の厚さが薄くても、基板の反りの発生を抑えることができるとともに、有効な厚さのＢＳＦ層を形成できる太陽電池用の裏面電極の製造方法を得ることを目的としている。   The present invention has been made to solve the above-described problems. Even when the thickness of the substrate is small, the occurrence of warpage of the substrate can be suppressed and a BSF layer having an effective thickness can be formed. It aims at obtaining the manufacturing method of the back electrode for solar cells which can be performed.

この発明に係る太陽電池の製造方法は、基板の受光面と反対側の表面に起点層を形成する工程と、起点層の表面に電極となる主構成層を形成する工程と、起点層と基板の表面とで合金層を形成する熱処理工程とを含むものである。   The method for manufacturing a solar cell according to the present invention includes a step of forming a starting layer on a surface opposite to a light receiving surface of a substrate, a step of forming a main constituent layer serving as an electrode on the surface of the starting layer, and the starting layer and the substrate. And a heat treatment step of forming an alloy layer with the surface.

この発明に係る太陽電池の製造方法においては、熱処理によって基板と電極となる主構成層との間に、合金層の起点となる起点層を形成することにより、均一な合金層を形成することができる。そのため、主構成層の厚さが薄くとも、必要な厚さのＢＳＦ層を形成することができるので、基板の反りの発生を抑えることができる。   In the method for manufacturing a solar cell according to the present invention, a uniform alloy layer can be formed by forming a starting layer serving as a starting point of the alloy layer between the substrate and the main constituent layer serving as the electrode by heat treatment. it can. Therefore, even if the main component layer is thin, the BSF layer having a necessary thickness can be formed, and thus the occurrence of warpage of the substrate can be suppressed.

実施の形態１．
図１は、この発明を実施するための実施の形態１における、太陽電池の製造方法を示す工程図である。図１において、多結晶シリコンの基板１の主面１ａは、太陽光などの光が入射する受光面であり、裏面１ｂに電極が形成される。多結晶シリコン基板１の厚さは約２５０μｍである。裏面１ｂの表面に起点層２となる膜厚約１００ｎｍのアルミニウム膜を物理蒸着法で形成する。物理蒸着法として、例えば抵抗加熱蒸着法を用いることができる。次に、このアルミニウム膜の起点層２の上に、図２に示すように、アルミニウムの粒子を含有した印刷ペーストを用いて、スクリーン印刷法により膜厚約２０μｍの主構成層３を形成する。アルミニウムの粒子の平均粒径は約５μｍである。起点層２の形成面積は、主構成層４の形成面積より大きいように構成する。さらに、この基板を大気中にて８００℃で３０分の熱処理を行う。この熱処理中に起点層２のアルミニウムが基板１の表面（裏面１ｂ）と反応溶融して、図３に示すように合金層４が形成されるとともに、主構成層３に含まれるアルミニウムが合金層４と基板１とに拡散していき、基板１の内部にＢＳＦ層５が形成される。ＢＳＦ層５は、アルミニウムが基板材料であるシリコンに拡散されて形成されたアルミニウムを含有したシリコン層である。主構成層３の外側の主要部分は電極６となる。 Embodiment 1 FIG.
FIG. 1 is a process diagram showing a method for manufacturing a solar cell in Embodiment 1 for carrying out the present invention. In FIG. 1, a main surface 1a of a polycrystalline silicon substrate 1 is a light receiving surface on which light such as sunlight is incident, and an electrode is formed on a back surface 1b. The thickness of the polycrystalline silicon substrate 1 is about 250 μm. An aluminum film having a film thickness of about 100 nm to be the starting layer 2 is formed on the surface of the back surface 1b by physical vapor deposition. As the physical vapor deposition method, for example, a resistance heating vapor deposition method can be used. Next, as shown in FIG. 2, a main constituent layer 3 having a film thickness of about 20 μm is formed on the starting layer 2 of the aluminum film by screen printing using a printing paste containing aluminum particles. The average particle diameter of the aluminum particles is about 5 μm. The formation area of the starting layer 2 is configured to be larger than the formation area of the main component layer 4. Further, this substrate is heat-treated at 800 ° C. for 30 minutes in the atmosphere. During this heat treatment, the aluminum of the starting layer 2 reacts and melts with the front surface (back surface 1b) of the substrate 1 to form an alloy layer 4 as shown in FIG. 3, and the aluminum contained in the main component layer 3 is an alloy layer. 4 and the substrate 1, and a BSF layer 5 is formed inside the substrate 1. The BSF layer 5 is a silicon layer containing aluminum formed by diffusing aluminum into silicon as a substrate material. The main part outside the main component layer 3 is an electrode 6.

このように構成された太陽電池の製造方法によると、起点層２は基板の表面と面状に連続して接触している連続膜であるので、熱処理中に形成される合金層４が基板１の表面全体に渡って均一に形成されるとともに、主構成層３から拡散してきたアルミニウムが均一にかつ速やかに基板１内部に拡散していくので、主構成層３が基板の反りを発生させない比較的薄い膜厚（約２０μｍ）であても、ＢＳＦ層５が４〜５μｍの深さまで均一に形成される。ＢＳＦ層５の厚さが４〜５μｍあれば、裏面に移動してきたキャリアを追い返す効果は十分に発揮できる。したがって、基板の反りが発生せずに、必要とする膜厚のＢＳＦ層５を形成すことができる。また、起点層２の形成面積は、主構成層４の形成面積より大きいように構成されているので、電極６の基板１側には電極６のすべての面に渡ってＢＳＦ層５が形成されている。   According to the method for manufacturing a solar cell configured as described above, the starting layer 2 is a continuous film that is in continuous contact with the surface of the substrate in a plane, so that the alloy layer 4 formed during the heat treatment is formed on the substrate 1. Since the aluminum diffused from the main constituent layer 3 is uniformly and rapidly diffused into the substrate 1, the main constituent layer 3 does not cause warpage of the substrate. Even if the film thickness is very thin (about 20 μm), the BSF layer 5 is uniformly formed to a depth of 4 to 5 μm. If the thickness of the BSF layer 5 is 4 to 5 μm, the effect of repelling the carriers that have moved to the back surface can be sufficiently exerted. Therefore, the BSF layer 5 having a required film thickness can be formed without causing warpage of the substrate. Further, since the formation area of the starting layer 2 is configured to be larger than the formation area of the main component layer 4, the BSF layer 5 is formed over the entire surface of the electrode 6 on the substrate 1 side of the electrode 6. ing.

比較のために、太陽電池の裏面電極をスクリーン印刷のみで作製した比較例を説明する。図４は、比較例の製造方法を示す工程図である。図４において、基板１の裏面１ｂに、電極６となるアルミニウムの粒子を含有した印刷ペーストを直接印刷する。このとき、印刷膜厚は、本実施の形態と同じように基板の反りが発生しない、約２０μｍとする。この基板を大気中にて８００℃で３０秒の熱処理を行う。   For comparison, a comparative example in which the back electrode of the solar cell is produced only by screen printing will be described. FIG. 4 is a process diagram showing a manufacturing method of a comparative example. In FIG. 4, a printing paste containing aluminum particles to be the electrode 6 is directly printed on the back surface 1 b of the substrate 1. At this time, the printed film thickness is set to about 20 μm so that the substrate does not warp as in the present embodiment. This substrate is heat-treated at 800 ° C. for 30 seconds in the atmosphere.

このような工程で作製された太陽電池においては、熱処理中に電極６中のアルミニウムの粒子が基板１の表面（裏面１ｂ）と反応溶融して、図５に示すように合金層４が形成されるとともに、アルミニウムが合金層４と基板１とに拡散していき、ＢＳＦ層５が形成される。このとき、アルミニウムの粒子の中心粒径が約５μｍであり印刷膜厚が約２０μｍと薄いので、アルミニウムの微粒子が完全に基板１の表面を覆い尽くしていないため、合金層４が一様に形成されず、部分的に点在するような状態になる。その結果、ＢＳＦ層５も膜厚分布の大きい不均一なものとなりその平均膜厚も約３μｍとなり、裏面に移動してきたキャリアを追い返す効果が十分に発揮されない。   In the solar cell manufactured by such a process, the aluminum particles in the electrode 6 react and melt with the front surface (back surface 1b) of the substrate 1 during the heat treatment, and the alloy layer 4 is formed as shown in FIG. At the same time, aluminum diffuses into the alloy layer 4 and the substrate 1 to form the BSF layer 5. At this time, since the center particle diameter of the aluminum particles is about 5 μm and the printed film thickness is as thin as about 20 μm, the aluminum fine particles do not completely cover the surface of the substrate 1, so that the alloy layer 4 is uniformly formed. Not partly scattered. As a result, the BSF layer 5 is also non-uniform with a large film thickness distribution, the average film thickness is about 3 μm, and the effect of repelling the carriers that have moved to the back surface is not sufficiently exhibited.

また、比較例においては、合金層４が点在するような状態で形成されているので、電極６と基板１との密着力も不均一となり、電極６の一部が剥離する場合もある。一方、本実施の形態のように、起点層を基板の裏面に渡って均一に形成しておれば、電極と基板との密着力も均一になるので、電極の剥離も起こらない。   In the comparative example, since the alloy layer 4 is formed in a scattered state, the adhesion force between the electrode 6 and the substrate 1 becomes non-uniform, and a part of the electrode 6 may be peeled off. On the other hand, if the starting layer is formed uniformly over the back surface of the substrate as in the present embodiment, the adhesion between the electrode and the substrate becomes uniform, so that the electrode does not peel off.

なお、比較例において、印刷膜厚を２０μｍ以上にすると、図５に示すような合金層の不均一な状態はある程度改善されるが、熱処理中の印刷膜の収縮が大きくなり、応力が大きくなって厚さ約２５０μｍ以下の基板では基板の反りが顕著になる。したがって、スクリーン印刷のみで電極を作製する方法では、基板の反りを抑えて必要となる均一な膜厚のＢＳＦ層を形成することはできない。   In the comparative example, when the printed film thickness is 20 μm or more, the non-uniform state of the alloy layer as shown in FIG. 5 is improved to some extent, but the shrinkage of the printed film during the heat treatment increases and the stress increases. In the case of a substrate having a thickness of about 250 μm or less, the warpage of the substrate becomes remarkable. Therefore, the method for producing electrodes only by screen printing cannot form a BSF layer having a uniform film thickness that is required while suppressing warping of the substrate.

ＢＳＦ層を形成する元素を十分に基板に拡散させるためには、主構成層の材料と基板とで熱処理中に合金層を形成することが有効であるが、この合金層が電極の全面に渡って均質に形成されることが重要である。そのためには、基板面上に、合金層の発生の起点となる領域を、なるべく多く均質に形成する必要がある。さらに、起点となる領域上に、拡散元素を供給する領域となる主構成層の形成が必要である。比較例において、主構成層を直接基板の表面に印刷した場合、上述のように主構成層と基板の表面との単位面積当たりの接触面積が小さくなる。本実施の形態においては、起点層と基板の表面との単位面積当たりの接触面積が、主構成層と起点層の表面との単位面積当たりの接触面積より大きいので、電極の全面に渡って均一な合金層を形成することができる。   In order to sufficiently diffuse the elements forming the BSF layer into the substrate, it is effective to form an alloy layer during the heat treatment with the material of the main constituent layer and the substrate, but this alloy layer extends over the entire surface of the electrode. It is important that they are formed homogeneously. For this purpose, it is necessary to form as many regions as possible on the substrate surface as starting points for the generation of the alloy layer as uniformly as possible. Furthermore, it is necessary to form a main constituent layer that serves as a region for supplying a diffusing element on a region that serves as a starting point. In the comparative example, when the main constituent layer is printed directly on the surface of the substrate, the contact area per unit area between the main constituent layer and the surface of the substrate becomes small as described above. In the present embodiment, the contact area per unit area between the starting layer and the surface of the substrate is larger than the contact area per unit area between the main constituent layer and the surface of the starting layer, so that it is uniform over the entire surface of the electrode. A simple alloy layer can be formed.

基板としては、多結晶シリコンのほかに、単結晶シリコン、ガリウムヒ素などの材料を用いることができる。起点層の材質としては、これらの基板材料と容易に合金層を形成できる材料であればよい。例えば起点層の材料としては、本実施の形態に用いたアルミニウムのほかに、アルミニウム合金、Ａｌ−Ｓｉ合金が有効である。共晶合金のように分相化しても実用上問題はない。Ａｌ−Ｓｉ合金の場合には、上述のような基板材料すべてにおいて有効である。   As the substrate, in addition to polycrystalline silicon, materials such as single crystal silicon and gallium arsenide can be used. The starting layer may be made of any material that can easily form an alloy layer with these substrate materials. For example, as the material for the starting layer, an aluminum alloy or an Al—Si alloy is effective in addition to the aluminum used in the present embodiment. There is no practical problem even if phase separation is performed as in a eutectic alloy. In the case of an Al—Si alloy, it is effective in all the substrate materials as described above.

なお、本実施の形態においては、起点層を物理蒸着法で形成したが、化学蒸着法、スパッタ法などの連続膜が形成できる他の成膜方法を用いることもできる。また、起点層の厚さは、熱処理中に合金層の形成の起点となればよいため、最低限の厚さであればよい。１０ｎｍ以上の厚さであれば、合金層の形成の起点となる。それ以上の厚さでもとくに問題はないが、実際には主構成層よりも厚いことは起点層としての利用の目的からは効果が失われることとなる。蒸着法などの連続的な膜形成の場合には、プロセス的なコスト、時間などの点で起点層を厚くするメリットは少ない。   In the present embodiment, the starting layer is formed by physical vapor deposition, but other film formation methods that can form a continuous film such as chemical vapor deposition and sputtering can also be used. Further, the thickness of the starting layer may be a minimum thickness as long as it is a starting point for forming the alloy layer during the heat treatment. If the thickness is 10 nm or more, it is the starting point for forming the alloy layer. A thickness greater than that is not particularly problematic, but in fact, if it is thicker than the main constituent layer, the effect is lost for the purpose of use as a starting layer. In the case of continuous film formation such as vapor deposition, there are few merits to thicken the starting layer in terms of process cost and time.

実施の形態２．
実施の形態１では起点層の材料としてアルミニウム膜を蒸着したが、実施の形態２においては、アルミニウムとシリコンの共晶組成であるＡｌ−Ｓｉ合金膜を起点層として蒸着したものである。Ａｌ−Ｓｉ合金膜のＡｌの占める比率は１２．６ｗｔ％であり、膜厚は約５０ｎｍである。Ａｌ−Ｓｉ合金膜の融点は、５７７℃であり、ＡｌおよびＳｉのそれぞれの融点である６６０℃および１４１４℃より低い。次に、このＡｌ−Ｓｉ合金膜の起点層の上に、実施の形態１と同様に、アルミニウムの微粒子を含有した印刷ペーストを用いて、スクリーン印刷法により膜厚約１５μｍの主構成層を形成する。さらに、この基板を大気中にて８００℃で３０分の熱処理を行う。 Embodiment 2. FIG.
In the first embodiment, an aluminum film is vapor-deposited as a starting layer material. In the second embodiment, an Al—Si alloy film having a eutectic composition of aluminum and silicon is vapor-deposited as a starting layer. The proportion of Al in the Al—Si alloy film is 12.6 wt%, and the film thickness is about 50 nm. The melting point of the Al—Si alloy film is 575 ° C., which is lower than the melting points of Al and Si, which are 660 ° C. and 1414 ° C., respectively. Next, a main component layer having a film thickness of about 15 μm is formed on the starting layer of the Al—Si alloy film by screen printing using a printing paste containing aluminum fine particles, as in the first embodiment. To do. Further, this substrate is heat-treated at 800 ° C. for 30 minutes in the atmosphere.

このように構成された太陽電池の作製方法においては、起点層がＡｌ基板のシリコンよりも低融点のＡｌ−Ｓｉ合金膜で構成されているので、シリコンの含有率の多い合金層の融点がシリコン基板の融点よりも低くなり、主構成層から拡散してきたアルミニウムが実施の形態１よりもさらに均一にかつ速やかに合金層および基板内部に拡散していくので、主構成層が実施の形態１よりも薄い膜厚（約１５μｍ）であても、ＢＳＦ層が約５μｍの深さまで均一に形成される。   In the manufacturing method of the solar cell thus configured, since the starting layer is composed of an Al—Si alloy film having a lower melting point than that of silicon of the Al substrate, the melting point of the alloy layer having a high silicon content is silicon. Since the melting point of the substrate is lower than the melting point of the substrate and the aluminum diffused from the main constituent layer diffuses more uniformly and quickly into the alloy layer and the substrate than in the first embodiment, the main constituent layer is the same as in the first embodiment. Even with a thin film thickness (about 15 μm), the BSF layer is uniformly formed to a depth of about 5 μm.

実施の形態３．
実施の形態２では、起点層となるＡｌ−Ｓｉ合金膜を物理蒸着法で形成したが、実施の形態３においては、Ａｌ−Ｓｉ合金膜をスクリーン印刷法で形成したものである。実施の形態１と同様な多結晶シリコン基板の表面に、Ａｌ−Ｓｉ合金の微粒子を含んだ印刷ペーストを厚さ８μｍで印刷する。Ａｌ−Ｓｉ合金の微粒子の中心粒径は約２μｍであり、その組成は、Ａｌが２０ｗｔ％である。印刷膜を８０℃で３０分間乾燥し、実施の形態１と同様に、この印刷膜の上にアルミニウムの微粒子を含有した印刷ペーストを用いて、スクリーン印刷法により膜厚約２０μｍの主構成層を形成する。アルミニウムの微粒子の平均粒径は約８μｍである。この基板を大気中にて８００℃で３０秒の熱処理を行う。この熱処理中に起点層のＡｌ−Ｓｉ合金の微粒子が基板の表面と反応溶融して合金層が形成されるとともに、主構成層に含まれるアルミニウムが合金層と基板とに拡散していき、基板の内部に深さ４〜５μｍのＢＳＦ層が形成される。主構成層の外側の主要部分は電極となる。 Embodiment 3 FIG.
In the second embodiment, the Al—Si alloy film serving as the starting layer is formed by physical vapor deposition. However, in the third embodiment, the Al—Si alloy film is formed by screen printing. A printing paste containing Al—Si alloy fine particles is printed to a thickness of 8 μm on the surface of the same polycrystalline silicon substrate as in the first embodiment. The center particle diameter of the fine particles of the Al—Si alloy is about 2 μm, and the composition thereof is 20 wt% Al. The printed film was dried at 80 ° C. for 30 minutes, and the main constituent layer having a film thickness of about 20 μm was formed by screen printing using a printing paste containing aluminum fine particles on the printed film as in the first embodiment. Form. The average particle diameter of the aluminum fine particles is about 8 μm. This substrate is heat-treated at 800 ° C. for 30 seconds in the atmosphere. During this heat treatment, the Al—Si alloy fine particles of the starting layer react and melt with the surface of the substrate to form an alloy layer, and aluminum contained in the main constituent layer diffuses into the alloy layer and the substrate. A BSF layer having a depth of 4 to 5 μm is formed inside the substrate. The main part outside the main component layer is an electrode.

このように構成された太陽電池の作製方法においては、主構成層に用いたアルミニウムの微粒子よりも起点層に用いたＡｌ−Ｓｉ合金の微粒子の方が粒径は小さいので、アルミニウムの微粒子を直接基板に印刷するよりもＡｌ−Ｓｉ合金の微粒子と基板との接触点が多い。つまり、起点層と基板の表面との単位面積当たりの接触面積が、主構成層と前記起点層の表面との単位面積当たりの接触面積より大きくなる。そのため、起点層と基板との界面に形成される合金層が、実施の形態１で説明した比較例よりも均一に形成される。アルミニウムの粒子を中心粒径が約２μｍまで細粒化して用いることも考えられるが、アルミニウムの粒子を細粒化することは、アルミニウム微粒子の急激な酸化による発熱などを抑制するために取扱いが非常に難しくなる。Ａｌ−Ｓｉ合金は、アルミニウムよりも酸化されにくいため、微粒子化が可能であり、本実施の形態においては、比較的取扱いが簡単なＡｌ−Ｓｉ合金の微粒子を起点層に用いているので、基板表面全体に渡って均一な合金層が形成できるとともに、主構成層から拡散してきたアルミニウムが均一にかつ速やかに基板内部に拡散していくので、主構成層が基板の反りを発生させない比較的薄い膜厚（約２０μｍ）であても、ＢＳＦ層が約５μｍの深さまで均一に形成される。   In the method of manufacturing the solar cell thus configured, the Al—Si alloy fine particles used in the starting layer have a smaller particle size than the aluminum fine particles used in the main constituent layer. There are more contact points between the Al—Si alloy particles and the substrate than when printing on the substrate. That is, the contact area per unit area between the origin layer and the surface of the substrate is larger than the contact area per unit area between the main constituent layer and the surface of the origin layer. Therefore, the alloy layer formed at the interface between the starting layer and the substrate is formed more uniformly than the comparative example described in the first embodiment. Although it is conceivable to use aluminum particles with a center particle size of about 2 μm, it is possible to reduce the size of aluminum particles to prevent heat generation due to rapid oxidation of aluminum particles. It becomes difficult. Since the Al—Si alloy is less susceptible to oxidation than aluminum, it can be finely divided. In this embodiment, since the Al—Si alloy fine particles that are relatively easy to handle are used for the starting layer, the substrate A uniform alloy layer can be formed over the entire surface, and aluminum diffused from the main constituent layer is uniformly and quickly diffused into the substrate, so that the main constituent layer is relatively thin and does not cause warping of the substrate. Even with a film thickness (about 20 μm), the BSF layer is uniformly formed to a depth of about 5 μm.

なお、本実施の形態では、起点層および主構成層を形成する方法としてスクリーン印刷法を用いたが、例えばスピンコート法、ディプ法、噴霧法など、微粒子で構成された材料を基板表面に均一な膜を形成する他の方法を用いることもできる。   In this embodiment, the screen printing method is used as a method for forming the starting layer and the main constituent layer. However, for example, a material composed of fine particles such as a spin coating method, a dip method, or a spraying method is uniformly applied to the substrate surface. Other methods of forming a thick film can also be used.

この発明の実施の形態１による太陽電池の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the solar cell by Embodiment 1 of this invention. この発明の実施の形態１による太陽電池の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the solar cell by Embodiment 1 of this invention. この発明の実施の形態１による太陽電池の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the solar cell by Embodiment 1 of this invention. この発明の実施の形態１における比較例の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the comparative example in Embodiment 1 of this invention. この発明の実施の形態１における比較例の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the comparative example in Embodiment 1 of this invention.

符号の説明Explanation of symbols

１ 基板
１ａ 主面
１ｂ 裏面
２ 起点層
３ 主構成層
４ 合金層
５ ＢＳＦ層
６ 電極 DESCRIPTION OF SYMBOLS 1 Substrate 1a Main surface 1b Back surface 2 Origin layer 3 Main component layer 4 Alloy layer 5 BSF layer 6 Electrode

Claims (8)

基板の受光面と反対側の表面に起点層を形成する工程と、
前記起点層の表面に電極となる主構成層を形成する工程と、
前記起点層と前記基板の表面とで合金層を形成する熱処理工程と
を含むことを特徴とする太陽電池の製造方法。 Forming a starting layer on the surface opposite to the light receiving surface of the substrate;
Forming a main constituent layer to be an electrode on the surface of the starting layer;
The manufacturing method of the solar cell characterized by including the heat treatment process which forms an alloy layer with the said origin layer and the surface of the said board | substrate. 起点層と基板の表面との単位面積当たりの接触面積が、主構成層と前記起点層の表面との単位面積当たりの接触面積より大きいことを特徴とする請求項１記載の太陽電池の製造方法。 2. The method of manufacturing a solar cell according to claim 1, wherein a contact area per unit area between the starting layer and the surface of the substrate is larger than a contact area per unit area between the main component layer and the surface of the starting layer. . 起点層は、連続膜であることを特徴とする請求項１記載の太陽電池の製造方法。 The method for manufacturing a solar cell according to claim 1, wherein the starting layer is a continuous film. 起点層を構成する材料は、前記起点層と基板の表面とで形成された合金層の融点が前記基板の融点よりも低くなる材料であることを特徴とする請求項１記載の太陽電池の製造方法。 2. The solar cell manufacturing method according to claim 1, wherein the material constituting the starting layer is a material in which the melting point of the alloy layer formed by the starting layer and the surface of the substrate is lower than the melting point of the substrate. Method. 起点層を構成する材料の融点は、主構成層を構成する材料の融点以下であることを特徴とする請求項１記載の太陽電池の製造方法。 The method for manufacturing a solar cell according to claim 1, wherein the melting point of the material constituting the starting layer is not higher than the melting point of the material constituting the main constituting layer. 基板は、多結晶シリコン、単結晶シリコンおよびガリウム砒素の少なくといずれかを含むことを特徴とする請求項１記載の太陽電池の製造方法。
起点層および主構成層を構成する材料は、シリコン、またはアルミニウムの少なくともいずれかを含むことを特徴とする請求項１記載の太陽電池の製造方法。 2. The method of manufacturing a solar cell according to claim 1, wherein the substrate includes at least one of polycrystalline silicon, single crystal silicon, and gallium arsenide.
The method for manufacturing a solar cell according to claim 1, wherein the material constituting the starting layer and the main constituent layer includes at least one of silicon and aluminum. 起点層の厚さは、主構成層の厚さ以下であることを特徴とする請求項１記載の太陽電池の製造方法。 The method for manufacturing a solar cell according to claim 1, wherein the thickness of the starting layer is equal to or less than the thickness of the main constituent layer. 起点層を形成する工程は、物理蒸着法あるいは印刷法であることを特徴とする請求項１記載の太陽電池の製造方法。 2. The method for manufacturing a solar cell according to claim 1, wherein the step of forming the starting layer is a physical vapor deposition method or a printing method.
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