JP4747480B2 - ORGANIC ELECTROLUMINESCENT ELEMENT, DISPLAY ELEMENT AND LIGHTING DEVICE - Google Patents

Description

【００５８】
【化３】

【００５９】
【化４】

【００６０】
【化５】

【００６１】
【化６】

【００６２】
上記一般式１のＲ_１およびＲ_２は独立に１価の置換基を表し、Ｘ_１は＝Ｃ（Ｒ_３）−を表し、Ｘ_２は＝Ｃ（Ｒ_４）−を表す。ここにおいてＲ_１、Ｒ_２、Ｒ_３、Ｒ_４の例としては、前述した連結基Ａを修飾する置換基の例として挙げた置換基と同じ置換基が挙げられる。また、Ｒ_１とＲ_３ 、Ｒ _２ とＲ _４ がそれぞれ互いに結合して環構造を形成してもよい。
【００６３】
以下に、一般式１の連結基Ａに結合する本発明の含窒素芳香族化合物残基の例及び参考の例を示すが、一般式１で表される化合物の構造がこれらの例によって限定されるものではない。
【００６４】
【化７】

【００６５】
【化８】

【００６６】
一般式１で表される化合物は例えばTetrahedron Lett.，39(1998)，2367-2370ページ、日本国特許3161360号、Angew．Chem.Int.Ed.，37(1998)，2046-2067ページ、Tetrahedron Lett.，41(2000)，481-484ページ、Synth.Commun.，11(7) (1981)，513-519ページ、およびChem．Rev.，2002，102，1359-51469ページ等に記載の合成反応等、当業に従事する技術者には周知の合成方法によって製造することができる。
【００６７】
本発明に用いられる一般式１で表される化合物は、後述する有機エレクトロルミネッセンス素子の正孔輸送層、電子輸送層、発光層のいずれに用いることも可能であるが、電子輸送層ないし発光層に用いることが好ましい。また、発光層において蛍光性もしくはリン光性の化合物へエネルギーを移動させて自身は発光することのない、当業に従事する技術者に「ホスト化合物」として知られる材料としても、好ましく用いることができる。
【００６８】
上記一般式２で表される化合物におけるＲ₁、Ｒ₂、Ｘ₁、Ｘ₂は一般式１のＲ₁、Ｒ₂、Ｘ₁、Ｘ₂で説明したものと同様である。
【００６９】
一般式２で表される化合物の例としてはピリドインドールである。これらの化合物はさらに置換されていてもよく、置換基の例としては前述したＲ_１およびＲ_２の例として挙げたのと同様の置換基を挙げることができる。好ましい置換基としてはアルキル基、アリール基、ヘテロアリール基、アルコキシ基、アルキルチオ基、アリールオキシ基、アリールチオ基、シアノ基、フッ素原子であり、とくに好ましくはアルキル基、アリール基、ヘテロアリール基、フッ素原子である。
【００７０】
また、一般式２で表される化合物の分子量は６００〜２０００であることが好ましい。分子量が６００〜２０００であるとＴｇ（ガラス転移温度）が上昇し、熱安定性が向上し、素子寿命が改善される。より好ましい分子量は８００〜２０００である。
【００７１】
《有機ＥＬ素子の構成層》
本発明の有機ＥＬ素子の構成層について説明する。
【００７２】
本発明において、陰極、陽極および有機化合物層の層構成の好ましい具体例を以下に示すが、これに限定されるものではない。
（ｉ）陽極／発光層／電子輸送層／陰極
（ii）陽極／正孔輸送層／発光層／電子輸送層／陰極
（iii）陽極／正孔輸送層／発光層／正孔阻止層／電子輸送層／陰極
（iv）陽極／正孔輸送層／発光層／正孔阻止層／電子輸送層／陰極バッファー層／陰極
（ｖ）陽極／陽極バッファー層／正孔輸送層／発光層／正孔阻止層／電子輸送層／陰極バッファー層／陰極
《陽極》
陽極について説明する。
【００７３】
有機ＥＬ素子における陽極としては、仕事関数の大きい（４ｅＶ以上）金属、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが好ましく用いられる。このような電極物質の具体例としてはＡｕ等の金属、ＣｕＩ、インジウムチンオキシド（ＩＴＯ）、ＳｎＯ２、ＺｎＯ等の導電性透明材料が挙げられる。また、ＩＤＩＸＯ（Ｉｎ２Ｏ３−ＺｎＯ）等非晶質で透明導電膜を作製可能な材料を用いてもよい。陽極は、これらの電極物質を蒸着やスパッタリング等の方法により、薄膜を形成させ、フォトリソグラフィー法で所望の形状のパターンを形成してもよく、あるいはパターン精度をあまり必要としない場合は（１００μｍ以上程度）、上記電極物質の蒸着やスパッタリング時に所望の形状のマスクを介してパターンを形成してもよい。この陽極より発光を取り出す場合には、透過率を１０％より大きくすることが望ましく、また、陽極としてのシート抵抗は数百Ω／□以下が好ましい。さらに膜厚は材料にもよるが、通常１０〜１０００ｎｍ、好ましくは１０〜２００ｎｍの範囲で選ばれる。
【００７４】
《陰極》
次に、陰極について説明する。
【００７５】
陰極としては、仕事関数の小さい（４ｅＶ以下）金属（電子注入性金属と称する）、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが用いられる。このような電極物質の具体例としては、ナトリウム、ナトリウム−カリウム合金、マグネシウム、リチウム、マグネシウム／銅混合物、マグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ２Ｏ３）混合物、インジウム、リチウム／アルミニウム混合物、希土類金属等が挙げられる。これらの中で、電子注入性及び酸化等に対する耐久性の点から、電子注入性金属とこれより仕事関数の値が大きく安定な金属である第二金属との混合物、例えばマグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ２Ｏ３）混合物、リチウム／アルミニウム混合物、アルミニウム等が好適である。陰極は、これらの電極物質を蒸着やスパッタリング等の方法により、薄膜を形成させることにより、作製することができる。また、陰極としてのシート抵抗は数百Ω／□以下が好ましく、膜厚は通常１０ｎｍ〜１０００ｎｍ、好ましくは５０ｎｍ〜２００ｎｍの範囲で選ばれる。なお、発光を透過させるため、有機ＥＬ素子の陽極または陰極のいずれか一方が、透明または半透明であれば発光輝度が向上し好都合である。
【００７６】
《注入層》：電子注入層、正孔注入層
次に、本発明の有機ＥＬ素子の層として用いられる、注入層について説明する。
【００７７】
注入層は必要に応じて設け、電子注入層と正孔注入層があり、上記のごとく陽極と発光層または正孔輸送層の間、及び、陰極と発光層または電子輸送層との間に存在させてもよい。
【００７８】
注入層とは、駆動電圧低下や発光輝度向上のために電極と有機層間に設けられる層のことで、「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日 エヌ・ティー・エス社発行）」の第２編第２章「電極材料」（１２３〜１６６頁）に詳細に記載されており、正孔注入層（陽極バッファー層）と電子注入層（陰極バッファー層）とがある。
【００７９】
陽極バッファー層（正孔注入層）は、特開平９−４５４７９号公報、同９−２６００６２号公報、同８−２８８０６９号公報等にもその詳細が記載されており、具体例として、銅フタロシアニンに代表されるフタロシアニンバッファー層、酸化バナジウムに代表される酸化物バッファー層、アモルファスカーボンバッファー層、ポリアニリン（エメラルディン）やポリチオフェン等の導電性高分子を用いた高分子バッファー層等が挙げられる。
【００８０】
陰極バッファー層（電子注入層）は、特開平６−３２５８７１号公報、同９−１７５７４号公報、同１０−７４５８６号公報等にもその詳細が記載されており、具体的にはストロンチウムやアルミニウム等に代表される金属バッファー層、フッ化リチウムに代表されるアルカリ金属化合物バッファー層、フッ化マグネシウムに代表されるアルカリ土類金属化合物バッファー層、酸化アルミニウムに代表される酸化物バッファー層等が挙げられる。
【００８１】
上記バッファー層（注入層）はごく薄い膜であることが望ましく、素材にもよるが、その膜厚は０．１ｎｍ〜１００ｎｍの範囲が好ましい。
【００８２】
《阻止層》：正孔阻止層、電子阻止層
阻止層は、上記のごとく、有機化合物薄膜の基本構成層の他に必要に応じて設けられるものである。例えば特開平１１−２０４２５８号、同１１−２０４３５９号、及び「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日 エヌ・ティー・エス社発行）」の２３７頁等に記載されている正孔阻止（ホールブロック）層がある。
【００８３】
正孔阻止層とは広い意味では電子輸送層であり、電子を輸送する機能を有しつつ正孔を輸送する能力が著しく小さい材料からなり、電子を輸送しつつ正孔を阻止することで電子と正孔の再結合確率を向上させることができる。
【００８４】
一方、電子阻止層とは広い意味では正孔輸送層であり、正孔を輸送する機能を有しつつ電子を輸送する能力が著しく小さい材料からなり、正孔を輸送しつつ電子を阻止することで電子と正孔の再結合確率を向上させることができる。
【００８５】
《発光層》
次に発光層について説明する。
【００８６】
発光層は、電極または電子輸送層、正孔輸送層から注入されてくる電子および正孔が再結合して発光する層であり、発光する部分は発光層の層内であっても発光層と隣接層との界面であっても良い。
【００８７】
発光層に使用される材料（以下、発光材料という）は、蛍光またはリン光を発する有機化合物または錯体であることが好ましく、有機ＥＬ素子の発光層に使用される公知のものの中から適宜選択して用いることができる。特に発光材料としてリン光発光するリン光性化合物を用いるのが好ましく、これにより、より一層効率よく高輝度に発光することができる。
【００８８】
このような発光材料は主として有機化合物であり、所望の色調により、例えば、Ｍａｃｒｏｍｏｌ．Ｓｙｎｔｈ．，１２５巻，１７〜２５頁に記載の化合物等を用いることができる。
【００８９】
発光材料は、発光性能の他に、正孔輸送機能や電子輸送機能を併せ持っていても良く、正孔輸送材料や電子輸送材料の殆どが、発光材料としても使用できる。
【００９０】
発光材料は、ｐ−ポリフェニレンビニレンやポリフルオレンのような高分子材料でも良く、さらに前記発光材料を高分子鎖に導入した、または前記発光材料を高分子の主鎖とした高分子材料を使用しても良い。
【００９１】
この発光層は、上記化合物を、例えば真空蒸着法、スピンコート法、キャスト法、ＬＢ法などの公知の薄膜化法により製膜して形成することができる。発光層としての膜厚は、特に制限はないが、通常は５ｎｍ〜５μｍの範囲で選ばれる。この発光層は、これらの発光材料一種又は二種以上からなる一層構造であってもよいし、あるいは、同一組成又は異種組成の複数層からなる積層構造であってもよい。本発明の有機ＥＬ素子の好ましい態様は、発光層が二種以上の材料からなり、その内の一種が本発明の化合物であるときである。
【００９２】
また、この発光層は、特開昭５７−５１７８１号公報に記載されているように、樹脂などの結着材と共に上記発光材料を溶剤に溶かして溶液としたのち、これをスピンコート法などにより薄膜化して形成することができる。このようにして形成された発光層の膜厚については、特に制限はなく、状況に応じて適宜選択することができるが、通常は５ｎｍ〜５μｍの範囲である。
【００９３】
本発明においては、発光層にその主たる構成成分である上記の有機化合物に加えて、それらの発光極大波長よりも長波な蛍光極大波長を有する蛍光性化合物を少なくとも１種含有させてもよい。このように主たる構成成分に加えて発光層になんらかの化合物を含有させた場合、主たる構成成分はホスト化合物あるいは単にホスト、加えられた化合物はドーパントと呼ばれるが、このような形態の場合、発光層の主たる構成成分である先述の有機化合物がホスト化合物であり、加えられた蛍光性化合物がドーパントであり、この場合においては蛍光性ドーパントである。蛍光性ドーパントはホスト化合物に励起されて蛍光を発し、その結果としてこのように構成された有機ＥＬ素子からは、蛍光性化合物からの発光が取出されることになる。このような用途に用いることのできる蛍光性化合物としてはクマリン系色素、ピラン系色素、シアニン系色素、クロコニウム系色素、スクアリウム系色素、オキソベンツアントラセン系色素、フルオレセイン系色素、ローダミン系色素、ピリリウム系色素、ペリレン系色素、スチルベン系色素、ポリチオフェン系色素、又は希土類錯体系蛍光体等が挙げられる。用いる蛍光性化合物としては溶液状態における蛍光量子収率の高いものが好ましく、蛍光量子収率１０％以上、特に３０％以上が好ましい。蛍光量子収率は、第４版実験化学講座７の分光IIの３６２頁（１９９２年版、丸善）に記載の方法により測定することができる。
【００９４】
また、上記の形態において蛍光性ドーパントを加えたのと同様に、発光層を構成する化合物の発光極大波長よりも長波な発光極大波長を有するリン光性化合物をドーパントとして加えてもよい。リン光性化合物（ドーパント）を発光層に加えた場合、ホスト化合物からリン光性ドーパントへのエネルギー移動によって、有機ＥＬ素子からはリン光発光が取出される。既に述べたとおり、有機ＥＬ素子としてはリン光発光を利用する形態が発光効率の観点から好ましく、本発明においても同様に、少なくとも発光成分の一部がリン光発光によるものである有機ＥＬ素子が好ましい。
【００９５】
本発明に係る有機エレクトロルミネッセンス素子においては先に述べた発光効率の観点から、本発明に係る一般式１で表される化合物をホスト化合物として、リン光性化合物とともに発光層を構成したリン光発光性有機エレクトロルミネッセンス素子であることがとくに好ましい。
【００９６】
本発明におけるリン光性化合物とは励起三重項からの発光が観測される化合物であり、リン光量子収率が、２５℃において０．００１以上の化合物である。リン光量子収率は好ましくは０．０１以上、更に好ましくは０．１以上である。
【００９７】
上記リン光量子収率は、第４版実験化学講座７の分光IIの３９８頁（１９９２年版、丸善）に記載の方法により測定できる。溶液中でのリン光量子収率は種々の溶媒を用いて測定できるが、本発明に用いられるリン光性化合物は、任意の溶媒の何れかにおいて上記リン光量子収率が達成されれば良い。
【００９８】
本発明で用いられるリン光性化合物としては、好ましくは元素の周期律表で８族の金属を含有する錯体系化合物であり、更に好ましくは、イリジウム化合物、オスミウム化合物、又は白金化合物（白金錯体系化合物）であり、中でも最も好ましいのはイリジウム化合物である。
【００９９】
以下に、本発明で用いられるリン光性化合物の具体例を示すが、これらに限定されるものではない。これらの化合物は、例えば、Ｉｎｏｒｇ．Ｃｈｅｍ．４０巻、１７０４〜１７１１に記載の方法等により合成できる。
【０１００】
【化９】

【０１０１】
【化１０】

【０１０２】
【化１１】

【０１０３】
さらに、ホスト化合物とリン光性化合物の他に、リン光性化合物からの発光の極大波長よりも長波な領域に蛍光極大波長を有する蛍光性化合物を少なくとも１種含有させてもよい。この場合、ホスト化合物とリン光性ドーパントからのエネルギー移動により、有機ＥＬ素子としての電界発光は蛍光性化合物からの発光が得られる。
【０１０４】
また、蛍光性もしくはリン光性ドーパントを複数種類用いてこれらからの発光を同時に取り出すことにより、複数の発光極大波長をもつ発光素子を構成することもできる。例えばホスト化合物を兼ねる発光性化合物としてポリビニルカルバゾールを、蛍光性ドーパントとしてクマリン６とナイルレッドを用いることにより、ポリビニルカルバゾールからの青色発光と、クマリン６からの緑色発光、ナイルレッドからの赤色発光を同時に取り出して、白色に発光する素子を構成することができる。リン光発光型の有機ＥＬ素子においても同様に、複数種類のリン光性ドーパントを用いることによって発光の混色を行うことができる。薄型であること、および樹脂基板上に形成することが可能であるという有機ＥＬ素子の特長を活かして、これをパネル状その他の形状の照明装置に利用する場合を考慮すると、白色発光素子を構成することは実用的に有用である。現在のところ単一の発光材料で白色発光を示すものがないため、複数の発光材料により複数の発光色を同時に発光させて混色により白色発光を得ている。複数の発光色の組み合わせとしては、青色、緑色、青色の３原色の３つの発光極大波長を含有させたものでも良いし、青色と黄色、青緑と橙色等の補色の関係を利用した２つの発光極大波長を含有したものでも良い。これらの混色した発光は先に述べたとおり、ドーパントを用いることによって行うことがで、ドーパントの種類と量を変化させることによって、発光色の色調を制御することができる。
【０１０５】
《正孔輸送層》
次に正孔輸送層について説明する。
【０１０６】
正孔輸送層とは正孔を輸送する機能を有する材料からなり、広い意味で正孔注入層、電子阻止層も正孔輸送層に含まれる。正孔輸送層は単層もしくは複数層設けることができる。
【０１０７】
正孔輸送材料としては、特に制限はなく、従来、光導伝材料において、正孔の電荷注入輸送材料として慣用されているものやＥＬ素子の正孔注入層、正孔輸送層に使用される公知のものの中から任意のものを選択して用いることができる。
【０１０８】
正孔輸送材料は、正孔の注入もしくは輸送、電子の障壁性のいずれかを有するものであり、有機物、無機物のいずれであってもよい。例えばトリアゾール誘導体、オキサジアゾール誘導体、イミダゾール誘導体、ポリアリールアルカン誘導体、ピラゾリン誘導体及びピラゾロン誘導体、フェニレンジアミン誘導体、アリールアミン誘導体、アミノ置換カルコン誘導体、オキサゾール誘導体、スチリルアントラセン誘導体、フルオレノン誘導体、ヒドラゾン誘導体、スチルベン誘導体、シラザン誘導体、アニリン系共重合体、また、導電性高分子オリゴマー、特にチオフェンオリゴマー等が挙げられる。
【０１０９】
正孔輸送材料としては、上記のものを使用することができるが、ポルフィリン化合物、芳香族第三級アミン化合物及びスチリルアミン化合物、特に芳香族第三級アミン化合物を用いることが好ましい。
【０１１０】
芳香族第三級アミン化合物及びスチリルアミン化合物の代表例としては、Ｎ，Ｎ，Ｎ’，Ｎ’−テトラフェニル−４，４’−ジアミノフェニル；Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフェニル）−〔１，１’−ビフェニル〕−４，４’−ジアミン（ＴＰＤ）；２，２−ビス（４−ジ−ｐ−トリルアミノフェニル）プロパン；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）シクロヘキサン；Ｎ，Ｎ，Ｎ’，Ｎ’−テトラ−ｐ−トリル−４，４’−ジアミノビフェニル；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）−４−フェニルシクロヘキサン；ビス（４−ジメチルアミノ−２−メチルフェニル）フェニルメタン；ビス（４−ジ−ｐ−トリルアミノフェニル）フェニルメタン；Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ジ（４−メトキシフェニル）−４，４’−ジアミノビフェニル；Ｎ，Ｎ，Ｎ’，Ｎ’−テトラフェニル−４，４’−ジアミノジフェニルエーテル；４，４’−ビス（ジフェニルアミノ）クオードリフェニル；Ｎ，Ｎ，Ｎ−トリ（ｐ−トリル）アミン；４−（ジ−ｐ−トリルアミノ）−４’−〔４−（ジ−ｐ−トリルアミノ）スチリル〕スチルベン；４−Ｎ，Ｎ−ジフェニルアミノ−（２−ジフェニルビニル）ベンゼン；３−メトキシ−４’−Ｎ，Ｎ−ジフェニルアミノスチルベンゼン；Ｎ−フェニルカルバゾール、さらには、米国特許第５，０６１，５６９号明細書に記載されている２個の縮合芳香族環を分子内に有するもの、例えば４，４’−ビス〔Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ〕ビフェニル（ＮＰＤ）、特開平４−３０８６８８号公報に記載されているトリフェニルアミンユニットが３つスターバースト型に連結された４，４’，４”−トリス〔Ｎ−（３−メチルフェニル）−Ｎ−フェニルアミノ〕トリフェニルアミン（ＭＴＤＡＴＡ）等が挙げられる。
【０１１１】
さらにこれらの材料を高分子鎖に導入した、またはこれらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【０１１２】
また、ｐ型−Ｓｉ，ｐ型−ＳｉＣ等の無機化合物も正孔注入材料、正孔輸送材料として使用することができる。
【０１１３】
また、本発明においては正孔輸送層の正孔輸送材料は４１５ｎｍ以下に蛍光極大波長を有することが好ましい。すなわち、正孔輸送材料は、正孔輸送能を有しつつかつ、発光の長波長化を防ぎ、なおかつ高Ｔｇである化合物が好ましい。
【０１１４】
この正孔輸送層は、上記正孔輸送材料を、例えば真空蒸着法、スピンコート法、キャスト法、インクジェット法、ＬＢ法等の公知の方法により、薄膜化することにより形成することができる。正孔輸送層の膜厚については特に制限はないが、通常は５〜５０００ｎｍ程度である。この正孔輸送層は、上記材料の一種または二種以上からなる一層構造であってもよい。
【０１１５】
《電子輸送層》
次に電子輸送層について説明する。
【０１１６】
電子輸送層とは電子を輸送する機能を有する材料からなり、広い意味で電子注入層、正孔阻止層も電子輸送層に含まれる。電子輸送層は単層もしくは複数層設けることができる。
【０１１７】
従来、単層の電子輸送層、及び複数層とする場合は発光層に対して陰極側に隣接する電子輸送層に用いられる電子輸送材料（正孔阻止材料を兼ねる）としては、下記の材料が知られている。
【０１１８】
さらに、電子輸送層は、陰極より注入された電子を発光層に伝達する機能を有していればよく、その材料としては従来公知の化合物の中から任意のものを選択して用いることができる。
【０１１９】
この電子輸送層に用いられる材料（以下、電子輸送材料という）の例としては、ニトロ置換フルオレン誘導体、ジフェニルキノン誘導体、チオピランジオキシド誘導体、ナフタレンペリレンなどの複素環テトラカルボン酸無水物、カルボジイミド、フレオレニリデンメタン誘導体、アントラキノジメタン及びアントロン誘導体、オキサジアゾール誘導体などが挙げられる。さらに、上記オキサジアゾール誘導体において、オキサジアゾール環の酸素原子を硫黄原子に置換したチアジアゾール誘導体、電子吸引基として知られているキノキサリン環を有するキノキサリン誘導体も、電子輸送材料として用いることができる。
【０１２０】
さらにこれらの材料を高分子鎖に導入した、またはこれらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【０１２１】
また、８−キノリノール誘導体の金属錯体、例えばトリス（８−キノリノール）アルミニウム（Ａｌｑ）、トリス（５，７−ジクロロ−８−キノリノール）アルミニウム、トリス（５，７−ジブロモ−８−キノリノール）アルミニウム、トリス（２−メチル−８−キノリノール）アルミニウム、トリス（５−メチル−８−キノリノール）アルミニウム、ビス（８−キノリノール）亜鉛（Ｚｎｑ）など、及びこれらの金属錯体の中心金属がＩｎ、Ｍｇ、Ｃｕ、Ｃａ、Ｓｎ、Ｇａ又はＰｂに置き替わった金属錯体も、電子輸送材料として用いることができる。その他、メタルフリー若しくはメタルフタロシアニン、又はそれらの末端がアルキル基やスルホン酸基などで置換されているものも、電子輸送材料として好ましく用いることができる。また、発光層の材料として例示したジスチリルピラジン誘導体も、電子輸送材料として用いることができるし、正孔注入層、正孔輸送層と同様に、ｎ型−Ｓｉ、ｎ型−ＳｉＣなどの無機半導体も電子輸送材料として用いることができる。
【０１２２】
電子輸送層に用いられる好ましい化合物は、４１５ｎｍ以下に蛍光極大波長を有することが好ましい。すなわち、電子輸送層に用いられる化合物は、電子輸送能を有しつつかつ、発光の長波長化を防ぎ、なおかつ高Ｔｇである化合物が好ましい。
【０１２３】
《基体（基板、基材、支持体等ともいう）》
本発明の有機ＥＬ素子は基体上に形成されているのが好ましい。
【０１２４】
本発明の有機ＥＬ素子に用いることができる基体としては、ガラス、プラスチック等の種類には特に限定はなく、また、透明のものであれば特に制限はないが、好ましく用いられる基板としては例えばガラス、石英、光透過性樹脂フィルムを挙げることができる。特に好ましい基体は、有機ＥＬ素子にフレキシブル性を与えることが可能な樹脂フィルムである。
【０１２５】
樹脂フィルムとしては、例えばポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリエーテルスルホン（ＰＥＳ）、ポリエーテルイミド、ポリエーテルエーテルケトン、ポリフェニレンスルフィド、ポリアリレート、ポリイミド、ポリカーボネート（ＰＣ）、セルローストリアセテート（ＴＡＣ）、セルロースアセテートプロピオネート（ＣＡＰ）等からなるフィルム等が挙げられる。
【０１２６】
樹脂フィルムの表面には、無機物もしくは有機物の被膜またはその両者のハイブリッド被膜が形成されていてもよい。
【０１２７】
本発明の有機ＥＬ素子の発光の室温における外部取り出し効率は１％以上であることが好ましく、より好ましくは２％以上である。ここに、外部取り出し量子効率（％）＝有機ＥＬ素子外部に発光した光子数／有機ＥＬ素子に流した電子数×１００である。
【０１２８】
また、カラーフィルター等の色相改良フィルター等を併用してもよい。
《有機ＥＬ素子の作製方法》
本発明の有機ＥＬ素子の作製方法の一例として、陽極／正孔注入層／正孔輸送層／発光層／電子輸送層／電子注入層／陰極からなる有機ＥＬ素子の作製法について説明する。
【０１２９】
まず適当な基体上に、所望の電極物質、例えば陽極用物質からなる薄膜を、１μｍ以下、好ましくは１０ｎｍ〜２００ｎｍの膜厚になるように、蒸着やスパッタリング等の方法により形成させ、陽極を作製する。次に、この上に素子材料である正孔注入層、正孔輸送層、発光層、電子輸送層、電子注入層、正孔阻止層の有機化合物薄膜を形成させる。
【０１３０】
この有機化合物薄膜の薄膜化の方法としては、前記の如くスピンコート法、キャスト法、インクジェット法、蒸着法、印刷法等があるが、均質な膜が得られやすく、かつピンホールが生成しにくい等の点から、真空蒸着法またはスピンコート法が特に好ましい。さらに層ごとに異なる製膜法を適用してもよい。製膜に蒸着法を採用する場合、その蒸着条件は、使用する化合物の種類等により異なるが、一般にボート加熱温度５０〜４５０℃、真空度１０−６Ｐａ〜１０−２Ｐａ、蒸着速度０．０１ｎｍ〜５０ｎｍ／秒、基板温度−５０℃〜３００℃、膜厚０．１ｎｍ〜５μｍの範囲で適宜選ぶことが望ましい。
【０１３１】
これらの層の形成後、その上に陰極用物質からなる薄膜を、１μｍ以下好ましくは５０ｎｍ〜２００ｎｍの範囲の膜厚になるように、例えば蒸着やスパッタリング等の方法により形成させ、陰極を設けることにより、所望の有機ＥＬ素子が得られる。この有機ＥＬ素子の作製は、一回の真空引きで一貫して正孔注入層から陰極まで作製するのが好ましいが、途中で取り出して異なる製膜法を施してもかまわない。その際、作業を乾燥不活性ガス雰囲気下で行う等の配慮が必要となる。
【０１３２】
本発明においては、発光層形成時のみシャドーマスクを設け、他層は共通であるのでシャドーマスク等のパターニングは不要であり、一面に蒸着法、キャスト法、スピンコート法、インクジェット法、印刷法等で膜を形成できる。
【０１３３】
発光層のみパターニングを行う場合、その方法に限定はないが、好ましくは蒸着法、インクジェット法、印刷法である。蒸着法を用いる場合においてはシャドーマスクを用いたパターニングが好ましい。
【０１３４】
また作製順序を逆にして、陰極、電子注入層、電子輸送層、発光層、正孔輸送層、正孔注入層、陽極の順に作製することも可能である。このようにして得られた有機ＥＬ素子に、直流電圧を印加する場合には、陽極を＋、陰極を−の極性として電圧２〜４０Ｖ程度を印加すると、発光が観測できる。また、逆の極性で電圧を印加しても電流は流れずに発光は全く生じない。さらに、交流電圧を印加する場合には、陽極が＋、陰極が−の状態になったときのみ発光する。なお、印加する交流の波形は任意でよい。
【０１３５】
本発明の有機ＥＬ素子は、画像を投影するタイプのプロジェクション装置や、静止画像や動画像を直接視認するタイプの表示デバイス、ディスプレー等の表示装置に用いることができる。表示デバイス、ディスプレーとしてはテレビ、パソコン、モバイル機器、ＡＶ機器、文字放送表示、自動車内の情報表示等が挙げられる。特に静止画像や動画像を再生する表示装置として使用してもよく、動画再生用の表示装置として使用する場合の駆動方式は単純マトリックス（パッシブマトリックス）方式でもアクティブマトリックス方式でもどちらでもよい。
【０１３６】
異なる発光色を有する本発明の有機ＥＬ素子を２種以上使用することにより、フルカラー表示装置を作製することが可能である。
【０１３７】
また、本発明の有機ＥＬ素子は、発光光源としては家庭用照明、車内照明、時計や表示手段として液晶素子を用いている表示装置のバックライト、看板広告、信号機、光記憶媒体の光源、電子写真複写機の光源、光通信処理機の光源、光センサーの光源等の照明装置に用いることができるがこれに限定するものではない。
【０１３８】
さらに、本発明に係る有機ＥＬ素子に共振器構造を持たせた有機ＥＬ素子として用いてもよい。
【０１３９】
このような共振器構造を有した有機ＥＬ素子の使用目的としては光記憶媒体の光源、電子写真複写機の光源、光通信処理機の光源、光センサーの光源等が挙げられるが、これらに限定されない。また、レーザー発振をさせることにより、上記用途に使用してもよい。
【０１４０】
《表示装置》
本発明の有機ＥＬ素子から構成される表示装置の一例を図面に基づいて以下に説明する。
【０１４１】
図１は、有機ＥＬ素子から構成される表示装置の一例を示した模式図である。有機ＥＬ素子の発光により画像情報の表示を行う、例えば、携帯電話等のディスプレイの模式図である。
【０１４２】
ディスプレイ１は、複数の画素を有する表示部Ａ、画像情報に基づいて表示部Ａの画像走査を行う制御部Ｂ等からなる。
【０１４３】
制御部Ｂは、表示部Ａと電気的に接続され、複数の画素それぞれに外部からの画像情報に基づいて走査信号と画像データ信号を送り、走査信号により走査線毎の画素が画像データ信号に応じて順次発光して画像走査を行って画像情報を表示部Ａに表示する。
【０１４４】
図２は、表示部Ａの模式図である。
表示部Ａは基板上に、複数の走査線５及びデータ線６を含む配線部と、複数の画素３等とを有する。表示部Ａの主要な部材の説明を以下に行う。
【０１４５】
図においては、画素３の発光した光が、白矢印方向（下方向）へ取り出される場合を示している。
【０１４６】
配線部の走査線５及び複数のデータ線６は、それぞれ導電材料からなり、走査線５とデータ線６は格子状に直交して、直交する位置で画素３に接続している（詳細は図示せず）。
【０１４７】
画素３は、走査線５から走査信号が印加されると、データ線６から画像データ信号を受け取り、受け取った画像データに応じて発光する。発光の色が赤領域の画素、緑領域の画素、青領域の画素を、適宜、同一基板上に並置することによって、フルカラー表示が可能となる。
【０１４８】
次に、画素の発光プロセスを説明する。
図３は、画素の模式図である。
【０１４９】
画素は、有機ＥＬ素子１０、スイッチングトランジスタ１１、駆動トランジスタ１２、コンデンサ１３等を備えている。複数の画素に有機ＥＬ素子１０として、赤色、緑色、青色発光の有機ＥＬ素子を用い、これらを同一基板上に並置することでフルカラー表示を行うことができる。
【０１５０】
図３において、制御部Ｂからデータ線６を介してスイッチングトランジスタ１１のドレインに画像データ信号が印加される。そして、制御部Ｂから走査線５を介してスイッチングトランジスタ１１のゲートに走査信号が印加されると、スイッチングトランジスタ１１の駆動がオンし、ドレインに印加された画像データ信号がコンデンサ１３と駆動トランジスタ１２のゲートに伝達される。
【０１５１】
画像データ信号の伝達により、コンデンサ１３が画像データ信号の電位に応じて充電されるとともに、駆動トランジスタ１２の駆動がオンする。駆動トランジスタ１２は、ドレインが電源ライン７に接続され、ソースが有機ＥＬ素子１０の電極に接続されており、ゲートに印加された画像データ信号の電位に応じて電源ライン７から有機ＥＬ素子１０に電流が供給される。
【０１５２】
制御部Ｂの順次走査により走査信号が次の走査線５に移ると、スイッチングトランジスタ１１の駆動がオフする。しかし、スイッチングトランジスタ１１の駆動がオフしてもコンデンサ１３は充電された画像データ信号の電位を保持するので、駆動トランジスタ１２の駆動はオン状態が保たれて、次の走査信号の印加が行われるまで有機ＥＬ素子１０の発光が継続する。順次走査により次に走査信号が印加されたとき、走査信号に同期した次の画像データ信号の電位に応じて駆動トランジスタ１２が駆動して有機ＥＬ素子１０が発光する。
【０１５３】
すなわち、有機ＥＬ素子１０の発光は、複数の画素それぞれの有機ＥＬ素子１０に対して、アクティブ素子であるスイッチングトランジスタ１１と駆動トランジスタ１２を設けて、複数の画素３それぞれの有機ＥＬ素子１０の発光を行っている。このような発光方法をアクティブマトリクス方式と呼んでいる。
【０１５４】
ここで、有機ＥＬ素子１０の発光は、複数の階調電位を持つ多値の画像データ信号による複数の階調の発光でもよいし、２値の画像データ信号による所定の発光量のオン、オフでもよい。
【０１５５】
また、コンデンサ１３の電位の保持は、次の走査信号の印加まで継続して保持してもよいし、次の走査信号が印加される直前に放電させてもよい。
【０１５６】
本発明においては、上述したアクティブマトリクス方式に限らず、走査信号が走査されたときのみデータ信号に応じて有機ＥＬ素子を発光させるパッシブマトリクス方式の発光駆動でもよい。
【０１５７】
図４は、パッシブマトリクス方式による表示装置の模式図である。図４において、複数の走査線５と複数の画像データ線６が画素３を挟んで対向して格子状に設けられている。
【０１５８】
順次走査により走査線５の走査信号が印加されたとき、印加された走査線５に接続している画素３が画像データ信号に応じて発光する。
【０１５９】
パッシブマトリクス方式では画素３にアクティブ素子が無く、製造コストの低減が計れる。
【０１６０】
【実施例】
以下、実施例を挙げて本発明を詳細に説明するが、本発明の態様はこれに限定されない。
【０１６１】
実施例１
《化合物１−１（Ａ、Ｂ、Ｃ、Ｄ）〜１−８（Ａ、Ｂ、Ｃ、Ｄ）の調製》
〈化合物１−１の合成及びサンプル１−１（Ａ、Ｂ、Ｃ、Ｄ）の調製〉
窒素雰囲気下、酢酸パラジウム４５ｍｇにトリ（ｔｅｒｔ−ブチル）ホスフィン０．２ｍｌを加えて、５０℃で３０分間撹拌した。これにキシレン６０ｍｌ、カルバゾール１．２ｇ、４，４’−ジブロモビフェニル１．０ｇ、ナトリウム−ｔｅｒｔ−ブトキシド０．９ｇを加えて、還流温度にて８時間撹拌を行った。反応混合物を放冷後、シリカゲルカラムクロマトグラフィーにより精製した後に再結晶して、前述した一般式１で表される化合物である４，４’−ジカルバゾリルビフェニル（化合物１−１）を０．６７ｇ得た（収率４２％）。得られた化合物１−１の構造はＮＭＲスペクトルおよび質量分析スペクトルにより同定した。
【０１６２】
【化１２】

【０１６３】
なお、得られた化合物１−１を昇華精製して得たサンプルおよびカルバゾールの、高速液体クロマトグラフィー分析および液体クロマトグラフィー質量分析の結果から、得られたサンプルには原料であるカルバゾールが０．５４質量％含まれていることが判明した。これをサンプル１−１Ａとする。
【０１６４】
さらに、同様にして合成を行ったがシリカゲルカラムクロマトグラフィーを繰り返して精製を行った後に再結晶と昇華精製を行い得られたサンプル１−１Ｂ、サンプル１−１Ｃおよびサンプル１−１Ｄを調製し、これらについてもサンプル１−１Ａと同様に分析を行い、サンプル１−１Ｂには０．３８質量％、サンプル１−１Ｃには０．２４質量％、サンプル１−１Ｄには０．０６質量％の原料であるカルバゾール（一般式２で表される化合物）が含まれていることが判明した。すなわち、サンプル１−１Ａ、１−１Ｂ、１−１Ｃ、１−１Ｄは、精製により化合物１−１に含有される一般式２で表される化合物の含有率が異なるものであり、一般式２で表される化合物の含有率が１−１Ａ＞１−１Ｂ＞１−１Ｃ＞１−１Ｄとなるようにしたものである（一般式２で表される含有率が多い順にＡ、Ｂ、Ｃ、Ｄ）とする。
【０１６５】
〈化合物１−２の合成及びサンプル１−２（Ａ、Ｂ、Ｃ、Ｄ）の調製〉
窒素雰囲気下、酢酸パラジウム４５ｍｇにトリ（ｔｅｒｔ−ブチル）ホスフィン０．２ｍｌを加えて、５０℃で３０分間撹拌した。これにキシレン６０ｍｌ、カルバゾール０．８ｇ、１，３，５−トリヨードベンゼン１．０ｇ、炭酸ルビジウム２．４ｇを加えて、還流温度にて８時間撹拌を行った。反応混合物を放冷後、シリカゲルカラムクロマトグラフィーにより精製した後に再結晶して、一般式１で表される化合物である１，３，５−トリカルバゾリルベンゼン（化合物１−２）を４３０ｍｇ得た（収率３４％）。
【０１６６】
【化１３】

【０１６７】
得られた化合物１−２の構造はＮＭＲスペクトルおよび質量分析スペクトルにより同定した。
【０１６８】
さらに、得られた化合物１−２を上述した精製方法と同様の方法で一般式２で表される化合物の含有率が異なるサンプル（１−２Ａ、１−２Ｂ、１−２Ｃ、１−２Ｄ）を調製した。
【０１６９】
〈化合物１−３〜１−８の合成及びサンプル１−３〜１−８（Ａ、Ｂ、Ｃ、Ｄ）の調製〉
公知の製造方法を用いて化合物１−３〜１−８を合成し、さらに、上述した精製方法と同様にしてそれぞれの化合物について一般式２で表される化合物の含有率が異なるサンプル（Ａ、Ｂ、Ｃ、Ｄ）を調製した。
【０１７０】
【化１４】

【０１７１】
【化１５】

【０１７２】
《有機ＥＬ素子１−１〜１−３２の作製》
陽極として１００ｍｍ×１００ｍｍ×１．１ｍｍのガラス基板上にＩＴＯ（インジウムチンオキシド）を１５０ｎｍ成膜した基板（ＮＨテクノグラス社製ＮＡ−４５）にパターニングを行った後、このＩＴＯ透明電極を設けた透明支持基板をイソプロピルアルコールで超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行なった。この透明支持基板を市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートにα−ＮＰＤを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートに、合成した化合物１−１（サンプル１−１Ａ）を２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにバソキュプロイン（ＢＣＰ）を２００ｍｇ入れ、更に別のモリブデン製抵抗加熱ボートにＡｌｑ₃を２００ｍｇ入れ、真空蒸着装置に取付けた。
【０１７３】
次いで、真空槽を４×１０^-4Ｐａまで減圧した後、α−ＮＰＤの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで透明支持基板に蒸着し、膜厚４５ｎｍの正孔輸送層を設けた。さらに化合物１−１（サンプル１Ａ）の入った前記加熱ボートに通電して加熱し、それぞれ蒸着速度０．２ｎｍ／ｓｅｃで前記正孔輸送層上に蒸着して膜厚２０ｎｍの発光層を設けた。尚、蒸着時の基板温度は室温であった。更に、ＢＣＰの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで前記発光層の上に蒸着して膜厚１０ｎｍの正孔阻止の役割も兼ねた電子輸送層を設けた。その上に、更に、Ａｌｑ₃の入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／ｓｅｃで前記電子輸送層の上に蒸着して更に膜厚４０ｎｍの電子注入層を設けた。尚、蒸着時の基板温度は室温であった。
【０１７４】
引き続きフッ化リチウム０．５ｎｍ及びアルミニウム１１０ｎｍを蒸着して陰極を形成し、有機ＥＬ素子１−１を作製した。
【０１７５】
上記で使用した化合物の構造を以下に示す。
【０１７６】
【化１６】

【０１７７】
さらに、有機ＥＬ素子１−１における化合物１−１（サンプル１−１Ａ）を表１に示すように置き換えた以外は有機ＥＬ素子１−１の作製方法と同様にして、有機ＥＬ素子１−２〜１−３２を作製した。
【０１７８】
有機ＥＬ素子の層中での一般式２で表される化合物の含有率の測定は下記の手法を用いた。
〈発光層中の一般式２で表される化合物の含有率の測定〉
１００ｍｍ×１００ｍｍ×１．１ｍｍのガラス基板上をイソプロピルアルコールで超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行なった。この透明支持基板を市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートにサンプル１−１Ａを２００ｍｇ入れて、真空蒸着装置に取付けた。
【０１７９】
真空槽を４×１０^-4Ｐａまで減圧した後、有機ＥＬ素子１−１の発光層を形成するのと同じ条件で、サンプル１−１Ａで表される化合物の入った前記加熱ボートに通電して加熱し、ガラス基板上に蒸着を行って蒸着膜を得た。
【０１８０】
得られたガラス基板上の蒸着膜をトルエンにて溶解し、得られた溶液を高速液体クロマトグラフィーによって分析して層中の原料であるカルバゾール（一般式２で表される化合物）の含有率を測定した。さらに、サンプル１−１Ａを他のサンプル１−１（Ｂ、Ｃ、Ｄ）、１−２（Ａ、Ｂ、Ｃ、Ｄ）〜１−８（Ａ、Ｂ、Ｃ、Ｄ）に変更して作製した蒸着膜でも同様の測定を行い、この測定結果を、有機ＥＬ素子１−１〜１−３２の発光層中の一般式２で表される化合物の含有率とした。
【０１８１】
《有機ＥＬ素子１−１〜１−３２の評価》
有機ＥＬ素子１−１〜１−３２の温度２３℃、窒素雰囲気下で１０Ｖ直流電圧を印加した時の発光輝度（ｃｄ／ｍ²）および発光効率（ｌｍ／Ｗ）を測定した。発光輝度については、ＣＳ−１０００（ミノルタ製）を用いて測定した。
【０１８２】
さらに１０ｍＡ／ｃｍ²の一定電流で駆動したときに、初期輝度が元の半分に低下するのに要した時間を測定し、これを半減寿命時間として耐久性の指標とした。
【０１８３】
その結果を、同じ化合物を用いた有機ＥＬ素子のうちで、蒸着膜中の一般式２で表される不純物の含有率が最も高い素子に対する結果を１００とした相対値として、表１に示した。
【０１８４】
【表１】

【０１８５】
表１から明らかなように、一般式１で表される化合物を含有する層に含まれる、一般式２で表される不純物の含有率が０．５質量％未満の場合には層を有する有機ＥＬ素子の性能は大きく改善される。とくにこの効果は耐久性に関して顕著であり、０．１質量％以下にまで不純物の含有を抑制した層を有する有機ＥＬ素子においてはとくに大きな改善効果がある。
【０１８６】
また、層中に含まれる一般式２の化合物の分子量がある程度以上に大きい場合、いくぶん改善効果が小さくなる傾向があるが、これは一般式２で表される不純物の分子が大きくなった結果、ある程度には不純物の安定性が高くなったためであろうと推測される。
【０１８７】
実施例２
《有機ＥＬ素子２−１〜２−１６の作製及び評価》
実施例１の有機ＥＬ素子１−３の電子輸送層におけるＢＣＰを表２に示す実施例１で調製した化合物に置き換えた以外は、有機ＥＬ素子１−３と全く同じ方法で作製した有機ＥＬ素子２−１〜２−１６について、実施例１と同様の方法で、電子輸送層中の一般式２で表される化合物の含有量、発光輝度、発光効率及び半減寿命時間（耐久性）を測定した。測定結果を表３に示す。
【０１８８】
【表２】

【０１８９】
表２から明らかなように、いずれの化合物についても一般式２で表される不純物の混入を抑制することは、該化合物を用いた有機化合物層が電子輸送層として機能する場合においても有機ＥＬ素子の特性、とくに耐久性について顕著な改善効果をもたらすことが分かった。
【０１９０】
実施例３
《有機ＥＬ素子３−１〜３−３２の作製及び評価》
実施例１の有機ＥＬ素子１−１の作製方法において、別のモリブデン製抵抗加熱ボートにリン光性物質であるＩｒ−１を１００ｍｇ入れて真空蒸着装置に取付け、発光層をサンプル１−１ＡとＩｒ−１の入った加熱ボートにそれぞれ通電しサンプル１−１Ａを０．２ｎｍ／ｓｅｃ、Ｉｒ−１を０．０１２ｎｍ／ｓｅｃの蒸着速度で共蒸着させた膜厚２０ｎｍの発光層とした以外は、有機ＥＬ素子１−１と同様の方法で有機ＥＬ素子３−１を作製した。
【０１９１】
同様にして実施例１の有機ＥＬ素子１−２〜１−３２の発光層を上述した方法でＩｒ−１と共蒸着させた発光層とした有機ＥＬ素子３−２〜３−３２を作製した。
【０１９２】
得られたリン光発光型有機ＥＬ素子３−１〜３−３２について、実施例１と同様にして、発光層中の一般式２で表される化合物の含有量、発光輝度、発光効率、耐久性を評価した結果を表３に示す。
【０１９３】
【表３】

【０１９４】
表３から明らかなように、リン光発光型の有機ＥＬ素子を作製する場合においても一般式２で表される化合物の混入を抑制することは、いずれの化合物をホスト化合物として用いる場合においても有機ＥＬ素子の特性、とくに耐久性について顕著な改善効果をもたらすことが分かった。
【０１９５】
実施例４
《有機ＥＬ素子４−１〜４−１６の作製及び評価》
実施例１の有機ＥＬ素子１−１の作製において、別のモリブデン製抵抗加熱ボートにリン光性物質であるＩｒ−６を１００ｍｇ入れて、さらに別のモリブデン製抵抗加熱ボートにリン光性物質であるＩｒ−１２を１００ｍｇ入れて真空蒸着装置に取付け、発光層を、サンプル１−１ＡとＩｒ−６とＩｒ−１２の入った加熱ボートにそれぞれ通電し、サンプル１−１Ａを０．５ｎｍ／ｓｅｃ、Ｉｒ−６を０．００５ｎｍ／ｓｅｃ、Ｉｒ−１２を０．０２ｎｍ／ｓｅｃの蒸着速度で共蒸着させた膜厚３０ｎｍの発光層とした以外は、有機ＥＬ素子１−１と同様の方法で２波長発光型の有機ＥＬ素子４−１を作製した。Ｉｒ−６のリン光発光は赤色であり、Ｉｒ−１２のリン光発光は青色であるので、該有機ＥＬ素子からの発光は２つの発光極大波長を有しており、人間の視覚には白色の発光として認識される。
【０１９６】
同様にして実施例１の有機ＥＬ素子１−２〜１−４、１−９〜１−１６、１−２１〜１−２４の発光層を上述した方法で、Ｉｒ−６とＩｒ−１２と共蒸着させた発光層とした有機ＥＬ素子４−２〜４−１６を作製した。実施例１と同様の方法で、発光層中の一般式２で表される化合物の含有量、発光輝度、発光効率及び半減寿命時間（耐久性）を測定した。測定結果を表４に示す。
【０１９７】
【表４】

【０１９８】
表４の結果から明らかなように、リン光発光型白色発光有機ＥＬ素子を作製する場合においても一般式２で表される不純物の混入を抑制することは、いずれの化合物をホスト化合物として用いる場合においても有機ＥＬ素子の特性、とくに耐久性について顕著な改善効果をもたらす。
【０１９９】
実施例５
実施例３の有機ＥＬ素子３−４（緑色）のＩｒ−１をＩｒ−６、Ｉｒ−１２に変更した以外は有機ＥＬ素子３−４と同様の方法で有機ＥＬ素子５−１（赤色）、５−２（青色）を作製した。
【０２００】
これらの素子を同一基板上に並置して、図１，２に示すアクティブマトリクス方式フルカラー表示装置を作製した。即ち同一基板上に、複数の走査線５及びデータ線６を含む配線部と、並置した複数の画素３（発光の色が赤領域の画素、緑領域の画素、青領域の画素等）とを有し、配線部の走査線５及び複数のデータ線６はそれぞれ導電材料からなり、走査線５とデータ線６は格子状に直交して、直交する位置で画素３に接続している（詳細は図示せず）。前記複数画素３は、それぞれの発光色に対応した有機ＥＬ素子、アクティブ素子であるスイッチングトランジスタと駆動トランジスタそれぞれが設けられたアクティブマトリクス方式で駆動されており、走査線５から走査信号が印加されると、データ線６から画像データ信号を受け取り、受け取った画像データに応じて発光する。この様に各赤、緑、青の画素を適宜、並置することによって、フルカラー表示が可能となる。
【０２０１】
該フルカラー表示装置を駆動することにより、輝度の高く耐久性の良好な、鮮明なフルカラー動画表示が得られた。
【０２０２】
【発明の効果】
本発明により、高い発光輝度および優れた量子効率と同時に、とくに高い耐久性を有する有機エレクトロルミネッセンス素子、およびそれを備えた表示装置もしくは照明装置を提供することができた。
【図面の簡単な説明】
【図１】有機ＥＬ素子から構成される表示装置の一例を示した図である。
【図２】表示部Ａの模式図である。
【図３】画素の模式図である。
【図４】パッシブマトリックス方式による表示装置の模式図である。
【符号の説明】
１ ディスプレイ
３ 画素
５ 走査線
６ データ線
７ 電源ライン
１０ 有機ＥＬ素子
１１ スイッチングトランジスタ
１２ 駆動トランジスタ
１３ コンデンサ
Ａ 表示部
Ｂ 制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence element (hereinafter sometimes referred to as an organic EL element), a display device, and a lighting device. Specifically, the organic electroluminescence element has emission luminance and luminous efficiency, and is particularly excellent in durability. The present invention relates to a display device or a lighting device having the same.
[0002]
[Prior art]
Conventionally, there is an electroluminescence display (ELD) as a light-emitting electronic display device. As a component of ELD, an inorganic electroluminescent element and an organic electroluminescent element are mentioned. Inorganic electroluminescent elements have been used as planar light sources, but an alternating high voltage is required to drive the light emitting elements.
[0003]
On the other hand, an organic electroluminescence device has a structure in which a light emitting layer containing a light emitting compound is sandwiched between a cathode and an anode, and excitons (exciton) are injected by injecting electrons and holes into the light emitting layer and recombining them. ) And emits light using the emission of light (fluorescence / phosphorescence) when the exciton is deactivated, and can emit light at a voltage of several V to several tens of V. Since it is a self-luminous type, it has a wide viewing angle, high visibility, and since it is a thin-film type complete solid-state device, it has attracted attention from the viewpoints of space saving and portability.
[0004]
For the development of organic electroluminescence elements for practical use in the future, organic electroluminescence elements that emit light efficiently and with high brightness with lower power consumption are desired. For example, stilbene derivatives, distyrylarylene derivatives Alternatively, a technique for doping a tristyrylarylene derivative with a small amount of phosphor to improve emission luminance and extend the lifetime of the device (for example, see Patent Document 1), using an 8-hydroxyquinoline aluminum complex as a host compound, An element having an organic light-emitting layer doped with a trace amount of phosphor (for example, see Patent Document 2), an element having an organic light-emitting layer doped with a quinacridone dye as a host compound using 8-hydroxyquinoline aluminum complex (For example, refer to Patent Document 3).
[0005]
In the technique disclosed in the above document, when the emission from the excited singlet is used, the generation ratio of the singlet exciton and the triplet exciton is 1: 3, so the generation probability of the luminescent excited species is 25%. Since the light extraction efficiency is about 20%, the limit of the external extraction quantum efficiency (ηext) is set to 5%.
[0006]
However, since Princeton University has reported on organic electroluminescence devices using phosphorescence emission from excited triplets (see, for example, Non-Patent Document 1), research on materials that exhibit phosphorescence at room temperature has become active. (For example, see Non-Patent Document 2 and Patent Document 4).
[0007]
When excited triplets are used, the upper limit of internal quantum efficiency is 100%, so in principle the luminous efficiency is four times that of excited singlets, and the performance is almost the same as that of cold cathode tubes. It can be applied to and attracts attention.
[0008]
For example, many compounds have been studied focusing on heavy metal complexes such as iridium complex systems (see, for example, Non-Patent Document 3).
[0009]
Further, studies using tris (2-phenylpyridine) iridium as a dopant have been made (for example, see Non-Patent Document 2).
[0010]
In addition, L as a dopant₂Ir (acac) eg (ppy)₂Ir (acac) (see, for example, Non-Patent Document 4) and tris (2- (p-tolyl) pyridine) iridium (Ir (ptpy)) as a dopant_Three), Tris (benzo [h] quinoline) iridium (Ir (bzq))_Three), Ir (bzq)₂Studies using ClP (Bu) 3 or the like (for example, see Non-Patent Document 5) are being conducted.
[0011]
In addition, in order to obtain high luminous efficiency, a hole transporting compound is used as a host of the phosphorescent compound (see, for example, Non-Patent Document 6).
[0012]
Further, various electron transporting materials are used as phosphorescent compound hosts by doping them with a novel iridium complex (for example, see Non-Patent Document 4). Furthermore, high luminous efficiency is obtained by introducing a hole blocking layer (see, for example, Non-Patent Document 5).
[0013]
However, although the external extraction efficiency of nearly 20%, which is the theoretical limit, has been achieved for green light emission, sufficient efficiency has not yet been obtained for other light emission colors, and improvements are necessary. In the organic electroluminescence element for practical use, further development of an organic electroluminescence element that emits light efficiently and with high luminance with low power consumption is desired.
[0014]
At the same time, there is a strong demand for organic electroluminescence elements having element durability, that is, a light emission lifetime, which is practically used as a device for display applications and illumination applications. In this regard, studies have been made from various directions so far. For example, Patent Documents 5, 6, and 7 describe an approach from the viewpoint of element sealing, and Patent Document 8 describes an appropriate energy level. Patent Document 9 discloses an approach for improving the durability by adding a dopant having an element. Patent Document 9 discloses a method of enclosing a hygroscopic agent in an airtight space formed by a substrate material, an element, and an encapsulant constituting the element. Needless to say, the charge transporting material constituting the device and the material itself used for the light emitting layer have been studied to construct a more durable organic electroluminescence device. There are a great many disclosures such as Patent Documents 10, 11, 12, and 13.
[0015]
Furthermore, regarding these organic materials, the influence of the impurities contained in the organic compound layer in the element formed by the material on the durability of the formed organic electroluminescence element has been studied. For example, Patent Document 14 describes the amount of impurities contained in the organic compound layer constituting the element, and Patent Document 15 describes the amount of impurities derived from the cross-coupling reaction when synthesizing the organic electroluminescent material. Reference 16 shows that impurities containing halogen atoms affect the durability of the device.
[0016]
These various approaches can be used together as long as they do not cancel each other. Therefore, a technical approach for further enhancing the durability of the organic electroluminescence device continues to be sought, and a new technology for improving the durability is still awaited.
[0017]
[Patent Document 1]
Japanese Patent No. 3093796
[0018]
[Patent Document 2]
Japanese Unexamined Patent Publication No. 63-264692
[0019]
[Patent Document 3]
JP-A-3-255190
[0020]
[Patent Document 4]
US Pat. No. 6,097,147
[0021]
[Patent Document 5]
JP 2002-31559 A
[0022]
[Patent Document 6]
Japanese Patent Laid-Open No. 08-236271
[0023]
[Patent Document 7]
JP 2002-367771 A
[0024]
[Patent Document 8]
Japanese Patent Application Laid-Open No. 07-065958
[0025]
[Patent Document 9]
JP 2002-198170 A
[0026]
[Patent Document 10]
JP 2002-363227 A
[0027]
[Patent Document 11]
Japanese Patent Laid-Open No. 2002-352961
[0028]
[Patent Document 12]
JP 2002-356462 A
[0029]
[Patent Document 13]
JP 2002-363550 A
[0030]
[Patent Document 14]
JP 2002-373785 A
[0031]
[Patent Document 15]
JP 2002-373786 A
[0032]
[Patent Document 16]
International Patent WO 00/41443
[0033]
[Non-Patent Document 1]
M.M. A. Baldo et al. , Nature, 395, 151-154 (1998)
[0034]
[Non-Patent Document 2]
M.M. A. Baldo et al. , Nature, 403, 17, 750-753 (2000)
[0035]
[Non-Patent Document 3]
S. Lamansky et al. , J .; Am. Chem. Soc. , 123, 4304 (2001)
[0036]
[Non-Patent Document 4]
M.M. E. Thompson et al. , The 10th International Workshop on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu)
[0037]
[Non-Patent Document 5]
Moon-Jae Youn. Og, Tetsuo Tsutsui et al. , The 10th International Works on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu)
[0038]
[Non-Patent Document 6]
Ikai et al. , The 10th International Workshop on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu)
[0039]
[Problems to be solved by the invention]
The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide an organic electroluminescence device having particularly high durability at the same time as high emission luminance and excellent quantum efficiency, and the same. It is to provide a display device or a lighting device.
[0040]
[Means for Solving the Problems]
The object of the present invention is achieved by the following constitution.
[0041]
  (1) It has at least one layer containing a pyridoindole compound represented by the general formula 1 and the content of the pyridoindole compound represented by the general formula 2 is 0.5 mass. Organic electroluminescent element characterized by being less than%.
(In the above general formulas 1 and 2, A represents a linking group, R₁And R₂Independently represents a monovalent substituent, and m represents an integer of 2 to 6. X₁= C (R₃)-, At this time R₃Represents a monovalent substituent, and X₂= C (R₄)-, At this time R₄Represents a monovalent substituentThe)
  (2) The organic electroluminescence device according to (1), wherein the content of the compound represented by the general formula 2 is less than 0.1% by mass.
[0044]
  (3The molecular weight of the compound represented by the general formula 2 is less than 250 (1)Or (2)The organic electroluminescent element of description.
[0045]
  (4The light emission when an electric field is applied includes phosphorescent light emission (1) to (1)3The organic electroluminescent element of any one of 1).
[0046]
  (5) It emits white light (1) to (4The organic electroluminescent element of any one of 1).
[0047]
  (6(1) to (5The display element provided with the organic electroluminescent element of any one of 1).
[0048]
  (7(1) to (5The lighting device provided with the organic electroluminescent element according to any one of the above.
[0049]
  (8()7And a liquid crystal element as a display means.
[0050]
As a result of repeated studies, the present inventors have had a great influence on the durability of the manufactured device when impurities derived from the structural unit are mixed in a layer containing an organic electroluminescent material having a specific structural unit. As a result, the present invention was completed.
[0051]
Hereinafter, the present invention will be described in more detail.
The organic electroluminescent element of the present invention has at least one layer containing the compound represented by the above general formula 1 between the cathode and the anode. Further, the layer containing the compound represented by the general formula 1 has a content of the compound represented by the general formula 2 of less than 0.5% by mass.
[0052]
The organic electroluminescent device according to the present invention has a layer containing the compound of the general formula 1, and suppresses the content of the compound of the general formula 2 contained in the layer to at least less than 0.5% by mass. By doing so, high luminance and excellent quantum efficiency are realized, and at the same time, high durability is realized.
[0053]
The durability of the device is deteriorated by containing the compound of the general formula 2, and the mechanism is not necessarily fascinating, but the compound of the general formula 2 is poorer in electrical and thermal stability than the compound of the general formula 1. Therefore, it is considered that the decomposition occurs in a relatively short time during electroluminescence. The decomposition product generated thereby forms a trap level in the organic electroluminescence device, or reacts with the compound of the general formula 1 to promote the decomposition of the compound, so that the device can be obtained in a relatively short time. It can be estimated that it will deteriorate. This effect appears strongly when the molecular weight of the compound of the general formula 2 is small, and is particularly remarkable when the molecular weight of the compound of the general formula 2 is smaller than 250.
[0054]
In the present invention, the layer containing the compound represented by the general formula 1 preferably has a content of the compound represented by the general formula 2 of less than 0.3% by mass, more preferably 0.1% by mass. Thus, an organic electroluminescence device having extremely high durability as well as higher emission luminance and excellent quantum efficiency can be obtained.
[0055]
  The organic electroluminescent material of the general formula 1 is a compound having a structure in which a structural part having m nitrogen-containing aromatic rings is connected to the linking group A. Where m is2A compound in which m hydrogen atoms are bonded to the linking group A, that is, a compound from which A is derived is represented by methane, ethene, acetylene, benzene, naphthalene, azulene, anthracene, phenanthrene, fluorene, pyrene In addition to hydrocarbon compounds such as tetracene, borane, ammonia, silane, hydrogen sulfide, water and other heteroatoms bonded to hydrogen, furan, thiophene, selenophene, pyrrole, pyridine, pyrazine, pyrimidine, pyrazole, imidazole, triazole , Triazine, thiazole, oxadiazole, thiadiazole and other heteroaromatic compounds, as well as benzofuran, dibenzothiophene, indole, isoindole, carbazole, benzthiazole, benzimidazole, pyrazoloimidazole, La pyrazolotriazole, quinoline, quinoline, may acridine, pyridoindole, Jipiridopiroru, purine, cinnoline, phenoxazine, and the like condensed polycyclic aromatic compounds such as phenothiazine. The linking group A derived from these compounds may have a substituent, and examples thereof include an alkyl group (for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a tert-butyl group, a pentyl group, Hexyl group, octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, etc.), cycloalkyl group (for example, cyclopentyl group, cyclohexyl group, etc.), alkenyl group (for example, vinyl group, allyl group, etc.), alkynyl group ( For example, ethynyl group, propargyl group, etc.), aryl group (eg, phenyl group, naphthyl group, etc.), heteroaryl group (eg, furyl group, thienyl group, pyridyl group, pyridazyl group, pyrimidyl group, pyrazyl group, triazyl group, Imidazolyl, pyrazolyl, thiazolyl, benzimidazolyl, benzoo Sazolyl group, quinazolyl group, phthalazyl group, etc.), heterocyclic group (eg, pyrrolidyl group, imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (eg, methoxy group, ethoxy group, propyloxy group, pentyloxy group, Hexyloxy group, octyloxy group, dodecyloxy group, etc.), cycloalkoxy group (eg, cyclopentyloxy group, cyclohexyloxy group, etc.), aryloxy group (eg, phenoxy group, naphthyloxy group, etc.), alkylthio group (eg, Methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecylthio group, etc.), cycloalkylthio group (for example, cyclopentylthio group, cyclohexylthio group, etc.), arylthio group (for example, phenylthio group) , Naphthylthio group, etc.), alkoxycarbonyl group (eg, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl group, octyloxycarbonyl group, dodecyloxycarbonyl group, etc.), aryloxycarbonyl group (eg, phenyloxycarbonyl group) , Naphthyloxycarbonyl group, etc.), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group, dodecylaminosulfonyl group) Group, phenylaminosulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group, etc.), acyl group (for example, acetyl group, ethylcarbo group) Nyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecylcarbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group, etc.), acyloxy group (for example, acetyloxy) Group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group, etc.), amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonylamino group, propyl) Carbonylamino group, pentylcarbonylamino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octylcarbonylamino group, dode Carbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group, etc.), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, cyclohexylaminocarbonyl group) Octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylaminocarbonyl group, etc.), ureido group (for example, methylureido group, ethylureido group, pentyl) Ureido group, cyclohexylureido group, octylureido group, dodecylureido group, phenylureido group, naphthylureido group, 2-pyridylaminoureido ), Sulfinyl groups (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecylsulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group, etc.), Alkylsulfonyl groups (eg, methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group, etc.), arylsulfonyl groups (phenylsulfonyl group, naphthylsulfonyl group, 2-pyridylsulfonyl) Group), amino group (for example, amino group, ethylamino group, dimethylamino group, butylamino group, cyclopentylamino group, 2-ethylhexylamino group, Dodecylamino group, diphenylamino group, anilino group, ethyltolylamino group, naphthylamino group, 2-pyridylamino group, etc.), fluorinated hydrocarbon group (for example, fluoromethyl group, trifluoromethyl group, pentafluoroethyl group, penta) Fluorophenyl group, etc.), cyano group, mercapto group, silyl group (for example, trimethylsilyl group, triisopropylsilyl group, triphenylsilyl group, phenyldiethylsilyl group, etc.), fluorine atom and the like. These substituents may be further substituted with the above substituents. In addition, a plurality of these substituents may be bonded to each other to form a ring. In addition, 2-6 nitrogen-containing aromatic rings couple | bonded with A may mutually be same or different.
[0056]
Examples of the linking group A are shown below, but the structure of the compound represented by the general formula 1 according to the present invention is not limited by these examples.
[0057]
[Chemical 2]

[0058]
[Chemical Formula 3]

[0059]
[Formula 4]

[0060]
[Chemical formula 5]

[0061]
[Chemical 6]

[0062]
  R in the above general formula 1₁And R₂Independently represents a monovalent substituent, and X₁= C (R₃)-, X₂= C (R₄)-. Where R₁, R₂, R₃, R₄Examples thereof include the same substituents as the substituents exemplified as the substituents for modifying the linking group A described above. R₁And R₃ , R ₂ And R ₄ EachCombined with each otherA ring structure may be formed.
[0063]
  Below, it binds to the linking group A of general formula 1.Of the present inventionExamples of nitrogen-containing aromatic compound residuesAnd reference examplesHowever, the structure of the compound represented by the general formula 1 is not limited by these examples.
[0064]
[Chemical 7]

[0065]
[Chemical 8]

[0066]
The compound represented by the general formula 1 is, for example, Tetrahedron Lett., 39 (1998), pages 2367-2370, Japanese Patent No. 3161360, Angew. Chem. Int. Ed., 37 (1998), pages 2046-2067, Tetrahedron Lett., 41 (2000), pages 481-484, Synth. Commun., 11 (7) (1981), pages 513-519, and Chem. Rev., 2002, 102, pages 1359-51469 etc., etc. can be produced by a synthesis method well known to those skilled in the art.
[0067]
The compound represented by the general formula 1 used in the present invention can be used for any of a hole transport layer, an electron transport layer, and a light-emitting layer of an organic electroluminescence element to be described later. It is preferable to use for. It is also preferably used as a material known as a “host compound” to those skilled in the art who do not emit light by transferring energy to a fluorescent or phosphorescent compound in the light emitting layer. it can.
[0068]
R in the compound represented by the above general formula 2₁, R₂, X₁, X₂Is R of general formula 1₁, R₂, X₁, X₂This is the same as that described in.
[0069]
  Examples of compounds represented by general formula 2IsRedondoLeis there. These compounds may be further substituted, and examples of the substituent include R described above.₁And R₂The same substituents as mentioned as examples can be mentioned. Preferred substituents are alkyl groups, aryl groups, heteroaryl groups, alkoxy groups, alkylthio groups, aryloxy groups, arylthio groups, cyano groups, fluorine atoms, and particularly preferably alkyl groups, aryl groups, heteroaryl groups, fluorine atoms. Is an atom.
[0070]
Moreover, it is preferable that the molecular weight of the compound represented by General formula 2 is 600-2000. When the molecular weight is 600 to 2000, Tg (glass transition temperature) increases, thermal stability is improved, and device lifetime is improved. A more preferred molecular weight is 800-2000.
[0071]
<< Constituent layers of organic EL elements >>
The constituent layers of the organic EL element of the present invention are described.
[0072]
In the present invention, preferred specific examples of the layer constitution of the cathode, the anode and the organic compound layer are shown below, but are not limited thereto.
(I) Anode / light emitting layer / electron transport layer / cathode
(Ii) Anode / hole transport layer / light emitting layer / electron transport layer / cathode
(Iii) Anode / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode
(Iv) Anode / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode buffer layer / cathode
(V) Anode / anode buffer layer / hole transport layer / light emitting layer / hole blocking layer / electron transport layer / cathode buffer layer / cathode
"anode"
The anode will be described.
[0073]
As the anode in the organic EL element, an electrode material made of a metal, an alloy, an electrically conductive compound and a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode materials include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO2, and ZnO. Alternatively, an amorphous material such as IDIXO (In2O3-ZnO) that can form a transparent conductive film may be used. For the anode, a thin film may be formed by depositing these electrode materials by a method such as vapor deposition or sputtering, and a pattern having a desired shape may be formed by a photolithography method, or when the pattern accuracy is not required (100 μm or more) Degree), a pattern may be formed through a mask having a desired shape when the electrode material is deposited or sputtered. When light emission is extracted from the anode, it is desirable that the transmittance is greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.
[0074]
"cathode"
Next, the cathode will be described.
[0075]
As the cathode, a material having a work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al2O3) mixture. , Indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function value than this, such as a magnesium / silver mixture, magnesium, from the viewpoint of electron injectability and durability against oxidation, / Aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al2O3) mixtures, lithium / aluminum mixtures, aluminum and the like are preferred. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 1000 nm, preferably 50 nm to 200 nm. In order to transmit light, if either one of the anode or the cathode of the organic EL element is transparent or translucent, the light emission luminance is improved, which is convenient.
[0076]
<< Injection layer >>: Electron injection layer, hole injection layer
Next, the injection layer used as the layer of the organic EL element of the present invention will be described.
[0077]
The injection layer is provided as necessary, and there are an electron injection layer and a hole injection layer, and as described above, exists between the anode and the light emitting layer or the hole transport layer, and between the cathode and the light emitting layer or the electron transport layer. You may let them.
[0078]
An injection layer is a layer provided between an electrode and an organic layer in order to lower drive voltage or improve light emission luminance. “Organic EL element and its forefront of industrialization (issued on November 30, 1998 by NTS Corporation) 2), Chapter 2, “Electrode Materials” (pages 123 to 166) in detail, and includes a hole injection layer (anode buffer layer) and an electron injection layer (cathode buffer layer).
[0079]
The details of the anode buffer layer (hole injection layer) are described in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069 and the like. As a specific example, copper phthalocyanine is used. Examples thereof include a phthalocyanine buffer layer represented by an oxide, an oxide buffer layer represented by vanadium oxide, an amorphous carbon buffer layer, and a polymer buffer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.
[0080]
The details of the cathode buffer layer (electron injection layer) are described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, and the like. Specifically, strontium, aluminum, etc. Metal buffer layer typified by lithium, alkali metal compound buffer layer typified by lithium fluoride, alkaline earth metal compound buffer layer typified by magnesium fluoride, oxide buffer layer typified by aluminum oxide, etc. .
[0081]
The buffer layer (injection layer) is preferably a very thin film, and although it depends on the material, the film thickness is preferably in the range of 0.1 nm to 100 nm.
[0082]
<< Blocking layer >>: Hole blocking layer, electron blocking layer
As described above, the blocking layer is provided as necessary in addition to the basic constituent layer of the organic compound thin film. For example, JP-A-11-204258, JP-A-11-204359, and “Organic EL devices and their forefront of industrialization” (issued on November 30, 1998 by NTS, Inc.), page 237, etc. There is a hole blocking layer.
[0083]
The hole blocking layer is an electron transport layer in a broad sense, and is made of a material that has a function of transporting electrons and has a very small ability to transport holes. By blocking holes while transporting electrons, And the recombination probability of holes can be improved.
[0084]
On the other hand, the electron blocking layer is a hole transport layer in a broad sense, made of a material that has a function of transporting holes and has a very small ability to transport electrons, and blocks electrons while transporting holes. Thus, the probability of recombination of electrons and holes can be improved.
[0085]
<Light emitting layer>
Next, the light emitting layer will be described.
[0086]
The light-emitting layer is a layer that emits light by recombination of electrons and holes injected from the electrode, the electron transport layer, or the hole transport layer. It may be an interface with an adjacent layer.
[0087]
The material used for the light emitting layer (hereinafter referred to as the light emitting material) is preferably an organic compound or complex that emits fluorescence or phosphorescence, and is appropriately selected from known materials used for the light emitting layer of the organic EL device. Can be used. In particular, it is preferable to use a phosphorescent compound that emits phosphorescence as the light-emitting material, whereby light can be emitted more efficiently and with high luminance.
[0088]
Such a light-emitting material is mainly an organic compound, and has a desired color tone, for example, Macromol. Synth. 125, pages 17 to 25, and the like.
[0089]
The light emitting material may have a hole transport function and an electron transport function in addition to the light emitting performance, and most of the hole transport material and the electron transport material can be used as the light emitting material.
[0090]
The light-emitting material may be a polymer material such as p-polyphenylene vinylene or polyfluorene, and a polymer material in which the light-emitting material is introduced into a polymer chain or the light-emitting material is a polymer main chain is used. May be.
[0091]
This light emitting layer can be formed by forming the above compound by a known thinning method such as a vacuum deposition method, a spin coating method, a casting method, or an LB method. Although the film thickness as a light emitting layer does not have a restriction | limiting in particular, Usually, it selects in the range of 5 nm-5 micrometers. This light emitting layer may have a single layer structure composed of one or two or more of these light emitting materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions. A preferred embodiment of the organic EL device of the present invention is when the light emitting layer is composed of two or more materials, and one of them is the compound of the present invention.
[0092]
Further, as described in JP-A-57-51781, this light emitting layer is prepared by dissolving the above light emitting material in a solvent together with a binder such as a resin, and then using a spin coating method or the like. It can be formed as a thin film. There is no restriction | limiting in particular about the film thickness of the light emitting layer formed in this way, Although it can select suitably according to a condition, Usually, it is the range of 5 nm-5 micrometers.
[0093]
In the present invention, the light emitting layer may contain at least one fluorescent compound having a fluorescence maximum wavelength longer than the emission maximum wavelength in addition to the organic compound as the main component. In this way, when a compound is contained in the light emitting layer in addition to the main constituent component, the main constituent component is called a host compound or simply a host, and the added compound is called a dopant. The aforementioned organic compound as the main constituent component is a host compound, and the added fluorescent compound is a dopant, and in this case, a fluorescent dopant. The fluorescent dopant is excited by the host compound to emit fluorescence, and as a result, light emission from the fluorescent compound is taken out from the organic EL device thus configured. Fluorescent compounds that can be used in such applications include coumarin dyes, pyran dyes, cyanine dyes, croconium dyes, squalium dyes, oxobenzanthracene dyes, fluorescein dyes, rhodamine dyes, pyrylium dyes. Examples thereof include dyes, perylene dyes, stilbene dyes, polythiophene dyes, and rare earth complex phosphors. As the fluorescent compound to be used, those having a high fluorescence quantum yield in a solution state are preferable, and the fluorescence quantum yield is preferably 10% or more, particularly preferably 30% or more. The fluorescence quantum yield can be measured by the method described in Spectroscopic II, page 362 (1992 version, Maruzen) of the Fourth Edition Experimental Chemistry Course 7.
[0094]
Moreover, you may add the phosphorescent compound which has a light emission maximum wavelength longer than the light emission maximum wavelength of the compound which comprises a light emitting layer as a dopant similarly to having added the fluorescent dopant in said form. When a phosphorescent compound (dopant) is added to the light emitting layer, phosphorescence emission is extracted from the organic EL element by energy transfer from the host compound to the phosphorescent dopant. As already described, the form using phosphorescence emission is preferable from the viewpoint of light emission efficiency as the organic EL element. Similarly, in the present invention, an organic EL element in which at least a part of the light emitting component is due to phosphorescence emission is also used. preferable.
[0095]
In the organic electroluminescence device according to the present invention, from the viewpoint of the luminous efficiency described above, phosphorescence emission in which the compound represented by the general formula 1 according to the present invention is used as a host compound and a light emitting layer is formed with a phosphorescent compound. A conductive organic electroluminescence element is particularly preferable.
[0096]
The phosphorescent compound in the present invention is a compound in which light emission from an excited triplet is observed, and is a compound having a phosphorescence quantum yield of 0.001 or more at 25 ° C. The phosphorescence quantum yield is preferably 0.01 or more, more preferably 0.1 or more.
[0097]
The phosphorescence quantum yield can be measured by the method described in Spectroscopic II, page 398 (1992 edition, Maruzen) of Experimental Chemistry Course 4 of the 4th edition. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescence quantum yield used in the present invention is only required to achieve the phosphorescence quantum yield in any solvent.
[0098]
The phosphorescent compound used in the present invention is preferably a complex compound containing a group 8 metal in the periodic table of elements, more preferably an iridium compound, an osmium compound, or a platinum compound (platinum complex system). Compound), and most preferred is an iridium compound.
[0099]
Specific examples of the phosphorescent compound used in the present invention are shown below, but are not limited thereto. These compounds are described, for example, in Inorg. Chem. 40, 1704-1711, and the like.
[0100]
[Chemical 9]

[0101]
[Chemical Formula 10]

[0102]
Embedded image

[0103]
Furthermore, in addition to the host compound and the phosphorescent compound, at least one fluorescent compound having a fluorescence maximum wavelength may be contained in a region longer than the maximum wavelength of light emission from the phosphorescent compound. In this case, electroluminescence as an organic EL element can be emitted from the fluorescent compound by energy transfer from the host compound and the phosphorescent dopant.
[0104]
In addition, a light-emitting element having a plurality of light emission maximum wavelengths can be configured by simultaneously using a plurality of types of fluorescent or phosphorescent dopants and taking out light emitted therefrom. For example, by using polyvinyl carbazole as a luminescent compound that also serves as a host compound and coumarin 6 and Nile red as fluorescent dopants, blue luminescence from polyvinyl carbazole, green luminescence from coumarin 6 and red luminescence from Nile red can be simultaneously used. An element that emits white light can be formed. Similarly, in the phosphorescent organic EL element, light emission can be mixed by using a plurality of types of phosphorescent dopants. Taking advantage of the characteristics of the organic EL element that it is thin and can be formed on a resin substrate, a white light-emitting element is constructed considering the case of using it for a panel or other lighting device It is practically useful to do. At present, there is no single light emitting material that exhibits white light emission, and therefore, a plurality of light emitting colors are simultaneously emitted by a plurality of light emitting materials to obtain white light emission by color mixing. As a combination of a plurality of luminescent colors, those containing three luminescence maximum wavelengths of three primary colors of blue, green, and blue may be used. The thing containing the light emission maximum wavelength may be used. As described above, the light emission of these mixed colors can be performed by using a dopant, and the color tone of the emission color can be controlled by changing the kind and amount of the dopant.
[0105]
《Hole transport layer》
Next, the hole transport layer will be described.
[0106]
The hole transport layer is made of a material having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. The hole transport layer can be provided as a single layer or a plurality of layers.
[0107]
The hole transport material is not particularly limited, and is conventionally used as a hole charge injection / transport material in an optical transmission material or a well-known material used for a hole injection layer or a hole transport layer of an EL element. Any one can be selected and used.
[0108]
The hole transport material has one of hole injection or transport and electron barrier properties, and may be either organic or inorganic. For example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbenes Derivatives, silazane derivatives, aniline copolymers, conductive polymer oligomers, particularly thiophene oligomers, and the like can be given.
[0109]
As the hole transport material, those described above can be used, but it is preferable to use a porphyrin compound, an aromatic tertiary amine compound and a styrylamine compound, particularly an aromatic tertiary amine compound.
[0110]
Representative examples of aromatic tertiary amine compounds and styrylamine compounds include N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl; N, N′-diphenyl-N, N′— Bis (3-methylphenyl)-[1,1′-biphenyl] -4,4′-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl; 1,1-bis (4-di-p-tolyl) Aminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N′-diphenyl-N, N ′ − (4-methoxyphenyl) -4,4′-diaminobiphenyl; N, N, N ′, N′-tetraphenyl-4,4′-diaminodiphenyl ether; 4,4′-bis (diphenylamino) quadriphenyl; N, N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 ′-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenylamino- (2-diphenylvinyl) benzene; 3-methoxy-4′-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and two more described in US Pat. No. 5,061,569 Having a condensed aromatic ring of, for example, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPD), JP-A-4-308 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units described in Japanese Patent No. 88 are linked in a starburst type ( MTDATA) and the like.
[0111]
Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.
[0112]
In addition, inorganic compounds such as p-type-Si and p-type-SiC can also be used as the hole injection material and the hole transport material.
[0113]
In the present invention, the hole transport material of the hole transport layer preferably has a fluorescence maximum wavelength at 415 nm or less. That is, the hole transport material is preferably a compound that has a hole transport ability, prevents the emission of light from becoming longer, and has a high Tg.
[0114]
The hole transport layer can be formed by thinning the hole transport material by a known method such as a vacuum deposition method, a spin coating method, a casting method, an ink jet method, or an LB method. Although there is no restriction | limiting in particular about the film thickness of a positive hole transport layer, Usually, it is about 5-5000 nm. The hole transport layer may have a single layer structure composed of one or more of the above materials.
[0115]
《Electron transport layer》
Next, the electron transport layer will be described.
[0116]
The electron transport layer is made of a material having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. The electron transport layer can be provided as a single layer or a plurality of layers.
[0117]
Conventionally, in the case of a single-layer electron transport layer and a plurality of layers, the following materials are used as the electron transport material (also serving as a hole blocking material) used for the electron transport layer adjacent to the cathode side with respect to the light emitting layer. Are known.
[0118]
Further, the electron transport layer only needs to have a function of transmitting electrons injected from the cathode to the light emitting layer, and any material can be selected from conventionally known compounds. .
[0119]
Examples of materials used for this electron transport layer (hereinafter referred to as electron transport materials) include heterocyclic tetracarboxylic acid anhydrides such as nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, naphthalene perylene, carbodiimides, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material.
[0120]
Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.
[0121]
In addition, metal complexes of 8-quinolinol derivatives such as tris (8-quinolinol) aluminum (Alq), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) aluminum, Tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and the central metals of these metal complexes are In, Mg, Cu Metal complexes replaced with Ca, Sn, Ga, or Pb can also be used as electron transport materials. In addition, metal-free or metal phthalocyanine, or those having terminal ends substituted with an alkyl group or a sulfonic acid group can be preferably used as the electron transport material. In addition, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and similarly to the hole injection layer and the hole transport layer, inorganic such as n-type-Si and n-type-SiC. A semiconductor can also be used as an electron transport material.
[0122]
It is preferable that the preferable compound used for an electron carrying layer has a fluorescence maximum wavelength in 415 nm or less. That is, the compound used for the electron transport layer is preferably a compound that has an electron transport ability, prevents emission of longer wavelengths, and has a high Tg.
[0123]
<< Substrate (also referred to as substrate, substrate, support, etc.) >>
The organic EL device of the present invention is preferably formed on a substrate.
[0124]
The substrate that can be used in the organic EL device of the present invention is not particularly limited in the type of glass, plastic, and the like, and is not particularly limited as long as it is transparent. , Quartz, and a light-transmitting resin film. A particularly preferable substrate is a resin film that can give flexibility to the organic EL element.
[0125]
Examples of the resin film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), and cellulose triacetate. Examples thereof include films made of (TAC), cellulose acetate propionate (CAP) and the like.
[0126]
An inorganic or organic coating or a hybrid coating of both may be formed on the surface of the resin film.
[0127]
The external extraction efficiency at room temperature of light emission of the organic EL device of the present invention is preferably 1% or more, more preferably 2% or more. Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons sent to the organic EL element × 100.
[0128]
Further, a hue improving filter such as a color filter may be used in combination.
<< Method for producing organic EL element >>
As an example of the method for producing the organic EL device of the present invention, a method for producing an organic EL device comprising an anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode will be described.
[0129]
First, a thin film made of a desired electrode material, for example, an anode material is formed on a suitable substrate by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably 10 nm to 200 nm, thereby producing an anode. To do. Next, an organic compound thin film of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a hole blocking layer, which are element materials, is formed thereon.
[0130]
As described above, there are spin coating methods, casting methods, ink jet methods, vapor deposition methods, printing methods, and the like as methods for thinning the organic compound thin films, but it is easy to obtain a uniform film and pinholes are not easily generated. In view of the above, the vacuum deposition method or the spin coating method is particularly preferable. Further, different film forming methods may be applied for each layer. When employing a vapor deposition method for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally a boat heating temperature of 50 to 450 ° C., a vacuum degree of 10 −6 Pa to 10 −2 Pa, a vapor deposition rate of 0.01 nm to It is desirable to select appropriately within the range of 50 nm / second, substrate temperature of −50 ° C. to 300 ° C., and film thickness of 0.1 nm to 5 μm.
[0131]
After forming these layers, a thin film made of a cathode material is formed thereon by a method such as vapor deposition or sputtering so as to have a film thickness of 1 μm or less, preferably in the range of 50 nm to 200 nm, and a cathode is provided. Thus, a desired organic EL element can be obtained. The organic EL element is preferably produced from the hole injection layer to the cathode consistently by a single evacuation, but may be taken out halfway and subjected to different film forming methods. At that time, it is necessary to consider that the work is performed in a dry inert gas atmosphere.
[0132]
In the present invention, a shadow mask is provided only at the time of forming the light emitting layer, and other layers are common, so patterning of the shadow mask or the like is unnecessary, and a vapor deposition method, a cast method, a spin coating method, an ink jet method, a printing method, etc. Can form a film.
[0133]
When patterning is performed only on the light emitting layer, the method is not limited. However, a vapor deposition method, an inkjet method, and a printing method are preferable. In the case of using a vapor deposition method, patterning using a shadow mask is preferable.
[0134]
In addition, it is also possible to reverse the production order and produce the cathode, the electron injection layer, the electron transport layer, the light emitting layer, the hole transport layer, the hole injection layer, and the anode in this order. When a DC voltage is applied to the organic EL device thus obtained, light emission can be observed by applying a voltage of about 2 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Further, even when a voltage is applied with the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The alternating current waveform to be applied may be arbitrary.
[0135]
The organic EL device of the present invention can be used in a projection apparatus that projects an image, a display device that directly visually recognizes a still image or a moving image, and a display device such as a display. Examples of the display device and display include a television, a personal computer, a mobile device, an AV device, a character broadcast display, and an information display in an automobile. In particular, it may be used as a display device for reproducing still images and moving images, and the driving method when used as a display device for reproducing moving images may be either a simple matrix (passive matrix) method or an active matrix method.
[0136]
By using two or more kinds of the organic EL elements of the present invention having different emission colors, a full-color display device can be produced.
[0137]
In addition, the organic EL element of the present invention includes a home lighting as a light emitting light source, an interior lighting, a backlight of a display device using a liquid crystal element as a clock or a display means, a signboard advertisement, a traffic light, a light source of an optical storage medium, an electronic Although it can be used for illumination devices such as a light source of a photocopier, a light source of an optical communication processor, and a light source of an optical sensor, it is not limited thereto.
[0138]
Furthermore, the organic EL device according to the present invention may be used as an organic EL device having a resonator structure.
[0139]
Examples of the purpose of use of the organic EL element having such a resonator structure include a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processor, and a light source of an optical sensor. Not. Moreover, you may use for the said use by making a laser oscillation.
[0140]
<Display device>
An example of a display device composed of the organic EL element of the present invention will be described below based on the drawings.
[0141]
FIG. 1 is a schematic diagram illustrating an example of a display device including organic EL elements. It is a schematic diagram of a display such as a mobile phone that displays image information by light emission of an organic EL element.
[0142]
The display 1 includes a display unit A having a plurality of pixels, a control unit B that performs image scanning of the display unit A based on image information, and the like.
[0143]
The control unit B is electrically connected to the display unit A, and sends a scanning signal and an image data signal to each of the plurality of pixels based on image information from the outside. The pixels for each scanning line are converted into image data signals by the scanning signal. In response to this, light is sequentially emitted and image scanning is performed to display image information on the display unit A.
[0144]
FIG. 2 is a schematic diagram of the display unit A.
The display unit A includes a wiring unit including a plurality of scanning lines 5 and data lines 6, a plurality of pixels 3 and the like on a substrate. The main members of the display unit A will be described below.
[0145]
In the figure, the light emitted from the pixel 3 is extracted in the direction of the white arrow (downward).
[0146]
The scanning lines 5 and the plurality of data lines 6 in the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a lattice shape and are connected to the pixels 3 at the orthogonal positions (details are shown in FIG. Not shown).
[0147]
When a scanning signal is applied from the scanning line 5, the pixel 3 receives an image data signal from the data line 6 and emits light according to the received image data. Full color display is possible by appropriately arranging pixels in the red region, the green region, and the blue region that emit light on the same substrate.
[0148]
Next, the light emission process of the pixel will be described.
FIG. 3 is a schematic diagram of a pixel.
[0149]
The pixel includes an organic EL element 10, a switching transistor 11, a driving transistor 12, a capacitor 13, and the like. A full color display can be performed by using red, green, and blue light emitting organic EL elements as the organic EL elements 10 in a plurality of pixels, and juxtaposing them on the same substrate.
[0150]
In FIG. 3, an image data signal is applied from the control unit B to the drain of the switching transistor 11 through the data line 6. When a scanning signal is applied from the control unit B to the gate of the switching transistor 11 via the scanning line 5, the driving of the switching transistor 11 is turned on, and the image data signal applied to the drain is supplied to the capacitor 13 and the driving transistor 12. Is transmitted to the gate.
[0151]
By transmitting the image data signal, the capacitor 13 is charged according to the potential of the image data signal, and the drive of the drive transistor 12 is turned on. The drive transistor 12 has a drain connected to the power supply line 7 and a source connected to the electrode of the organic EL element 10, and the power supply line 7 connects to the organic EL element 10 according to the potential of the image data signal applied to the gate. Current is supplied.
[0152]
When the scanning signal is moved to the next scanning line 5 by the sequential scanning of the control unit B, the driving of the switching transistor 11 is turned off. However, even if the driving of the switching transistor 11 is turned off, the capacitor 13 maintains the potential of the charged image data signal, so that the driving of the driving transistor 12 is kept on and the next scanning signal is applied. Until then, the light emission of the organic EL element 10 continues. When the scanning signal is next applied by sequential scanning, the driving transistor 12 is driven according to the potential of the next image data signal synchronized with the scanning signal, and the organic EL element 10 emits light.
[0153]
That is, the organic EL element 10 emits light by the switching transistor 11 and the driving transistor 12 that are active elements for the organic EL elements 10 of the plurality of pixels, and the organic EL elements 10 of the plurality of pixels 3 emit light. It is carried out. Such a light emitting method is called an active matrix method.
[0154]
Here, the light emission of the organic EL element 10 may be light emission of a plurality of gradations by a multi-value image data signal having a plurality of gradation potentials, or on / off of a predetermined light emission amount by a binary image data signal. But you can.
[0155]
The potential of the capacitor 13 may be held continuously until the next scanning signal is applied, or may be discharged immediately before the next scanning signal is applied.
[0156]
In the present invention, not only the active matrix method described above, but also a passive matrix light emission drive in which the organic EL element emits light according to the data signal only when the scanning signal is scanned.
[0157]
FIG. 4 is a schematic view of a passive matrix display device. In FIG. 4, a plurality of scanning lines 5 and a plurality of image data lines 6 are provided in a lattice shape so as to face each other with the pixel 3 interposed therebetween.
[0158]
When the scanning signal of the scanning line 5 is applied by sequential scanning, the pixels 3 connected to the applied scanning line 5 emit light according to the image data signal.
[0159]
In the passive matrix system, the pixel 3 has no active element, and the manufacturing cost can be reduced.
[0160]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this.
[0161]
Example 1
<< Preparation of Compounds 1-1 (A, B, C, D) to 1-8 (A, B, C, D) >>
<Synthesis of Compound 1-1 and Preparation of Sample 1-1 (A, B, C, D)>
Under a nitrogen atmosphere, 0.2 ml of tri (tert-butyl) phosphine was added to 45 mg of palladium acetate, and the mixture was stirred at 50 ° C. for 30 minutes. To this, 60 ml of xylene, 1.2 g of carbazole, 1.0 g of 4,4′-dibromobiphenyl and 0.9 g of sodium tert-butoxide were added, and the mixture was stirred at reflux temperature for 8 hours. The reaction mixture was allowed to cool, purified by silica gel column chromatography, and recrystallized to convert 4,4′-dicarbazolylbiphenyl (compound 1-1), which is the compound represented by the above general formula 1, into 0. Obtained .67 g (42% yield). The structure of the obtained compound 1-1 was identified by NMR spectrum and mass spectrometry spectrum.
[0162]
Embedded image

[0163]
From the results of high-performance liquid chromatography analysis and liquid chromatography mass spectrometry of the sample and carbazole obtained by sublimation purification of the obtained compound 1-1, the obtained sample contains 0.54 of carbazole as a raw material. It was found to be contained by mass%. This is designated as Sample 1-1A.
[0164]
Furthermore, synthesis was performed in the same manner, but after refining by repeating silica gel column chromatography, Sample 1-1B, Sample 1-1C and Sample 1-1D obtained by recrystallization and sublimation purification were prepared, These samples were also analyzed in the same manner as Sample 1-1A, 0.38% by mass for Sample 1-1B, 0.24% by mass for Sample 1-1C, and 0.06% by mass for Sample 1-1D. It was found that the raw material carbazole (compound represented by the general formula 2) was included. That is, Samples 1-1A, 1-1B, 1-1C, and 1-1D differ in the content of the compound represented by General Formula 2 contained in Compound 1-1 by purification. The content of the compound represented by formula (1) is such that 1-1A> 1-1B> 1-1C> 1-1D (A, B, C in descending order of the content represented by general formula 2) , D).
[0165]
<Synthesis of Compound 1-2 and Preparation of Sample 1-2 (A, B, C, D)>
Under a nitrogen atmosphere, 0.2 ml of tri (tert-butyl) phosphine was added to 45 mg of palladium acetate, and the mixture was stirred at 50 ° C. for 30 minutes. To this, 60 ml of xylene, 0.8 g of carbazole, 1.0 g of 1,3,5-triiodobenzene and 2.4 g of rubidium carbonate were added and stirred at reflux temperature for 8 hours. The reaction mixture was allowed to cool, purified by silica gel column chromatography, and recrystallized to obtain 430 mg of 1,3,5-tricarbazolylbenzene (Compound 1-2), which is a compound represented by General Formula 1. (Yield 34%).
[0166]
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[0167]
The structure of the obtained compound 1-2 was identified by NMR spectrum and mass spectrometry spectrum.
[0168]
Furthermore, the sample (1-2A, 1-2B, 1-2C, 1-2D) from which the content rate of the compound represented by General formula 2 differs by the method similar to the refinement | purification method mentioned above is obtained. Was prepared.
[0169]
<Synthesis of Compounds 1-3 to 1-8 and Preparation of Samples 1-3 to 1-8 (A, B, C, D)>
Compounds 1-3 to 1-8 were synthesized using a known production method, and samples (A, B, C, D) were prepared.
[0170]
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[0171]
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[0172]
<< Production of Organic EL Elements 1-1 to 1-32 >>
After patterning on a substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) having a film of 150 nm of ITO (indium tin oxide) formed on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, this ITO transparent electrode was provided. The transparent support substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum deposition apparatus, while 200 mg of α-NPD was placed in a molybdenum resistance heating boat, and the synthesized compound 1-1 (sample 1) was added to another molybdenum resistance heating boat. 200 mg of -1A), 200 mg of bathocuproine (BCP) in another molybdenum resistance heating boat, and Alq in another molybdenum resistance heating boat_Three200 mg was added and attached to a vacuum deposition apparatus.
[0173]
The vacuum chamber is then 4 × 10^-FourAfter depressurizing to Pa, the heating boat containing α-NPD was energized and heated, and deposited on a transparent support substrate at a deposition rate of 0.1 nm / sec to provide a 45 nm thick hole transport layer. Further, the heating boat containing the compound 1-1 (sample 1A) was energized and heated, and was deposited on the hole transport layer at a deposition rate of 0.2 nm / sec to provide a light emitting layer having a thickness of 20 nm. . In addition, the substrate temperature at the time of vapor deposition was room temperature. In addition, an electron transport layer that also serves as a hole blocking function with a film thickness of 10 nm is provided by energizing and heating the heating boat containing BCP and depositing on the light emitting layer at a deposition rate of 0.1 nm / sec. It was. In addition, Alq_ThreeThe heating boat containing was heated by energizing, and was deposited on the electron transport layer at a deposition rate of 0.1 nm / sec to further provide an electron injection layer having a thickness of 40 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.
[0174]
Then, 0.5 nm of lithium fluoride and 110 nm of aluminum were vapor-deposited, the cathode was formed, and the organic EL element 1-1 was produced.
[0175]
The structure of the compound used above is shown below.
[0176]
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[0177]
Further, the organic EL element 1-2 was made in the same manner as the organic EL element 1-1 except that the compound 1-1 (sample 1-1A) in the organic EL element 1-1 was replaced as shown in Table 1. ˜1-32 was produced.
[0178]
The following method was used to measure the content of the compound represented by Formula 2 in the layer of the organic EL element.
<Measurement of content of compound represented by general formula 2 in light-emitting layer>
A 100 mm × 100 mm × 1.1 mm glass substrate was ultrasonically cleaned with isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus, and 200 mg of sample 1-1A was placed in a molybdenum resistance heating boat and attached to the vacuum vapor deposition apparatus.
[0179]
Vacuum tank 4 × 10^-FourAfter reducing the pressure to Pa, under the same conditions as those for forming the light emitting layer of the organic EL element 1-1, the heating boat containing the compound represented by Sample 1-1A was energized and heated, and the glass substrate was then heated. Vapor deposition was performed to obtain a deposited film.
[0180]
The deposited film on the obtained glass substrate was dissolved in toluene, and the resulting solution was analyzed by high performance liquid chromatography to determine the content of carbazole (compound represented by the general formula 2) as a raw material in the layer. It was measured. Furthermore, sample 1-1A is changed to other samples 1-1 (B, C, D), 1-2 (A, B, C, D) to 1-8 (A, B, C, D). The same measurement was performed on the produced deposited film, and the measurement result was defined as the content of the compound represented by Formula 2 in the light emitting layer of the organic EL elements 1-1 to 1-32.
[0181]
<< Evaluation of Organic EL Elements 1-1 to 1-32 >>
Luminance (cd / m) when organic EL elements 1-1 to 1-32 are applied at a temperature of 23 ° C. and a DC voltage of 10 V in a nitrogen atmosphere.²) And luminous efficiency (lm / W). The light emission luminance was measured using CS-1000 (Minolta).
[0182]
10 mA / cm²The time required for the initial luminance to drop to half of the original luminance when measured at a constant current was measured, and this was used as a durability index as the half-life time.
[0183]
The results are shown in Table 1 as relative values with the result for an element having the highest impurity content represented by the general formula 2 in the deposited film among organic EL elements using the same compound as 100. .
[0184]
[Table 1]

[0185]
As is apparent from Table 1, the organic compound having a layer when the content of the impurity represented by the general formula 2 contained in the layer containing the compound represented by the general formula 1 is less than 0.5% by mass. The performance of the EL element is greatly improved. In particular, this effect is remarkable in terms of durability, and there is a particularly significant improvement effect in an organic EL element having a layer in which the content of impurities is suppressed to 0.1% by mass or less.
[0186]
In addition, when the molecular weight of the compound of the general formula 2 contained in the layer is larger than a certain level, the improvement effect tends to be somewhat reduced. This is because the molecule of the impurity represented by the general formula 2 is large. It is presumed that the stability of impurities has increased to some extent.
[0187]
Example 2
<< Production and Evaluation of Organic EL Elements 2-1 to 2-16 >>
An organic EL device produced in exactly the same manner as the organic EL device 1-3, except that the BCP in the electron transport layer of the organic EL device 1-3 of Example 1 was replaced with the compound prepared in Example 1 shown in Table 2. For 2-1 to 2-16, the content, emission luminance, luminous efficiency, and half-life time (durability) of the compound represented by Formula 2 in the electron transport layer were measured in the same manner as in Example 1. did. Table 3 shows the measurement results.
[0188]
[Table 2]

[0189]
As is clear from Table 2, for any compound, the contamination of the impurity represented by the general formula 2 is suppressed even when the organic compound layer using the compound functions as an electron transport layer. It has been found that it brings about a remarkable improvement effect on the properties of the resin, particularly the durability.
[0190]
Example 3
<< Production and Evaluation of Organic EL Elements 3-1 to 3-32 >>
In the manufacturing method of the organic EL element 1-1 of Example 1, 100 mg of Ir-1 which is a phosphorescent substance was put in another molybdenum resistance heating boat and attached to a vacuum evaporation apparatus, and a light emitting layer was attached to Sample 1-1A. Except that the heating boat containing Ir-1 was energized and the sample 1-1A was co-deposited at a deposition rate of 0.2 nm / sec and Ir-1 was deposited at a deposition rate of 0.012 nm / sec, except that the light emitting layer had a thickness of 20 nm. The organic EL element 3-1 was produced by the same method as the organic EL element 1-1.
[0191]
Similarly, organic EL elements 3-2 to 3-32 were produced in which the light-emitting layers of the organic EL elements 1-2 to 1-32 of Example 1 were co-evaporated with Ir-1 by the method described above. .
[0192]
About the obtained phosphorescence-emitting organic EL elements 3-1 to 3-32, in the same manner as in Example 1, the content of the compound represented by the general formula 2 in the light emitting layer, light emission luminance, light emission efficiency, durability The results of evaluating the properties are shown in Table 3.
[0193]
[Table 3]

[0194]
As is clear from Table 3, even when a phosphorescent organic EL device is produced, the mixing of the compound represented by the general formula 2 is suppressed even when any compound is used as the host compound. It was found that the characteristics of the EL element, particularly the durability, are significantly improved.
[0195]
Example 4
<< Production and Evaluation of Organic EL Elements 4-1 to 4-16 >>
In the production of the organic EL element 1-1 of Example 1, 100 mg of Ir-6, which is a phosphorescent substance, was put into another molybdenum resistance heating boat, and further, another phosphoric resistance substance was put into another molybdenum resistance heating boat. 100 mg of Ir-12 is put in a vacuum deposition apparatus, and the light emitting layer is energized through heating boats containing Sample 1-1A, Ir-6, and Ir-12, respectively, and Sample 1-1A is 0.5 nm / sec. In the same manner as the organic EL element 1-1 except that a light emitting layer having a film thickness of 30 nm is formed by co-evaporation of Ir-6 at a deposition rate of 0.005 nm / sec and Ir-12 at 0.02 nm / sec. A two-wavelength light emitting type organic EL element 4-1 was produced. The phosphorescence emission of Ir-6 is red and the phosphorescence emission of Ir-12 is blue. Therefore, the emission from the organic EL element has two emission maximum wavelengths, and is white for human vision. It is recognized as luminescence.
[0196]
Similarly, the light-emitting layers of the organic EL elements 1-2 to 1-4, 1-9 to 1-16, and 21 to 1 to 24 of Example 1 were formed by the above-described method using Ir-6 and Ir-12. Organic EL elements 4-2 to 4-16 were produced as co-evaporated light emitting layers. In the same manner as in Example 1, the content, light emission luminance, light emission efficiency, and half-life time (durability) of the compound represented by Formula 2 in the light emitting layer were measured. Table 4 shows the measurement results.
[0197]
[Table 4]

[0198]
As is apparent from the results in Table 4, even when a phosphorescent white light-emitting organic EL device is produced, suppression of the impurity represented by the general formula 2 indicates that any compound is used as a host compound. In this case, the characteristics of the organic EL element, particularly the durability, are remarkably improved.
[0199]
Example 5
The organic EL element 5-1 (red) was the same as the organic EL element 3-4 except that Ir-1 of the organic EL element 3-4 (green) of Example 3 was changed to Ir-6 and Ir-12. 5-2 (blue) was produced.
[0200]
These elements were juxtaposed on the same substrate to produce an active matrix type full-color display device shown in FIGS. That is, a wiring portion including a plurality of scanning lines 5 and data lines 6 and a plurality of juxtaposed pixels 3 (light emission color is a red region pixel, a green region pixel, a blue region pixel, etc.) on the same substrate. Each of the scanning lines 5 and the plurality of data lines 6 in the wiring portion is made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a lattice shape and are connected to the pixels 3 at the orthogonal positions (details) Is not shown). The plurality of pixels 3 are driven by an active matrix system provided with an organic EL element corresponding to each emission color, a switching transistor as an active element, and a driving transistor, and a scanning signal is applied from a scanning line 5. Then, an image data signal is received from the data line 6 and light is emitted according to the received image data. In this way, full-color display is possible by appropriately juxtaposing the red, green, and blue pixels.
[0201]
By driving the full-color display device, a clear full-color moving image display with high luminance and good durability was obtained.
[0202]
【The invention's effect】
According to the present invention, it is possible to provide an organic electroluminescence element having particularly high durability as well as high emission luminance and excellent quantum efficiency, and a display device or lighting device including the same.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a display device including organic EL elements.
FIG. 2 is a schematic diagram of a display unit A. FIG.
FIG. 3 is a schematic diagram of a pixel.
FIG. 4 is a schematic view of a passive matrix display device.
[Explanation of symbols]
1 Display
3 pixels
5 scanning lines
6 data lines
7 Power line
10 Organic EL elements
11 Switching transistor
12 Driving transistor
13 Capacitor
A display
B Control unit

Claims (8)

It has at least one layer containing a pyridoindole compound represented by the following general formula 1, and the content of the pyridoindole compound represented by the following general formula 2 is less than 0.5% by mass. An organic electroluminescence device characterized in that there is.

(In the above general formulas 1 and 2, A represents a linking group, R ₁ and R ₂ independently represent a monovalent substituent, m represents an integer of 2 to 6. X ₁ represents ═C (R ₃₎ - the stands, the case _{R 3} represents a monovalent substituent, _{X 2} is = C _{(R 4)} - represents, to a table at this time _{R 4} is a monovalent substituent).   The organic electroluminescence device according to claim 1, wherein the content of the compound represented by the general formula 2 is less than 0.1% by mass.   The organic electroluminescence device according to claim 1 or 2, wherein the compound represented by the general formula 2 has a molecular weight of less than 250.   The organic electroluminescence element according to any one of claims 1 to 3, wherein light emission when an electric field is applied includes phosphorescence light emission.   The organic electroluminescence element according to any one of claims 1 to 4, wherein the organic electroluminescence element emits white light.   The display element provided with the organic electroluminescent element of any one of Claims 1-5.   The illuminating device provided with the organic electroluminescent element of any one of Claims 1-5.   A display device comprising the illumination device according to claim 7 and a liquid crystal device as a display means.

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