JP4578695B2 - Method for creating photoelectric conversion element - Google Patents

Description

【００４０】
（ただし、R_aは水素原子または置換基を表し、置換基としてはたとえば、ハロゲン原子、炭素原子数１〜12の置換または無置換のアルキル基、炭素原子数７〜12の置換または無置換のアラルキル基、炭素原子数６〜12の置換または無置換のアリール基、あるいは前述の酸性基（これらの酸性基は塩を形成していてもよい）やキレート化基が挙げられ、アルキル基およびアラルキル基のアルキル部分は直鎖状でも分岐状でもよく、またアリール基およびアラルキル基のアリール部分は単環でも多環（縮合環、環集合）でもよい。）により表される化合物から選ばれた有機配位子を表す。B-a、B-bおよびB-cは同一でも異なっていてもよく、いずれか１つまたは２つでもよい。
【００４１】
有機金属錯体色素の好ましい具体例を以下に示すが、本発明はこれらに限定されるものではない。
【００４２】
【化２】

【００４３】
【化３】

【００４４】
（b）メチン色素
本発明に使用する色素の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などのポリメチン色素である。本発明で好ましく用いられるポリメチン色素の例は、特開平１１−３５８３６号、特開平１１−６７２８５号、特開平１１−８６９１６号、特開平１１−９７７２５号、特開平１１−１５８３９５号、特開平１１−１６３３７８号、特開平１１−２１４７３０号、特開平１１−２１４７３１号、特開平１１−２３８９０５号、特開２０００−２６４８７号、欧州特許８９２４１１号、同９１１８４１号および同９９１０９２号の各明細書に記載の色素である。好ましいメチン色素の具体例を下に示す。
【００４５】
【化４】

【００４６】
【化５】

【００４７】
（４）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か、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。前者の場合、浸漬法、ディップ法、ローラ法、エアーナイフ法等が使用可能である。浸漬法の場合、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。また後者の塗布方法としては、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、スプレー法等がある。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事もできる。
【００４８】
色素を溶解する溶媒として好ましいのは、例えば、アルコール類（メタノール、エタノール、t-ブタノール、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）やこれらの混合溶媒が挙げられる。
【００４９】
色素の全吸着量は、感光層の単位面積（１m²）当たり0.01〜100mmol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の範囲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における増感効果が十分に得られる。これに対し、色素が少なすぎると増感効果が不十分となり、また色素が多すぎると半導体に付着していない色素が浮遊し、増感効果を低減させる原因となる。色素の吸着量を増大させるためには、吸着前に加熱処理を行うのが好ましい。加熱処理後、半導体微粒子表面に水が吸着するのを避けるため、常温に戻さずに、半導体電極基板の温度が60〜150℃の間で素早く色素の吸着操作を行うのが好ましい。また、色素間の凝集などの相互作用を低減する目的で、無色の化合物を色素に添加し、半導体微粒子に共吸着させてもよい。この目的で有効な化合物は界面活性な性質、構造をもった化合物であり、例えば、カルボキシル基を有するステロイド化合物（例えばケノデオキシコール酸）や下記の例のようなスルホン酸塩類が挙げられる。
【００５０】
【化６】

【００５１】
未吸着の色素は、吸着後速やかに洗浄により除去するのが好ましい。湿式洗浄槽を使い、アセトニトリル等の極性溶剤、アルコール系溶剤のような有機溶媒で洗浄を行うのが好ましい。色素を吸着した後にアミン類や４級塩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、好ましい４級塩としてはテトロ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。これらが液体の場合はそのまま用いてもよいし、有機溶媒に溶解して用いてもよい。
【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層である。本発明で用いることのできる代表的な電荷輸送材料の例としては、(i)イオン輸送材料として、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、酸化還元対イオンを含有する溶融塩電解質、さらには固体電解質が挙げられ、これら電解質を含む組成物（電解質組成物）を電荷輸送層に用いることができる。
また、イオンがかかわる電荷輸送材料のほかに、(ii)固体中のキャリアー移動がかかわる電荷輸送材料として、電子輸送材料や正孔（ホール）輸送材料を用いることもできる。これらの電荷輸送材料は、併用することができる。
【００５３】
（１）溶融塩電解質
溶融塩電解質は、光電変換効率と耐久性の両立という観点から特に好ましい。
溶融塩電解質とは、室温において液状であるか、または低融点の電解質であり、例えばWO95/18456号、特開平8-259543号、電気化学，第65巻，11号，923頁（1997年）等に記載されているピリジニウム塩、イミダゾリウム塩、トリアゾリウム塩等の既知の電解質を挙げることができる。１００℃以下、特に室温付近において液状となる溶融塩が好ましい。
【００５４】
好ましく用いることのできる溶融塩としては、下記一般式（Y-a）、（Y-b）及び（Y-c）のいずれかにより表されるものが挙げられる。
【００５５】
【化７】

【００５６】
一般式（Y-a）中、Q_y1は窒素原子と共に５又は６員環の芳香族カチオンを形成しうる原子団を表す。Q_y1は炭素原子、水素原子、窒素原子、酸素原子及び硫黄原子からなる群から選ばれる１種以上の原子により構成されるのが好ましい。Q_y1により形成される５員環は、オキサゾール環、チアゾール環、イミダゾール環、ピラゾール環、イソオキサゾール環、チアジアゾール環、オキサジアゾール環、トリアゾール環、インドール環またはピロール環であるのが好ましく、オキサゾール環、チアゾール環又はイミダゾール環であるのがより好ましく、オキサゾール環又はイミダゾール環であるのが特に好ましい。Q_y1により形成される６員環は、ピリジン環、ピリミジン環、ピリダジン環、ピラジン環又はトリアジン環であるのが好ましく、ピリジン環であるのがより好ましい。
【００５７】
一般式（Y-b）中、A_y1は窒素原子又はリン原子を表す。
【００５８】
一般式（Y-a）、（Y-b）及び（Y-c）中のR_y1〜R_y6はそれぞれ独立に置換又は無置換のアルキル基（好ましくは炭素原子数１〜24、直鎖状であっても分岐状であっても、また環式であってもよく、例えばメチル基、エチル基、プロピル基、イソプロピル基、ペンチル基、ヘキシル基、オクチル基、2-エチルヘキシル基、t-オクチル基、デシル基、ドデシル基、テトラデシル基、2-ヘキシルデシル基、オクタデシル基、シクロヘキシル基、シクロペンチル基等）、或いは置換又は無置換のアルケニル基（好ましくは炭素原子数２〜24、直鎖状であっても分岐状であってもよく、例えばビニル基、アリル基等）を表し、より好ましくは炭素原子数２〜18のアルキル基又は炭素原子数２〜18のアルケニル基であり、特に好ましくは炭素原子数２〜６のアルキル基である。
【００５９】
また、一般式（Y-b）中のR_y1〜R_y4のうち２つ以上が互いに連結してA_y1を含む非芳香族環を形成してもよく、一般式（Y-c）中のR_y1〜R_y6のうち２つ以上が互いに連結して環構造を形成してもよい。
【００６０】
一般式（Y-a）、（Y-b）及び（Y-c）中のQ_y1及びR_y1〜R_y6は置換基を有していてもよく、好ましい置換基の例としては、ハロゲン原子（F、Cl、Br、I等）、シアノ基、アルコキシ基（メトキシ基、エトキシ基、メトキシエトキシ基、メトキシエトキシエトキシ基等）、アリーロキシ基（フェノキシ基等）、アルキルチオ基（メチルチオ基、エチルチオ基等）、アルコキシカルボニル基（エトキシカルボニル基等）、炭酸エステル基（エトキシカルボニルオキシ基等）、アシル基（アセチル基、プロピオニル基、ベンゾイル基等）、スルホニル基（メタンスルホニル基、ベンゼンスルホニル基等）、アシルオキシ基（アセトキシ基、ベンゾイルオキシ基等）、スルホニルオキシ基（メタンスルホニルオキシ基、トルエンスルホニルオキシ基等）、ホスホニル基（ジエチルホスホニル基等）、アミド基（アセチルアミノ基、ベンゾイルアミノ基等）、カルバモイル基（N,N-ジメチルカルバモイル基等）、アルキル基（メチル基、エチル基、プロピル基、イソプロピル基、シクロプロピル基、ブチル基、2-カルボキシエチル基、ベンジル基等）、アリール基（フェニル基、トルイル基等）、複素環基（ピリジル基、イミダゾリル基、フラニル基等）、アルケニル基（ビニル基、1-プロペニル基等）、シリル基、シリルオキシ基等が挙げられる。
【００６１】
一般式（Y-a）、（Y-b）又は（Y-c）により表される化合物は、Q_y1又はR_y1〜R_y6を介して多量体を形成してもよい。
【００６２】
これらの溶融塩は、単独で使用しても、２種以上混合して使用してもよく、また、ヨウ素アニオンを他のアニオンで置き換えた溶融塩と併用することもできる。ヨウ素アニオンと置き換えるアニオンとしては、ハロゲン化物イオン（Cl^-、Br^-等）、SCN^-、BF₄ ^-、PF₆ ^-、ClO₄ ^-、(CF₃SO₂)₂N^-、(CF₃CF₂SO₂)₂N^-、CH₃SO₃ ^-、CF₃SO₃ ^-、CF₃COO^-、Ph₄B^-、(CF₃SO₂)₃C^-等が好ましい例として挙げられ、SCN^-、CF₃SO₃ ^-、CF₃COO^-、(CF₃SO₂)₂N^-又はBF₄ ^-であるのがより好ましい。また、LiIなど他のヨウ素塩やCF₃COOLi、CF₃COONa、LiSCN、NaSCNなどのアルカリ金属塩を添加することもできる。アルカリ金属塩の添加量は、0.02〜２質量％程度であるのが好ましく、0.1〜１質量％がさらに好ましい。
【００６３】
本発明で好ましく用いられる溶融塩の具体例を以下に挙げるが、これらに限定されるわけではない。
【００６４】
【化８】

【００６５】
【化９】

【００６６】
【化１０】

【００６７】
【化１１】

【００６８】
【化１２】

【００６９】
【化１３】

【００７０】
上記溶融塩電解質は常温で溶融状態であるものが好ましく、溶媒を用いない方が好ましい。後述する溶媒を添加しても構わないが、溶融塩の含有量は電解質組成物全体に対して50質量％以上であるのが好ましく、90質量％以上であるのが特に好ましい。また、塩のうち、50質量％以上がヨウ素塩であることが好ましい。
【００７１】
上記電解質組成物にはヨウ素を添加するのが好ましく、この場合、ヨウ素の含有量は、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。
【００７２】
（２）電解液
電荷輸送層に電解液を使用する場合、電解液は電解質、溶媒、および添加物から構成されることが好ましい。本発明の電解質はＩ₂とヨウ化物の組み合わせ（ヨウ化物としてはＬｉＩ、ＮａＩ、ＫＩ、ＣｓＩ、ＣａＩ₂などの金属ヨウ化物、あるいは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など４級アンモニウム化合物のヨウ素塩など）、Ｂｒ₂と臭化物の組み合わせ（臭化物としてはＬｉＢｒ、ＮａＢｒ、ＫＢｒ、ＣｓＢｒ、ＣａＢｒ₂などの金属臭化物、あるいは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など４級アンモニウム化合物の臭素塩など）のほか、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などの金属錯体、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などのイオウ化合物、ビオロゲン色素、ヒドロキノン−キノンなどを用いることができる。この中でもI₂とＬｉＩやピリジニウムヨーダイド、イミダゾリウムヨーダイドなど４級アンモニウム化合物のヨウ素塩を組み合わせた電解質が好ましい。上述した電解質は混合して用いてもよい。
【００７３】
好ましい電解質濃度は0.1M以上10M以下であり、さらに好ましくは0.2M以上4M以下である。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0.01M以上0.5M以下である。
【００７４】
電解質に使用する溶媒は、粘度が低くイオン易動度を向上したり、も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などのカーボネート化合物、３−メチル−２−オキサゾリジノンなどの複素環化合物、ジオキサン、ジエチルエーテルなどのエーテル化合物、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などの鎖状エーテル類、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などのアルコール類、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、グリセリンなど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、ベンゾニトリルなどのニトリル化合物、ジメチルスルフォキシド、スルフォランなど非プロトン極性物質、水などが挙げられ、これらを混合して用いることもできる。
【００７５】
また、本発明では、J. Am. Ceram. Soc .,80 (12)3157-3171(1997)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や電解液に添加することが好ましい。塩基性化合物を添加する場合の好ましい濃度範囲は0.05M以上2M以下である。
【００７６】
（３）ゲル電解質
本発明では、電解質はポリマー添加、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させる場合は、“Polymer Electrolyte Revi ews-１および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、ポリフッ化ビニリデンを好ましく使用することができる。オイルゲル化剤添加によりゲル化させる場合は工業科学雑誌（J. Chem Soc. Japan, Ind. Chem.Sec., 46,779(1943)、J. Am. Chem. Soc., 111,5542(1989)、J. Chem. Soc., Chem. Com mun., 1993, 390、Angew. Chem. Int. Ed. Engl., 35,1949(1996)、Chem. Lett., 1996, 885、J. Chm. Soc., Chem. Commun., 1997,545）に記載されている化合物を使用することができるが、好ましい化合物は分子構造中にアミド構造を有する化合物である。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号公報に記載されており、本発明にも適用できる。
【００７７】
また、ポリマーの架橋反応により電解質をゲル化させる場合、架橋可能な反応性基を含有するポリマーおよ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（例えば、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、ピペラジン環など）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（例えば、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−不飽和スルホニル基含有化合物、α、β−不飽和カルボニル基含有化合物、α、β−不飽和ニトリル基含有化合物など）であり、特開２０００−１７０７６号、同２０００−８６７２４号公報に記載されている架橋技術も適用できる。
【００７８】
（４）正孔輸送材料
本発明では、溶融塩などのイオン伝導性電解質の替わりに、有機または無機あるいはこの両者を組み合わせた固体の正孔輸送材料を使用することができる。
（a）有機正孔輸送材料
本発明に適用可能な有機正孔輸送材料としては、J.Hagen et al.,Synthetic Metal 89(1997)215-220、Nature,Vol.395, 8 Oct. 1998,p583-585およびWO97/10617、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、特開平4−308688号公報、米国特許第4，764，625号、特開平3−269084号公報、特開平4−129271号公報、特開平4−175395号公報、特開平4−264189号公報、特開平4−290851号公報、特開平4−364153号公報、特開平5−25473号公報、特開平5−239455号公報、特開平5−320634号公報、特開平6−1972号公報、特開平7-138562号、特開平7-252474号、特開平11-144773等に示される芳香族アミン類や、特開平11-149821号、特開平11-148067号、特開平11-176489号公報等に記載のトリフェニレン誘導体類を好ましく用いることができる。また、Adv. Mater. 1997,9,N0.7,p557、Angew. Chem. Int. Ed. Engl. 1995, 34, No.3,p303-307、JACS,Vol120, N0.4,1998,p664-672等に記載されているオリゴチオフェン化合物、K. Murakoshi et al.,;Chem. Lett. 1997, p471に記載のポリピロール、“Handbook of Organic Conductive Molecules and Polymers Vol.1,2,3,4”（NALWA著、WILEY出版）に記載されているポリアセチレンおよびその誘導体、ポリ(p-フェニレン) およびその誘導体、ポリ( p-フェニレンビニレン) およびその誘導体、ポリチエニレンビニレンおよびその誘導体、ポリチオフェンおよびその誘導体、ポリアニリンおよびその誘導体、ポリトルイジンおよびその誘導体等の導電性高分子を好ましく使用することができる。
【００７９】
正孔（ホール）輸送材料にはNature,Vol.395, 8 Oct. 1998,p583-585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添加したり、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[(CF₃SO₂)₂N]のような塩を添加しても構わない。
【００８０】
（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る。この目的のｐ型無機化合物半導体は、バンドギャップが2eV以上であることが好ましく、さらに2.5eV以上であることが好ましい。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できる条件から、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ってくるが、一般に4.5eV以上5.5eV以下であることが好ましく、さらに4.7eV以上5.3eV以下であることが好ましい。好ましいｐ型無機化合物半導体は一価の銅を含む化合物半導体であり、一価の銅を含む化合物半導体の例としてはCuI, CuSCN, CuInSe₂, Cu(In,Ga)Se₂, CuGaSe₂, Cu₂O, CuS, CuGaS₂, CuInS₂, CuAlSe₂などが挙げられる。この中でもCuIおよび CuSCNが好ましく、CuIが最も好ましい。このほかのｐ型無機化合物半導体として、GaP、NiO、CoO、FeO、Bi₂O₃、MoO₂、Cr₂O₃等を用いることができる。
【００８１】
（５）電荷輸送層の形成
電荷輸送層の形成方法に関しては２通りの方法が考えられる。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。
【００８２】
前者の場合、電荷輸送層の挟み込み方法として、浸漬等による毛管現象を利用する常圧プロセス、また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。
【００８３】
後者の場合、湿式の電荷輸送層においては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ことになる。またゲル電解質の場合には湿式で塗布して重合等の方法により固体化する方法があり、その場合には乾燥、固定化した後に対極を付与することもできる。電解液のほか湿式有機正孔輸送材料やゲル電解質を付与する方法としては、前述の半導体微粒子層や色素の付与と同様の方法を利用できる。
【００８４】
固体電解質や固体の正孔（ホール）輸送材料の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、光電解重合法等の手法により電極内部に導入することができる。無機固体化合物の場合も、キャスト法、塗布法、スピンコート法、浸漬法、電解析出法、無電解メッキ法等の手法により電極内部に導入することができる。
【００８５】
（D）対極
対極は前記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材としては、金属（例えば白金、金、銀、銅、アルミニウム、マグネシウム、インジウム等）、炭素、または導電性金属酸化物（インジウム−スズ複合酸化物、フッ素ドープ酸化スズ、等）が挙げられる。この中でも白金、金、銀、銅、アルミニウム、マグネシウムを対極層として好ましく使用することができる。対極の好ましい支持基板の例は、ガラスまたはプラスチックであり、これに上記の導電剤を塗布または蒸着して用いる。対極導電層の厚さは特に制限されないが、3nm〜10μmが好ましい。対極層の表面抵抗は低い程よい。好ましい表面抵抗の範囲としては50Ω／□以下であり、さらに好ましくは20Ω／□以下である。
【００８６】
導電性支持体と対極のいずれか一方また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。このような対極としては、金属または導電性の酸化物を蒸着したガラスまたはプラスチック、あるいは金属薄膜を使用できる。
【００８７】
対極は、電荷輸送層上に直接導電材を塗布、メッキまたは蒸着（PVD、CVD）するか、導電層を有する基板の導電層側を貼り付ければよい。また、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。なお、好ましい金属リードの材質および設置方法、金属リード設置による入射光量の低下等は導電性支持体の場合と同じである。
【００８８】
（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、予め導電性支持体と感光層の間に緻密な半導体の薄膜層を下塗り層として塗設しておくことが好ましく、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。下塗り層として好ましいのはTiO₂、SnO₂、Fe₂O₃、WO₃、ZnO、Nb₂O₅であり、さらに好ましくはTiO₂である。下塗り層は、例えばElectrochim. Acta 40, 643-652(1995)に記載されているスプレーパイロリシス法の他、スパッタ法等により塗設することができる。下塗り層の好ましい膜厚は5〜1000nm以下であり、10〜500nmがさらに好ましい。
【００８９】
また、電極として作用する導電性支持体と対極の一方または両方の外側表面、導電層と基板の間または基板の中間に、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には、その材質に応じて塗布法、蒸着法、貼り付け法等を用いることができる。
【００９０】
（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。図２〜図９に本発明に好ましく適用できる光電変換素子の内部構造を例示する。
【００９１】
図２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は、透明基板50a上に一部金属リード11を設け、さらに透明導電層10aを設け、下塗り層60、感光層20、電荷輸送層30および対極導電層40をこの順で設け、さらに支持基板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は、支持基板50上にさらに導電層10を有し、下塗り層60を介して感光層20を設け、さらに電荷輸送層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は、透明基板50a上に一部金属リード11を設け、さらに透明導電層10a（または40a）を設けたもの１組の間に下塗り層60と感光層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である。図６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および対極導電層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、さらに電荷輸送層30および透明対極導電層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、さらに電荷輸送層30および透明対極導電層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、さら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または金属リード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。
【００９２】
〔２〕光電池
本発明の光電池は、上記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。光電池は構成物の劣化や内容物の揮散を防止するために、側面をポリマーや接着剤等で密封するのが好ましい。導電性支持体および対極にリードを介して接続される外部回路自体は公知のものでよい。本発明の光電変換素子を太陽電池に適用する場合、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得る。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など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、本発明の色素増感型太陽電池も使用目的や使用場所および環境により、適宜これらのモジュール構造を選択できる。具体的には、特開2000-268892号公報に記載の構造や態様とすることが好ましい。
【００９３】
【実施例】
以下、本発明を実施例によって具体的に説明する。
【００９４】
１．塗布液の作製
（１）ZnO含有TiO₂分散液の調製
オートクレーブ温度を240℃にした以外はバルベらのジャーナル・オブ・アメリカン・セラミック・ソサエティ 第80巻3157頁記載の方法と同様の方法で二酸化チタン濃度１０重量％の二酸化チタン分散物を得た。できた二酸化チタン粒子の平均粒径は約１７nmであった。TiO₂分散物１００ｇに２ｇのポリエチレングリコール（分子量20000、和光純薬製）、１０ｇのエタノール、１．５ｍｌの１Ｎ水酸化カリウム水溶液を添加し、２０分間よく撹拌した。この液にさらにZnO（粒径２０ｎｍ、または粒径３００ｎｍ、いずれも和光純薬製）を表１に示す量だけ添加し、１時間撹拌し、塗布液Ａ−１からＡ−６を得た。
【００９５】
（２）MgO含有TiO₂分散液の調製
ZnOに代えてMgO（粒径２００ｎｍ、和光純薬製）を表１に示す量だけ添加する以外は（１）と同様にして塗布液Ｂ−１からＢ−３を得た。
【００９６】
（３）比較用分散液の調製
ZnOを添加しない以外は（１）と同様の方法で比較用TiO₂分散液Cを調製した。
【００９７】
【表１】

【００９８】
２．色素を吸着した二酸化チタン電極の作成
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（日本板硝子製、表面抵抗は約１０Ω／cm²）の導電面側に上記で得た塗布液をドクターブレードを用いて塗布し、２５℃で３０分間乾燥した後、電気炉（ヤマト科学製マッフル炉ＦＰ−３２型）で４５０℃にて３０分間焼成した。
つぎに、希硝酸（比重１．３８の硝酸を１０倍に希釈したもの）を溶解液として上記で作成した塗布物を３０分間浸漬し、乾燥後４５０℃にて１０分間再焼成した。このとき作成した塗布物の重量を測定し、塗布前の重量と比較することにより半導体微粒子の塗布量を求めた。次に、下記の色素（Ａ）０．３ミリモル／ｌを含む吸着液に１６時間浸漬した。吸着温度は２５℃、吸着液の溶媒はエタノール、ｔ−ブタノール、アセトニトリルの１：１：２（体積比）混合物である。
色素の吸着した二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た。
【００９９】
【化１４】

【０１００】
３．光電変換素子（光電気化学電池）の作成
上述のようにして作成した色素増感されたＴｉＯ₂電極基板を２cm×２cmの大きさに切断し、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０．７モル／リットル，ヨウ素０．０５モル／リットル、ｔ−ブチルピリジン０．０８モル／ｌのプロピオニトリル溶液）をしみこませてＴｉＯ₂電極中に導入することにより、表２に示す光電変換素子Ｃ−１〜Ｃ−１０を得た。
【０１０１】
本実施例により、図１０に示したとおり、導電性ガラス１（ガラス２上に導電剤層３が設層されたもの）、色素を吸着したＴｉＯ₂電極４、電解液５、白金層６およびガラス７が順に積層された光電変換素子が作成された。
【０１０２】
４．色素吸着量の測定
上記のようにして作成した色素吸着ＴｉＯ₂電極を１平方センチメートルの大きさに切り取り、０．１Nの水酸化カリウム水溶液に浸漬して溶出した色素溶液の吸光度から色素吸着量を求めた。単位面積あたりの色素吸着量が大きいほど、感光層の表面粗さが大きいと推定される。結果を表２に示す。
【０１０３】
５．光電変換効率の測定
５００Ｗのキセノンランプ（ウシオ製）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。この光の強度は垂直面において１００mW/cm²であった。光電変換素子（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２には実施例で作成された光電変換素子の変換効率を示した。
【０１０４】
【表２】

【０１０５】
Ｃ−１〜Ｃ−９（本発明）とＣ−１０（比較例）との比較から、本発明の方法を用いた光電変換素子はそうでない光電変換素子に比べて変換効率が高い事がわかる。ＺｎＯとＭｇＯでは、ＺｎＯの方が良好な結果を与えた。同じＺｎＯ同士の比較では粒径２０ｎｍのものの方が粒径３００ｎｍのものよりも良好な結果を与えた。
また、本発明の方法を用いた光電変換素子の方が、ＴｉＯ₂塗布量を同じにしたときの色素吸着量は多く、素子の作成過程における焼結によって感光層の表面粗さが低下するのも防止している。
【０１０６】
【発明の効果】
実施例の結果から本発明によって、従来よりも変換効率の改善された色素増感光電変換素子が得られたことは明らかである。
【図面の簡単な説明】
【図１】本発明の好ましい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】実施例で作成した光電変換素子の構成を示す断面図である。
【符号の説明】
１ 導電性ガラス
２ ガラス
３ 導電剤層
４ 色素吸着ＴｉＯ２電極
５ 電解液
６ 白金層
７ ガラス
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 photoelectric conversion element, and more particularly to a photoelectric conversion element using semiconductor fine particles sensitized with a dye.
[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, or combinations thereof have been put to practical use as photoelectric conversion elements.
[0003]
U.S. Pat. Nos. 4,927,721, 4,684,537, 5,084,365, 5,350,644, 5,463,057, 5,525,440, WO98 / 50393, and JP-A-7-249790, JP-A-10-504521 Discloses a photoelectric conversion element using semiconductor fine particles sensitized with a dye (hereinafter abbreviated as a dye-sensitized photoelectric conversion element), or a material and a manufacturing technique for producing the photoelectric conversion element. The advantage of this method is that an inexpensive oxide semiconductor such as titanium dioxide can be used without being purified with high purity, and therefore a relatively inexpensive photoelectric conversion element can be provided.
In particular, in these methods, it is a technical point to create voids in the layer of semiconductor fine particles, and simultaneously ensure a surface area for sufficiently adsorbing the dye and a space for diffusing the electrolyte. As a method for forming such voids, a method is used in which an organic substance (for example, polyethylene glycol, polystyrene, etc.) that decomposes and disappears into carbon dioxide and water by firing is applied together with semiconductor fine particles and heated to 300 ° C. to 600 ° C. ing.
However, in spite of such technical ideas, these photoelectric conversion elements do not always have a sufficiently high conversion efficiency, and further improvement in conversion efficiency has been desired.
Further, it is known that the surface of the layer is smoothed by sintering in the step of converting the semiconductor fine particles into the semiconductor fine particle layer, and the surface roughness is lowered.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a dye-sensitized photoelectric conversion element having improved conversion efficiency.
[0005]
[Means for Solving the Problems]
  As a result of research, the following (1) to (4) Was found to be suitable for the purposes of the present invention.
(1) A method for producing a photoelectric conversion element having at least a semiconductor fine particle layer and a conductive support,
  A dispersion obtained by mixing semiconductor fine particles and MgO or ZnO as soluble fine particles is applied onto the conductive support, and a semiconductor fine particle layer comprising a soluble portion made of the soluble fine particles and an insoluble portion made of the semiconductor fine particles is formed. After forming
  A method for producing a photoelectric conversion element, wherein a gap is generated by dissolving and removing the soluble portion.
(2) The method for producing a photoelectric conversion element according to (1), wherein the semiconductor fine particles adsorb a dye.
(3) The method for producing a photoelectric conversion element according to (1) or (2), wherein the semiconductor fine particles are an oxide semiconductor selected from titanium oxide, niobium oxide, tin oxide, and tungsten oxide.
(4) The method for producing a photoelectric conversion element according to any one of (1) to (3), wherein the soluble particles are dissolved and removed by being immersed in an acid or a water-soluble ligand..
In addition, this invention is said (1)-(4), But other matters are listed below for reference.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[1] Photoelectric conversion element
As shown in FIG. 1, the photoelectric conversion element of the present invention is preferably formed by laminating a conductive layer 10, an undercoat layer 60, a photosensitive layer 20, a charge transport layer 30, and a counter conductive layer 40 in this order. And the charge transport material 23 that has penetrated into the gaps between the semiconductor fine particles 21 and the semiconductor fine particles 21 sensitized by the above. The charge transport material 23 is composed of the same components as the material used for the charge transport layer 30. Further, a substrate 50 may be provided as a base for the conductive layer 10 and / or the counter electrode conductive layer 40 in order to impart strength to the photoelectric conversion element. In the present invention, the layer composed of the conductive layer 10 and the optional substrate 50 is hereinafter referred to as “conductive support”, and the layer composed of the counter electrode conductive layer 40 and the optional substrate 50 is referred to as “counter electrode”.
In the present invention, the photosensitive layer 20 may be composed of a plurality of layers having different light scattering properties.
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. A photocell is made for the purpose of generating electrical work by connecting this photoelectric conversion element to an external load (power generation), and a photosensor is made for the purpose of sensing optical information. Among the photovoltaic cells, the case where the charge transport material 23 is mainly made 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.
[0007]
(A) Conductive support
The conductive support is composed of (1) a single layer of a conductive layer, or (2) two layers of a conductive layer and a substrate. If a conductive layer that can maintain sufficient strength and sealing properties is used, a substrate is not always necessary.
[0008]
In the case of (1), a conductive layer having sufficient strength as metal and having conductivity is used.
[0009]
In the case of (2), a substrate having a conductive layer containing a conductive agent on the photosensitive layer side can be used. Preferred conductive agents include metals (eg, platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), carbon, or conductive metal oxides (indium-tin composite oxide (ITO), tin oxide doped with fluorine). Etc.). The thickness of the conductive layer is preferably about 0.02 to 10 μm.
[0010]
The lower the surface resistance of the conductive support, the better. The range of the 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 / □.
[0011]
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, preferably 50% or more, and particularly preferably 70% or more.
[0012]
The transparent conductive support is preferably formed by applying or vapor-depositing a transparent conductive layer made of a conductive metal oxide on the surface of a transparent substrate such as glass or plastic. In particular, conductive glass in which a conductive layer made of tin dioxide doped with fluorine is deposited on a transparent substrate made of low-cost soda-lime float glass is preferable. In order to obtain a flexible photoelectric conversion element or solar cell at low cost, it is preferable to use a transparent polymer film provided with a conductive layer. Transparent polymer film materials include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polyester (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), and polyarylate. (PAr), polysulfone (PSF), polyester sulfone (PES), polyetherimide (PEI), cyclic polyolefin, brominated phenoxy and the like. In order to ensure sufficient transparency, the amount of conductive metal oxide applied is 1 m of glass or plastic support.²The amount is preferably 0.01 to 100 g.
[0013]
It is preferable to use a metal lead for the purpose of reducing the resistance of the transparent conductive support. The material of the metal lead is preferably a metal such as aluminum, copper, silver, gold, platinum, nickel, and particularly preferably aluminum and silver. The metal lead is preferably installed on a transparent substrate by vapor deposition, sputtering, or the like, and a transparent conductive layer made of tin oxide doped with fluorine or an ITO film is preferably provided thereon. 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%.
[0014]
(B) Photosensitive layer
The photosensitive layer is a dye-sensitized layer of semiconductor fine particles. In the photosensitive layer, the semiconductor acts as a so-called photoconductor, absorbs light, separates charges, and generates 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 the electrons. The semiconductor used in the present invention is preferably an n-type semiconductor that gives an anode current when conductor electrons become carriers under photoexcitation.
[0015]
In the present invention, the photosensitive layer is prepared as follows.
First, a mixed dispersion solution of semiconductor fine particles and soluble fine particles is prepared, and this is applied or printed on a support and heat-treated. Subsequently, it is immersed in a solution for dissolving soluble fine particles (hereinafter referred to as a dissolving solution) to remove the soluble fine particles. As a result, a semiconductor fine particle layer in which the portion where the soluble fine particles are present becomes voids is obtained. This is heat-treated and then immersed in a dye solution to obtain a dye-sensitized semiconductor fine particle layer, that is, a photosensitive layer. Hereinafter, each component and manufacturing process will be described in detail.
[0016]
(1) Semiconductor fine particles
Semiconductor fine particles include simple semiconductors such as silicon and germanium, III-V compound semiconductors, metal chalcogenides (eg oxides, sulfides, selenides, etc.), or compounds having a perovskite structure (eg strontium titanate, titanium). Calcium oxide, sodium titanate, barium titanate, potassium niobate, etc.) can be used.
[0017]
Preferred metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxides, cadmium, zinc, lead, silver, antimony or Bismuth sulfide, cadmium or lead selenide, cadmium telluride and the like. Examples of other compound semiconductors include phosphides such as zinc, gallium, indium, and cadmium, gallium-arsenic or copper-indium selenides, and copper-indium sulfides.
[0018]
Preferred specific examples of the semiconductor used in the present invention include Si and TiO.₂, SnO₂, Al₂O_Three, Fe₂O_Three, WO_Three, Nb₂O_Five, CdS, Bi₂S_Three, CdSe, CdTe, GaP, InP, GaAs, CuInS₂, CuInSe₂And more preferably TiO₂, SnO₂, WO_Three, Nb₂O_Five, TiO₂, Al₂O_ThreeAnd particularly preferably TiO₂It is. Further, two or more kinds of semiconductor fine particles may be mixed and used.
[0019]
The particle size of the semiconductor fine particles is generally on the order of nm to μm, but the average particle size of the primary particles obtained from the diameter when the projected area is converted into a circle is preferably 5 to 500 nm, more preferably 10 to 300 nm. preferable.
[0020]
Semiconductor fine particles are prepared by Sakuo Sakuo's "Sol-gel Method Science" Agne Jofusha (1998), Technical Information Association "Sol-gel Method Thin Film Coating Technology" (1995), etc. The sol-gel method described, Tadao Sugimoto's "Synthesis of monodisperse particles by the new synthesis gel-sol method and size morphology control", Materia, Vol. 35, No. 9, pp. 1012-1018 (1996) The gel-sol method described in 1 is preferred. Also preferred is a method developed by Degussa to produce an oxide by high-temperature hydrolysis of chloride in an oxyhydrogen salt.
[0021]
When the semiconductor fine particles are titanium oxide, the above sol-gel method, gel-sol method, and high-temperature hydrolysis method in oxyhydrogen salt of chloride are preferred, but Kiyoshi Manabu's “Titanium oxide properties and applied technology” The sulfuric acid method and the chlorine method described in Gihodo Publishing (1997) can also be used. Further, as the sol-gel method, the method described in Journal of American Ceramic Society of Barbe et al., Vol. 80, No. 12, pp. 3157-3171 (1997), the chemistry of Burnside et al. The method described in Materials, Vol. 10, No. 9, pages 2419-2425 is also preferable.
[0022]
(2) Soluble fine particles
In the present invention, soluble fine particles are used for elution by soaking in a solution to form voids. The soluble fine particles may be fine particles having a property of maintaining a fine particle state in a specific solvent and dissolving when immersed in another solvent or solution. For example, organic fine particles that are insoluble in water and soluble in specific organic solvents, inorganic fine particles that are insoluble in specific organic solvents and soluble in water, insoluble in neutral or basic water, acid or acidic Water-soluble basic oxides or hydroxide fine particles, transition metal chalcogenides soluble in specific water-soluble ligands or water-soluble chelating agents, transition metal halide fine particles, etc. should be used as soluble fine particles it can.
Among these, basic oxide fine particles (for example, ZnO, MgO, Ag)₂O) and transition metal oxide fine particles (for example, iron oxide, nickel oxide, cobalt oxide, copper oxide, etc.) are preferable. Of these, MgO and ZnO are particularly preferred.
[0023]
The soluble fine particles are removed by the dissolving liquid and play a role of creating voids in the semiconductor fine particle layer. Therefore, the particle diameter of the soluble fine particles is selected depending on the desired size of the voids. The particle diameter of the soluble fine particles is preferably 5 to 1500 nm, and more preferably 10 to 500 nm.
If the amount of the soluble fine particles is small, the effect is small, and if the amount is too large, the mechanical strength of the semiconductor fine particle layer is lowered. In the present invention, the addition amount of the soluble fine particles is preferably 0.1% by weight or more and 50% by weight or less, more preferably 1% by weight or more and 20% by weight or less with respect to the semiconductor fine particles.
[0024]
Semiconductor fine particles and soluble fine particles having the same composition may be used. In this case, a soluble portion and an insoluble portion are provided in the photosensitive layer from fine particles having the same composition. For example, if the fine particles are removed using semiconductor fine particles with different particle sizes, or if the surface of the fine particles is treated to make it slightly soluble or insoluble, soluble parts and insoluble parts are formed in fine particles of the same composition. It becomes possible to make it.
[0025]
(3) Method for applying semiconductor fine particles and soluble fine particles
In addition to the sol-gel method described above, a method for producing a dispersion of semiconductor fine particles includes a method of grinding with a mortar, a method of dispersing while grinding using a mill, or a fine particle in a solvent when synthesizing a semiconductor. The method of depositing and using as it is is mentioned. A dispersion of soluble fine particles can be prepared in the same manner as the semiconductor fine particle dispersion. The semiconductor fine particle dispersion and the soluble fine particle dispersion may be separately dispersed and mixed, or may be simultaneously dispersed. Semiconductor fine particles and soluble fine particles are mixed before coating. A dispersion in which semiconductor fine particles and soluble fine particles are mixed is hereinafter simply referred to as a dispersion.
[0026]
Examples of the dispersion medium include water or various organic solvents (for example, methanol, ethanol, isopropyl alcohol, dichloromethane, acetone, acetonitrile, ethyl acetate, and the like). At the time of dispersion, a polymer such as polyethylene glycol, a surfactant, an acid, a chelating agent, or the like may be used as a dispersion aid as necessary. By changing the molecular weight of polyethylene glycol, a film that does not easily peel off can be formed, and the viscosity of the dispersion can be adjusted. Therefore, it is preferable to add polyethylene glycol.
[0027]
As application methods, roller method, dip method, etc. as application system, air knife method, blade method, etc. as metering system, and application and metering can be made the same part, disclosed in Japanese Patent Publication No. 58-4589 The wire bar method, the slide hopper method, the extrusion method, the curtain method, etc. described in US Pat. Nos. 2,681,294, 2761419, 2761791 and the like are preferable. 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. From these, a preferred film forming method is selected according to the liquid viscosity and the wet thickness.
[0028]
The viscosity of the dispersion liquid of semiconductor fine particles and soluble fine particles greatly depends on the kind and dispersibility of the semiconductor fine particles and soluble fine particles, the type of solvent used, and additives such as surfactants and binders. For high-viscosity liquids (for example, 0.01 to 500 Poise), an extrusion method, a casting method, a screen printing method and the like are preferable. For low-viscosity liquids (for example, 0.1 Poise or less), the slide hopper method, wire bar method, or spin method is preferable, and a uniform layer can be formed. In addition, even if it is a low-viscosity liquid if there is a certain amount of application | coating, the application | coating by the extrusion method is possible. Thus, a wet film forming method may be selected as appropriate according to the viscosity of the coating solution, the coating amount, the support, the coating speed, and the like.
[0029]
Moreover, you may apply | coat multilayered the dispersion liquid from which a component differs. For multilayer coating, an extrusion method or a slide hopper method is suitable. In the case of applying multiple layers, the multiple layers may be applied at the same time, or may be sequentially applied several times to several dozen times. A screen printing method can also be preferably used as long as it is sequentially overcoated. In the case of a multilayer structure, the structure of the present invention must be applied to at least one layer in order to increase the conversion efficiency.
[0030]
Next, a film containing semiconductor fine particles and soluble fine particles is immersed in a dissolving solution, and only soluble fine particles are dissolved to form a semiconductor fine particle layer having voids. At this time, the dissolving liquid is not particularly limited as long as it does not substantially dissolve the semiconductor fine particles and dissolves the soluble fine particles. That is, the solution is selected according to the solubility of the soluble fine particles.
For example, when the soluble fine particles are organic fine particles that are soluble in a specific organic solvent, the solution is the specific organic solvent. If the soluble fine particles are inorganic compound fine particles soluble in water, the solution is water. When the soluble fine particles are fine particles of basic oxide or hydroxide that are insoluble in neutral or basic water and soluble in acid or acidic water, the solution is an acid. In this case, the acid is, for example, various mineral acids (for example, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, perchloric acid, etc.) or an aqueous solution thereof, various organic acids, an aqueous solution thereof, or an organic solvent solution. When the soluble fine particles are transition metal chalcogenides or transition metal halides soluble in a specific water-soluble ligand or water-soluble chelating agent, the solution is an aqueous solution containing these ligands or chelating agents. Basic oxide fine particles (eg ZnO, MgO, Ag) as soluble fine particles₂O) and transition metal oxide fine particles (for example, iron oxide, nickel oxide, cobalt oxide, copper oxide, etc.) have been described above. Correspondingly, as the solution, mineral acid, various ligands (for example, thiocyanate, thiosulfate, halide salt, cyanide salt, cyanate, etc.) or various chelating agents (for example, ethylenediamine Acetate, nitrilotriacetate, iminodiacetate, pyridinecarboxylate, hydroxyquinoline derivative, 1,3-diketone derivative, 2,2′-bipyridine derivative, etc.) are preferred.
[0031]
As a dipping method, a sheet-like material in which semiconductor fine particles and soluble fine particles are coated on a support may be dipped one by one in a solution, or may be passed through a bath of solution while being continuously applied. . There is no particular limitation on the immersion time, but it is typically 1 minute to 1 hour.
[0032]
After the semiconductor fine particles are coated on the conductive support, the semiconductor fine particles are brought into electronic contact with each other, and heat treatment (baking) is performed in order to improve the strength of the semiconductor fine particle layer and the adhesion to the support. Is preferred. A preferable heating temperature range is 40 ° C. or more and 700 ° C. or less, and more preferably 100 ° C. or more and 600 ° C. or less. The heating time is about 10 minutes to 10 hours. When using a support 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 support. Moreover, it is preferable that it is as low as possible also from a viewpoint of cost.
In the case of the present invention, the heat treatment may be performed before or after immersion in the solution. Moreover, you may perform twice before and behind immersion of a solution. When a multilayered photosensitive layer is obtained, coating and heat treatment may be sequentially repeated.
[0033]
In order to increase the surface area of the semiconductor fine particles after heat treatment or after immersion in the solution, increase the purity in the vicinity of the semiconductor fine particles, and increase the efficiency of electron injection from the dye to the semiconductor fine particles, for example, a chemical using a titanium tetrachloride aqueous solution A plating process or an electrochemical plating process using a titanium trichloride aqueous solution may be performed.
[0034]
In general, as the photosensitive layer becomes thicker, the amount of supported dye per unit projected area increases, so the light capture rate increases. However, the diffusion distance of the generated electrons increases, so the loss due to charge recombination also increases. Accordingly, the preferred thickness of the photosensitive layer is 0.1 to 100 μm. When used for a solar cell, the thickness of the photosensitive layer is preferably 1 to 30 μm, more preferably 2 to 25 μm. The total coating amount of semiconductor fine particles is 1m on the support.²0.5 to 100 g per unit is preferable, and 5 to 50 g is more preferable. Further, the larger the surface area, the greater the amount of dye adsorbed and the higher the light capture rate, so the surface area in the state where the photosensitive layer is coated on the support is preferably 10 times or more the projected area, Further, it is preferably 100 times or more. The upper limit is not particularly limited, but is usually about 300 to 1000 times. In order to increase the surface area relative to the projected area, it is preferable to increase the surface roughness of the photosensitive layer.
[0035]
(4) Dye
The sensitizing dye used in the photosensitive layer can be arbitrarily used as long as it is a compound that has absorption in the visible region and near infrared region and can sensitize a semiconductor. However, an organometallic complex dye, a methine dye, a porphyrin dye, or a phthalocyanine System dyes are preferred. 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 together or mixed. In this case, it is possible to select the dye to be used or mixed and the ratio thereof so as to match the wavelength range and intensity distribution of the target light source.
[0036]
Such a dye preferably has an appropriate interlocking group capable of adsorbing to the surface of the semiconductor fine particles. Preferred linking groups include COOH groups, OH groups, SO₂H group, -P (O) (OH)₂Group or -OP (O) (OH)₂An acidic group such as a group, or a chelating group having π conductivity such as oxime, dioxime, hydroxyquinoline, salicylate or α-ketoenolate. Among them, COOH group, -P (O) (OH)₂Group or -OP (O) (OH)₂The group is particularly preferred. These 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.
[0037]
Hereinafter, preferred sensitizing dyes used in the photosensitive layer will be specifically described.
(A) Organometallic complex dye
When the dye is a metal complex dye, a metal phthalocyanine dye, a metal porphyrin dye or a ruthenium complex dye is preferable, and a ruthenium complex dye is particularly preferable. Examples of ruthenium complex dyes include, for example, U.S. Pat. / 50393, JP-A 2000-26487, and the like.
[0038]
Further, the ruthenium complex dye used in the present invention has the following general formula (I):
(A1) pRu (B-a) (B-b) (B-c) (I)
Is preferably represented by: In the general formula (I), A1 represents a monodentate or bidentate ligand, Cl, SCN, H₂Preference is given to ligands selected from the group consisting of O, Br, I, CN, NCO and SeCN, and derivatives of β-diketones, oxalic acid and dithiocarbamic acid. p is an integer of 0-3. B-a, B-b and B-c are each independently represented by the following formulas B-1 to B-10:
[0039]
[Chemical 1]

[0040]
(However, R_aRepresents a hydrogen atom or a substituent. Examples of the substituent include a halogen atom, a substituted or unsubstituted alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 12 carbon atoms, and a carbon atom. Examples of the substituted or unsubstituted aryl group of 6 to 12 or the above-mentioned acidic groups (these acidic groups may form a salt) and chelating groups are included. The alkyl part of the alkyl group and the aralkyl group is The aryl part of the aryl group and the aralkyl group may be monocyclic or polycyclic (fused ring, ring assembly). ) Represents an organic ligand selected from the compounds represented by: B-a, B-b and B-c may be the same or different, and may be any one or two.
[0041]
Although the preferable specific example of an organometallic complex pigment | dye is shown below, this invention is not limited to these.
[0042]
[Chemical 2]

[0043]
[Chemical Formula 3]

[0044]
(B) Methine dye
Preferred methine dyes for use in the present invention are polymethine dyes such as cyanine dyes, merocyanine dyes, squarylium dyes. Examples of polymethine dyes preferably used in the present invention include JP-A-11-35836, JP-A-11-67285, JP-A-11-86916, JP-A-11-97725, JP-A-11-158395, and JP-A-11. -163378, JP-A-11-214730, JP-A-11-214731, JP-A-11-238905, JP-A2000-26487, European Patents 892411, 911841, and 991092 It is a pigment. Specific examples of preferred methine dyes are shown below.
[0045]
[Formula 4]

[0046]
[Chemical formula 5]

[0047]
(4) Adsorption of dye to semiconductor fine particles
In order to adsorb the dye to the semiconductor fine particles, a method of immersing a conductive support having a well-dried semiconductor fine particle layer in the dye solution or coating the dye fine solution on the semiconductor fine particle layer can be used. In the former case, an immersion method, a dip method, a roller method, an air knife method or the like can be used. In the case of the immersion method, 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. Examples of the latter application method include a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, and a spray method. Further, the 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.
[0048]
Preferred solvents for dissolving the dye include, for example, alcohols (methanol, ethanol, t-butanol, benzyl alcohol, etc.), nitriles (acetonitrile, propionitrile, 3-methoxypropionitrile, etc.), nitromethane, halogenated compounds, etc. Hydrocarbon (dichloromethane, dichloroethane, chloroform, chlorobenzene, etc.), ethers (diethyl ether, tetrahydrofuran, etc.), dimethyl sulfoxide, amides (N, N-dimethylformamide, N, N-dimethylacetamide, etc.), N-methyl Pyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters (ethyl acetate, butyl acetate, etc.), carbonates (diethyl carbonate, ethylene carbonate, propylene carbonate, etc.), ketones (acetone, 2-butanone) , Cyclohexanone, etc.), Examples include hydrocarbons (hexane, petroleum ether, benzene, toluene, etc.) and mixed solvents thereof.
[0049]
The total amount of dye adsorbed is the unit area of the photosensitive layer (1m²) Is preferably from 0.01 to 100 mmol. Further, the adsorption amount of the dye to the semiconductor fine particles is preferably in the range of 0.01 to 1 mmol per 1 g of the semiconductor fine particles. By using such an amount of dye adsorbed, a sensitizing effect in a semiconductor can be sufficiently obtained. On the other hand, if the amount of the dye is too small, the sensitizing effect becomes insufficient, and if the amount of the dye is too large, the dye not attached to the semiconductor floats, which causes a reduction in the sensitizing effect. In order to increase the adsorption amount of the dye, it is preferable to perform a heat treatment before the adsorption. In order to avoid water adsorbing on the surface of the semiconductor fine particles after the heat treatment, it is preferable to quickly perform the dye adsorption operation at a temperature of the semiconductor electrode substrate of 60 to 150 ° C. without returning to normal temperature. Further, for the purpose of reducing the interaction such as aggregation between the dyes, a colorless compound may be added to the dyes and co-adsorbed on the semiconductor fine particles. Compounds effective for this purpose are compounds having surface active properties and structures, and examples thereof include steroid compounds having a carboxyl group (for example, chenodeoxycholic acid) and sulfonates such as the following examples.
[0050]
[Chemical 6]

[0051]
The unadsorbed dye is preferably removed by washing immediately after adsorption. It is preferable to use a wet cleaning tank and perform cleaning with a polar solvent such as acetonitrile or an organic solvent such as an alcohol solvent. After adsorbing the dye, the surface of the semiconductor fine particles may be treated with an amine or a quaternary salt. Preferable amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like, and preferable quaternary salts include tetrobutylammonium iodide, tetrahexylammonium iodide and the like. When these are liquids, they may be used as they are, or may be used after being dissolved in an organic solvent.
[0052]
(C) Charge transport layer
The charge transport layer is a layer containing a charge transport material having a function of replenishing electrons to the oxidant of the dye. Examples of typical charge transport materials that can be used in the present invention include: (i) a solution (electrolyte) in which redox pair ions are dissolved as an ion transport material; Examples include so-called gel electrolytes impregnated in the above, molten salt electrolytes containing redox counterions, and solid electrolytes, and compositions containing these electrolytes (electrolyte compositions) can be used for the charge transport layer.
In addition to charge transport materials that involve ions, (ii) electron transport materials and hole transport materials can also be used as charge transport materials that involve carrier movement in solids. These charge transport materials can be used in combination.
[0053]
(1) Molten salt electrolyte
The molten salt electrolyte is particularly preferable from the viewpoint of achieving both photoelectric conversion efficiency and durability.
The molten salt electrolyte is an electrolyte that is liquid at room temperature or has a low melting point. For example, WO95 / 18456, JP-A-8-259543, Electrochemistry, Vol. 65, No. 11, p. 923 (1997) And the like, known electrolytes such as pyridinium salts, imidazolium salts, and triazolium salts described in the above. A molten salt that becomes liquid at 100 ° C. or lower, particularly near room temperature, is preferred.
[0054]
Examples of the molten salt that can be preferably used include those represented by any of the following general formulas (Y-a), (Y-b), and (Y-c).
[0055]
[Chemical 7]

[0056]
Q in general formula (Y-a)_y1Represents an atomic group capable of forming a 5- or 6-membered aromatic cation with a nitrogen atom. Q_y1Is preferably composed of at least one atom selected from the group consisting of carbon atom, hydrogen atom, nitrogen atom, oxygen atom and sulfur atom. Q_y1The 5-membered ring formed by is preferably an oxazole ring, thiazole ring, imidazole ring, pyrazole ring, isoxazole ring, thiadiazole ring, oxadiazole ring, triazole ring, indole ring or pyrrole ring, A thiazole ring or an imidazole ring is more preferable, and an oxazole ring or an imidazole ring is particularly preferable. Q_y1The 6-membered ring formed by is preferably a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring or triazine ring, and more preferably a pyridine ring.
[0057]
In general formula (Y-b), A_y1Represents a nitrogen atom or a phosphorus atom.
[0058]
R in general formulas (Y-a), (Y-b) and (Y-c)_y1~ R_y6Each independently represents a substituted or unsubstituted alkyl group (preferably having 1 to 24 carbon atoms, which may be linear or branched or cyclic, such as a methyl group or an ethyl group Propyl group, isopropyl group, pentyl group, hexyl group, octyl group, 2-ethylhexyl group, t-octyl group, decyl group, dodecyl group, tetradecyl group, 2-hexyldecyl group, octadecyl group, cyclohexyl group, cyclopentyl group, etc. ), Or a substituted or unsubstituted alkenyl group (preferably having 2 to 24 carbon atoms, which may be linear or branched, such as vinyl group, allyl group, etc.), more preferably carbon An alkyl group having 2 to 18 atoms or an alkenyl group having 2 to 18 carbon atoms is preferable, and an alkyl group having 2 to 6 carbon atoms is particularly preferable.
[0059]
In addition, R in the general formula (Y-b)_y1~ R_y4Two or more of them connected to each other_y1May form a non-aromatic ring containing R in the general formula (Y-c)_y1~ R_y6Two or more of them may be connected to each other to form a ring structure.
[0060]
Q in general formulas (Y-a), (Y-b) and (Y-c)_y1And R_y1~ R_y6May have a substituent, and examples of preferable substituents include halogen atoms (F, Cl, Br, I, etc.), cyano groups, alkoxy groups (methoxy group, ethoxy group, methoxyethoxy group, methoxyethoxy group). Ethoxy groups, etc.), aryloxy groups (phenoxy groups, etc.), alkylthio groups (methylthio groups, ethylthio groups, etc.), alkoxycarbonyl groups (ethoxycarbonyl groups, etc.), carbonate groups (ethoxycarbonyloxy groups, etc.), acyl groups (acetyl groups) , Propionyl group, benzoyl group, etc.), sulfonyl group (methanesulfonyl group, benzenesulfonyl group, etc.), acyloxy group (acetoxy group, benzoyloxy group, etc.), sulfonyloxy group (methanesulfonyloxy group, toluenesulfonyloxy group, etc.), Phosphonyl group (such as diethylphosphonyl group), amide group (a Tilamino group, benzoylamino group, etc.), carbamoyl group (N, N-dimethylcarbamoyl group, etc.), alkyl group (methyl group, ethyl group, propyl group, isopropyl group, cyclopropyl group, butyl group, 2-carboxyethyl group, Benzyl group etc.), aryl group (phenyl group, toluyl group etc.), heterocyclic group (pyridyl group, imidazolyl group, furanyl group etc.), alkenyl group (vinyl group, 1-propenyl group etc.), silyl group, silyloxy group etc. Is mentioned.
[0061]
The compound represented by the general formula (Y-a), (Y-b) or (Y-c) is Q_y1Or R_y1~ R_y6A multimer may be formed via
[0062]
These molten salts may be used singly or as a mixture of two or more, and may be used in combination with a molten salt in which the iodine anion is replaced with another anion. Anions that replace iodine anions include halide ions (Cl^-, Br^-Etc.), SCN^-, BF_Four ^-, PF₆ ^-, ClO_Four ^-, (CF_ThreeSO₂)₂N^-, (CF_ThreeCF₂SO₂)₂N^-, CH_ThreeSO_Three ^-, CF_ThreeSO_Three ^-, CF_ThreeCOO^-, Ph_FourB^-, (CF_ThreeSO₂)_ThreeC^-Etc. are mentioned as preferred examples, such as SCN.^-, CF_ThreeSO_Three ^-, CF_ThreeCOO^-, (CF_ThreeSO₂)₂N^-Or BF_Four ^-It is more preferable that Also, other iodine salts such as LiI and CF_ThreeCOOLi, CF_ThreeAlkali metal salts such as COONa, LiSCN and NaSCN can also be added. The addition amount of the alkali metal salt is preferably about 0.02 to 2% by mass, and more preferably 0.1 to 1% by mass.
[0063]
Specific examples of the molten salt preferably used in the present invention are listed below, but are not limited thereto.
[0064]
[Chemical 8]

[0065]
[Chemical 9]

[0066]
Embedded image

[0067]
Embedded image

[0068]
Embedded image

[0069]
Embedded image

[0070]
The molten salt electrolyte is preferably in a molten state at room temperature, and preferably does not use a solvent. Although the solvent described later may be added, the content of the molten salt is preferably 50% by mass or more, and particularly preferably 90% by mass or more with respect to the entire electrolyte composition. Moreover, it is preferable that 50 mass% or more is an iodine salt among salts.
[0071]
It is preferable to add iodine to the electrolyte composition. In this case, the content of iodine is preferably 0.1 to 20% by mass, and preferably 0.5 to 5% by mass with respect to the entire electrolyte composition. More preferred.
[0072]
(2) Electrolyte
When an electrolytic solution is used for the charge transport layer, the electrolytic solution is preferably composed of an electrolyte, a solvent, and an additive. The electrolyte of the present invention is I₂And iodide (as iodide, LiI, NaI, KI, CsI, CaI₂Metal iodides such as tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide and the like quaternary ammonium compounds such as iodine salts), Br₂And bromide combinations (LiBr, NaBr, KBr, CsBr, CaBr as bromides)₂Metal bromide such as tetraalkylammonium bromide, pyridinium bromide, bromide salts of quaternary ammonium compounds), metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions, sodium polysulfide, Sulfur compounds such as alkylthiol-alkyldisulfides, viologen dyes, hydroquinone-quinones, and the like can be used. I among them₂An electrolyte that combines an iodine salt of a quaternary ammonium compound such as LiI, pyridinium iodide, and imidazolium iodide is preferable. The electrolytes described above may be used in combination.
[0073]
A preferable electrolyte concentration is 0.1 M or more and 10 M or less, and more preferably 0.2 M or more and 4 M or less. In addition, when iodine is added to the electrolytic solution, the preferable concentration of iodine is 0.01M or more and 0.5M or less.
[0074]
The solvent used for the electrolyte is desirably a compound having a low viscosity and improving ion mobility, or having a high dielectric constant and an effective carrier concentration, thereby exhibiting excellent ion conductivity. Examples of the solvent 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, and polyethylene. Chain ethers such as 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, polypropylene glycol monoalkyl ether, ethylene glycol, Propylene glycol, polyethylene glycol, polyp Examples include polyhydric alcohols such as pyrene glycol and glycerol, nitrile compounds such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile, aprotic polar substances such as dimethyl sulfoxide and sulfolane, and water. Can also be used in combination.
[0075]
In the present invention, bases such as tert-butylpyridine, 2-picoline, 2,6-lutidine and the like described in J. Am. Ceram. Soc., 80 (12) 3157-3171 (1997) are also used. It is preferable to add a functional compound to the aforementioned molten salt electrolyte or electrolytic solution. A preferable concentration range when adding a basic compound is 0.05M or more and 2M or less.
[0076]
(3) Gel electrolyte
In the present invention, the electrolyte is used by gelling (solidifying) the above-mentioned molten salt electrolyte or electrolyte 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. You can also In the case of gelation by adding a polymer, compounds described in “Polymer Electrolyte Reviews-1 and 2” (JRMacCallum and CA Vincent, edited by ELSEVIER APPLIED SCIENCE) can be used. Vinylidene chloride can be preferably used. In the case of gelation by adding an oil gelling agent, an industrial scientific journal (J. Chem Soc. Japan, Ind. Chem. Sec., 46,779 (1943), J. Am. Chem. Soc., 111,5542 (1989), J Chem. Soc., Chem. Com mun., 1993, 390, Angew. Chem. Int. Ed. Engl., 35, 1949 (1996), Chem. Lett., 1996, 885, J. Chm. Soc., Chem. Commun., 1997, 545) can be used, but preferred compounds are those having an amide structure in the molecular structure. An example of gelling the electrolytic solution is described in JP-A-11-185863, and an example of gelling the molten salt electrolyte is described in JP-A-2000-58140, which can also be applied to the present invention.
[0077]
Further, when the electrolyte is gelled by a polymer crosslinking reaction, it is desirable to use a polymer containing a crosslinkable reactive group and a crosslinking agent in combination. In this case, preferred crosslinkable reactive groups are amino groups and nitrogen-containing heterocycles (eg, pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, etc.) Preferred crosslinking agents include bifunctional or higher functional reagents capable of electrophilic reaction with nitrogen atoms (for example, alkyl halides, halogenated aralkyls, sulfonic acid esters, acid anhydrides, acid chlorides, isocyanate compounds, α , Β-unsaturated sulfonyl group-containing compound, α, β-unsaturated carbonyl group-containing compound, α, β-unsaturated nitrile group-containing compound, etc.), which are disclosed in JP-A Nos. 2000-17076 and 2000-86724. The described crosslinking techniques can also be applied.
[0078]
(4) Hole transport material
In the present invention, instead of an ion-conducting electrolyte such as a molten salt, a solid hole transport material that is organic or inorganic or a combination of both can be used.
(A) Organic hole transport material
Organic hole transport materials applicable to the present invention include J. Hagen et al., Synthetic Metal 89 (1997) 215-220, Nature, Vol. 395, 8 Oct. 1998, p583-585 and WO97 / 10617, JP-A-59-194393, JP-A-5-234681, U.S. Pat.No. 4,923,774, JP-A-4-308688, U.S. Pat.No. 4,764,625, JP-A-3-269084 No. 4, JP-A-4-129271, JP-A-4-175395, JP-A-4-264189, JP-A-4-290851, JP-A-4-364153, JP-A-5-25473. Aromatics shown in JP-A-5-239455, JP-A-5-320634, JP-A-6-1972, JP-A-7-138562, JP-A-7-252474, JP-A-11-144773, etc. Amines and triphenylene derivatives described in JP-A-11-149821, JP-A-11-148067, JP-A-11-176489 and the like can be preferably used. Also, Adv. Mater. 1997, 9, N0.7, p557, Angew. Chem. Int. Ed. Engl. 1995, 34, No. 3, p303-307, JACS, Vol120, N0.4, 1998, p664- 672, oligothiophene compounds described in K. Murakoshi et al.,; Chem. Lett. 1997, p471, “Handbook of Organic Conductive Molecules and Polymers Vol. 1, 2, 3, 4” ( Polyacetylene and its derivatives described in NALWA, published by WILEY), poly (p-phenylene) and its derivatives, poly (p-phenylenevinylene) and its derivatives, polythienylene vinylene and its derivatives, polythiophene and its derivatives, Conductive polymers such as polyaniline and derivatives thereof and polytoluidine and derivatives thereof can be preferably used.
[0079]
Hole transport materials contain tris (4-bromophenyl) aminium hexachloroantimonate to control dopant levels as described in Nature, Vol. 395, 8 Oct. 1998, p583-585. Li [(CF to add compounds containing such cation radicals or to control the potential of oxide semiconductor surfaces (space charge layer compensation)_ThreeSO₂)₂A salt such as N] may be added.
[0080]
(B) Inorganic hole transport material
A p-type inorganic compound semiconductor can be used as the inorganic hole transport material. The p-type inorganic compound semiconductor for this purpose preferably has a band gap of 2 eV or more, and 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-adsorbing electrode from the condition that the holes of the dye can be reduced. 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 eV or more and 5.5 eV or less, and more preferably 4.7 eV or more and 5.3 eV or less. Preferred p-type inorganic compound semiconductors are compound semiconductors containing monovalent copper. Examples of compound semiconductors containing monovalent copper include CuI, CuSCN, and CuInSe.₂, Cu (In, Ga) Se₂, CuGaSe₂, Cu₂O, CuS, CuGaS₂, CuInS₂, CuAlSe₂Etc. Among these, CuI and CuSCN are preferable, and CuI is most preferable. Other p-type inorganic compound semiconductors include GaP, NiO, CoO, FeO, and Bi.₂O_Three, MoO₂, Cr₂O_ThreeEtc. can be used.
[0081]
(5) Formation of charge transport layer
There are two possible methods for forming the charge transport layer. 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 provided directly on the photosensitive layer, and a counter electrode is subsequently provided.
[0082]
In the former case, as a method for sandwiching the charge transport layer, a normal pressure process using a capillary phenomenon due to immersion 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.
[0083]
In the latter case, in the wet charge transport layer, a counter electrode is provided without being dried, and measures for preventing liquid leakage at the edge portion are taken. In the case of a gel electrolyte, there is a method in which it is applied in a wet manner and solidified by a method such as polymerization. In this case, the counter electrode can be applied after drying and fixing. As a method for applying the wet organic hole transporting material and the gel electrolyte in addition to the electrolytic solution, the same methods as those for the semiconductor fine particle layer and the dye can be used.
[0084]
In the case of a solid electrolyte or a solid hole transport material, 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 technique such as a vacuum deposition method, a casting method, a coating method, a spin coating method, a dipping method, an electrolytic polymerization method, or a photoelectrolytic polymerization method. Also in the case of an inorganic solid compound, it can be introduced into the electrode by techniques such as casting, coating, spin coating, dipping, electrolytic deposition, and electroless plating.
[0085]
(D) Counter electrode
Similar to the conductive support described above, the 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. As a conductive material used for the counter electrode conductive layer, metal (for example, platinum, gold, silver, copper, aluminum, magnesium, indium, etc.), carbon, or conductive metal oxide (indium-tin composite oxide, fluorine-doped tin oxide, Etc.). Among these, platinum, gold, silver, copper, aluminum, and magnesium can be preferably used as the counter electrode layer. An example of a preferable supporting substrate for the counter electrode is glass or plastic, and the above-described conductive agent is applied or vapor-deposited on the glass or plastic. The thickness of the counter electrode conductive layer is not particularly limited, but is preferably 3 nm to 10 μm. The lower the surface resistance of the counter electrode layer, the better. The range of the surface resistance is preferably 50Ω / □ or less, more preferably 20Ω / □ or less.
[0086]
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 the 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. As such a counter electrode, glass or plastic on which a metal or a conductive oxide is deposited, or a metal thin film can be used.
[0087]
The counter electrode may be formed by directly applying, plating or vapor-depositing (PVD, CVD) a conductive material on the charge transport layer, or attaching the conductive layer side of the substrate having the conductive layer. Further, 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 metal lead material and installation method, the reduction in the amount of incident light due to the metal lead installation, and the like are the same as in the case of the conductive support.
[0088]
(E) Other layers
In order to prevent a short circuit between the counter electrode and the conductive support, it is preferable to coat a dense semiconductor thin film layer as an undercoat layer between the conductive support and the photosensitive layer in advance. This is particularly effective when a hole transport material is used. Preferred as an undercoat layer is TiO₂, SnO₂, Fe₂O_Three, WO_Three, ZnO, Nb₂O_FiveAnd more preferably TiO₂It is. The undercoat layer can be applied by, for example, a sputtering method in addition to the spray pyrolysis method described in Electrochim. Acta 40, 643-652 (1995). The preferred thickness of the undercoat layer is from 5 to 1000 nm, more preferably from 10 to 500 nm.
[0089]
Further, 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 acting as an electrode, between the conductive layer and the substrate, or in the middle of the substrate. For forming these functional layers, a coating method, a vapor deposition method, a bonding method, or the like can be used depending on the material.
[0090]
(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 depending on 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. 2 to 9 illustrate the internal structure of a photoelectric conversion element that can be preferably applied to the present invention.
[0091]
In FIG. 2, a photosensitive layer 20 and a charge transport layer 30 are interposed between a transparent conductive layer 10a and a transparent counter electrode conductive layer 40a, and light is incident from both sides. In FIG. 3, a part of the metal lead 11 is provided on the transparent substrate 50a, the transparent conductive layer 10a is further provided, the undercoat layer 60, the photosensitive layer 20, the charge transport layer 30 and the counter electrode conductive layer 40 are provided in this order and further supported. A substrate 50 is disposed, and light is incident from the conductive layer side. In FIG. 4, a conductive layer 10 is further provided on a support substrate 50, a photosensitive layer 20 is provided through an undercoat layer 60, a charge transport layer 30 and a transparent counter electrode conductive layer 40a are provided, and a metal lead 11 is partially provided. The transparent substrate 50a provided with the metal lead 11 side is arranged inside, and light is incident from the counter electrode side. FIG. 5 shows that an undercoat layer 60, a photosensitive layer 20, and a charge transport layer 30 are interposed between a pair of metal leads 11 provided on a transparent substrate 50a and a transparent conductive layer 10a (or 40a). In this structure, light enters from both sides. In FIG. 6, 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 are provided on a transparent substrate 50a, and a support substrate 50 is disposed thereon. It is a structure where light enters. 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, the charge transport layer 30 and the transparent counter electrode conductive layer 40a are provided, and the transparent substrate 50a is disposed thereon. In this structure, light is incident from the counter electrode side. In FIG. 8, a transparent conductive layer 10a is provided 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 substrate 50a is provided thereon. It is arranged and has a structure in which light enters from both sides. 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 structure in which light is incident from the counter electrode side.
[0092]
[2] Photocell
The photovoltaic cell of the present invention is one in which the photoelectric conversion element is made to work with an external load.
Of the photovoltaic cells, 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. In order to prevent deterioration of components and volatilization of the contents of the photovoltaic cell, it is preferable to seal the side surface with a polymer or an adhesive. The external circuit itself connected to the conductive support and the counter electrode via a lead may be a known one. 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 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 an amorphous silicon solar cell, and the like are known, and the dye-sensitized solar cell of the present invention is also used. These module structures can be appropriately selected depending on the place of use and the environment. Specifically, the structure and aspect described in JP-A-2000-268892 are preferable.
[0093]
【Example】
Hereinafter, the present invention will be specifically described by way of examples.
[0094]
1. Preparation of coating solution
(1) ZnO-containing TiO₂Preparation of dispersion
A titanium dioxide dispersion having a titanium dioxide concentration of 10% by weight was obtained in the same manner as described in Barbe et al., Journal of American Ceramic Society, Vol. 80, page 3157, except that the autoclave temperature was 240 ° C. The average particle diameter of the resulting titanium dioxide particles was about 17 nm. TiO₂To 100 g of the dispersion, 2 g of polyethylene glycol (molecular weight 20000, manufactured by Wako Pure Chemical Industries), 10 g of ethanol, and 1.5 ml of 1N aqueous potassium hydroxide solution were added and stirred well for 20 minutes. ZnO (particle size 20 nm or particle size 300 nm, both manufactured by Wako Pure Chemical Industries) was added to this solution in the amount shown in Table 1, and the mixture was stirred for 1 hour to obtain coating solutions A-1 to A-6.
[0095]
(2) MgO-containing TiO₂Preparation of dispersion
Coating solutions B-1 to B-3 were obtained in the same manner as in (1) except that MgO (particle size 200 nm, manufactured by Wako Pure Chemical Industries) was added in an amount shown in Table 1 instead of ZnO.
[0096]
(3) Preparation of comparative dispersion
TiO for comparison in the same way as (1) except that ZnO is not added₂Dispersion C was prepared.
[0097]
[Table 1]

[0098]
2. Preparation of dye-adsorbed titanium dioxide electrode
Transparent conductive glass coated with tin oxide doped with fluorine (manufactured by Nippon Sheet Glass, surface resistance is about 10Ω / cm²The coating solution obtained above was applied to the conductive surface side using a doctor blade, dried at 25 ° C. for 30 minutes, and then heated at 450 ° C. for 30 minutes in an electric furnace (Yamato Scientific muffle furnace FP-32 type). Baked.
Next, the above-prepared coating material was immersed for 30 minutes in dilute nitric acid (diluted nitric acid having a specific gravity of 1.38 10 times), dried, and refired at 450 ° C. for 10 minutes. The weight of the coated product prepared at this time was measured and compared with the weight before coating to determine the coating amount of the semiconductor fine particles. Next, it was immersed for 16 hours in an adsorption solution containing 0.3 mmol / l of the following dye (A). The adsorption temperature is 25 ° C., and the solvent of the adsorbent is a 1: 1: 2 (volume ratio) mixture of ethanol, t-butanol, and acetonitrile.
The dye-adsorbed titanium dioxide electrode was washed with ethanol and acetonitrile sequentially.
[0099]
Embedded image

[0100]
3. Creation of photoelectric conversion element (photoelectrochemical cell)
Dye-sensitized TiO prepared as described above₂The electrode substrate was cut into a size of 2 cm × 2 cm and overlapped with a platinum-deposited glass having the same size (see FIG. 10). Next, an electrolytic solution (0.7 mol / liter of 1,3-dimethylimidazolium iodide, 0.05 mol / liter of iodine, 0.08 mol / liter of t-butylpyridine is used by utilizing capillary action in the gap between the two glasses. 1) propionitrile solution) soaked in TiO₂By introducing into the electrodes, photoelectric conversion elements C-1 to C-10 shown in Table 2 were obtained.
[0101]
According to this example, as shown in FIG. 10, the conductive glass 1 (the one in which the conductive agent layer 3 is formed on the glass 2), the TiO adsorbing the pigment₂A photoelectric conversion element in which the electrode 4, the electrolytic solution 5, the platinum layer 6, and the glass 7 were sequentially laminated was produced.
[0102]
4). Measurement of dye adsorption
Dye-adsorbed TiO prepared as described above₂The electrode was cut into a size of 1 square centimeter, and the amount of dye adsorbed was determined from the absorbance of the dye solution eluted by immersion in a 0.1N aqueous potassium hydroxide solution. It is presumed that the surface roughness of the photosensitive layer increases as the dye adsorption amount per unit area increases. The results are shown in Table 2.
[0103]
5. Measurement of photoelectric conversion efficiency
Simulated sunlight was generated by passing light from a 500 W xenon lamp (USHIO) through a spectral filter (AM1.5 manufactured by Oriel). The intensity of this light is 100 mW / cm on the vertical plane.²Met. A silver paste was applied to the end of the conductive glass of the photoelectric conversion element (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 2 shows the conversion efficiency of the photoelectric conversion elements prepared in the examples.
[0104]
[Table 2]

[0105]
From comparison between C-1 to C-9 (present invention) and C-10 (comparative example), it can be seen that the photoelectric conversion element using the method of the present invention has higher conversion efficiency than the other photoelectric conversion elements. . Of ZnO and MgO, ZnO gave better results. In comparison between the same ZnO, the results with a particle size of 20 nm were better than those with a particle size of 300 nm.
In addition, the photoelectric conversion element using the method of the present invention is TiO 2.₂When the coating amount is the same, the amount of dye adsorbed is large, and the surface roughness of the photosensitive layer is prevented from being lowered by sintering in the process of producing the element.
[0106]
【The invention's effect】
From the results of the examples, it is apparent that a dye-sensitized photoelectric conversion element having improved conversion efficiency as compared with the prior art was obtained by the present invention.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 2 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 3 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 4 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 5 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 6 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 7 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 8 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 9 is a partial cross-sectional view showing the structure of a preferred photoelectric conversion element of the present invention.
FIG. 10 is a cross-sectional view illustrating a configuration of a photoelectric conversion element created in an example.
[Explanation of symbols]
1 Conductive glass
2 Glass
3 Conductive agent layer
4 Dye adsorption TiO2 electrode
5 Electrolyte
6 Platinum layer
7 Glass
10 Conductive layer
10a Transparent conductive layer
11 Metal lead
20 Photosensitive layer
21 Semiconductor fine particles
22 Dye
23 Charge transport materials
30 Charge transport layer
40 Counter conductive layer
40a Transparent counter electrode conductive layer
50 substrates
50a transparent substrate
60 Undercoat layer

Claims (4)

A method for producing a photoelectric conversion element having at least a semiconductor fine particle layer and a conductive support,
A dispersion obtained by mixing semiconductor fine particles and MgO or ZnO as soluble fine particles is applied onto the conductive support, and a semiconductor fine particle layer comprising a soluble portion made of the soluble fine particles and an insoluble portion made of the semiconductor fine particles is formed. After forming
A method for producing a photoelectric conversion element, wherein a gap is generated by dissolving and removing the soluble portion.   The method for producing a photoelectric conversion element according to claim 1, wherein the semiconductor fine particles adsorb a dye.   The method for producing a photoelectric conversion element according to claim 1, wherein the semiconductor fine particles are an oxide semiconductor selected from titanium oxide, niobium oxide, tin oxide, and tungsten oxide. The method for producing a photoelectric conversion element according to any one of claims 1 to 3, wherein soluble particles are dissolved and removed by immersion in an acid or a water-soluble ligand .

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