JP4088471B2 - Organic light emitting device and method for manufacturing the same - Google Patents
Organic light emitting device and method for manufacturing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、平面型表示装置や、各種光源として、通信、照明その他の用途に供される有機エレクトロルミネッセンス（ＥＬ）素子に関するものであって、より詳しくは、その光の取り出し効率を向上させるための改良に関する。
【０００２】
【従来の技術】
従来より、平面型表示装置として、液晶表示装置が広く用いられている。液用装置は、応答速度が遅い、視野角が狭い等の欠点を有することから、その解消のために多くの新方式が提案されている。しかしながら、その対策のためのコストが装置の低価格化に対する障害になっていて、さらにこれらの対策によっても、未だ十分な特性を有する液晶表示装置は得られていない。
【０００３】
近年、広範囲な応用が期待できる新たな表示装置用の素子として、自発光であることから本質的に視認性に優れ、応答速度も速いＥＬ素子が注目を集めている。
特に有機材料を発光層の全部またはその一部の層に用いた有機ＥＬ素子は、上記の利点に加えて、その発光層を室温で蒸着、塗布などの簡単な方法で形成することができるため、製造コスト上の魅力もあり、盛んに開発が行なわれている。また。有機ＥＬ素子は、薄くさらに面発光が可能なことから、従来、蛍光管と導光板とを組み合わせて用いていた液晶表示装置のバックライトの代替としても期待されている。
【０００４】
有機ＥＬ素子は、陽極から注入された正孔と陰極から注入された電子を発光層において結合させて発光を得るものであり、電極材料や発光材料についてはもちろん、発光層と陽極または陰極との間に発光以外の機能を有する層が配された素子も、古くから多くの研究がなされていて、数多く提案されている。たとえば、陽極と発光層の間に正孔輸送層が、陰極と発光層の間に電子輸送層が配される。また、陽極と正極輸送層の間に正孔注入層が設けられたものや、陰極との界面に電子注入層が設けられたものも提案されている。発光層として、上記のような機能を有するとともに、それ自体が発光するいわゆる正孔輸送性発光層や電子輸送性発光層が設けられたものもある。各層に役割を機能分離させて担わせることにより、各層に適切な材料選択が可能となって、素子の特性も向上している。
【０００５】
たとえば、Ｔａｎｇらは、透明基板上に透明陽極、正孔輸送層、発光層および反射陰極を有する素子であって、透明陽極としてＩＴＯ（インジウム錫酸化物）、正孔輸送層として厚さが７５ｎｍのジアミン誘導体層、発光層として厚さが６０ｎｍのアルミキノリン錯体層、反射陰極として電子注入性と安定性を併せ持つＭａＡｇ合金を用いた素子を提案している。（C. W. Tang and S. A. Vanslyke: Appl. Phys. Lett. 51 (1987) 913.）。この提案では、特に陰極の改良もさることながら、ジアミン誘導体からなる正孔輸送層を用いたことが注目される。ジアミン誘導体は、透明性および成膜性に優れることから、これを採用することで、十分な透明性を有し、されに７５ｎｍの膜圧においてもピンホール等の無い均一な正孔輸送層を得ることを可能にしている。したがって、発光層も含めた素子の相膜厚を１５０ｎｍ程度にまで十分に薄くして、比較的低電圧でも高輝度の発光が得られるようになっている。具体的には、１０Ｖの低い電圧で１０００ｃｄ／ｍ2以上の高い輝度と、１．５ｌｍ／Ｗ以上の高い効率を実現している。
【０００６】
このＴａｎｇらの提案がきっかけとなって、陰極のさらなる改良や、電子注入層の挿入、正孔注入層の挿入などの素子構成上の工夫などが、現在に至るまでさらに活発に検討されている。
以下、現在一般に検討されている有機ＥＬ素子について概説する。
透明基板上に透明陽極、正孔輸送層、発光層および陰極が、この順に積層して配される。また、透明陽極と正孔輸送層の間に正孔注入層が、発光層と陰極の間に電子輸送層が、さらには陰極との界面に電子注入層が設けられることもある。透明基板としては、一般にコーニング１７３７等のガラス基板が広く用いられている。ここで、厚さが０．７ｍｍ程度のものが強度と重量の観点から扱いやすい。
透明陽極としては、たとえば、スパッタ、エレクトロンビーム蒸着、イオンプレーティング等により形成されたＩＴＯ膜が用いられている。膜厚は必要とされるシート抵抗値と可視光透過率を考慮して決定される。有機ＥＬ素子は駆動電流密度が比較的高いため、一般に、シート抵抗を小さくする目的で１００ｎｍ以上の厚さのものが用いられることが多い。
【０００７】
正孔輸送層には、Ｎ，Ｎ’−ビス（３−メチルフェニル）−Ｎ，Ｎ’−ジフェニルベンジジン（以下ＴＰＤと称する）、Ｎ，Ｎ’−ピス（α−ナフチル）−Ｎ，Ｎ’−ジフェニルベンジジン（以下ＮＰＤと称する）等、Ｔａｎｇらの用いたジアミン誘導体、特に特開昭５９-１９４３９３号公報で提案されたＱ１−Ｇ−Ｑ２構造のジアミン誘導体の真空蒸着膜が幅広く用いられている。これらの材料は、一般に透明性に優れ、８０ｎｍ程度の厚さでもほぼ透明であり、成膜性にも優れる。したがって、これらの材料を用いることで、素子の厚さを１００ｎｍ程度にまで薄くしても、ピンホールなどの欠陥が発生し難く、短絡などの信頼性に関わる問題が発生し難くなる。
【０００８】
発光層には、一般に、Ｔａｎｇらの報告と同様に真空蒸着により形成された厚さが数十ｎｍのトリス（８−キノリノラト）アルミニウム（以下Ａｌｑと称する）等の電子輸送性発光材料からなる膜が用いられる。種々の発光色を実現するなどの目的で、発光層には比較的薄い膜が用いられる。さらにこれに積層して厚さが２０ｎｍ程度の電子輸送層を配した、いわゆるダブルヘテロ構造が採用されることもある。
陰極には、Ｔａｎｇらの提案したＭｇＡｇ合金やＡｌＬｉ合金などの仕事関数が小さく電子注入障壁の低い金属と比較的仕事関数が大きく安定な金属との合金や、ＬｉＦなど種々の電子注入層と積層したアルミニウムなどが用いられることが多い。
【０００９】
以上のように、低分子有機材料を用いた真空蒸着法によりこれらの層を積層して形成した有機ＥＬ素子が活発に検討されているが、一方で、種々の有機材料を溶媒中に溶解または分散させた塗料の塗布膜を積層して形成した有機ＥＬ素子もまた、近年活発に検討されている。
たとえば、米国特許第５２４７１９０号（Ｒ．Ｈ．Ｆｒｉｅｎｄら）には、共役発光ポリマーを塗布して形成した膜を用いた有機ＥＬ素子が開示されている。同文献には、ガラス基板上に陰極として、表面に僅かな酸化層を有する厚さが約２０ｎｍのアルミニウム蒸着膜を形成し、さらにこの上に、１０〜２５ミリリットルのメタノールに１ｇの割合でポリパラフェニレンビニレン（以下ＰＰＶと称す）の前駆体を溶解させた塗料をスピンコート法によって塗布したのち、真空中で３００℃で、１２時間の熱処理を行って、厚さが１００〜３００ｎｍのＰＰＶ膜を得たとある。半透明の陽極として、厚さが約２０〜３０ｎｍの金またはアルミニウムからなる膜が蒸着によって形成され、その上に発光層として厚さが２００ｎｍのＰＰＶ膜が形成された素子の場合、４０Ｖの電圧印加で強いＥＬ発光が得られたとある。また、ガラス基板上にＩＴＯからなる透明陽極がイオンビームスパッタ法により形成され、発光層として上記と同様に厚さ７０ｎｍのＰＰＶ層が形成され、さらに陰極として厚さ約５０ｎｍのアルミニウム蒸着膜が形成された素子では、１４Ｖから電流が流れ始め発光が観察されたとある。
【００１０】
ポリマーの塗布としては、スピンコート法以外にも、インクジェット法や印刷法も提案されている。例えば、特開平１０−１２３７７号公報には、ガラス上にＴＦＴアレイとＩＴＯ透明画素電極まで形成した基板上に、ポリマー前駆体としてポリテトラヒドロチオフェニルフェニレンを塗布、これを加熱して厚さ０．０５μｍの正孔注入層を形成した後、インクジェット法によってＲＧＢ画素に対応した発光層を形成し、その上に厚さが０．１〜０．２μｍのＭｇＡｇ電極を形成した直視型の有機ＥＬ表示体が提案されている。ここで、赤色発光材料にはシアノポリフェニレンビニレン、緑色発光材料にはポリフェニレンビニレン、青色発光材料にはポリフェニレンビニレンおよびポリアルキルフェニレンからなり、液体状でケンブリッジディスプレイテクノロジー社から入手したものを使用したとある。また、特開平３−２６９９９５号公報には、トリフェニルジアミン誘導体等の低分子有機材料のトルエン溶液を用いた印刷法によりパターン成膜を行って作製した素子が提案されている。
【００１１】
有機ＥＬ素子の開発における主たる課題として、光取出し効率の向上、低電圧駆動、消費電力の低減および長寿命化が挙げられる。このうち光取出し効率の向上は、素子の長寿命化、駆動電圧の低減等、他の課題をも同時に解決させることに寄与するため、素子の構造的な改良を含め広く検討が行われている。
【００１２】
液晶表示装置のバックライト用途においても、偏光を発する電界発光素子が検討されている。
上記のような従来の有機ＥＬ素子では、発光層内の発光材料分子の配向は無秩序であって、基板の主面に対して平行なもの、垂直なもの、その中間の角度を有するものなどが無秩序に混在する。したがって、発光層より発せられる光は、振動面に偏りのないいわゆる自然光となる。液晶表示装置のバックライトからの光は、偏光板を透過したのちに、画像等の表示に寄与する。したがって、バックライトより発せられる光は、自然光であることからその多くは、偏光板によって排除される。そこで、発光材料分子を特定方向に配向させることによって、発光層より発せられる光を偏光とする技術が、偏光板を透過する際のロスを最小限とし、さらには液晶パネルとバックライトの間に偏光板を介在させる必要を無くすことができるとして注目されている。
【００１３】
たとえば、特開平８−３０６９５４号公報には、基板上に形成された有機発光層の表面をラビング処理し、さらに熱処理することにより、層中の有機発光材料（π−共役型高分子）の主鎖をラビング方向に配向させた有機発光ダイオードが提案されている。
しかしながら、この方法によると、従来の素子の製造方法に、ラビング処理とともに熱処理工程を付加する必要がある。さらに、熱処理において有機発光材料の軟化点以上にまで加熱する必要があり、樹脂製の基板を用いることは困難である。
【００１４】
特開平９−１１５６６９号公報には、その上に発光層を形成しようとする下地層の表面に配向処理を施すことで、発光層内の分子を特定方向に配向させる方法が提案されていて、配向処理として、具体的にはバフ研磨および傾斜蒸着が挙げられている。
同提案によると、その実施例のように電極となるＩＴＯ層上に発光材料を含む層（発光層）を直接形成する場合には有用であるが、発光機能層が多層であって、発光層すなわち実際に発光する層に接してホール輸送層、電子注入届等が形成される場合には、これらの層へのバフ研磨はかえって歩留まりの低下をもたらす。
【００１５】
【発明が解決しようとする課題】
本発明は、上記問題点を解決するためのものであり、高い光取出し効率を有し、さらに樹脂製の基板を用いることができる有機電界発光素子を提供することを目的とする。また、そのような優れた有機発光素子を、容易な方法で生産性良く製造することを目的とする。
【００１６】
【課題を解決するための手段】
本発明は、発光層中の有機発光材料分子の発光遷移モーメントの方向が基板の主面に対してなす角度が、素子の光取り出し効率に大きな影響を及ぼすことに着目してなされたものである。一般に、有機発光素子はアモルファスな膜で構成されるため、各発光材料分子の発光遷移モーメントはランダムな方向を示している。したがって、全反射角以上すなわち発光面の法線に対して臨界角以上に出射した光は素子外部に取り出すことができない。
そこで、本発明では、容易な方法で有機発光材料分子の発光遷移モーメントの方向を基板の主面と平行な特定の方向に配向させて、光取り出し効率を向上させる。
本発明では、たとえば、樹脂製の基板上に塗布等、公知の方法によって形成された有機発光材料膜を基板ととも特定の方向に延伸して、膜内の分子を延伸方向に配向させる。このいわゆる一軸延伸によって、有機発光材料膜中の分子は、概ねその主鎖が延伸方向と平行に配向し、所望の振動面を有する偏光を発する発光層が得られる。
また、有機発光材料膜の形成に先立って、それを形成しようとする表面に、有機発光材料の配向を規制する膜、いわゆる配向膜を形成する。
【００１７】
【発明の実施の形態】
本発明の一形態では、フィルム状のものを含む樹脂製基板の上に、有機導電材料を含む導電膜を形成し、さらに導電膜の上に、有機発光材料膜を形成したのち、有機発光材料膜を基板とともに延伸して、有機発光材料膜中の有機発光材料分子をその主鎖が延伸方向と略平行になるよう配向させる。なお、延伸率を大きくすると、有機発光材料分子をより均一に配向させることができる。その主鎖が均一な発光層を安定して得るためには、１．５倍程度に延伸することが好ましい。
両極間に配される層（以下、機能層とする）のうち、少なくともそれ自体が発光する層すなわち発光層に加工される膜までが形成された後に、上記の延伸処理が施される。したがって、延伸処理される膜には、発光層に加工される有機発光材料膜のみならず、それと積層して配される種々の膜も含まれる。
【００１８】
延伸の前に、基板の表面に一方の電極としてまたはそれに加工するための導電膜が形成される。発光層を狭持して配される一対の電極は、直流あるいは交流の電圧を発光層に印加するものであって、通常直流で駆動される有機発光素子の場合は、陰極と陽極を指す。一対の電極のいずれか一方または両方には、発光層より発せられた光を取り出すために、透明導電材が用いられる。一方の電極側のみから光を取り出す場合、光を有効利用するため、他方の側の電極には一般にＭｇＡｇ合金やＡｌＬｉ合金など、光反射性を有する金属性のものが用いられたり、透明電極とともに金属膜など反射用の部材が配される。
基板と有機発光材料膜の間に配される導電膜は、基板および有機発光材料膜を延伸する際にともに延伸されることから、主としてポリチオフェン、ポリピロール等、透明性および可とう性を有する有機導電材料からなるものが用いられる。すなわち、本発明の有機発光素子は、基板を透過した光を外部に出射させる。ともに透明な有機導電材料からなる陽極および陰極を用い、反射部材をさらに配する場合には、両極またはそれに加工するための膜を形成した後に、基板とともに延伸処理してもよい。
多層構造の発光機能層がはいされる場合には、たとえば各層の形成において一軸配向処理する。また、全ての層を形成した後に一軸配向処理しても、いずれの層内の分子も同一方向に配向させることができる。
【００１９】
本発明の他の形態では、有機発光材料膜の形成に先立って、それを形成しようとする表面に、有機発光材料分子の配向を規制する膜、いわゆる配向膜を形成する。配向膜には、たとえばポリイミドや、直鎖状炭素鎖を含むシラン系化合物が用いられる。
配向膜は、たとえば、基板上に塗布されたプレポリマーに偏光紫外線を照射して硬化させることにより形成する。
また、形成しようとする膜の下地層が既に形成された基板を、単分子吸着物質を含む液に付着させ、さらに付着した余剰の液を除去するためにそれを洗浄槽中に入れて洗浄した後、その主面を特定方向（鉛直方向を含む）に傾斜させて液切りしながら引き上げる。これにより、洗浄槽から取り出す際に基板を引き上げる方向に、有機発光材料分子を配向させることができる配向膜が形成される。なお、必要に応じて、基板に付着して形成された単分子膜を、偏光紫外線の照射等によって固定する。
発光層とそれよりも下層に位置する導電膜との間に正孔輸送層など他の機能層が配される場合には、構成分子の配向が規制された層の上層に配される機能層の構成分子の配向も、規制された機能層の構成分子に追随するため、その導電層上に配向膜を配するのみであっても、発光層またはそれに加工される発光材料膜の構成分子を所望の方向に配向させることができる。
【００２０】
もちろん、上記の一軸延伸による配向と配向膜による配向規制を組み合わせて用いてもよい。
本発明は、それ自体が光を発する単層の発光層を有する有機ＥＬ素子に適用されるとともに、電子輸送層、正孔輸送層等の機能層を含む多層構造の発光機能層を有する有機ＥＬ素子にも適用される。
表示装置においては、一般に表示装置の表面、すなわちその光の出射面に反射陰極による外光反射の防止やコントラスト向上のため、偏光板が配される。発光層より発せられる光の振動面をこの偏光板の透過軸と平行にすると、偏光板を透過する際のロスを最小限にすることができ、より取出し効率を高くすることができる。
【００２１】
【実施例】
以下、本発明の好ましい実施例を詳細に説明する。
【００２２】
《実施例１》
基板としての市販の透明なポリエステルフィルム（基板サイズ：１０ｃｍ×１０ｃｍ、厚さ３０μｍ）上に、ポリチオフェン誘導体（バイエル株式会社製）を塗布したのち、これを空気中で１５０℃で３０分間、加熱処理して、透明陽極として厚さが１００ｎｍでポリ（３，４−エチレンジオキシチオフェン）（ＰＥＤＯＴ）からなる有機導電膜を形成した。
【００２３】
形成された透明陽極上に、以下のようにして、正孔輸送層、発光層および電子輸送層からなる発光機能層を形成した。
まず、正孔輸送層および発光層に加工される膜をそれぞれ高真空蒸着装置（日本真空技術株式会社製、ＥＢＶ−６ＤＡ型を改造したもの）を用いた蒸着によって積層して形成した。この装置の主たる排気装置は、排気速度が１５００リットル／分のターボ分子ポンプ（大阪真空株式会社製、ＴＣ１５００）であり、到達真空度は約１×１０-6Ｔｏｒｒ（≒１．３３×１０-4Ｐａ）以下である。全ての有機化合物の蒸着は、タングステン製の抵抗加熱式蒸着ポートに直流電源（菊水電子株式会社製、ＰＡＫ１０-７０Ａ）を接続して、真空度が２〜３×１０-6Ｔｏｒｒの範囲で行った。
【００２４】
高真空蒸着装置の真空槽内に配置した基板上に、正孔輸送層としてＮ，Ｎ'−ビス（４'−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（ＴＰＴ、保土ケ谷化学株式会社製）を蒸着速度０．３ｎｍ／秒で蒸着するとともに、４−Ｎ，Ｎ−ジフェニルアミノ−α−フェニルスチルベン（ＰＳ）を蒸着速度０．０１ｎｍ／秒で蒸着（共蒸着）して、厚さ約８０ｎｍのブレンド型正孔輸送層としての膜を形成した。
次に、この膜の上に、４，４’−ビス［２，２−ビス（４−メチルフェニル）ビニル］ビフェニル（ＤＴＶＢｉ）を蒸着速度０．３ｎｍ／秒で蒸着するとともに、４，４’−ビス｛２−［９−エチルカルバゾル−３−イル］ビニル｝ビフェニル（ＢＣｚＶＢｉ）を蒸着速度０．０１ｎｍ／秒で共蒸着して、いわゆるドーピング型発光層としての厚さが約１００ｎｍの発光材料膜を形成した。
【００２５】
次に、基板を真空槽から雰囲気を乾燥窒素に置換されたグローブボックス内に移動させたのち、室温で基板全体をその一辺と平行の方向に１０ｃｍ一軸延伸した。延伸して加工された透明陽極、正孔輸送層および発光層の厚さは、それぞれ約５０ｎｍ、約４０ｎｍおよび約５０ｎｍであった。
【００２６】
以上のようにして延伸処理が施された基板を、再度真空槽内に戻し、電子輸送層として、トリス（８−キノリノラト）アルミニウム（Ａｌｑ３、同仁化学株式会社製）からなる厚さ約２０ｎｍの膜を０．３ｎｍ／秒の蒸着速度で形成した。
【００２７】
形成された発光機能層の上に、以下のようにして、反射陰極を形成した。
アルミニウム・リチウム合金（高純度化学株式会社製、Ａｌ／Ｌｉの重量比が９９／１）をソースに用いた低温蒸着によって、発光機能層の上に約０．１ｎｍ／秒の蒸着速度で厚さ約１ｎｍのリチウム膜を形成し、さらに、そのソースを昇温してリチウムがほとんど除去されたソースを用いて、リチウム膜上に約１．５ｎｍ／秒の蒸着速度で厚さが約１００ｎｍのアルミニウム膜を形成して、積層型の反射陰極を得た。
以上のようにして得られた有機発光素子を実施例１の素子とする。
【００２８】
《実施例２》
実施例１で用いたものと同様の透明ポリエステルフィルム上に、透明陽極として、厚さが１００ｎｍの有機導電膜を形成した後、乾燥窒素に置換したグローブボックス内で、その上にポリ［２−メトキシ−５−（２’−エチル）ヘキシロキシ−ｐ−フェニレンビニレン］（ＭＥＨ-ＰＰＶ）を１０ｍｇ／ｍｌの濃度でキシレンに溶解した塗料をスピンコート法によって塗布し、さらに乾燥窒素グローブボックス内で１００℃、３０分間加熱処理して、厚さが約２００ｎｍの発光材料膜を形成した。
グローブボックス内で、室温で基板全体をその一辺と平行の方向に１０ｃｍ一軸延伸した。延伸して加工された透明陽極および発光層の厚さは、それぞれ約５０ｎｍおよび約１００ｎｍであった。
【００２９】
延伸処理が施された基板を真空槽内に配置し、実施例１と同様に、その表面に反射陰極として厚さ約２０ｎｍのカルシウム膜と厚さ約１００ｎｍのアルミニウム膜を積層して形成した。
以上のようにして得られた有機発光素子を実施例２の素子とする。
【００３０】
《実施例３》
実施例１と同様に表面に透明陽極として厚さが１００ｎｍの導電性高分子膜を形成した透明ポリエステルフィルムを、室温でその一辺と平行の方向に１０ｃｍ一軸延伸した。延伸して加工された透明陽極の厚さは、約５０ｎｍであった。
透明陽極上に、発光機能層として、実施例１と同様にして厚さが約８０ｎｍの正孔輸送層および厚さが約２００ｎｍの発光層を蒸着により形成した。
ついで、発光機能層が形成された基板の表面に、反射陰極として厚さが約２０ｎｍのカルシウム膜と厚さが約１００ｎｍのアルミニウム膜を積層して形成した。
以上のようにして得られた有機発光素子を実施例３の素子とする。
【００３１】
《実施例４》
実施例１と同様にして基板上に透明陽極を形成した後、その表面に以下のようにして、単分子膜からなる配向膜を形成した。
まず、相対湿度３０％以下の乾燥雰囲気中で、基板を化学吸着液に約一時間浸漬した。なお、化学吸着液は、基板に直接塗布しても良い。ここで用いた化学吸着液は、感光性基と直鎖状炭素鎖とケイ素とを含む下記の一般式（１）で表されるシラン系界面活性剤（化学吸着物質）を、その濃度が約１重量％になるよう、よく脱水された非水系有機溶媒（ヘキサデカン）に溶解して調製したものである。直鎖状炭素鎖は、たとえば炭化水素基等である。
【００３２】
【化１】
その後、化学吸着液から基板を取り出し、基板に付着した余剰の試薬を除去するために、よく脱水された非水系有機溶媒（ｎ−ヘキサン）の洗浄槽で約１０分の洗浄を３回行った後、基板を引き上げて液切りした。さらに、水分を含む空気中にこの基板を暴露し、基板に化学吸着した界面活性剤分子を空気中の水と反応させて厚さが約１．８ｎｍの単分子膜を形成した。
次に、偏光板（ＨＮＰ’Ｂ、ポラロイド社製）の露光用フォトマスクを単分子膜の上に重ね合わせ、これに超高圧水銀灯を用いて３６５ｎｍの紫外光（ＵＶ光）を１００ｍＪ／ｃｍ2になるように照射する配向固定処理を行った。
なお、ＦＴ−ＩＲ分析により、単分子膜は偏光したＵＶ光の照射により、偏光方向に配向されると共に、光重合が進行し、分子同士が感光性基で重合されたことを確認した。
【００３４】
次に、配向膜の上に、実施例１と同様の蒸着によって正孔輸送層、発光層および電子輸送層からなる発光機能層を積層して形成した。さらに、一軸延伸を行うことなしに、その上に反射陰極を形成した。
以上のようにして得られた有機発光素子を実施例４の素子とする。
【００３５】
《実施例５》
実施例４と同様にして、基板上に透明陽極を形成し、さらに基板への化学吸着液の供給および３回の洗浄ののち、ｎ−ヘキサン中に浸漬した基板を、その主面の法線方向を水平にして、鉛直方向に２ｃｍ／秒の速度で引き上げて液切りした。
波より取り出した基板を、実施例４と同様にして水分を含む空気中に暴露し、基板に化学吸着した界面活性剤分子を水と反応させて、配向膜としての厚さ約１． ８ｎｍの単分子膜を形成した。ここで、形成された配向膜は、それに接して形成される膜の分子を、上記の液切りの際の引き上げ方向に配向させることができる。すなわち、実施例４のように偏光紫外線を照射する必要はない。
【００３６】
次に、配向膜の上に、実施例１と同様の蒸着によって、正孔輸送層、発光層および電子輸送層からなる発光機能層を積層して形成した。さらに、一軸延伸を行うことなしに、その上に反射陰極を形成した。
以上のようにして得られた有機発光素子を実施例５の素子とする。
【００３７】
《実施例６》
実施例４と同様にして、基板上に透明陽極を形成し、さらに基板への化学吸着液の付着および３回の洗浄ののち、ｎ−ヘキサン中の基板を、その主面の法線方向を水平にして、鉛直方向に２ｃｍ／秒の速度で引き上げて液切りした。
その後、基板表面に化学吸着した界面活性剤分子に、その液切り方向（引き上げ方向）に偏向した紫外線を照射することによって、配向膜としての単分子膜を形成した。
次に、配向膜の上に、実施例１と同様の蒸着によって、正孔輸送層、発光層および電子輸送層からなる発光機能層を積層して形成した。さらに、一軸延伸を行うことなしに、その上に反射陰極を形成した。
以上のようにして得られた有機発光素子を実施例６の素子とする。
【００３８】
《実施例７》
実施例４と同様にして、基板上に透明陽極を形成し、さらに単分子吸着および偏光紫外線照射によって偏光膜を形成したのち、基板を乾燥置換したグローブボックス内へ移動させ、一方向に基板全体を１０ｃｍ一軸延伸した。
その後、実施例１と同様の蒸着によって、配向膜上に正孔輸送層、発光層、電子輸送層および反射陰極としての膜を積層して形成した。
以上のようにして得られた有機発光素子を実施例７の素子とする。
【００３９】
《実施例８》
実施例１と同様にして、基板上に透明陽極を形成した後、基板全体を一方向に１０ｃｍ一軸延伸した。さらに、実施例４と同様にして、延伸処理が施された基板上に、単分子吸着および偏光紫外線照射によって配向膜を形成した。
形成された配向膜の上に、実施例１と同様の蒸着によって、正孔輸送層、発光層、電子輸送層および反射陰極としての膜をそれぞれ形成した。
以上のようにして得られた有機発光素子を実施例８の素子とする。
【００４０】
《比較例１》
実施例１と同様にして、透明陽極、正孔輸送層および発光層として、厚さが約５０ｎｍのＰＥＤＯＴ膜、厚さが約４０ｎｍのＴＰＴ／ＰＳ共蒸着膜および厚さが約５０ｎｍのＤＴＶＢｉ膜を積層して形成して、発光素子を得た。この延伸処理を施していない発光素子を比較例１の素子とする。
【００４１】
《比較例２》
実施例２と同様にして、基板上に厚さが約５０ｎｍの透明陽極、約１００ｎｍの発光材料膜および厚さが約１２０ｎｍも反射陰極を形成して、発光素子を得た。この延伸処理を施していない発光素子を比較例２の素子とする。
【００４２】
以上のようにして得られた実施例および比較例の有機ＥＬ素子を、再度、乾燥窒素置換したグローブボックス内に移動させたのち、その性能を以下のようにして評価した。
初期性能として、発光効率［ｃｄ／Ａ］、１０００ｃｄ／ｍ2発光時の駆動電圧［Ｖ］、および偏光比として、直線偏光板を配向方向に配置した場合の輝度とその直角方向に配置した場合の輝度の比を求めた。
また、寿命として、素子をその初期輝度が１０００ｃｄ／ｍ2となる電流値の直流定電流で連続して発光させ、輝度が５００ｃｄ／ｍ2まで半減するまでの時間を求めた。ＤＣ駆動電源に直流定電流電源（アドバンテスト株式会社製、商品名マルチチャンネルカレントボルテージコントローラーＴＲ６１６３）を用い、電圧電流特性を測定するとともに、輝度計（東京光学機械株式会社製、商品名トプコンルミネセンスメーターＢＭ−８）によって輝度を測定した。また、輝度ムラ、黒点（非発光部）等の発光画像品質は、５０倍の光学顕微鏡により観察した。
これらの評価結果を表１に示す。
【００４３】
【表１】
表より明らかなように、いずれの実施例の素子も、偏光を発し、比較例と比べて発光効率は向上し駆動電圧は低くなる。さらに寿命は飛躍的に向上する。
また、輝度ムラや黒点等の不具合も無く、長寿命で安定した特性を発揮する。
【００４５】
【発明の効果】
本発明によると、高い光取出し効率を有し、さらに樹脂製の基板を用いることができる有機電界発光素子を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence (EL) element used for flat panel display devices and various light sources for communications, illumination, and other purposes, and more specifically to improve the light extraction efficiency. Regarding improvements.
[0002]
[Prior art]
Conventionally, liquid crystal display devices have been widely used as flat display devices. Since the liquid device has drawbacks such as a slow response speed and a narrow viewing angle, many new methods have been proposed to solve this problem. However, the cost for the countermeasure is an obstacle to the reduction of the price of the device, and even with these countermeasures, a liquid crystal display device having sufficient characteristics has not yet been obtained.
[0003]
In recent years, as a new element for a display device that can be expected to be applied in a wide range, an EL element that is excellent in visibility and has a high response speed has attracted attention because it is self-luminous.
In particular, an organic EL element using an organic material for all or a part of the light emitting layer can be formed by a simple method such as vapor deposition or coating at room temperature in addition to the above-mentioned advantages. Because of its attractive manufacturing cost, it is being actively developed. Also. Since the organic EL element is thin and capable of surface emission, it is expected to be used as an alternative to a backlight of a liquid crystal display device that has conventionally been used in combination with a fluorescent tube and a light guide plate.
[0004]
An organic EL element is a device in which holes injected from an anode and electrons injected from a cathode are combined in a light emitting layer to obtain light emission. Of course, not only electrode materials and light emitting materials but also light emitting layers and anodes or cathodes. Many researches have been made for a device in which layers having functions other than light emission are arranged, and many have been proposed. For example, a hole transport layer is disposed between the anode and the light emitting layer, and an electron transport layer is disposed between the cathode and the light emitting layer. Also proposed are those in which a hole injection layer is provided between the anode and the positive electrode transport layer, and those in which an electron injection layer is provided at the interface with the cathode. As the light emitting layer, there is a light emitting layer provided with a so-called hole transporting light emitting layer or an electron transporting light emitting layer that has the above-described function and emits light itself. By causing each layer to have a function separated from each other, an appropriate material can be selected for each layer, and the characteristics of the element are improved.
[0005]
For example, Tang et al. Is an element having a transparent anode, a hole transport layer, a light emitting layer, and a reflective cathode on a transparent substrate, with ITO (indium tin oxide) as the transparent anode and a thickness of 75 nm as the hole transport layer. A device using a diamine derivative layer, an aluminum quinoline complex layer having a thickness of 60 nm as a light emitting layer, and a MaAg alloy having both electron injection property and stability as a reflective cathode is proposed. (CW Tang and SA Vanslyke: Appl. Phys. Lett. 51 (1987) 913.). In this proposal, it is noticed that a hole transport layer made of a diamine derivative is used, in addition to improving the cathode. Since the diamine derivative is excellent in transparency and film formability, by adopting this, a uniform hole transport layer having sufficient transparency and having no pinholes even at a film pressure of 75 nm is obtained. Making it possible to get. Therefore, the phase film thickness of the element including the light emitting layer is sufficiently reduced to about 150 nm so that high luminance light emission can be obtained even at a relatively low voltage. Specifically, 1000 cd / m at a low voltage of 10V 2 The above high brightness and high efficiency of 1.5 lm / W or more are realized.
[0006]
The Tang et al.'S proposal has led to further active investigations of device improvements such as further improvement of the cathode and insertion of the electron injection layer and hole injection layer. .
Hereinafter, an outline of organic EL elements that are currently being examined generally will be described.
A transparent anode, a hole transport layer, a light emitting layer, and a cathode are laminated in this order on the transparent substrate. Further, a hole injection layer may be provided between the transparent anode and the hole transport layer, an electron transport layer may be provided between the light emitting layer and the cathode, and an electron injection layer may be provided at the interface with the cathode. In general, a glass substrate such as Corning 1737 is widely used as the transparent substrate. Here, a thickness of about 0.7 mm is easy to handle from the viewpoint of strength and weight.
As the transparent anode, for example, an ITO film formed by sputtering, electron beam evaporation, ion plating, or the like is used. The film thickness is determined in consideration of the required sheet resistance value and visible light transmittance. Since the organic EL element has a relatively high driving current density, generally, an organic EL element having a thickness of 100 nm or more is often used for the purpose of reducing the sheet resistance.
[0007]
The hole transport layer includes N, N′-bis (3-methylphenyl) -N, N′-diphenylbenzidine (hereinafter referred to as TPD), N, N′-pis (α-naphthyl) -N, N ′. -Diphenylbenzidine (hereinafter referred to as NPD) and other diamine derivatives used by Tang et al., In particular, vacuum-deposited films of diamine derivatives having a Q1-G-Q2 structure proposed in JP-A-59-194393 are widely used. Yes. These materials are generally excellent in transparency, are almost transparent even at a thickness of about 80 nm, and are excellent in film formability. Therefore, by using these materials, even if the thickness of the element is reduced to about 100 nm, defects such as pinholes are hardly generated, and problems related to reliability such as a short circuit are hardly generated.
[0008]
The light emitting layer is generally a film made of an electron transporting light emitting material such as tris (8-quinolinolato) aluminum (hereinafter referred to as Alq) having a thickness of several tens of nanometers formed by vacuum deposition as reported by Tang et al. Is used. For the purpose of realizing various emission colors, a relatively thin film is used for the light emitting layer. Furthermore, a so-called double heterostructure in which an electron transport layer having a thickness of about 20 nm is disposed thereon may be employed.
For the cathode, alloys such as MgAg alloy and AlLi alloy proposed by Tang et al. With a metal having a small work function and a low electron injection barrier and a metal having a relatively large work function and a stable metal, and various electron injection layers such as LiF are laminated. Aluminum is often used.
[0009]
As described above, an organic EL element formed by laminating these layers by a vacuum deposition method using a low molecular organic material has been actively studied. On the other hand, various organic materials are dissolved or dissolved in a solvent. In recent years, organic EL devices formed by laminating dispersed coating films of paint have also been actively studied.
For example, US Pat. No. 5,247,190 (RH Friends et al.) Discloses an organic EL device using a film formed by applying a conjugated light-emitting polymer. In this document, an aluminum deposited film having a thickness of about 20 nm having a slight oxide layer on the surface is formed as a cathode on a glass substrate, and further, a polysiloxane is deposited at a rate of 1 g in 10 to 25 ml of methanol. After a coating material in which a precursor of paraphenylene vinylene (hereinafter referred to as PPV) is dissolved is applied by a spin coating method, heat treatment is performed at 300 ° C. for 12 hours in a vacuum to form a PPV film having a thickness of 100 to 300 nm. I got it. In the case of a device in which a film made of gold or aluminum having a thickness of about 20 to 30 nm is formed by vapor deposition as a translucent anode and a PPV film having a thickness of 200 nm is formed thereon as a light emitting layer, a voltage of 40V It is said that strong EL emission was obtained by application. In addition, a transparent anode made of ITO is formed on a glass substrate by ion beam sputtering, a PPV layer having a thickness of 70 nm is formed as a light emitting layer, and an aluminum deposited film having a thickness of about 50 nm is formed as a cathode. In the obtained device, current started to flow from 14 V, and light emission was observed.
[0010]
In addition to the spin coating method, an ink jet method and a printing method have been proposed as the polymer coating. For example, in Japanese Patent Laid-Open No. 10-12377, polytetrahydrothiophenylphenylene is applied as a polymer precursor on a substrate in which a TFT array and an ITO transparent pixel electrode are formed on glass, and this is heated to a thickness of 0. A direct-view type organic EL display in which a 05 μm hole injection layer is formed, a light emitting layer corresponding to RGB pixels is formed by an inkjet method, and a MgAg electrode having a thickness of 0.1 to 0.2 μm is formed thereon. The body has been proposed. Here, it is said that the red light emitting material is cyanopolyphenylene vinylene, the green light emitting material is polyphenylene vinylene, the blue light emitting material is polyphenylene vinylene and polyalkylphenylene, and the liquid material obtained from Cambridge Display Technology is used. . Japanese Patent Laid-Open No. 3-269995 proposes an element produced by pattern film formation by a printing method using a toluene solution of a low molecular organic material such as a triphenyldiamine derivative.
[0011]
Major issues in the development of organic EL elements include improved light extraction efficiency, low voltage drive, reduced power consumption, and longer life. Of these, the improvement in light extraction efficiency contributes to solving other problems at the same time, such as extending the life of the element and reducing the drive voltage. .
[0012]
An electroluminescent element that emits polarized light is also being studied for backlight applications of liquid crystal display devices.
In the conventional organic EL element as described above, the orientation of the light emitting material molecules in the light emitting layer is disordered, and is parallel to, perpendicular to the main surface of the substrate, or has an intermediate angle. Mixed in disorder. Therefore, the light emitted from the light emitting layer becomes so-called natural light with no bias on the vibration surface. The light from the backlight of the liquid crystal display device contributes to the display of images and the like after passing through the polarizing plate. Therefore, since the light emitted from the backlight is natural light, most of it is excluded by the polarizing plate. Therefore, by aligning the light emitting material molecules in a specific direction, the technology for polarizing the light emitted from the light emitting layer minimizes the loss when passing through the polarizing plate, and further between the liquid crystal panel and the backlight. Attention has been focused on eliminating the need to interpose a polarizing plate.
[0013]
For example, in Japanese Patent Application Laid-Open No. 8-306954, the surface of an organic light emitting layer formed on a substrate is subjected to a rubbing treatment, and further subjected to a heat treatment, so that the organic light emitting material (π-conjugated polymer) in the layer is mainly processed. Organic light emitting diodes in which the chains are oriented in the rubbing direction have been proposed.
However, according to this method, it is necessary to add a heat treatment step together with the rubbing treatment to the conventional device manufacturing method. Furthermore, it is necessary to heat the organic light-emitting material to a temperature above the softening point of the heat treatment, and it is difficult to use a resin substrate.
[0014]
Japanese Patent Application Laid-Open No. 9-115669 proposes a method of orienting the surface of a base layer on which a light emitting layer is to be formed so as to align molecules in the light emitting layer in a specific direction. Specific examples of the alignment treatment include buffing and inclined vapor deposition.
According to the proposal, it is useful when a layer containing a light emitting material (light emitting layer) is directly formed on an ITO layer as an electrode as in the embodiment. That is, when a hole transport layer, an electron injection report, or the like is formed in contact with a layer that actually emits light, buff polishing to these layers, on the contrary, brings about a decrease in yield.
[0015]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an organic electroluminescence device that has high light extraction efficiency and can use a resin substrate. Another object of the present invention is to produce such an excellent organic light-emitting device with an easy method and high productivity.
[0016]
[Means for Solving the Problems]
The present invention has been made by paying attention to the fact that the angle formed by the direction of the light emitting transition moment of the organic light emitting material molecules in the light emitting layer with respect to the main surface of the substrate greatly affects the light extraction efficiency of the device. . In general, since an organic light emitting element is composed of an amorphous film, the light emission transition moment of each light emitting material molecule shows a random direction. Therefore, light emitted above the total reflection angle, that is, above the critical angle with respect to the normal of the light emitting surface, cannot be extracted outside the device.
Therefore, in the present invention, the direction of the light emission transition moment of the organic light emitting material molecules is oriented in a specific direction parallel to the main surface of the substrate by an easy method, thereby improving the light extraction efficiency.
In the present invention, for example, an organic light emitting material film formed by a known method such as coating on a resin substrate is stretched in a specific direction together with the substrate, and molecules in the film are oriented in the stretching direction. By so-called uniaxial stretching, molecules in the organic light-emitting material film can obtain a light-emitting layer that emits polarized light having a desired vibration plane with its main chain oriented in parallel with the stretching direction.
Prior to the formation of the organic light emitting material film, a film for regulating the orientation of the organic light emitting material, a so-called alignment film, is formed on the surface on which the organic light emitting material film is to be formed.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment of the present invention, a conductive film containing an organic conductive material is formed on a resin substrate including a film-like material, and an organic light-emitting material film is further formed on the conductive film. The film is stretched together with the substrate, and the organic light emitting material molecules in the organic light emitting material film are oriented so that the main chain thereof is substantially parallel to the stretching direction. Note that when the stretching ratio is increased, the organic light emitting material molecules can be more uniformly oriented. In order to stably obtain a light emitting layer having a uniform main chain, it is preferably stretched about 1.5 times.
Of the layers arranged between the two electrodes (hereinafter referred to as functional layers), at least the layer that itself emits light, that is, the film that is processed into the light emitting layer, is formed, and then the above-described stretching treatment is performed. Accordingly, the stretched film includes not only an organic light emitting material film processed into a light emitting layer but also various films arranged in a laminated manner therewith.
[0018]
Prior to stretching, a conductive film is formed on the surface of the substrate as one of the electrodes or for processing. The pair of electrodes arranged with the light emitting layer interposed therebetween applies a direct current or alternating current voltage to the light emitting layer, and in the case of an organic light emitting element driven usually by direct current, indicates a cathode and an anode. A transparent conductive material is used for either one or both of the pair of electrodes in order to extract light emitted from the light emitting layer. When taking out light from only one electrode side, in order to use light effectively, the other side electrode is generally made of a metallic material having light reflectivity, such as MgAg alloy or AlLi alloy, or with a transparent electrode. A reflective member such as a metal film is disposed.
Since the conductive film disposed between the substrate and the organic light emitting material film is stretched when the substrate and the organic light emitting material film are stretched, the organic conductive material having transparency and flexibility such as polythiophene and polypyrrole is mainly used. What consists of material is used. That is, the organic light-emitting device of the present invention emits light transmitted through the substrate to the outside. In the case where an anode and a cathode both made of a transparent organic conductive material are used and a reflecting member is further arranged, after forming both electrodes or a film for processing the electrodes, the reflecting member may be stretched together with the substrate.
When a light emitting functional layer having a multilayer structure is applied, for example, a uniaxial orientation treatment is performed in the formation of each layer. Further, even if uniaxial orientation treatment is performed after all layers are formed, molecules in any layer can be oriented in the same direction.
[0019]
In another embodiment of the present invention, prior to the formation of the organic light emitting material film, a film that regulates the orientation of organic light emitting material molecules, a so-called alignment film, is formed on the surface on which the organic light emitting material film is to be formed. For the alignment film, for example, polyimide or a silane compound containing a linear carbon chain is used.
The alignment film is formed by, for example, irradiating a prepolymer applied on a substrate with polarized ultraviolet rays and curing it.
In addition, the substrate on which the underlayer of the film to be formed has already been formed is attached to a liquid containing a monomolecular adsorbing substance, and further, it is placed in a cleaning tank and cleaned in order to remove the excess liquid attached. Thereafter, the main surface is tilted in a specific direction (including the vertical direction) and pulled up while draining. Thereby, an alignment film capable of aligning the organic light emitting material molecules in the direction of pulling up the substrate when taking out from the cleaning tank is formed. If necessary, the monomolecular film formed on the substrate is fixed by irradiation with polarized ultraviolet rays or the like.
When another functional layer such as a hole transport layer is disposed between the light emitting layer and the conductive film located below it, the functional layer disposed above the layer in which the orientation of the constituent molecules is regulated Since the orientation of the constituent molecules of the light-emitting layer follows the constituent molecules of the regulated functional layer, the constituent molecules of the light-emitting layer or the light-emitting material film processed by the light-emitting layer can be obtained even if only the orientation film is disposed on the conductive layer. It can be oriented in a desired direction.
[0020]
Of course, you may use combining the alignment by said uniaxial stretching and the alignment regulation by an alignment film.
INDUSTRIAL APPLICABILITY The present invention is applied to an organic EL device having a single light emitting layer that emits light, and an organic EL having a multilayer light emitting functional layer including functional layers such as an electron transport layer and a hole transport layer. This also applies to the element.
In a display device, generally, a polarizing plate is disposed on the surface of the display device, that is, on the light emission surface thereof in order to prevent reflection of external light by a reflective cathode and to improve contrast. When the vibration plane of the light emitted from the light emitting layer is parallel to the transmission axis of the polarizing plate, the loss when passing through the polarizing plate can be minimized and the extraction efficiency can be further increased.
[0021]
【Example】
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0022]
Example 1
A polythiophene derivative (manufactured by Bayer Co., Ltd.) is applied on a commercially available transparent polyester film (substrate size: 10 cm × 10 cm, thickness 30 μm) as a substrate, followed by heat treatment at 150 ° C. for 30 minutes in the air. Then, an organic conductive film made of poly (3,4-ethylenedioxythiophene) (PEDOT) having a thickness of 100 nm was formed as a transparent anode.
[0023]
On the formed transparent anode, a light emitting functional layer including a hole transport layer, a light emitting layer, and an electron transport layer was formed as follows.
First, films to be processed into a hole transport layer and a light emitting layer were formed by laminating each by vapor deposition using a high vacuum vapor deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd., modified EBV-6DA type). The main exhaust device of this device is a turbo molecular pump (TC 1500, manufactured by Osaka Vacuum Co., Ltd.) with an exhaust speed of 1500 liters / minute, and the ultimate vacuum is about 1 × 10. -6 Torr (≈1.33 × 10 -Four Pa) or less. For vapor deposition of all organic compounds, a direct current power source (manufactured by Kikusui Electronics Co., Ltd., PAK10-70A) is connected to a resistance heating type vapor deposition port made of tungsten, and the degree of vacuum is 2 to 3 × 10. -6 Performed in the range of Torr.
[0024]
N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (TPT, Hodogaya Chemical Co., Ltd.) as a hole transport layer on a substrate placed in a vacuum chamber of a high vacuum deposition apparatus. Co., Ltd.) was vapor-deposited at a vapor deposition rate of 0.3 nm / sec, and 4-N, N-diphenylamino-α-phenylstilbene (PS) was vapor-deposited (co-vapor deposition) at a vapor deposition rate of 0.01 nm / sec. A film as a blended hole transport layer having a thickness of about 80 nm was formed.
Next, 4,4′-bis [2,2-bis (4-methylphenyl) vinyl] biphenyl (DTVBi) is deposited on the film at a deposition rate of 0.3 nm / sec. -Bis {2- [9-ethylcarbazol-3-yl] vinyl} biphenyl (BCzVBi) is co-evaporated at a deposition rate of 0.01 nm / second to emit light having a thickness of about 100 nm as a so-called doped light-emitting layer A material film was formed.
[0025]
Next, after moving the substrate from the vacuum chamber into a glove box where the atmosphere was replaced with dry nitrogen, the entire substrate was stretched uniaxially by 10 cm in a direction parallel to one side at room temperature. The stretched and processed transparent anode, hole transport layer and light emitting layer had thicknesses of about 50 nm, about 40 nm and about 50 nm, respectively.
[0026]
The substrate subjected to the stretching treatment as described above is returned again into the vacuum chamber, and a film having a thickness of about 20 nm made of tris (8-quinolinolato) aluminum (Alq3, manufactured by Dojin Chemical Co., Ltd.) as an electron transport layer. Was formed at a deposition rate of 0.3 nm / second.
[0027]
On the formed light emitting functional layer, a reflective cathode was formed as follows.
Thickness at a deposition rate of about 0.1 nm / second on the light-emitting functional layer by low-temperature deposition using an aluminum / lithium alloy (manufactured by High-Purity Chemical Co., Ltd., Al / Li weight ratio 99/1) as a source. An aluminum film having a thickness of about 100 nm is formed on the lithium film at a deposition rate of about 1.5 nm / second using a source from which lithium is formed by forming a lithium film of about 1 nm and raising the temperature of the source to remove most of the lithium. A film was formed to obtain a laminated reflective cathode.
The organic light emitting device obtained as described above is referred to as the device of Example 1.
[0028]
Example 2
An organic conductive film having a thickness of 100 nm was formed as a transparent anode on the same transparent polyester film as used in Example 1, and then the poly [2- A paint in which methoxy-5- (2′-ethyl) hexyloxy-p-phenylenevinylene] (MEH-PPV) was dissolved in xylene at a concentration of 10 mg / ml was applied by a spin coating method, and was further applied in a dry nitrogen glove box. A light emitting material film having a thickness of about 200 nm was formed by heat treatment at 30 ° C. for 30 minutes.
Within the glove box, the entire substrate was uniaxially stretched 10 cm in the direction parallel to one side at room temperature. The thickness of the stretched and processed transparent anode and light emitting layer was about 50 nm and about 100 nm, respectively.
[0029]
The substrate subjected to the stretching treatment was placed in a vacuum chamber, and a calcium film having a thickness of about 20 nm and an aluminum film having a thickness of about 100 nm were stacked on the surface as a reflective cathode in the same manner as in Example 1.
The organic light emitting device obtained as described above is referred to as the device of Example 2.
[0030]
Example 3
A transparent polyester film having a conductive polymer film with a thickness of 100 nm as a transparent anode formed on the surface in the same manner as in Example 1 was uniaxially stretched by 10 cm in a direction parallel to one side thereof at room temperature. The thickness of the transparent anode processed by stretching was about 50 nm.
On the transparent anode, a hole transport layer having a thickness of about 80 nm and a light emitting layer having a thickness of about 200 nm were formed by vapor deposition in the same manner as in Example 1 as a light emitting functional layer.
Next, a calcium film having a thickness of about 20 nm and an aluminum film having a thickness of about 100 nm were stacked as a reflective cathode on the surface of the substrate on which the light emitting functional layer was formed.
The organic light emitting device obtained as described above is referred to as the device of Example 3.
[0031]
Example 4
A transparent anode was formed on the substrate in the same manner as in Example 1, and then an alignment film made of a monomolecular film was formed on the surface as follows.
First, the substrate was immersed in the chemical adsorption solution for about one hour in a dry atmosphere with a relative humidity of 30% or less. The chemical adsorption liquid may be directly applied to the substrate. The chemical adsorption solution used here is a silane-based surfactant (chemical adsorption material) represented by the following general formula (1) containing a photosensitive group, a linear carbon chain and silicon, and the concentration thereof is about It was prepared by dissolving in a well-dehydrated non-aqueous organic solvent (hexadecane) so as to be 1% by weight. The straight carbon chain is, for example, a hydrocarbon group.
[0032]
[Chemical 1]
Thereafter, the substrate was taken out from the chemical adsorption solution, and in order to remove excess reagent adhering to the substrate, washing was performed about 10 minutes three times in a well-dehydrated non-aqueous organic solvent (n-hexane) washing tank. Thereafter, the substrate was pulled up and drained. Further, the substrate was exposed to air containing moisture, and the surfactant molecules chemically adsorbed on the substrate were reacted with water in the air to form a monomolecular film having a thickness of about 1.8 nm.
Next, a photomask for exposure of a polarizing plate (HNP'B, Polaroid Co., Ltd.) is superimposed on the monomolecular film, and 365 nm ultraviolet light (UV light) is 100 mJ / cm using an ultrahigh pressure mercury lamp. 2 The orientation fixing process of irradiating was performed.
By FT-IR analysis, it was confirmed that the monomolecular film was aligned in the polarization direction by irradiation with polarized UV light, and photopolymerization proceeded, and the molecules were polymerized with a photosensitive group.
[0034]
Next, a light emitting functional layer including a hole transport layer, a light emitting layer, and an electron transport layer was laminated on the alignment film by vapor deposition similar to that in Example 1. Further, a reflective cathode was formed thereon without performing uniaxial stretching.
The organic light emitting device obtained as described above is referred to as the device of Example 4.
[0035]
Example 5
In the same manner as in Example 4, a transparent anode was formed on the substrate, and the substrate immersed in n-hexane after supplying the chemisorbed liquid to the substrate and washing three times was used as the normal to the main surface. The direction was horizontal, and the liquid was pulled up in the vertical direction at a speed of 2 cm / sec to drain the liquid.
The substrate taken out from the wave was exposed to moisture-containing air in the same manner as in Example 4, and the surfactant molecules chemically adsorbed on the substrate were reacted with water to obtain a thickness of about 1. A monomolecular film of 8 nm was formed. Here, the formed alignment film can orient the molecules of the film formed in contact with the alignment film in the pulling direction at the time of the above draining. That is, it is not necessary to irradiate polarized ultraviolet rays as in the fourth embodiment.
[0036]
Next, a light emitting functional layer composed of a hole transport layer, a light emitting layer, and an electron transport layer was formed on the alignment film by vapor deposition similar to that in Example 1. Further, a reflective cathode was formed thereon without performing uniaxial stretching.
The organic light emitting device obtained as described above is referred to as the device of Example 5.
[0037]
Example 6
In the same manner as in Example 4, a transparent anode was formed on the substrate, and after the chemical adsorption liquid was attached to the substrate and washed three times, the substrate in n-hexane was changed in the normal direction of its main surface. The liquid was leveled and pulled up in the vertical direction at a speed of 2 cm / sec to drain the liquid.
Thereafter, the surfactant molecules chemically adsorbed on the substrate surface were irradiated with ultraviolet rays deflected in the liquid draining direction (pulling direction) to form a monomolecular film as an alignment film.
Next, a light emitting functional layer composed of a hole transport layer, a light emitting layer, and an electron transport layer was formed on the alignment film by vapor deposition similar to that in Example 1. Further, a reflective cathode was formed thereon without performing uniaxial stretching.
The organic light emitting device obtained as described above is referred to as the device of Example 6.
[0038]
Example 7
In the same manner as in Example 4, after forming a transparent anode on the substrate and further forming a polarizing film by monomolecular adsorption and irradiation with polarized UV light, the substrate is moved into a glove box where the substrate is dried and replaced. Was uniaxially stretched 10 cm.
Thereafter, a hole transport layer, a light emitting layer, an electron transport layer, and a film as a reflective cathode were laminated on the alignment film by vapor deposition in the same manner as in Example 1.
The organic light emitting device obtained as described above is referred to as the device of Example 7.
[0039]
Example 8
In the same manner as in Example 1, after forming a transparent anode on the substrate, the entire substrate was uniaxially stretched 10 cm in one direction. Further, in the same manner as in Example 4, an alignment film was formed on the substrate subjected to the stretching treatment by monomolecular adsorption and polarized ultraviolet irradiation.
On the formed alignment film, a hole transport layer, a light emitting layer, an electron transport layer, and a film as a reflective cathode were formed by vapor deposition similar to Example 1, respectively.
The organic light emitting device obtained as described above is referred to as the device of Example 8.
[0040]
<< Comparative Example 1 >>
In the same manner as in Example 1, as a transparent anode, a hole transport layer and a light emitting layer, a PEDOT film having a thickness of about 50 nm, a TPT / PS co-deposited film having a thickness of about 40 nm, and a DTVBi film having a thickness of about 50 nm Are stacked to obtain a light emitting element. The light emitting element that has not been subjected to the stretching treatment is referred to as an element of Comparative Example 1.
[0041]
<< Comparative Example 2 >>
In the same manner as in Example 2, a transparent anode having a thickness of about 50 nm, a light emitting material film having a thickness of about 100 nm, and a reflective cathode having a thickness of about 120 nm were formed on the substrate to obtain a light emitting device. The light emitting element that has not been subjected to the stretching treatment is referred to as an element of Comparative Example 2.
[0042]
The organic EL elements of Examples and Comparative Examples obtained as described above were moved again into a glove box substituted with dry nitrogen, and the performance was evaluated as follows.
As the initial performance, luminous efficiency [cd / A], 1000 cd / m 2 As the driving voltage [V] at the time of light emission and the polarization ratio, the ratio of the luminance when the linearly polarizing plate was arranged in the alignment direction and the luminance when arranged in the direction perpendicular thereto was determined.
Further, as the lifetime, the element has an initial luminance of 1000 cd / m. 2 The light is continuously emitted at a constant DC current having a current value of 500 cd / m. 2 The time until halving was obtained. A DC constant current power supply (trade name: Multichannel Current Voltage Controller TR6163, manufactured by Advantest Corporation) is used as a DC drive power supply, and voltage and current characteristics are measured. The brightness was measured by BM-8). Further, emission image quality such as luminance unevenness and black spots (non-light emitting portion) was observed with a 50 × optical microscope.
These evaluation results are shown in Table 1.
[0043]
[Table 1]
As is apparent from the table, the elements of all the examples emit polarized light, and the light emission efficiency is improved and the driving voltage is lowered as compared with the comparative example. Furthermore, the service life is dramatically improved.
In addition, there are no problems such as luminance unevenness and black spots, and long life and stable characteristics are exhibited.
[0045]
【The invention's effect】
According to the present invention, it is possible to provide an organic electroluminescent element having high light extraction efficiency and capable of using a resin substrate.
Claims (3)
前記一方の電極および前記発光層が、同一方向に延伸されて形成されたものである有機発光素子。 A resin substrate, one electrode including an organic conductive material disposed on the substrate, a light emitting layer including an organic light emitting material disposed on the electrode, and the other disposed on the light emitting layer in a stacked manner An electrode, the main chain of the organic conductive material in the one electrode and the main chain of the organic light emitting material in the light emitting layer are oriented in the same direction substantially parallel to the surface of the substrate,
The one electrode and the light emitting layer, der Ru organic light emitting element that is formed by extending in the same direction.
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| JP5521252B2 (en) * | 2008-10-21 | 2014-06-11 | 国立大学法人京都工芸繊維大学 | Benzene compounds |
| US8962364B2 (en) | 2010-03-16 | 2015-02-24 | Konica Minolta Holdings, Inc. | Production method for organic electroluminescent element |
| JP5981736B2 (en) * | 2011-04-12 | 2016-08-31 | ユー・ディー・シー アイルランド リミテッド | ORGANIC ELECTROLUMINESCENT ELEMENT, AND LIGHT EMITTING DEVICE, DISPLAY DEVICE AND LIGHTING DEVICE USING THE ORGANIC ELECTROLUMINESCENT ELEMENT |
| JP6000703B2 (en) * | 2011-08-12 | 2016-10-05 | キヤノン株式会社 | ORGANIC EL ELEMENT, AND LIGHT EMITTING DEVICE, IMAGE FORMING DEVICE, LIGHT EMITTING ELEMENT ARRAY, IMAGING DEVICE, DISPLAY DEVICE USING THE SAME |
| JP7140469B2 (en) * | 2016-07-15 | 2022-09-21 | キヤノン株式会社 | Photoelectric conversion device and imaging system |
| CN113471396A (en) * | 2021-07-02 | 2021-10-01 | 合肥福纳科技有限公司 | Electroluminescent device, light-emitting diode, and preparation method and application of thin film |
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