JP2004238213A - Method of manufacturing titanium oxide particle and photoelectric conversion device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing titanium oxide sol suitable for a photoelectric conversion device and a dyestuff-sensitized photoelectric conversion device having excellent photoelectric conversion efficiency. <P>SOLUTION: The method of manufacturing titanium oxide particles by the hydrolysis of orthotitanic ester includes a process for heating the titanium oxide sol produced by the hydrolysis in the presence of tetraalkylammonium hydroxide at ≥200°C for ≥10 hr in a pressure vessel. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４４】
（ｂ） メチン色素
好ましいメチン色素は、シアニン色素、メロシアニン色素、スクワリリウム色素等のポリメチン色素である。好ましいポリメチン色素の例としては、特開平１１−３５８３６号公報、同１１−１５８３９５号公報、同１１−１６３３７８号公報、同１１−２１４７３０号公報、同１１−２１４７３１号公報、欧州特許第８９２４１１号明細書及び同第９１１８４１号明細書に記載の色素が挙げられる。これらのポリメチン色素の合成法については、エフ・エム・ハーマー（Ｆ． Ｍ． Ｈａｍｅｒ）著「ヘテロサイクリック・コンパウンズ−シアニンダイズ・アンド・リレィティド・コンパウンズ（Ｈｅｔｅｒｏｃｙｃｌｉｃ Ｃｏｍｐｏｕｎｄｓ − Ｃｙａｎｉｎｅ Ｄｙｅｓ ａｎｄ Ｒｅｌａｔｅｄ Ｃｏｍｐｏｕｎｄｓ）」， ジョン・ウィリー・アンド・サンズ（Ｊｏｈｎ Ｗｉｌｅｙ ＆ Ｓｏｎｓ）社， ニューヨーク， ロンドン， １９６４年、デー・エム・スターマー（Ｄ． Ｍ． Ｓｔｕｒｍｅｒ）著「ヘテロサイクリック・コンパウンズ−スペシャル・トピックス・イン・ヘテロサイクリック・ケミストリー（Ｈｅｔｅｒｏｃｙｃｌｉｃ Ｃｏｍｐｏｕｎｄｓ − Ｓｐｅｃｉａｌｔｏｐｉｃｓ ｉｎ Ｈｅｔｅｒｏｃｙｃｌｉｃ Ｃｈｅｍｉｓｔｒｙ）」， ジョン・ウィリー・アンド・サンズ（Ｊｏｈｎ Ｗｉｌｅｙ ＆ Ｓｏｎｓ）社， ニューヨーク，ロンドン， １９７７年， 第１８章， 第１４節， ｐ．８２〜５１５、「ロッズ・ケミストリー・オブ・カーボン・コンパウンズ（Ｒｏｄｄ’ｓ Ｃｈｅｍｉｓｔｒｙ ｏｆ Ｃａｒｂｏｎ Ｃｏｍｐｏｕｎｄｓ）」， 第２版， エルセビア・サイエンス・パブリック・カンパニー・インク（Ｅｌｓｅｖｉｅｒ Ｓｃｉｅｎｃｅ Ｐｕｂｌｉｓｈｉｎｇ Ｃｏｍｐａｎｙ Ｉｎｃ．）社， ニューヨーク， １９７７年， 第ＩＶ巻， ｐａｒｔ Ｂ， 第１５章， ｐ．３６９−４２２、英国特許第１，０７７，６１１号明細書、「Ｕｋｒａｉｎｓｋｉｉ Ｋｈｉｍｉｃｈｅｓｋｉｉ Ｚｈｕｒｎａｌ」， 第４０巻， 第３号， ｐ．２５３−２５８、「ダイズ・アンド・ピグメンツ（Ｄｙｅｓ ａｎｄ Ｐｉｇｍｅｎｔｓ）」， 第２１巻， ｐ．２２７−２３４、これらの引用文献等に記載されている。
【００４５】
（５） 半導体微粒子への色素の吸着
半導体微粒子に色素を吸着させる際には、色素の溶液中によく乾燥した半導体微粒子層を有する導電性支持体を浸漬する方法、又は色素の溶液を半導体微粒子層に塗布する方法を用いることができる。前者の方法の場合、浸漬法、ディップ法、ローラ法、エアーナイフ法等が利用可能である。浸漬法を用いる場合、色素の吸着は室温で行ってもよいし、特開平７−２４９７９０号に記載されているように加熱還流して行ってもよい。後者の方法の場合、ワイヤーバー法、スライドホッパー法、エクストルージョン法、カーテン法、スピン法、スプレー法等が利用できる。また、インクジェット法等によって色素を画像状に塗布し、この画像そのものを光電変換素子とすることもできる。
【００４６】
色素の溶液（吸着液）に用いる溶媒は、好ましくはアルコール類（メタノール、エタノール、ｔ−ブチルアルコール、ベンジルアルコール等）、ニトリル類（アセトニトリル、プロピオニトリル、３−メトキシプロピオニトリル等）、ニトロメタン、ハロゲン化炭化水素（ジクロロメタン、ジクロロエタン、クロロホルム、クロロベンゼン等）、エーテル類（ジエチルエーテル、テトラヒドロフラン等）、ジメチルスルホキシド、アミド類（Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジメチルアセタミド等）、Ｎ−メチルピロリドン、１，３−ジメチルイミダゾリジノン、３−メチルオキサゾリジノン、エステル類（酢酸エチル、酢酸ブチル等）、炭酸エステル類（炭酸ジエチル、炭酸エチレン、炭酸プロピレン等）、ケトン類（アセトン、２−ブタノン、シクロヘキサノン等）、炭化水素（へキサン、石油エーテル、ベンゼン、トルエン等）又はこれらの混合溶媒である。
【００４７】
色素の吸着量は、半導体微粒子層の単位面積（１ｍ^２）当たり０．０１〜１００ ｍｍｏｌとするのが好ましい。また色素の半導体微粒子に対する吸着量は、半導体微粒子１ｇ当たり０．０１〜１ｍｍｏｌであるのが好ましい。このような色素の吸着量とすることにより半導体微粒子の増感効果が十分に得られる。色素の吸着量が少なすぎると増感効果が不十分となり、色素の吸着量が多すぎると半導体に付着していない色素が浮遊し、増感効果が低減する。色素の吸着量を増やすためには、吸着前に半導体微粒子を加熱処理するのが好ましい。半導体微粒子表面に水が吸着するのを避けるために、加熱処理後には常温に戻さずに半導体微粒子層の温度が６０〜１５０℃の間で素早く色素の吸着を行うのが好ましい。
【００４８】
色素間の凝集等の相互作用を低減するために、界面活性剤としての性質を持つ無色の化合物を色素吸着液に添加し、半導体微粒子に共吸着させてよい。このような無色の化合物の例としては、カルボキシル基やスルホ基を有するステロイド化合物（コール酸、デオキシコール酸、ケノデオキシコール酸、タウロデオキシコール酸等）や、下記のようなスルホン酸塩類等が挙げられる。
【００４９】
【化２】

【００５０】
未吸着の色素は、吸着工程後、速やかに洗浄により除去するのが好ましい。洗浄は湿式洗浄槽中でアセトニトリル、アルコール系溶剤のような有機溶媒等を用いて行うのが好ましい。
【００５１】
色素を吸着した後、アミン類、４級アンモニウム塩、少なくとも１つのウレイド基を有するウレイド化合物、少なくとも１つのシリル基を有するシリル化合物、アルカリ金属塩、アルカリ土類金属塩等を用いて半導体微粒子の表面を処理してもよい。好ましいアミン類の例としてはピリジン、４−ｔ−ブチルピリジン、ポリビニルピリジン等が挙げられる。好ましい４級アンモニウム塩の例としてはテトラブチルアンモニウムヨージド、テトラヘキシルアンモニウムヨージド等が挙げられる。これらは有機溶媒に溶解して用いてもよく、液体の場合はそのまま用いてもよい。
【００５２】
（Ｃ） 電荷輸送層
電荷輸送層は、色素の酸化体に電子を補充する機能を有する電荷輸送材料を含有する。本発明で用いる電荷輸送材料は、（ｉ）イオンが関わる電荷輸送材料であっても、（ｉｉ）固体中のキャリアー移動が関わる電荷輸送材料であってもよい。（ｉ）イオンが関わる電荷輸送材料としては、酸化還元対イオンを含有する溶融塩電解質組成物、酸化還元対のイオンが溶解した溶液（電解液）、酸化還元対の溶液をポリマーマトリクスのゲルに含浸したいわゆるゲル電解質組成物、固体電解質組成物等が挙げられ、（ｉｉ）固体中のキャリアー移動が関わる電荷輸送材料としては、電子輸送材料や正孔（ホール）輸送材料等が挙げられる。これらの電荷輸送材料は複数併用してもよい。本発明では、電荷輸送層に溶融塩電解質組成物又はゲル電解質組成物を用いるのが好ましい。
【００５３】
（１） 溶融塩電解質組成物
溶融塩電解質組成物は溶融塩を含む。溶融塩電解質組成物は常温で液体であるのが好ましい。主成分である溶融塩は室温において液状であるか、又は低融点の電解質であり、その一般的な例としては国際公開第９５／１８４５６号パンフレット、特開平８−２５９５４３号公報、「電気化学」， １９９７年， 第６５巻， 第１１号， ｐ．９２３等に記載のピリジニウム塩、イミダゾリウム塩、トリアゾリウム塩等が挙げられる。溶融塩の融点は５０℃以下であるのが好ましく、２５℃以下であるのが特に好ましい。溶融塩の具体例は特開２００１−３２００６８号公報の段落番号００６６〜００８２に詳しく記載されている。
【００５４】
溶融塩は単独で使用しても２種以上混合して使用してもよい。また、ＬｉＩ、ＮａＩ、ＫＩ、ＬｉＢＦ_４、ＣＦ_３ＣＯＯＬｉ、ＣＦ_３ＣＯＯＮａ、ＬｉＳＣＮ、ＮａＳＣＮ等のアルカリ金属塩を併用することもできる。アルカリ金属塩の添加量は、組成物全体に対して２質量％以下であるのが好ましく、１質量％以下がさらに好ましい。また、溶融塩電解質組成物に含まれるアニオンの５０モル％以上がヨウ化物イオンであることが好ましい。
【００５５】
通常、溶融塩電解質組成物はヨウ素を含有する。ヨウ素の含有量は、溶融塩電解質組成物全体に対して０．１〜２０質量％であるのが好ましく、０．５〜５質量％であるのがより好ましい。
【００５６】
溶融塩電解質組成物の揮発性は低いことが好ましく、溶媒を含まないことが好ましい。溶媒を添加する場合でも、溶媒の添加量は溶融塩電解質組成物全体に対して３０質量％以下に留めることが好ましい。溶融塩電解質組成物は後述のようにゲル化して使用してもよい。
【００５７】
（２）電解液
電解液は電解質、溶媒及び添加物から構成されることが好ましい。電解液に用いる電解質の例としては、Ｉ_２とヨウ化物（ＬｉＩ、ＮａＩ、ＫＩ、ＣｓＩ、ＣａＩ_２等の金属ヨウ化物、テトラアルキルアンモニウムヨーダイド、ピリジニウムヨーダイド、イミダゾリウムヨーダイド等の４級アンモニウム化合物ヨウ素塩等）の組み合わせ、Ｂｒ_２と臭化物（ＬｉＢｒ、ＮａＢｒ、ＫＢｒ、ＣｓＢｒ、ＣａＢｒ_２等の金属臭化物、テトラアルキルアンモニウムブロマイド、ピリジニウムブロマイド等の４級アンモニウム化合物臭素塩等）の組み合わせ、フェロシアン酸塩−フェリシアン酸塩やフェロセン−フェリシニウムイオン等の金属錯体、ポリ硫化ナトリウム、アルキルチオール−アルキルジスルフィド等のイオウ化合物、ビオロゲン色素、ヒドロキノン−キノン等が挙げられる。中でも、Ｉ_２とＬｉＩ又はピリジニウムヨーダイド、イミダゾリウムヨーダイド等の４級アンモニウム化合物ヨウ素塩を組み合わせた電解質が好ましい。電解質は混合して用いてもよい。
【００５８】
電解液中の電解質濃度は好ましくは０．１〜１０ Ｍであり、より好ましくは０．２〜４Ｍである。また、電解液にヨウ素を添加する場合の好ましいヨウ素の添加濃度は０．０１〜０．５ Ｍである。
【００５９】
電解液に使用する溶媒は、粘度が低くイオン移動度を向上したり、若しくは誘電率が高く有効キャリアー濃度を向上したりして、優れたイオン伝導性を発現できる化合物であることが望ましい。このような溶媒の例としては、エチレンカーボネート、プロピレンカーボネート等のカーボネート化合物、３−メチル−２−オキサゾリジノン等の複素環化合物、ジオキサン、ジエチルエーテル等のエーテル化合物、エチレングリコールジアルキルエーテル、プロピレングリコールジアルキルエーテル、ポリエチレングリコールジアルキルエーテル、ポリプロピレングリコールジアルキルエーテル等の鎖状エーテル類、メタノール、エタノール、エチレングリコールモノアルキルエーテル、プロピレングリコールモノアルキルエーテル、ポリエチレングリコールモノアルキルエーテル、ポリプロピレングリコールモノアルキルエーテル等のアルコール類、エチレングリコール、プロピレングリコール、ポリエチレングリコール、ポリプロピレングリコール、グリセリン等の多価アルコール類、アセトニトリル、グルタロジニトリル、メトキシアセトニトリル、プロピオニトリル、ベンゾニトリル等のニトリル化合物、ジメチルスルホキシド、スルフォラン等の非プロトン極性物質、水等が挙げられる。これらの溶媒は混合して用いることもできる。
【００６０】
また、「ジャーナル・オブ・ジ・アメリカン・セラミック・ソサイエティ（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ａｍｅｒｉｃａｎ Ｃｅｒａｍｉｃ Ｓｏｃｉｅｔｙ）」，１９９７年，第８０巻，第１２号，ｐ．３１５７−３１７１に記載されているようなｔｅｒｔ−ブチルピリジンや、２−ピコリン、２，６−ルチジン等の塩基性化合物を前述の溶融塩電解質組成物や電解液に添加することが好ましい。塩基性化合物を電解液に添加する場合の好ましい濃度範囲は０．０５〜２Ｍである。溶融塩電解質組成物に添加する場合、塩基性化合物はイオン性基を有することが好ましい。溶融塩電解質組成物全体に対する塩基性化合物の質量比は好ましくは１〜４０質量％であり、より好ましくは５〜３０質量％である。
【００６１】
（３） ゲル電解質組成物
本発明では、ポリマー添加、オイルゲル化剤添加、多官能モノマー類を含む重合、ポリマーの架橋反応等の手法により、前述の溶融塩電解質組成物や電解液をゲル化（固体化）させて使用することもできる。ポリマー添加によりゲル化する場合は、「ポリマー・エレクトロライト・レビューズ（Ｐｏｌｙｍｅｒ Ｅｌｅｃｔｒｏｌｙｔｅ Ｒｅｖｉｅｗｓ）−１及び２」（Ｊ． Ｒ． ＭａｃＣａｌｌｕｍとＣ． Ａ． Ｖｉｎｃｅｎｔの共編、ＥＬＳＥＶＩＥＲ ＡＰＰＬＩＥＤ ＳＣＩＥＮＣＥ）に記載された化合物を使用することができるが、特にポリアクリロニトリル及びポリフッ化ビニリデンが好ましく使用できる。オイルゲル化剤添加によりゲル化する場合は「工業科学雑誌（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ ｏｆＪａｐａｎ， Ｉｎｄｕｓｔｒｉａｌ Ｃｈｅｍｉｓｔｒｙ Ｓｅｃｔｉｏｎｓ）」， １９４３年， 第４６巻， ｐ．７７９、「ジャーナル・オブ・ジ・アメリカン・ケミカル・ソサイエティ（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ）」， １９８９年， 第１１１巻， ｐ．５５４２、「ジャーナル・オブ・ザ・ケミカル・ソサイエティ， ケミカル・コミュニケーションズ（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ， Ｃｈｅｍｉｃａｌ Ｃｏｍｍｕｎｉｃａｔｉｏｎｓ）」， １９９３年， ｐ．３９０、「Ａｎｇｅｗａｎｄｔｅ Ｃｈｅｍｉｅ Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｅｄｉｔｉｏｎ ｉｎ Ｅｎｇｌｉｓｈ」， １９９６年， 第３５巻， ｐ．１９４９、「ケミストリー・レターズ（Ｃｈｅｍｉｓｔｒｙ Ｌｅｔｔｅｒｓ）」， １９９６年， ｐ．８８５、及び「ジャーナル・オブ・ザ・ケミカル・ソサイエティ， ケミカル・コミュニケーションズ（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ， Ｃｈｅｍｉｃａｌ Ｃｏｍｍｕｎｉｃａｔｉｏｎｓ）」， １９９７年， ｐ．５４５に記載されている化合物を使用することができるが、アミド構造を有する化合物を使用するのが好ましい。電解液をゲル化した例は特開平１１−１８５８６３号公報に、溶融塩電解質をゲル化した例は特開２０００−５８１４０号公報にも記載されており、これらも本発明に適用できる。
【００６２】
また、ポリマーの架橋反応によりゲル化させる場合、架橋可能な反応性基を含有するポリマー及び架橋剤を併用することが望ましい。この場合、好ましい架橋可能な反応性基は、アミノ基、含窒素複素環（ピリジン環、イミダゾール環、チアゾール環、オキサゾール環、トリアゾール環、モルホリン環、ピペリジン環、ピペラジン環等）であり、好ましい架橋剤は、窒素原子に対して求電子反応可能な２官能以上の試薬（ハロゲン化アルキル類、ハロゲン化アラルキル類、スルホン酸エステル類、酸無水物、酸クロライド類、イソシアネート化合物、α，β−不飽和スルホニル化合物、α，β−不飽和カルボニル化合物、α，β−不飽和ニトリル化合物等）である。特開２０００−１７０７６号公報及び同２０００−８６７２４号公報に記載されている架橋技術も適用できる。
【００６３】
（４） 正孔輸送材料
本発明では、溶融塩等のイオン伝導性電解質のかわりに、有機固体正孔輸送材料、無機固体正孔輸送材料、或いはこの両者を組み合わせた材料を使用することができる。
【００６４】
（ａ） 有機正孔輸送材料
本発明において好ましく使用できる有機正孔輸送材料の例としては、ジェイ・ハーゲン（Ｊ． Ｈａｇｅｎ）等著， 「シンセティック・メタル（Ｓｙｎｔｈｅｔｉｃ Ｍｅｔａｌ）」，１９９７年， 第８９巻， ｐ．２１５−２２０、「ネイチャー（Ｎａｔｕｒｅ）」， １９９８年， 第３９５巻， 第８号Ｏｃｔ．， ｐ５８３−５８５、国際公開第９７／１０６１７号パンフレット、特開昭５９−１９４３９３号公報、特開平５−２３４６８１号公報、米国特許第４，９２３，７７４号明細書、特開平４−３０８６８８号公報、米国特許第４，７６４，６２５号明細書、特開平３−２６９０８４号公報、同４−１２９２７１号公報、同４−１７５３９５号公報、同４−２６４１８９号公報、同４−２９０８５１号公報、同４−３６４１５３号公報、同５−２５４７３号公報、同５−２３９４５５号公報、同５−３２０６３４号公報、同６−１９７２号公報、同７−１３８５６２号公報、同７−２５２４７４号公報、同１１−１４４７７３号公報等に記載の芳香族アミン類、特開平１１−１４９８２１号公報、同１１−１４８０６７号公報、同１１−１７６４８９号公報等に記載のトリフェニレン誘導体類等が挙げられる。また、「アドバンスド・マテリアルズ（Ａｄｖａｎｃｅｄ Ｍａｔｅｒｉａｌｓ）」， １９９７年， 第９巻， 第７号， ｐ．５５７、「Ａｎｇｅｗａｎｄｔｅ Ｃｈｅｍｉｅ Ｉｎｔｅｒｎａｔｉｏｎａｌ Ｅｄｉｔｉｏｎ ｉｎ Ｅｎｇｌｉｓｈ」， １９９５年， 第３４巻， 第３号， ｐ．３０３−３０７、「ジャーナル・オブ・ジ・アメリカン・ケミカル・ソサイエティ（Ｊｏｕｒｎａｌ ｏｆ ｔｈｅ Ａｍｅｒｉｃａｎ Ｃｈｅｍｉｃａｌ Ｓｏｃｉｅｔｙ）」， １９９８年， 第１２０巻， 第４号，ｐ．６６４−６７２等に記載のオリゴチオフェン化合物、Ｋ． Ｍｕｒａｋｏｓｈｉ， ｅｔ ａｌ．， 「ケミストリー・レターズ（Ｃｈｅｍｉｓｔｒｙ Ｌｅｔｔｅｒｓ）」， １９９７年， ｐ．４７１に記載のポリピロール、ＮＡＬＷＡ著「ハンドブック・オブ・オーガニック・コンダクティブ・モレキュールズ・アンド・ポリマーズ（Ｈａｎｄｂｏｏｋ ｏｆ Ｏｒｇａｎｉｃ Ｃｏｎｄｕｃｔｉｖｅ Ｍｏｌｅｃｕｌｅｓ ａｎｄ Ｐｏｌｙｍｅｒｓ）」， 第１，２，３，４巻， ＷＩＬＥＹ出版に記載のポリアセチレン及びその誘導体、ポリ（ｐ−フェニレン）及びその誘導体、ポリ（ｐ−フェニレンビニレン）及びその誘導体、ポリチエニレンビニレン及びその誘導体、ポリチオフェン及びその誘導体、ポリアニリン及びその誘導体、ポリトルイジン及びその誘導体等の導電性高分子も好ましく使用することができる。
【００６５】
「ネイチャー（Ｎａｔｕｒｅ）」， １９９８年， 第３９５巻， 第８号Ｏｃｔ．， ｐ．５８３−５８５に記載されているように、ドーパントレベルをコントロールするためにトリス（４−ブロモフェニル）アミニウムヘキサクロロアンチモネートのようなカチオンラジカルを含有する化合物を正孔輸送材料に添加してもよい。また、酸化物半導体表面のポテンシャル制御（空間電荷層の補償）を行うためにＬｉ［（ＣＦ_３ＳＯ_２）_２Ｎ］のような塩を添加してもよい。
【００６６】
（ｂ）無機正孔輸送材料
無機正孔輸送材料としてはｐ型無機化合物半導体を用いることができ、そのバンドギャップは好ましくは２ｅＶ以上、より好ましくは２．５ｅＶ以上である。また、ｐ型無機化合物半導体のイオン化ポテンシャルは、色素の正孔を還元するためには色素吸着電極のイオン化ポテンシャルより小さいことが必要である。使用する色素によってｐ型無機化合物半導体のイオン化ポテンシャルの好ましい範囲は異なるが、一般に好ましくは４．５〜５．５ ｅＶ、より好ましくは４．７〜５．３ ｅＶである。好ましいｐ型無機化合物半導体は１価の銅を含む化合物半導体であり、その例としてはＣｕＩ、ＣｕＳＣＮ、ＣｕＩｎＳｅ_２、Ｃｕ（Ｉｎ，Ｇａ）Ｓｅ_２、ＣｕＧａＳｅ_２、Ｃｕ_２Ｏ、ＣｕＳ、ＣｕＧａＳ_２、ＣｕＩｎＳ_２、ＣｕＡｌＳｅ_２等が挙げられる。中でも、ＣｕＩ及びＣｕＳＣＮが好ましく、ＣｕＩが最も好ましい。他のｐ型無機化合物半導体の例としては、ＧａＰ、ＮｉＯ、ＣｏＯ、ＦｅＯ、Ｂｉ_２Ｏ_３、ＭｏＯ_２、Ｃｒ_２Ｏ_３等が挙げられる。
【００６７】
（５） 電荷輸送層の形成
電荷輸送層は２通りの方法のいずれかにより形成できる。１つは感光層の上に先に対極を貼り合わせておき、その間隙に液状の電荷輸送層を挟み込む方法である。もう１つは感光層上に直接電荷輸送層を付与する方法で、対極はその後付与することになる。
【００６８】
前者の方法の場合、電荷輸送層を挟み込む際には、浸漬等による毛管現象を利用する常圧プロセス又は常圧より低い圧力にして間隙の気相を液相に置換する真空プロセスを利用できる。
【００６９】
後者の方法において、湿式の電荷輸送層を用いる場合は、通常未乾燥のまま対極を付与しエッジ部の液漏洩防止措置を施す。またゲル電解質組成物を用いる場合には、これを湿式で塗布した後で重合等の方法により固体化してよい。固体化は対極を付与する前に行っても後に行ってもよい。電解液、湿式有機正孔輸送材料、ゲル電解質組成物等からなる電荷輸送層を形成する場合は、前述の半導体微粒子層の形成方法と同様の方法を利用できる。
【００７０】
固体電解質組成物や固体正孔輸送材料を用いる場合には、真空蒸着法やＣＶＤ法等のドライ成膜処理で電荷輸送層を形成し、その後対極を付与することもできる。有機正孔輸送材料は真空蒸着法、キャスト法、塗布法、スピンコート法、浸漬法、電解重合法、光電解重合法等により電極内部に導入することができる。無機固体化合物はキャスト法、塗布法、スピンコート法、浸漬法、電解析出法、無電解メッキ法等により電極内部に導入することができる。
【００７１】
（Ｄ） 対極
対極は前述の導電性支持体と同様に、導電性材料からなる対極導電層の単層構造でもよいし、対極導電層と支持基板から構成されていてもよい。対極導電層に用いる導電剤の例としては、金属（白金、金、銀、銅、アルミニウム、マグネシウム、インジウム等）、炭素、導電性金属酸化物（インジウム−スズ複合酸化物、フッ素ドープ酸化スズ等）等が挙げられる。この中でも白金、金、銀、銅、アルミニウム及びマグネシウムが好ましい。対極に用いる基板は、好ましくはガラス基板又はプラスチック基板であり、これに上記の導電剤を塗布又は蒸着して用いることができる。対極導電層の厚さは特に制限されないが、好ましくは３ｎｍ〜１０μｍである。対極導電層の表面抵抗は低い程よく、好ましくは５０Ω／□以下、より好ましくは２０Ω／□以下である。
【００７２】
導電性支持体と対極のいずれか一方又は両方から光を照射してよいので、感光層に光が到達するためには、導電性支持体と対極の少なくとも一方が実質的に透明であればよい。発電効率の向上の観点からは導電性支持体を透明にして光を導電性支持体側から入射させるのが好ましい。この場合、対極は光を反射する性質を有するのが好ましい。このような性質を得るためには、対極として金属又は導電性酸化物を蒸着したガラス又はプラスチック、或いは金属薄膜を使用してよい。
【００７３】
対極は電荷輸送層上に直接導電剤を塗布、メッキ又は蒸着（ＰＶＤ、ＣＶＤ）するか、導電層を有する基板の導電層側を貼り付けて設置すればよい。導電性支持体の場合と同様に、特に対極が透明の場合には、対極の抵抗を下げる目的で金属リードを用いるのが好ましい。金属リードの好ましい態様は導電性支持体の場合と同じである。
【００７４】
（Ｅ） その他の層
対極と導電性支持体の短絡を防止するため、導電性支持体と感光層の間には緻密な半導体の薄膜層を下塗り層として予め塗設しておくことが好ましい。この下塗り層により短絡を防止する方法は、電荷輸送層に電子輸送材料や正孔輸送材料を用いる場合は特に有効である。下塗り層は好ましくはＴｉＯ_２、ＳｎＯ_２、Ｆｅ_２Ｏ_３、ＷＯ_３、ＺｎＯ又はＮｂ_２Ｏ_５からなり、さらに好ましくはＴｉＯ_２からなる。下塗り層は、例えばＥｌｅｃｔｒｏｃｈｉｍ． Ａｃｔａ， ４０， ６４３−６５２ （１９９５）に記載のスプレーパイロリシス法や、スパッタ法等により塗設することができる。下塗り層の膜厚は好ましくは５〜１０００ ｎｍであり、より好ましくは１０〜５００ ｎｍである。
【００７５】
また、導電性支持体と対極の一方又は両方の外側表面、導電層と基板の間又は基板の中間に、保護層、反射防止層等の機能性層を設けてもよい。これらの機能性層の形成方法は、その材質に応じて塗布法、蒸着法、貼り付け法等から適宜選択できる。
【００７６】
（Ｆ） 光電変換素子の内部構造の具体例
上述のように、光電変換素子の内部構造は目的に合わせ様々な形態が可能である。大きく２つに分ければ、両面から光の入射が可能な構造と、片面からのみ可能な構造が可能である。本発明の光電変換素子の好ましい内部構造の例を、前述の図１及び図２〜図９に示す。
【００７７】
図２に示す構造は、透明導電層１０ａと透明対極導電層４０ａとの間に、感光層２０と電荷輸送層３０とを介在させたものであり、両面から光が入射する構造となっている。図３に示す構造は、透明基板５０ａ上に一部金属リード１１を設け、その上に透明導電層１０ａを設け、下塗り層６０、感光層２０、電荷輸送層３０及び対極導電層４０をこの順で設け、更に支持基板５０を配置したものであり、導電層側から光が入射する構造となっている。図４に示す構造は、支持基板５０上に導電層１０を有し、下塗り層６０を介して感光層２０を設け、更に電荷輸送層３０と透明対極導電層４０ａとを設け、一部に金属リード１１を設けた透明基板５０ａを金属リード１１側を内側にして配置したものであり、対極側から光が入射する構造である。図５に示す構造は、透明基板５０ａ上に一部金属リード１１を設け、更に透明導電層１０ａ（又は４０ａ）を設けたもの１組の間に下塗り層６０、感光層２０及び電荷輸送層３０を介在させたものであり、両面から光が入射する構造である。図６に示す構造は、透明基板５０ａ上に透明導電層１０ａ、下塗り層６０、感光層２０、電荷輸送層３０及び対極導電層４０を設け、この上に支持基板５０を配置したものであり、導電層側から光が入射する構造である。図７に示す構造は、支持基板５０上に導電層１０を有し、下塗り層６０を介して感光層２０を設け、更に電荷輸送層３０及び透明対極導電層４０ａを設け、この上に透明基板５０ａを配置したものであり、対極側から光が入射する構造である。図８に示す構造は、透明基板５０ａ上に透明導電層１０ａを有し、下塗り層６０を介して感光層２０を設け、更に電荷輸送層３０及び透明対極導電層４０ａを設け、この上に透明基板５０ａを配置したものであり、両面から光が入射する構造となっている。図９に示す構造は、支持基板５０上に導電層１０を設け、下塗り層６０を介して感光層２０を設け、更に固体の電荷輸送層３０を設け、この上に一部対極導電層４０又は金属リード１１を有するものであり、対極側から光が入射する構造となっている。
【００７８】
［３］ 光電池
本発明の光電池は、上記本発明の光電変換素子に外部負荷で仕事をさせるようにしたものである。光電池のうち、電荷輸送材料が主としてイオン輸送材料からなる場合を特に光電気化学電池と呼び、また、太陽光による発電を主目的とする場合を太陽電池と呼ぶ。
【００７９】
光電池の側面は、構成物の劣化や内容物の揮散を防止するためにポリマーや接着剤等で密封するのが好ましい。導電性支持体及び対極にリードを介して接続する外部回路自体は公知のものでよい。
【００８０】
本発明の光電変換素子を太陽電池に適用する場合も、そのセル内部の構造は基本的に上述した光電変換素子の構造と同じである。また、本発明の光電変換素子を用いた色素増感型太陽電池は、従来の太陽電池モジュールと基本的には同様のモジュール構造をとりうる。太陽電池モジュールは、一般的には金属、セラミック等の支持基板の上にセルが構成され、その上を充填樹脂や保護ガラス等で覆い、支持基板の反対側から光を取り込む構造をとるが、支持基板に強化ガラス等の透明材料を用い、その上にセルを構成してその透明の支持基板側から光を取り込む構造とすることも可能である。具体的には、スーパーストレートタイプ、サブストレートタイプ、ポッティングタイプと呼ばれるモジュール構造、アモルファスシリコン太陽電池等で用いられる基板一体型モジュール構造等が知られており、本発明の光電変換素子を用いた色素増感型太陽電池も使用目的や使用場所及び環境により、適宜モジュール構造を選択できる。具体的には、特願平１１−８４５７号、特開２０００−２６８８９２号等に記載の構造や態様とすることが好ましい。
【００８１】
【実施例】
本発明を以下の実施例によりさらに詳細に説明するが、本発明はそれらに限定されるものではない。
【００８２】
実施例１
酸化チタン粒子の調製
（１） 色素担持用酸化チタン粒子の調製
０．０２モル／リットルの希硝酸４４０ ｍｌに酢酸３０ ｍｌ及びオルトチタン酸テトライソプロピル（和光純薬工業（株）製）７９ ｍｌを一気に添加して１０分間撹拌し、白色の沈殿を得た。この沈殿を濾別した後、再び０．０２モル／リットルの希硝酸４４０ ｍｌ及び酢酸３０ ｍｌを添加した。得られた懸濁液を７０℃で５時間加熱撹拌し、半透明のゾル状液を得た。このゾルを内のりがテフロン（登録商標）製のオートクレーブに移し、２２５℃で１０時間加熱した。放冷後、得られた懸濁液を遠心分離し、酸化チタン粒子の分散物（ＴＤＤ−１）を得た。この分散物は固形分含有率１５質量％であった。また、Ｘ線回折法の結果から、結晶子サイズが１２．２ｎｍのアナターゼであることがわかった。なお、結晶子サイズはＣｕ−Ｋα線における２θ＝２５．２°（ｈｋｌ＝１０１）のピークにおける半値幅をもとに算出した。
【００８３】
（２） 光散乱用酸化チタン粒子の調製
テトラエチルアンモニウムヒドロキシドの０．３５モル／リットル水溶液３２０ ｍｌに５５℃でオルトチタン酸テトライソプロピル（和光純薬工業（株））５０ ｍｌを一気に添加した。次に温度を８０℃に上げ、３０分間撹拌し透明なゾルを得た。このゾルを内のりがテフロン（登録商標）製のオートクレーブに移し、２００℃で１０時間加熱した。放冷後、得られた酸化チタン粒子は沈降していたので、上澄み液をデカンテーションで除いた。これに１モル／リットル硝酸水溶液を加え酸性とした後、遠心分離と加水を繰り返して洗浄し、酸化チタン粒子のウェットケーキを得た。このウェットケーキを純水で希釈し固形分含有率を１５質量％に調整し、光散乱用酸化チタン粒子分散物（ＴＤＳ−１）を得た。また、Ｘ線回折法の結果から、結晶子サイズが２７．９ ｎｍのアナターゼであることがわかった。一方、高分解能ＳＥＭ（走査電子顕微鏡）写真から、１次粒径１００〜４００ ｎｍの粒度分布の広い粒子であることを確認した。次に、オートクレーブ中での加熱条件を表１に示す通りに変更した以外はＴＤＳ−１と同様の方法で、本発明の方法による酸化チタン粒子（表１のＴＤＳ−２〜７）、及び比較用酸化チタン粒子（表１のＴＤＳ−８〜９）を作製した。
【００８４】
【表１】

【００８５】
実施例２
光電変換素子の作製と評価
（１） 酸化チタン塗布液の調製
色素担持用酸化チタン分散物（ＴＤＤ−１）８．５ ｇ、表２に示す光散乱用酸化チタン分散物（ＴＤＳ−１〜９）１．５ ｇ、ポリエチレングリコール（分子量２００００、和光純薬工業（株）製）０．６ ｇ、及び水２．５ ｇを加えてよく撹拌し、ポリエチレングリコールを完全に溶解した。これにエタノール１ｍｌ及び濃硝酸０．４ ｍｌを加えて粘度を調節し、酸化チタン塗布液（Ｃ−１〜Ｃ−９）を作製した。
【００８６】
（２） 色素増感酸化チタン電極の作製
フッ素をドープした酸化スズをコーティングした透明導電性ガラス（日本板硝子（株）製、表面抵抗は約１０Ω／ｃｍ^２）の導電面側に塗布液（Ｃ−１〜Ｃ−９）を、ドクターブレードを用いてそれぞれ塗布した。２５℃で３０分間乾燥した後、電気炉（ヤマト科学（株）製マッフル炉ＦＰ−３２型）により４５０℃で３０分間焼成した。塗布、焼成前後の質量変化より単位面積あたりの塗布量を計算で求めた。
【００８７】
焼成後、下記構造の色素（Ａ）０．３ミリモル／リットルを含む吸着液に４時間浸漬した。吸着温度は４０℃とし、吸着液の溶媒はエタノール：ｔ−ブタノール：アセトニトリル＝１：１：２（体積比）の混合溶媒を用いた。色素の染着した酸化チタン電極をエタノール、アセトニトリルで順次洗浄し、色素増感酸化チタン電極（Ｅ−１〜Ｅ−９）を作製した。
【００８８】
（色素Ａ）
【化３】

【００８９】
（３） 赤色光吸光度の測定
酸化チタン粒子の光散乱性を評価するため、作製した色素増感酸化チタン電極（Ｅ−１〜Ｅ−９）の赤色光吸光度（透過濃度）をＸ−ＲＩＴＥ社製フォトグラフィックデンシトメーター３０１型を用いて測定した。結果を表２に示す。
【００９０】
【表２】

【００９１】
表２から本発明の方法による酸化チタン粒子を用いた色素増感酸化チタン電極Ｅ−１〜７は、比較用の酸化チタン粒子を用いた色素増感酸化チタン電極Ｅ−８、９に比べて赤色光吸光度が高いことがわかる。本発明の方法による酸化チタン粒子同士では、オートクレーブ中で１０時間加熱成長させた粒子を用いたＥ−１〜３よりも、２０時間以上加熱成長させた粒子を用いたＥ−４〜７の方が赤色光吸光度が高い。オートクレーブ中での熟成時間が同じ場合、加熱温度が高いものほど赤色光吸光度が高い。
【００９２】
（４） 光電変換素子の作製
上述のようにして作製した色素増感酸化チタン電極基板（２ｃｍ×２ｃｍ）をこれと同じ大きさの白金蒸着ガラスと重ね合わせた（図１０参照）。次に、両ガラスの隙間に毛細管現象を利用して電解液（ヨウ化１，３−ジメチルイミダゾリウム０．６５モル／リットル，ヨウ素０．０５モル／リットル、及びｔ−ブチルピリジン０．１モル／リットルのアセトニトリル溶液）をしみこませてＴｉＯ_２電極中に導入することにより、表３に示す光電変換素子ＳＣ−１〜ＳＣ−９を得た。これらの光電変換素子は図１０に示すように、導電性ガラス１（ガラス２上に導電層３が設層されたもの）、色素吸着酸化チタン層４、電荷輸送層５、白金層６及びガラス７が順に積層された構造を有する。
【００９３】
【表３】

【００９４】
（５） 光電変換効率の測定
５００ Ｗのキセノンランプ（ウシオ（株）製）の光を分光フィルター（Ｏｒｉｅｌ社製ＡＭ１．５）を通すことにより模擬太陽光を発生させた。光の強度は垂直面において１００ ｍＷ／ｃｍ^２であった。光電気化学電池の導電性ガラスの端部に銀ペーストを塗布して負極とし、この負極と白金蒸着ガラス（正極）を電流電圧測定装置（ケースレーＳＭＵ２３８型）に接続した。模擬太陽光を垂直に照射しながら、電流電圧特性を測定し、変換効率を求めた。表４に作製した光電変換素子の光電変換特性を示す。
【００９５】
【表４】

【００９６】
本発明の光電変換素子ＳＣ−１〜７は比較用の光電変換素子ＳＣ−８、９に比べて変換効率が高いことがわかる。この原因は主として短絡電流の増加による。また、本発明の方法による酸化チタン粒子同士の比較では、オートクレーブ中で１０時間加熱成長させた粒子を用いたＳＣ−１〜３よりも、２０時間以上加熱成長させた粒子を用いたＳＣ−４〜７の方が短絡電流および変換効率が高い。オートクレーブ中での熟成時間が同じ場合、加熱温度が高いものほど変換効率が高い光電変換素子が得られた。
【００９７】
【発明の効果】
上記の通り、本発明の酸化チタン粒子の製造方法はテトラアルキルアンモニウムヒドロキシドの存在下で行う酸化チタンゾル生成工程と、２００℃以上で１０時間以上加熱する粒子成長工程を含むので、光散乱性の高い酸化チタン粒子が得られる。そのため、変換効率に優れた色素増感光電変換素子を得ることが可能である。
【図面の簡単な説明】
【図１】本発明の好ましい一実施例による光電変換素子の構造を示す部分断面図である。
【図２】本発明の好ましい別の実施例による光電変換素子の構造を示す部分断面図である。
【図３】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図４】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図５】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図６】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図７】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図８】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図９】本発明の好ましいさらに別の実施例による光電変換素子の構造を示す部分断面図である。
【図１０】実施例２で作製した光電変換素子の構造を示す部分断面図である。
【符号の説明】
１０・・・導電層
１０ａ・・・透明導電層
１１・・・金属リード
２０・・・感光層
２１・・・半導体微粒子
２２・・・色素
２３・・・電荷輸送材料
３０・・・電荷輸送層
４０・・・対極導電層
４０ａ・・・透明対極導電層
５０・・・基板
５０ａ・・・透明基板
６０・・・下塗り層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing titanium oxide particles and a photoelectric conversion element using the same, and more particularly to a method for producing titanium oxide particles suitable for a photoelectric conversion element including dye-sensitized titanium oxide particles, and a photoelectric conversion device using the same. The present invention relates to a conversion element.
[0002]
[Prior art]
Photoelectric conversion elements are used in various optical sensors, copying machines, and photovoltaic power generation devices. Various systems such as those using metals, semiconductors, organic pigments and dyes, and combinations of these have been put to practical use as photoelectric conversion elements.
[0003]
For example, a photoelectric conversion element using semiconductor fine particles sensitized with a dye (hereinafter referred to as “dye-sensitized photoelectric conversion element”), and a material and a manufacturing technique for producing the photoelectric conversion element are disclosed (for example, patents). References 1-9.) The advantage of the dye-sensitized photoelectric conversion element is that titanium oxide particles can be used, so that an inexpensive photoelectric conversion element can be provided.
[0004]
In general, the sol-gel method is preferably used for producing the titanium oxide particles. The sol-gel method is a fine particle synthesis method widely known in the art, and includes a titanium oxide sol generation step, a particle growth step, and a post-treatment step. Each of these steps has been reported in detail (for example, see Non-Patent Document 1), and an example in which titanium oxide particles produced by a sol-gel method are applied to a dye-sensitized photoelectric conversion element has also been reported. (For example, refer nonpatent literature 2.).
[0005]
Usually, two kinds of titanium oxides having different particle size distributions are used in the dye-sensitized photoelectric conversion element. One is titanium oxide particles having a particle diameter of 10 to 20 nm for the purpose of supporting a dye. The other is a titanium oxide particle having a particle size of 100 to 500 nm with high light scattering. Titanium oxide particles having high light scattering properties have an effect of increasing the absorbance of the photoelectric conversion element with respect to red light and increasing the conversion efficiency of the photoelectric conversion element. In this field, increasing the conversion efficiency of the photoelectric conversion element is the most important issue, and in order to achieve this issue, titanium oxide particles having high light scattering properties are always required. Non-Patent Document 1 describes that tetraammonium hydroxide is added in the hydrolysis step of the sol-gel method in order to obtain titanium oxide particles having high photo-confusing properties, but the performance is insufficient. Met.
[0006]
[Patent Document 1]
US Pat. No. 4,927,721 [Patent Document 2]
US Pat. No. 4,684,537 [Patent Document 3]
US Pat. No. 5,084,365 [Patent Document 4]
US Pat. No. 5,350,644 [Patent Document 5]
US Pat. No. 5,463,057 [Patent Document 6]
US Pat. No. 5,525,440 [Patent Document 7]
International Publication No. 98/50393 Pamphlet [Patent Document 8]
JP-A-7-249790 [Patent Document 9]
JP 10-504521A [Non-Patent Document 1]
S. D. Burnside, et al., “Chemistry of Materials”, 1998, Vol. 10, No. 9, p. 2419-2425
[Non-Patent Document 2]
“Journal of the American Ceramic Society”, 1997, Vol. 80, p. 3157-3171
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for producing titanium oxide particles having excellent light scattering properties, and a dye-sensitized photoelectric conversion element having high red light absorbance and improved conversion efficiency using the particles.
[0008]
[Means for Solving the Problems]
As a result of diligent research in view of the above object, the present inventor has found that titanium oxide particles having a particle size of 100 to 500 nm with good light scattering, red light absorbance is high and conversion efficiency is high by means of the following (1) to (7). The inventors discovered that improved dye-sensitized photoelectric conversion elements and solar cells can be obtained and arrived at the present invention.
(1) A method for producing titanium oxide particles by hydrolysis of orthotitanate, wherein the titanium oxide sol produced by hydrolysis is in a pressure vessel in the presence of tetraalkylammonium hydroxide at 200 ° C. or more for 10 hours or more. The manufacturing method of the titanium oxide particle characterized by including the process of heating.
(2) The method for producing titanium oxide particles according to (1), wherein the concentration of tetraalkylammonium hydroxide is 0.1 mol / liter or more and 1 mol / liter or less.
(3) The method for producing titanium oxide particles according to (1) or (2), wherein the heating temperature is 240 ° C. or higher.
(4) The method for producing titanium oxide particles according to any one of (1) to (3), wherein tetraethylammonium hydroxide is used as the tetraalkylammonium hydroxide.
(5) A dye-sensitized photoelectric conversion element comprising titanium oxide particles produced by the method according to (1) to (4).
(6) The dye according to (5), wherein the proportion of titanium oxide particles produced by the method according to (1) to (4) in the total titanium oxide particles is 5 to 40% by mass. Intensified photoelectric conversion element.
(7) A solar cell using the dye-sensitized photoelectric conversion element according to (5) and (6).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The method for producing titanium oxide particles of the present invention basically follows the sol-gel method. The production method of the present invention includes a titanium oxide sol production step (peptization step), a particle growth step, and a post-treatment step. Hereinafter, each process of the manufacturing method of a titanium oxide particle is demonstrated.
[0010]
[1] Production method of titanium oxide particles (A) Titanium oxide sol production step Orthotitanate ester (for example, methyl orthotitanate, ethyl orthotitanate, isopropyl orthotitanate, butyl orthotitanate, etc.) is converted to tetraalkylammonium hydroxide ( For example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, etc.) are added to an aqueous solution and hydrolyzed. The method of addition may be mixed at once, or a dropping method may be used. After the addition, the mixture is heated and stirred for 10 minutes to 3 hours to obtain a transparent titanium oxide sol. Although there is no restriction | limiting in particular in heating temperature, Usually, it is 50-100 degreeC.
[0011]
Tetraalkylammonium hydroxide has a catalytic action for titanium oxide synthesis. As a result of the study by the present inventors, it has been found that a trialkylamine is produced by partial decomposition in a particle growth step described later. That is, tetramethylammonium hydroxide produces trimethylamine with a strong malodor, and tetrapropylammonium hydroxide and tetrabutylammonium hydroxide produce tripropylamine and tributylamine that are insoluble in water, both of which are problematic in terms of manufacturing suitability. . For this reason, tetraethylammonium hydroxide is particularly preferred as the tetraalkylammonium hydroxide used in the present invention.
[0012]
The concentration of tetraalkylammonium hydroxide is related to the heating time until a transparent sol is obtained. The higher the concentration, the shorter the heating time. The concentration of tetraalkylammonium hydroxide is preferably from 0.1 to 1 mol / liter, more preferably from 0.2 to 0.5 mol / liter.
[0013]
The titanium oxide sol obtained by the above method contains alcohol generated by hydrolysis of orthotitanate. This sol can be used as it is in the next particle growth step, but if necessary, the alcohol may be removed by dialysis or distillation.
[0014]
(B) Particle growth step The titanium oxide sol obtained in the above step is transferred to a pressure vessel and heated to grow titanium oxide particles having a particle size of 100 to 500 nm. Examples of the pressure vessel include a stainless steel autoclave, a titanium autoclave, and a stainless steel autoclave whose inner shell is titanium or Teflon (registered trademark). The autoclave is preferably provided with a stirring device.
[0015]
When the titanium oxide particles obtained by the method of the present invention are applied to a dye-sensitized photoelectric conversion element, it is particularly effective to use them as light scattering particles. When used as light scattering particles, the average particle size is preferably from 100 to 500 nm, more preferably from 200 to 400 nm. The particle size depends on the heating temperature in this step, and the particle size increases as the heating temperature increases. As heating conditions, a pressure vessel is used as described above, and heating is performed at 200 ° C. or more for 10 hours or more in the presence of tetraalkylammonium hydroxide. In order to obtain titanium oxide particles for a dye-sensitized photoelectric conversion element, heating at 200 to 300 ° C. for 10 hours or more is preferable, heating at 240 to 300 ° C. for 10 hours or more is more preferable, and 240 to 300 ° C. It is particularly preferred to heat for at least 20 hours. The upper limit of the heating time is not particularly limited, but the effect of the present invention is exhibited by heating for 100 hours or less. Moreover, the density | concentration of the tetraalkylammonium hydroxide in this process may be the same as the density | concentration in a titanium oxide sol production | generation process, 0.1-1 mol / liter is preferable and 0.2-0.5 mol / liter is more preferable.
[0016]
(C) The titanium oxide dispersion obtained by the post-treatment particle growth step is concentrated or solvent-substituted by post-treatment. A dry powder, an aqueous dispersion, an aqueous dispersion paste, an organic solvent dispersion, an organic solvent dispersion paste or the like is finally prepared according to the purpose of use. As a concentration method, a method of standing or centrifuging after centrifuging, a method of distilling off water under reduced pressure, or the like can be used. As a solvent replacement method, a method of repeating centrifugation, decantation, and solvent addition is generally used. As a thickener for obtaining a paste, various polymers (for example, polystyrene sulfonate, polyacrylic acid and salts thereof, polyethylene oxide, polypropylene oxide, polyacrylamide, etc.), polysaccharides, gelatin, various low molecular thickeners (Citronellol, nerol, terpineol, etc.) are preferred. The content of titanium oxide in the aqueous dispersion, aqueous dispersion paste, organic solvent dispersion, organic solvent dispersion paste and the like is 1 to 80% by mass, preferably 10 to 30% by mass.
[0017]
[2] Photoelectric Conversion Element The photoelectric conversion element of the present invention is preferably formed by laminating a conductive layer 10, a photosensitive layer 20, a charge transport layer 30, and a counter electrode conductive layer 40 in this order as shown in FIG. Is composed of a semiconductor fine particle 21 sensitized with a dye 22 and a charge transport material 23 that has penetrated into the gaps between the semiconductor fine particles 21. The charge transport material 23 in the photosensitive layer 20 is usually the same material used for the charge transport layer 30. An undercoat layer 60 may be provided between the conductive layer 10 and the photosensitive layer 20. Further, the substrate 50 may be provided as a base of the conductive layer 10 and / or the counter electrode conductive layer 40 in order to give strength to the photoelectric conversion element. In the present invention, the layer composed of the conductive layer 10 and the optionally provided substrate 50 is referred to as “conductive support”, and the layer composed of the counter electrode conductive layer 40 and the optionally provided substrate 50 is referred to as “counter electrode”. In addition, the conductive layer 10, the counter electrode conductive layer 40, and the substrate 50 in FIG. 1 may be the transparent conductive layer 10a, the transparent counter electrode conductive layer 40a, and the transparent substrate 50a, respectively. Among such photoelectric conversion elements, a photoelectric cell is connected to an external load to perform electrical work (power generation), and an optical sensor is formed for the purpose of sensing optical information. Among photovoltaic cells, those in which the charge transport material is mainly composed of an ion transport material are called photoelectrochemical cells, and those whose main purpose is power generation by sunlight are called solar cells.
[0018]
In the photoelectric conversion element shown in FIG. 1, light incident on the photosensitive layer 20 including the semiconductor fine particles 21 sensitized by the dye 22 excites the dye 22 and the high energy electrons in the excited dye 22 and the like are semiconductor fine particles. 21 is passed to the conduction band 21 and further diffused to reach the conductive layer 10. At this time, the dye 22 is an oxidant. In the photovoltaic cell, the electrons in the conductive layer 10 return to the oxidized form of the dye 22 through the counter electrode conductive layer 40 and the charge transport layer 30 while working in the external circuit, and the dye 22 is regenerated. The photosensitive layer 20 functions as a negative electrode, and the counter electrode conductive layer 40 functions as a positive electrode. At the boundary of each layer (for example, the boundary between the conductive layer 10 and the photosensitive layer 20, the boundary between the photosensitive layer 20 and the charge transport layer 30, the boundary between the charge transport layer 30 and the counter electrode conductive layer 40, etc.) They may be diffusively mixed with each other. Each layer and configuration will be described in detail below.
[0019]
(A) Conductive support The conductive support comprises (1) a single layer of a conductive layer or (2) two layers of a conductive layer and a substrate. In the case of (1), as the material of the conductive layer, the conductive layer can have sufficient strength and hermeticity and has conductivity (for example, platinum, gold, silver, copper, zinc, titanium, aluminum, A metal material such as an alloy containing these can be used. In the case of (2), a substrate having a conductive layer made of a conductive agent on the photosensitive layer side can be used as the conductive support. Examples of preferable conductive agents include metals (platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), carbon and conductive metal oxides (indium-tin composite oxide, tin oxide doped with fluorine, etc.) Is mentioned. The thickness of the conductive layer is preferably about 0.02 to 10 μm.
[0020]
The lower the surface resistance of the conductive support, the better. This surface resistance is preferably 100Ω / □ or less, more preferably 40Ω / □ or less. The lower limit of the surface resistance is not particularly limited, but is usually about 0.1Ω / □.
[0021]
When irradiating light from the conductive support side, the conductive support is preferably substantially transparent. Substantially transparent means that the light transmittance is 10% or more. The light transmittance of the conductive support is preferably 50% or more, particularly preferably 70% or more.
[0022]
As the transparent conductive support, one formed by applying a transparent conductive layer made of a conductive metal oxide on the surface of a transparent substrate made of glass, plastic, or the like by vapor deposition or the like can be preferably used. Examples of a preferable material for forming the transparent conductive layer include fluorine-doped tin dioxide. As the transparent substrate, a glass substrate made of soda lime float glass advantageous in terms of cost and strength, a transparent polymer film useful for obtaining a flexible photoelectric conversion element at low cost, and the like can be used. Examples of the material forming the transparent polymer film include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), Examples include polyarylate (PAr), polysulfone (PSF), polyester sulfone (PES), polyetherimide (PEI), cyclic polyolefin, and brominated phenoxy resin. In order to ensure sufficient transparency, the coating amount of the conductive metal oxide is preferably 0.01 to 100 g per 1 m ² of glass or plastic substrate.
[0023]
For the purpose of reducing the resistance of the transparent conductive support, a metal lead can be used as a current collector. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, or silver, and particularly preferably made of aluminum or silver. It is preferable to provide a metal lead on the transparent substrate by vapor deposition, sputtering, or the like, and provide a transparent conductive layer made of tin oxide doped with fluorine, ITO film or the like on the metal lead. It is also preferable that a metal lead is provided on the transparent conductive layer after the transparent conductive layer is provided on the transparent substrate. The decrease in the amount of incident light due to the installation of the metal lead is preferably within 10%, more preferably 1 to 5%.
[0024]
(B) Photosensitive layer In the photosensitive layer, the semiconductor fine particles act as a photoconductor and absorb light to separate charges and generate electrons and holes. In the dye-sensitized semiconductor fine particles, light absorption and generation of electrons and holes thereby occur mainly in the dye, and the semiconductor fine particles play a role of receiving and transmitting these electrons or holes. The semiconductor used in the present invention is preferably an n-type semiconductor in which conductor electrons become carriers under photoexcitation and give an anode current.
[0025]
(1) Semiconductor The photoelectric conversion element of the present invention uses the above-described titanium oxide fine particles as a semiconductor. The titanium oxide constituting the photoelectric conversion element is preferably a mixture of the following two types (1) and (2).
(1) Fine particle titanium oxide for dye support (2) Fine particle titanium oxide for light confusion (1) For the titanium oxide (1), titanium oxide fine particles produced by the method of the present invention or other titanium oxide fine particles may be used. However, anatase is preferred. The crystallite size calculated based on the half width of the diffraction peak at 2θ = 25.2 ° (hkl = 101) in Cu—Kα ray of the titanium oxide fine particles of (1) is preferably 8 to 16 nm, 10-13 nm is more preferable. In (2), fine titanium oxide particles produced by the method of the present invention are used.
[0026]
The mixing ratio (mass ratio) of the above (1) and (2) is 50 to 99% by mass for small particles (1) and 1 to 50% for large particles (2) with respect to the total titanium oxide particles. %, More preferably 60 to 95% by weight of small particles and 5 to 40% by weight of large particles, 70 to 95% by weight of small particles and 5 to 30% by weight of large particles. More preferably. The production method of the titanium oxide fine particles used for the photoelectric conversion element of the present invention is as described above.
[0027]
(2) Semiconductor fine particle layer When forming a semiconductor fine particle layer composed of the above-mentioned semiconductor fine particles on a conductive support, a method of applying a dispersion or colloidal solution containing semiconductor fine particles on the conductive support is used. Is common. Considering mass production of photoelectric conversion elements, physical properties of a dispersion or colloidal solution containing semiconductor fine particles, flexibility of a conductive support, etc., it is relatively desirable to use a wet film forming method. As a wet film forming method, a coating method and a printing method are typical.
[0028]
Examples of methods for preparing a dispersion of semiconductor fine particles include a method of using the dispersion or colloidal solution prepared by the sol-gel method as described above, a method of grinding with a mortar, and a method of dispersing while grinding using a mill. Etc.
[0029]
The dispersion medium used for the dispersion of semiconductor fine particles may be water or various organic solvents (methanol, ethanol, isopropyl alcohol, dichloromethane, acetone, acetonitrile, ethyl acetate, etc.). When dispersing, if necessary, a polymer such as polyethylene glycol, a surfactant, an acid, a chelating agent, or the like may be used as a dispersion aid. By changing the molecular weight of polyethylene glycol, the viscosity of the dispersion can be adjusted and a semiconductor fine particle layer that is difficult to peel off can be formed. Therefore, it is preferable to add polyethylene glycol.
[0030]
Examples of preferable coating methods include the roller method and dip method as application systems, the air knife method and blade method as metering systems, and Japanese Patent Publication No. 58-4589 as the application and metering can be made the same part. Examples thereof include the disclosed wire bar method, the slide hopper method, the extrusion method, the curtain method and the like described in US Pat. Nos. 2,681,294, 2,761,419, 2,761791, and the like. Moreover, a spin method and a spray method are also preferable as a general purpose machine. As the wet printing method, intaglio, rubber plate, screen printing and the like are preferred, including the three major printing methods of letterpress, offset and gravure. A film forming method may be selected from these according to the liquid viscosity and the wet thickness.
[0031]
The viscosity of the dispersion of semiconductor fine particles greatly depends on the type and dispersibility of the semiconductor fine particles, the type of solvent used, surfactants, binders and other additives. When the dispersion has a high viscosity (for example, 0.01 to 500 poise), it is preferable to use an extrusion method, a casting method, or a screen printing method. When the viscosity is low (for example, 0.1 poise or less), it is preferable to use a slide hopper method, a wire bar method, or a spin method in order to form a uniform film. When the coating amount is large to some extent, it is possible to apply the extrusion method even if the viscosity is low. Thus, a film forming method may be appropriately selected according to the viscosity of the dispersion, the coating amount, the support, the coating speed, and the like.
[0032]
The semiconductor fine particle layer is not limited to a single layer, and a multilayer coating of semiconductor fine particle dispersions having different particle diameters or a multilayer coating containing different types of semiconductor fine particles (or different binders, additives, etc.) You can also Multi-layer coating is also effective when the film thickness is insufficient with a single coating. The extrusion method and slide hopper method are suitable for multilayer coating. In the case of applying multiple layers, the multiple layers may be applied at the same time, or may be applied one after the other several times. A screen printing method can also be preferably used for successive overcoating.
[0033]
In general, as the semiconductor fine particle layer thickness (same as the photosensitive layer thickness) increases, the amount of supported dye increases per unit projected area and thus the light capture rate increases. Loss due to coupling also increases. Therefore, the preferred thickness of the semiconductor fine particle layer is 0.1 to 100 μm. When using the photoelectric conversion element of this invention for a solar cell, the thickness of a semiconductor fine particle layer becomes like this. Preferably it is 1-30 micrometers, More preferably, it is 2-25 micrometers. The coating amount of the semiconductor fine particles per 1 m ^{2 of the} conductive support is preferably 0.5 to 400 g, more preferably 5 to 100 g.
[0034]
After coating the semiconductor fine particles on the conductive support, it is preferable to heat-treat the semiconductor fine particles to bring them into electronic contact and improve the coating strength and the adhesion to the conductive support. The heating temperature in the heat treatment is preferably 40 to 700 ° C, more preferably 100 to 600 ° C. The heating time is about 10 minutes to 10 hours. When using a substrate having a low melting point or softening point such as a polymer film, high temperature treatment is not preferable because it causes deterioration of the substrate. Also from the viewpoint of cost, it is preferable to perform the heat treatment at the lowest possible temperature. When the heat treatment is performed in the presence of small semiconductor fine particles of 5 nm or less, mineral acid, or the like, the heating temperature can be lowered.
[0035]
A pressure treatment may be performed instead of the heat treatment. The pressure treatment method is described in a book by Lindstrom et al., “Journal of photochemistry and photobiology”, 2001 (Elsevier), vol. 145, p. 107-112. When the pressure treatment is performed, a binder such as a polymer is not used in the semiconductor fine particle coating solution.
[0036]
After the heat treatment or pressure treatment, for example, chemical plating treatment using a titanium tetrachloride aqueous solution or electrochemical plating treatment using a titanium trichloride aqueous solution as described in US Pat. No. 5,084,365 is performed. May be.
[0037]
The semiconductor fine particle layer preferably has a large surface area so that a large amount of dye can be adsorbed. The surface area of the semiconductor fine particle layer applied on the conductive support is preferably 10 times or more, more preferably 100 times or more the projected area. This upper limit is not particularly limited, but is usually about 1000 times.
[0038]
(3) Processing In the present invention, the semiconductor fine particles used for the photosensitive layer may be processed with a solution of a metal compound. As the metal compound, for example, a metal alkoxide or halide selected from the group consisting of scandium, yttrium, lanthanoid, zirconium, hafnium, niobium, tantalum, gallium, indium, germanium, and tin can be used. The metal compound solution (treatment liquid) is usually an aqueous solution or an alcohol solution. Note that “treatment” means an operation of bringing the semiconductor fine particles into contact with the treatment liquid for a certain period of time before adsorbing the pigment to the semiconductor fine particles. The metal compound may or may not be adsorbed on the semiconductor fine particles after contact. The treatment is preferably performed after the semiconductor fine particle layer is formed.
[0039]
As a specific method for the treatment, a method of immersing semiconductor fine particles in the treatment liquid (immersion method) is a preferred example. Moreover, the method (spray method) which sprays a process liquid in a spray form for a fixed time is also applicable. Although the temperature (immersion temperature) of the process liquid at the time of performing an immersion method is not specifically limited, Typically, it is -10-70 degreeC, Preferably it is 0-40 degreeC. The treatment time is also not particularly limited, and is typically 1 minute to 24 hours, preferably 30 minutes to 15 hours. After the immersion, the semiconductor fine particles may be washed with a solvent such as distilled water. Moreover, you may bake in order to strengthen the coupling | bonding of the substance adhering to semiconductor fine particle by the immersion process. The firing conditions may be set similarly to the above-described heat treatment conditions.
[0040]
(4) The sensitizing dye used in the dye photosensitive layer is not particularly limited as long as it has absorption characteristics in the visible region and near infrared region and can sensitize a semiconductor. However, metal complex dyes, methine dyes, porphyrin dyes And phthalocyanine dyes can be preferably used, among which metal complex dyes are particularly preferable. Phthalocyanines, naphthalocyanines, metal phthalocyanines, metal naphthalocyanines, porphyrins such as tetraphenylporphyrin and tetraazaporphyrin, metal porphyrins, derivatives thereof, and the like can also be used. Dyes used for dye lasers can also be used in the present invention. Moreover, in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency, two or more kinds of dyes can be used in combination. In this case, it is possible to select the dye to be used in combination and its ratio so as to match the wavelength range and intensity distribution of the target light source.
[0041]
The dye preferably has an appropriate interlocking group having an adsorption ability with respect to the surface of the semiconductor fine particles. Examples of preferred linking groups include: —COOH groups, —OH groups, —SO ₂ H groups, —P (O) (OH) ₂ groups and —OP (O) (OH) ₂ groups, and Chelating groups having π conductivity such as oximes, dioximes, hydroxyquinolines, salicylates and α-ketoenolates. Among them, -COOH group, -P (O) (OH) ₂ group and -OP (O) (OH) ₂ group are particularly preferable. These bonding groups may form a salt with an alkali metal or the like, or may form an internal salt. In the case of a polymethine dye, if the methine chain contains an acidic group as in the case where the methine chain forms a squarylium ring or a croconium ring, this part may be used as a linking group. Hereinafter, preferred sensitizing dyes used in the photosensitive layer will be specifically described.
[0042]
(A) Metal Complex Dye The metal atom of the metal complex dye used in the present invention is preferably ruthenium Ru. Examples of ruthenium complex dyes include U.S. Pat. Nos. 4,927,721, 4,684,537, 5,084,365, 5,350,644, 5,463,057, 5,525,440. JP-A-7-249790, JP-A-10-504512, WO98 / 50393 pamphlet, JP-A-2000-26487, and the like. Specific examples of preferable metal complex dyes include those described in paragraph numbers 0051 to 0057 of JP-A No. 2001-320068. The most typical metal complex dyes include the following D-1 and D-2.
[0043]
[Chemical 1]

[0044]
(B) Methine dyes Preferred methine dyes are polymethine dyes such as cyanine dyes, merocyanine dyes and squarylium dyes. Examples of preferred polymethine dyes include JP-A-11-35836, JP-A-11-158395, JP-A-11-163378, JP-A-11-214730, JP-A-11-214731, and European Patent 892411. And dyes described in JP-A-911841. For methods for synthesizing these polymethine dyes, FM Hammer, “Heterocyclic Compounds-Cyanine Dies and Related Compounds”, “Heterocyclic Compounds—Cyanine Compounds and Related Compounds”. John Wiley & Sons, New York, London, 1964, D.M. Sturmer, "Heterocyclic Compounds-Special Topics in Heterocy" Click Chemistry-Heterocyclic Compounds in Heterocyclic Chemist y) ", John Wiley & Sons (John Wiley & Sons), Inc., New York, London, 1977, Chapter 18, Section 14, p. 82-515, “Rod's Chemistry of Carbon Compounds”, 2nd edition, Elsevier Science Public Inc., New York, Inc. 1977, Volume IV, part B, Chapter 15, p. 369-422, British Patent No. 1,077,611, “Ukrainski Kimicheskii Zhurnal”, Vol. 40, No. 3, p. 253-258, “Dyes and Pigments”, Vol. 21, p. 227-234, these references, etc.
[0045]
(5) Adsorption of dye to semiconductor fine particles When a dye is adsorbed to semiconductor fine particles, a method of immersing a conductive support having a well-dried semiconductor fine particle layer in a dye solution, or a solution of dye is used as a semiconductor fine particle A method of applying to the layer can be used. In the case of the former method, a dipping method, a dip method, a roller method, an air knife method, etc. can be used. When the immersion method is used, the adsorption of the dye may be performed at room temperature, or may be performed by heating and refluxing as described in JP-A-7-249790. In the case of the latter method, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, a spray method, or the like can be used. In addition, a dye can be applied in an image form by an inkjet method or the like, and the image itself can be used as a photoelectric conversion element.
[0046]
The solvent used for the dye solution (adsorption solution) is preferably alcohols (methanol, ethanol, t-butyl alcohol, benzyl alcohol, etc.), nitriles (acetonitrile, propionitrile, 3-methoxypropionitrile, etc.), nitromethane, etc. Halogenated hydrocarbons (dichloromethane, dichloroethane, chloroform, chlorobenzene, etc.), ethers (diethyl ether, tetrahydrofuran, etc.), dimethyl sulfoxide, amides (N, N-dimethylformamide, N, N-dimethylacetamide, etc.), N-methylpyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters (ethyl acetate, butyl acetate, etc.), carbonates (diethyl carbonate, ethylene carbonate, propylene carbonate, etc.), ketones (acetone, - butanone, cyclohexanone), hydrocarbons (hexane, petroleum ether, benzene, toluene, etc.) or a mixed solvent thereof.
[0047]
The amount of the dye adsorbed is preferably 0.01 to 100 mmol per unit area (1 m ² ) of the semiconductor fine particle layer. Moreover, it is preferable that the adsorption amount with respect to the semiconductor fine particle of a pigment | dye is 0.01-1 mmol per g of semiconductor fine particles. By using such an amount of adsorbed dye, the effect of sensitizing the semiconductor fine particles can be sufficiently obtained. If the amount of dye adsorbed is too small, the sensitizing effect will be insufficient, and if the amount of dye adsorbed is too large, the dye not attached to the semiconductor will float and the sensitizing effect will be reduced. In order to increase the adsorption amount of the dye, it is preferable to heat-treat the semiconductor fine particles before the adsorption. In order to avoid water adsorbing on the surface of the semiconductor fine particles, it is preferable to quickly adsorb the dye when the temperature of the semiconductor fine particle layer is between 60 to 150 ° C. without returning to room temperature after the heat treatment.
[0048]
In order to reduce the interaction such as aggregation between the dyes, a colorless compound having properties as a surfactant may be added to the dye adsorbing liquid and co-adsorbed on the semiconductor fine particles. Examples of such colorless compounds include steroid compounds having a carboxyl group or a sulfo group (cholic acid, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, etc.), sulfonates as described below, and the like. .
[0049]
[Chemical 2]

[0050]
It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Cleaning is preferably performed in a wet cleaning tank using an organic solvent such as acetonitrile or an alcohol solvent.
[0051]
After adsorbing the dye, the fine particles of the semiconductor particles are formed using amines, quaternary ammonium salts, ureido compounds having at least one ureido group, silyl compounds having at least one silyl group, alkali metal salts, alkaline earth metal salts, etc. The surface may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferable quaternary ammonium salts include tetrabutylammonium iodide and tetrahexylammonium iodide. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.
[0052]
(C) Charge transport layer The charge transport layer contains a charge transport material having a function of replenishing electrons to the oxidant of the dye. The charge transport material used in the present invention may be (i) a charge transport material related to ions, or (ii) a charge transport material related to carrier movement in a solid. (I) As a charge transport material in which ions are involved, a molten salt electrolyte composition containing a redox counter ion, a solution (electrolytic solution) in which redox pair ions are dissolved, and a redox couple solution into a polymer matrix gel Examples include so-called gel electrolyte compositions and solid electrolyte compositions impregnated, and (ii) charge transport materials that involve carrier movement in solids include electron transport materials and hole transport materials. A plurality of these charge transport materials may be used in combination. In the present invention, it is preferable to use a molten salt electrolyte composition or a gel electrolyte composition for the charge transport layer.
[0053]
(1) Molten salt electrolyte composition The molten salt electrolyte composition contains a molten salt. The molten salt electrolyte composition is preferably liquid at room temperature. The molten salt as the main component is a liquid at room temperature or is an electrolyte having a low melting point, and general examples thereof include WO95 / 18456, JP-A-8-259543, “Electrochemistry”. 1997, Vol. 65, No. 11, p. Pyridinium salts, imidazolium salts, triazolium salts described in 923, and the like. The melting point of the molten salt is preferably 50 ° C. or less, and particularly preferably 25 ° C. or less. Specific examples of the molten salt are described in detail in paragraph numbers 0066 to 0082 of JP-A No. 2001-320068.
[0054]
The molten salt may be used alone or in combination of two or more. Alkali metal salts such as LiI, NaI, KI, LiBF ₄ , CF ₃ COOLi, CF ₃ COONa, LiSCN, NaSCN can also be used in combination. The addition amount of the alkali metal salt is preferably 2% by mass or less, more preferably 1% by mass or less, based on the entire composition. Moreover, it is preferable that 50 mol% or more of the anions contained in the molten salt electrolyte composition is iodide ions.
[0055]
Usually, the molten salt electrolyte composition contains iodine. The content of iodine is preferably 0.1 to 20% by mass, and more preferably 0.5 to 5% by mass with respect to the entire molten salt electrolyte composition.
[0056]
The molten salt electrolyte composition preferably has low volatility and preferably does not contain a solvent. Even when a solvent is added, the amount of the solvent added is preferably 30% by mass or less with respect to the entire molten salt electrolyte composition. The molten salt electrolyte composition may be used after gelation as described below.
[0057]
(2) Electrolytic solution The electrolytic solution is preferably composed of an electrolyte, a solvent and an additive. Examples of electrolytes used in the electrolyte include quaternary compounds such as I ₂ and iodides (metal iodides such as LiI, NaI, KI, CsI, and CaI ₂ , tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide, etc. A combination of Br ₂ and bromide (a metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr ₂ , a quaternary ammonium compound bromide such as tetraalkylammonium bromide, pyridinium bromide, etc.) Examples thereof include metal complexes such as Russianate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, and hydroquinone-quinone. Among them, an electrolyte in which I ₂ and LiI or a quaternary ammonium compound iodine salt such as pyridinium iodide, imidazolium iodide, or the like is combined is preferable. The electrolyte may be used as a mixture.
[0058]
The electrolyte concentration in the electrolytic solution is preferably 0.1 to 10M, more preferably 0.2 to 4M. Moreover, the preferable addition density | concentration of iodine when adding iodine to electrolyte solution is 0.01-0.5M.
[0059]
The solvent used in the electrolytic solution is desirably a compound having a low viscosity and improving ion mobility, or having a high dielectric constant and an effective carrier concentration, and can exhibit excellent ion conductivity. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane and diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether , Chain ethers such as polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether, alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether and polypropylene glycol monoalkyl ether, ethylene Glycol, propylene glycol, polyethylene glycol, polypropylene Glycol, polyhydric alcohols such as glycerin, acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile, dimethyl sulfoxide, aprotic polar substances such as sulfolane, water and the like. These solvents can also be used as a mixture.
[0060]
Also, “Journal of the American Ceramic Society”, 1997, Vol. 80, No. 12, p. It is preferable to add a basic compound such as tert-butylpyridine, 2-picoline, or 2,6-lutidine as described in 3157-3171 to the aforementioned molten salt electrolyte composition or electrolytic solution. A preferable concentration range when adding the basic compound to the electrolytic solution is 0.05 to 2M. When added to the molten salt electrolyte composition, the basic compound preferably has an ionic group. The mass ratio of the basic compound to the entire molten salt electrolyte composition is preferably 1 to 40% by mass, more preferably 5 to 30% by mass.
[0061]
(3) Gel electrolyte composition In the present invention, the aforementioned molten salt electrolyte composition or electrolyte solution is gelled by a technique such as addition of a polymer, addition of an oil gelling agent, polymerization including polyfunctional monomers, or a crosslinking reaction of the polymer ( (Solidification) can also be used. In the case of gelation by polymer addition, it was described in “Polymer Electrolyte Reviews-1 and 2” (J. R. MacCallum and C. A. Vincent co-edited, ELSEVIER APPLIED SCIENCE). Although a compound can be used, especially polyacrylonitrile and polyvinylidene fluoride can be preferably used. In the case of gelation by addition of an oil gelling agent, “Journal of the Chemical Society of Japan, Industrial Chemistry Sections”, 1943, 46, p. 779, “Journal of the American Chemical Society”, 1989, Vol. 111, p. 5542, “Journal of the Chemical Society, Chemical Communications”, 1993, p. 390, “Angewandte Chemie International Edition in England”, 1996, Vol. 35, p. 1949, “Chemistry Letters”, 1996, p. 885, and "Journal of the Chemical Society, Chemical Communications," 1997, p. Although the compound described in 545 can be used, it is preferable to use a compound having an amide structure. An example of gelling the electrolytic solution is described in JP-A No. 11-185863, and an example of gelling the molten salt electrolyte is also described in JP-A No. 2000-58140, which can also be applied to the present invention.
[0062]
Moreover, when making it gelatinize by the crosslinking reaction of a polymer, it is desirable to use together the polymer and crosslinking agent containing the reactive group which can be bridge | crosslinked. In this case, preferred crosslinkable reactive groups are amino groups and nitrogen-containing heterocycles (pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, etc.), and preferred bridges. The agent is a bifunctional or higher functional reagent capable of electrophilic reaction with nitrogen atom (halogenated alkyls, halogenated aralkyls, sulfonic acid esters, acid anhydrides, acid chlorides, isocyanate compounds, α, β-inactive Saturated sulfonyl compounds, α, β-unsaturated carbonyl compounds, α, β-unsaturated nitrile compounds, etc.). The cross-linking techniques described in JP 2000-17076 A and 2000-86724 can also be applied.
[0063]
(4) Hole transport material In the present invention, an organic solid hole transport material, an inorganic solid hole transport material, or a combination of both can be used instead of an ion conductive electrolyte such as a molten salt. .
[0064]
(A) Organic hole transport material Examples of organic hole transport materials that can be preferably used in the present invention include J. Hagen et al., “Synthetic Metal”, 1997, 89th. Volume, p. 215-220, “Nature”, 1998, Vol. 395, No. 8 Oct. , P583-585, pamphlet of International Publication No. 97/10617, JP-A-59-194393, JP-A-5-234681, US Pat. No. 4,923,774, JP-A-4-308688. U.S. Pat. No. 4,764,625, JP-A-3-2699084, 4-129271, 4-175395, 4-264189, 4-290851, No. 4-364153, No. 5-25473, No. 5-239455, No. 5-320634, No. 6-1972, No. 7-138562, No. 7-252474, No. 11 Aromatic amines described in JP-A Nos. 1441473 and the like, JP-A Nos. 11-149821, 11-148067, and 11-176 And triphenylene derivatives described in Japanese Patent No. 489. Also, “Advanced Materials”, 1997, Vol. 9, No. 7, p. 557, “Angewandte Chemie International Edition in England”, 1995, Vol. 34, No. 3, p. 303-307, “Journal of the American Chemical Society”, 1998, Vol. 120, No. 4, p. Oligothiophene compounds described in 664-672 and the like; Murakoshi, et al. "Chemistry Letters", 1997, p. Polypyrrole described in 471, Polyacety described in NALWA, “Handbook of Organic Conductives and Polymers”, Volumes 1, 2, 3, and 4, WILEY Publishing. Conductivity such as derivatives thereof, poly (p-phenylene) and derivatives thereof, poly (p-phenylene vinylene) and derivatives thereof, polythienylene vinylene and derivatives thereof, polythiophene and derivatives thereof, polyaniline and derivatives thereof, polytoluidine and derivatives thereof, etc. Can also be preferably used.
[0065]
“Nature”, 1998, Vol. 395, No. 8 Oct. , P. 583-585, compounds containing cation radicals such as tris (4-bromophenyl) aminium hexachloroantimonate may be added to the hole transport material to control the dopant level. . Further, a salt such as Li [(CF ₃ SO ₂ ) ₂ N] may be added in order to perform potential control (space charge layer compensation) of the oxide semiconductor surface.
[0066]
(B) Inorganic hole transport material A p-type inorganic compound semiconductor can be used as the inorganic hole transport material, and the band gap is preferably 2 eV or more, more preferably 2.5 eV or more. Also, the ionization potential of the p-type inorganic compound semiconductor needs to be smaller than the ionization potential of the dye adsorption electrode in order to reduce the holes of the dye. Although the preferable range of the ionization potential of the p-type inorganic compound semiconductor varies depending on the dye used, it is generally preferably 4.5 to 5.5 eV, more preferably 4.7 to 5.3 eV. Preferred p-type inorganic compound semiconductor is a compound semiconductor containing monovalent copper, _CuI and examples _{thereof, CuSCN, CuInSe 2, Cu (} In, Ga) Se 2, CuGaSe 2, Cu 2 O, CuS, CuGaS 2, CuInS _2, CuAlSe _2, and the like. Among these, CuI and CuSCN are preferable, and CuI is most preferable. Examples of other p-type inorganic compound semiconductors include GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , Cr ₂ O _{3 and the} like.
[0067]
(5) Formation of charge transport layer The charge transport layer can be formed by one of two methods. One is a method in which a counter electrode is first bonded onto the photosensitive layer, and a liquid charge transport layer is sandwiched between the gaps. The other is a method in which a charge transport layer is directly provided on the photosensitive layer, and the counter electrode is subsequently provided.
[0068]
In the case of the former method, when the charge transport layer is sandwiched, a normal pressure process using capillary action due to immersion or the like, or a vacuum process in which the gas phase in the gap is replaced with a liquid phase at a pressure lower than normal pressure can be used.
[0069]
In the latter method, when a wet charge transport layer is used, a counter electrode is usually applied in an undried state to prevent liquid leakage at the edge. Moreover, when using a gel electrolyte composition, you may solidify by methods, such as superposition | polymerization, after apply | coating this with a wet process. Solidification may be performed before or after applying the counter electrode. In the case of forming a charge transport layer made of an electrolytic solution, a wet organic hole transport material, a gel electrolyte composition, or the like, the same method as the method for forming a semiconductor fine particle layer described above can be used.
[0070]
When a solid electrolyte composition or a solid hole transport material is used, a charge transport layer can be formed by a dry film forming process such as a vacuum deposition method or a CVD method, and then a counter electrode can be provided. The organic hole transport material can be introduced into the electrode by a vacuum deposition method, a casting method, a coating method, a spin coating method, a dipping method, an electrolytic polymerization method, a photoelectrolytic polymerization method or the like. The inorganic solid compound can be introduced into the electrode by a casting method, a coating method, a spin coating method, a dipping method, an electrolytic deposition method, an electroless plating method, or the like.
[0071]
(D) Similarly to the conductive support described above, the counter electrode counter electrode may have a single-layer structure of a counter electrode conductive layer made of a conductive material, or may be composed of a counter electrode conductive layer and a support substrate. Examples of the conductive agent used for the counter electrode conductive layer include metal (platinum, gold, silver, copper, aluminum, magnesium, indium, etc.), carbon, conductive metal oxide (indium-tin composite oxide, fluorine-doped tin oxide, etc.) ) And the like. Among these, platinum, gold, silver, copper, aluminum and magnesium are preferable. The substrate used for the counter electrode is preferably a glass substrate or a plastic substrate, and can be used by applying or vapor-depositing the above-mentioned conductive agent. The thickness of the counter electrode conductive layer is not particularly limited, but is preferably 3 nm to 10 μm. The surface resistance of the counter electrode conductive layer is preferably as low as possible, preferably 50Ω / □ or less, more preferably 20Ω / □ or less.
[0072]
Since light may be irradiated from either or both of the conductive support and the counter electrode, in order for light to reach the photosensitive layer, at least one of the conductive support and the counter electrode may be substantially transparent. . From the viewpoint of improving power generation efficiency, it is preferable to make the conductive support transparent so that light is incident from the conductive support side. In this case, the counter electrode preferably has a property of reflecting light. In order to obtain such properties, glass or plastic on which a metal or conductive oxide is deposited or a metal thin film may be used as a counter electrode.
[0073]
The counter electrode may be installed by directly applying, plating, or vapor-depositing (PVD, CVD) a conductive agent on the charge transport layer, or by attaching the conductive layer side of the substrate having the conductive layer. As in the case of the conductive support, it is preferable to use a metal lead for the purpose of reducing the resistance of the counter electrode, particularly when the counter electrode is transparent. The preferred embodiment of the metal lead is the same as that of the conductive support.
[0074]
(E) In order to prevent short circuit between the other layer counter electrode and the conductive support, it is preferable that a dense semiconductor thin film layer is preliminarily applied as an undercoat layer between the conductive support and the photosensitive layer. This method of preventing a short circuit by the undercoat layer is particularly effective when an electron transport material or a hole transport material is used for the charge transport layer. The undercoat layer is preferably made of TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , ZnO or Nb ₂ O ₅ , more preferably TiO ₂ . The undercoat layer is, for example, Electrochim. Acta, 40, 643-652 (1995), and can be applied by a spray pyrolysis method, a sputtering method, or the like. The thickness of the undercoat layer is preferably 5 to 1000 nm, more preferably 10 to 500 nm.
[0075]
In addition, a functional layer such as a protective layer or an antireflection layer may be provided on the outer surface of one or both of the conductive support and the counter electrode, between the conductive layer and the substrate, or in the middle of the substrate. The method for forming these functional layers can be appropriately selected from a coating method, a vapor deposition method, a pasting method, and the like according to the material.
[0076]
(F) Specific Example of Internal Structure of Photoelectric Conversion Element As described above, the internal structure of the photoelectric conversion element can take various forms according to the purpose. If roughly divided into two, a structure that allows light to enter from both sides and a structure that allows only one side are possible. Examples of a preferable internal structure of the photoelectric conversion element of the present invention are shown in FIG. 1 and FIGS.
[0077]
In the structure shown in FIG. 2, the photosensitive layer 20 and the charge transport layer 30 are interposed between the transparent conductive layer 10a and the transparent counter electrode conductive layer 40a, and light is incident from both sides. . In the structure shown in FIG. 3, the metal lead 11 is partially provided on the transparent substrate 50a, the transparent conductive layer 10a is provided thereon, and the undercoat layer 60, the photosensitive layer 20, the charge transport layer 30, and the counter electrode conductive layer 40 are arranged in this order. In addition, a support substrate 50 is arranged, and light is incident from the conductive layer side. In the structure shown in FIG. 4, the conductive layer 10 is provided on the support substrate 50, the photosensitive layer 20 is provided via the undercoat layer 60, the charge transport layer 30 and the transparent counter electrode conductive layer 40a are further provided, and a metal is partially formed. The transparent substrate 50a provided with the lead 11 is arranged with the metal lead 11 side inward, and has a structure in which light enters from the counter electrode side. In the structure shown in FIG. 5, the primer layer 60, the photosensitive layer 20, and the charge transport layer 30 are provided between a pair of metal leads 11 provided on a transparent substrate 50 a and a transparent conductive layer 10 a (or 40 a). In this structure, light enters from both sides. The structure shown in FIG. 6 is obtained by providing a transparent conductive layer 10a, an undercoat layer 60, a photosensitive layer 20, a charge transport layer 30 and a counter electrode conductive layer 40 on a transparent substrate 50a, and placing a support substrate 50 thereon. In this structure, light enters from the conductive layer side. In the structure shown in FIG. 7, the conductive layer 10 is provided on the support substrate 50, the photosensitive layer 20 is provided via the undercoat layer 60, and the charge transport layer 30 and the transparent counter electrode conductive layer 40a are further provided thereon. 50a is arranged and light is incident from the counter electrode side. The structure shown in FIG. 8 has a transparent conductive layer 10a on a transparent substrate 50a, a photosensitive layer 20 is provided via an undercoat layer 60, a charge transport layer 30 and a transparent counter electrode conductive layer 40a are provided, and a transparent layer is provided thereon. A substrate 50a is disposed, and light is incident from both sides. In the structure shown in FIG. 9, the conductive layer 10 is provided on the support substrate 50, the photosensitive layer 20 is provided via the undercoat layer 60, and the solid charge transport layer 30 is further provided. It has a metal lead 11 and has a structure in which light enters from the counter electrode side.
[0078]
[3] Photocell The photocell of the present invention is one in which the photoelectric conversion element of the present invention is caused to work with an external load. Among photocells, the case where the charge transport material is mainly composed of an ion transport material is particularly called a photoelectrochemical cell, and the case where the main purpose is power generation by sunlight is called a solar cell.
[0079]
The side surface of the photovoltaic cell is preferably sealed with a polymer, an adhesive or the like in order to prevent deterioration of the constituents and volatilization of the contents. The external circuit itself connected to the conductive support and the counter electrode via a lead may be a known one.
[0080]
Even when the photoelectric conversion element of the present invention is applied to a solar cell, the structure inside the cell is basically the same as the structure of the photoelectric conversion element described above. Moreover, the dye-sensitized solar cell using the photoelectric conversion element of the present invention can basically have the same module structure as a conventional solar cell module. The solar cell module generally has a structure in which cells are formed on a support substrate such as metal or ceramic, and the cell is covered with a filling resin or protective glass, and light is taken in from the opposite side of the support substrate. It is also possible to use a transparent material such as tempered glass for the support substrate, configure a cell thereon, and take in light from the transparent support substrate side. Specifically, a module structure called a super straight type, a substrate type, a potting type, a substrate integrated module structure used in amorphous silicon solar cells, and the like are known, and dye sensitization using the photoelectric conversion element of the present invention is known. As for the type solar cell, the module structure can be appropriately selected according to the purpose of use, the place of use and the environment. Specifically, the structures and embodiments described in Japanese Patent Application No. 11-8457, Japanese Patent Application Laid-Open No. 2000-268892, and the like are preferable.
[0081]
【Example】
The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
[0082]
Example 1
Preparation of Titanium Oxide Particles (1) Preparation of Titanium Oxide Particles for Dye Support 30 ml of acetic acid and tetraisopropyl orthotitanate (manufactured by Wako Pure Chemical Industries, Ltd.) in 440 ml of dilute nitric acid of 0.02 mol / liter It was added at once and stirred for 10 minutes to obtain a white precipitate. After the precipitate was filtered off, 440 ml of 0.02 mol / liter dilute nitric acid and 30 ml of acetic acid were added again. The obtained suspension was heated and stirred at 70 ° C. for 5 hours to obtain a translucent sol-like liquid. The sol was transferred to an autoclave manufactured by Teflon (registered trademark), and heated at 225 ° C. for 10 hours. After standing to cool, the resulting suspension was centrifuged to obtain a dispersion of titanium oxide particles (TDD-1). This dispersion had a solid content of 15% by mass. Moreover, it turned out that it is anatase whose crystallite size is 12.2 nm from the result of X-ray diffraction method. The crystallite size was calculated based on the half width at the peak of 2θ = 25.2 ° (hkl = 101) in the Cu-Kα line.
[0083]
(2) Preparation of titanium oxide particles for light scattering 50 ml of tetraisopropyl orthotitanate (Wako Pure Chemical Industries, Ltd.) was added at once to 320 ml of a 0.35 mol / liter aqueous solution of tetraethylammonium hydroxide at 55 ° C. Next, the temperature was raised to 80 ° C. and stirred for 30 minutes to obtain a transparent sol. The sol was transferred to an autoclave made of Teflon (registered trademark) by Inner and heated at 200 ° C. for 10 hours. After cooling, the resulting titanium oxide particles had settled, and the supernatant was removed by decantation. A 1 mol / liter nitric acid aqueous solution was added thereto to make the solution acidic, and then centrifugal separation and water addition were repeatedly washed to obtain a wet cake of titanium oxide particles. This wet cake was diluted with pure water to adjust the solid content to 15% by mass to obtain a titanium oxide particle dispersion (TDS-1) for light scattering. Moreover, it turned out that it is anatase whose crystallite size is 27.9 nm from the result of the X-ray-diffraction method. On the other hand, it was confirmed from high-resolution SEM (scanning electron microscope) photographs that the particles have a primary particle size of 100 to 400 nm and a wide particle size distribution. Next, titanium oxide particles according to the method of the present invention (TDS-2 to 7 in Table 1) and comparison were performed in the same manner as TDS-1 except that the heating conditions in the autoclave were changed as shown in Table 1. Titanium oxide particles for use (TDS-8 to 9 in Table 1) were prepared.
[0084]
[Table 1]

[0085]
Example 2
Production and Evaluation of Photoelectric Conversion Element (1) Preparation of Titanium Oxide Coating Liquid Titanium Oxide Dispersion for Dye Support (TDD-1) 8.5 g, Titanium Oxide Dispersion for Light Scattering (TDS-1 to 9) shown in Table 2 ) 1.5 g, polyethylene glycol (molecular weight 20000, Wako Pure Chemical Industries, Ltd.) 0.6 g, and water 2.5 g were added and stirred well to completely dissolve the polyethylene glycol. To this, 1 ml of ethanol and 0.4 ml of concentrated nitric acid were added to adjust the viscosity, and titanium oxide coating solutions (C-1 to C-9) were prepared.
[0086]
(2) Preparation of dye-sensitized titanium oxide electrode Coating liquid (C on the conductive surface side of transparent conductive glass (manufactured by Nippon Sheet Glass Co., Ltd., surface resistance is about 10Ω / cm ² ) coated with tin oxide doped with fluorine. -1 to C-9) were applied using a doctor blade. After drying at 25 ° C. for 30 minutes, it was fired at 450 ° C. for 30 minutes in an electric furnace (Maffle furnace FP-32 type manufactured by Yamato Scientific Co., Ltd.). From the mass change before and after coating and firing, the coating amount per unit area was calculated.
[0087]
After calcination, it was immersed for 4 hours in an adsorbing solution containing 0.3 mmol / l of the dye (A) having the following structure. The adsorption temperature was 40 ° C., and the solvent of the adsorbent was a mixed solvent of ethanol: t-butanol: acetonitrile = 1: 1: 2 (volume ratio). The dyed titanium oxide electrode was washed sequentially with ethanol and acetonitrile to prepare dye-sensitized titanium oxide electrodes (E-1 to E-9).
[0088]
(Dye A)
[Chemical 3]

[0089]
(3) Measurement of red light absorbance In order to evaluate the light scattering property of titanium oxide particles, the red light absorbance (transmission density) of the produced dye-sensitized titanium oxide electrodes (E-1 to E-9) was measured by X-RITE. Measurement was performed using a photographic densitometer type 301 manufactured by the Company. The results are shown in Table 2.
[0090]
[Table 2]

[0091]
From Table 2, the dye-sensitized titanium oxide electrodes E-1 to E-7 using the titanium oxide particles according to the method of the present invention are compared with the dye-sensitized titanium oxide electrodes E-8 and 9 using the titanium oxide particles for comparison. It can be seen that the red light absorbance is high. Among the titanium oxide particles according to the method of the present invention, E-4 to 7 using particles heated and grown for 20 hours or more than E-1 to 3 using particles heated and grown for 10 hours in an autoclave. Has high red light absorbance. When the aging time in the autoclave is the same, the higher the heating temperature, the higher the red light absorbance.
[0092]
(4) Production of photoelectric conversion element A dye-sensitized titanium oxide electrode substrate (2 cm × 2 cm) produced as described above was superposed on platinum-deposited glass having the same size (see FIG. 10). Next, an electrolytic solution (0.63 mol / liter of iodide 1,3-dimethylimidazolium, 0.05 mol / liter of iodine, and 0.1 mol of t-butylpyridine is used by utilizing capillary action in the gap between the two glasses. / Liter of acetonitrile solution) was soaked and introduced into the TiO ₂ electrode to obtain photoelectric conversion elements SC-1 to SC-9 shown in Table 3. As shown in FIG. 10, these photoelectric conversion elements are composed of conductive glass 1 (a conductive layer 3 formed on glass 2), a dye-adsorbed titanium oxide layer 4, a charge transport layer 5, a platinum layer 6 and glass. 7 has a layered structure.
[0093]
[Table 3]

[0094]
(5) Measurement of photoelectric conversion efficiency Simulated sunlight was generated by passing light from a 500 W xenon lamp (manufactured by Ushio Corporation) through a spectral filter (AM1.5 manufactured by Oriel). The intensity of light was 100 mW / cm ² on the vertical plane. A silver paste was applied to the end of the conductive glass of the photoelectrochemical cell to form a negative electrode, and this negative electrode and platinum-deposited glass (positive electrode) were connected to a current-voltage measuring device (Keutley SMU238 type). While simulating sunlight was irradiated vertically, current-voltage characteristics were measured to obtain conversion efficiency. Table 4 shows the photoelectric conversion characteristics of the produced photoelectric conversion elements.
[0095]
[Table 4]

[0096]
It can be seen that the photoelectric conversion elements SC-1 to SC-7 of the present invention have higher conversion efficiency than the comparative photoelectric conversion elements SC-8 and SC-9. This is mainly due to an increase in short circuit current. Moreover, in the comparison between the titanium oxide particles by the method of the present invention, SC-4 using particles grown by heating for 20 hours or more than SC-1 to 3 using particles heated and grown for 10 hours in an autoclave. ˜7 has higher short circuit current and conversion efficiency. When the aging time in the autoclave was the same, a photoelectric conversion element having a higher conversion efficiency was obtained as the heating temperature was higher.
[0097]
【The invention's effect】
As described above, the method for producing titanium oxide particles of the present invention includes a titanium oxide sol production step performed in the presence of tetraalkylammonium hydroxide and a particle growth step of heating at 200 ° C. or higher for 10 hours or more. High titanium oxide particles can be obtained. Therefore, it is possible to obtain a dye-sensitized photoelectric conversion element excellent in conversion efficiency.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a structure of a photoelectric conversion element according to a preferred embodiment of the present invention.
FIG. 2 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to another preferred embodiment of the present invention.
FIG. 3 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 4 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 5 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 6 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 7 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 8 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 9 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
10 is a partial cross-sectional view illustrating a structure of a photoelectric conversion element manufactured in Example 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Conductive layer 10a ... Transparent conductive layer 11 ... Metal lead 20 ... Photosensitive layer 21 ... Semiconductor fine particle 22 ... Dye 23 ... Charge transport material 30 ... Charge transport layer 40 ... Counter electrode conductive layer 40a ... Transparent counter electrode conductive layer 50 ... Substrate 50a ... Transparent substrate 60 ... Undercoat layer

Claims (7)

A method for producing titanium oxide particles by hydrolysis of orthotitanate, wherein the titanium oxide sol produced by the hydrolysis is heated in a pressure vessel at 200 ° C. or more for 10 hours or more in the presence of tetraalkylammonium hydroxide. The manufacturing method of the titanium oxide particle characterized by including. The method for producing titanium oxide particles according to claim 1, wherein the concentration of tetraalkylammonium hydroxide is 0.1 to 1 mol / liter. The method for producing titanium oxide particles according to claim 1 or 2, wherein the heating temperature is 240 ° C or higher. The method for producing titanium oxide particles according to any one of claims 1 to 3, wherein tetraethylammonium hydroxide is used as the tetraalkylammonium hydroxide. A dye-sensitized photoelectric conversion element comprising titanium oxide particles produced by the method according to claim 1. 6. The dye-sensitized photoelectric conversion element according to claim 5, wherein a ratio of the titanium oxide particles in all titanium oxide particles is 5 to 40% by mass. The solar cell using the dye-sensitized photoelectric conversion element of Claim 5 or 6.

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