JP4222500B2 - Silicon-based thin film photoelectric conversion device - Google Patents

Silicon-based thin film photoelectric conversion device Download PDF

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JP4222500B2
JP4222500B2 JP2002100664A JP2002100664A JP4222500B2 JP 4222500 B2 JP4222500 B2 JP 4222500B2 JP 2002100664 A JP2002100664 A JP 2002100664A JP 2002100664 A JP2002100664 A JP 2002100664A JP 4222500 B2 JP4222500 B2 JP 4222500B2
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photoelectric conversion
thin film
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JP2003298088A (en
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裕子 多和田
丞 福田
憲治 山本
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Kaneka Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、薄膜光電変換装置の変換効率の改善に関するもので、特に電極層または光電変換ユニット間に配置する光散乱層に関するものである。
【０００２】
【従来の技術】
近年、例えば多結晶シリコンや微結晶シリコンのような結晶質シリコンを含む薄膜を利用した光電変換装置の開発が精力的に行われている。これらの光電変換装置の開発では、安価な基板上に低温プロセスで良質の結晶質シリコン薄膜を形成することによる低コスト化と高効率化の両立が目的となっている。こうした光電変換装置は、太陽電池、光センサなど、さまざまな用途への応用が期待されている。
【０００３】
光電変換装置の一例として、基板上に、透明電極と、一導電型層、結晶質シリコン系光電変換層および逆導電型層を含む光電変換ユニットと、光反射性金属層を含む裏面電極とを順次形成した構造を有するものが知られている。この光電変換装置では、光電変換層が薄いと光吸収係数の小さな長波長領域の光が十分に吸収されないため、光電変換量は本質的に光電変換層の膜厚によって制約を受ける。そこで、光電変換層を含む光電変換ユニットに入射した光をより有効に利用するために、光入射側の透明電極に表面凹凸（表面テクスチャ）構造を設けて光を光電変換ユニット内へ散乱させ、さらに金属電極で反射した光を乱反射させる工夫がなされている。
【０００４】
また、薄膜光電変換装置の変換効率を高めるための他の手段として、裏面金属層と薄膜半導体層の間に適当な光学的性質を有する透明層を介在させ、多重干渉効果により裏面金属反射層の反射率を高める方法がある。例えば、薄膜半導体層と金属層との間に透明層として酸化亜鉛（ＺｎＯ）を介在させる場合がある。
【０００５】
さらに、金属層と透明層の２層からなる裏面反射層に、テクスチャ構造を組み合わせることも知られていた。
【０００６】
【発明が解決しようとする課題】
入射した光を散乱させることを目的に、光入射側透明電極の表面凹凸の深さを大きくした場合、その上に形成する導電型層であるｐ層の膜厚に分布ができ、開放電圧（Ｖｏｃ）が低下する。また、光電変換層として結晶質シリコンを用いた薄膜光電変換装置の場合は、凹凸の深さが大きいと、凹部から結晶粒界が発生しやすくなり、光電変換層の膜質の低下や内部短絡を起こしやすくなってしまう等の問題点があった。
【０００７】
また、裏面金属反射層の反射率を高めるために介在させる透明層についても表面凹凸が形成されていれば、光閉じ込め効果が得られる。しかし、基板上に直接形成する電極の場合とは異なり、薄膜光電変換ユニット上に形成する場合は、形成方法や温度条件等の制約から、所望の表面凹凸構造を高い精度で形成することは難しかった。
【０００８】
【課題を解決するための手段】
本発明者等は上記課題に鑑み鋭意検討を行った結果、光入射側から順に、透光性基板、透光性導電酸化物電極層、シリコン系光電変換ユニット、光散乱層、および光反射性金属電極層を含み、その光散乱層が第一の透明導電性薄膜と透明絶縁性薄膜と第二の透明導電性薄膜を含んで構成されており、第一の透明導電性薄膜および第二の透明導電性薄膜は透明導電性酸化物である酸化亜鉛を含んで形成されており、透明絶縁性薄膜は前記酸化亜鉛に比べて小さな屈折率を有する絶縁性材料である酸化珪素を含み、１ｎｍ以上５０ｎｍ以下の範囲内の厚さを有するとともに３０％以上７０％以下の表面被覆率を生じるように分散させられている薄膜光電変換装置を見出した。
【０００９】
また、光散乱層と光反射性金属電極層との間にもう一つの光電変換ユニットを含む膜光電変換装置をも見出した。
【００１０】
この様な構成によれば、光散乱層の必要な導電性と光散乱を両立させて、光電変換ユニットの光吸収量を増加させることが可能となり、より高い光電変換効率を有する光電変換装置を提供することが可能となる。
【００１２】
本発明の薄膜光電変換装置に用いられる光電変換ユニットとしては、少なくとも１つの結晶質シリコン系光電変換ユニットを含むことが好ましい。
【００１５】
【発明の実施の形態】
本発明の一つの実施の形態による薄膜光電変換装置の模式的な断面図を図１に示す。以下、図１を用いて本発明を詳細に説明するが、本発明はこれに限定されるものではない。
【００１６】
図１に示す薄膜光電変換装置は、透明基板１上に第一の電極層２（通常、透明電極が使用される）、光電変換ユニット１０、第二の電極層が形成されている。ここで、第二の電極層は、光散乱層３と光反射性金属層４から構成されており（必要に応じ他の層を介在させることも可能である）、特に図１においては光散乱層３は、更に第一の透明導電性薄膜３ａ、透明絶縁性薄膜３ｂ、第二の透明導電性薄膜３ｃから形成されている。図１の薄膜光電変換装置は、透明基板１側から入射する光５を光電変換ユニット１０により光電変換するものである。
【００１７】
透明基板１は、ガラスやフィルム等が用いられるが、光電変換層へより多くの太陽光を透過し吸収させるために、できるだけ透明であることが好ましい。同様の意図から、太陽光が入射する基板表面での光反射ロスを低減させるために無反射コーティングを行うと高効率化が図れる。
【００１８】
第一の電極層２としては、透明導電性酸化物（ＴＣＯ）が用いられ、例えば酸化錫（ＳｎＯ2）からなる平均粒径が２００〜９００ｎｍの表面凹凸を有する導電性の膜が熱ＣＶＤ法により形成される。ＴＣＯとしては、ＳｎＯ2、インジウム錫酸化物（ＩＴＯ）、酸化亜鉛（ＺｎＯ）などが用いられる。第一の電極層２は単層構造でも多層構造であってもよい。この第一の電極層２は光電変換装置の光入射側に位置することから、基板同様に透明であることが好ましく、例えば透明基板１と第一の電極層２をあわせた層の透過率は、５００〜１１００ｎｍの波長の光に対して８０％以上であることが好ましい。
【００１９】
第一の電極層２上には、光電変換ユニット１０が形成される（但し、必ずしも直接第一の電極層に接触している必要はない）。特に光電変換ユニット１０としては、結晶質シリコン系光電変換ユニットであることが好ましい。光電変換ユニット１０は図示したように１つでもよいが、２つ以上積層してもよい。なお、本願明細書における、「結晶質」，「微結晶」との用語は、部分的に非晶質を含むものも含むものとする。また、本願明細書における「結晶質シリコン系光電変換ユニット」との用語は、真性光電変換層１０２が結晶質であることを意味するものであり、一導電型層１０１、逆導電型層１０３が結晶質でもそうでなくてもよいものとする。
【００２０】
図１に示す光電変換ユニット１０は、一導電型層１０１、真性光電変換層１０２および逆導電型層１０３を有している。一導電型層１０１はｐ型層でもｎ型層でもよく、これに対応して逆導電型層１０３はｎ型層またはｐ型層になる。ただし、通常の光電変換装置では光の入射側にｐ型層が配置されるので、一般的に一導電型層１０１はｐ型層、逆導電型層１０３はｎ型層である。通常、ｐ型層やｎ型層の導電型層は光電変換ユニット内に拡散電位を生じさせる役割を果たし、この拡散電位の大きさによって薄膜光電変換装置の特性の一つである開放端電圧（Ｖｏｃ）が左右される。しかし、これらの導電型層は光電変換には寄与しない不活性な層であり、導電型層にドープされた不純物によって吸収される光は基本的に発電に寄与しない。従って、ｐ層やｎ層の導電型層の膜厚は、十分な拡散電位を生じさせる範囲内で可能な限り薄くすることが好ましい。
【００２１】
光電変換ユニット１０として結晶質シリコン系薄膜光電変換ユニットが形成される場合は、ｐｉｎ型の順に基板温度を４００℃以下とした低温のプラズマＣＶＤ法により各半導体層を積層して形成することが好ましい。具体的には、例えば導電型決定不純物原子であるボロンが０．０１原子％以上ドープされたｐ型微結晶シリコン系層１０１、光電変換層となる真性結晶質シリコン層１０２、および導電型決定不純物原子であるリンが０．０１原子％以上ドープされたｎ型微結晶シリコン系層１０３をこの順に堆積すればよい。しかし、これら各層は上記に限定されず、例えばｐ型層として非晶質シリコン膜や、非晶質または微結晶のシリコンカーバイド、シリコンゲルマニウムなどの合金材料を用いてもよい。なお、導電型（ｐ型、ｎ型）微結晶シリコン系層の膜厚は３ｎｍ以上１００ｎｍ以下が好ましく、５ｎｍ以上５０ｎｍ以下がさらに好ましい。
【００２２】
また、「シリコン系」の材料には、非晶質または結晶質のシリコンに加え、非晶質または結晶質のシリコンカーバイドやシリコンゲルマニウムなど、シリコンを５０％以上含む半導体材料も該当するものとする。
【００２３】
真性光電変換層１０２である結晶質シリコン光電変換層は、一般的に４００℃以下の低温で形成することにより、結晶粒界や粒内における欠陥を終端させて不活性化させる水素原子を多く含む。この観点から、光電変換層１０２の水素含有量は１〜３０原子％の範囲内にあることが好ましい。この層は、導電型決定不純物原子の密度が１×１０18ｃｍ-3以下で、実質的に真性半導体薄膜として形成される。さらに、真性結晶質シリコン層に含まれる結晶粒の多くは、第一の電極層側から柱状に延びて成長し、その膜面に平行に（１１０）の優先配向面を有することが好ましい。なぜなら、このような結晶配向を有する結晶質シリコン薄膜は、第一の電極層（透明電極）２の表面が実質的に平坦である場合でも、その上に堆積される光電変換ユニットの表面は微細な凹凸を含む表面テクスチャ構造を示す。更に、第一の電極層（透明電極）２の表面が凹凸を含む表面テクスチャ構造を有する場合、光電変換ユニットの表面は、第一の電極層（透明電極）２の表面に比べて凹凸の粒径の小さなテクスチャ構造が生じるため、広範囲の波長領域の光を反射させるのに適した光閉じ込め効果の大きな構造となり好ましい。また、真性結晶質シリコン層の膜厚は０．１μｍ以上１０μｍ以下が好ましい。ただし、薄膜光電変換ユニット１０としては、太陽光の主波長域（４００〜１２００ｎｍ）に吸収を有するものが好ましいため、真性結晶質シリコン層に代えて、合金材料である非晶質シリコンカーバイド層（例えば１０原子％以下の炭素を含有する非晶質シリコンからなる非晶質シリコンカーバイド層）や非晶質シリコンゲルマニウム層（例えば３０原子％以下のゲルマニウムを含有する非晶質シリコンからなる非晶質シリコンゲルマニウム層）を形成してもよい。
【００２４】
図１では、以上のようにして光電変換ユニット１０を形成した後、本発明の特徴となる光散乱層３が形成されており、更に光散乱層３は、第一の透明導電性薄膜３ａと透明絶縁性薄膜３ｂと第二の透明導電性薄膜３ｃから形成されている。光電変換ユニットにおける光吸収を高めるためには、光散乱層において効率よく光散乱が行われることが重要である。この為には光散乱層に、光電変換ユニット構成材料の屈折率に対し、よりかけ離れた値の屈折率を有する材料を配置することが好ましく、特に屈折率１．７以下の材料を用いることが好ましい。具体的には、ＳｉＯ2、ＭｇＦ2、ＣａＦ2等を積層するのが好ましく、この中でも、屈折率が小さく、かつ太陽光の主波長領域で光吸収が少ない透明材料であるＳｉＯ2（屈折率約１．５）が好適である。また、これらの光散乱性の高い材料は、光が光電変換ユニットを透過してから、光散乱を受けて再度光電変換ユニットに入射するまでの間に光が吸収されてしまう割合を低くする為、より光電変換ユニットに近い側、特に界面に近い位置に配置することが有利である。
【００２５】
一方、電極の一部である光散乱層には、膜厚方向に電流を流す必要があるため、上記の屈折率１．７以下の材料が比較的絶縁性の高い材料、即ち透明絶縁性薄膜３ｂである場合には、これら材料に特定の配置を取らせる必要があり、例えば表面被覆率を制御することで、膜厚方向の電流の流れを確保することができる。特に、膜厚方向の電流の流れの確保と光散乱の程度の関係から、表面被覆率は３０〜７０％、より好ましくは５０〜７０％であることが好ましい。この様な方法は、屈折率１．７以下の材料として、ＳｉＯ2を使用する際に有効である。また、同様の理由、更に生産性の点から、例えばＳｉＯ2の様な透明絶縁性薄膜の膜厚は１〜５０ｎｍが好ましく、５〜３０ｎｍがより好ましい。
【００２６】
また、光散乱層３に適度な導電性を持たせるために、前記透明絶縁性薄膜３ｂ以外に、透明導電性薄膜を配置させることが好ましい。透明導電性薄膜自体にも光散乱層としての機能を持たせるには、屈折率が２程度の透明導電性酸化物薄膜、例えばＺｎＯ、ＳｎＯ2、ＩＴＯ等により形成するのが好ましく、透明絶縁性薄膜（例えばＳｉＯ2）を透明導電性酸化物層で挟む構造とすることがより好ましい。光散乱層３全体としては、３０〜１５０ｎｍの範囲内の厚さであることが好ましく、５０〜１１０ｎｍがより好ましい。これよりも薄すぎれば、十分な光散乱効果と多重干渉効果が得られず、逆に厚すぎれば光散乱層内での吸収ロスによる影響が発生する。良好な導電性を確保するために光電変換ユニット１０と透明絶縁性薄膜３ｂとの間に透明導電性薄膜３ａを形成する場合、透明導電性薄膜３ａの厚さは５ｎｍ以上が好ましいが、無くてもよい。
【００２７】
光散乱層３を光電変換ユニット１０上に形成させる方法は特に限定されないが、下地となる光電変換ユニット１０にダメージが少なく低温で形成できる方法が望ましい。例えば、２００℃以下の条件でスパッタ法やＭＯＣＶＤ法により形成することが好ましい。特に、光電変換ユニット１０上に直接形成する透明導電性薄膜３ａは、ＭＯＣＶＤ法によって形成することが好適である。
【００２８】
光反射性金属層４としては、Ａｌ、Ａｇ、Ａｕ、Ｃｕ、ＰｔおよびＣｒから選ばれる少なくとも一つの材料からなる少なくとも一層を配置することが好ましく、その形成方法としてはスパッタ法または蒸着法が利用できる。
【００２９】
本発明のもう一つの実施の形態によるハイブリッド型薄膜光電変換装置の模式的な断面図を図２に示すが、本発明はこれに限定されるものではない。
【００３０】
図２に示す薄膜光電変換装置は、透明基板１上に、第一の電極層（通常、透明電極が使用される）２、第一の光電変換ユニット２０、透明導電性薄膜６ａ、透明絶縁性薄膜６ｂ、透明導電性薄膜６ｃからなる光散乱層６、第二の光電変換ユニット２１、透明導電層７、及び光反射性金属層４が順次積層された構造を有している。
【００３１】
光電変換ユニットは図示したように２つでもよいが、３つ以上積層してもよい。また、３つ以上の光電変換ユニットを積層した場合、光散乱層６は各光電変換ユニット間に形成されてもよいが、１層でもよい。
【００３２】
２つ以上の光電変換ユニットを積層した薄膜光電変換装置（通常、タンデム型薄膜光電変換装置と呼ばれる）では、光電変換装置の光入射側に大きなバンドギャップを有する光電変換ユニットを配置し、その後ろに順に小さなバンドギャップを有する（例えばＳｉ−Ｇｅ合金の）光電変換ユニットを配置することにより、入射光の広い波長範囲にわたって光電変換を可能にし、これによって装置全体としての変換効率の向上が図られる。タンデム型薄膜光電変換装置の中でも、非晶質光電変換ユニットと結晶質光電変換ユニットを積層したものはハイブリッド型薄膜光電変換装置と称されるが、この場合には、上記の理由から、第一の光電変換ユニットとして非晶質光電変換ユニットを配置し、第二の光電変換ユニットとして結晶質光電変換ユニットを配置することが好ましい。
【００３３】
図２の第一の光電変換ユニット２０として非晶質シリコン系光電変換ユニットを形成し、第二の光電変換ユニット２１として結晶質シリコン系薄膜光電変換ユニットを形成する場合には、いずれもｐｉｎ型の順に基板温度を４００℃以下とした低温のプラズマＣＶＤ法により形成することが好ましい。
【００３４】
中間層として用いられる光散乱層６は、光散乱層６に到達した光の一部を光散乱層６よりも光入射側に位置する光電変換ユニット（例えば第一の光電変換ユニット２０）へ反射させ、残りの光を後方に位置する光電変換ユニット（例えば第二の光電変換ユニット２１）へ透過させる役割を果たす。光散乱層において効率よく光散乱させる為には光散乱層に、光電変換ユニット構成材料の屈折率に対し、よりかけ離れた値の屈折率を有する材料を配置することが好ましく、特に屈折率１．７以下の材料を用いることが好ましい。具体的には、ＳｉＯ2、ＭｇＦ2、ＣａＦ2等を積層するのが好ましく、この中でも、屈折率が小さく、かつ太陽光の主波長領域で光吸収が少ない透明材料であるＳｉＯ2（屈折率約１．５）が好適である。
【００３５】
一方、光散乱層６には、膜厚方向に電流を流す必要があるため、上記の屈折率１．７以下の材料が比較的絶縁性の高い材料、即ち透明絶縁性薄膜６ｂである場合には、これら材料に特定の配置を取らせる必要があり、例えば表面被覆率を制御することで、膜厚方向の電流の流れを確保することができる。特に、膜厚方向の電流の流れの確保と光散乱の程度の関係から、表面被覆率は３０〜７０％、より好ましくは５０〜７０％であることが好ましい。この様な方法は、屈折率１．７以下の材料として、ＳｉＯ2を使用する際に有効である。
【００３６】
また、光散乱層６に適度な導電性を持たせるために、前記透明絶縁性薄膜６ｂ以外に、透明導電性薄膜を配置させることが好ましい。透明導電性薄膜自体にも光散乱層としての機能を持たせるには、屈折率が２程度の透明導電性酸化物薄膜、例えばＺｎＯ、ＳｎＯ2、ＩＴＯ等により形成するのが好ましく、透明絶縁性薄膜（例えばＳｉＯ2）を透明導電性酸化物層で挟む構造とすることがより好ましい。光散乱層６全体としては、第二の電極層の一部として用いる場合よりも薄い１０〜１００ｎｍの範囲３０〜１５０ｎｍの範囲内の厚さであることが好ましく、２０〜７０ｎｍがより好ましい。これよりも薄すぎれば、十分な光散乱効果と多重干渉効果が得られず、逆に厚すぎれば光散乱層内での吸収ロスによる影響が発生する。
【００３７】
第二の光電変換ユニット２１上には、透明導電層７と光反射性金属層４からなる第二の電極層が形成される。透明導電層７の代わりに、図１で用いた光散乱層を適用しても構わない。
【００３８】
本説明では、基板側から光を入射する構造を採用しているが、逆に基板上に第二の電極層、光電変換ユニットを形成した後に第一の電極層を形成するような構造であってもよい。
【００３９】
【実施例】
以下、本発明を比較例とともにいくつかの実施例に基づいて詳細に説明するが、本発明はその趣旨を超えない限り以下の記載例に限定されるものではない。
【００４０】
（実施例１）
実施例１として、図１に示される薄膜光電変換装置で、特に光電変換ユニットが結晶質シリコン系光電変換ユニットであるものを作製した。
【００４１】
厚み１．１ｍｍ、１２７ｍｍ角のガラス基板１上に、第一の電極層（透明電極）２として厚さ８００ｎｍのピラミッド状ＳｎＯ2膜を熱ＣＶＤ法にて形成した。得られた第一の電極層（透明電極）２のシート抵抗は約９Ω／□であった。この第一の電極層（透明電極）２の上に、厚さ１５ｎｍのｐ型微結晶シリコン層１０１、厚さ２．０μｍの真性結晶質シリコン光電変換層１０２、及び厚さ１５ｎｍのｎ型微結晶シリコン層１０３からなる結晶質シリコン光電変換ユニット１０を順次プラズマＣＶＤ法で形成した。結晶質シリコン光電変換ユニットを形成した後、基板を大気中に取り出し、光散乱層３の第一の透明導電性薄膜３ａとしてＭＯＣＶＤ法により１５０℃の温度で厚さ５ｎｍのＺｎＯ膜を形成した。ＭＯＣＶＤ法にて形成する際、ドーパントとしてＢ2Ｈ6ガスを用いた。続いて、透明絶縁性薄膜３ｂとしてスパッタ法により１５０℃の温度で厚さ４ｎｍのＳｉＯ2膜を形成した。この時、表面被覆率を制御するために、直径２ｍｍの穴を多数あけたメタルマスクを用いた。ＳｉＯ2の被覆率は、５０％であった。その後、第二の透明導電性薄膜３ｃとして、３ａと同様に厚さ８０ｎｍのＺｎＯ膜を形成した。
【００４２】
最後に、第二の電極層４として厚さ３００ｎｍのＡｇをスパッタ法にて形成した。
【００４３】
以上のようにして得られた結晶質シリコン系薄膜光電変換装置（受光面積１ｃｍ2）にＡＭ１．５の光を１００ｍＷ／ｃｍ2の光量で照射して出力特性を測定したところ、開放電圧（Ｖｏｃ）が０．５２Ｖ、短絡電流密度（Ｊｓｃ）が２４．７ｍＡ／ｃｍ2、曲線因子（Ｆ．Ｆ．）が７０．４％、そして変換効率が９．０４％であった。
【００４４】
（実施例２〜８）
実施例２〜８においても、実施例１と同様に結晶質シリコン系薄膜光電変換装置を作製した。ただし、実施例１と異なるのは、光散乱層３の透明導電性薄膜３ａ及び透明絶縁性薄膜３ｂの膜厚、透明絶縁性薄膜３ｂの表面被覆率である。
【００４５】
実施例１と同様に、それぞれの実施例にて得られた結晶質シリコン系薄膜光電変換装置（受光面積１ｃｍ2）の各出力特性を測定した。得られた結果を表１に示す。
【００４６】
（比較例１）
比較例１として、図１における光散乱層３の代わりに単一の透明導電層を形成した結晶質シリコン系薄膜光電変換装置を作製した。単一の透明導電層として、ＭＯＣＶＤ法により１５０℃の温度で厚さ１００ｎｍのＺｎＯ膜を形成した。ＭＯＣＶＤ法にて形成する際、ドーパントとしてＢ2Ｈ6ガスを用いた。その他の構成については、実施例１と同様にして作製し、同様の出力特性測定を行った。得られた結果を表１に示す。
【００４７】
【表１】

Figure 0004222500
【００４８】
表１の結果より、実施例１〜８はいずれも比較例１に比べ、ＪｓｃおよびＥｆｆ．ともに向上している。
【００４９】
実施例１〜４は、透明絶縁性薄膜３ｂの膜厚を変化させているが、膜厚が厚くなるにつれてＪｓｃの値も増加している。透明絶縁性薄膜３ｂは厚いほど光散乱効果が大きくなることから、入射光は光電変換ユニットとの界面近傍にある屈折率の最も小さな透明絶縁性薄膜３ｂで反射、散乱されていると考えられる。そのため、透明導電性薄膜と光反射性金属層の界面での反射が主である比較例１に比べて、透明導電性薄膜内での吸収ロスも減少していると考えられる。一方、透明絶縁性薄膜３ｂの膜厚は厚くなるにつれて、若干ではあるがＦ．Ｆ．が低下する傾向が見られる。これは透明絶縁性薄膜３ｂが厚くなったことにより、光散乱層の導電性が低下したと考えられる。従って、実施例１〜４の場合は、透明絶縁性薄膜３ｂの膜厚が１０ｎｍのときにＪｓｃとＦ．Ｆ．のバランスがとれ、最もＥｆｆ．が高くなっている。
【００５０】
実施例５は、光電変換ユニット上に形成される透明導電性薄膜３ａの膜厚を薄くしたものである。実施例６は、透明導電性薄膜３ａを挿入せず、更に透明絶縁性薄膜３ｂの表面被覆率を３０％にしたものである。表１には示していないが、透明絶縁性薄膜３ｂの表面被覆率が５０％のままで、透明導電性薄膜３ａを挿入しないものは、Ｆ．Ｆ．が大幅に低下し、比較例１よりもＥｆｆ．が低いものとなった。従って、透明導電性薄膜３ａの膜厚は５ｎｍ以上が好ましい。実施例６より、透明導電性薄膜３ａを挿入しない場合は、透明絶縁性薄膜３ｂの膜厚を薄くし、更に表面被覆率を低下させることにより、Ｆ．Ｆ．は維持できるる。しかし、光散乱効果を得るためには、表面被覆率３０％以上が好ましい。
【００５１】
実施例３、７および８の比較から、透明絶縁性薄膜３ｂでの光反射効果を有効に得るためには、透明絶縁性薄膜３ｂの表面被覆率が５０％以上であることが好ましい。また、屈折率が最も小さな透明絶縁性薄膜３ｂの不連続性が光散乱効果を高めているとも考えられるので、５０〜７０％の表面被覆率が好ましい。
【００５２】
（実施例９）
実施例９としては、図２に示されるようなハイブリッド型薄膜光電変換装置を作製した。実施例１で用いた第一の電極層（透明電極）２付きガラス基板上に、厚さ１５ｎｍのｐ型非晶質シリコンカーバイド層２０１、厚さ０．２５μｍの真性非晶質シリコン光電変換層２０２、及び厚さ１５ｎｍのｎ型微結晶シリコン層２０３を順次プラズマＣＶＤ法で形成した。続いて、光散乱層６を実施例１と同様の方法にて形成した。ただし、ＺｎＯからなる透明導電性薄膜６ａは１０ｎｍ、ＳｉＯ2からなる透明絶縁性薄膜６ｂは１０ｎｍ、ＺｎＯからなる透明導電性薄膜６ｃは１０ｎｍの膜厚とした。引き続き、プラズマＣＶＤ法にて、厚さ１５ｎｍのｐ型微結晶シリコン層２１１、厚さ２．０μｍの真性結晶質シリコン光電変換層２１２、及び厚さ１５ｎｍのｎ型微結晶シリコン層２１３を順次形成した。その後、透明導電層７として厚さ９０ｎｍのＺｎＯと、光反射性金属層４として厚さ３００ｎｍのＡｇをスパッタ法にて順次形成した。
【００５３】
実施例１と同様の方法にて、得られたハイブリッド型薄膜光電変換装置（受光面積１ｃｍ2）の出力特性を測定したところ、Ｖｏｃが１．３４Ｖ、Ｊｓｃが１２．１ｍＡ／ｃｍ2、Ｆ．Ｆ．が７２．４％、そして変換効率が１１．７％であった。
【００５４】
（比較例２）
比較例２においては、実施例９と同様の手順にて非晶質シリコン光電変換ユニットを形成した後、基板を大気中に取り出し、光散乱層６の代わりにスパッタ法にて１５０℃の温度で厚さ３０ｎｍのＺｎＯ膜を形成した以外は同じ方法でハイブリッド型薄膜光電変換装置を作製した。
【００５５】
以上のようにして得られたシリコン系薄膜光電変換装置（受光面積１ｃｍ2）を、実施例１と同様の方法にて出力特性したところ、Ｖｏｃが１．３２Ｖ、Ｊｓｃが１１．７ｍＡ／ｃｍ2、Ｆ．Ｆ．が７１．８％、そして変換効率が１１．１％であった。
【００５６】
実施例９は比較例２に比べ、Ｊｓｃが上昇している。これは中間層として、光散乱層を挿入したことにより、入射光が光散乱層内で不連続に介在する低屈折率層にて一部光入射側に位置する光電変換ユニットに反射され光入射側に位置する光電変換ユニットの感度が上昇したこと、および光散乱層よりも後方に位置する光電変換ユニットにも光散乱層で吸収されること無く透過した光が光散乱層と裏面電極間で散乱し、効率よく吸収されたことによると考えられる。また、実施例９では、光散乱層形成時に光電変換ユニットへのダメージが少ないＭＯＣＶＤ法を使用したため、ＶｏｃおよびＦ．Ｆ．が向上したと考えられる。
【００５７】
【発明の効果】
以上詳細に説明したように、本発明の薄膜光電変換装置によれば、光電変換ユニットと光反射性金属電極層との間に光散乱層を挿入することにより、変換効率を改善することができる。光散乱層は、第一の透明導電性薄膜と透明絶縁性薄膜と第二の透明導電性薄膜を含んで構成されており、透明導電性薄膜は透明導電性酸化物である酸化亜鉛を含んで形成されているために、透明導電性薄膜自体にも光散乱層としての機能を持たせることができる。また、透明絶縁性薄膜は酸化亜鉛に比べて小さな屈折率を有する絶縁性材料である酸化珪素が、１ｎｍ以上５０ｎｍ以下の範囲内の厚さを有するとともに、３０％以上７０％以下の表面被覆率を生じるように分散させられているために、必要な導電性と光散乱を両立することが可能となる。この様な構成によれば、光電変換ユニットの光吸収量を増加させることが可能となり、より高い光電変換効率を有する光電変換装置を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明に係る薄膜光電変換装置の一例を示す断面図。
【図２】本発明に係るハイブリッド型薄膜光電変換装置の一例を示す断面図。
【符号の説明】
１ 透明基板
２ 第一の電極層
１０ 光電変換ユニット
１０１ 一導電型層
１０２ 真性光電変換層
１０３ 逆導電型層
３ 光散乱層
３ａ 第一の透明導電性薄膜
３ｂ 透明絶縁性薄膜
３ｃ 第二の透明導電性薄膜
４ 光反射性金属層
５ 太陽光
２０ 第一の光電変換ユニット
２０１ 一導電型層
２０２ 真性光電変換層
２０３ 逆導電型層
２１ 第二の光電変換ユニット
２１１ 一導電型層
２１２ 真性光電変換層
２１３ 逆導電型層
６ 光散乱層
６ａ 透明導電性酸化物層
６ｂ 絶縁性酸化物層
６ｃ 透明導電性酸化物層
７ 透明導電層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in conversion efficiency of a thin film photoelectric conversion device, and particularly relates to a light scattering layer disposed between electrode layers or photoelectric conversion units.
[0002]
[Prior art]
In recent years, for example, photoelectric conversion devices using thin films containing crystalline silicon such as polycrystalline silicon and microcrystalline silicon have been vigorously developed. The development of these photoelectric conversion devices aims to achieve both cost reduction and high efficiency by forming a high-quality crystalline silicon thin film on an inexpensive substrate by a low temperature process. Such photoelectric conversion devices are expected to be applied to various uses such as solar cells and optical sensors.
[0003]
As an example of a photoelectric conversion device, on a substrate, a transparent electrode, a photoelectric conversion unit including a one-conductivity type layer, a crystalline silicon-based photoelectric conversion layer, and a reverse conductivity type layer, and a back electrode including a light-reflective metal layer What has the structure formed sequentially is known. In this photoelectric conversion device, if the photoelectric conversion layer is thin, light in a long wavelength region with a small light absorption coefficient is not sufficiently absorbed, and thus the photoelectric conversion amount is essentially limited by the film thickness of the photoelectric conversion layer. Therefore, in order to more effectively use the light incident on the photoelectric conversion unit including the photoelectric conversion layer, a surface unevenness (surface texture) structure is provided on the transparent electrode on the light incident side to scatter the light into the photoelectric conversion unit, Furthermore, the device which diffusely reflects the light reflected by the metal electrode is made.
[0004]
Further, as another means for increasing the conversion efficiency of the thin film photoelectric conversion device, a transparent layer having appropriate optical properties is interposed between the back surface metal layer and the thin film semiconductor layer, and the back surface metal reflective layer is formed by the multiple interference effect. There are ways to increase reflectivity. For example, zinc oxide (ZnO) may be interposed as a transparent layer between the thin film semiconductor layer and the metal layer.
[0005]
Furthermore, it has also been known to combine a texture structure with a back surface reflection layer composed of two layers, a metal layer and a transparent layer.
[0006]
[Problems to be solved by the invention]
In order to scatter incident light, when the depth of the surface unevenness of the light incident side transparent electrode is increased, the thickness of the p layer, which is a conductive type layer formed thereon, can be distributed, and the open circuit voltage ( Voc) decreases. In addition, in the case of a thin film photoelectric conversion device using crystalline silicon as the photoelectric conversion layer, if the depth of the unevenness is large, a crystal grain boundary is likely to be generated from the concave portion, which causes deterioration of the film quality of the photoelectric conversion layer and internal short circuit. There were problems such as being easy to wake up.
[0007]
Moreover, if the surface unevenness | corrugation is formed also about the transparent layer interposed in order to raise the reflectance of a back surface metal reflective layer, the light confinement effect will be acquired. However, unlike the case of an electrode formed directly on a substrate, it is difficult to form a desired surface concavo-convex structure with high accuracy when it is formed on a thin film photoelectric conversion unit due to restrictions on the formation method and temperature conditions. It was.
[0008]
[Means for Solving the Problems]
  As a result of intensive studies in view of the above problems, the present inventors, in order, from the light incident side, a translucent substrate, a translucent conductive oxide electrode layer, a silicon-based photoelectric conversion unit, a light scattering layer, and a light reflectivity A light scattering layer comprising a metal electrode layerIncludes a first transparent conductive thin film, a transparent insulating thin film, and a second transparent conductive thin film, and the first transparent conductive thin film and the second transparent conductive thin film are transparent conductive oxides. The transparent insulating thin film is formed by containing zinc oxide which isInsulating material with a smaller refractive index than zinc oxideContains silicon oxide, 1nm or more5030% or more with a thickness in the range of nm or less70A thin-film photoelectric conversion device that has been dispersed so as to produce a surface coverage of less than or equal to 50% has been found.
[0009]
  Also,Another photoelectric conversion unit is included between the light scattering layer and the light reflective metal electrode layerMembrane photoelectric conversion deviceAlsoI found it.
[0010]
  According to such a configuration,By combining the necessary conductivity and light scattering of the light scattering layer,The light absorption amount of the photoelectric conversion unit can be increased, and a photoelectric conversion device having higher photoelectric conversion efficiency can be provided.
[0012]
The photoelectric conversion unit used in the thin film photoelectric conversion device of the present invention preferably includes at least one crystalline silicon-based photoelectric conversion unit.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic cross-sectional view of a thin film photoelectric conversion device according to one embodiment of the present invention. Hereinafter, the present invention will be described in detail with reference to FIG. 1, but the present invention is not limited thereto.
[0016]
In the thin film photoelectric conversion device shown in FIG. 1, a first electrode layer 2 (usually a transparent electrode is used), a photoelectric conversion unit 10, and a second electrode layer are formed on a transparent substrate 1. Here, the second electrode layer is composed of a light scattering layer 3 and a light reflective metal layer 4 (other layers can be interposed as required), and in particular in FIG. The layer 3 is further formed of a first transparent conductive thin film 3a, a transparent insulating thin film 3b, and a second transparent conductive thin film 3c. The thin-film photoelectric conversion device of FIG. 1 performs photoelectric conversion of light 5 incident from the transparent substrate 1 side by a photoelectric conversion unit 10.
[0017]
The transparent substrate 1 is made of glass, film, or the like, but is preferably as transparent as possible in order to transmit and absorb more sunlight into the photoelectric conversion layer. For the same purpose, high efficiency can be achieved by applying an anti-reflective coating to reduce the light reflection loss on the substrate surface on which sunlight is incident.
[0018]
As the first electrode layer 2, a transparent conductive oxide (TCO) is used, for example, tin oxide (SnO).2The conductive film having surface irregularities having an average particle diameter of 200 to 900 nm is formed by a thermal CVD method. As TCO, SnO2Indium tin oxide (ITO), zinc oxide (ZnO), or the like is used. The first electrode layer 2 may have a single layer structure or a multilayer structure. Since the first electrode layer 2 is located on the light incident side of the photoelectric conversion device, the first electrode layer 2 is preferably transparent like the substrate. For example, the transmittance of the combined layer of the transparent substrate 1 and the first electrode layer 2 is 80% or more with respect to light having a wavelength of 500 to 1100 nm.
[0019]
The photoelectric conversion unit 10 is formed on the first electrode layer 2 (however, it is not always necessary to be in direct contact with the first electrode layer). In particular, the photoelectric conversion unit 10 is preferably a crystalline silicon photoelectric conversion unit. Although the photoelectric conversion unit 10 may be one as illustrated, two or more may be stacked. In the specification of the present application, the terms “crystalline” and “microcrystal” include those partially including amorphous. In addition, the term “crystalline silicon-based photoelectric conversion unit” in this specification means that the intrinsic photoelectric conversion layer 102 is crystalline, and the one conductivity type layer 101 and the reverse conductivity type layer 103 are It may be crystalline or not.
[0020]
A photoelectric conversion unit 10 illustrated in FIG. 1 includes a one-conductivity type layer 101, an intrinsic photoelectric conversion layer 102, and a reverse conductivity type layer 103. The one conductivity type layer 101 may be a p-type layer or an n-type layer, and the opposite conductivity type layer 103 becomes an n-type layer or a p-type layer correspondingly. However, since a p-type layer is disposed on the light incident side in a normal photoelectric conversion device, the one-conductivity type layer 101 is generally a p-type layer, and the reverse conductivity type layer 103 is an n-type layer. Usually, the p-type layer and the n-type conductive layer play a role of generating a diffusion potential in the photoelectric conversion unit, and an open-end voltage (one of the characteristics of the thin film photoelectric conversion device) depending on the magnitude of the diffusion potential ( Voc) is affected. However, these conductive layers are inactive layers that do not contribute to photoelectric conversion, and light absorbed by impurities doped in the conductive layers basically does not contribute to power generation. Accordingly, it is preferable that the film thickness of the p-type and n-type conductive layers be as thin as possible within a range that generates a sufficient diffusion potential.
[0021]
When a crystalline silicon-based thin film photoelectric conversion unit is formed as the photoelectric conversion unit 10, it is preferable to stack and form each semiconductor layer by a low-temperature plasma CVD method in which the substrate temperature is 400 ° C. or lower in order of the pin type. . Specifically, for example, a p-type microcrystalline silicon layer 101 doped with 0.01 atomic% or more of boron, which is a conductivity type determining impurity atom, an intrinsic crystalline silicon layer 102 to be a photoelectric conversion layer, and a conductivity type determining impurity An n-type microcrystalline silicon layer 103 doped with 0.01 atomic% or more of phosphorus, which is an atom, may be deposited in this order. However, these layers are not limited to the above. For example, an amorphous silicon film, an amorphous or microcrystalline silicon carbide, or an alloy material such as silicon germanium may be used as the p-type layer. Note that the film thickness of the conductive (p-type, n-type) microcrystalline silicon-based layer is preferably 3 nm to 100 nm, and more preferably 5 nm to 50 nm.
[0022]
In addition to amorphous or crystalline silicon, “silicon-based” materials also include semiconductor materials containing 50% or more of silicon, such as amorphous or crystalline silicon carbide and silicon germanium. .
[0023]
The crystalline silicon photoelectric conversion layer, which is the intrinsic photoelectric conversion layer 102, generally contains a large number of hydrogen atoms that are deactivated by terminating defects in crystal grain boundaries and grains by being formed at a low temperature of 400 ° C. or lower. . From this viewpoint, the hydrogen content of the photoelectric conversion layer 102 is preferably in the range of 1 to 30 atomic%. This layer has a conductivity type determining impurity atom density of 1 × 1018cm-3In the following, it is substantially formed as an intrinsic semiconductor thin film. Further, most of the crystal grains contained in the intrinsic crystalline silicon layer preferably grow in a columnar shape from the first electrode layer side and have a (110) preferential orientation plane parallel to the film surface. This is because the crystalline silicon thin film having such a crystal orientation has a fine surface of the photoelectric conversion unit deposited thereon even when the surface of the first electrode layer (transparent electrode) 2 is substantially flat. The surface texture structure including various irregularities is shown. Furthermore, when the surface of the first electrode layer (transparent electrode) 2 has a surface texture structure including irregularities, the surface of the photoelectric conversion unit is more irregular than the surface of the first electrode layer (transparent electrode) 2. Since a texture structure having a small diameter is generated, a structure having a large light confinement effect suitable for reflecting light in a wide wavelength range is preferable. The film thickness of the intrinsic crystalline silicon layer is preferably 0.1 μm or more and 10 μm or less. However, since the thin film photoelectric conversion unit 10 preferably has absorption in the main wavelength region (400 to 1200 nm) of sunlight, an amorphous silicon carbide layer (alloy material) is used instead of the intrinsic crystalline silicon layer ( For example, an amorphous silicon carbide layer made of amorphous silicon containing 10 atomic% or less of carbon or an amorphous silicon germanium layer (for example, amorphous made of amorphous silicon containing 30 atomic% or less of germanium) A silicon germanium layer) may be formed.
[0024]
In FIG. 1, after the photoelectric conversion unit 10 is formed as described above, the light scattering layer 3 that is a feature of the present invention is formed, and the light scattering layer 3 further includes the first transparent conductive thin film 3a and It is formed from a transparent insulating thin film 3b and a second transparent conductive thin film 3c. In order to enhance light absorption in the photoelectric conversion unit, it is important that light scattering is performed efficiently in the light scattering layer. For this purpose, it is preferable to dispose a material having a refractive index far away from the refractive index of the constituent material of the photoelectric conversion unit in the light scattering layer, and in particular, use a material having a refractive index of 1.7 or less. preferable. Specifically, SiO2, MgF2, CaF2Of these, SiO is a transparent material having a low refractive index and low light absorption in the dominant wavelength region of sunlight.2(Refractive index of about 1.5) is preferred. In addition, these highly light-scattering materials reduce the proportion of light that is absorbed between the time when light passes through the photoelectric conversion unit and the time after receiving light scattering and entering the photoelectric conversion unit again. It is advantageous to dispose it at a position closer to the photoelectric conversion unit, particularly at a position close to the interface.
[0025]
On the other hand, since it is necessary to pass an electric current through the light scattering layer which is a part of the electrode in the film thickness direction, the material having a refractive index of 1.7 or less is a material having a relatively high insulating property, that is, a transparent insulating thin film. In the case of 3b, it is necessary to make these materials have a specific arrangement. For example, by controlling the surface coverage, a current flow in the film thickness direction can be ensured. In particular, the surface coverage is preferably from 30 to 70%, more preferably from 50 to 70%, from the relationship between securing the flow of current in the film thickness direction and the degree of light scattering. In such a method, as a material having a refractive index of 1.7 or less, SiO 22It is effective when using. Further, from the same reason and also from the viewpoint of productivity, for example, SiO2The thickness of the transparent insulating thin film as described above is preferably 1 to 50 nm, and more preferably 5 to 30 nm.
[0026]
In order to give the light scattering layer 3 appropriate conductivity, it is preferable to arrange a transparent conductive thin film in addition to the transparent insulating thin film 3b. In order to give the transparent conductive thin film itself a function as a light scattering layer, a transparent conductive oxide thin film having a refractive index of about 2, such as ZnO, SnO, etc.2It is preferable to form the transparent insulating thin film (for example, SiO2) Is more preferably sandwiched between transparent conductive oxide layers. The light scattering layer 3 as a whole preferably has a thickness in the range of 30 to 150 nm, more preferably 50 to 110 nm. If it is too thin, sufficient light scattering effect and multiple interference effect cannot be obtained. Conversely, if it is too thick, an influence due to absorption loss in the light scattering layer occurs. When the transparent conductive thin film 3a is formed between the photoelectric conversion unit 10 and the transparent insulating thin film 3b in order to ensure good conductivity, the thickness of the transparent conductive thin film 3a is preferably 5 nm or more. Also good.
[0027]
The method for forming the light scattering layer 3 on the photoelectric conversion unit 10 is not particularly limited, but a method that can be formed at a low temperature with little damage to the photoelectric conversion unit 10 as a base is desirable. For example, it is preferably formed by sputtering or MOCVD under conditions of 200 ° C. or lower. In particular, the transparent conductive thin film 3a formed directly on the photoelectric conversion unit 10 is preferably formed by the MOCVD method.
[0028]
As the light reflective metal layer 4, it is preferable to dispose at least one layer made of at least one material selected from Al, Ag, Au, Cu, Pt and Cr, and a sputtering method or a vapor deposition method is used as the formation method. it can.
[0029]
FIG. 2 shows a schematic cross-sectional view of a hybrid thin film photoelectric conversion device according to another embodiment of the present invention, but the present invention is not limited to this.
[0030]
The thin film photoelectric conversion device shown in FIG. 2 has a first electrode layer (usually a transparent electrode is used) 2, a first photoelectric conversion unit 20, a transparent conductive thin film 6a, and a transparent insulating material on a transparent substrate 1. The light scattering layer 6 comprising the thin film 6b, the transparent conductive thin film 6c, the second photoelectric conversion unit 21, the transparent conductive layer 7, and the light reflective metal layer 4 are sequentially laminated.
[0031]
Although two photoelectric conversion units may be used as illustrated, three or more photoelectric conversion units may be stacked. When three or more photoelectric conversion units are stacked, the light scattering layer 6 may be formed between the photoelectric conversion units, but may be a single layer.
[0032]
In a thin film photoelectric conversion device in which two or more photoelectric conversion units are stacked (usually called a tandem type thin film photoelectric conversion device), a photoelectric conversion unit having a large band gap is arranged on the light incident side of the photoelectric conversion device, and behind that By arranging photoelectric conversion units (for example, Si-Ge alloy) having a small band gap in order, photoelectric conversion can be performed over a wide wavelength range of incident light, thereby improving the conversion efficiency of the entire apparatus. . Among tandem-type thin film photoelectric conversion devices, a laminate of an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit is called a hybrid thin film photoelectric conversion device. It is preferable to dispose an amorphous photoelectric conversion unit as the photoelectric conversion unit and a crystalline photoelectric conversion unit as the second photoelectric conversion unit.
[0033]
When an amorphous silicon-based photoelectric conversion unit is formed as the first photoelectric conversion unit 20 in FIG. 2 and a crystalline silicon-based thin film photoelectric conversion unit is formed as the second photoelectric conversion unit 21, both are of the pin type. The substrate is preferably formed by a low-temperature plasma CVD method in which the substrate temperature is 400 ° C. or lower.
[0034]
The light scattering layer 6 used as the intermediate layer reflects a part of the light reaching the light scattering layer 6 to a photoelectric conversion unit (for example, the first photoelectric conversion unit 20) located on the light incident side of the light scattering layer 6. The remaining light is transmitted through a photoelectric conversion unit (for example, the second photoelectric conversion unit 21) located behind. In order to efficiently scatter light in the light scattering layer, it is preferable to dispose a material having a refractive index far away from the refractive index of the constituent material of the photoelectric conversion unit in the light scattering layer. It is preferable to use a material of 7 or less. Specifically, SiO2, MgF2, CaF2Of these, SiO is a transparent material having a low refractive index and low light absorption in the dominant wavelength region of sunlight.2(Refractive index of about 1.5) is preferred.
[0035]
On the other hand, since it is necessary to pass an electric current through the light scattering layer 6 in the film thickness direction, when the material having a refractive index of 1.7 or less is a relatively highly insulating material, that is, the transparent insulating thin film 6b. These materials need to have a specific arrangement. For example, by controlling the surface coverage, a current flow in the film thickness direction can be secured. In particular, the surface coverage is preferably from 30 to 70%, more preferably from 50 to 70%, from the relationship between securing the flow of current in the film thickness direction and the degree of light scattering. In such a method, as a material having a refractive index of 1.7 or less, SiO 22It is effective when using.
[0036]
In order to give the light scattering layer 6 appropriate conductivity, it is preferable to dispose a transparent conductive thin film in addition to the transparent insulating thin film 6b. In order to give the transparent conductive thin film itself a function as a light scattering layer, a transparent conductive oxide thin film having a refractive index of about 2, such as ZnO, SnO, etc.2It is preferable to form the transparent insulating thin film (for example, SiO2) Is more preferably sandwiched between transparent conductive oxide layers. The light scattering layer 6 as a whole preferably has a thickness within the range of 10 to 100 nm, 30 to 150 nm, and more preferably 20 to 70 nm, compared with the case where the light scattering layer 6 is used as a part of the second electrode layer. If it is too thin, sufficient light scattering effect and multiple interference effect cannot be obtained. Conversely, if it is too thick, an influence due to absorption loss in the light scattering layer occurs.
[0037]
On the second photoelectric conversion unit 21, a second electrode layer composed of the transparent conductive layer 7 and the light reflective metal layer 4 is formed. The light scattering layer used in FIG. 1 may be applied instead of the transparent conductive layer 7.
[0038]
In this description, a structure in which light is incident from the substrate side is adopted. Conversely, the structure is such that the first electrode layer is formed after the second electrode layer and the photoelectric conversion unit are formed on the substrate. May be.
[0039]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated in detail based on some Examples with a comparative example, this invention is not limited to the following description examples, unless the meaning is exceeded.
[0040]
Example 1
As Example 1, a thin-film photoelectric conversion device shown in FIG. 1 was produced, in particular, the photoelectric conversion unit being a crystalline silicon-based photoelectric conversion unit.
[0041]
A pyramid-shaped SnO having a thickness of 800 nm as a first electrode layer (transparent electrode) 2 on a glass substrate 1 having a thickness of 1.1 mm and 127 mm square.2A film was formed by a thermal CVD method. The sheet resistance of the obtained first electrode layer (transparent electrode) 2 was about 9Ω / □. On this first electrode layer (transparent electrode) 2, a p-type microcrystalline silicon layer 101 having a thickness of 15 nm, an intrinsic crystalline silicon photoelectric conversion layer 102 having a thickness of 2.0 μm, and an n-type microcrystalline silicon layer having a thickness of 15 nm. Crystalline silicon photoelectric conversion units 10 composed of the crystalline silicon layer 103 were sequentially formed by a plasma CVD method. After forming the crystalline silicon photoelectric conversion unit, the substrate was taken out into the atmosphere, and a ZnO film having a thickness of 5 nm was formed as a first transparent conductive thin film 3a of the light scattering layer 3 at a temperature of 150 ° C. by MOCVD. B as a dopant when forming by MOCVD2H6Gas was used. Subsequently, SiO 4 having a thickness of 4 nm is formed at a temperature of 150 ° C. by sputtering as the transparent insulating thin film 3b.2A film was formed. At this time, in order to control the surface coverage, a metal mask having many holes with a diameter of 2 mm was used. SiO2The coverage of was 50%. Thereafter, a ZnO film having a thickness of 80 nm was formed as the second transparent conductive thin film 3c in the same manner as 3a.
[0042]
Finally, Ag having a thickness of 300 nm was formed as the second electrode layer 4 by sputtering.
[0043]
The crystalline silicon-based thin film photoelectric conversion device obtained as described above (light receiving area of 1 cm)2) AM1.5 light 100mW / cm2When the output characteristics were measured by irradiating with an amount of light, the open circuit voltage (Voc) was 0.52 V, and the short circuit current density (Jsc) was 24.7 mA / cm.2The fill factor (FF) was 70.4% and the conversion efficiency was 9.04%.
[0044]
(Examples 2 to 8)
In Examples 2 to 8, crystalline silicon-based thin film photoelectric conversion devices were produced in the same manner as in Example 1. However, the difference from Example 1 is the film thickness of the transparent conductive thin film 3a and the transparent insulating thin film 3b of the light scattering layer 3, and the surface coverage of the transparent insulating thin film 3b.
[0045]
Similar to Example 1, the crystalline silicon-based thin film photoelectric conversion device (light receiving area 1 cm) obtained in each example2) Was measured. The obtained results are shown in Table 1.
[0046]
(Comparative Example 1)
As Comparative Example 1, a crystalline silicon thin film photoelectric conversion device in which a single transparent conductive layer was formed instead of the light scattering layer 3 in FIG. As a single transparent conductive layer, a ZnO film having a thickness of 100 nm was formed at a temperature of 150 ° C. by MOCVD. B as a dopant when forming by MOCVD2H6Gas was used. Other configurations were produced in the same manner as in Example 1, and the same output characteristic measurement was performed. The obtained results are shown in Table 1.
[0047]
[Table 1]
Figure 0004222500
[0048]
From the results shown in Table 1, Examples 1 to 8 are all Jsc and Eff. Both have improved.
[0049]
In Examples 1 to 4, although the film thickness of the transparent insulating thin film 3b is changed, the value of Jsc increases as the film thickness increases. Since the light scattering effect increases as the transparent insulating thin film 3b becomes thicker, it is considered that incident light is reflected and scattered by the transparent insulating thin film 3b having the smallest refractive index in the vicinity of the interface with the photoelectric conversion unit. Therefore, it is considered that the absorption loss in the transparent conductive thin film is also reduced as compared with Comparative Example 1 in which reflection at the interface between the transparent conductive thin film and the light reflective metal layer is the main. On the other hand, as the film thickness of the transparent insulating thin film 3b increases, F. F. There is a tendency to decrease. This is considered that the conductivity of the light-scattering layer was lowered due to the thick transparent insulating thin film 3b. Therefore, in Examples 1-4, when the film thickness of the transparent insulating thin film 3b is 10 nm, Jsc and F.E. F. Is balanced, the most Eff. Is high.
[0050]
In Example 5, the transparent conductive thin film 3a formed on the photoelectric conversion unit is thinned. In Example 6, the transparent conductive thin film 3a was not inserted, and the surface coverage of the transparent insulating thin film 3b was 30%. Although not shown in Table 1, the surface coverage of the transparent insulating thin film 3b remains 50% and the transparent conductive thin film 3a is not inserted. F. Was significantly reduced, and Eff. Became low. Therefore, the thickness of the transparent conductive thin film 3a is preferably 5 nm or more. From Example 6, when the transparent conductive thin film 3a is not inserted, the film thickness of the transparent insulating thin film 3b is reduced, and the surface coverage is further reduced. F. Can be maintained. However, in order to obtain a light scattering effect, a surface coverage of 30% or more is preferable.
[0051]
From the comparison of Examples 3, 7 and 8, in order to effectively obtain the light reflection effect on the transparent insulating thin film 3b, the surface coverage of the transparent insulating thin film 3b is preferably 50% or more. Moreover, since it is thought that the discontinuity of the transparent insulating thin film 3b having the smallest refractive index enhances the light scattering effect, a surface coverage of 50 to 70% is preferable.
[0052]
Example 9
As Example 9, a hybrid thin film photoelectric conversion device as shown in FIG. 2 was produced. On the glass substrate with the first electrode layer (transparent electrode) 2 used in Example 1, a p-type amorphous silicon carbide layer 201 having a thickness of 15 nm and an intrinsic amorphous silicon photoelectric conversion layer having a thickness of 0.25 μm. 202 and a 15 nm thick n-type microcrystalline silicon layer 203 were sequentially formed by a plasma CVD method. Subsequently, the light scattering layer 6 was formed by the same method as in Example 1. However, the transparent conductive thin film 6a made of ZnO is 10 nm, SiO2The transparent insulating thin film 6b made of 10 nm was made 10 nm, and the transparent conductive thin film 6c made of ZnO was made 10 nm. Subsequently, a p-type microcrystalline silicon layer 211 having a thickness of 15 nm, an intrinsic crystalline silicon photoelectric conversion layer 212 having a thickness of 2.0 μm, and an n-type microcrystalline silicon layer 213 having a thickness of 15 nm are sequentially formed by plasma CVD. did. Thereafter, ZnO having a thickness of 90 nm as the transparent conductive layer 7 and Ag having a thickness of 300 nm as the light reflective metal layer 4 were sequentially formed by sputtering.
[0053]
In the same manner as in Example 1, the obtained hybrid thin film photoelectric conversion device (light receiving area 1 cm)2) Output characteristics were measured, Voc was 1.34V, Jsc was 12.1 mA / cm.2, F. F. Was 72.4%, and the conversion efficiency was 11.7%.
[0054]
(Comparative Example 2)
In Comparative Example 2, after the amorphous silicon photoelectric conversion unit was formed in the same procedure as in Example 9, the substrate was taken out into the atmosphere, and instead of the light scattering layer 6, it was sputtered at a temperature of 150 ° C. A hybrid thin-film photoelectric conversion device was manufactured by the same method except that a ZnO film having a thickness of 30 nm was formed.
[0055]
The silicon-based thin film photoelectric conversion device obtained as described above (light receiving area 1 cm)2) In the same manner as in Example 1, Voc is 1.32 V, Jsc is 11.7 mA / cm.2, F. F. Was 71.8%, and the conversion efficiency was 11.1%.
[0056]
In Example 9, compared with Comparative Example 2, Jsc is increased. This is because the light scattering layer is inserted as an intermediate layer so that incident light is partially reflected by the photoelectric conversion unit located on the light incident side in the low refractive index layer that is discontinuously interposed in the light scattering layer. The sensitivity of the photoelectric conversion unit located on the side has increased, and light that has passed through the photoelectric conversion unit located behind the light scattering layer without being absorbed by the light scattering layer is between the light scattering layer and the back electrode. This is considered to be due to scattering and efficient absorption. In Example 9, since the MOCVD method with little damage to the photoelectric conversion unit was used when forming the light scattering layer, Voc and F.I. F. Is thought to have improved.
[0057]
【The invention's effect】
As explained in detail above, the present inventionofThin film photoelectric converterAccording toPhotoelectric conversion unit and light reflective metalBetween the electrode layersConversion efficiency by inserting a light scattering layerImprovebe able to.The light scattering layer includes a first transparent conductive thin film, a transparent insulating thin film, and a second transparent conductive thin film, and the transparent conductive thin film includes zinc oxide which is a transparent conductive oxide. Since it is formed, the transparent conductive thin film itself can also have a function as a light scattering layer. In addition, the transparent insulating thin film has a thickness in the range of 1 nm to 50 nm of silicon oxide, which is an insulating material having a smaller refractive index than zinc oxide, and has a surface coverage of 30% to 70%. Therefore, it is possible to achieve both necessary conductivity and light scattering. According to such a configuration, the light absorption amount of the photoelectric conversion unit can be increased, and a photoelectric conversion device having higher photoelectric conversion efficiency can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of a thin film photoelectric conversion device according to the present invention.
FIG. 2 is a cross-sectional view showing an example of a hybrid thin film photoelectric conversion device according to the present invention.
[Explanation of symbols]
1 Transparent substrate
2 First electrode layer
10 Photoelectric conversion unit
101 One conductivity type layer
102 Intrinsic photoelectric conversion layer
103 Reverse conductivity type layer
3 Light scattering layer
3a First transparent conductive thin film
3b Transparent insulating thin film
3c Second transparent conductive thin film
4 Light reflective metal layer
5 sunlight
20 First photoelectric conversion unit
201 One conductivity type layer
202 Intrinsic photoelectric conversion layer
203 Reverse conductivity type layer
21 Second photoelectric conversion unit
211 One conductivity type layer
212 Intrinsic photoelectric conversion layer
213 Reverse conductivity type layer
6 Light scattering layer
6a Transparent conductive oxide layer
6b Insulating oxide layer
6c Transparent conductive oxide layer
7 Transparent conductive layer

Claims (4)

光入射側から順に、透光性基板、透光性導電酸化物電極層、シリコン系光電変換ユニット、光散乱層、および光反射性金属電極層を含み、
前記光散乱層は、第一の透明導電性薄膜と透明絶縁性薄膜と第二の透明導電性薄膜を含んで構成されており、
前記第一の透明導電性薄膜および第二の透明導電性薄膜は透明導電性酸化物である酸化亜鉛を含んで形成されており、
前記透明絶縁性薄膜は前記酸化亜鉛に比べて小さな屈折率を有する絶縁性材料である酸化珪素を含んで形成されており、１ｎｍ以上５０ｎｍ以下の範囲内の厚さを有するとともに、３０％以上７０％以下の表面被覆率を生じるように分散させられていることを特徴とする薄膜光電変換装置。In order from the light incident side, including a translucent substrate, a translucent conductive oxide electrode layer, a silicon-based photoelectric conversion unit, a light scattering layer, and a light reflective metal electrode layer,
The light scattering layer includes a first transparent conductive thin film, a transparent insulating thin film, and a second transparent conductive thin film,
The first transparent conductive thin film and the second transparent conductive thin film are formed including zinc oxide which is a transparent conductive oxide,
The transparent insulating thin film is formed by containing silicon oxide which is an insulating material having a refractive index smaller than that of the zinc oxide, and has a thickness in the range of 1 nm to 50 nm, and 30% A thin film photoelectric conversion device which is dispersed so as to produce a surface coverage of 70 % or less. 前記光散乱層と前記光反射性金属電極層との間にもう一つの光電変換ユニットを含むことを特徴とする請求項１に記載の薄膜光電変換装置。  The thin film photoelectric conversion device according to claim 1, further comprising another photoelectric conversion unit between the light scattering layer and the light reflective metal electrode layer. 前記光電変換ユニットとして、結晶質シリコン系光電変換ユニットを含むことを特徴とする請求項１または２に記載の薄膜光電変換装置。  The thin film photoelectric conversion device according to claim 1, wherein the photoelectric conversion unit includes a crystalline silicon-based photoelectric conversion unit. 前記光散乱層の光入射側に非晶質光電変換ユニットを含み、前記光散乱層の光入射側と反対側に結晶質光電変換ユニットを含むことを特徴とする請求項２に記載の薄膜光電変換装置。  The thin film photoelectric device according to claim 2, further comprising an amorphous photoelectric conversion unit on a light incident side of the light scattering layer, and a crystalline photoelectric conversion unit on a side opposite to the light incident side of the light scattering layer. Conversion device.
JP2002100664A 2002-04-02 2002-04-02 Silicon-based thin film photoelectric conversion device Expired - Fee Related JP4222500B2 (en)

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