JP3679561B2 - Photoelectric conversion element - Google Patents

Description

【００６５】
図13に示すように、上部透明電極（ITO）まで形成した基板の一辺に絶縁性両面テープを貼り、図3に示すCuワイヤー、Agクラッド層、カーボンペーストからなる集電電極の一端を該両面テープに固着し、更に該集電電極の上から該両面テープにバスバーを固着し、全体を加熱してカーボンペーストを融着させ、集電電極とバスバーを固定した。
【００６６】
この太陽電池(実1)と同じものを数枚作製した。そのひとつの断面形状を透過型電子顕微鏡(TEM)で観察したところ第1のi層は第1図な柱状結晶粒の長手方向は前記基板の法線方向に対して傾いて配置している構造のが形成されていることが分った。また下部導電層(透明導電層及び反射層)の表面粗さRaを測定したところ、長さ50μmあたりの平均は0.32μmであることが分った。また角度G(下部導電層の微小領域の法線と基板主面の法線がなす角度)が15度以上、45度以下である割合を計数したところ91%であった。また角度Fが20度以下である柱状結晶粒全体容積のi層全体容積に対する割合Kは90%だった。
【００６７】
(比較例1)
下部導電層として、透明導電層は設けずに通常のスパッタリング法を用いてほぼ平面状のAgのみを形成し、図2の断面形状を有する太陽電池を作製した。また第1のi層はRFプラズマCVD法を用いて表1bに示す条件で形成した。それ以外は実施例1と同様な太陽電池(図2の光電変換素子)を作製した。
【００６８】
形成条件を表２に示す。
【００６９】
【表２】

【００７０】
この太陽電池(比1)と同じものを数枚作製した。そのひとつの断面形状を透過型電子顕微鏡(TEM)で観察したところ第1のi層は第2図のように柱状微結晶シリコンが形成されていることが分った。また下部導電層の表面粗さRaを測定したところ、長さ50μmあたりの平均は0.02μmであることが分った。
【００７１】
まず、実施例1の太陽電池(実1)と比較例1(比1)の太陽電池の初期特性(光導電特性、リーク電流、低照度開放電圧)を測定した。
【００７２】
ソーラーシュミレーター(AM1.5 100mW/cm2 表面温度25℃)を用いて光電変換効率、開放電圧、短絡光電流を測定したところ、本発明の光電変換素子がそれぞれ1.29倍、1.04倍、1.23倍優れていた。
【００７３】
次に、照度500ルクス程度の蛍光灯下(低照度)における開放電圧を測定したところ、(実1)の太陽電池のほうが(比1)のものよりも1.2倍優れていることが分った。暗所において逆バイアスを印加し、リーク電流を測定したところ、本発明の太陽電池(実1)のリーク電流は比較例1(比1)の約8分の1程度と小さく優れていることが分った。
【００７４】
次に(実1)、(比1)の太陽電池の光照射試験を行なった。上記のシュミレーター(AM1.5 100mW/cm2 表面温度50℃)に1000時間暴露させところ、ともに試験後の外観不良は見いだされなかった。
【００７５】
光照射試験後の光電変換効率、開放電圧、短絡光電流、低照度の開放電圧、リーク電流を測定したところ、低照度の開放電圧、リーク電流の試験前後での低下に差が見られた。
【００７６】
試験前後における低照度の開放電圧比 (試験後の低照度開放電圧 / 試験前の低照度開放電圧)は(実1)では0.95、(比1)では0.92であった。さらに試験前後におけるリーク電流の比 (試験後のリーク電流 / 試験前のリーク電流)は(実1)では1.2、(比1)では2.2であった。
【００７７】
以上のように本発明の光電変換素子は従来の光電変換素子に対して優れていることが分った。
【００７８】
さらに前述の「ねじり試験」を行った。二つの太陽電池には試験後の外観不良は見いだされなかった。
【００７９】
ねじり試験後の光電変換効率、開放電圧、短絡光電流、低照度の開放電圧、リーク電流を測定したところ、光電変換効率、開放電圧、低照度の開放電圧、リーク電流の試験前後での低下に差が見られた。
【００８０】
試験前後における光電変換効率の比 (試験後の光電変換効率 / 試験前の光電変換効率)は(実1)では0.98、(比1)では0.70であった。試験前後における開放電圧の比 (試験後の開放電圧 / 試験前の開放電圧)は(実1)では0.99、(比1)では0.84であった。
【００８１】
また試験前後における低照度の開放電圧比 (試験後の低照度開放電圧 / 試験前の低照度開放電圧)は(実1)では0.96、(比1)では0.87であった。
【００８２】
さらに試験前後におけるリーク電流の比 (試験後のリーク電流 / 試験前のリーク電流)は(実1)では1.1、(比1)では3.1であった。
【００８３】
以上のように本発明の光電変換素子は従来の光電変換素子に対して優れていることが分った。
【００８４】
同様に結晶系太陽電池関連のJIS C 8917に記載の降ひょう試験を行なった。氷球の直径は25mm、終速度23m/secの条件で10回、万遍なく落下させた。試験後上記と同様な評価を行なったところ(実1)の太陽電池は同様に(比1)の太陽電池よりも優れていることが分った。
【００８５】
(実施例2)
他の実施形態の例として、図1-bの太陽電池を作製した。具体的には、基板 ステンレス(SUS430 10×10cm2 厚さ0.2mm) / 反射層 Al / 透明導電層 ZnO / 第1のドープ層 a-Si:H:P / 第1のi層 μc-Si:H / 第2のドープ層 μc-Si:H:B / 第3のドープ層 a-Si:H:P / 第2のi層 a-Si:H / 第4のドープ層 μc-Si:H:B /上部透明電極 ITO / 集電電極 Cuワイヤー/Ag/C の材料で構成された太陽電池(実2)をいくつか作製した。
【００８６】
形成条件を表３に示す。
【００８７】
【表３】

【００８８】
この太陽電池の断面をTEMで観察したところ、第1のi層は図1-bのような微結晶構造になっていることが分かった。また下部導電層(透明導電層/反射層)の表面粗さRaを測定したところ、長さ50μmあたりの平均は0.29μmであることが分った。また角度G(下部導電層の微小領域の法線と基板主面の法線がなす角度)が15度以上、45度以下である割合を計数したところ93%であった。また角度Fが20度以下である柱状結晶粒全体容積の第1のi層全体容積に対する割合Kは94%だった。
【００８９】
(比較例2)
図2のような構成を有する比較例1(表1b)の太陽電池において第2のドープ層と上部透明電極の間に実施例2と同様な第3のドープ層、第2のi層、第4のドープ層を積層し、光電変換素子(比2)をいくつか作製した。この太陽電池の断面をTEMで観察したところ、第1のi層は図2のような微結晶構造になっていることが分かった。実施例1と同様な測定、および試験を行なったところ、(実2)の太陽電池は(比2)の太陽電池よりも優れていることが分った。
【００９０】
(実施例3)
基板には長尺シートを用い、生産性の高いRoll-to-Roll方式で反射層、透明導電層を順次形成した。さらに、光起電力層、上部透明電極を形成する際にもRoll-to-Roll方式を採用した。以下にその詳細を説明する。
【００９１】
図10の装置1000は可とう性(柔軟性)を有する長尺シート状の基板1001の表面上にいくつかの薄膜を真空中で連続的に形成することのできる薄膜形成装置である。1001はステンレスなどの可とう性を有する長尺基板、1008はこの基板をロール状に巻きつけた送り出しロール、1009は該基板を巻き取る巻き取りロール、1002は送り出しロールを内部に固定することのできる真空容器で、配管1018を介してロータリーポンプなどの真空ポンプ1016が接続されている。同様に巻き取りロール1009は真空容器1007に固定され、真空ポンプが接続されている。
【００９２】
真空容器1002と1007の間にはガスゲート1021と呼ばれる基板の通路と、DCマグネトロンスパッタリング法によって所望の薄膜を形成する真空容器1003、1004、1005、1006が図10のように接続されている。ガスゲート1021には図のようにガス導入管1010を接続してAr等の掃気用ガス1011を流入させ、異なる種類の薄膜を形成する真空容器の間でガスの相互拡散が起こらないようにすることができる。そのため良好な接合を形成できるものである。ガスゲートは各真空容器の間に接続されているが連続する真空容器で同じ薄膜を形成する場合にはガスゲートをその間に具備する必要はない。
【００９３】
真空容器1003、1004、1005、1006には配管1019を通して拡散ポンプ1017が接続され、さらに配管を通してロータリーポンプなどの真空ポンプが接続されている。さらに真空容器1003、1004、1005、1006の内部には基板を加熱するヒーター1014、所望の薄膜を形成するためのターゲット1023、磁石を内蔵した電極1013、スパッタリング用のガス1022を導入するためのガス導入管1020が具備されている。また各電極にはDC電源1012が接続されている。
【００９４】
以下にこの装置の使用方法を述べる。まずステンレスなどの可とう性を有する長尺基板を巻いた送り出しロール1008を真空容器1002内に固定し、基板先端を各ガスゲート、真空容器1003、1004、1005、1006を通して真空容器1007内部に固定された巻き取りロール1009に巻き付ける。
【００９５】
各真空ポンプを起動し各真空容器の内圧が数mTorrになるまで真空排気する。ガス導入管1010からArガスを、1020からは所望のガスを導入し、各ヒーター電源を入れ、基板を矢印1024の方向に搬送する。基板の温度が一定になったところで各DC電源を入れ、真空容器1003、1004、1005、1006の中でプラズマ1015を生起し、所望の薄膜を形成する。
【００９６】
基板の終端部にさしかかったら搬送を止め、各DC電源、各ヒーター電源を切り、基板を冷却する。基板の温度が室温程度になったら各真空容器をリークし、巻き取りロールを取りだす。
【００９７】
厚さ0.15mmのステンレス基板(SUS430)を使用し、上記の方法で、表3に示す条件で反射層、透明導電層を連続的に形成した。この下部導電層(透明導電層/反射層)の断面形状をSEMで観察したところ、図1のような形状をなしていることが分った。また長さ50μmあたりの平均表面粗さRaは0.35μmであった。また角度Gが15度以上、45度以下である割合を計数したところ90%であった。
【００９８】
次にRoll-to-Roll方式を用いて透明導電層の上に光起電力層を形成する装置を詳細に説明する。図11の装置は長尺基板上に6層からなる光起電力層を連続的に形成する装置であり、一部の真空容器は図から省略した。1101は下部導電層を形成した長尺基板、1108はこの基板をロール状に巻きつけた送り出しロール、1109は該基板を巻き取る巻き取りロール、1102は送り出しロールを内部に固定することのできる真空容器で、配管1118を介してロータリーポンプなどの真空ポンプ1116が接続されている。同様に巻き取りロール1109は真空容器1107に固定され、真空ポンプが接続されている。真空容器1102と1107の間には、所望の薄膜を形成する真空容器1103-a、1104、1103-b(不図示)、1103-c(不図示)、1103-d、1103-eが順次配置され、各真空容器の間にガスゲート1121が接続されている。各ガスゲート1121には図のようにガス導入管1110を接続してAr、H2、He等の掃気用ガス1111を流入させ、異なる種類の薄膜を形成する真空容器の間でガスの相互拡散が起こらないようにすることができる。このため該p-i-n接合は非常に良好なものである。連続する真空容器で同じ薄膜を形成する場合にはガスゲートをその間に具備する必要はない。
【００９９】
真空容器1103-a、1103-b、1103-c、1103-d、1103-eにおいてはRFプラズマCVD法(電源周波数 13.56MHz)を実施することができる。該真空容器には配管1118を通してロータリーポンプとガス導入管1120が接続され、内部にはヒーター1114とRF電極1113が固定されている。該RF電極にはRF電源1112が接続されている。また、真空容器1104においては高周波プラズマCVD法(電源周波数 150MHz)を実施することができる。該真空容器には配管1119を通して拡散ポンプ1117が接続され、さらに配管を通してロータリーポンプなどの真空ポンプが接続されている。さらにガス導入管が接続され、内部にはヒーター1127と高周波電極1126が固定されている。該高周波電極には高周波電源1125(周波数 150MHz)が接続されている。
【０１００】
以下にこの装置の使用方法を述べる。まず下部導電層まで形成された上記のステンレス基板を巻いた送り出しロール1108を真空容器1102内に固定し、基板先端を各ガスゲート、各真空容器を通して真空容器1107内部に固定された巻き取りロール1109に巻き付ける。各真空ポンプを起動し各真空容器の内圧が数mTorrになるまで真空排気する。ガス導入管1110からH2ガスを、ガス導入管1120からは光起電力層形成用のガスを導入し、各ヒーター電源を入れ、基板を矢印1124の方向に搬送する。基板の温度が一定になったところで各RF電源、高周波電源を入れ、マッチングを調整して各真空容器内部にプラズマ1115を生起し、所望の薄膜を形成する。基板の終端部にさしかかたら搬送を止め、各DC電源、各マイクロ波電源、DC電源および各ヒーター電源を切り、基板を冷却する。基板の温度が室温程度になったら各真空容器をリークし、巻き取りロールを取りだす。上記のような方法を用いて表3に示す条件で、第1のドープ層 a-Si:H:P / 第1のi層 μc-Si:H / 第2のドープ層 μc-Si:H:B / 第3のドープ層 a-Si:H:P / 第2のi層 a-Si:H / 第4のドープ層 μc-Si:H:B を形成した。
【０１０１】
取りだしたロール状の太陽電池を図10の装置を使用して連続的に上部透明電極(ITO)を形成した。その際、真空容器1006内部のターゲットをITOにし、真空容器1003、1004、1005ではプラズマを生起せず、真空容器1006のみでITOからなる上部透明電極を第4のドープ層上に形成した。各層の形成条件は表４に示した。
【０１０２】
【表４】

【０１０３】
取りだしたロール状の太陽電池を30×30cm2の大きさに切り、次に図1-aのように実施例1と同様な集電電極とバスバーを取り付け、図4のように4つの太陽電池を直列化し、各太陽電池とは並列にバイパスダイオードを接続した。次に、厚さ0.3mmの支持基板の上にEVA、ナイロン樹脂、EVA、ガラス不織布、直列化した太陽電池、ガラス不織布、EVA、ガラス不織布、EVA、ガラス不織布、フッ素樹脂を重ねあわせて加熱真空封止(ラミネーション)した。
【０１０４】
上記のように作製した35×130cm2の大きさの太陽電池モジュール(実3)を実施例1と同様な測定および試験を行なったところ、初期特性、ねじり試験、降ひょう試験のいずれの場合にも(実1)の太陽電池よりもさらに優れた特性であった。また該太陽電池モジュール(実3)を屋外に3カ月放置し、屋外暴露試験を行なった。その外観変化はほとんど見られず、光電変換効率の低下は5%程度であった。
【０１０５】
以上のように本発明の光電変換モジュールは優れた特性を有するものであることが分った。
【０１０６】
(実施例4)
実施例1において第1のi層の膜厚を2μmとする以外は実施例1と同様な太陽電池(実4)を作製した。断面をTEMで観察したところ第1のi層の構造は図１のようになっていることが分かった。実施例1と同様な測定、および試験を行なったところ、(実4)の太陽電池は(実1)の太陽電池と同様に優れていることが分った。
【０１０７】
(実施例5)
他の実施形態の例として、下部導電層が単一層からなる太陽電池を作製した。該下部導電層は膜厚0.5μmの銀の層からなり、スパッタリング法で形成され、形成温度を350℃にすることによって該層の表面形状を凹凸化(テクスチャー化)した。断面を観察して角度G(下部導電層の微小領域の法線と基板主面の法線がなす角度)が15度以上、45度以下である割合を計数したところ91%であった。実施例1と同じ光起電力層と上部透明電極、集電電極を該下部導電層上に形成し、図1の太陽電池(実5)をいくつか作製した。実施例1と同様な測定、および試験を行なったところ、(実5)の太陽電池は(実1)の太陽電池と同様に優れていることが分った。
【０１０８】
(実施例6)
他の実施形態の例として、第1のドープ層を a-Si:H:P/μc-Si:H:Pからなる積層構造とした図5の光起電力層を有する図1-bの太陽電池を作製した。実施例2において第1のドープ層を a-Si:H:P/μc-Si:H:P とする以外は実施例2と同様な太陽電池(実6)を作製した。実施例1と同様な測定、および試験を行なったところ、(実4)の太陽電池は(実2)の太陽電池と同様に優れていることが分った。
【０１０９】
【発明の効果】
本発明の光電変換素子によれば、光電変換素子の光電変換効率、開放電圧、短絡光電流、低照度開放電圧、リーク電流といった特性を向上できるものである。また屋外暴露試験、機械的強度、長時間光照射における耐久性を向上できるものである。さらに光電変換素子のコストを大幅に低減できるものである。
【図面の簡単な説明】
【図１】下部導電層及びi層に特徴を有する本発明の光電変換素子
【図２】従来の光電変換素子
【図３】集電電極の一例
【図４】本発明の光電変換素子のモジュール化の一例
【図５】第1のドープ層に特徴を有する本発明の光電変換素子
【図６】下部導電層の表面荒さと光電変換効率の関係
【図７】図1aで定義される角度Gが15度以上45度以下である割合と光電変換効率の関係
【図８】本発明の光電変換素子の下部導電層、上部透明電極を形成する装置
【図９】本発明の光電変換素子の光起電力層を形成する装置
【図１０】本発明の光電変換素子の下部導電層、上部透明電極を連続的に形成する装置
【図１１】本発明の光電変換素子の光起電力層を連続的に形成する装置
【図１２】ａは図12bで定義される角度Fが0度以上20度以下である割合と光電変換効率との関係ｂは角度Fを定義する図
【図１３】本発明の光電変換素子にバスバーを設けた例
【符号の説明】
１０１ 基板
１０２ 下部導電層
１０２ａ 反射層
１０２ｂ 透明導電層
１０３ 第１のドープ層
１０４ 第１のｉ層
１０５ 第２のドープ層
１０６ 上部透明電極
１０７ 集電電極
１０８ バスバー
１０９ 両面テープ
１１０ 第３のドープ層
１１１ 第２のｉ層
１１２ 第４のドープ層
１２０ 角度Ｇ
２０１ 基板
２０２ 下部導電層
２０３ 第１のドープ層
２０４ 第１のｉ層
２０５ 第２のドープ層
２０６ 上部透明電極
２０７ 集電電極
３０１ 銅ワイヤ
３０２ 銀クラッド層
３０３ カーボンペースト層
３０６ 上部透明電極の表面
３０７ 集電電極
４０１ 支持基板
４０２，４０４，４０９，４１１ ＥＶＡ
４０３ ナイロン樹脂
４０５，４０８，４１０，４１２ ガラス不織布
４０６ バイパスダイオード
４０７ 光電変換素子
４１３ フッ素樹脂
４１４ バスバー
５０３ａ 第１のドープ層ａ
５０３ｂ 第１のドープ層ｂ
５０４ 第１のｉ層
５０５ 第２のドープ層
５０６ 第３のドープ層
５０７ 第２のｉ層
５０８ 第４のドープ層
８０１ 堆積室
８０２ 基板ホルダー
８０３ 基板
８０４ ヒーター
８０５ マッチングボックス
８０６ ＲＦ電源
８０７ 反射層用のターゲット
８０８ 透明導電層用のターゲット
８１０，８１１ ＤＣ電源
８１３，８１４ シャッター
８１６ 排気管
８１７ ガス導入管
８１８ 回転軸
８１９ プラズマ
９０１ 反応室
９０２ 下部導電層を形成した基板
９０３ ヒーター
９０４ コンダクタンスバルブ
９０８ 高周波電極
９０９ 高周波電源
９１０ プラズマ
９１１ シャッター
９１３ 排気方向
９１４ 排気管
９１５ ガス導入管
９１６ ガス導入方向
１００１ 長尺基板
１００２，１００３，１００４，１００５，１００６，１００７ 真空容器
１００８ 送り出しロール
１００９ 巻き取りロール
１０１０ ガス導入管
１０１１ 掃気用ガス
１０１２ ＤＣ電源
１０１３ 電極
１０１４ ヒーター
１０１５ プラズマ
１０１６ 真空ポンプ
１０１７ 拡散ポンプ
１０１８，１０１９ 排気管
１０２０ ガス導入管
１０２１ ガスゲート
１０２２ ガス
１０２３ ターゲット
１０２４ 基板搬送方向
１１０１ 下部導電層を形成した長尺基板
１１０２，１１０３−ａ，１１０３−ｂ，１１０３−ｃ，１１０３−ｄ，１１０３−ｅ，１１０３−ｆ，１１０４，１１０７ 真空容器
１１０８ 送り出しロール
１１０９ 巻き取りロール
１１１０ 掃気ガス導入管
１１１１ 掃気用ガス
１１１２ ＲＦ電源
１１１３ ＲＦ電極
１１１４ ヒーター
１１１５ プラズマ
１１１６ 真空ポンプ
１１１７ 拡散ポンプ
１１１８，１１１９ 排気管
１１２０ ガス導入管
１１２１ ガスゲート
１１２２ ガス
１１２４ 基板搬送方向
１１２５ 高周波電源
１１２６ 高周波電極
１１２７ ヒーター[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-single-crystal photoelectric conversion element having an improved surface shape of a lower conductive layer, a crystal structure of an i layer, and a structure of a doped layer.
[0002]
[Prior art]
Conventionally, studies have been made on improvement of photoelectric conversion efficiency and improvement of light degradation of a photoelectric conversion element using a pin junction of a non-single crystal semiconductor.
[0003]
It is known that increasing the dopant concentration in the doped layer decreases the activation energy of the doped layer, increases the built-in potential of the pin junction, and increases the open-circuit voltage of the device.
[0004]
It is also known to improve photodegradation by using a microcrystalline material for the i-type semiconductor layer.
[0005]
IEEE WCPEC; 1994 Hawaii p409 "INTRINSIC MICROCRYSTALLINE (μc-Si: H)-A PROMISSING NEW THIN FILM SOLAR CELL MATERIAL", J. Meier, A. Shah) As can be seen from the above, a photoelectric conversion efficiency of 4.6% was obtained by the plasma CVD method using VHF (70 MHz), and it has been reported that the solar cell does not show any photodegradation. Furthermore, a stacked solar cell of amorphous silicon and microcrystalline silicon was produced, and an initial photoelectric conversion efficiency of 9.1% was obtained.
[0006]
In addition, it is known to provide a transparent conductive layer between a substrate or a metal layer and a semiconductor layer. This prevents the elements of the metal layer from diffusing or migrating into the semiconductor layer and shunting the photoelectric conversion element. Further, by having an appropriate resistance, a short circuit due to a defect such as a pinhole in the semiconductor layer is prevented. Furthermore, the irregularities on the surface increase the irregular reflection of incident light and reflected light, thereby extending the optical path length in the semiconductor layer.
[0007]
[Problems to be solved by the invention]
However, a solar cell using the above-described microcrystalline silicon-based material has a photoelectric conversion efficiency of 4.6% and is not yet practical. In addition, in the a-Si / μc-Si type stacked solar cell, the initial photoelectric conversion efficiency is 9.1%, but there is a problem that the light degradation of the a-Si layer on the light incident side is large. Furthermore, since the μc-Si layer is as thick as 3.6 μm and the deposition rate is as slow as 1.2 A / sec, the layer formation time is about 8 hours, which is not practically practical.
[0008]
[Means for solving the problems]
In a photoelectric conversion element having a substrate, a lower conductive layer, a first doped layer, an i layer, a second doped layer, and an upper conductive layer, the surface of the lower conductive layer has an uneven shape, and the i layer is a columnar crystal The photoelectric conversion element is characterized in that it contains grains and the longitudinal direction of the columnar crystal grains is inclined with respect to the normal direction of the substrate. When numerically defined, a straight line A passing through the columnar crystal grain and parallel to the longitudinal direction thereof, the shortest of the interface 1 between the first doped layer and the i layer, and the interface 2 between the second doped layer and the i layer Of the straight lines connecting the distances, the ratio of the angle formed by the straight lines B passing through the columnar crystal grains A to 20 degrees or less is 70% or more with respect to the total volume of the i layer.
[0009]
Further, a third doped layer, a second i layer, and a fourth doped layer are provided between the second doped layer and the upper conductive layer, and the second i layer is amorphous silicon. 2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element has a thickness of 0.1 μm or more and 0.4 μm or less.
[0010]
The first and / or third doped layer has a layered structure composed of a layer made of a microcrystalline silicon semiconductor material and a layer made of an amorphous silicon semiconductor material, and a layer made of the microcrystalline silicon semiconductor material Is a photoelectric conversion element in contact with the i layer.
[0011]
According to the photoelectric conversion element of the present invention, characteristics such as photoelectric conversion efficiency, open circuit voltage, short-circuit photocurrent, low illuminance open voltage, and leakage current of the photoelectric conversion element can be improved. In addition, it can improve durability in outdoor exposure tests, mechanical strength, and long-term light irradiation. Furthermore, the cost of the photoelectric conversion element can be greatly reduced.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1a is a schematic cross-sectional view of the photoelectric conversion element of the present invention, 101 is a substrate, 102 is a lower conductive layer comprising two layers of a reflective layer 102a and a transparent conductive layer 102b, and 103 is a non-single-crystal silicon-based semiconductor material The first doped layer 104 is made of a microcrystalline silicon-based semiconductor material and has i-type conductivity, and 105 is made of a non-single-crystal silicon-based semiconductor material and has a conductivity opposite to that of the first doped layer. It is a layer which has property. The layer structure of 103-104-105 forms a pin junction and has a function of generating photovoltaic power. 103, 104, and 105 are collectively referred to as a photovoltaic layer. 106 is an upper transparent electrode, and 107 is a collector electrode.
[0013]
The lower conductive layer 102, the i layer 104, and the first doped layer 103 of the present invention have the following characteristics.
[0014]
(1) The relationship between the direction of columnar crystal grains, mechanical strength, and photoelectric conversion efficiency was investigated. As shown in FIG. 12-b, a straight line A passing through a certain columnar crystal grain A and parallel to its longitudinal direction, the interface 1 between the first doped layer and the first i layer, the second doped layer and the first The frequency distribution of the angle F formed by the straight line B passing through the columnar crystal grain A among the straight lines connecting the shortest distance to the interface 2 of the i layer was investigated. Then, when the relationship between the ratio K of the total volume of columnar crystal grains having an angle F of 20 degrees or less to the total volume of the first i layer and the photoelectric conversion efficiency after the `` torsion test '' was examined, the result as shown in FIG. became. That is, it was found that when the ratio K is 70% or more, good photoelectric conversion efficiency is exhibited, and when the ratio K is 70% or less, the open-circuit voltage decreases and the photoelectric conversion efficiency decreases. The “torsion test” was based on JIS C8917 A-10 of the crystalline solar cell. The condition was that a twist of height h = 5 mm was repeated 50 times for an area of 10 cm × 10 cm.
[0015]
(2) The lower conductive layer 102 of the present invention has a surface roughness Ra of a length of about several tens of microns on the surface of 0.1 μm or more and 1 μm or less. Then, the (surface roughness) x (refractive index of the first i layer) and the wavelength of visible light or infrared light are comparable, and the optical confinement effect is exhibited, and the short-circuit photocurrent of the photoelectric conversion element is dramatically improved. To do.
[0016]
The long wave light that could not be absorbed inside the first i layer is reflected by the lower conductive layer and enters the i layer again, but the light is scattered on the surface of the lower conductive layer, so that interference occurs inside the i layer. It does not occur, there is no region that strongly absorbs light, and light deterioration can be further suppressed. Similarly, since there is no region that hardly absorbs light, the open circuit voltage can be improved.
[0017]
The relationship between surface roughness and photoelectric conversion efficiency was investigated. The results are shown in FIG. It was found that the conversion efficiency was excellent within the range of the surface roughness.
[0018]
(3) The area where the angle G (120) between the normal line of the surface of the lower conductive layer and the normal line of the main surface of the substrate in a small area of about several hundred angstroms is 15 degrees or more and 45 degrees or less is the entire surface area By setting it to 80% or more, the thickness distribution of the first i layer is small, and since there is almost no region where the film thickness is extremely thin, the leakage current is small, and thus the open-circuit voltage can be increased. Further, the light confinement effect is further exhibited.
[0019]
The relationship between the distribution of the angle (angle G) between the normal to the microregion of the lower conductive layer and the normal of the main surface of the substrate and the photoelectric conversion characteristics of the solar cell after the “torsion test” was investigated. The angle G is shown in FIG. FIG. 7 shows the relationship between the angle G and the photoelectric conversion efficiency after the “torsion test”. It has been found that when the ratio of the angle G is 80% or less, the shunt resistance decreases (weak short circuit state) and the photoelectric conversion efficiency decreases.
[0020]
(4) Although the optical carrier generated in the i layer moves due to the internal electric field, the internal electric field is substantially parallel to a straight line connecting the shortest distance between the first doped layer and the second doped layer. Therefore, in the present invention, the longitudinal direction of the columnar crystal grains contained in the i layer is substantially parallel to the straight line connecting the shortest distance between the first doped layer and the second doped layer, and the longitudinal direction of the columnar crystal grains is By setting the length to 100 Å or more and 0.3 μm or less, the opportunity to pass through the interface existing between the crystal grains is reduced, so that the fill factor and the short-circuit current are improved.
[0021]
Further, since the opportunity for carriers to pass through the interface is reduced, the carrier recombination rate can be suppressed. Therefore, the light deterioration can be further suppressed. Further, since the directions of the columnar crystal grains are substantially aligned, the interface state of the columnar crystal grains is small. Therefore, the open circuit voltage can be improved.
[0022]
Furthermore, the light absorption coefficient is higher than that of single crystal silicon, and the absorption coefficient of long-wave light is higher than that of amorphous silicon-based semiconductor materials. Therefore, even long-wave light (infrared light) is effectively absorbed, so that a sufficient short-circuit current can be obtained even with a film thickness of about 3 μm.
[0023]
Further, since the region between the columnar crystal grains is occupied by a good amorphous silicon-based semiconductor material containing hydrogen, there is almost no probability that optical carriers are trapped in this region.
[0024]
In addition, the longitudinal direction of the columnar crystal grains generally has an angle of 10 degrees or more and 50 degrees or less with respect to the normal line of the main surface of the substrate, and can be relaxed by external twisting. Accordingly, when the roll-to-roll method is performed, even if a long substrate is wound on a roll, film peeling does not occur. Since the film does not peel off, it can be formed on a curved substrate. Similarly, the photoelectric conversion element of the present invention formed on a planar substrate can be easily used by being bent. In particular, when the photoelectric conversion element of the present invention is used as a solar cell, it can also be used on a curved plane such as a wall surface of a building.
[0025]
Furthermore, since the short-circuit current can be improved as described above, the first i layer can be made thinner, so that the light degradation can be improved, the productivity can be improved, and the power cost can be reduced.
[0026]
(5) In the i layer, a minute region made of an amorphous silicon-based semiconductor material is present in a volume ratio of 50% or less with respect to the entire region of the i layer. Therefore, the open circuit voltage can be improved as compared with the photoelectric conversion element in which the entire region of the first i layer is made of the microcrystalline silicon-based semiconductor material.
[0027]
Although the reason is unknown, the leakage current can be reduced, so that the open circuit voltage can be further increased. In addition, the entire region of the first i layer is more resistant to external force than the photoelectric conversion element made of a microcrystalline silicon-based semiconductor material. Because the flexibility of the amorphous Si-Si network is superior to that of the microcrystalline Si-Si, the region of the amorphous silicon semiconductor material contained in the first i layer is an external force. It seems to be effective in mitigating Furthermore, it is considered that it is also effective in relieving internal stress.
[0028]
When the volume ratio is 50% or more, photodegradation increases, so it is desirable to have a stacked element structure having a structure such as a-Si / μc-Si.
[0029]
(6) In the case of a stack cell as shown in FIG. 1b, a third doped layer 110, a second i layer 111, and a fourth doped layer 112 are sequentially stacked on the pin junctions 103 to 105 described above. And the thickness of the second i layer 111 is not less than 0.1 μm and not more than 0.4 μm. Thus, in order from the light incident side, the second i layer is composed of a semiconductor material having a large absorption coefficient of short-wave light, such as a-Si, and then absorbs long-wave light, such as μc-Si. By configuring the first i layer with a semiconductor material having a large coefficient, the spectral sensitivity can be increased with respect to light in a wider wavelength range.
[0030]
Furthermore, the open circuit voltage can be increased more than the photoelectric conversion element in which the first i layer is made of μc-Si, and the photoelectric conversion efficiency can be improved. In addition, by connecting the i layers having different spectral sensitivities in this way, the second i layer made of μc-Si can be made thinner, so that the fill factor (curve factor, FF) of photoconductive characteristics can be improved. .
[0031]
In addition, since the second i layer of the present invention has a thin film thickness of 0.1 μm or more and 0.4 μm or less, photodegradation can be suppressed as much as possible even if an amorphous semiconductor is used for the second i layer.
[0032]
Furthermore, although the reason is not clear, the leakage current of the photoelectric conversion element can be reduced by stacking the second i layer made of an amorphous silicon-based semiconductor material. Therefore, the open circuit voltage can be further increased.
[0033]
In particular, when the photoelectric conversion element of the present invention is used as an optical sensor or an image sensor, it is important to reduce leakage current. In addition, when the photoelectric conversion element of the present invention is used as a solar cell, a high open-circuit voltage can be output even under irradiation light with low illuminance, so that the power generation efficiency is high even on a cloudy day, morning, evening, etc. There is no extreme fall.
[0034]
Further, as described above, since the lower conductive layer is not flat, light does not cause interference inside the second i layer, and therefore there is no region that strongly absorbs light, so that light degradation can be further suppressed. . Similarly, since there is no region that hardly absorbs light, the open circuit voltage can be improved.
[0035]
(7) Method of forming the first i layer
i layer 104 is a plasma CVD method using an electromagnetic wave having a frequency of 30 MHz or more and 600 MHz or less, and the pressure is 1 mTorr or more and 1 Torr or less, using silicon-containing gas and hydrogen gas as source gas, It is formed under the condition that the ratio is 0.5% or more and 30% or less.
[0036]
The plasma CVD method can generate electromagnetic waves at a lower pressure than the RF (industrially 13.56MHz) plasma CVD method using electromagnetic waves having the above frequencies, thus eliminating the generation of polysilane in the gas phase. And a high-quality microcrystalline silicon-based semiconductor material can be formed.
[0037]
In addition, since plasma can be generated at a low pressure, the plasma can be expanded, which is very suitable for manufacturing a photoelectric conversion element having a large area. Moreover, since the deposition rate can be increased for these reasons, the throughput is increased, which is industrially advantageous. In addition, since the gas containing silicon is diluted in a large amount with hydrogen gas, the supply of radicals containing hydrogen to the film forming surface is larger than in the case of forming a normal amorphous silicon-based semiconductor thin film. A microcrystalline silicon-based semiconductor thin film can be formed.
[0038]
Furthermore, since a negative self-bias is usually generated in the discharge electrode, high-energy positive ion species can be prevented from being irradiated onto the film forming surface, and a high-quality microcrystalline silicon-based semiconductor thin film Can be formed.
[0039]
Although the reason is unknown, the microcrystalline structure as in the present invention can be formed with good reproducibility by using such a method. In addition, the gas decomposition efficiency is better than that of the RF plasma CVD method, so that the gas utilization efficiency is excellent, which is industrially advantageous.
[0040]
(8) Method of forming the second i layer
Examples of the material for the second i layer include amorphous silicon-based semiconductor materials such as a-Si, a-SiC, and a-SiO. In particular, a-Si is excellent. Further, B or the like may be added to make the i layer more intrinsic. The concentration of H, Cl, and F atoms for compensating for dangling bonds is preferably 0.1% or more and 10% or less. A plasma CVD method is usually used to form this layer. Of these, the RF plasma CVD method is preferred. The deposition rate is preferably 1 A / sec or more and 20 A / sec or less, the formation temperature is 150 ° C. or more and 350 ° C. or less, and the pressure is 0.1 Torr or more and 5 Torr or less. In particular, when forming a doped layer having a microcrystalline structure, a silicon-containing gas and a hydrogen gas are used as source gases, and the silicon-containing gas to hydrogen gas may be formed at a ratio of 2% to 50%. desirable.
[0041]
(9) At least one of the first doped layer 103, the second doped layer 105, the third doped layer 110, and the fourth doped layer 112 is made of a microcrystalline silicon-based semiconductor material, To do.
[0042]
When a microcrystalline silicon-based semiconductor material is used for the doped layer, the carrier density of the layer can be increased, so that the open-circuit voltage of the photoelectric conversion element is improved. Furthermore, the microcrystalline silicon-based semiconductor material has a smaller absorption coefficient in the visible light region than that of the amorphous silicon-based semiconductor material, so that when used as a window layer on the light incident side, the short-circuit current increases. is there.
[0043]
Furthermore, when a microcrystalline silicon-based semiconductor material is used for the first doped layer 103 and the second doped layer 105, since there is no abrupt change at the interface with the first i layer 104, there are few interface states, light The fill factor of the conductive property is improved.
[0044]
(10) As shown in FIG. 5, the first doped layer is made of a layer (503a) made of an amorphous silicon semiconductor material on the lower conductive layer side and a microcrystalline silicon semiconductor material on the first i layer side. A stacked structure with the layer (503b) is preferable. The third doped layer may have the same configuration. Thus, the fill factor of a photoelectric conversion element can be improved by making a doped layer into a laminated structure.
[0045]
(11) Method for forming transparent conductive layer of the present invention
Consists of materials selected from zinc oxide, tin oxide, indium oxide, ITO, and zinc sulfide. However, zinc oxide or tin oxide is desirable from the viewpoint of high plasma resistance, ease of control of the surface shape, and cost.
[0046]
A DC magnetron sputtering method with a high deposition rate is used, and the deposition rate is usually 10 (堆積 / sec) or more and 200 (以上 / sec) or less. Further, it is important to form at a temperature of 100 ° C. or more and 500 ° C. or less. A temperature of 150 ° C. or more and 400 ° C. or less is particularly suitable. A transparent conductive layer having a cross-sectional shape as in the present invention can be obtained at such deposition rate and formation temperature, and the transmittance becomes 90% or more with light of 500 nm or more. In order to form irregularities, the surface of the substrate may be appropriately etched using an acidic solution such as HNO 3, HF, HCl, H 2 SO 4 after the layer is formed by the above method.
[0047]
Other components will be described below.
[0048]
(substrate)
As the substrate 101, metal, resin, glass, ceramics, semiconductor bulk, or the like is used. The surface may have fine irregularities. Moreover, it can respond to continuous film-forming by setting it as a long shape. Stainless steel, polyimide, and the like are particularly preferable because they have flexibility.
[0049]
(Reflective layer)
The reflective layer 102a has a role as an electrode and a reflective layer that reflects light reaching the substrate and reuses it in the semiconductor layer. Al, Cu, Ag, Au, or the like is formed by a method such as vapor deposition, sputtering, plating, or printing.
[0050]
By having irregularities on the surface, there is an effect that the optical path length of the reflected light in the semiconductor layer is extended and the short-circuit current is increased.
[0051]
When the substrate has conductivity, the reflective layer may not be formed.
[0052]
(Upper transparent electrode)
The upper transparent electrode 106 can also serve as an antireflection film by setting its film thickness appropriately.
[0053]
The transparent electrode 106 is formed of a material such as ITO, ZnO, or InO3 using a method such as vapor deposition, CVD, spraying, spin-on, or immersion. You may contain the substance which changes electrical conductivity in these compounds.
[0054]
(Collector electrode)
The collecting electrode 107 is provided to improve the collecting efficiency. As the forming method, there are a method of forming a metal of an electrode pattern by sputtering using a mask, a method of printing a conductive paste or a solder paste, and a method of fixing a metal wire with a conductive paste. An example using copper wire is shown in FIG. A silver cladding layer is formed around the thin copper wire. This layer has a function of reducing contact resistance with the copper wire. Further, a carbon paste layer using an acrylic resin as a binder is formed around the silver clad layer. This layer has a function of maintaining adhesion with the upper transparent electrode and a function of reducing contact resistance with the silver clad layer. It also has a function of preventing silver in the silver cladding layer from diffusing into the photovoltaic layer.
[0055]
Further, a bus bar or the like for taking out electric power is formed as shown in FIG. A plurality of collecting electrodes are arranged on the surface of the element without intersecting, and one end thereof is brought into electrical contact with 108 bus bars. The 108 bus bars are formed on the 107, and use a metal material having good conductivity such as a Cu plate. Further, an insulating double-sided tape is disposed between the bus bar and the upper transparent electrode so as to be in close contact with the upper transparent electrode.
[0056]
FIG. 4 shows an example of modularizing the photoelectric conversion element of the present invention. A plurality of photoelectric conversion elements are serialized as shown in FIG. 4, and 406 bypass diodes are connected in parallel with each photoelectric conversion element, so that even if one photoelectric conversion element is shaded, other photoelectric conversion elements All the generated voltage is not applied to the photoelectric conversion element. In addition, since the photoelectric conversion module of the present invention is sealed with a fluororesin and a support substrate after arranging each member as shown in FIG. 4, it is possible to suppress the intrusion of water vapor.
[0057]
【Example】
The present invention will be specifically described below by taking a solar cell as an example of the photoelectric conversion element, but the present invention is not limited to this.
[0058]
(Example 1)
The solar cell of Fig. 1a with one pin junction was fabricated. Specifically, substrate stainless steel (SUS430 10 × 10cm2 thickness 0.2mm) / reflective layer Ag / transparent conductive layer ZnO / first doped layer a-Si: H: P / first i layer μc-Si: H / Second doped layer μc-Si: H: B / Upper transparent electrode ITO / Current collecting electrode A solar cell made of Cu wire / Ag / C (Fig. 3) was fabricated.
[0059]
Here, the reflective layer and the transparent conductive layer were formed by sputtering using the apparatus shown in FIG. 8, the photovoltaic layer was formed using the apparatus shown in FIG. 9, and the first i layer used a high frequency of 500 MHz. The doped layer was formed by the plasma CVD method, the RF plasma CVD method, and the upper transparent electrode layer was formed by the sputtering method.
[0060]
The procedure for forming the lower conductive layer, the reflective layer, and the transparent conductive layer using the sputtering method is described below. Figure 8 shows an apparatus that can perform sputter etching and DC magnetron sputtering. 801 is a cylindrical deposition chamber, 802 is a substrate holder, 803 is a substrate, 804 is a heater, 804 is a matching box, 806 is an RF power supply, and 807 is a reflection. Metal target for layer formation, 808 is a target for transparent conductive layer formation, 810 and 811 are DC power supplies, 813 and 814 are shutters, 816 is an exhaust pipe, 817 is a gas introduction pipe, 818 is a rotating shaft, and 819 is plasma is there. In addition, although not shown, there are a gas supply device connected to the gas introduction pipe 817 and a vacuum pump connected to the exhaust pipe 816. 821 is an arrow indicating the exhaust direction. First, the acid-washed and organic-washed substrate 803 is attached to a disk-shaped substrate holder, and a rotating shaft 818 that is the central axis of the disk-shaped substrate holder is rotated. Using an oil diffusion pump / rotary pump (not shown), the inside of the deposition chamber is evacuated to 5 × 10E-6 Torr, Ar is introduced from the gas introduction pipe, and RF power is introduced from the 806 RF power source to the inside of the deposition chamber. , Ar plasma is generated. Adjust the 805 matching circuit to minimize reflected power. At this time, the substrate is sputter-etched (reverse sputtering) to obtain a clean surface. Next, set the heater to the formation temperature of the reflective layer, and when it reaches the predetermined temperature, turn on the DC power of 810, generate Ar plasma 819, open the shutter 813, the reflective layer has the predetermined film thickness If only formed, close the shutter and turn off the DC power. Next, the heater is set so as to reach the formation temperature of the transparent conductive layer, and when the predetermined temperature is reached, the DC power supply of 811 is turned on, Ar plasma is generated, the shutter 814 is opened, and the transparent conductive layer is a predetermined film. When it is thick enough, close the shutter and turn off the DC power.
[0061]
FIG. 9 shows an apparatus capable of performing plasma CVD, 901 is a reaction chamber, 902 is a substrate on which a lower conductive layer is formed, 903 is a heater, 904 is a conductance valve, 908 is a high-frequency electrode, and 909 is a matching circuit. A built-in high frequency power source (500 MHz), 910 is plasma, 911 is a shutter, 914 is an exhaust pipe, and 915 is a gas introduction pipe. Reference numeral 913 denotes an exhaust direction, and 916 denotes a gas introduction direction. Although not shown in the figure, a vacuum pump such as an oil diffusion pump / rotary pump is connected to the exhaust pipe in the figure, and a gas introduction device is connected to the gas introduction pipe in the figure. The plasma CVD apparatus is configured as described above.
[0062]
The actual layer formation using this plasma CVD apparatus is performed in the following procedure. First, the substrate 902 on which the lower conductive layer is formed is attached to the heater 903 inside the reaction chamber 901, and evacuated with a vacuum pump such as an oil diffusion pump / rotary pump so that the pressure inside the reaction chamber becomes 1 × 10E-4 Torr or less. To do. When the pressure becomes 1 × 10E-4 Torr or less, gases such as H 2 and He are introduced into the reaction chamber from the gas introduction tube 915, a heater is turned on, and the substrate 902 is set to a desired temperature. When the temperature of the substrate is stabilized, the raw material gas is introduced from the gas introduction pipe, the high frequency power source 909 is turned on, and the high frequency power is introduced from the high frequency electrode 908 into the reaction chamber. The conductance valve 904 is adjusted so that a desired pressure is obtained when the plasma 910 is generated. At this time, it is preferable to adjust the matching circuit to minimize the reflected power. Next, the shutter 911 is opened, and when a layer having a desired film thickness is formed, the shutter is closed, introduction of high-frequency power and introduction of source gas are stopped, and preparation for forming the next layer is performed. In order to perform the RF plasma CVD method with this apparatus, an RF power source (13.56 MHz) is connected instead of the above-described high frequency power source 909, and plasma is generated by introducing RF power.
[0063]
Specific conditions are shown in Table 1.
[0064]
[Table 1]

[0065]
As shown in FIG. 13, an insulating double-sided tape is applied to one side of the substrate formed up to the upper transparent electrode (ITO), and one end of the collector electrode made of Cu wire, Ag cladding layer, and carbon paste shown in FIG. The bus bar was fixed to the tape, and the bus bar was fixed to the double-sided tape from above the current collecting electrode. The whole was heated to fuse the carbon paste, and the current collecting electrode and the bus bar were fixed.
[0066]
Several of the same solar cells (Ex. 1) were produced. When one of the cross-sectional shapes is observed with a transmission electron microscope (TEM), the first i layer is a structure in which the longitudinal direction of the columnar crystal grains is inclined with respect to the normal direction of the substrate as shown in FIG. It was found that was formed. Further, when the surface roughness Ra of the lower conductive layer (transparent conductive layer and reflective layer) was measured, it was found that the average per 50 μm length was 0.32 μm. Further, the ratio of the angle G (the angle formed by the normal of the minute region of the lower conductive layer and the normal of the main surface of the substrate) being 15 degrees or more and 45 degrees or less was 91%. In addition, the ratio K of the total volume of columnar grains having an angle F of 20 degrees or less to the total volume of the i layer was 90%.
[0067]
(Comparative Example 1)
As the lower conductive layer, a transparent conductive layer was not provided, and only a substantially planar Ag was formed using a normal sputtering method, and a solar cell having the cross-sectional shape of FIG. 2 was produced. The first i layer was formed using the RF plasma CVD method under the conditions shown in Table 1b. Otherwise, a solar cell similar to that of Example 1 (photoelectric conversion element in FIG. 2) was produced.
[0068]
Table 2 shows the formation conditions.
[0069]
[Table 2]

[0070]
Several of the same solar cells (ratio 1) were produced. When one of the cross-sectional shapes was observed with a transmission electron microscope (TEM), it was found that columnar microcrystalline silicon was formed in the first i layer as shown in FIG. When the surface roughness Ra of the lower conductive layer was measured, it was found that the average per 50 μm length was 0.02 μm.
[0071]
First, the initial characteristics (photoconductive characteristics, leakage current, low illuminance open voltage) of the solar cell of Example 1 (Act 1) and the solar cell of Comparative Example 1 (Ratio 1) were measured.
[0072]
Photoelectric conversion efficiency, open-circuit voltage, and short-circuit photocurrent were measured using a solar simulator (AM1.5 100mW / cm2 surface temperature 25 ° C), and the photoelectric conversion elements of the present invention were 1.29 times, 1.04 times, and 1.23 times better, respectively. It was.
[0073]
Next, when the open-circuit voltage was measured under a fluorescent lamp (low illuminance) with an illuminance of about 500 lux, it was found that the solar cell of (Real 1) was 1.2 times better than that of (Ratio 1). . When a reverse bias was applied in a dark place and the leakage current was measured, the leakage current of the solar cell of the present invention (Act 1) was as small as about 1/8 of Comparative Example 1 (Ratio 1) and was excellent. I understand.
[0074]
Next, a light irradiation test of the solar cells of (Ex. 1) and (Ratio 1) was performed. When exposed to the above simulator (AM1.5 100 mW / cm2 surface temperature 50 ° C.) for 1000 hours, no poor appearance after the test was found.
[0075]
When photoelectric conversion efficiency, open circuit voltage, short-circuit photocurrent, low illuminance open voltage, and leakage current after the light irradiation test were measured, differences in the low illuminance open voltage and leakage current before and after the test were observed.
[0076]
The ratio of open circuit voltage at low illuminance before and after the test (low illuminance open voltage after test / low illuminance open voltage before test) was 0.95 for (Real 1) and 0.92 for (Ratio 1). Furthermore, the ratio of the leakage current before and after the test (leakage current after the test / leakage current before the test) was 1.2 in (Real 1) and 2.2 in (Ratio 1).
[0077]
As described above, it has been found that the photoelectric conversion element of the present invention is superior to the conventional photoelectric conversion element.
[0078]
Furthermore, the above-mentioned “torsion test” was performed. In the two solar cells, no poor appearance after the test was found.
[0079]
After measuring the photoelectric conversion efficiency, open circuit voltage, short-circuit photocurrent, low illuminance open voltage, and leak current after the torsion test, the photoelectric conversion efficiency, open voltage, low illuminance open voltage, and leak current decreased before and after the test. There was a difference.
[0080]
The ratio of photoelectric conversion efficiency before and after the test (photoelectric conversion efficiency after the test / photoelectric conversion efficiency before the test) was 0.98 in (Real 1) and 0.70 in (Ratio 1). The ratio of open-circuit voltage before and after the test (open-circuit voltage after test / open-circuit voltage before test) was 0.99 for (Real 1) and 0.84 for (Ratio 1).
[0081]
In addition, the ratio of open voltage of low illuminance before and after the test (low illuminance open voltage after test / low illuminance open voltage before test) was 0.96 for (Real 1) and 0.87 for (Ratio 1).
[0082]
Further, the ratio of leakage current before and after the test (leakage current after the test / leakage current before the test) was 1.1 in (Real 1) and 3.1 in (Ratio 1).
[0083]
As described above, it has been found that the photoelectric conversion element of the present invention is superior to the conventional photoelectric conversion element.
[0084]
Similarly, a hail test described in JIS C 8917 related to crystalline solar cells was performed. The ice ball was dropped uniformly 10 times under the conditions of 25 mm in diameter and a final velocity of 23 m / sec. When the same evaluation as described above was performed after the test, it was found that the solar cell of (Example 1) was similarly superior to the solar cell of (Ratio 1).
[0085]
(Example 2)
As an example of another embodiment, the solar cell of FIG. Specifically, substrate stainless steel (SUS430 10 × 10cm2 thickness 0.2mm) / reflective layer Al / transparent conductive layer ZnO / first doped layer a-Si: H: P / first i layer μc-Si: H / Second doped layer μc-Si: H: B / Third doped layer a-Si: H: P / Second i layer a-Si: H / Fourth doped layer μc-Si: H: B / Top transparent electrode ITO / Collector electrode Several solar cells (2) made of Cu wire / Ag / C material were fabricated.
[0086]
Table 3 shows the formation conditions.
[0087]
[Table 3]

[0088]
When the cross section of this solar cell was observed by TEM, it was found that the first i layer had a microcrystalline structure as shown in FIG. Further, when the surface roughness Ra of the lower conductive layer (transparent conductive layer / reflective layer) was measured, it was found that the average per 50 μm length was 0.29 μm. Further, when the angle G (angle formed by the normal line of the minute region of the lower conductive layer and the normal line of the substrate main surface) was 15 degrees or more and 45 degrees or less was counted, it was 93%. In addition, the ratio K of the total volume of columnar grains having an angle F of 20 degrees or less to the total volume of the first i layer was 94%.
[0089]
(Comparative Example 2)
In the solar cell of Comparative Example 1 (Table 1b) having the configuration as shown in FIG. 2, the third doped layer, the second i layer, and the second similar to those of Example 2 between the second doped layer and the upper transparent electrode. Four doped layers were stacked to produce several photoelectric conversion elements (ratio 2). When the cross section of this solar cell was observed by TEM, it was found that the first i layer had a microcrystalline structure as shown in FIG. When the same measurement and test as in Example 1 were performed, it was found that the solar cell of (Act 2) was superior to the solar cell of (Ratio 2).
[0090]
(Example 3)
A long sheet was used for the substrate, and a reflective layer and a transparent conductive layer were sequentially formed by a highly productive roll-to-roll method. In addition, the roll-to-roll method was adopted when forming the photovoltaic layer and the upper transparent electrode. Details will be described below.
[0091]
An apparatus 1000 in FIG. 10 is a thin film forming apparatus capable of continuously forming several thin films in a vacuum on the surface of a long sheet-like substrate 1001 having flexibility (flexibility). 1001 is a long substrate having flexibility such as stainless steel, 1008 is a feed roll in which this substrate is wound in a roll shape, 1009 is a take-up roll for winding the substrate, and 1002 is for fixing the feed roll inside. A vacuum pump 1016 such as a rotary pump is connected via a pipe 1018. Similarly, the take-up roll 1009 is fixed to the vacuum vessel 1007 and connected to a vacuum pump.
[0092]
A substrate passage called a gas gate 1021 and vacuum vessels 1003, 1004, 1005 and 1006 for forming a desired thin film by a DC magnetron sputtering method are connected between the vacuum vessels 1002 and 1007 as shown in FIG. As shown in the figure, a gas introduction pipe 1010 is connected to the gas gate 1021 so that a scavenging gas 1011 such as Ar flows into the gas gate 1021 so that gas mutual diffusion does not occur between vacuum vessels forming different types of thin films. Can do. Therefore, a good bond can be formed. Although the gas gate is connected between the vacuum vessels, it is not necessary to provide the gas gate between them when the same thin film is formed by the continuous vacuum vessels.
[0093]
A diffusion pump 1017 is connected to the vacuum containers 1003, 1004, 1005, and 1006 through a pipe 1019, and further, a vacuum pump such as a rotary pump is connected through the pipe. Further, inside the vacuum vessels 1003, 1004, 1005, and 1006, a heater 1014 for heating the substrate, a target 1023 for forming a desired thin film, an electrode 1013 with a built-in magnet, and a gas for introducing a sputtering gas 1022 An inlet tube 1020 is provided. A DC power source 1012 is connected to each electrode.
[0094]
The method of using this apparatus will be described below. First, a feed roll 1008 wound with a flexible long substrate such as stainless steel is fixed in the vacuum vessel 1002, and the tip of the substrate is fixed inside the vacuum vessel 1007 through each gas gate, vacuum vessel 1003, 1004, 1005, 1006. Wrap around the take-up roll 1009.
[0095]
Each vacuum pump is started and evacuated until the internal pressure of each vacuum vessel reaches several mTorr. Ar gas is introduced from the gas introduction pipe 1010 and a desired gas is introduced from 1020, each heater is turned on, and the substrate is conveyed in the direction of arrow 1024. When the temperature of the substrate becomes constant, each DC power source is turned on, and plasma 1015 is generated in the vacuum vessels 1003, 1004, 1005, and 1006 to form a desired thin film.
[0096]
When it reaches the end of the board, stop the transport, turn off each DC power source and each heater power source, and cool the board. When the temperature of the substrate reaches room temperature, each vacuum vessel is leaked and the take-up roll is taken out.
[0097]
Using a stainless steel substrate (SUS430) having a thickness of 0.15 mm, a reflective layer and a transparent conductive layer were continuously formed by the above method under the conditions shown in Table 3. When the cross-sectional shape of the lower conductive layer (transparent conductive layer / reflective layer) was observed with an SEM, it was found that the shape was as shown in FIG. The average surface roughness Ra per 50 μm length was 0.35 μm. The ratio of the angle G being 15 degrees or more and 45 degrees or less was 90%.
[0098]
Next, an apparatus for forming a photovoltaic layer on a transparent conductive layer using a roll-to-roll method will be described in detail. The apparatus of FIG. 11 is an apparatus for continuously forming six photovoltaic layers on a long substrate, and some vacuum vessels are omitted from the drawing. 1101 is a long substrate on which a lower conductive layer is formed, 1108 is a delivery roll wound around the substrate, 1109 is a take-up roll for winding the substrate, 1102 is a vacuum that can fix the delivery roll inside A vacuum pump 1116 such as a rotary pump is connected to the container via a pipe 1118. Similarly, the take-up roll 1109 is fixed to the vacuum vessel 1107 and connected to a vacuum pump. Between the vacuum vessels 1102 and 1107, vacuum vessels 1103-a, 1104, 1103-b (not shown), 1103-c (not shown), 1103-d and 1103-e for forming a desired thin film are sequentially arranged. The gas gate 1121 is connected between the vacuum vessels. As shown in the figure, each gas gate 1121 is connected to a gas introduction pipe 1110 to flow in a scavenging gas 1111 such as Ar, H2, and He, and gas mutual diffusion occurs between vacuum vessels forming different types of thin films. Can not be. For this reason, the pin junction is very good. When the same thin film is formed in a continuous vacuum vessel, it is not necessary to provide a gas gate therebetween.
[0099]
In the vacuum vessels 1103-a, 1103-b, 1103-c, 1103-d, and 1103-e, an RF plasma CVD method (power supply frequency: 13.56 MHz) can be performed. A rotary pump and a gas introduction pipe 1120 are connected to the vacuum container through a pipe 1118, and a heater 1114 and an RF electrode 1113 are fixed inside. An RF power source 1112 is connected to the RF electrode. In the vacuum vessel 1104, a high-frequency plasma CVD method (power supply frequency 150 MHz) can be performed. A diffusion pump 1117 is connected to the vacuum container through a pipe 1119, and a vacuum pump such as a rotary pump is further connected through the pipe. Further, a gas introduction pipe is connected, and a heater 1127 and a high-frequency electrode 1126 are fixed inside. A high-frequency power source 1125 (frequency 150 MHz) is connected to the high-frequency electrode.
[0100]
The method of using this apparatus will be described below. First, the feed roll 1108 wound with the stainless steel substrate formed up to the lower conductive layer is fixed in the vacuum vessel 1102, and the substrate tip is attached to the take-up roll 1109 fixed inside the vacuum vessel 1107 through each gas gate and each vacuum vessel. Wrap. Each vacuum pump is started and evacuated until the internal pressure of each vacuum vessel reaches several mTorr. The H2 gas is introduced from the gas introduction pipe 1110, the gas for forming the photovoltaic layer is introduced from the gas introduction pipe 1120, each heater is turned on, and the substrate is conveyed in the direction of the arrow 1124. When the substrate temperature becomes constant, each RF power source and high frequency power source are turned on, matching is adjusted, plasma 1115 is generated inside each vacuum vessel, and a desired thin film is formed. If it reaches the end of the substrate, the conveyance is stopped, each DC power source, each microwave power source, DC power source and each heater power source are turned off, and the substrate is cooled. When the temperature of the substrate reaches about room temperature, each vacuum vessel is leaked and the winding roll is taken out. Using the method as described above, under the conditions shown in Table 3, the first doped layer a-Si: H: P / first i layer μc-Si: H / second doped layer μc-Si: H: B / third doped layer a-Si: H: P / second i layer a-Si: H / fourth doped layer μc-Si: H: B were formed.
[0101]
The rolled solar cell taken out was continuously formed with an upper transparent electrode (ITO) using the apparatus of FIG. At that time, the target inside the vacuum vessel 1006 was set to ITO, plasma was not generated in the vacuum vessels 1003, 1004, and 1005, and the upper transparent electrode made of ITO was formed on the fourth dope layer only by the vacuum vessel 1006. The formation conditions of each layer are shown in Table 4.
[0102]
[Table 4]

[0103]
Cut the roll-shaped solar cell taken out to 30 x 30 cm2, and then attach the same collector electrode and bus bar as in Example 1 as shown in Fig. 1-a, and install four solar cells as shown in Fig. 4. In series, a bypass diode was connected in parallel with each solar cell. Next, EVA, nylon resin, EVA, glass nonwoven fabric, serialized solar cells, glass nonwoven fabric, EVA, glass nonwoven fabric, EVA, glass nonwoven fabric, and fluororesin are layered on a 0.3mm thick support substrate and heated in vacuum Sealed (laminated).
[0104]
When the solar cell module (actual 3) having a size of 35 × 130 cm2 produced as described above was subjected to the same measurement and test as in Example 1, in any of the initial characteristics, torsion test, and hail test ( The characteristics were even better than the solar cell of Example 1). The solar cell module (Act 3) was left outdoors for 3 months and an outdoor exposure test was conducted. There was almost no change in the appearance, and the decrease in photoelectric conversion efficiency was about 5%.
[0105]
As described above, it was found that the photoelectric conversion module of the present invention has excellent characteristics.
[0106]
(Example 4)
A solar cell (Example 4) similar to that of Example 1 was produced except that the film thickness of the first i layer in Example 1 was changed to 2 μm. When the cross section was observed by TEM, it was found that the structure of the first i layer was as shown in FIG. When the same measurement and test as in Example 1 were performed, it was found that the solar cell of (Example 4) was as excellent as the solar cell of (Example 1).
[0107]
(Example 5)
As an example of another embodiment, a solar cell having a single lower conductive layer was fabricated. The lower conductive layer was made of a silver layer having a thickness of 0.5 μm, formed by sputtering, and the surface shape of the layer was made uneven (textured) by setting the formation temperature to 350 ° C. By observing the cross section, the angle G (angle formed by the normal of the microregion of the lower conductive layer and the normal of the main surface of the substrate) was counted to be 91% when counted from 15 degrees to 45 degrees. The same photovoltaic layer, upper transparent electrode, and current collecting electrode as in Example 1 were formed on the lower conductive layer, and several solar cells (Example 5) shown in FIG. 1 were produced. When the same measurement and test as in Example 1 were performed, it was found that the solar cell of (Example 5) was superior to the solar cell of (Example 1).
[0108]
(Example 6)
As an example of another embodiment, the solar of FIG. 1-b having the photovoltaic layer of FIG. 5 in which the first doped layer has a stacked structure made of a-Si: H: P / μc-Si: H: P. A battery was produced. A solar cell (Example 6) was produced in the same manner as in Example 2 except that the first doped layer in Example 2 was changed to a-Si: H: P / μc-Si: H: P. When the same measurement and test as in Example 1 were performed, it was found that the solar cell of (Ex. 4) was as excellent as the solar cell of (Ex. 2).
[0109]
【The invention's effect】
According to the photoelectric conversion element of the present invention, characteristics such as photoelectric conversion efficiency, open circuit voltage, short-circuit photocurrent, low illuminance open voltage, and leakage current of the photoelectric conversion element can be improved. In addition, it can improve durability in outdoor exposure tests, mechanical strength, and long-term light irradiation. Furthermore, the cost of the photoelectric conversion element can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a photoelectric conversion element of the present invention characterized by a lower conductive layer and an i layer.
FIG. 2 shows a conventional photoelectric conversion element.
FIG. 3 shows an example of a collecting electrode
FIG. 4 shows an example of modularization of the photoelectric conversion element of the present invention.
FIG. 5 is a photoelectric conversion element of the present invention characterized by a first doped layer
FIG. 6: Relationship between surface roughness of lower conductive layer and photoelectric conversion efficiency
FIG. 7 shows the relationship between the rate at which the angle G defined in FIG. 1a is between 15 degrees and 45 degrees and the photoelectric conversion efficiency.
FIG. 8 shows an apparatus for forming a lower conductive layer and an upper transparent electrode of a photoelectric conversion element of the present invention.
FIG. 9 shows an apparatus for forming a photovoltaic layer of a photoelectric conversion element of the present invention.
FIG. 10 shows an apparatus for continuously forming the lower conductive layer and the upper transparent electrode of the photoelectric conversion element of the present invention.
FIG. 11 shows an apparatus for continuously forming a photovoltaic layer of the photoelectric conversion element of the present invention.
FIG. 12A is a diagram defining the angle F, where b is the relationship between the rate at which the angle F defined in FIG.
FIG. 13 shows an example in which a bus bar is provided in the photoelectric conversion element of the present invention.
[Explanation of symbols]
101 substrate
102 Lower conductive layer
102a Reflective layer
102b Transparent conductive layer
103 First doped layer
104 1st i layer
105 Second doped layer
106 Upper transparent electrode
107 Current collecting electrode
108 Busbar
109 Double-sided tape
110 Third doped layer
111 second i layer
112 Fourth doped layer
120 angle G
201 substrate
202 Lower conductive layer
203 first doped layer
204 1st i-layer
205 Second doped layer
206 Upper transparent electrode
207 Current collecting electrode
301 copper wire
302 Silver clad layer
303 Carbon paste layer
306 Surface of upper transparent electrode
307 Current collecting electrode
401 Support substrate
402, 404, 409, 411 EVA
403 Nylon resin
405, 408, 410, 412 Glass nonwoven fabric
406 Bypass diode
407 photoelectric conversion element
413 Fluorine resin
414 Busbar
503a First doped layer a
503b First doped layer b
504 1st i layer
505 Second doped layer
506 Third doped layer
507 second i layer
508 Fourth doped layer
801 Deposition chamber
802 Substrate holder
803 substrate
804 heater
805 Matching box
806 RF power supply
807 Target for reflective layer
808 Target for transparent conductive layer
810,811 DC power supply
813,814 Shutter
816 Exhaust pipe
817 Gas introduction pipe
818 axis of rotation
819 Plasma
901 Reaction chamber
902 Substrate on which lower conductive layer is formed
903 Heater
904 conductance valve
908 High frequency electrode
909 high frequency power supply
910 Plasma
911 Shutter
913 Exhaust direction
914 Exhaust pipe
915 Gas introduction pipe
916 Gas introduction direction
1001 Long substrate
1002, 1003, 1004, 1005, 1006, 1007 vacuum vessel
1008 Delivery roll
1009 Winding roll
1010 Gas introduction pipe
1011 Scavenging gas
1012 DC power supply
1013 electrode
1014 Heater
1015 Plasma
1016 Vacuum pump
1017 Diffusion pump
1018, 1019 Exhaust pipe
1020 Gas inlet pipe
1021 gas gate
1022 gas
1023 target
1024 Board transfer direction
1101 Long substrate with lower conductive layer formed
1102, 1103-a, 1103-b, 1103-c, 1103-d, 1103-e, 1103-f, 1104, 1107 Vacuum container
1108 Delivery roll
1109 Winding roll
1110 Scavenging gas introduction pipe
1111 Scavenging gas
1112 RF power supply
1113 RF electrode
1114 Heater
1115 Plasma
1116 Vacuum pump
1117 Diffusion pump
1118, 1119 Exhaust pipe
1120 Gas introduction pipe
1121 gas gate
1122 gas
1124 Board transfer direction
1125 high frequency power supply
1126 High frequency electrode
1127 Heater

Claims (11)

In a photoelectric conversion element having a substrate, a lower conductive layer, a first doped layer, an i layer, a second doped layer, and an upper conductive layer, the surface of the lower conductive layer has an uneven shape, and the i layer has a columnar crystal And the longitudinal direction of the columnar crystal grains is inclined with respect to the normal direction of the substrate , the straight line A passing through the columnar crystal grains and parallel to the longitudinal direction, and the first doped layer Of the straight line connecting the shortest distance between the interface 1 of the i-layer and the second doped layer and the interface 2 of the i-layer with the straight line B passing through the columnar crystal grain A is 20 degrees or less Is 70% or more based on the total volume of the i layer .   2. The photoelectric conversion element according to claim 1, wherein the lower conductive layer located between the substrate and the semiconductor layer has a surface roughness Ra at a length of about several tens of μm of 0.1 μm to 1 μm. .   The area where the normal direction of the surface of the lower conductive layer in the micro area of the lower conductive layer is 15 degrees or more and 45 degrees or less with respect to the normal line of the main surface of the substrate is 80% or more of the entire surface area. The photoelectric conversion element according to claim 1.   2. The photoelectric conversion element according to claim 1, wherein the length of the columnar crystal grains in the longitudinal direction is 100 angstroms or more and 0.3 [mu] m or less.   The photoelectric conversion element according to claim 1, wherein the i layer has a thickness of 0.3 μm or more and 3 μm or less.   2. The photoelectric conversion element according to claim 1, wherein a minute region made of an amorphous silicon-based semiconductor material is present in the i layer at a volume ratio of 50% or less with respect to the entire region of the i layer. .   The i layer is formed by a plasma CVD method using an electromagnetic wave having a frequency of 30 MHz or more and 600 MHz or less, using a silicon-containing gas and a hydrogen gas as source gases, a pressure of 1 mTorr or more and 1 Torr or less, 2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element is formed under a condition that the ratio is 0.5% or more and 30% or less.   A third doped layer, a second i layer, and a fourth doped layer are provided between the second doped layer and the upper conductive layer, and the second i layer is an amorphous silicon-based semiconductor. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element has a thickness of 0.1 μm or more and 0.4 μm or less. 9. The photoelectric conversion element according to claim 8, wherein at least one doped layer includes a microcrystalline silicon-based semiconductor material. The first and / or third doped layer has a layered structure with a layer made of a microcrystalline silicon semiconductor material and a layer made of an amorphous silicon semiconductor material, and a layer made of the microcrystalline silicon semiconductor material 9. The photoelectric conversion element according to claim 8, wherein is in contact with the i layer.   The photoelectric conversion element according to claim 1, wherein the substrate is a strip-like long substrate.

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