JP4248793B2 - Method for manufacturing thin film solar cell - Google Patents

Description

【０１１０】
【表２】

【０１１１】
以下に実施例１〜１１および比較例１および２について、表１と表２を用いて詳細に説明する。
【０１１２】
実施例１〜１１における透明導電層のエッチング処理後の表面形状は、何れも図２に示すような表面形状に形成されており、透明導電層の表面には複数の穴が形成され、その穴の内部と穴が形成されていない部分の何れの表面にも微細な凹凸が形成されていた。しかし、比較例１および２では、実施例１〜１１と比較して、穴の最大直径範囲が広がり、穴の数が増加し、逆に穴の内部における微細な凹凸はより小さくなり、数も減少していた。
【０１１３】
また、光電変換層の配向性Ｉ₂₂₀／Ｉ₁₁₁は、実施例１〜１１および比較例１および２ともに、５．０もしくはそれ以上の値が得られたことから、何れの薄膜太陽電池の光電変換層についても欠陥の少ない良好な膜が形成されていると考えられる。
【０１１４】
実施例１〜１１および比較例１・２の薄膜太陽電池の電流−電圧特性を比較すると、何れの薄膜太陽電池も同程度の開放電圧および形状因子が得られているにも関わらず、比較例１および２の短絡電流が実施例１〜１１と比較して低くなっている。つまり、実施例１〜１１に比べて、比較例１および２の光閉込効果が十分でないことがわかる。透明導電層１１ｂの表面形状については、実施例１〜１１に見られた穴の表面の微細な凹凸が光閉込に大きく寄与しているものと考えられる。これは、穴の表面に微細な凹凸が形成されていることで、入射光に対して十分な光散乱を生じさるとともに、透明導電層とその上に堆積されるシリコン薄膜との界面における反射を低減し、光電変換層１７への効果的な光入射を促進することができたことによるものと考えられる。
【０１１５】
また、実施例１〜１１の中では、実施例２が最も低い短絡電流値となった。これは、アルコール誘導体の含有量が少なかったため、光閉込に十分な微細な凹凸が穴表面に形成されていなかったことによるものと考えられる。
【０１１６】
したがって、透明導電層にアルコール誘導体を含むエッチング液を用いた表面処理を施すことにより、表面が十分な光散乱を促し、光電変換層において十分な光閉込効果を得て、高い光電変換効率を有する薄膜太陽電池を容易に製造することが可能となることがわかった。
【０１１７】
なお、実施例１〜１１では、基板１１ａ上に形成された透明導電層１１ｂのみにエッチングによる表面処理を施したが、裏面電極１６側の裏面反射層１５として用いた透明導電層にも同様の処理を施した場合でも同様の効果を得ることができる。
【０１１８】
（実施例１２）
実施例１２として、図３に示すような、サブストレート型構造で単接合型の薄膜太陽電池５０を形成した。
【０１１９】
実施例１２に係る薄膜太陽電池５０は、図３に示すように、ステンレス基板４０ａとその上に形成された裏面電極４０ｂと透明導電層４０ｃとからなる太陽電池用基板４０上に、光電変換層４５、透明導電層４４がこの順に積層されて形成されている。
【０１２０】
光電変換層４５は、ｎ型結晶質シリコン層４１、ｉ型結晶質シリコン層４２およびｐ型結晶質シリコン層４３を備えている。
【０１２１】
このようなサブストレート型構造で単接合型の薄膜太陽電池５０を、以下のような手順で形成した。
【０１２２】
まず、表面が平滑なステンレス基板４０ａ上に、電子ビーム蒸着法により裏面電極４０ｂとして銀を厚さ５００ｎｍで形成し、その後、マグネトロンスパッタリング法により裏面反射層として、透明導電層４０ｃを酸化亜鉛を用いて厚さ５０ｎｍで形成し、太陽電池用基板４０とした。
【０１２３】
次いで、得られた太陽電池用基板４０の上に、高周波プラズマＣＶＤ法により、透明導電層４０ｃの上に厚さ３０ｎｍのｎ型結晶質シリコン層４１、厚さ２μｍのｉ型結晶質シリコン層４２、厚さ２０ｎｍのｐ型結晶質シリコン層４３を順に積層することで、光電変換層４５を作製した。製膜時の基板温度は各々の層において２００℃とした。
【０１２４】
ｎ型結晶質シリコン層４１の形成時には、ＳｉＨ₄ガスを流量比で５倍のＨ₂ガスにより希釈したものを原料ガスとして用いるとともに、さらにＰＨ₃ガスをＳｉＨ₄ガス流量に対して０．０１％添加して製膜した。また、ｉ型結晶質シリコン層４２の形成時にはｎ型結晶質シリコン層４１と同様の原料ガスを、ｐ型結晶質シリコン層４３の形成時には、さらにＢ₂Ｈ₆ガスをＳｉＨ₄ガス流量に対して０．１％添加して用いた。
【０１２５】
その後、マグネトロンスパッタリング法により基板温度１５０℃、製膜圧力０．３ｍＴｏｒｒで、透明導電層４４として酸化亜鉛を厚さ１０００ｎｍとなるように形成した。透明導電層４４には、１×１０²¹／ｃｍ³程度のガリウムが添加されている。この結果、得られた透明導電層４４のシート抵抗は１０Ω／□であり、波長８００ｎｍの光に対する透過率は８０％であった。また、透明導電層４４に対してＸ線回折法を行ったところ、（０００１）回折ピークの積分強度が全回折ピークの積分強度の和に対して７５％であった。
【０１２６】
続いて、透明導電層４４表面に対してエッチング処理を行った。エッチング液として用いた酸性溶液は、最終的に全容液中にエチルアルコールを３０重量％含むように調合したエチルアルコールと水との混合液に、塩酸濃度０．３５重量％となるように塩酸を加えることで作製した。順次、透明導電層４４まで堆積した基板を、液温２５℃で、上記エッチング液に１００秒浸した後、表面を純水で十分に洗浄し、透明導電層４４側から光を入射するサブストレート型構造で単接合型の薄膜太陽電池５０を得た。
【０１２７】
エッチング後の透明導電層４４の表面を走査型電子顕微鏡で観察したところ、形状は概略円形の穴で、穴の最大直径範囲は２００〜１０００ｎｍで、その個数密度はおよそ０．８個／μｍ²程度であった。
【０１２８】
この穴および周辺の表面を更に詳細に調べるため、原子間力顕微鏡での観察を行った。
【０１２９】
実施例１で示した図２を用いて、透明導電層４４の表面の概略を模式的に説明すれば、透明導電層４４の表面に形成された穴の深さ２１は８０〜６００ｎｍ程度であった。さらに上記穴の表面には微細な凹凸が形成されており、この凹凸の大きさ（凹凸の高低差）２３は１０〜１８０ｎｍ程度で、凹凸の間隔２４は８０〜６００ｎｍ程度であった。また、穴表面以外の部分に形成されている微細な凹凸の大きさは１０〜５０ｎｍ程度であった。
【０１３０】
（比較例３）
比較例３として、アルコール誘導体を含有させず、水に所定量の塩酸を加えて作製した０．３５重量％の塩酸溶液を用いて、透明導電層表面のエッチング処理を行い、それ以外は実施例１２と同様にしてサブストレート型構造で単接合型の薄膜太陽電池を作製した。
【０１３１】
エッチング後の透明導電層の表面を走査型電子顕微鏡で観察したところ、形状は概略円形の穴で、穴の最大直径範囲は４００〜１２００ｎｍであり、個数密度はおよそ２．８個／μｍ²程度形成されていることが分かった。
【０１３２】
実施例１２と同様にしてこの穴および周辺の表面を更に詳細に調べるため、原子間力顕微鏡での観察を行った。本比較例３における透明導電層の表面は、比較例１に係る薄膜太陽電池の透明導電層の表面として示した図５と同様である。よって、本比較例３に係る薄膜太陽電池の透明導電層について、図５を用いて説明する。なお、本比較例３における上記穴の深さ１０１は、３００〜８００ｎｍ程度であり、穴の表面に形成されている微細な凹凸は１０ｎｍ以下と小さく、その数も少なかった。
【０１３３】
一方、上記穴が形成されていない表面の凹凸は大きく、穴と凹凸の区別が困難となる。なお、個数密度２．８個／μｍ²は、先の実施例１２では穴のない表面における微細な凹凸として分類していたものが、本比較例においては、穴と分類されるほど凹凸のサイズが大きくなったことにより密度が増加したものと考えられる。
【０１３４】
以上のような実施例１２および比較例３に係る薄膜太陽電池のＡＭ１．５（１００ｍＷ／ｃｍ²）照射条件下における電流−電圧特性を表３に示す。
【０１３５】
【表３】

【０１３６】
表３において、実施例１２と比較例３とを比較したところ、開放電圧および形状因子の値はほとんど変わらないが、短絡電流については実施例１２の方が比較例３よりも高い値が得られたことがわかる。
【０１３７】
すなわち、実施例１２に係るサブストレート型構造の薄膜太陽電池５０の透明導電層４４については、本発明の実施例１２に係る簡便なエッチング処理により、透明導電層４４の表面に複数の穴が形成され、かつその穴の表面に微細な凹凸が生じることで、光閉込に有効な光散乱効果と透明導電層４４表面上における反射低減効果とを得ることができ、短絡電流が比較例３に係る薄膜太陽電池よりも大きくなったものと考えられる。
【０１３８】
なお、実施例１２は、透明導電層４４のみにエッチングによる表面処理を施した薄膜太陽電池であったが、裏面電極４０ｂ側の裏面反射層として用いた透明導電層４０ｃにも同様の処理を施した場合でも、同様の効果を得ることができる。
【０１３９】
（実施例１３）
実施例１３に係るスーパーストレート型構造で多接合型の薄膜太陽電池６０は、図４に示すように、基板１１ａとその上に形成された透明導電層１１ｂ、第１シリコン光電変換層２７、第２透明導電層１１ｃ、第２シリコン光電変換層３７、裏面反射層１５、裏面電極１６がこの順に積層されて構成されている。
【０１４０】
第１シリコン光電変換層２７は、ｐ型非晶質シリコン層１２ａ、ｉ型非晶質シリコン層１３ａおよびｎ型非晶質シリコン層１４ａから構成されており、第２シリコン光電変換層３７は、ｐ型シリコン層１２ｂ、ｉ型シリコン層１３ｂおよびｎ型シリコン層１４ｂから構成されている。
【０１４１】
以上のような構成の多接合型薄膜太陽電池は、以下のように製造することができる。
【０１４２】
まず、実施例１と同様にして、表面が平滑な基板１１ａ上に、マグネトロンスパッタリング法により、基板温度１５０℃、製膜圧力０．３ｍＴｏｒｒで、透明導電層１１ｂとして酸化亜鉛を厚さ１２００ｎｍとなるように形成し、続いて、透明導電層１１ｂ表面のエッチングを行うことで太陽電池用基板１１を形成した。透明導電層１１ｂに対しては、実施例１と同様に、アルコール誘導体を含むエッチング液により表面処理を行うことにより、透明導電層１１ｂの表面に、基板１１ａには至らない概略円形の穴が多数形成され、さらにその穴の内部には多数の微細な凹凸が形成されていることが原子間力顕微鏡で確認できた。
【０１４３】
このようにして得られた太陽電池用基板１１上に、高周波プラズマＣＶＤ装置を用いて、高周波プラズマＣＶＤ法により、厚さ２０ｎｍのｐ型非晶質シリコン層１２ａ、厚さ３００ｎｍのｉ型非晶質シリコン層１３ａ、厚さ３０ｎｍのｎ型非晶質シリコン層１４ａを順に積層することで、第１シリコン光電変換層２７を作製した。なお、製膜時の基板温度は、各々の層において２００℃とした。
【０１４４】
ｐ型非晶質シリコン層１２ａ形成時には、ＳｉＨ₄ガスを流量比で５倍のＨ₂ガスにより希釈したものを原料ガスとして用いるとともに、さらにＢ₂Ｈ₆ガスをＳｉＨ₄ガス流量に対して０．０１％添加して製膜した。また、ｉ型非晶質シリコン層１３ａは、ｐ型非晶質シリコン層１２ａと同様の原料ガスを、ｎ型非晶質シリコン層１４ａは、さらにＰＨ₃ガスをＳｉＨ₄ガス流量に対して０．０１％添加して用いた。
【０１４５】
第１シリコン光電変換層２７を堆積した太陽電池用基板１１を、プラズマＣＶＤ装置から一旦取り出し、再度、マグネトロンスパッタリング法により第２透明導電層１１ｃとして、酸化亜鉛を透明導電層１１ｂと同じ条件で膜厚５ｎｍ製膜した。
【０１４６】
次いで、第２透明導電層１１ｃ上に、実施例１の光電変換層１７と同じ条件で、第２シリコン光電変換層３７を作成した。
【０１４７】
第２シリコン光電変換層３７を形成した後にＸ線回折法を行ったところ、（２２０）Ｘ線回折ピークの積分強度I₂₂₀と（１１１）Ｘ線回折ピークの積分強度Ｉ₁₁₁の比Ｉ₂₂₀／Ｉ₁₁₁は５．５であり、実施例１の場合と差はなかった。
【０１４８】
その後、実施例１と同様に、裏面反射層１５および裏面電極１６を形成し、基板１１ａから光を入射するスーパーストレート型構造で多接合型の薄膜太陽電池６０を得た。
【０１４９】
（比較例４）
比較例４として、アルコール誘導体を含有せず、水に所定量の塩酸を加えて作製した０．３５重量％の塩酸溶液を用いて、透明導電層１１ｂ表面のエッチング処理を行った以外は、実施例１３と同様にして、比較例４に係る多接合型の薄膜太陽電池を作製した。
【０１５０】
第２シリコン光電変換層３７を形成した後でＸ線回折法を行ったところ、（２２０）Ｘ線回折ピークの積分強度Ｉ₂₂₀と（１１１）Ｘ線回折ピークの積分強度Ｉ₁₁₁の比Ｉ₂₂₀／Ｉ₁₁₁は５．０であった。
【０１５１】
以上のような実施例１３および比較例４で得られた多接合型の薄膜太陽電池のＡＭ１．５（１００ｍＷ／ｃｍ²）照射条件下における電流−電圧特性を表４に示す。
【０１５２】
【表４】

【０１５３】
表４において、実施例１３と比較例４を比較すると、開放電圧および形状因子の値はほとんど変わらないが、短絡電流については実施例１３の方が高い値が得られたことがわかる。
【０１５４】
これは、多接合型構造の薄膜太陽電池における透明導電層についても、本発明による簡便なエッチング処理により、透明導電層１１ｂ表面に複数の穴が形成され、かつその穴の表面に微細な凹凸が生じることで、光閉込に有効な光散乱効果と透明導電層１１ｂと第１シリコン光電変換層２７との界面における反射低減の効果とが得られたためであると考えられる。
【０１５５】
なお、実施例１３に係る薄膜太陽電池では、透明導電層１１ｂのみにエッチングによる表面処理を施したが、裏面電極側の裏面反射層１５として用いた透明導電層や第１シリコン光電変換層２７と第２シリコン光電変換層３７との間に挿入される第２透明導電層１１ｃにも同様の処理を施してもよい。
【０１５６】
以上、透明導電層１１ｂ・４４として酸化亜鉛層を有する薄膜太陽電池を用いて、本発明に係る実施形態について説明したが、本発明は上述した実施形態および実施例に限定されるものではない。上記にて説明した透明導電層の種類、およびエッチャントの種類以外にも、本発明と同様の効果を得ることができ、さらに、酸強度もしくはアルカリ強度の異なるエッチング液を用いた場合でも、基本的には本発明と同様の効果を得ることができる。
【０１５７】
【発明の効果】
本発明の薄膜太陽電池の製造方法は、以上のように、透明導電層の表面を、下記の構造式（１）で示されるアルコール誘導体を少なくとも１種類含むエッチング液を用いてエッチングする製造方法である。
Ａ−（ＯＨ）ⁿ ・・・・・（１）
（ｎは１〜４の整数、Ａは炭素原子を介して水酸基と結合した脂肪族炭化水素残基である）。
【０１５８】
それゆえ、エッチング液に含まれるアルコール誘導体の性質により、透明導電層の表面に、良好な光閉込効果を得るために有効な複数の穴、その穴の部分の微細な凹凸を形成することができるため、光電変換層において良好な光閉込効果を得て、高い光電変換効率を有する薄膜太陽電池を安価かつ容易に製造することができるという効果を奏する。
【０１５９】
すなわち、本発明の薄膜太陽電池の製造方法によれば、上記構造式で示したアルコール誘導体を含むエッチング液を用いてエッチングを行うため、アルコール誘導体の性質により、穴を拡大する方向に進行する異方性エッチングの働きを適度に抑え、エッチングの初期段階で生じた穴の表面に対してエッチングが進行し、穴が形成された部分にさらに微細な凹凸を形成することができる。つまり、上記構造式で示したアルコール誘導体を含む酸あるいはアルカリ性溶液を用いれば、穴の大きさを拡大する方向にはエッチングが進行せず、所望の複数の穴とその穴の表面に複数の微細な凹凸を形成することができる。
【０１６０】
よって、大掛かりな設備等を必要とせずに、透明導電層に形成された複数の穴と微細な凹凸により、太陽光スペクトルの中心波長４００〜６５０ｎｍ程度の光だけでなく、これらより長い波長の光に対しても十分な光散乱を生じさせて、光電変換層における良好な光閉込効果を利用して、高い光電変換効率を有する薄膜太陽電池を安価かつ容易に得ることができる。
【０１６１】
上記アルコール誘導体は、エチルアルコール、メチルアルコール、イソプロピルアルコール、エチレングリコール、グリセリン、プロピレングリコールである。
【０１６２】
それゆえ、アルコール誘導体の働きにより、異方性エッチングを抑制することで、形成された穴が拡大されることを防止し、良好な光散乱を実現する所望の穴および凹凸を安価かつ容易に形成することができるという効果を奏する。
【０１６３】
上記エッチング液は、上記アルコール誘導体を全溶液のうち１０ｗｔ％以上含有している。
【０１６４】
それゆえ、エッチング液にアルコール誘導体を含有させることによって得られる効果を十分に得ることができ、所望の穴および凹凸を形成して、高い光電変換効率を有する薄膜太陽電池を製造できるという効果を奏する。
【０１６５】
上記透明導電層は、酸化亜鉛を含有している。
【０１６６】
それゆえ、酸化亜鉛の特性である耐プラズマ性が得られ、プラズマＣＶＤ法による光電変換層堆積時における水素プラズマによる透明導電層の透過率低下を生じさせること無く、良好な特性を有した薄膜太陽電池を得ることができるという効果を奏する。
【０１６７】
上記エッチングは、エッチング液の温度範囲を５℃以上４０℃以下として行われることがより好ましい。
【０１６８】
上記アルコール誘導体を含むエッチング液の温度を４０℃より高い温度でエッチングを行った場合には、揮発性の高いアルコール誘導体においては、酸あるいはアルカリ性のエッチャントによる異方性エッチングの働きが強くなり、好適な光閉込効果を得られる穴および凹凸を形成することが困難になる。一方、５℃より低い温度では、エッチング処理速度の低下を招き、生産効率の低下を招く。
【０１６９】
それゆえ、本発明の薄膜太陽電池の製造方法では、上記エッチング液の温度を上記範囲内になるように管理してエッチングを行うことにより、光閉込効果に有効な穴および凹凸を形成することができるという効果を奏する。
【０１７０】
本発明により製造される薄膜太陽電池は、上記製造方法により製造された構成である。
【０１７１】
それゆえ、光閉込効果を得るために有効な穴および凹凸を上記透明導電層の表面に形成することができ、安価な製造方法で、光電変換層の膜質を損なうことなく、十分な光散乱による光閉込効果を活用して、高い光電変換効率を有する薄膜太陽電池を得ることができるという効果を奏する。
【０１７２】
上記エッチングにより上記透明導電層の表面に形成される穴の直径は２００〜２０００ｎｍ、穴の深さは５０〜１２００ｎｍであって、微細な凹凸の高低差は１０〜３００ｎｍである。
【０１７３】
それゆえ、上記透明導電層に形成された複数の穴と微細な凹凸により、太陽光スペクトルの中心波長４００〜６５０ｎｍ程度の光だけでなく、これらより長い波長の光に対しても十分な光散乱を生じさせて有効な光閉込効果を得ることができ、高い光電変換効率を有する薄膜太陽電池を得ることができるという効果を奏する。
【０１７４】
本発明のエッチング液は、以上のように、上記薄膜太陽電池の製造方法で用いられることを特徴としている。
【０１７５】
それゆえ、光閉込効果を得るために有効な穴および凹凸を上記透明導電層の表面に形成することができ、安価な方法で、十分な光散乱に起因する光閉込効果の活用により、高い光電変換効率を有する薄膜太陽電池を得ることができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明の一実施形態および実施例１に係るスーパーストレート型の単接合型薄膜太陽電池の構造を概略的に示す断面図である。
【図２】本発明の実施例１に係る薄膜太陽電池における酸化亜鉛を含む透明導電層の表面形状を概略的に示す断面図である。
【図３】本発明の実施例１２に係るサブストレート型の薄膜太陽電池の構造を概略的に示す断面図である。
【図４】本発明の実施例１３に係る多接合型薄膜太陽電池の構造を概略的に示す断面図である。
【図５】比較例１に係る薄膜太陽電池における酸化亜鉛を含む透明導電層の表面形状を概略的に示す断面図である。
【符号の説明】
１１ 太陽電池基板
１１ａ 基板
１１ｂ 透明導電層
１１ｃ 第２透明導電層
１２ ｐ型シリコン層
１２ａ ｐ型非晶質シリコン層
１３ ｉ型シリコン層
１３ａ ｉ型非晶質シリコン層
１４ ｎ型シリコン層
１４ａ ｎ型非晶質シリコン層
１５ 裏面反射層
１６ 裏面電極
１７ 光電変換層
２１ 穴の深さ
２２ 穴の直径
２３ 凹凸の大きさ（凹凸の高低差）
２４ 凹凸の間隔
２７ 第１シリコン光電変換層
３７ 第２シリコン光電変換層
４０ 太陽電池用基板
４０ａ 基板
４０ｂ 裏面電極
４０ｃ 透明導電層
４１ ｎ型シリコン層
４２ ｉ型シリコン層
４３ ｐ型シリコン層
４４ 透明導電層
４５ 光電変換層[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for producing a thin film solar cell having high photoelectric conversion efficiency.To the lawIt is related.
[0002]
[Prior art]
Currently, fossil fuels such as petroleum, which are used as a major energy source, are concerned about future supply and demand, and have problems such as carbon dioxide emissions that cause global warming. Thus, in recent years, solar cells have attracted attention as an alternative energy source for fossil fuels such as petroleum.
[0003]
As this solar cell, a silicon semiconductor having a pn junction is used in order to convert light energy into electricity, and single crystal silicon is preferably used from the viewpoint of photoelectric conversion efficiency. However, solar cells using single crystal silicon have problems such as supply of raw materials, an increase in area, and cost reduction.
[0004]
As one means for solving this problem, some solar cells using a thin film amorphous silicon as a photoelectric conversion layer have been put into practical use.
[0005]
Furthermore, in order to obtain higher photoelectric conversion efficiency, introduction of a thin film crystalline silicon into a photoelectric conversion layer instead of an amorphous material has been studied. This thin crystalline silicon can be formed by a chemical vapor deposition method (hereinafter referred to as a CVD method) as in the case of amorphous, and is a polycrystalline silicon thin film. Below, the solar cell which introduce | transduced such a thin film crystalline silicon is shown as a polycrystalline silicon thin film solar cell.
[0006]
In thin film solar cells, effective utilization of the light confinement effect is important in order to increase the photoelectric conversion efficiency. The light confinement effect means that the surface of the transparent conductive layer or metal layer in contact with the photoelectric conversion layer is made uneven, the light is scattered at the interface to extend the optical path length, and the light absorption in the photoelectric conversion layer is increased. It is an effect that can be done.
[0007]
As a thin film solar cell that can effectively utilize such a light confinement effect, Japanese Patent Application Laid-Open No. 2000-252504 has a surface uneven structure of a light-reflective metal layer and unevenness finer than the surface uneven structure. The surface texture structure of the transparent conductive oxide layer is shown.
[0008]
[Problems to be solved by the invention]
However, since the thin film solar cell disclosed in the above publication needs to be laminated with a plurality of layers whose sizes are controlled when forming fine irregularities, the manufacturing process becomes complicated and the manufacturing cost is reduced. It has the problem of causing an increase.
[0009]
In particular, in the method of manufacturing a thin film solar cell as described above, boron is generally used, and since diborane or the like is used as the boron source, a special material high-pressure gas facility or the like is required, and a large capital investment is required. Necessary.
[0010]
  The present invention has been made in view of the above-described problems, and the object thereof is to obtain a sufficient light confinement effect by forming desired irregularities on a transparent conductive layer at low cost and easily. Of thin film solar cells with high photoelectric conversion efficiencyThe lawIt is to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, a method for manufacturing a thin film solar cell of the present invention is a thin film solar cell including at least a substrate, a transparent conductive layer, and a photoelectric conversion layer. Etching is performed using an etching solution containing at least one alcohol derivative represented by (1).
A- (OH)ⁿ  (1)
(N is an integer of 1 to 4, and A is an aliphatic hydrocarbon residue bonded to a hydroxyl group via a carbon atom).
[0012]
According to the above manufacturing method, due to the nature of the alcohol derivative contained in the etching solution, the surface of the transparent conductive layer has a plurality of holes effective for obtaining a good light confinement effect, and fine irregularities at the hole portions. Therefore, a thin film solar cell having high photoelectric conversion efficiency can be easily and inexpensively manufactured by obtaining a good light confinement effect in the photoelectric conversion layer.
[0013]
That is, conventionally, a transparent conductive layer such as zinc oxide, which is a polycrystalline thin film, is etched using an acid or alkaline etchant, so that only a specific portion of the crystal grains along the crystal grain boundaries are etched at the initial stage of etching. Can be selectively etched to form a plurality of holes. However, when etching is further advanced, the etching progresses as a whole, and the holes formed at the initial stage of etching become larger with the lapse of the etching time, and eventually the film itself is not completely etched, and the light It is impossible to form minute irregularities effective for the confinement effect in the hole portion. In particular, the tendency is remarkable in an etchant using an aqueous solution, and it has been difficult to manufacture a thin-film solar cell capable of obtaining a good light confinement effect.
[0014]
Therefore, according to the method for manufacturing a thin-film solar cell of the present invention, etching is performed using an etching solution containing an alcohol derivative represented by the above structural formula. It is possible to moderately suppress the action of isotropic etching, and the etching proceeds on the surface of the hole generated in the initial stage of etching, so that finer irregularities can be formed in the portion where the hole is formed. In other words, if an acid or alkaline solution containing an alcohol derivative represented by the above structural formula is used, etching does not proceed in the direction of expanding the hole size, and a plurality of desired holes and a plurality of fine particles are formed on the surface of the holes. Unevenness can be formed.
[0015]
Therefore, without requiring large-scale equipment or the like, not only light having a central wavelength of the solar spectrum of about 400 to 650 nm but also light having a wavelength longer than these due to a plurality of holes and fine irregularities formed in the transparent conductive layer. In addition, sufficient light scattering can be caused, and a thin film solar cell having high photoelectric conversion efficiency can be obtained inexpensively and easily by utilizing a good light confinement effect in the photoelectric conversion layer.
[0016]
In addition, the manufacturing method of the thin film solar cell of this invention is applicable irrespective of the structure of thin film solar cells, such as a super straight type thin film solar cell and a substrate type thin film solar cell.
[0017]
  The alcohol derivatives are ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol, glycerin, propylene glycol.The
[0018]
This suppresses anisotropic etching by the action of an alcohol derivative, preventing the formed hole from being enlarged, and forming desired holes and irregularities that realize good light scattering inexpensively and easily. can do.
[0019]
  The etching solution contains 10 wt% or more of the alcohol derivative in the total solution.The
[0020]
Thereby, the effect obtained by including an alcohol derivative in the etching solution can be sufficiently obtained, and desired holes and irregularities can be formed to manufacture a thin film solar cell having high photoelectric conversion efficiency.
[0021]
  The transparent conductive layer contains zinc oxide.The
[0022]
The transparent conductive layer used in the thin film solar cell is required to have a high transmittance in order to guide the incident sunlight to the photoelectric conversion layer without losing it. However, SnO does not contain zinc oxide₂When the photoelectric conversion layer is deposited on the transparent conductive layer using the plasma CVD method, blackening occurs due to reduction by hydrogen plasma contained in the process gas. The transmittance of the layer is lowered, and consequently the characteristics of the thin film solar cell are lowered. In the method for producing a thin film solar cell of the present invention, as described above, since the transparent conductive layer contains zinc oxide, plasma resistance is obtained, and transparent by hydrogen plasma at the time of deposition of the photoelectric conversion layer by the plasma CVD method. A thin film solar cell having good characteristics can be obtained without causing a decrease in the transmittance of the conductive layer.
[0023]
The etching is more preferably performed at an etching solution temperature range of 5 ° C. to 40 ° C.
[0024]
When etching is performed at an etching solution containing the above alcohol derivative at a temperature higher than 40 ° C., the highly volatile alcohol derivative has a strong anisotropic etching action with an acid or alkaline etchant. It is difficult to form holes and irregularities that can obtain a good light confinement effect. On the other hand, when the temperature is lower than 5 ° C., the etching processing rate is lowered and the production efficiency is lowered.
[0025]
Therefore, in the method for manufacturing a thin-film solar cell of the present invention, holes and irregularities effective for the light confinement effect can be formed by performing etching while controlling the temperature of the etching solution to be within the above range. it can.
[0026]
  The present inventionManufactured byThe thin film solar cell is manufactured by the above manufacturing method.
[0027]
This makes it possible to form effective holes and irregularities on the surface of the transparent conductive layer in order to obtain a light confinement effect, and with an inexpensive manufacturing method, without damaging the film quality of the crystalline silicon photoelectric conversion layer. A thin-film solar cell having high photoelectric conversion efficiency can be obtained by utilizing the light confinement effect caused by light scattering.
[0028]
  The diameter of the hole formed in the surface of the transparent conductive layer by the etching is 200 to 2000 nm, the depth of the hole is 50 to 1200 nm, and the height difference of the fine unevenness is 10 to 300 nm.The
[0029]
Thereby, due to the plurality of holes and fine irregularities formed in the transparent conductive layer, sufficient light scattering is possible not only for light having a central wavelength of the solar spectrum of about 400 to 650 nm but also for light having longer wavelengths than these. As a result, an effective light confinement effect can be obtained, and a thin film solar cell having high photoelectric conversion efficiency can be obtained.
[0030]
In order to solve the above-described problems, the etching solution of the present invention is characterized by being used in the above-described method for manufacturing a thin film solar cell.
[0031]
According to the above configuration, effective holes and irregularities can be formed on the surface of the transparent conductive layer to obtain a light confinement effect, and the light confinement effect due to sufficient light scattering can be achieved by an inexpensive method. By utilizing this, a thin film solar cell having high photoelectric conversion efficiency can be obtained.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
  Manufacturing method of thin film solar cell of the present inventionTo the lawAn embodiment relating to the present invention will be described below with reference to FIGS.
[0033]
As shown in FIG. 1, the thin film solar cell of the present embodiment is a super straight type thin film solar cell 20 that performs photoelectric conversion in the photoelectric conversion layer 17 by making light incident from the substrate 11 a side.
[0034]
The thin-film solar cell 20 is configured by laminating a photoelectric conversion layer 17, a back reflection layer 15, and a back electrode 16 in this order on a solar cell substrate 11 including a substrate 11 a and a transparent conductive layer 11 b formed thereon. ing.
[0035]
The photoelectric conversion layer 17 includes a p-type silicon layer 12, an i-type silicon layer 13, and an n-type silicon layer 14.
[0036]
The thin-film solar cell 20 of the present embodiment can draw out the electrodes 18 from the transparent conductive layer 11 b and the back electrode 16, and can take out electricity generated by photoelectric conversion via the electrodes 18.
[0037]
For the substrate 11a, for example, a plastic substrate such as glass or acrylic is used as the translucent insulating substrate.
[0038]
The transparent conductive layer 11b is formed on the substrate 11a and is formed using zinc oxide (ZnO) having high plasma resistance. However, the transparent conductive layer 11b is not limited to this, for example, SnO₂, InO_ThreeFurther, it may be a single layer such as ITO or a composite layer obtained by laminating these layers.
[0039]
The transparent conductive layer 11b has a thickness of 0.1 nm to 2 μm, and is formed by sputtering because the transmittance and resistivity of the transparent conductive layer 11b can be easily controlled to those suitable for a crystalline silicon thin film solar cell. ing. Moreover, in order to reduce a resistivity, the impurity may contain. The impurities include group III elements such as gallium and aluminum, and the concentration thereof is, for example, 5 × 10 5.²⁰~ 5x10^{twenty one}/ Cm^ThreeIt is. In addition to the sputtering method, it is also possible to form by vacuum deposition method, EB deposition method, atmospheric pressure CVD method, reduced pressure CVD method, sol-gel method, electrodeposition method or the like.
[0040]
The surface of the transparent conductive layer 11b is formed with a number of roughly spherical holes that do not reach the substrate 11a by surface treatment using an etchant containing an alcohol derivative, and finer irregularities are formed on the surface of the holes. Yes.
[0041]
These holes and fine irregularities generate a scattering or reflection state of sunlight suitable for the light absorption characteristics of the photoelectric conversion layer 17, and are suitable for reducing the defect density of the crystalline photoelectric conversion layer laminated thereon. Number, size, shape, depth, etc. A detailed description of these holes and fine irregularities will be described in detail later.
[0042]
The photoelectric conversion layer 17 is formed on the transparent conductive layer 11b, and is usually formed by a pin junction. Here, the photoelectric conversion layer 17 may be a layer containing crystalline silicon or amorphous silicon, but in the single-junction thin film solar cell 20 shown in FIG. 1, the photoelectric conversion layer 17 is made of crystalline silicon. More preferably, it is a layer containing.
[0043]
In the photoelectric conversion layer 17, all of the pin junction p-type silicon layer 12, i-type silicon layer 13, and n-type silicon layer 14 are formed of crystalline silicon. However, the present invention is not limited to this, and in addition to the i-type silicon layer 13, only one of the p-type silicon layer 12 and the n-type silicon layer 14 in contact with the transparent conductive layer 11b is crystallized. It may be a layer made of quality silicon.
[0044]
In addition, crystalline silicon includes alloyed silicon such as Si to which carbon is added._xC_1-x, Si with germanium added_xGe_1-xOr silicon to which other impurities or the like are added.
[0045]
The p-type silicon layer 12 constituting the photoelectric conversion layer 17 is a layer containing a group III element (for example, boron, aluminum, germanium, indium, titanium, etc.). The p-type silicon layer 12 may be a single layer, or may be formed of a composite layer having a different group III element concentration or gradually changing for each stacked layer. The group III element concentration is, for example, about 0.01 to 8 atomic%, and the thickness of the p-type silicon layer 12 may be, for example, about 1 to 200 nm.
[0046]
The p-type silicon layer 12 may be formed by any method as long as it can form a silicon layer having p-type conductivity, and a general method for forming the silicon layer is a CVD method. Here, this CVD method may be any of atmospheric pressure CVD, low pressure CVD, plasma CVD, ECR plasma CVD, high temperature CVD, low temperature CVD, etc., but is based on a high frequency in the frequency band from RF to VHF, ECR plasma. It is preferable to form the film by a CVD method or a combination thereof. For example, when the plasma CVD method is used, the conditions are that the frequency is about 10 to 200 MHz, the power is several W to several kW, the pressure in the chamber is about 0.1 to 20 Torr, and the substrate temperature is about room temperature to about 600 ° C. Good.
[0047]
Examples of the silicon-containing gas used to form the silicon layer include SiH_Four, Si₂H₆, SiF_Four, SiH₂Cl₂, SiCl_FourEtc. The silicon-containing gas is usually H₂Used with inert gas such as Ar, He, Ne, Xe, etc.₂It is preferable to use a gas. The mixing ratio of the silicon-containing gas and the dilution gas may be, for example, about 1: 1 to 1: 100 in volume ratio while being constant or changing.
[0048]
Further, as a doping gas, a gas arbitrarily containing a group III element, for example, B₂H₆Etc. can be used. In this case, the mixing ratio between the silicon-containing gas and the group III element-containing gas can be adjusted as appropriate according to the size of the film forming apparatus such as CVD, the desired group III element concentration, and the like. For example, the capacity ratio can be about 1: 0.001 to 1: 1. The group III element doping may be performed simultaneously with the formation of the crystalline silicon layer as described above. After the silicon film is formed, ion implantation, surface treatment of the crystalline silicon layer, solid layer diffusion, etc. You may carry out using the method of. Furthermore, fluorine gas may be added to the silicon-containing gas. As the fluorine-containing gas used here, for example, F₂, SiF_Four, SiH₂F₂The specification amount of the fluorine-containing gas in this case is, for example, about 0.01 to 10 times that of hydrogen gas.
[0049]
The i-type silicon layer 13 is a layer that does not substantially exhibit p-type and n-type conductivity, but has a very weak p-type or n-type conductivity that does not impair the photoelectric conversion function. May be. The i-type silicon layer 13 can be formed by, for example, plasma CVD, and the film thickness is, for example, about 0.1 to 10 μm. The i-type silicon layer 13 can be formed by substantially the same method as the p-type silicon layer 12 except that the gas used does not contain a group III element.
[0050]
The n-type silicon layer 14 has a thickness of, for example, about 10 to 100 nm, and the p-type silicon layer 12 and the i-type silicon layer 13 except that a gas containing a group V element as a dopant gas, for example, PH3 is used. It can be formed similarly. Examples of the impurity serving as a donor include phosphorus, arsenic, and antimony. The impurity concentration is 10¹⁸-10²⁰cm^-3Any degree is acceptable.
[0051]
The photoelectric conversion layer 17 has a wavelength that cannot be used for photoelectric conversion in amorphous silicon by forming at least one active layer of the layers constituting the photoelectric conversion layer 17 from silicon containing silicon or a silicon alloy. Long wavelength light of 700 nm or more can be fully utilized.
[0052]
This is due to the difference in photosensitivity between amorphous silicon having high short wavelength sensitivity and crystalline silicon having high long wavelength sensitivity.
[0053]
In particular, the integrated intensity I of the (220) X-ray diffraction peak of the active layer made of silicon or a silicon alloy containing the crystalline material.₂₂₀And the integrated intensity I of the (111) X-ray diffraction peak I₁₁₁Ratio I₂₂₀/ I₁₁₁Is 5 or more, an active layer with very few defects is formed, and a high-quality photoelectric conversion layer 17 can be obtained.
[0054]
On the photoelectric conversion layer 17, a transparent conductive layer is formed as the back surface reflection layer 15 as necessary. Similar to the transparent conductive layer 11b on the light incident side, this transparent conductive layer is, for example, SnO.₂, InO_ThreeSputtering method, vacuum deposition method, EB deposition method, atmospheric pressure CVD method, reduced pressure CVD method, sol-gel method, electrodeposition method, etc., using a single layer of transparent conductive material such as ZnO, ITO, or a composite layer obtained by laminating these layers In the same manner as the transparent conductive layer 11b, the sputtering method may be used in view of the advantage that the transmittance and resistivity are easily controlled to values suitable for the crystalline silicon solar cell. preferable.
[0055]
Further, as the back electrode 16, a single layer of metal such as silver or aluminum having a relatively high reflectivity, or a composite layer obtained by laminating these is formed by sputtering, vacuum deposition, EB deposition, atmospheric pressure CVD. It is formed by a method, a low pressure CVD method, a sol-gel method, an electrodeposition method or the like.
[0056]
Here, the details of the plurality of holes on the surface of the transparent conductive layer 11b and the fine irregularities generated on the surface will be described.
[0057]
Usually, zinc oxide or the like used as the transparent conductive layer 11b is desirably low resistance because it is used as an electrode, and a film quality that contains a large amount of crystalline material is used. For this reason, the film surface and the film have a plurality of grain boundaries, and it is observed by a scanning electron microscope or X-ray diffraction that the film is a polycrystalline thin film having a particle diameter of several tens to several hundreds of nanometers. . When the transparent conductive layer 11b is oriented in the specific axis direction with respect to the substrate surface, the influence of the plane orientation dependency in the processing such as etching is eliminated, and the transparent conductive layer 11b is formed on the photoelectric conversion layer 17 side surface. A plurality of holes and fine irregularities generated on the surfaces of the holes can be formed uniformly. Therefore, the photoelectric conversion characteristics of the thin film solar cell 20 can be made uniform. Moreover, the depth of the hole formed after an etching process becomes large with the improvement of orientation, and long wavelength light with a wavelength of 700 nm or more can be absorbed effectively.
[0058]
From the above, for example, when zinc oxide is used for the transparent conductive layer 11b, the integrated intensity of the (0001) diffraction peak obtained by the X-ray diffraction method is 70 with respect to the sum of the integrated intensity of all diffraction peaks. % Or more is preferable from the viewpoint of electrical and optical characteristics.
[0059]
And as a suitable structure for obtaining the light confinement effect, in order to form a plurality of holes and fine irregularities on the surface of the transparent conductive layer 11b, a transparent structure is formed by the following means. It was found that the surface treatment of the conductive layer 11b may be performed.
[0060]
This specific method is as follows.
[0061]
That is, in the manufacturing method of the thin film solar cell 20 of the present embodiment, the surface of the transparent conductive layer 11b is etched with an alcohol derivative represented by the following structural formula (1) using an acid or alkaline etching solution containing at least one kind.
A- (OH)_n    (1)
(N is an integer of 1 to 4, and A is an aliphatic hydrocarbon residue bonded to a hydroxyl group via a carbon atom).
[0062]
Normally, a transparent conductive layer such as zinc oxide, which is a polycrystalline thin film, is etched with an acid or alkaline etchant so that only a specific surface of the crystal grain is dominantly etched along the grain boundary at the initial stage of etching. A plurality of holes. When the etching is further advanced, the etching progresses as a whole, and the holes formed in the initial stage of the etching become larger with the lapse of the etching time, and finally the transparent conductive layer itself is lost. This tendency is particularly remarkable in the etchant using an aqueous solution. Therefore, when etching is stopped to such an extent that the hole does not reach the underlying substrate or film, fine irregularities effective to obtain a good light confinement effect on the surface of the transparent conductive layer forming the hole Can not form.
[0063]
Therefore, according to the method for manufacturing a thin film solar cell of the present invention, the size of the hole generated in the initial stage of etching is expanded by etching with an acid or alkaline solution containing the alcohol derivative represented by the above structural formula. Instead, a desired plurality of holes can be formed on the surface of the hole, and a plurality of fine irregularities can be formed on the surface of the hole.
[0064]
This is because the alcohol derivative contained in the etching solution moderately suppresses the action of anisotropic etching that proceeds in the direction of expanding the hole, and promotes etching on the surface of the hole generated in the initial stage of etching. It is thought that it is because it is doing.
[0065]
The alcohol derivative contained in the acid or alkaline solution for etching the surface of the transparent conductive layer 11b may be any one that has a function of suppressing anisotropic etching and has hydration properties. Specifically, for example, the same etching can be performed with ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol, glycerin, and propylene glycol.
[0066]
In the etching solution, the alcohol derivative is preferably contained at 10% or more of the total solution amount. This is because if it is less than 10%, a sufficient effect cannot be obtained by containing the alcohol derivative.
[0067]
Furthermore, when the surface of the transparent conductive layer 11b is etched with an acid or alkaline solution containing an alcohol derivative, it is preferable to etch the etching solution in a temperature range of 5 ° C. or more and 40 ° C. or less.
[0068]
This is because the etching solution contains an alcohol derivative, and at a temperature higher than 40 ° C., the highly volatile alcohol derivative cannot fully exert its effect, but is anisotropic due to an acid or alkaline etchant. This is because the action of the reactive etching becomes strong and it becomes difficult to form a suitable light confinement structure. On the other hand, if it is 5 ° C. or lower, the etching process rate is lowered and the production is not efficient. Considering from the viewpoint of manufacturing cost, treatment at room temperature which does not require equipment for raising and lowering the etching solution is preferable, and the present invention can sufficiently exhibit its effect even at room temperature.
[0069]
Examples of the melt in an acidic solution containing an alcohol derivative include one or a mixture of two or more inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, and perchloric acid. Among them, hydrochloric acid is used. For example, it can be used as an acidic solution having a concentration of about 0.05 to 5% by weight.
[0070]
Examples of the alkaline solution containing an alcohol derivative include sodium hydroxide, hydrazine, potassium hydroxide, calcium hydroxide, and a mixture of two or more. Among these, sodium hydroxide is used. preferable. These alkaline solutions are preferably used at a concentration of about 1 to 10% by weight.
[0071]
The diameter of the hole suitable for the absorption characteristics of the photoelectric conversion layer 17 is about 200 to 2000 nm, and particularly preferably about 400 to 1200 nm. The depth of the hole is about 50 to 1200 nm, and particularly preferably about 100 nm to 800 nm. Furthermore, the height difference of the fine irregularities is about 10 to 300 nm, and preferably about 20 to 200 nm.
[0072]
Further, in order to produce a better light scattering or reflection state, it is preferable that fine irregularities are also formed on the surface other than the hole formed on the surface of the transparent conductive layer 11b. Thereby, the light scattering effect can be further enhanced, an effective light confinement effect can be obtained in the photoelectric conversion layer 17, and a thin film solar cell having high photoelectric conversion efficiency can be obtained. In this case, the height difference of the unevenness is about 10 to 300 nm, and more preferably about 20 to 200 nm.
[0073]
As described above, sufficient light scattering can be caused not only for light having a central wavelength of the solar spectrum of about 400 to 650 nm but also for light having a longer wavelength than these. Therefore, in response to this sufficient light scattering, a sufficient light confinement effect can be obtained also in the photoelectric conversion layer 17, and as a result, a thin film solar cell having high photoelectric conversion efficiency can be obtained. In addition, although light scattering has a magnitude of the effect obtained by the uneven shape, it is not such that the effect is not obtained by the shape, for example, a shape such as a substantially cube, rectangular parallelepiped, cylinder, cone, sphere, hemisphere, Or what is necessary is just the shape which combined these.
[0074]
A good light confinement effect leads to an effect that the film thickness of each layer of the photoelectric conversion layer 17 can be reduced. In particular, in the case of an amorphous silicon solar cell, it is possible to suppress deterioration in photoelectric conversion efficiency due to the Stabler-Wronski effect. In addition, in the case of crystalline silicon solar cells that require a thickness of several μm, which is several to tens of times that of amorphous silicon, due to the light absorption characteristics, the film formation time is greatly reduced. can do. That is, light confinement can be improved for all aspects of high efficiency, stabilization, and cost reduction, which are major issues for the practical application of thin film solar cells.
[0075]
In addition, when the present invention is applied to a thin film solar cell having a super straight type structure as shown in FIG. 1, fine irregularities on the surface of the hole of the transparent conductive layer 11b are deposited on the transparent conductive layer 11b. It acts as a thin layer having an optical characteristic intermediate to that of the silicon thin film, reduces reflection at the interface between the transparent conductive layer 11b and the silicon thin film deposited thereon, and is effective for the photoelectric conversion layer 17. Light incidence can be promoted. Therefore, high photoelectric conversion efficiency can be obtained as a thin film solar cell having a super straight type structure.
[0076]
On the other hand, when the present invention is applied to a thin film solar cell 50 having a substrate type structure as shown in FIG. 3, the fine irregularities formed on the surface of the hole of the transparent conductive layer 44 are the transparent conductive layer 44 and its It acts as a thin layer having optical properties intermediate to the protective film or atmosphere deposited thereon, and can reduce reflection at the interface between the transparent conductive layer 44 and the protective film or atmosphere deposited thereon. . Therefore, as the substrate-type thin film solar cell 50, effective light incidence to the photoelectric conversion layer 45 can be promoted, and high photoelectric conversion efficiency can be obtained.
[0077]
Thus, as a structural form of the thin film solar cell 20 of the present invention, in addition to the super straight type thin film solar cell 20 in which light is incident from the substrate 11a side as shown in FIG. 1 described in the present embodiment, A thin film solar cell 50 having a substrate type structure in which light is incident from the respective crystalline silicon layers 41 to 43 side as shown in FIG. 3 may be used.
[0078]
  The thin film solar cell of the present inventionPondIn the manufacturing method, without depositing a plurality of layers subjected to unevenness control, a surface treatment for a simple transparent conductive layer 11b using an etchant containing an alcohol derivative is used to form a structure such as a super straight type or a substrate type. Regardless, a thin film solar cell having high photoelectric conversion efficiency can be obtained. However, in the thin film solar cell 20 having a super straight structure, it is more preferable because a high-quality polycrystalline semiconductor layer can be formed on the transparent conductive layer 11b.
[0079]
In the present embodiment, the single-junction thin-film solar cell 20 shown in FIG. 1 has been described as an example. However, the present invention is not limited to this. For example, a plurality of pin junctions as shown in FIG. The multi-junction thin film solar cell 60 may be used.
[0080]
In the multi-junction thin film solar cell 60, all the first and second silicon photoelectric conversion layers 27 and 37 may not be layers containing crystalline silicon or amorphous silicon. And a layer containing amorphous silicon may be stacked.
[0081]
In the multi-junction thin-film solar cell 60 shown in FIG. 4, it is preferable that a layer containing crystalline silicon and a layer containing amorphous silicon are mixed. The first and second silicon photoelectric conversion layers 27 and 37 containing crystalline silicon are not limited to polycrystals and single crystals, and all crystals such as so-called microcrystals or microcrystals, unless otherwise noted. Includes state. These crystal states may exist over the entire first and second silicon photoelectric conversion layers 27 and 37, or may be entirely present in each layer constituting the first and second silicon photoelectric conversion layers 27 and 37. Or you may exist partially.
[0082]
  Hereinafter, the thin film solar cell according to the present inventionPondExamples relating to the manufacturing method will be specifically described.
[0083]
Example 1
The single-junction thin-film solar cell according to Example 1 has the same configuration as the super-straight single-junction thin-film solar cell of FIG. 1 described in the above embodiment.
[0084]
A method for manufacturing a super-straight type single-junction thin film solar cell according to Example 1 will be described below.
[0085]
First, a glass plate having a smooth surface is used as the substrate 11a, and zinc oxide is formed as a transparent conductive layer 11b with a thickness of 1200 nm on the substrate 11a by a magnetron sputtering method at a substrate temperature of 150 ° C. and a film forming pressure of 0.3 mTorr. A solar cell substrate 11 was formed.
[0086]
The transparent conductive layer 11b has 1 × 10^{twenty one}/cm^ThreeAbout gallium is added. As a result, the sheet resistance of the obtained transparent conductive layer 11b was 10Ω / □, and the transmittance for light having a wavelength of 800 nm was 80%. Further, when the X-ray diffraction method was performed on the transparent conductive layer 11b, the integrated intensity of the (0001) diffraction peak was 75% with respect to the sum of the integrated intensity of all the diffraction peaks.
Subsequently, the surface of the transparent conductive layer 11b was etched.
The acidic solution used as the etching solution was a mixture of ethyl alcohol and water prepared so as to contain 30% by weight of ethyl alcohol in the final volume, and hydrochloric acid was added to a hydrochloric acid concentration of 0.35% by weight. In addition, it produced. After the solar cell substrate 11 was immersed in this etching solution at a liquid temperature of 25 ° C. for 150 seconds, the surface of the solar cell substrate 11 was sufficiently washed with pure water. When the surface of the transparent conductive layer 11b after etching was observed with a scanning electron microscope, holes having a substantially circular shape were formed, the maximum diameter range of the holes was 300 to 1000 nm, and the number density was about 1 / μm²It was about.
[0087]
In order to examine the hole and the surrounding surface in more detail, an observation with an atomic force microscope was performed.
[0088]
The depth 21 of the hole formed in the surface of the transparent conductive layer 11b in the surface of the transparent conductive layer 11b obtained by these observations was about 100 to 800 nm as shown in FIG. Furthermore, fine irregularities are formed on the surface portion of the transparent conductive layer 11b forming the hole, and the size of the fine irregularities (difference level difference) is about 20 to 150 nm. The interval 24 was about 80 to 400 nm. Moreover, fine irregularities were formed in addition to the hole portions, and the size of the fine irregularities was about 30 to 60 nm. That is, it was found that the transparent conductive layer 11b has a structure in which finer irregularities are formed in the formed hole portion.
[0089]
Subsequently, a p-type silicon layer 12 having a thickness of about 20 nm and an i-type silicon layer 13 having a thickness of about 2 μm are formed on the transparent conductive layer 11b on the obtained solar cell substrate 11 by high-frequency plasma CVD. A photoelectric conversion layer 17 made of crystalline silicon was produced by laminating an n-type silicon layer 14 having a thickness of about 30 nm in this order. The substrate temperature during film formation was 200 ° C. in each layer.
[0090]
When the p-type silicon layer 12 is formed, SiH_FourGas is 5 times higher in flow rate ratio₂A material diluted with gas is used as a raw material gas, and further B₂H₆Gas is SiH_FourA film was formed by adding 0.1% to the gas flow rate. Further, when the i-type silicon layer 13 is formed, the same source gas as that of the p-type silicon layer 12 is used. When the n-type silicon layer 14 is formed, SiH is used._FourPH against gas flow rate_ThreeThe gas was used by adding 0.01%.
[0091]
After taking out from a plasma CVD apparatus (not shown) once, when the X-ray diffraction method was performed with respect to the obtained photoelectric converting layer 17, the integrated intensity I of a (220) X-ray diffraction peak was obtained.₂₂₀And (111) X-ray diffraction peak integrated intensity I₁₁₁Ratio I₂₂₀/ I₁₁₁Was 5.5.
[0092]
Here, the actually obtained X-ray diffraction peaks are not information of the i-type silicon layer 13 alone in the photoelectric conversion layer 17, but the p-type silicon layer 12 and the n-type silicon layer are compared with the i-type silicon layer. Since the film thickness 14 is very thin, it can be considered that the crystal orientation of the i-type silicon layer 13 is reflected.
[0093]
Thereafter, zinc oxide is formed as a back surface reflection layer 15 to a thickness of about 50 nm by magnetron sputtering, and silver is formed as a back surface electrode 16 to a thickness of about 500 nm by an electron beam evaporation method. Light is incident from the substrate 11a side. A single-junction thin-film solar cell 20 having a super straight structure was obtained.
[0094]
(Examples 2 to 4)
As Examples 2 to 4, etching solutions were prepared so that the amount of ethyl alcohol contained in a 0.35 wt% hydrochloric acid solution was 8 wt%, 10 wt%, and 90 wt% with respect to the total solution amount. The treatment time when containing 8% by weight of ethyl alcohol was 130 seconds, the treatment time when containing 10% by weight was 140 seconds, the treatment time when containing 90% by weight was 180 seconds, and otherwise the same as in Example 1. Thus, single-junction thin-film solar cells were manufactured with the super-straight structure according to Examples 2 to 4, respectively. Then, the surface shape of the transparent conductive layer 11b and the characteristics of the thin film solar cell when the surface of the transparent conductive layer 11b was etched with each etching solution were examined.
[0095]
Before forming the photoelectric conversion layer 17 containing crystalline silicon, the surface of the transparent conductive layer 11b was observed with a scanning electron microscope. The maximum diameter of the hole was 100 to 1800 nm in the treatment with 8% by weight of ethyl alcohol. In the treatment of 10% by weight, the range was 200 to 1400 nm, and in the treatment of 90% by weight of ethyl alcohol, the range was 200 to 1000 nm. The shape is almost a circular hole, and the number density is 2 / μm in the treatment with 8% by weight of ethyl alcohol.²In the treatment with 10% by weight of ethyl alcohol, 1.6 pieces / μm²In the treatment with 90% by weight of ethyl alcohol, 1 piece / μm²It was about.
[0096]
Then, in the same manner as in Example 1, in order to examine the hole and the surrounding surface in more detail, observation with an atomic force microscope was performed. The outline of the surface of the transparent conductive layer 11b will be schematically described with reference to FIG. 2 shown in the first embodiment.
[0097]
As a result, the depth 21 of the hole is 300 to 1100 nm in the treatment of 8% by weight of ethyl alcohol according to Example 2, 200 to 1000 nm in the treatment of 10% by weight of ethyl alcohol according to Example 3, and according to Example 4. In the treatment with 90% by weight of ethyl alcohol, the thickness was 80 to 700 nm.
[0098]
Further, fine irregularities are also formed on the surface of the hole and on the surface where no hole is formed, and the size 23 of the fine irregularity on the surface of the hole (the height difference of the irregularities) is 8% by weight of ethyl alcohol. The treatment was 10 to 40 nm, the treatment with 10% by weight of ethyl alcohol was 10 to 80 nm, and the treatment with 90% by weight of ethyl alcohol was 30 to 250 nm. The fine uneven spacing 24 was 300 to 1000 nm in the treatment with 8% by weight of ethyl alcohol, 200 to 800 nm in the treatment with 10% by weight of ethyl alcohol, and 80 to 500 nm in the treatment with 90% by weight of ethyl alcohol. Furthermore, the size of the fine irregularities on the surface where no hole is formed is 100 to 300 nm for the treatment with 8% by weight of ethyl alcohol, 100 to 200 nm for the treatment with 10% by weight of ethyl alcohol, and 90% by weight of ethyl alcohol. It was 20 to 40 nm.
[0099]
Here, when the thin film solar cells according to Examples 1 to 4 were compared, when the alcohol content was reduced, the number of holes increased and the number increased, whereas conversely, the fine irregularities on the hole surface decreased and the number increased. There was a tendency to decrease. This is considered to be because anisotropic etching becomes stronger as the content of the alcohol derivative decreases.
[0100]
(Examples 5 to 9)
As Examples 5-9, methyl alcohol, isopropyl alcohol, ethylene glycol, glycerin, and propylene glycol were respectively added at predetermined concentrations as alcohol derivatives contained in a 0.35 wt% hydrochloric acid solution used for etching the surface of the transparent conductive layer 11b. A single-junction thin-film solar cell having a super-straight structure according to Examples 5 to 9 was produced in the same manner as in Example 1 except that the mixture with water was used.
[0101]
(Example 10)
As Example 10, as an etching solution on the surface of the transparent conductive layer 11b, hydrofluoric acid, which is a mixed acid of hydrofluoric acid and nitric acid in which nitric acid is mixed with hydrofluoric acid at a volume ratio of 1: 200, is 0.1% by weight. In the same manner as in Example 1, except that an acidic solution was prepared using water and ethylene glycol, the amount of ethylene glycol contained in the whole solution was 30% by weight, and the treatment time was 60 seconds. A single-junction thin-film solar cell with a straight structure was fabricated.
[0102]
(Example 11)
As Example 11, an alkaline solution was prepared using water and ethyl alcohol so as to be a 1 wt% sodium hydroxide solution as an etching solution on the surface of the transparent conductive layer 11b, and the ethyl alcohol contained in the whole solution A single-junction thin-film solar cell with a superstrate structure was fabricated in the same manner as in Example 1 except that the amount was 30% by weight and the treatment time was 100 seconds.
[0103]
(Comparative Example 1)
As Comparative Example 1, the surface of the transparent conductive layer was etched for 120 seconds using a 0.35 wt% hydrochloric acid solution containing no alcohol derivative and adding a predetermined amount of hydrochloric acid to water. In the same manner as in Example 1, a single-junction thin-film solar cell having a super straight structure was manufactured.
[0104]
In the thin film solar cell according to Comparative Example 1, when the surface of the transparent conductive layer was observed with a scanning electron microscope before the photoelectric conversion layer was formed, a substantially circular hole was formed, and the maximum diameter of the hole was The range is 80 to 2000 nm, and the number density is about 2.5 / μm.²It was formed to some extent.
[0105]
In the same manner as in Example 1, in order to examine the hole and the surrounding surface in more detail, observation with an atomic force microscope was performed.
[0106]
In the thin film solar cell of Comparative Example 1, the surface of the transparent conductive layer obtained by the etching treatment had a hole depth 101 of about 300 to 1100 nm as shown in FIG. Moreover, the fine unevenness | corrugation currently formed in the surface of a hole was as small as 10 nm or less, and the number was also small. On the other hand, the unevenness on the surface where the hole was not formed was large, and it was difficult to distinguish between the hole and the unevenness. Number density 2.5 / μm²Is classified as fine unevenness on the surface without holes in Examples 1 to 11 above, but in this comparative example, the density increases as the size of the unevenness increases as it is classified as a hole. It is thought that.
[0107]
(Comparative Example 2)
As Comparative Example 2, as the etching solution on the surface of the transparent conductive layer, hydrofluoric acid, which is a mixed acid of hydrofluoric acid and nitric acid in which nitric acid is mixed with hydrofluoric acid at a volume ratio of 1: 200, is 0.1% by weight. A super solution was prepared in the same manner as in Example 1 except that an acidic solution was prepared using water and n-butanol, the amount of n-butanol contained in the whole solution was 30% by weight, and the treatment time was 60 seconds. A single-junction thin-film solar cell with a straight structure was fabricated.
[0108]
  The thin film solar cell of the present invention as described aboveManufacturing methodFor Examples 1 to 11 and Comparative Examples 1 and 2 according to Table 1, the surface shape of the transparent conductive layer 11b and the orientation of the photoelectric conversion layer 17 are shown in Table 1. AM1.5 (100 mW / cm of this thin-film solar cell)²) Current-voltage characteristics under irradiation conditions are shown in Table 2, respectively.
[0109]
[Table 1]

[0110]
[Table 2]

[0111]
Examples 1 to 11 and Comparative Examples 1 and 2 will be described in detail below using Tables 1 and 2.
[0112]
The surface shape after the etching treatment of the transparent conductive layer in each of Examples 1 to 11 is formed into a surface shape as shown in FIG. 2, and a plurality of holes are formed on the surface of the transparent conductive layer. Fine irregularities were formed on the surface of each of the inside and the portion where no hole was formed. However, in Comparative Examples 1 and 2, as compared with Examples 1 to 11, the maximum diameter range of the hole is widened, the number of holes is increased, and on the contrary, the fine unevenness inside the hole is smaller, and the number is also increased. It was decreasing.
[0113]
In addition, the orientation I of the photoelectric conversion layer₂₂₀/ I₁₁₁In Examples 1 to 11 and Comparative Examples 1 and 2, a value of 5.0 or more was obtained, so that a good film with few defects was formed for the photoelectric conversion layer of any thin film solar cell. It is thought that.
[0114]
When the current-voltage characteristics of the thin film solar cells of Examples 1 to 11 and Comparative Examples 1 and 2 are compared, the comparative example is obtained regardless of whether the thin film solar cells have the same open circuit voltage and form factor. The short circuit current of 1 and 2 is low compared with Examples 1-11. That is, it can be seen that the light confinement effect of Comparative Examples 1 and 2 is not sufficient as compared with Examples 1-11. About the surface shape of the transparent conductive layer 11b, it is thought that the fine unevenness | corrugation of the surface of the hole seen in Examples 1-11 has contributed largely to light confinement. This is because fine irregularities are formed on the surface of the hole, so that sufficient light scattering is generated for incident light and reflection at the interface between the transparent conductive layer and the silicon thin film deposited thereon is performed. This is considered to be due to the fact that it was possible to reduce and promote effective light incidence on the photoelectric conversion layer 17.
[0115]
Moreover, in Examples 1-11, Example 2 became the lowest short circuit current value. This is considered to be because fine irregularities sufficient for light confinement were not formed on the hole surface because the content of the alcohol derivative was small.
[0116]
Therefore, by applying a surface treatment using an etchant containing an alcohol derivative to the transparent conductive layer, the surface promotes sufficient light scattering, obtains a sufficient light confinement effect in the photoelectric conversion layer, and achieves high photoelectric conversion efficiency. It turned out that it becomes possible to manufacture the thin film solar cell which has it easily.
[0117]
In Examples 1 to 11, only the transparent conductive layer 11b formed on the substrate 11a was subjected to surface treatment by etching, but the same applies to the transparent conductive layer used as the back surface reflective layer 15 on the back electrode 16 side. Even when the treatment is performed, the same effect can be obtained.
[0118]
Example 12
As Example 12, a single-junction thin film solar cell 50 having a substrate structure as shown in FIG. 3 was formed.
[0119]
As shown in FIG. 3, the thin-film solar cell 50 according to Example 12 includes a photoelectric conversion layer on a solar cell substrate 40 including a stainless steel substrate 40a, a back electrode 40b formed thereon, and a transparent conductive layer 40c. 45 and the transparent conductive layer 44 are laminated in this order.
[0120]
The photoelectric conversion layer 45 includes an n-type crystalline silicon layer 41, an i-type crystalline silicon layer 42, and a p-type crystalline silicon layer 43.
[0121]
A single-junction thin film solar cell 50 having such a substrate type structure was formed by the following procedure.
[0122]
First, on the stainless steel substrate 40a having a smooth surface, silver is formed with a thickness of 500 nm as the back electrode 40b by electron beam evaporation, and then the transparent conductive layer 40c is used as the back reflective layer by magnetron sputtering using zinc oxide. The substrate 40 for solar cells was formed with a thickness of 50 nm.
[0123]
Next, an n-type crystalline silicon layer 41 having a thickness of 30 nm and an i-type crystalline silicon layer 42 having a thickness of 2 μm are formed on the transparent conductive layer 40c on the obtained solar cell substrate 40 by high-frequency plasma CVD. The photoelectric conversion layer 45 was produced by sequentially stacking the p-type crystalline silicon layer 43 having a thickness of 20 nm. The substrate temperature during film formation was 200 ° C. in each layer.
[0124]
When the n-type crystalline silicon layer 41 is formed, SiH_FourGas is 5 times higher in flow rate ratio₂A gas diluted with gas is used as a raw material gas, and further PH_ThreeGas is SiH_FourA film was formed by adding 0.01% to the gas flow rate. Further, when forming the i-type crystalline silicon layer 42, the same source gas as that of the n-type crystalline silicon layer 41 is used.₂H₆Gas is SiH_FourIt was used by adding 0.1% to the gas flow rate.
[0125]
Thereafter, zinc oxide was formed to a thickness of 1000 nm as the transparent conductive layer 44 by a magnetron sputtering method at a substrate temperature of 150 ° C. and a film forming pressure of 0.3 mTorr. The transparent conductive layer 44 has 1 × 10^{twenty one}/ Cm^ThreeAbout gallium is added. As a result, the sheet resistance of the obtained transparent conductive layer 44 was 10Ω / □, and the transmittance for light having a wavelength of 800 nm was 80%. When the X-ray diffraction method was performed on the transparent conductive layer 44, the integrated intensity of the (0001) diffraction peak was 75% with respect to the sum of the integrated intensity of all the diffraction peaks.
[0126]
Subsequently, an etching process was performed on the surface of the transparent conductive layer 44. The acidic solution used as the etching solution was a mixture of ethyl alcohol and water prepared so as to contain 30% by weight of ethyl alcohol in the final volume, and hydrochloric acid was added to a hydrochloric acid concentration of 0.35% by weight. Made by adding. The substrate on which the transparent conductive layer 44 is sequentially deposited is immersed in the etching solution at a liquid temperature of 25 ° C. for 100 seconds, and then the surface is thoroughly washed with pure water, and the substrate on which light enters from the transparent conductive layer 44 side. A single-junction thin-film solar cell 50 having a mold structure was obtained.
[0127]
When the surface of the transparent conductive layer 44 after etching was observed with a scanning electron microscope, the shape was a substantially circular hole, the maximum diameter range of the hole was 200 to 1000 nm, and the number density was approximately 0.8 / μm.²It was about.
[0128]
In order to examine the hole and the surrounding surface in more detail, observation with an atomic force microscope was performed.
[0129]
If the outline of the surface of the transparent conductive layer 44 is schematically described using FIG. 2 shown in Example 1, the depth 21 of the hole formed in the surface of the transparent conductive layer 44 is about 80 to 600 nm. It was. Further, fine irregularities were formed on the surface of the hole, and the size of the irregularities (the height difference of the irregularities) 23 was about 10 to 180 nm, and the interval 24 between the irregularities was about 80 to 600 nm. Moreover, the size of the fine unevenness formed on the portion other than the hole surface was about 10 to 50 nm.
[0130]
(Comparative Example 3)
As Comparative Example 3, the surface of the transparent conductive layer was etched using a 0.35 wt% hydrochloric acid solution prepared by adding a predetermined amount of hydrochloric acid to water without containing an alcohol derivative. In the same manner as in No. 12, a single-junction thin film solar cell having a substrate type structure was produced.
[0131]
When the surface of the transparent conductive layer after etching was observed with a scanning electron microscope, the shape was a substantially circular hole, the maximum diameter range of the hole was 400 to 1200 nm, and the number density was approximately 2.8 / μm.²It was found that it was formed to some extent.
[0132]
In the same manner as in Example 12, in order to investigate the hole and the surrounding surface in more detail, observation with an atomic force microscope was performed. The surface of the transparent conductive layer in Comparative Example 3 is the same as FIG. 5 shown as the surface of the transparent conductive layer of the thin film solar cell according to Comparative Example 1. Therefore, the transparent conductive layer of the thin film solar cell according to Comparative Example 3 will be described with reference to FIG. In addition, the depth 101 of the hole in Comparative Example 3 was about 300 to 800 nm, and the fine irregularities formed on the surface of the hole were as small as 10 nm or less, and the number thereof was also small.
[0133]
On the other hand, the unevenness of the surface where the hole is not formed is large, and it becomes difficult to distinguish the hole and the unevenness. The number density is 2.8 / μm.²Is classified as fine irregularities on the surface without holes in the previous Example 12, but in this comparative example, the density increases as the size of the irregularities increases as it is classified as holes. it is conceivable that.
[0134]
AM1.5 (100 mW / cm) of the thin film solar cell according to Example 12 and Comparative Example 3 as described above²Table 3 shows the current-voltage characteristics under irradiation conditions.
[0135]
[Table 3]

[0136]
In Table 3, when Example 12 and Comparative Example 3 are compared, the values of the open circuit voltage and the shape factor are hardly changed, but the value of Example 12 is higher than that of Comparative Example 3 for the short circuit current. I understand that.
[0137]
That is, for the transparent conductive layer 44 of the substrate type thin film solar cell 50 according to Example 12, a plurality of holes are formed on the surface of the transparent conductive layer 44 by a simple etching process according to Example 12 of the present invention. In addition, since fine irregularities are generated on the surface of the hole, a light scattering effect effective for light confinement and a reflection reducing effect on the surface of the transparent conductive layer 44 can be obtained. It is thought that it became larger than the thin film solar cell which concerns.
[0138]
Although Example 12 was a thin film solar cell in which only the transparent conductive layer 44 was subjected to a surface treatment by etching, the same treatment was applied to the transparent conductive layer 40c used as the back surface reflective layer on the back electrode 40b side. Even in this case, the same effect can be obtained.
[0139]
(Example 13)
As shown in FIG. 4, the super-straight type multi-thin film solar cell 60 according to Example 13 includes a substrate 11a, a transparent conductive layer 11b formed thereon, a first silicon photoelectric conversion layer 27, a first The two transparent conductive layers 11c, the second silicon photoelectric conversion layer 37, the back reflective layer 15, and the back electrode 16 are laminated in this order.
[0140]
The first silicon photoelectric conversion layer 27 includes a p-type amorphous silicon layer 12a, an i-type amorphous silicon layer 13a, and an n-type amorphous silicon layer 14a. The p-type silicon layer 12b, the i-type silicon layer 13b, and the n-type silicon layer 14b are included.
[0141]
The multi-junction thin film solar cell having the above-described configuration can be manufactured as follows.
[0142]
First, in the same manner as in Example 1, zinc oxide is formed to a thickness of 1200 nm as the transparent conductive layer 11b on the substrate 11a having a smooth surface by a magnetron sputtering method at a substrate temperature of 150 ° C. and a film forming pressure of 0.3 mTorr. Then, the substrate 11 for solar cells was formed by etching the surface of the transparent conductive layer 11b. As in Example 1, the transparent conductive layer 11b is subjected to surface treatment with an etchant containing an alcohol derivative, so that many transparent circular holes that do not reach the substrate 11a are formed on the surface of the transparent conductive layer 11b. The atomic force microscope confirmed that a large number of fine irregularities were formed inside the hole.
[0143]
A p-type amorphous silicon layer 12a having a thickness of 20 nm and an i-type amorphous film having a thickness of 300 nm are formed on the solar cell substrate 11 thus obtained by a high-frequency plasma CVD method using a high-frequency plasma CVD apparatus. A first silicon photoelectric conversion layer 27 was fabricated by sequentially stacking a porous silicon layer 13a and an n-type amorphous silicon layer 14a having a thickness of 30 nm. The substrate temperature during film formation was 200 ° C. for each layer.
[0144]
When forming the p-type amorphous silicon layer 12a, SiH_FourGas is 5 times higher in flow rate ratio₂A material diluted with gas is used as a raw material gas, and further B₂H₆Gas is SiH_FourA film was formed by adding 0.01% to the gas flow rate. The i-type amorphous silicon layer 13a is made of the same source gas as that of the p-type amorphous silicon layer 12a, and the n-type amorphous silicon layer 14a is further made PH_ThreeGas is SiH_Four0.01% added to the gas flow rate was used.
[0145]
The solar cell substrate 11 on which the first silicon photoelectric conversion layer 27 is deposited is once taken out from the plasma CVD apparatus, and again as a second transparent conductive layer 11c by a magnetron sputtering method, zinc oxide is formed under the same conditions as the transparent conductive layer 11b. A 5 nm thick film was formed.
[0146]
Subsequently, the 2nd silicon photoelectric converting layer 37 was created on the 2nd transparent conductive layer 11c on the same conditions as the photoelectric converting layer 17 of Example 1. FIG.
[0147]
When the X-ray diffraction method was performed after forming the second silicon photoelectric conversion layer 37, the integrated intensity I of the (220) X-ray diffraction peak was obtained.₂₂₀And the integrated intensity I of the (111) X-ray diffraction peak₁₁₁Ratio I₂₂₀/ I₁₁₁Was 5.5, which was not different from that in Example 1.
[0148]
Thereafter, similarly to Example 1, the back surface reflection layer 15 and the back surface electrode 16 were formed, and a multi-junction type thin film solar cell 60 having a super straight type structure in which light was incident from the substrate 11a was obtained.
[0149]
(Comparative Example 4)
Comparative Example 4 was carried out except that the surface of the transparent conductive layer 11b was etched using a 0.35 wt% hydrochloric acid solution prepared by adding a predetermined amount of hydrochloric acid to water without containing an alcohol derivative. In the same manner as in Example 13, a multi-junction thin film solar cell according to Comparative Example 4 was produced.
[0150]
When the X-ray diffraction method was performed after forming the second silicon photoelectric conversion layer 37, the integrated intensity I of the (220) X-ray diffraction peak was obtained.₂₂₀And the integrated intensity I of the (111) X-ray diffraction peak₁₁₁Ratio I₂₂₀/ I₁₁₁Was 5.0.
[0151]
AM1.5 (100 mW / cm) of the multi-junction thin film solar cell obtained in Example 13 and Comparative Example 4 as described above.²Table 4 shows the current-voltage characteristics under irradiation conditions.
[0152]
[Table 4]

[0153]
In Table 4, when Example 13 and Comparative Example 4 are compared, the values of the open circuit voltage and the form factor are hardly changed, but it is understood that the value of Example 13 is higher for the short circuit current.
[0154]
This is also because the transparent conductive layer in the multi-junction type thin film solar cell has a plurality of holes formed on the surface of the transparent conductive layer 11b by the simple etching process according to the present invention, and fine irregularities are formed on the surface of the holes. This is considered to be because the light scattering effect effective for light confinement and the effect of reducing reflection at the interface between the transparent conductive layer 11b and the first silicon photoelectric conversion layer 27 were obtained.
[0155]
In the thin film solar cell according to Example 13, only the transparent conductive layer 11b was subjected to surface treatment by etching. However, the transparent conductive layer used as the back surface reflective layer 15 on the back electrode side and the first silicon photoelectric conversion layer 27 A similar process may be applied to the second transparent conductive layer 11c inserted between the second silicon photoelectric conversion layer 37 and the second silicon photoelectric conversion layer 37.
[0156]
As mentioned above, although embodiment which concerns on this invention was described using the thin film solar cell which has a zinc oxide layer as transparent conductive layer 11b * 44, this invention is not limited to embodiment mentioned above and an Example. In addition to the type of transparent conductive layer and the type of etchant described above, the same effect as the present invention can be obtained, and even when etching solutions having different acid strength or alkali strength are used The same effect as the present invention can be obtained.
[0157]
【The invention's effect】
The manufacturing method of the thin film solar cell of this invention is a manufacturing method which etches the surface of a transparent conductive layer using the etching liquid which contains at least 1 type of the alcohol derivative shown by following Structural formula (1) as mentioned above. is there.
A- (OH)ⁿ  (1)
(N is an integer of 1 to 4, and A is an aliphatic hydrocarbon residue bonded to a hydroxyl group via a carbon atom).
[0158]
Therefore, due to the nature of the alcohol derivative contained in the etching solution, it is possible to form a plurality of holes effective for obtaining a good light confinement effect on the surface of the transparent conductive layer, and fine irregularities in the hole portions. Therefore, it is possible to obtain a good light confinement effect in the photoelectric conversion layer and to produce a thin film solar cell having high photoelectric conversion efficiency at low cost and easily.
[0159]
That is, according to the method for manufacturing a thin-film solar cell of the present invention, etching is performed using the etching solution containing the alcohol derivative represented by the above structural formula, and therefore, the difference in the direction of expanding the hole due to the property of the alcohol derivative. It is possible to moderately suppress the action of isotropic etching, and the etching proceeds on the surface of the hole generated in the initial stage of etching, so that finer irregularities can be formed in the portion where the hole is formed. In other words, if an acid or alkaline solution containing an alcohol derivative represented by the above structural formula is used, etching does not proceed in the direction of expanding the hole size, and a plurality of desired holes and a plurality of fine particles are formed on the surface of the holes. Unevenness can be formed.
[0160]
Therefore, without requiring large-scale equipment or the like, not only light having a central wavelength of the solar spectrum of about 400 to 650 nm but also light having a wavelength longer than these due to a plurality of holes and fine irregularities formed in the transparent conductive layer. In addition, sufficient light scattering can be caused, and a thin film solar cell having high photoelectric conversion efficiency can be obtained inexpensively and easily by utilizing a good light confinement effect in the photoelectric conversion layer.
[0161]
  The alcohol derivatives are ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol, glycerin, propylene glycol.The
[0162]
Therefore, by suppressing the anisotropic etching by the action of the alcohol derivative, the formed hole is prevented from being enlarged, and desired holes and irregularities that realize good light scattering are formed inexpensively and easily. There is an effect that can be done.
[0163]
  The etching solution contains 10 wt% or more of the alcohol derivative in the total solution.The
[0164]
Therefore, the effect obtained by including the alcohol derivative in the etching solution can be sufficiently obtained, and the effect that the desired hole and unevenness can be formed and a thin film solar cell having high photoelectric conversion efficiency can be produced. .
[0165]
  The transparent conductive layer contains zinc oxide.The
[0166]
Therefore, the plasma resistance, which is the characteristic of zinc oxide, is obtained, and the thin film solar cell having good characteristics without causing a decrease in the transmittance of the transparent conductive layer due to hydrogen plasma when the photoelectric conversion layer is deposited by the plasma CVD method. There is an effect that a battery can be obtained.
[0167]
The etching is more preferably performed at an etching solution temperature range of 5 ° C. to 40 ° C.
[0168]
When etching is performed at an etching solution containing the above alcohol derivative at a temperature higher than 40 ° C., the highly volatile alcohol derivative has a strong anisotropic etching action with an acid or alkaline etchant. It is difficult to form holes and irregularities that can obtain a good light confinement effect. On the other hand, when the temperature is lower than 5 ° C., the etching processing rate is lowered and the production efficiency is lowered.
[0169]
Therefore, in the method for manufacturing a thin-film solar cell of the present invention, by performing etching while controlling the temperature of the etching solution to be within the above range, holes and irregularities effective for the light confinement effect are formed. There is an effect that can be.
[0170]
  The present inventionManufactured byThe thin film solar cell has a configuration manufactured by the above manufacturing method.
[0171]
Therefore, effective holes and irregularities can be formed on the surface of the transparent conductive layer to obtain a light confinement effect, and sufficient light scattering can be achieved with an inexpensive manufacturing method without impairing the film quality of the photoelectric conversion layer. By utilizing the light confinement effect of, a thin film solar cell having high photoelectric conversion efficiency can be obtained.
[0172]
  The diameter of the hole formed in the surface of the transparent conductive layer by the etching is 200 to 2000 nm, the depth of the hole is 50 to 1200 nm, and the height difference of the fine unevenness is 10 to 300 nm.The
[0173]
Therefore, due to the plurality of holes and fine irregularities formed in the transparent conductive layer, sufficient light scattering is possible not only for light having a central wavelength of the solar spectrum of about 400 to 650 nm but also for light having longer wavelengths than these. As a result, an effective light confinement effect can be obtained, and a thin film solar cell having high photoelectric conversion efficiency can be obtained.
[0174]
As described above, the etching solution of the present invention is used in the above-described method for manufacturing a thin-film solar cell.
[0175]
Therefore, effective holes and irregularities can be formed on the surface of the transparent conductive layer to obtain the light confinement effect, and by utilizing the light confinement effect due to sufficient light scattering in an inexpensive method, There exists an effect that the thin film solar cell which has high photoelectric conversion efficiency can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing the structure of a super-straight type single-junction thin-film solar cell according to an embodiment and Example 1 of the present invention.
FIG. 2 is a cross-sectional view schematically showing the surface shape of a transparent conductive layer containing zinc oxide in the thin-film solar cell according to Example 1 of the present invention.
FIG. 3 is a cross-sectional view schematically showing the structure of a substrate-type thin film solar cell according to Example 12 of the present invention.
FIG. 4 is a cross-sectional view schematically showing the structure of a multi-junction thin film solar cell according to Example 13 of the present invention.
5 is a cross-sectional view schematically showing the surface shape of a transparent conductive layer containing zinc oxide in a thin film solar cell according to Comparative Example 1. FIG.
[Explanation of symbols]
11 Solar cell substrate
11a substrate
11b Transparent conductive layer
11c Second transparent conductive layer
12 p-type silicon layer
12a p-type amorphous silicon layer
13 i-type silicon layer
13a i-type amorphous silicon layer
14 n-type silicon layer
14a n-type amorphous silicon layer
15 Back reflective layer
16 Back electrode
17 Photoelectric conversion layer
21 Hole depth
22 hole diameter
23 Uneven size (difference in height of unevenness)
24 Unevenness spacing
27 First silicon photoelectric conversion layer
37 Second silicon photoelectric conversion layer
40 Solar cell substrate
40a substrate
40b Back electrode
40c transparent conductive layer
41 n-type silicon layer
42 i-type silicon layer
43 p-type silicon layer
44 Transparent conductive layer
45 Photoelectric conversion layer

Claims (2)

In a thin film solar cell comprising at least a substrate, a transparent conductive layer, and a photoelectric conversion layer,
Etching the surface of the transparent conductive layer using an etchant containing at least one alcohol derivative represented by the following structural formula (1),
The etching solution is an acid or alkaline solution,
The etching solution contains water,
The alcohol derivative is ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol, glycerin, propylene glycol,
The etching solution is made using hydrochloric acid, hydrofluoric acid or sodium hydroxide,
The etching solution contains 10 wt% or more of the alcohol derivative in the total solution,
The transparent conductive layer contains zinc oxide ,
The hole formed in the surface of the transparent conductive layer by the etching has a diameter of 200 to 2000 nm, the depth of the hole is 50 to 1200 nm, and the height difference of fine irregularities is 10 to 300 nm. Manufacturing method of thin film solar cell.
A- (OH) ⁿ (1)
(N is an integer of 1 to 4, and A is an aliphatic hydrocarbon residue bonded to a hydroxyl group via a carbon atom.)   The method for manufacturing a thin-film solar cell according to claim 1, wherein the etching is performed at a temperature range of an etching solution of 5 ° C to 40 ° C.

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