JP4240889B2 - Method for forming transparent conductive film and method for producing photovoltaic element - Google Patents

Description

【００４８】
記号の説明（数値：相対値）
ａ：基板上に形成した膜の凸部の頂点間の平均距離
ｂ：膜の凸部の頂点と基板と平均距離
◎：１．００
○：０．９５〜１未満
△：０．９０〜０．９５未満
×：０．８０〜０．９０未満
【００４９】
この光電変換効率の低下の原因は、第１透明導電膜の成膜速度を速くする、及び／または膜厚１００ｎｍより厚くすることにより、核の密度が高くなり、隣接する凸部と連なり易く稜線が発生することによるものと考えられる。また、第１透明導電膜の膜厚が１ｎｍより薄いと本発明の効果は得られない。即ち、稜線領域は、他の領域に比べて上に形成された薄膜の膜厚が厚くなり易い。従って、その領域だけ開放電圧が低下し、素子全体としても光電変換効率が低下してしまうのである。
【００５０】
本発明においては稜線がほとんど形成されないので、素子全体の開放電圧は高いものである。また本発明においては、谷線の占める割合も従来のものよりも少ないため、光起電力素子の開放電圧が向上するものである。
【００５１】
一般に、谷の領域にはスパッタされる粒子にとって、谷領域を囲む山領域が障害となるため、膜形成が行われにくい。従って、谷の領域では形成される膜の膜厚が薄くなるので、その微小領域でのリーク電流が発生しやすくなり、素子全体の開放電圧を低下することになる。しかし、本発明においては谷の領域が少ないので開放電圧の低下が少ないものと考えられる。
【００５２】
以上の検討結果から、本発明における最適な第１透明導電膜１０３ａの凸部の頂点間の平均距離と膜の凸部の頂点と基板との平均距離の比の範囲は、好ましくは１：３〜４：１、より好ましくは１：２〜３：１、最適には１：１〜２：１である。膜厚の範囲は、好ましくは１〜１００ｎｍ、より好ましくは２〜８０ｎｍ、最適には３〜５０ｎｍが好ましい。
【００５３】
本発明において工程（５）及び工程（６）における成膜速度と膜厚を前述の特定の範囲に制御することは以下の理由により非常に重要である。
【００５４】
本発明者らの検討の結果、成膜速度と膜厚が、膜に形成される凹凸に大きく影響を与えることを見出した。
【００５５】
例えば、成膜速度が速い場合（例えば１０ｎｍ／ｓｅｃ）では、スパッタリングされたターゲット粒子が多量であるため、極めて短い時間で基板に粒子が堆積され凸部の頂点間距離が狭く、かつ凸部の高さは低いものとなる。
【００５６】
その後の膜成長は狭い凸部が主として成長するため、狭い頂点間距離に制限される。その結果、膜形成が進み膜厚が厚くなるにつれ、堆積された膜上の凹凸はよりなだらかなものになり、例えば光起電力素子の裏面反射層として使用する際に最適な凹凸とすることが困難になる。
【００５７】
一方、成膜速度が遅い場合（例えば１ｎｍ／ｓｅｃ）では、スパッタリングされたターゲット粒子が少量であるため、基板に堆積する粒子は少なく凸部の頂点間距離が広く、かつ凸部の高さは高いものとなる。しかし、この成膜速度が遅い場合でも成膜時間が長くなり、膜厚が必要以上に厚くなると、凸部の成長と共に隣り合う凸部の間に更に凸部が形成されてしまい、凸部の頂点間距離が若干狭くなり、結果として凹凸は若干なだらかになる傾向がある。これは、前述の第１透明導電膜の膜厚が１００ｎｍより厚くなると、凸部の頂点間の平均距離と膜の凸部の頂点と基板との平均距離の比が所望の範囲から外れ、光電変換効率の低下が発生することから分かり、成膜速度と共に膜厚を制御することは必要であると言える。
【００５８】
また、成膜速度が速い場合であっても、既に堆積された膜（即ち下地）に十分凹凸が形成されている場合は、膜堆積が進むにつれ凹凸がなだらかになる傾向はあるが、ある程度の凹凸を維持することができ、透明導電膜の形成に必要な時間が大幅に短縮することが可能になる。
【００５９】
従って、例えば光起電力素子の裏面反射層に必要な凹凸を形成する場合、第１工程において遅い成膜速度で、かつ特定の膜厚の膜を堆積させることにより、ある程度大きな凹凸を形成しておき、次いで第２工程で速い堆積速度で、第１工程で堆積した膜の上にさらに膜を堆積することにより、短時間で光起電力素子の裏面反射層に必要な凹凸を形成することが可能となる。
【００６０】
以上の検討結果から、本発明における最適な第１透明導電膜１０３ａと第２透明導電膜１０３ｂの成膜速度比の範囲は、好ましくは２〜１００、より好ましくは５〜５０、最適には７〜２０である。
【００６１】
上述のように、本発明においては成膜速度及び膜厚を同時に最適な範囲に制御することが非常に重要である。
【００６２】
図３は本発明による光起電力素子の断面の他の例であり、基板１０１上に反射膜１０２、透明導電膜１０３（第１工程部分（第１透明導電膜）１０３ａ、第２工程部分（第２透明導電膜）１０３ｂ、第３工程部分（第３透明導電膜）１０３ｃ）、半導体層１０５、透明電極１０６、及び集電電極１０７が順に積層されている。尚、裏面反射膜１０４は、反射膜１０２と透明導電膜１０３とからなる。
【００６３】
図４は図３に示す光起電力素子を基板上に作製するための製造装置の一例である。以下に、この装置による本発明の光起電力素子の製造方法の一例を説明する。
【００６４】
（１）基板２０５を基板ホルダー２０４にセットして、真空ポンプ（不図示）で成膜室２０１を真空排気する。基板の材料としては導電性のものであっても、また電気絶縁性のものであっても、さらには電気絶縁性の基板表面に導電処理を施したものでも良い。半導体結晶バルクでも良い。又、ガラス等の透光性のものであっても良いが、変形、歪みが少なく、所望の強度を有するものであることが好ましく、Ｆｅ、Ｎｉ、Ｃｒ、Ａｌ等の金属またはこれらの合金、ステンレス鋼などの薄板及びその複合体、及びポリエステル、ポリエチレン等の耐熱性合成樹脂のフィルム等が好ましい。
【００６５】
（２）成膜室２０１内を所定の圧力まで真空排気した後、原料ガス供給装置（不図示）がガス供給管２０６からアルゴンガスを供給し、不図示の排気バルブの開度を調整し、所定の圧力に調整する。
【００６６】
（３）回転軸２０３により基板ホルダー２０４を回転させる。
【００６７】
（４）ヒーター２０２の複数本の赤外線ランプを点灯し、反射膜１０２の成膜温度に加熱する。
【００６８】
（５）反射膜用のターゲット２０７にＤＣ電源２１１を入れアルゴンプラズマを生起し、シャッター２１５を開け、反射膜１０２を形成する。反射膜が所定の膜厚だけ堆積されたら、シャッター２１５を閉じ、ＤＣ電源２１１を切る。反射膜１０２の材料としては、反射率の高い材料が好ましく、金、銀、銅、アルミ及びこれらの合金が好ましい。
【００６９】
（６）次に、透明導電膜の形成温度になるようにヒーター２０２を設定し、所定の温度になったら、透明導電膜の第１工程用のターゲット２０８にＤＣ電源２１２を入れ、アルゴンプラズマを生起し、シャッター２１６を開け、透明導電膜の第１工程部分（核）１０３ａを生成する。核が所定の成膜速度条件で所定の大きさになったら、シャッター２１６を閉じ、ＤＣ電源２１２を切る。
【００７０】
（７）次に、透明導電膜の第２工程用のターゲット２０９にＤＣ電源２１３を入れ、アルゴンプラズマを生起し、シャッター２１７を開け、透明導電膜の第２工程部分１０３ｂを堆積する。第２工程部分が所定の成膜速度条件で所定の厚さだけ堆積されたら、シャッター２１７を閉じ、ＤＣ電源２１３を切る。
【００７１】
（８）次に、透明導電膜の第３工程用のターゲット２１０にＤＣ電源２１４を入れ、アルゴンプラズマを生起し、シャッター２１８を開け、透明導電膜の第３工程部分１０３ｃを堆積する。第３工程部分が所定の成膜速度条件で所定の厚さだけ堆積されたら、シャッター２１８を閉じ、ＤＣ電源２１４を切る。
【００７２】
透明導電膜の材料としては、透過率の高い材料が好ましく、亜鉛、スズ、インジウム、チタンの酸化物、及びこれらの複合化合物が好ましい。また、必要に応じて透明導電膜のスパッタ原料ガスとして、アルゴンと共に酸素、及び水蒸気を導入することは本発明において有効である。
【００７３】
この時、裏面反射膜１０４の表面に数百ｎｍの大きさの凹凸を作製することができ、光閉じ込め効果を利用できる。図３ではこの凹凸を摸式的に強調して記している。
【００７４】
以上のようにして、基板上に反射膜１０２と透明導電膜１０３（ａ〜ｃ）が連続して作製できる。更に別の堆積装置を用いて半導体層１０５、透明電極１０６を作製し、その上に集電電極１０７が形成される。更に保護樹脂を設けてもよい。
【００７５】
この様な手順によって作製した透明導電膜１０３（ａ〜ｃ）は、表面が凹凸形状となり、反射した光が半導体層１０５で効果的に吸収され光電気変換効率が向上する。
【００７６】
この透明導電膜１０３（ａ〜ｃ）の形成方法において、本発明ではその成膜速度条件を制御することを特徴とする。
【００７７】
具体的には、第１工程（６）で透明導電膜の第１工程部分１０３ａを遅い成膜速度で短時間のうちに形成する。これにより、最終的に透明導電膜の凸部の元となる核を所望する密度で形成することができる。
【００７８】
次に第２工程（７）で、第２工程部分１０３ｂを速い成膜速度で形成する。この工程で、第１工程で形成した核密度を損なうことなく、急速に核成長させる。形成物が基板及び第１工程で形成した核表面全体を覆い、すなわち核から膜へと移行した段階で第３工程（８）に入る。
【００７９】
第３工程では、第１工程よりも速く、第２工程よりも遅い成膜速度で第３工程部分１０３ｃを形成する。第１工程よりも速い成膜速度にすることで、膜凹部ヘの新たな核の生成を抑制しながら膜全体の成膜時間を短縮することができる。また、第２工程よりも遅い成膜速度にすることで、より緻密な膜質にすることができる。
【００８０】
ここで本発明の第１工程、第２工程はそれぞれ核生成工程、核成長工程であり、形成物も膜とは言い難い。そのため第１工程、及び第２工程において、成膜速度というのは厳密には適当ではない。したがって、本発明における成膜速度とは、下地の表面すべてが膜と同じ組成であるときの成膜速度（単位時間当りに堆積する膜の厚さ）と定義する。換言すれば、基板上の堆積物が島状の核から膜へ移行し、堆積物全面がほぼ均一に膜として成長するときの成膜速度である。これは本発明における第３工程に相当する工程での成膜速度である。これにより、第１〜第３工程を一般的な成膜速度で比較しうる。一般的に成膜速度を決定する要因は、ターゲットに印加される電圧や電流、スパッタガスの組成や濃度、成膜室の温度や圧力、ターゲットの組成や表面性などが挙げられるが、本発明においてはこれらを適宜制御することにより、結果として所望とする成膜速度が達成できればよい。
【００８１】
以上、各工程の成膜速度比を特定の範囲内に制御することで光電変換効率をより一層向上させ、かつ可撓性のある基板上に堆積しても密着性に優れ、膜剥がれに強く、緻密で耐候性及び電気特性にも優れた、最適な凹凸形状を有する裏面反射膜１０４を形成できる。
【００８２】
次に本発明の各工程における最適な成膜速度比及び凹凸の関係について説明する。
【００８３】
本発明者らの検討の結果、透明導電膜形成工程の成膜速度条件と膜厚が、最終的に膜に形成される凹凸に大きく影響を与えることを見出した。
【００８４】
例えば、核生成工程である第１工程から成膜速度が速い場合（例えば１０ｎｍ／ｓｅｃ以上）では、スパッタリングされたターゲット粒子が多量であるため、極めて短い時間で基板に粒子が堆積され、かつ核密度が高い。したがって核間距離が狭くなり、ターゲット粒子が分散されて核成長に寄与するため核の高さは低いものとなる。その後、核の部分は膜の形成に伴い凸部となるため、狭い核間距離がそのまま膜の凸間距離として維持される。その結果、膜形成が進み膜厚が厚くなるにつれ、堆積された膜上の凹凸はよりなだらかなものになり、例えば光起電力素子の裏面反射層として使用する際に最適な凹凸形状とすることが困難になる。しかし、成膜速度が速くても本発明の第２，第３工程のように、既に堆積された下地に十分な凹凸が形成されている場合は、膜堆積が進むにつれ凹凸がなだらかになる傾向はあるものの、ある程度の凹凸形状を維持することができる。
【００８５】
また、成膜速度が速いと透明導電膜を所望とする膜厚まで堆積させるのに必要な時間は大幅に短縮される。ただし、膜の緻密さという点では成膜速度が遅い方がよく、特に第３工程のように半導体層と接する透明導電膜表面はより緻密な構造である方がよい。緻密でないとひび割れなどが発生しやすくなり、これに起因するリーク電流による素子全体の開放電圧の低下をまねく。密着性の点からも透明導電膜表面は、緻密な構造であるほうがよい。
【００８６】
さらに、前述の成膜速度を決定する種々の要因を制御して成膜速度を速く設定すると、スパッタリング放電が立たなかったり、放電は立つものの途中で短絡現象が起こって放電が断続したり、あるいはそのまま放電が停止してしまうことがある。この短絡現象とは、放電中に電圧が異常に流れ放電が不安定な状態になったり、一時的に放電が途切れたりする現象を言う。短絡現象が起こると、逆に成膜速度が低下したり、膜厚分布のムラ、欠陥などによる膜質の低下などの悪影響を及ぼすため、特に連続成膜において大きな問題となる。さらに短絡現象が起こると、自己復帰することなくそのまま放電が立たなくなることもあり、生産性においても大きな問題となる。
【００８７】
そのため、本発明の第２工程のように膜の凹凸の形成に大きく影響する工程においては、第１工程で生成した核密度を維持し、急速かつ短時間のうちに膜状態へ移行させるため、可能な限り速い成膜速度条件にするほうがよく、第３工程のように膜の凹凸の形成にあまり影響がなく、所望する膜厚になるまで堆積する工程においては、膜質、成膜時間、放電の安定性の兼ね合いから最適な成膜速度条件にするほうがよい。
【００８８】
一方、第１工程から成膜速度が遅い場合（例えば１ｎｍ／ｓｅｃ）では、スパッタリングされたターゲット粒子が少量であるため、基板に堆積する粒子は少なく、核密度は低い。したがって、核間距離が広く、生成した核に集中して核成長が行われるため、核の高さは高いものとなる。しかし、この成膜速度が遅い場合でも、成膜時間が長くなるにつれて、核の成長と共に隣り合う核との間に新たな核が形成されてしまい、核間距離が狭くなる。その結果、膜の凹凸はなだらかになってしまう。これは、核生成工程（第１工程）での厚さが１００ｎｍより厚くなるとこの傾向が顕著になる。また、成膜速度が遅いと透明導電膜を所望とする膜厚まで堆積させるのに時間がかかってしまい、生産性の点でも問題がある。
【００８９】
また、放電開始直後から安定した成膜速度条件で膜を形成させるには、プレスパッタしたターゲットを使用することが望ましい。新品のターゲットでは、放電開始直後と放電終了直前でターゲットの表面性が変わり、成膜速度条件が成膜とともに経時的に変化していく。一方、プレスパッタしたターゲットは最初から表面が適度に荒れているため、放電開始直後と放電終了直前がほぼ同じ成膜速度条件にすることができる。成膜速度が遅い第１工程や膜成長工程で成膜速度が多少振れても膜の凹凸形状にあまり影響のない第３工程では、この成膜速度の安定性は特に大きな問題とはならない。しかし、成膜速度が速く、膜の凹凸の形成に重要な工程である第２工程においては効果が大きい。
【００９０】
したがって、例えば光起電力素子の裏面反射層に必要な凹凸を形成する場合、工程毎に成膜速度条件を変える以下の膜形成方法が最適である。
【００９１】
まず第１工程において、遅い成膜速度条件で、特定の大きさの核を生成させる。次に第２工程において、プレスパッタしたターゲットを用いて、速い成膜速度条件で核を急速に成長させ、核密度を維持しながら早急に核状態から膜状態へ移行させる。最後に第３工程において、第２工程よりもやや遅い成膜速度条件で膜を形成することで、より緻密な膜にすることができる。全体として成膜に要する時間も短縮でき、光起電力素子の裏面反射層に必要な凹凸の形成と膜質を得ることができる。
【００９２】
本発明者らが検討した結果、第２工程と第１工程および第３工程と第１工程における最適な成膜速度比の範囲は、好ましくは２〜１００、より好ましくは５〜５０、最適には７〜２０である。また、第３工程は第２工程よりも遅い成膜速度条件であればよいが、第２工程と第３工程における最適な成膜速度比の範囲は、好ましくは１〜１０、より好ましくは１〜３、最適には１．１〜２である。
【００９３】
第１工程での成膜厚さの範囲は好ましくは１〜１００ｎｍ、より好ましくは２〜８０ｎｍ、最適には３〜５０ｎｍが好ましい。１ｎｍより小さいと核としての機能が果たせず、本発明の効果は得られない。１００ｎｍより大きいと核密度が高くなってしまい、透明導電膜を所望とする凹凸形状にすることが難しい。
【００９４】
第２工程での成膜厚さは好ましくは５μｍ以下、より好ましくは１μｍ以下、特に好ましくは５００ｎｍ以下である。この厚さで核状態から膜状態への移行がほぼ完了し、第２工程での目的である凹凸形状の形成が可能となる。
【００９５】
第３工程での成膜厚さは最終形態である光起電力素子の特性に大きく影響するが、耐歪み性、耐衝撃性や密着性を考慮すれば５μｍ以下が望ましい。
【００９６】
なお、ここでは例としてバッチ方式を示したが、本発明はこの方式に限らず、枚葉式、或いはロール・ツー・ロール方式等の長尺基板を搬送する方式等にも適用できる。
【００９７】
【実施例】
以下に、本発明の実施例を図面に基づいて詳細に説明するが、本発明はこれらの実施例に限るものではない。
【００９８】
〔実施例１〕
本実施例においては、図１の断面模式図に示す構成の光起電力素子を図２の装置を用いて作成した。
【００９９】
具体的にはステンレス鋼の薄基板２０５を基板ホルダー２０４にセットして、真空ポンプ（不図示）により成膜室２０１を真空排気した。所定の圧力まで真空排気した後、原料ガス供給装置（不図示）がガス供給管２０６からアルゴンガスを３０ｓｃｃｍ供給し、不図示の排気バルブの開度を調整し圧力を０．３Ｐａに調整した。そして回転軸２０３により、基板ホルダーを回転させた。基板が１００℃になるようにヒーター２０２を設定し、赤外線ランプを点灯し加熱した。所定の温度になったらＤＣ電源２１１を入れ、反射膜用のアルミターゲット２０７にアルゴンプラズマを生起し、シャッター２１５を開け、反射膜１０２を形成した。反射膜を約１５０ｎｍ堆積し、シャッター２１５を閉じ、ＤＣ電源２１１を切った。
【０１００】
次に、２００℃になるようにヒーター２０２を設定し、所定の温度になったらＤＣ電源２１２を入れ、第１透明導電膜用の酸化亜鉛ターゲット２０８にアルゴンプラズマを生起し、シャッター２１６を開け、第１透明導電膜１０３ａを形成した。第１透明導電膜の成膜速度を０．５ｎｍ／ｓｅｃで約８ｎｍ堆積し、シャッター２１６を閉じ、ＤＣ電源２１２を切った。
【０１０１】
次にＤＣ電源２１３を入れ、第２透明導電膜用の酸化亜鉛ターゲット２０９にアルゴンプラズマを生起し、シャッター２１７を開け、第２透明導電膜１０３ｂを形成した。第２透明導電膜の成膜速度を１０ｎｍ／ｓｅｃで第２透明導電膜を約１μｍ堆積させ、シャッター２１７を閉じ、ＤＣ電源２１３を切った。
【０１０２】
第１透明導電膜と第２透明導電膜の成膜速度比は、２０であった。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約６０ヵ所あった。反射膜と透明導電膜の形成された基板を５ｃｍ×５ｃｍの大きさに切断し、他装置で半導体層、透明導電膜、電極を堆積させた。
【０１０３】
〔比較例１〕
実施例１における透明導電膜の形成を第２透明導電膜の条件で作成した以外は、実施例１と同様にして、図５に示す構成の光起電力素子を作成した。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約１４０ヵ所あった。
【０１０４】
〔評価１〕
実施例１で得られた光起電力素子（以下“試料実１”という）及び比較例１で得られた光起電力素子（以下“試料比１”という）のそれぞれについて初期特性をソーラーシュミレーター（ＡＭ１．５、１００ｍＷ／ｃｍ²、表面温度２５℃）を用いて光電変換効率を測定した。その結果、試料実１は試料比１と比較して、１．１２倍優れていることが分かった。
【０１０５】
〔実施例２〕
実施例１において第２透明導電膜の膜厚を約２μｍとした以外は実施例１と同様にして、図１に示す構成の光起電力素子を作成した。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約５５ヵ所あった。
【０１０６】
〔比較例２〕
実施例２における透明導電膜の形成を第２透明導電膜の条件で作成した以外は、実施例２と同様にして、図５に示す構成の光起電力素子を作成した。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約１３０ヵ所あった。
【０１０７】
〔評価２〕
実施例１及び比較例１における測定と同様にして評価した。その結果、実施例２で得られた光起電力素子は、実施例１で得られた光起電力素子と同様に光電変換効率の優れたものであることが分かった。
【０１０８】
〔実施例３〕
本実施例においては、図１の断面模式図に示す構成の光起電力素子を図６の装置を用いて作成した。
【０１０９】
図６の装置をメンテナンス等の為に大気開放した後、ロール状基板４０２を基板送り出し室４０１にセットし、反射膜作製室４０５、透明導電膜作製室４０６、０７、４０８、４０９、４１０、４１１のそれぞれに基板４０４を貫通させ、基板巻き取り室４１６のロール４１４に固定した。基板４０４には幅１２０ｍｍ、厚さ０．１５ｍｍ、長さ１５０ｍの表面に凹凸をダル仕上げで残したＳＵＳ４３０を使用した。
【０１１０】
続いて、圧力が０．１Ｐａ以下になるまで排気した。この後、反射膜作製室４０５と透明導電膜作製室４０６、４０７、４０８、４０９、４１０、４１１にガス供給管４５０、４５１、４５２、４５３、４５４、４５５、４５６から不活性ガスとしてアルゴンガスを各々３０ｓｃｃｍ供給した。また、ゲート４１５へもアルゴンガスを３０ｓｃｃｍ供給した。この状態で不図示の排気バルブの開度を調整して真空室内の圧力を０．３Ｐａに保った。
【０１１１】
反射膜作製室４０５、透明導電膜作製室４０６、４０７、４０８、４０９、４１０、４１１のそれぞれに１００Ｗの赤外線ランプ６本セットにしたヒータユニット４４０、４４１、４４２、４４３、４４４、４４５、４４６をステンレス製の反射板と共に設けておき基板の成膜面の裏面に熱電対を接触させて２００℃になるよう温度を制御して加熱した。
【０１１２】
続いて、サーボモータを動作し巻き取りロール２１７を回転させて、基板４０４の搬送を開始した。
【０１１３】
反射膜作製用のターゲット４２０には純度９９．９９重量％、２５ｃｍ×２５ｃｍのアルミニウムターゲットを用い、これにＤＣ電源４３０からの電力を入れアルゴンプラズマを生起し、反射膜を堆積した。基板４０４がターゲット４２０上を通過する間にアルミニウム反射膜１０２が約１５０ｎｍ堆積した。
【０１１４】
第１透明導電膜作製室４０６に基板４０４を引き続き搬送した。純度９９．９９重量％、２５ｃｍ×２５ｃｍの大きさの酸化亜鉛ターゲット４２１にＤＣ電源４３１からの電力を入れアルゴンプラズマを生起し、０．５ｎｍ／ｓｅｃで第１透明導電膜１０３ａを形成した。
【０１１５】
引き続き、第２透明導電膜作製室４０７、４０８、４０９、４１０、４１１に基板４０４を搬送した。純度９９．９９重量％、２５ｃｍ×２５ｃｍの大きさの酸化亜鉛ターゲット４２２、４２３、４２４、４２５、４２６を用いて各々ＤＣ電源４３２、４３３、４３４、４３５、４３６からの電力を入れアルゴンプラズマを生起し、１０ｎｍ／ｓｅｃで第２透明導電膜１０３ｂを形成した。裏面反射膜１０４の膜厚は約１μｍであった。なおこの時、透明導電膜は図１に示す表面形状に形成された。
【０１１６】
透明導電膜まで作製した基板４０４は、巻き取り室４１６で巻き取った。なお、透明導電膜の表面を傷つけないように、巻き取り時にポリエステルフィルムの合紙４１３を基板と基板の間に挟み込んだ。
【０１１７】
第１透明導電膜と第２透明導電膜の成膜速度比は、２０であった。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約６０ヵ所あった。反射膜と透明導電膜の形成された基板を５ｃｍ×５ｃｍの大きさに切断し、他装置で半導体層、透明導電膜、電極を堆積させた。
【０１１８】
〔比較例３〕
実施例３における透明導電膜の形成を第２透明導電膜の条件で作成した以外は、実施例３と同様にして、図５に示す構成の光起電力素子を作成した。反射膜と透明導電膜の形成された基板をＡＦＭで確認すると２５μｍ²当り凸部が約１４０ヵ所あった。
【０１１９】
〔評価３〕
実施例３で得られた光起電力素子（以下“試料実３”という）及び比較例３で得られた光起電力素子（以下“試料比３”という）のそれぞれについて初期特性をソーラーシュミレーター（ＡＭ１．５、１００ｍＷ／ｃｍ²、表面温度２５℃）を用いて光電変換効率を測定した。その結果、試料実３は試料比３と比較して、１．１２倍優れていることが分かった。
【０１２０】
〔実施例４〕
本実施例においては、図３の断面模式図に示す構成の光起電力素子を図４の装置で作製した。
【０１２１】
具体的にはステンレス基板２０５を基板ホルダー２０４にセットして、真空ポンプ（不図示）で成膜室２０１を真空排気した。所定の圧力まで真空排気した後、原料ガス供給装置（不図示）がガス供給管２０６からアルゴンガスを３０ｓｃｃｍ供給し、不図示の排気バルブの開度を調整し圧力を０．３Ｐａに調整した。回転軸２０３により基板ホルダーを回転させた。
【０１２２】
基板が１００℃になるようにヒーター２０２を設定し赤外線ランプを点灯し加熱した。所定の温度になったら反射膜用のアルミターゲット２０７にＤＣ電源２１１からの電力を入れアルゴンプラズマを生起し、シャッター２１５を開け、反射膜１０２を形成した。反射膜を約１５０ｎｍ堆積し、シャッター２１５を閉じ、ＤＣ電源２１１を切った。
【０１２３】
次に、２００℃になるようにヒーター２０２を設定し、所定の温度になったら、透明導電膜の第１工程用の酸化亜鉛ターゲット２０８にＤＣ電源２１２からの電力を入れ、アルゴンプラズマを生起し、シャッター２１６を開け、核（透明導電膜の第１工程部分１０３ａ）を形成した。第１工程の成膜速度は０．５ｎｍ／ｓｅｃとした。この成膜速度とは、下地が酸化亜鉛膜であるときの成膜速度を指している。この第１工程で生成した核が約８ｎｍの高さになったとき、シャッター２１６を閉じ、ＤＣ電源２１２を切った。
【０１２４】
次に、第２工程用の酸化亜鉛ターゲット２０９にＤＣ電源２１３からの電力を入れ、アルゴンプラズマを生起し、シャッター２１７を開け、透明導電膜の第２工程部分１０３ｂを形成した。ここで第２工程用の酸化亜鉛ターゲット２０９は、予めプレスパッタしたものを用いた。第２工程の成膜速度は１０ｎｍ／ｓｅｃとし、核状態から膜状態へ移行し、透明導電膜を約１５０ｎｍ堆積させ、シャッター２１７を閉じ、ＤＣ電源２１３を切った。第２工程と第１工程の成膜速度比は２０であった。
【０１２５】
次に、第３工程用の酸化亜鉛ターゲット２１０にＤＣ電源２１４からの電力を入れ、アルゴンプラズマを生起し、シャッター２１８を開け、透明導電膜の第３工程部分１０３ｃを形成した。第３工程の成膜速度は８ｎｍ／ｓｅｃとし、透明導電膜全体で約１．５μｍ堆積させ、シャッター２１８を閉じ、ＤＣ電源２１４を切った。第３工程と第１工程の成膜速度比は１６であった。
【０１２６】
上記の方法により、反射膜１０２と透明導電膜１０３（ａ〜ｃ）の形成された基板を５ｃｍ×５ｃｍの大きさに切断し、他装置で半導体層１０５、透明導電膜１０６、集電電極１０７を堆積した。
【０１２７】
〔実施例５〕
本実施例においては、図３の断面模式図に示す構成の光起電力素子を図６の装置で作製した。
【０１２８】
図６の装置をメンテナンス等の為に大気開放した後、ロール状基板４０２を基板送り出し室４０１にセットし、反射膜作製室４０５、透明導電膜作製室４０６、４０７、４０８、４０９、４１０、４１１それぞれに基板４０４を貫通させ、基板巻き取り室４１６のロール４１４に固定する。基板４０４には幅１２０ｍｍ、厚さ０．１５ｍｍ、長さ１５０ｍの表面に凹凸をダル仕上げで残したＳＵＳ４３０を使用した。
【０１２９】
続いて圧力が０．１Ｐａ以下になるまで膜作製室を排気した。この後、反射膜作製室４０５と透明導電膜作製室４０６、４０７、４０８、４０９、４１０、４１１にガス供給管４５０、４５１、４５２、４５３、４５４、４５５、４５６から不活性ガスとしてアルゴンガスを各々３０ｓｃｃｍ供給した。この状態で不図示の排気バルブの開度を調整して各膜作製室内の圧力を０．３Ｐａに保った。
【０１３０】
反射膜作製室４０５、透明導電膜作製室４０６、４０７、４０８、４０９、４１０、４１１それぞれに１００Ｗの赤外線ランプ６本セットにしたヒータユニット４４０、４４１、４４２、４４３、４４４、４４５、４４６をステンレス製の反射板と共に設けておき、基板の成膜面の裏面に熱電対を接触させて２００℃になるよう温度を制御して加熱した。
【０１３１】
続いてサーボモータ４１７を動作し、巻き取りロール４１４を回転させて基板４０４の搬送を開始した。
【０１３２】
反射膜作製用のターゲット４２０には純度９９．９９重量％、２５ｃｍ×２５ｃｍのアルミニウムターゲットを用い、このターゲット４２０にＤＣ電源４３０からの電力を入れアルゴンプラズマを生起し、反射膜１０２を堆積した。それにより、基板４０４がターゲット４２０上を通過する間にアルミニウム反射膜１０２を約１５０ｎｍ形成した。
【０１３３】
透明導電膜の第１工程に相当する作製室４０６に基板４０４を引き続き搬送した。純度９９．９９重量％、２５ｃｍ×２５ｃｍの大きさのプレスパッタした酸化亜鉛ターゲット４２１にＤＣ電源４３１からの電力を入れアルゴンプラズマを生起し、０．５ｎｍ／ｓｅｃの成膜速度条件で第１工程部分１０３ａを形成した。基板４０４がターゲット４２１上を通過する間に酸化亜鉛の核は約８ｎｍの高さに成長した。
【０１３４】
引き続き、透明導電膜の第２工程に相当する作製室４０７に基板４０４を搬送した。純度９９．９９重量％、２５ｃｍ×２５ｃｍの酸化亜鉛ターゲット４２２にＤＣ電源４３２からの電力を入れアルゴンプラズマを生起し、１０ｎｍ／ｓｅｃの成膜速度条件で第２工程部分１０３ｂを形成した。基板４０４がターゲット４２２上を通過する間に酸化亜鉛膜は約１００ｎｍの厚さに成長した。
【０１３５】
次に、透明導電膜の第３工程に相当する作製室４０８、４０９、４１０、４１１に基板４０４を搬送した。純度９９．９９重量％、２５ｃｍ×２５ｃｍの大きさの酸化亜鉛ターゲット４２３、４２４、４２５、４２６を用いて各々ＤＣ電源４３３、４３４、４３５、４３６からの電力を入れアルゴンプラズマを生起し、８ｎｍ／ｓｅｃの成膜速度条件で第３工程部分１０３ｃを形成した。第３工程を終了した段階で裏面反射膜１０４の膜厚は約１．５μｍであった。
【０１３６】
裏面反射膜１０４（反射膜１０２及び透明導電膜１０３ａ〜ｃ）を形成した基板４０４は巻き取り室４１６で巻き取った。なお透明導電膜の表面を傷つけないようにポリエステルフィルム製の合紙４１３を巻き取り時に基板と基板の間にはさみ込んだ。
【０１３７】
本実施例における透明導電膜の第２工程と第１工程の成膜速度比は２０であり、第３工程と第１工程の成膜速度比は１６であった。
【０１３８】
上記の方法により、裏面反射膜１０４の形成された基板を５ｃｍ×５ｃｍの大きさに切断し、他装置で半導体層１０５、透明導電膜１０６、集電電極１０７を堆積した。
【０１３９】
〔実施例６〕
実施例４における透明導電膜の形成において、第３工程を第２工程の条件で形成した以外は、実施例４と同様にして、図３に示す構成の光起電力素子を作製した。
【０１４０】
〔実施例７〕
実施例４における透明導電膜の形成において、第２工程でプレスパッタしたターゲットの代わりに新品のターゲットを使用して透明導電膜を形成した以外は、実施例４と同様にして、図３に示す構成の光起電力素子を作製した。
【０１４１】
〔比較例４〕
実施例４における透明導電膜の形成において、すべての工程を第２工程の条件で形成した以外は、実施例４と同様にして、図３に示す構成の光起電力素子を作製した。
【０１４２】
〔比較例５〕
実施例４における透明導電膜の形成において、第１工程における成膜速度条件を０．０８ｎｍ／ｓｅｃにして形成した以外は、実施例４と同様にして、図３に示す構成の光起電力素子を作製した。
【０１４３】
〔比較例６〕
実施例５における透明導電膜の形成において、すべての工程を第２工程の条件で形成した以外は、実施例５と同様にして、図３に示す構成の光起電力素子を作製した。
【０１４４】
〔評価４〕
上記の実施例４〜７及び比較例４〜６で作製した光起電力素子の初期特性をソーラーシュミレーター（ＡＭ１．５、１００ｍＷ／ｃｍ²、表面温度２５℃）を用いて光電変換効率を測定した結果を表２に示す。尚、光電変換効率の評価は、実施例４の光電変換効率を基準として、相対値が１．００であるときは◎、０．９５以上１．００未満は○、０．９０以上０．９５未満は△、０．９０未満は×として評価した。
【０１４５】
【表２】

【０１４６】
表２から明らかなように、比較例４、５、６のように成膜速度条件が本発明の条件から逸脱した場合、光電変換効率は著しく低下する。
【０１４７】
また、実施例６のように第３工程が第２工程と同じ成膜速度条件である場合には、実施例４に比べて光電変換効率が低い。したがって、第３工程の成膜速度を第２の成膜速度よりも遅くすることによって、より優れた効果が得られることが判る。
【０１４８】
さらに、実施例７のように第２工程に新品のターゲットを使用した場合には、実施例４に比べて光電変換効率が低い。したがって、第２工程におい、プレスパッタしたターゲットを使用することによって、より優れた効果が得られることが判る。
【０１４９】
【発明の効果】
以上説明したように、本発明の好適な実施例によれば、反射膜及び第１透明導電膜、第２透明導電膜の作成時に第１透明導電膜と第２透明導電膜の成膜速度比を管理することにより、透明導電膜の成膜速度が速くなり、光電変換効率の良好な堆積膜を作成することが可能になる。このことから、低コストでかつ信頼性の高い光起電力素子を作成することが可能になり、太陽電池の系統電力用としての本格的な普及に寄与するものである。
【０１５０】
また、本発明の好適な実施例にかかる透明導電膜の製造方法によれば、透明導電膜の形成工程において、各工程の成膜速度条件を管理することで、（１）光起電力素子の裏面反射膜として最適な表面形状を有し、（２）透明導電膜の形成速度が速く、（３）緻密な膜質の透明導電膜を形成することができる。そして、この透明導電膜を用いることで、光電変換効率の良好でかつ信頼性の高い光起電力素子を低コストで作製する事が可能である。
【図面の簡単な説明】
【図１】本発明による光起電力素子の断面構造の一例を示す模式図である。
【図２】本発明の光起電力素子を基板上に作製するための製造装置の一例を示す概略図である。
【図３】本発明による光起電力素子の断面構造の他の例を示す模式図である。
【図４】本発明の光起電力素子を基板上に作製するための製造装置の他の例を示す概略図である。
【図５】比較例の光起電力素子の断面構造を示す模式図である。
【図６】本発明の光起電力素子を長尺基板上に作製するためのロール・ツー・ロール方式の製造装置の一例を示す概略図である。
【図７】本発明の実験例における成膜速度比と光電変換効率との関係を示す説明図である。
【符号の説明】
１０１ 基板
１０２ 反射膜
１０３ａ 第１透明導電膜（第１工程部分）
１０３ｂ 第２透明導電膜（第２工程部分）
１０３ｃ 第３透明導電膜（第３工程部分）
１０４ 裏面反射膜
１０５ 半導体膜
１０６ 透明電極
１０７ 集電電極
２０１ 成膜室
２０２ ヒーター
２０３ 回転軸
２０４ 基板ホルダー
２０５ 基板
２０６ ガス供給管
２０７〜２１０ ターゲット
２１１〜２１４ 電源
２１５〜２１８ シャッター
２１９ プラズマ
３０１ 基板
３０２ 反射膜
３０３ 透明導電膜
３０４ 裏面反射膜
３０５ 半導体膜
３０６ 透明電極
３０７ 集電電極
４０１ 基板送り出し室
４０２ ロール状基板
４０３ ローラー
４０４ 基板
４０５ 反射膜作成室
４０６〜４１１ 透明導電膜作成室
４１６ 巻き取り室
４１４ ロール状基板
４１２ ステアリングローラー
４１３ 合紙
４２０〜４２６ ターゲット
４３０〜４３６ 電源
４４０〜４４６ ヒータ
４１５ マグネットローラー
４５０〜４５６ ガス供給管
４６０ 真空ポンプ[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for forming a transparent conductive film laminated on a substrate using a sputtering apparatus or the like.as well asManufacture of photovoltaic elementsOn the wayRelated.
[0002]
[Prior art]
Photovoltaic devices made of hydrogenated amorphous silicon, hydrogenated amorphous silicon germanium, hydrogenated amorphous silicon carbide, microcrystalline silicon, polycrystalline silicon, compound semiconductor, etc. improve collection efficiency at long wavelengths Therefore, a reflective film is provided on the back side of the element. It is desirable that such a reflection film has a reflection characteristic that is close to the energy band edge of the semiconductor material and exhibits an effective reflection characteristic at a wavelength at which absorption is reduced, that is, from 800 nm to 1200 nm. A material that sufficiently satisfies this condition is a metal such as gold, silver, copper, or aluminum.
[0003]
In addition, in order to confine light incident on the photovoltaic element in the semiconductor active layer, an optically transparent uneven layer may be provided in a predetermined reflection range. In general, such a concavo-convex layer is provided between the metal reflective film and the semiconductor active layer, and improves the short-circuit current density Jsc by effectively using the reflected light. As a method for making the surface of the transparent conductive film used as the light confinement layer uneven, there are the following conventional techniques.
[0004]
In JP-A-63-456, in a method of forming a polycrystalline metal oxide film by a vacuum deposition method, the metal oxide material is heated to a deposition rate of 15 to 30 liters / sec. It is described that a film having an uneven structure can be obtained on the surface of the film.
[0005]
In JP-A-8-32094, a transparent conductive film is composed of at least two layers, the film formation temperature or / and the film formation speed are controlled, one of which is a crystalline transparent conductive film, and one layer is an amorphous transparent film. It is described that a highly reliable solar cell can be obtained by using a conductive film.
[0006]
In Japanese Patent Laid-Open No. 10-310862, after heating and cooling the film forming chamber, a metal reflective film is formed on the substrate, contacted with active oxygen, and then a transparent conductive film is formed. It is described that a reflective film and a transparent conductive film having a high rate, low cost, and high reliability can be obtained stably.
[0007]
In JP-A-11-220154, after forming a metal reflective film on a substrate, the first transparent conductive film is formed in an atmosphere containing 50% or more of oxygen, and the temperature is higher than that in forming the argon atmosphere and the first transparent conductive film. Then, a second transparent conductive film is formed. As a result, the first transparent conductive film has a crystal grain c-axis parallel to the substrate, and the second transparent conductive film has a crystal grain c-axis perpendicular to the substrate so that ridges cannot be formed on the irregularities. It is described that a solar cell with improved photovoltaic characteristics and high reliability can be obtained.
[0008]
JP-A-6-116722 describes that a long substrate is moved and a metal layer and a transparent conductive film are continuously formed thereon by a sputtering method (Roll to Roll method).
[0009]
Thus, by adjusting the film formation rate and making the transparent conductive film multilayer, it is possible to obtain a high-quality deposited film.
[0010]
However, in order to mass-produce a good transparent conductive film at low cost by sputtering, there are problems to be solved as described below.
[0011]
[Problems to be solved by the invention]
Conventionally, in order to grow a transparent conductive film used as an optical confinement layer into an effective concavo-convex shape due to the characteristics of the photovoltaic device, the film thickness is extremely increased or / and the film formation speed is extremely decreased. And had to be deposited and formed. Such a thin film formation method has problems such as an increase in material cost and an increase in film formation time, and the manufacturing cost of the photovoltaic device is extremely high. In addition, it is difficult to obtain a good concavo-convex shape simply by increasing the film formation speed, resulting in instability of sputtering discharge and deterioration of film quality.
[0012]
Therefore, a main object of the present invention is to form a transparent conductive film having a concavo-convex shape having a high light confinement effect in a short time by a deposition forming method advantageous for cost reduction, and can be applied to a laminated structure of photovoltaic elements. Thus, an object of the present invention is to provide a method for producing a transparent conductive film with improved photovoltaic characteristics and improved mass productivity.
[0013]
[Means for Solving the Problems]
The present inventor has conducted intensive studies, particularly focusing on the relationship between the film forming speed condition, the surface shape of the deposited film, and the element configuration in order to achieve both high-level sputter film formation and stability. It was. As a result, the film formation speed condition and the film thickness at the initial stage of sputtering on the substrate are effective in improving the film characteristics, film structure and device characteristics of the transparent conductive film, and for the production of the transparent conductive film in a shorter time. The inventors have found that there is a great effect and have arrived at the present invention having the following configuration.
[0014]
  Therefore, the present invention provides a transparent conductive film having crystallinity on a substrate.By sputteringIn the forming method,
  A first step of forming a film at a first film formation rate and a second step of forming a film at a second film formation rate;
2 ≦ (second deposition rate) / (first deposition rate) ≦ 100
MeetAnd
  The film thickness in the first step is 1 to 100 nm
A method for forming a transparent conductive film is provided.
[0015]
The “film forming step” in the present invention is a concept including a step of forming a nucleus.
[0016]
  The method for forming a transparent conductive film of the present invention is as a further preferable feature,
“In the first step, nuclei are formed on the substrate, and in the second step, a transparent conductive film is formed covering the entire surface of the substrate surface and the surface of the nuclei.thing",
“The film thickness in the second step is 5 μm or less, more preferably 1 μm or less.”
“The ratio of the average distance between the vertices of the convex portions of the transparent conductive film formed in the first step to the average distance between the vertices of the convex portions and the substrate is 1: 3 to 4: 1. Performing the first step ",
“To form a transparent conductive film using a roll-to-roll method in which a long substrate is transported between rolls,”
“After the second step, there is a third step of forming a transparent conductive film at a third deposition rate, and the relationship between the deposition rates of each step is
2 <(second deposition rate) / (first deposition rate) ≦ 100
2 ≦ (third deposition rate) / (first deposition rate) <100
(Second film formation rate)> (Third film formation rate)
To meet ",
“The film thickness in the third step is set to 5 μm or less.thing",
"Use a pre-sputtered target in the second step",
including.
[0017]
Moreover, this invention provides the manufacturing method of the photovoltaic element characterized by including the process of forming a transparent conductive film with the formation method of the transparent conductive film of the said invention, and the process of forming a semiconductor layer.
[0020]
According to a method for forming a transparent conductive film according to a preferred embodiment of the present invention, an optimum surface shape as a back surface reflective film of a photovoltaic device is realized by managing a film formation speed ratio in each step of forming the transparent conductive film. In addition, the formation speed of the transparent conductive film can be increased, and a transparent conductive film having a concavo-convex shape with a high light confinement effect can be formed in a shorter time. And by using this transparent conductive film, it is possible to produce a photovoltaic device having good photoelectric conversion efficiency and high reliability at low cost.
[0021]
The present invention having the above-described configuration and the above-described prior art are greatly different in terms of idea and specific configuration.
[0022]
That is, Japanese Patent Application Laid-Open No. 63-456 is a technique that focuses on the film forming speed, but does not describe changing the film forming speed condition and forming the film in a shorter time.
[0023]
Japanese Patent Laid-Open No. 8-32094 pays attention to the fact that the transparent conductive film is a multilayer, but it is a combination of crystal and amorphous, and the configuration of the transparent conductive film is different. In addition, there is no description of positively changing the deposition rate condition during the formation of the crystalline transparent conductive layer. Furthermore, there is no description about controlling the film formation rate and the film structure by changing the film formation rate condition.
[0024]
Japanese Patent Application Laid-Open No. 10-310862 pays attention to the improvement of reflectance by forming a transparent conductive film after exposing the metal reflective film to active oxygen, and the surface shape by changing the film forming speed condition of the transparent conductive film. There is no suggestion of any change.
[0025]
Japanese Patent Application Laid-Open No. 11-220154 focuses on changing the film forming gas and film forming temperature to two layers of transparent conductive films in order to obtain an appropriate uneven surface shape. This is different from the present invention in which an appropriate uneven surface shape is obtained by changing.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In the following examples, the transparent conductive film formed in each step has crystallinity.
[0027]
FIG. 1 is an example of a cross-sectional structure of a photovoltaic device according to the present invention. On a substrate 101, a reflective film 102, a first transparent conductive film 103a, a second transparent conductive film 103b, a semiconductor layer 105, a transparent electrode 106, and Current collecting electrodes 107 are sequentially stacked. The back surface reflection film 104 includes the reflection film 102, the first transparent conductive film 103a, and the second transparent conductive film 103b.
[0028]
In the present specification, the phrase “on the substrate” includes the case “on the film (reflection film, metal layer, etc.) on the substrate”.
[0029]
FIG. 2 is an example of a manufacturing apparatus for producing the photovoltaic element shown in FIG. 1 on a substrate. With this apparatus, a film is formed according to the following procedure.
[0030]
(1) The substrate 205 is set on the substrate holder 204, and the film forming chamber 201 is evacuated by a vacuum pump (not shown). The material of the substrate may be a conductive material, an electrically insulating material, or an electrically insulating substrate surface subjected to a conductive treatment. A semiconductor crystal bulk may be used. Moreover, although it may be translucent, such as glass, it is preferable that it has a desired strength with little deformation and distortion, and a metal such as Fe, Ni, Cr, Al or an alloy thereof, Thin plates such as stainless steel and composites thereof, and films of heat-resistant synthetic resins such as polyester and polyethylene are preferred.
[0031]
(2) After evacuating to a predetermined pressure, a raw material gas supply device (not shown) supplies argon gas from the gas supply pipe 206 and adjusts the opening of an exhaust valve (not shown) to a predetermined pressure. The substrate holder is rotated by the rotation shaft 203.
[0032]
(3) A plurality of infrared lamps of the heater 202 are turned on and heated to the temperature at which the reflective film is formed.
[0033]
(4) The DC power supply 211 is turned on, argon plasma is generated in the target 207 for the reflective film, the shutter 215 is opened, and the reflective film 102 is formed. When the reflective film is deposited to a predetermined thickness, the shutter 215 is closed and the DC power supply 211 is turned off. As the material of the reflective film 102, a material having high reflectance is preferable, and gold, silver, copper, aluminum, and alloys thereof are preferable.
[0034]
(5) Next, the heater 202 is set so as to reach the formation temperature of the transparent conductive film. When the predetermined temperature is reached, the DC power supply 212 is turned on, and argon plasma is generated in the target 208 for the first transparent conductive film, The shutter 216 is opened and the first transparent conductive film 103a is deposited. When the first transparent conductive film is deposited to a predetermined film thickness at a predetermined film formation speed, the shutter 216 is closed and the DC power supply 211 is turned off.
[0035]
(6) Next, the DC power source 213 is turned on, argon plasma is generated in the target 209 for the second transparent conductive film, the shutter 217 is opened, and the second transparent conductive film 103b is deposited. When the second transparent conductive film is deposited to a predetermined film thickness at a predetermined film formation speed, the shutter 217 is closed and the DC power source 213 is turned off.
[0036]
As a material for the transparent conductive film, a material having high transmittance is preferable, and oxides of zinc, tin, indium, titanium, and composite compounds thereof are preferable. In addition, it is effective in the present invention to introduce oxygen and water vapor together with argon as the sputtering raw material gas for the material of the transparent conductive film as necessary.
[0037]
At this time, irregularities having a size of several hundreds of nanometers can be formed on the surface of the back reflective film 104, and the light scattering effect can be utilized. In FIG. 1, the unevenness is schematically emphasized.
[0038]
As described above, the reflective film and the transparent conductive film can be continuously formed on the substrate.
[0039]
Furthermore, a semiconductor layer and a transparent electrode are produced using another deposition apparatus, and a current collecting electrode is formed. Further, a protective resin may be provided.
[0040]
The reflective film and the transparent conductive film produced by such a procedure have a surface shape with no ridgeline and a small density of convex portions, and the reflected light is effectively absorbed by the semiconductor layer, thereby improving the photoelectric conversion efficiency.
[0041]
The inventor has found that the film formation speed of the first transparent conductive film after the formation of the reflective film in the above-described step (5) is related to the surface shape and the photoelectric conversion efficiency of the photovoltaic element. Specifically, the first transparent conductive film 103a formed in the step (5) is formed at a low film formation speed in a short time, and the second transparent conductive film 103b is formed at a high film formation speed at a ratio of these film formation speeds. Film formation while controlling the film thickness within a specific range to further improve the photoelectric conversion efficiency, and even when deposited on a flexible substrate, it has excellent adhesion, is resistant to film peeling, and is dense and weather resistant. In addition, it is possible to form the back reflective film 104 having an optimal uneven shape that is excellent in electrical characteristics.
[0042]
Next, the optimum film formation rate ratio and unevenness relationship between the first transparent conductive film 103a and the second transparent conductive film 103b of the present invention will be described.
[0043]
According to the above-mentioned process, the film forming speed of the first transparent conductive film 103a is 1 nm / sec, and the ratio of the average distance between the vertexes of the convex portions and the average distance between the vertexes of the convex portions of the film and the substrate is 1: 1. The back surface reflection film was formed in the same manner except that the film thickness was 5 nm and the film formation rate of the second transparent conductive film 103b was changed to create the transparent conductive film, and the semiconductor layer, the transparent electrode, and the collecting electrode were formed. Photovoltaic elements were created, and the initial characteristics of each were solar simulators (AM1.5, 100 mW / cm²The photoelectric conversion efficiency was measured using a surface temperature of 25 ° C.).
[0044]
As a result, as shown in FIG. 7, it can be seen that the efficiency decreases when the deposition rate ratio (the deposition rate of the second transparent conductive film 103b / the deposition rate of the first transparent conductive film 103a) is outside the desired range.
[0045]
Next, by changing the film thickness of the first transparent conductive film, the ratio of the average distance between the apexes of the convex portions and the average distance between the apexes of the convex portions of the film and the substrate is 1: 5 to 5: In the same manner except that the film forming speed ratio (film forming speed of the second transparent conductive film 103b / film forming speed of the first transparent conductive film 103a) is fixed to 10 in the range of 1, A semiconductor layer, a transparent electrode, and a collecting electrode are formed to create a photovoltaic device, and the initial characteristics of each are solar simulators (AM1.5, 100 mW / cm²The photoelectric conversion efficiency was measured using a surface temperature of 25 ° C.).
[0046]
As a result, as shown in Table 1, the efficiency decreases when the ratio between the average distance between the vertices of the convex portions and the average distance between the vertices of the convex portions of the film and the substrate is outside the desired range.
[0047]
[Table 1]

[0048]
Explanation of symbols (numeric value: relative value)
a: Average distance between the vertices of the convex portions of the film formed on the substrate
b: The average distance between the vertex of the convex portion of the film and the substrate
A: 1.00
○: 0.95 to less than 1
Δ: 0.90 to less than 0.95
X: 0.80 to less than 0.90
[0049]
The cause of the decrease in the photoelectric conversion efficiency is that by increasing the film forming speed of the first transparent conductive film and / or making it thicker than 100 nm, the density of the nuclei increases, and the ridge line tends to be connected to the adjacent convex part. This is thought to be due to the occurrence of Moreover, the effect of this invention will not be acquired if the film thickness of a 1st transparent conductive film is thinner than 1 nm. That is, in the ridge line region, the film thickness of the thin film formed thereon is likely to be thicker than other regions. Therefore, the open circuit voltage is reduced only in that region, and the photoelectric conversion efficiency of the entire device is also reduced.
[0050]
In the present invention, since almost no ridge line is formed, the open circuit voltage of the entire device is high. In the present invention, since the ratio of the valley line is smaller than that of the conventional one, the open circuit voltage of the photovoltaic element is improved.
[0051]
In general, for the particles to be sputtered in the valley region, the mountain region surrounding the valley region becomes an obstacle, so that film formation is difficult. Therefore, since the film thickness of the formed film is reduced in the valley region, a leak current is likely to occur in the minute region, and the open circuit voltage of the entire element is lowered. However, in the present invention, since the valley region is small, it is considered that the decrease in the open circuit voltage is small.
[0052]
From the above examination results, the range of the ratio of the average distance between the convex vertices of the first transparent conductive film 103a and the average distance between the convex vertices of the film and the substrate is preferably 1: 3. -4: 1, more preferably 1: 2 to 3: 1, optimally 1: 1 to 2: 1. The range of the film thickness is preferably 1 to 100 nm, more preferably 2 to 80 nm, and most preferably 3 to 50 nm.
[0053]
In the present invention, it is very important to control the film formation rate and the film thickness in the step (5) and the step (6) within the above-mentioned specific ranges for the following reasons.
[0054]
As a result of the study by the present inventors, it has been found that the film formation speed and the film thickness greatly affect the unevenness formed in the film.
[0055]
For example, when the film formation rate is high (for example, 10 nm / sec), the amount of sputtered target particles is large, so that the particles are deposited on the substrate in a very short time, and the distance between the apexes of the protrusions is narrow. The height is low.
[0056]
Subsequent film growth is limited to a narrow vertex distance because narrow convex portions mainly grow. As a result, as the film formation progresses and the film thickness increases, the unevenness on the deposited film becomes smoother, and for example, the optimal unevenness when used as a back surface reflective layer of a photovoltaic device can be made. It becomes difficult.
[0057]
On the other hand, when the film formation rate is slow (for example, 1 nm / sec), the amount of the sputtered target particles is small, so that the number of particles deposited on the substrate is small, the distance between the vertices of the protrusions is wide, and the height of the protrusions is It will be expensive. However, even when this film formation rate is slow, the film formation time becomes longer, and when the film thickness becomes thicker than necessary, a convex part is further formed between adjacent convex parts as the convex part grows, and the convex part The distance between the vertices is slightly narrowed, and as a result, the unevenness tends to be slightly gentle. This is because when the film thickness of the first transparent conductive film is greater than 100 nm, the ratio of the average distance between the vertices of the protrusions to the average distance between the vertices of the protrusions of the film and the substrate deviates from the desired range. It can be said that it is necessary to control the film thickness together with the film forming speed, as the conversion efficiency is lowered.
[0058]
Even when the film formation rate is high, if the film that has already been deposited (that is, the underlying layer) is sufficiently uneven, the unevenness tends to become gentle as the film deposition proceeds. Unevenness can be maintained, and the time required for forming the transparent conductive film can be significantly reduced.
[0059]
Therefore, for example, when forming the unevenness necessary for the back surface reflection layer of the photovoltaic element, a certain degree of unevenness is formed by depositing a film having a specific film thickness at a low film formation speed in the first step. Then, by depositing a film on the film deposited in the first step at a high deposition rate in the second step, the necessary irregularities can be formed in the back surface reflection layer of the photovoltaic element in a short time. It becomes possible.
[0060]
From the above examination results, the optimum range of the deposition rate ratio of the first transparent conductive film 103a and the second transparent conductive film 103b in the present invention is preferably 2 to 100, more preferably 5 to 50, and optimally 7. ~ 20.
[0061]
As described above, in the present invention, it is very important to simultaneously control the film forming speed and the film thickness within the optimum range.
[0062]
FIG. 3 shows another example of the cross section of the photovoltaic device according to the present invention. On the substrate 101, a reflective film 102, a transparent conductive film 103 (first process portion (first transparent conductive film) 103a, second process portion ( The second transparent conductive film) 103b, the third process portion (third transparent conductive film) 103c), the semiconductor layer 105, the transparent electrode 106, and the current collecting electrode 107 are sequentially stacked. The back surface reflection film 104 includes a reflection film 102 and a transparent conductive film 103.
[0063]
FIG. 4 shows an example of a manufacturing apparatus for producing the photovoltaic element shown in FIG. 3 on a substrate. Below, an example of the manufacturing method of the photovoltaic element of this invention by this apparatus is demonstrated.
[0064]
(1) The substrate 205 is set on the substrate holder 204, and the film forming chamber 201 is evacuated by a vacuum pump (not shown). The material of the substrate may be a conductive material, an electrically insulating material, or an electrically insulating substrate surface subjected to a conductive treatment. A semiconductor crystal bulk may be used. Moreover, although it may be translucent, such as glass, it is preferable that it has a desired strength with little deformation and distortion, such as metals such as Fe, Ni, Cr, Al or alloys thereof, Thin plates such as stainless steel and composites thereof, and films of heat-resistant synthetic resins such as polyester and polyethylene are preferred.
[0065]
(2) After evacuating the film formation chamber 201 to a predetermined pressure, a source gas supply device (not shown) supplies argon gas from the gas supply pipe 206, and adjusts the opening of an exhaust valve (not shown). Adjust to the prescribed pressure.
[0066]
(3) The substrate holder 204 is rotated by the rotating shaft 203.
[0067]
(4) A plurality of infrared lamps of the heater 202 are turned on and heated to the deposition temperature of the reflective film 102.
[0068]
(5) The DC power supply 211 is put into the target 207 for the reflective film to generate argon plasma, the shutter 215 is opened, and the reflective film 102 is formed. When the reflective film is deposited to a predetermined thickness, the shutter 215 is closed and the DC power supply 211 is turned off. As the material of the reflective film 102, a material having high reflectance is preferable, and gold, silver, copper, aluminum, and alloys thereof are preferable.
[0069]
(6) Next, the heater 202 is set so as to reach the formation temperature of the transparent conductive film. When the temperature reaches a predetermined temperature, the DC power supply 212 is put into the target 208 for the first step of the transparent conductive film, and argon plasma is generated. Occurs, the shutter 216 is opened, and the first process portion (core) 103a of the transparent conductive film is generated. When the nucleus becomes a predetermined size under a predetermined film forming speed condition, the shutter 216 is closed and the DC power supply 212 is turned off.
[0070]
(7) Next, the DC power source 213 is put into the target 209 for the second step of the transparent conductive film, argon plasma is generated, the shutter 217 is opened, and the second step portion 103b of the transparent conductive film is deposited. When the second process portion is deposited by a predetermined thickness under a predetermined film forming speed condition, the shutter 217 is closed and the DC power source 213 is turned off.
[0071]
(8) Next, the DC power source 214 is turned on to the target 210 for the third step of the transparent conductive film, argon plasma is generated, the shutter 218 is opened, and the third step portion 103c of the transparent conductive film is deposited. When the third process portion is deposited to a predetermined thickness under a predetermined film forming speed condition, the shutter 218 is closed and the DC power source 214 is turned off.
[0072]
As a material for the transparent conductive film, a material with high transmittance is preferable, and oxides of zinc, tin, indium, titanium, and composite compounds thereof are preferable. In addition, it is effective in the present invention to introduce oxygen and water vapor together with argon as the sputtering raw material gas for the transparent conductive film as necessary.
[0073]
At this time, irregularities having a size of several hundreds of nanometers can be formed on the surface of the back reflective film 104, and the light confinement effect can be utilized. In FIG. 3, the unevenness is schematically highlighted.
[0074]
As described above, the reflective film 102 and the transparent conductive film 103 (ac) can be continuously formed on the substrate. Furthermore, the semiconductor layer 105 and the transparent electrode 106 are produced using another deposition apparatus, and the current collecting electrode 107 is formed thereon. Further, a protective resin may be provided.
[0075]
The transparent conductive film 103 (ac) manufactured by such a procedure has an uneven surface, and the reflected light is effectively absorbed by the semiconductor layer 105, so that the photoelectric conversion efficiency is improved.
[0076]
In the method of forming the transparent conductive film 103 (ac), the present invention is characterized in that the film formation speed condition is controlled.
[0077]
Specifically, in the first step (6), the first step portion 103a of the transparent conductive film is formed in a short time at a low film formation rate. Thereby, the nucleus used as the origin of the convex part of a transparent conductive film can be finally formed with the desired density.
[0078]
Next, in the second step (7), the second step portion 103b is formed at a high deposition rate. In this step, the nucleus is rapidly grown without impairing the nucleus density formed in the first step. The formation process covers the entire surface of the substrate and the nucleus formed in the first step, that is, the third step (8) is entered at the stage of transition from the nucleus to the film.
[0079]
In the third step, the third step portion 103c is formed at a deposition rate that is faster than the first step and slower than the second step. By setting the film forming speed faster than that in the first step, it is possible to shorten the film forming time of the entire film while suppressing the generation of new nuclei in the film recesses. Further, a dense film quality can be obtained by setting the film forming speed slower than that in the second step.
[0080]
Here, the first step and the second step of the present invention are a nucleation step and a nucleation growth step, respectively, and the formed product is hardly a film. Therefore, in the first step and the second step, the film forming speed is not strictly appropriate. Therefore, the film formation rate in the present invention is defined as the film formation rate (the thickness of the film deposited per unit time) when the entire underlying surface has the same composition as the film. In other words, the deposition rate is when the deposit on the substrate moves from the island-shaped nucleus to the film and the entire deposit grows as a film almost uniformly. This is the film forming speed in the step corresponding to the third step in the present invention. Thereby, the first to third steps can be compared at a general film formation rate. In general, the factors that determine the deposition rate include the voltage and current applied to the target, the composition and concentration of the sputtering gas, the temperature and pressure of the deposition chamber, the composition and surface properties of the target, etc. In this case, it is sufficient that the desired film formation rate can be achieved as a result by appropriately controlling these.
[0081]
As mentioned above, the photoelectric conversion efficiency is further improved by controlling the film formation rate ratio in each step within a specific range, and even when deposited on a flexible substrate, it has excellent adhesion and is resistant to film peeling. Therefore, it is possible to form the back reflective film 104 having an optimal uneven shape, which is dense and excellent in weather resistance and electrical characteristics.
[0082]
Next, the optimum film deposition rate ratio and unevenness relationship in each step of the present invention will be described.
[0083]
As a result of the study by the present inventors, it has been found that the film forming speed condition and the film thickness in the transparent conductive film forming step greatly affect the irregularities finally formed on the film.
[0084]
For example, when the film formation rate is high from the first step, which is a nucleation step (for example, 10 nm / sec or more), since the sputtered target particles are large, the particles are deposited on the substrate in a very short time, and the nuclei High density. Accordingly, the internuclear distance is reduced, and the target particles are dispersed to contribute to nuclear growth, so that the height of the nucleus is low. Thereafter, since the core portion becomes a convex portion as the film is formed, the narrow internuclear distance is maintained as it is as the convex distance between the films. As a result, as the film formation progresses and the film thickness increases, the unevenness on the deposited film becomes smoother, for example, the optimal uneven shape when used as a back surface reflective layer of a photovoltaic device. Becomes difficult. However, even when the film forming speed is high, if the unevenness is already formed on the already deposited base as in the second and third steps of the present invention, the unevenness tends to become gentle as the film deposition proceeds. Although there is, it is possible to maintain a certain uneven shape.
[0085]
In addition, when the film formation rate is high, the time required for depositing the transparent conductive film to a desired film thickness is greatly reduced. However, in terms of the denseness of the film, it is better that the film formation rate is slow, and in particular, the surface of the transparent conductive film in contact with the semiconductor layer as in the third step should have a denser structure. If it is not dense, cracks and the like are likely to occur, and this leads to a decrease in the open-circuit voltage of the entire device due to the leak current. From the viewpoint of adhesion, the transparent conductive film surface should have a dense structure.
[0086]
Furthermore, if the film formation rate is set high by controlling various factors that determine the film formation rate described above, the sputtering discharge does not occur, the short circuit occurs in the middle of the discharge, but the discharge is intermittent, or The discharge may stop as it is. This short-circuit phenomenon refers to a phenomenon in which a voltage abnormally flows during discharge and the discharge becomes unstable, or the discharge is temporarily interrupted. When the short-circuit phenomenon occurs, the film forming speed is reduced, or the film quality is deteriorated due to unevenness in film thickness distribution, defects, and the like. Furthermore, if a short-circuit phenomenon occurs, there is a case where the discharge does not occur without self-recovery, which is a big problem in productivity.
[0087]
Therefore, in the step that greatly affects the formation of the unevenness of the film as in the second step of the present invention, in order to maintain the nucleus density generated in the first step and shift to the film state quickly and in a short time, It is better to set the film forming speed conditions as fast as possible. In the step of depositing until a desired film thickness is not affected as in the third step, there is not much influence on the formation of film irregularities. It is better to set the optimum film forming speed condition in consideration of the stability of the film.
[0088]
On the other hand, when the film formation rate is slow from the first step (for example, 1 nm / sec), the amount of sputtered target particles is small, so that the number of particles deposited on the substrate is small and the nuclear density is low. Therefore, since the internuclear distance is wide and the nuclear growth is concentrated on the generated nuclei, the height of the nuclei is high. However, even when the film formation rate is slow, as the film formation time becomes longer, new nuclei are formed between adjacent nuclei as the nuclei grow, and the internuclear distance becomes narrower. As a result, the unevenness of the film becomes smooth. This tendency becomes prominent when the thickness in the nucleation step (first step) is greater than 100 nm. Further, when the film forming speed is low, it takes time to deposit the transparent conductive film to a desired film thickness, which causes a problem in terms of productivity.
[0089]
In addition, in order to form a film at a stable film formation rate immediately after the start of discharge, it is desirable to use a pre-sputtered target. In a new target, the surface properties of the target change immediately after the start of discharge and immediately before the end of discharge, and the film formation speed condition changes with time. On the other hand, since the surface of the pre-sputtered target is moderately rough from the beginning, the film forming speed conditions can be made substantially the same immediately after the start of discharge and immediately before the end of discharge. The stability of the film formation rate is not a big problem in the first step where the film formation rate is slow or the third step which does not significantly affect the uneven shape of the film even if the film formation rate slightly fluctuates in the film growth step. However, the film forming speed is high, and the effect is large in the second step which is an important step for forming the unevenness of the film.
[0090]
Therefore, for example, when the necessary unevenness is formed on the back surface reflection layer of the photovoltaic element, the following film forming method in which the film forming speed condition is changed for each process is optimal.
[0091]
First, in the first step, nuclei having a specific size are generated under a slow film formation speed condition. Next, in the second step, using a pre-sputtered target, nuclei are rapidly grown under fast film formation speed conditions, and the state is rapidly changed from the nuclear state to the film state while maintaining the nuclear density. Finally, in the third step, a denser film can be formed by forming the film at a slightly slower film forming rate than in the second step. As a whole, the time required for film formation can be shortened, and formation of unevenness and film quality required for the back surface reflection layer of the photovoltaic element can be obtained.
[0092]
As a result of the study by the present inventors, the optimum range of the film formation rate ratio in the second step and the first step and the third step and the first step is preferably 2 to 100, more preferably 5 to 50, and optimally. Is 7-20. In addition, the third step may be any film forming speed condition that is slower than that of the second step, but the optimum range of the film forming rate ratio in the second step and the third step is preferably 1 to 10, more preferably 1 ~ 3, optimally 1.1 ~ 2.
[0093]
The range of the film thickness in the first step is preferably 1 to 100 nm, more preferably 2 to 80 nm, and most preferably 3 to 50 nm. If it is smaller than 1 nm, the function as a nucleus cannot be achieved, and the effect of the present invention cannot be obtained. If it is larger than 100 nm, the nuclear density becomes high, and it is difficult to make the transparent conductive film into a desired uneven shape.
[0094]
The film thickness in the second step is preferably 5 μm or less, more preferably 1 μm or less, and particularly preferably 500 nm or less. With this thickness, the transition from the nucleus state to the film state is almost completed, and the uneven shape, which is the purpose in the second step, can be formed.
[0095]
The film thickness in the third step greatly affects the characteristics of the photovoltaic element as the final form, but is preferably 5 μm or less in consideration of strain resistance, impact resistance and adhesion.
[0096]
Although the batch method is shown here as an example, the present invention is not limited to this method, and can be applied to a method of conveying a long substrate such as a single wafer method or a roll-to-roll method.
[0097]
【Example】
Examples of the present invention will be described below in detail with reference to the drawings. However, the present invention is not limited to these examples.
[0098]
[Example 1]
In this example, a photovoltaic device having the configuration shown in the schematic cross-sectional view of FIG. 1 was prepared using the apparatus of FIG.
[0099]
Specifically, a stainless steel thin substrate 205 was set on the substrate holder 204, and the film formation chamber 201 was evacuated by a vacuum pump (not shown). After evacuating to a predetermined pressure, a source gas supply device (not shown) supplied 30 sccm of argon gas from the gas supply pipe 206, and the opening of an exhaust valve (not shown) was adjusted to adjust the pressure to 0.3 Pa. Then, the substrate holder was rotated by the rotation shaft 203. The heater 202 was set so that the substrate became 100 ° C., and the infrared lamp was turned on to heat the substrate. When a predetermined temperature was reached, the DC power source 211 was turned on, argon plasma was generated in the aluminum target 207 for the reflective film, the shutter 215 was opened, and the reflective film 102 was formed. A reflective film was deposited to about 150 nm, the shutter 215 was closed, and the DC power source 211 was turned off.
[0100]
Next, the heater 202 is set to 200 ° C., and when a predetermined temperature is reached, the DC power supply 212 is turned on, argon plasma is generated in the zinc oxide target 208 for the first transparent conductive film, the shutter 216 is opened, A first transparent conductive film 103a was formed. The first transparent conductive film was deposited at a deposition rate of about 8 nm at 0.5 nm / sec, the shutter 216 was closed, and the DC power source 212 was turned off.
[0101]
Next, the DC power source 213 was turned on, argon plasma was generated in the zinc oxide target 209 for the second transparent conductive film, the shutter 217 was opened, and the second transparent conductive film 103b was formed. The second transparent conductive film was deposited to a thickness of about 1 μm at a deposition rate of 10 nm / sec, the shutter 217 was closed, and the DC power source 213 was turned off.
[0102]
The deposition rate ratio between the first transparent conductive film and the second transparent conductive film was 20. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 60 hitting protrusions. The substrate on which the reflective film and the transparent conductive film were formed was cut into a size of 5 cm × 5 cm, and a semiconductor layer, a transparent conductive film, and an electrode were deposited using another device.
[0103]
[Comparative Example 1]
A photovoltaic device having the configuration shown in FIG. 5 was prepared in the same manner as in Example 1 except that the transparent conductive film in Example 1 was formed under the conditions of the second transparent conductive film. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 140 hitting protrusions.
[0104]
[Evaluation 1]
The initial characteristics of the photovoltaic element obtained in Example 1 (hereinafter referred to as “Sample 1”) and the photovoltaic element obtained in Comparative Example 1 (hereinafter referred to as “Sample Ratio 1”) are solar simulators ( AM1.5, 100mW / cm²The photoelectric conversion efficiency was measured using a surface temperature of 25 ° C.). As a result, it was found that the sample 1 was 1.12 times better than the sample ratio 1.
[0105]
[Example 2]
A photovoltaic device having the structure shown in FIG. 1 was produced in the same manner as in Example 1 except that the film thickness of the second transparent conductive film was changed to about 2 μm in Example 1. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 55 hitting projections.
[0106]
[Comparative Example 2]
A photovoltaic device having the configuration shown in FIG. 5 was produced in the same manner as in Example 2 except that the transparent conductive film in Example 2 was formed under the conditions of the second transparent conductive film. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 130 hitting protrusions.
[0107]
[Evaluation 2]
Evaluation was performed in the same manner as the measurement in Example 1 and Comparative Example 1. As a result, it was found that the photovoltaic element obtained in Example 2 was excellent in photoelectric conversion efficiency like the photovoltaic element obtained in Example 1.
[0108]
Example 3
In this example, a photovoltaic device having the configuration shown in the schematic cross-sectional view of FIG. 1 was prepared using the apparatus of FIG.
[0109]
After the apparatus of FIG. 6 is opened to the atmosphere for maintenance or the like, the roll-shaped substrate 402 is set in the substrate delivery chamber 401, and the reflective film production chamber 405 and the transparent conductive film production chambers 406, 07, 408, 409, 410, 411 The substrate 404 was penetrated through each of these, and fixed to the roll 414 of the substrate winding chamber 416. As the substrate 404, SUS430 was used in which unevenness was left on the surface having a width of 120 mm, a thickness of 0.15 mm, and a length of 150 m by a dull finish.
[0110]
Then, it exhausted until the pressure became 0.1 Pa or less. Thereafter, argon gas is supplied as an inert gas from the gas supply pipes 450, 451, 452, 453, 454, 455, 456 to the reflective film manufacturing chamber 405 and the transparent conductive film manufacturing chambers 406, 407, 408, 409, 410, 411. 30 sccm of each was supplied. Also, 30 sccm of argon gas was supplied to the gate 415. In this state, the opening of an exhaust valve (not shown) was adjusted to keep the pressure in the vacuum chamber at 0.3 Pa.
[0111]
Heater units 440, 441, 442, 443, 444, 445, and 446, each having a set of six 100 W infrared lamps, are formed in the reflective film production chamber 405 and the transparent conductive film production chambers 406, 407, 408, 409, 410, and 411 It was provided with a stainless steel reflector, and a thermocouple was brought into contact with the back surface of the film-forming surface of the substrate, and the temperature was controlled to 200 ° C. and heating was performed.
[0112]
Subsequently, the servo motor was operated to rotate the take-up roll 217, and the conveyance of the substrate 404 was started.
[0113]
An aluminum target having a purity of 99.99% by weight and 25 cm × 25 cm was used as the target 420 for producing the reflective film, and power from the DC power source 430 was applied thereto to generate argon plasma, thereby depositing the reflective film. While the substrate 404 passed over the target 420, the aluminum reflective film 102 was deposited by about 150 nm.
[0114]
The substrate 404 was subsequently transferred to the first transparent conductive film manufacturing chamber 406. A first transparent conductive film 103a was formed at 0.5 nm / sec by supplying power from a DC power source 431 to a zinc oxide target 421 having a purity of 99.99 wt% and a size of 25 cm × 25 cm to generate argon plasma.
[0115]
Subsequently, the substrate 404 was transferred to the second transparent conductive film manufacturing chambers 407, 408, 409, 410, and 411. Using a zinc oxide target 422, 423, 424, 425, 426 with a purity of 99.99% by weight and a size of 25 cm × 25 cm, power is supplied from DC power sources 432, 433, 434, 435, 436, respectively, to generate argon plasma. Then, the second transparent conductive film 103b was formed at 10 nm / sec. The film thickness of the back reflecting film 104 was about 1 μm. At this time, the transparent conductive film was formed in the surface shape shown in FIG.
[0116]
The substrate 404 manufactured up to the transparent conductive film was wound up in the winding chamber 416. In order to prevent the surface of the transparent conductive film from being damaged, a polyester film interleaf 413 was sandwiched between the substrates during winding.
[0117]
The deposition rate ratio between the first transparent conductive film and the second transparent conductive film was 20. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 60 hitting protrusions. The substrate on which the reflective film and the transparent conductive film were formed was cut into a size of 5 cm × 5 cm, and a semiconductor layer, a transparent conductive film, and an electrode were deposited using another device.
[0118]
[Comparative Example 3]
A photovoltaic device having the structure shown in FIG. 5 was produced in the same manner as in Example 3 except that the transparent conductive film in Example 3 was formed under the conditions of the second transparent conductive film. When the substrate on which the reflective film and the transparent conductive film are formed is confirmed by AFM, it is 25 μm.²There were about 140 hitting protrusions.
[0119]
[Evaluation 3]
The initial characteristics of the photovoltaic element obtained in Example 3 (hereinafter referred to as “Sample 3”) and the photovoltaic element obtained in Comparative Example 3 (hereinafter referred to as “Sample Ratio 3”) are solar simulators ( AM1.5, 100mW / cm²The photoelectric conversion efficiency was measured using a surface temperature of 25 ° C.). As a result, it was found that Sample 3 was 1.12 times better than Sample Ratio 3.
[0120]
Example 4
In this example, a photovoltaic device having the configuration shown in the schematic cross-sectional view of FIG. 3 was produced using the apparatus of FIG.
[0121]
Specifically, the stainless steel substrate 205 was set on the substrate holder 204, and the film formation chamber 201 was evacuated by a vacuum pump (not shown). After evacuating to a predetermined pressure, a source gas supply device (not shown) supplied 30 sccm of argon gas from the gas supply pipe 206, and the opening of an exhaust valve (not shown) was adjusted to adjust the pressure to 0.3 Pa. The substrate holder was rotated by the rotating shaft 203.
[0122]
The heater 202 was set so that the substrate became 100 ° C., and the infrared lamp was turned on to heat the substrate. When a predetermined temperature was reached, power from the DC power source 211 was applied to the aluminum target 207 for the reflective film to generate argon plasma, the shutter 215 was opened, and the reflective film 102 was formed. A reflective film was deposited to about 150 nm, the shutter 215 was closed, and the DC power source 211 was turned off.
[0123]
Next, the heater 202 is set to 200 ° C., and when the temperature reaches a predetermined temperature, power from the DC power supply 212 is applied to the zinc oxide target 208 for the first step of the transparent conductive film to generate argon plasma. The shutter 216 was opened to form a nucleus (a first process portion 103a of the transparent conductive film). The film formation rate in the first step was 0.5 nm / sec. The film formation rate refers to the film formation rate when the base is a zinc oxide film. When the nucleus generated in the first step reached a height of about 8 nm, the shutter 216 was closed and the DC power source 212 was turned off.
[0124]
Next, power from the DC power source 213 was applied to the zinc oxide target 209 for the second step, argon plasma was generated, the shutter 217 was opened, and the second step portion 103b of the transparent conductive film was formed. Here, the pre-sputtered zinc oxide target 209 for the second step was used. The film formation speed in the second step was 10 nm / sec, the state shifted from the nuclear state to the film state, a transparent conductive film was deposited by about 150 nm, the shutter 217 was closed, and the DC power source 213 was turned off. The film formation rate ratio between the second step and the first step was 20.
[0125]
Next, power from the DC power source 214 was applied to the zinc oxide target 210 for the third step, argon plasma was generated, the shutter 218 was opened, and the third step portion 103c of the transparent conductive film was formed. The film formation rate in the third step was 8 nm / sec, and the entire transparent conductive film was deposited by about 1.5 μm, the shutter 218 was closed, and the DC power source 214 was turned off. The film formation rate ratio between the third step and the first step was 16.
[0126]
By the above method, the substrate on which the reflective film 102 and the transparent conductive films 103 (a to c) are formed is cut into a size of 5 cm × 5 cm, and the semiconductor layer 105, the transparent conductive film 106, and the collecting electrode 107 are cut with another device. Deposited.
[0127]
Example 5
In this example, the photovoltaic device having the configuration shown in the schematic cross-sectional view of FIG. 3 was produced using the apparatus of FIG.
[0128]
After the apparatus of FIG. 6 is opened to the atmosphere for maintenance or the like, the roll-shaped substrate 402 is set in the substrate delivery chamber 401, and the reflective film production chamber 405 and the transparent conductive film production chambers 406, 407, 408, 409, 410, 411 are set. Each of the substrates 404 is penetrated and fixed to the roll 414 of the substrate winding chamber 416. As the substrate 404, SUS430 was used in which unevenness was left on the surface having a width of 120 mm, a thickness of 0.15 mm, and a length of 150 m by a dull finish.
[0129]
Subsequently, the film production chamber was evacuated until the pressure became 0.1 Pa or less. Thereafter, argon gas is supplied as an inert gas from the gas supply pipes 450, 451, 452, 453, 454, 455, 456 to the reflective film manufacturing chamber 405 and the transparent conductive film manufacturing chambers 406, 407, 408, 409, 410, 411. 30 sccm of each was supplied. In this state, the opening of an unillustrated exhaust valve was adjusted to keep the pressure in each film production chamber at 0.3 Pa.
[0130]
Stainless steel heater units 440, 441, 442, 443, 444, 445, and 446, each set of six 100W infrared lamps in the reflective film production chamber 405 and the transparent conductive film production chambers 406, 407, 408, 409, 410, and 411, are stainless steel. A thermocouple was brought into contact with the back surface of the film-forming surface of the substrate, and the temperature was controlled to 200 ° C. to heat the substrate.
[0131]
Subsequently, the servo motor 417 was operated, the take-up roll 414 was rotated, and the conveyance of the substrate 404 was started.
[0132]
An aluminum target having a purity of 99.99% by weight and 25 cm × 25 cm was used as the target 420 for producing the reflective film. Electric power from the DC power source 430 was applied to the target 420 to generate argon plasma, and the reflective film 102 was deposited. Thereby, the aluminum reflective film 102 was formed to about 150 nm while the substrate 404 passed over the target 420.
[0133]
The substrate 404 was subsequently transferred to the manufacturing chamber 406 corresponding to the first step of the transparent conductive film. The first step is performed with a pre-sputtered zinc oxide target 421 having a purity of 99.99 wt% and a size of 25 cm × 25 cm by applying power from a DC power source 431 to generate argon plasma and forming a film at a deposition rate of 0.5 nm / sec. Part 103a was formed. While the substrate 404 passed over the target 421, zinc oxide nuclei grew to a height of about 8 nm.
[0134]
Subsequently, the substrate 404 was transferred to a manufacturing chamber 407 corresponding to the second step of the transparent conductive film. Electric power from a DC power source 432 was applied to a zinc oxide target 422 having a purity of 99.99 wt% and 25 cm × 25 cm to generate argon plasma, and the second process portion 103b was formed under a film forming speed condition of 10 nm / sec. While the substrate 404 passed over the target 422, the zinc oxide film grew to a thickness of about 100 nm.
[0135]
Next, the substrate 404 was transferred to the manufacturing chambers 408, 409, 410, and 411 corresponding to the third step of the transparent conductive film. Using a zinc oxide target 423, 424, 425, 426 having a purity of 99.99% by weight and a size of 25 cm × 25 cm, power is supplied from the DC power sources 433, 434, 435, 436, respectively, and argon plasma is generated. The third process portion 103c was formed under the film forming speed condition of sec. When the third step was completed, the film thickness of the back reflecting film 104 was about 1.5 μm.
[0136]
The substrate 404 on which the back surface reflection film 104 (the reflection film 102 and the transparent conductive films 103a to 103c) was formed was wound in the winding chamber 416. The interleaf paper 413 made of a polyester film was sandwiched between the substrates at the time of winding so as not to damage the surface of the transparent conductive film.
[0137]
In this example, the deposition rate ratio between the second step and the first step of the transparent conductive film was 20, and the deposition rate ratio between the third step and the first step was 16.
[0138]
By the above method, the substrate on which the back surface reflection film 104 was formed was cut into a size of 5 cm × 5 cm, and the semiconductor layer 105, the transparent conductive film 106, and the collecting electrode 107 were deposited using another device.
[0139]
Example 6
In the formation of the transparent conductive film in Example 4, a photovoltaic device having the configuration shown in FIG. 3 was produced in the same manner as in Example 4 except that the third step was formed under the conditions of the second step.
[0140]
Example 7
In the formation of the transparent conductive film in Example 4, the transparent conductive film is formed by using a new target instead of the target pre-sputtered in the second step, and shown in FIG. A photovoltaic device having the structure was fabricated.
[0141]
[Comparative Example 4]
In the formation of the transparent conductive film in Example 4, a photovoltaic device having the configuration shown in FIG. 3 was produced in the same manner as in Example 4 except that all the steps were formed under the conditions of the second step.
[0142]
[Comparative Example 5]
In the formation of the transparent conductive film in Example 4, the photovoltaic element having the structure shown in FIG. 3 was formed in the same manner as in Example 4 except that the film forming speed condition in the first step was 0.08 nm / sec. Was made.
[0143]
[Comparative Example 6]
In the formation of the transparent conductive film in Example 5, a photovoltaic element having the configuration shown in FIG. 3 was produced in the same manner as in Example 5 except that all the steps were formed under the conditions of the second step.
[0144]
[Evaluation 4]
The initial characteristics of the photovoltaic devices prepared in Examples 4 to 7 and Comparative Examples 4 to 6 are solar simulators (AM1.5, 100 mW / cm).²Table 2 shows the results of measuring the photoelectric conversion efficiency using a surface temperature of 25 ° C. The evaluation of the photoelectric conversion efficiency is based on the photoelectric conversion efficiency of Example 4 when the relative value is 1.00, ◯ when 0.95 or more and less than 1.00, or 0.90 or more and 0.95. Less than 0 was evaluated as Δ, and less than 0.90 was evaluated as ×.
[0145]
[Table 2]

[0146]
As is clear from Table 2, when the film formation speed condition deviates from the conditions of the present invention as in Comparative Examples 4, 5, and 6, the photoelectric conversion efficiency is significantly reduced.
[0147]
Further, when the third step is under the same film formation speed condition as that of the second step as in Example 6, the photoelectric conversion efficiency is lower than that in Example 4. Therefore, it can be seen that a more excellent effect can be obtained by making the film formation rate in the third step slower than the second film formation rate.
[0148]
Further, when a new target is used in the second step as in the seventh embodiment, the photoelectric conversion efficiency is lower than that in the fourth embodiment. Therefore, it can be seen that a more excellent effect can be obtained by using a pre-sputtered target in the second step.
[0149]
【The invention's effect】
As described above, according to a preferred embodiment of the present invention, the deposition rate ratio between the first transparent conductive film and the second transparent conductive film when the reflective film, the first transparent conductive film, and the second transparent conductive film are formed. By managing the above, the film formation speed of the transparent conductive film is increased, and it becomes possible to create a deposited film with good photoelectric conversion efficiency. From this, it becomes possible to produce a low-cost and highly reliable photovoltaic element, which contributes to the full-scale spread of solar cells for system power.
[0150]
Moreover, according to the manufacturing method of the transparent conductive film concerning the suitable Example of this invention, in the formation process of a transparent conductive film, by managing the film-forming speed | rate conditions of each process, (1) of a photovoltaic device It has an optimal surface shape as a back reflecting film, (2) the formation speed of the transparent conductive film is high, and (3) a transparent conductive film having a dense film quality can be formed. And by using this transparent conductive film, it is possible to produce a photovoltaic device with good photoelectric conversion efficiency and high reliability at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of a cross-sectional structure of a photovoltaic device according to the present invention.
FIG. 2 is a schematic view showing an example of a production apparatus for producing the photovoltaic element of the present invention on a substrate.
FIG. 3 is a schematic view showing another example of the cross-sectional structure of the photovoltaic device according to the present invention.
FIG. 4 is a schematic view showing another example of a production apparatus for producing the photovoltaic element of the present invention on a substrate.
FIG. 5 is a schematic view showing a cross-sectional structure of a photovoltaic element of a comparative example.
FIG. 6 is a schematic view showing an example of a roll-to-roll manufacturing apparatus for producing the photovoltaic element of the present invention on a long substrate.
FIG. 7 is an explanatory diagram showing a relationship between a film formation rate ratio and photoelectric conversion efficiency in an experimental example of the present invention.
[Explanation of symbols]
101 substrate
102 Reflective film
103a 1st transparent conductive film (1st process part)
103b Second transparent conductive film (second process part)
103c 3rd transparent conductive film (3rd process part)
104 Back reflective film
105 Semiconductor film
106 Transparent electrode
107 Current collecting electrode
201 Deposition chamber
202 heater
203 Rotating shaft
204 Substrate holder
205 substrates
206 Gas supply pipe
207-210 target
211-214 Power supply
215-218 shutter
219 Plasma
301 substrate
302 reflective film
303 Transparent conductive film
304 Back surface reflective film
305 Semiconductor film
306 Transparent electrode
307 Current collecting electrode
401 Substrate delivery chamber
402 Roll substrate
403 Roller
404 substrate
405 Reflection film creation room
406 to 411 Transparent conductive film creation room
416 Winding room
414 Roll substrate
412 Steering roller
413 slip sheet
420-426 target
430-436 power supply
440-446 Heater
415 Magnet Roller
450-456 gas supply pipe
460 vacuum pump

Claims (10)

In a method of forming a transparent conductive film having crystallinity on a substrate by sputtering ,
A first step of forming a film at a first film formation rate and a second step of forming a film at a second film formation rate;
2 ≦ (second film formation rate) / (first film formation rate) ≦ 100
Meet the,
The method for forming a transparent conductive film, wherein a film thickness in the first step is 1 to 100 nm .   2. The transparent conductive film according to claim 1, wherein a nucleus is formed on the substrate in the first step, and a transparent conductive film is formed covering the entire surface of the substrate surface and the surface of the nucleus in the second step. Method for forming a film. The method for forming a transparent conductive film according to claim 1 or 2, characterized in that the deposition thickness at the second step and 5μm or less. The method for forming a transparent conductive film according to claim 1 or 2, characterized in that the deposition thickness at the second step and 1μm or less. The ratio of the average distance between the vertices of the convex portions of the transparent conductive film formed in the first step and the average distance between the vertices of the convex portions and the substrate is 1: 3 to 4: 1. the method for forming a transparent conductive film according to any one of claims 1 to 4, characterized in that the first step. The method for forming a transparent conductive film according to any one of claims 1 to 5, characterized in that a transparent conductive film using a roll-to-roll method for transporting spanned a long substrate between the rolls . A third step of forming a transparent conductive film at a third film formation rate after the second step, and the relationship between the film formation rates of the respective steps is
2 <(second film formation rate) / (first film formation rate) ≦ 100
2 ≦ (third deposition rate) / (first deposition rate) <100
(Second film formation rate)> (Third film formation rate)
The method for forming a transparent conductive film according to any one of claims 1 to 6 and satisfies the. The method for forming a transparent conductive film according to claim 7 , wherein a film thickness in the third step is 5 μm or less. In the second step, the method of forming the transparent conductive film according to any one of claims 1 to 8, characterized by using a target made of pre-sputtering. Forming a transparent conductive film by the method according to any one of claims 1 to 9, a manufacturing method of a photovoltaic device which comprises a step of forming a semiconductor layer.

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