JP4354019B2 - Organic electroluminescence device - Google Patents

Description

【００４０】
（式中、Ｍｅは金属を表し、ｎは１〜３の整数である。Ｚは独立にそれぞれの場合において少なくとも２個の縮合芳香族環を持つ核を完成する原子を示す。）
式中の金属としては、キレート形成能のある１〜３価金属であればよく、例えば、リチウム、ナトリウム、カリウムのようなアルカリ金属、マグネシウムやカルシウムのようなアルカリ土類金属、あるいはホウ素やアルミニウムのような３価金属を挙げることができる。また、Ｚは少なくとも２個の縮合芳香族環を持つ複素環状核を完成する原子を表す。Ｚが完成する複素環状核としては、例えば、アゾール環やアジン環を挙げることができる。
【００４１】
前記有用なキレート化オキシノイド化合物としては、アルミニウムトリスオキシン、マグネシウムビスオキシン、ビス〔ベンゾ（ｆ）−８−キノリノール〕亜鉛、ビス（２−メチル−８−キノリノラート）アルミニウムオキサイド、インジウムトリスオキシン、アルミニウムトリス（５−メチルオキシン）、リチウムオキシン、ガリウムトリスオキシン、カルシウムビス（５−クロロオキシン）、ポリ〔亜鉛（ＩＩ）−ビス（８−ヒドロキシ−５−キノリノニル）メタン〕、ジリチウムエピンドリジオン等が挙げられる。
【００４２】
また、電子注入性の金属、合金、アルカリ土類金属酸化物と電子伝達性の化合物との混合比（重量比）は、１００：１〜１：２とすることが好ましい。
電子注入性の金属、合金と電子伝達性の化合物との混合層は、２元同時蒸着法により形成するのが好ましい。基板温度は、１０〜１００℃の間で設定すればよい。
【００４３】
更に他の好ましい例として、電子注入電極層が島状の電子注入域である構成を挙げることができる。ここで、島状とは、例えば図３に示すように、不連続に電子注入性化合物層が形成されていて、この層は有機層の表面を覆いつくすことがないことを意味する。
島状電子注入域は、例えば仕事関数３．８ｅＶ以下の低仕事関数の金属、酸化物、ホウ化金属、窒化金属、ケイ化金属などを島状に不連続に形成させたものであり、その形状及び大きさについては特に制限はないが、微粒子状または結晶状であって、大きさが０．５ｎｍ〜５μｍ程度のものが好ましい。
【００４４】
また、この電子注入域は、薄膜状を指すものでも、孤立原子分散の状態を示すものでもない。上記の低仕事関数の金属又は化合物が、粒子状の形態で導電性薄膜上又は有機化合物層内に分散されている状態を指す。このような分散により、有機化合物層と接触している面積が大きくなり、電子注入性が高まる。
上記島状電子注入域を構成する低仕事関数の金属及び合金としては、仕事関数３．８ｅＶ以下のものが好ましく、例えば、前記した金属及び合金を挙げることができる。また、低仕事関数の酸化物としては、アルカリ金属又はアルカリ土類金属の酸化物が好ましく、特にＣａＯ，ＢａＯ，ＳｒＯなどが好適であり、また、これらと他の金属酸化物との固溶体も好ましく挙げることができる。更に、低仕事関数のホウ化金属や窒化金属としては、例えば希土類のホウ化物、希土類のケイ化物あるいはＴｉＮなどが好ましく挙げられる。
【００４５】
島状電子注入域の形成方法としては、抵抗加熱蒸着法や電子ビーム蒸着法を採用することができる。後者の場合、高融点のホウ化金属、窒化金属または酸化物を電子ビーム蒸着により島状に不連続に形成させる。
本発明の有機ＥＬ素子において、電子注入電極層と非晶質透明導電膜を構成要素とする陰極の場合、劣化し易い電子注入電極層が非晶質透明導電膜で保護されることとなり、電子注入電極層を薄くすることができ、結果として、透明陰極を好適に作成できるという利点を有する。
【００４６】
本発明の有機ＥＬ素子においては、通常、基板上に陽極を積層しその上に有機層を積層する構成を採用するが、この場合、有機発光層を含む有機層の上に電子注入電極層を形成する。形成方法は、前記のとおりであるが、他の好ましい方法としてスパッタリング法があるが。この手法を用いるに際しては、プラズマにより有機層が損傷を受けないように注意する必要がある。
【００４７】
＜透明薄膜層＞
前記の構成の陰極においては、最外層が金属薄膜となるため、これを保護する層が必要となる。本発明の第１の目的は、光透過性を有する陰極を得ることにあるため、この層は光透過性を有する必要がある。
このような、層としてガラスやプラスチック製の公知の薄膜を用いることもできるが、基板上に陽極側から積層して有機ＥＬ素子を作製する場合には、金属薄膜上に、透明な誘電体薄膜あるいは透明導電膜を形成することが好ましい。誘電体薄膜を用いる場合には、屈折率の関係で光透過率が向上した透明保護膜を形成することができるという利点がある。
【００４８】
透明な誘電体薄膜としては、例えば、ＴｉＯ₂ 等の結晶性薄膜を用いることができる。また、透明導電膜としては、例えば、ＩＴＯ、ＳｎＯ₂ 等の結晶性の薄膜やＩｎ−Ｚｎ−Ｏ系等の非晶質透明導電膜を使用することができる。特に、非晶質透明導電膜を用いることは本発明の第２の目的である耐久性の向上の面でも好ましい。この層においては、導電性を必須としない。このため、透明な誘電体薄膜を用いる場合、リードは金属薄膜からとることになる。
この層の形成方法としては、ＲＦマグネトロンスパッタリング、特にヘリコンスパッタリングが好適に用いられる。
【００４９】
＜光透過率および面抵抗値＞
本発明の第１の目的を達成する有機ＥＬ素子においてはまた、陽極と陰極との間に有機発光層を含む有機層が挟持されているとともに、陰極の外側に透明薄膜層が形成されてなる構成であって、陰極と前記透明薄膜層からなる層の光透過率が６０％以上であり、かつ陰極と前記透明薄膜層からなる層または陰極の面抵抗値が１０Ω／□以下である素子構成を採用することができる。
この構成を満たす陰極としては、例えば、前記の構成を有するものを好適に挙げることができる。また、透明薄膜層は、前記と同様である。
【００５０】
ここで規定する光透過率とは、有機ＥＬ素子を構成する有機層に接する層（例えば、電子注入電極層）から陰極の外側に形成される透明薄膜までの光透過率である。
光透過率は、可視光域（３８０〜７００ｎｍ）のいずれか波長で透過率が６０％以上となればよい。光透過率の測定方法としては、公知の分光光度計を用いればよい。また、陰極とその外側に形成される透明薄膜層からなる層のみを作製して光透過率を測定する必要はなく、他の層を含めた光透過率が６０％以上であれば、この層の光透過率が６０％以上であるといえる。
【００５１】
ここで規定する面抵抗値（Ω／□）は、四探針法により測定した値である。具体的には、絶縁性の基板（例えば、ガラス基板）上に、当該有機ＥＬ素子における陰極およびその外側に形成される透明薄膜層からなる層と同じ構成の膜、または陰極と同じ構成の膜を形成し、四探針法により陰極またはその外側に形成される透明薄膜層表面の面抵抗値を測定する。このとき、面抵抗値を測定する層としては、電極リードを取り出す層を選択する。即ち、陰極から電極リードを取り出す場合は、陰極の面抵抗を測定し、陰極の外側に形成される透明薄膜層から電極リードを取り出す場合には、透明薄膜層の面抵抗を測定する。このようにして、測定された面抵抗値が本発明の規定する面抵抗値である。
【００５２】
ただし、陰極が電子注入電極層を含む構成の場合には、該層を除外した層を実際の素子構成の場合と同じ順序で積層して面抵抗を測定する。具体的には、例えば、透明薄膜層から電極リードを取り出すＥＬ素子の場合には、支持基板（通常はガラス）上に、透明導電膜、金属薄膜、透明薄膜層の順に積層し、この透明薄膜層の表面の面抵抗を本発明の面抵抗値とする。この場合において、金属薄膜から電極リードを取り出す場合には、金属薄膜の表面の面抵抗を本発明の面抵抗値とする。
【００５３】
＜有機層＞
本発明の有機ＥＬ素子において、陽極と陰極との間に介在する有機層は、少なくとも有機発光層を含む。有機層は、有機発光層のみからなる層であってもよく、また、有機発光層とともに、正孔注入輸送層などを積層した多層構造のものであってもよいよい。
【００５４】
この有機ＥＬ素子において、発光層は（１）電界印加時に、陽極又は正孔輸送層により正孔を注入することができ、かつ電子注入電極層より電子を注入することができる機能、（２）注入した電荷（電子と正孔）を電界の力で移動させる輸送機能、（３）電子と正孔の再結合の場を発光層内部に提供し、これを発光につなげる発光機能などを有している。この発光層に用いられる発光材料の種類については特に制限はなく、従来有機ＥＬ素子における公知のものを用いることができる。
【００５５】
また、正孔注入輸送層は、正孔伝達化合物からなる層であって、陽極より注入された正孔を発光層に伝達する機能を有し、この正孔注入輸送層を陽極と発光層との間に介在させることにより、より低い電界で多くの正孔が発光層に注入される。その上、電子注入層より発光層に注入された電子は、発光層と正孔注入輸送層の界面に存在する電子の障壁により、この発光層内の界面近くに蓄積されたＥＬ素子の発光効率を向上させ、発光性能の優れたＥＬ素子とする。この正孔注入輸送層に用いられる正孔伝達化合物については特に制限はなく、従来有機ＥＬ素子における正孔伝達化合物として公知のものを使用することができる。正孔注入輸送層は、単層のみでなく多層とすることもできる。
【００５６】
＜陽極＞
陽極は、仕事関数が４．８ｅＶ以上の導電性を示すものであれば特に制限はない。仕事関数が４．８ｅＶ以上の金属又は透明導電膜（導電性酸化物膜）又はこれらを組み合わせたものが好ましい。陽極は、必ずしも透明である必要はなく、黒色のカーボン層等をコーティングしてもよい。
【００５７】
好適な金属としては、例えば、Ａｕ，Ｐｔ，Ｎｉ，Ｐｄを挙げることができ、導電性酸化物としては、例えば、Ｉｎ−Ｚｎ−Ｏ，Ｉｎ−Ｓｎ−Ｏ，ＺｎＯ−Ａｌ，Ｚｎ−Ｓｎ−Ｏを挙げることができる。また、積層体としては、例えば、ＡｕとＩｎ−Ｚｎ−Ｏの積層体、ＰｔとＩｎ−Ｚｎ−Ｏの積層体、Ｉｎ−Ｓｎ−ＯとＰｔの積層体を挙げることができる。
【００５８】
また、陽極は、有機層との界面が仕事関数４．８ｅＶ以上であればよいため、陽極を２層とし、有機層と接しない側に仕事関数４．８ｅＶ以下の導電性膜を用いてもよい。この場合、Ａｌ，Ｔａ，Ｗ等の金属やＡｌ合金、Ｔａ−Ｗ合金等の合金等を用いることができる。また、ドープされたポリアニリンやドープされたポリフェニレンビニレン等のドープされた導電性高分子や、α−Ｓｉ，α−ＳｉＣ、α−Ｃなどの非晶質半導体、μＣ−Ｓｉ，μＣ−ＳｉＣ等の微結晶なども好ましく用いることができる。更には、黒色の半導性の酸化物であるＣｒ₂ Ｏ₃ ，Ｐｒ₂ Ｏ₅ ，ＮｉＯ，Ｍｎ₂ Ｏ₅ ，ＭｎＯ₂ 等を用いることができる。
【００５９】
陽極の膜厚は、５０〜３００ｎｍ程度とすることが好ましい。膜厚が５０ｎｍ未満では、抵抗値が高くなり過ぎる場合がある。一方、３００ｎｍを超えると、有機ＥＬ素子において、陽極がパターンされている端で生じる段差により上部の膜、例えば有機層や陰極が段差切れや断線を起こす場合がある。
【００６０】
＜有機ＥＬ素子の構成＞
本発明の有機ＥＬ素子は、陽極と陰極との間に有機発光層を含む有機層が介在しており、陰極は電子注入電極層、透明導電膜、金属薄膜とによって構成されており、しかも電子注入電極層が有機層と接するとともに陰極の外側に透明薄膜層が形成されてなる構成、あるいは陽極と陰極との間に有機発光層を含む有機層が挟持されてなるとともに陰極とその外側に形成される透明薄膜からなる層の光透過率が６０％以上であり、かつ陰極と前記透明薄膜層からなる層または陰極の面抵抗値が１０Ω／□以下である構成を具備していれば、本発明の第１の目的を達成することができる。また、上記の有機ＥＬ素子において透明導電膜として非晶質透明導電膜を採用することにより本発明の第２の目的を達成することができる。
【００６１】
また、更に他の構成を付加して、種々の機能を持たせることができる。以下に本発明の有機ＥＬ素子を利用した構成を例示する。
▲１▼ 透明陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜
▲２▼ 陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜／カラーフィルター
▲３▼ 陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜／色変換層
▲４▼ 透明陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜／黒色光吸収層
▲５▼ 透明陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜／背景色形成層
▲６▼ 黒色光吸収層／透明陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜
▲７▼ 背景色形成層／透明陽極／有機層／電子注入電極層／非晶質透明導電膜／金属薄膜／透明導電膜
前記▲１▼の構成の場合、両方の電極が透明なので、透明表示素子が形成される。
【００６２】
▲２▼や▲３▼の構成の場合、陽極を支持基板上に形成し、支持基板とは逆方向に発光の取り出しができるので、カラーフィルターや色変換層上に陽極を形成する必要がない。従って、陽極を形成する際に基板温度が１５０℃以上となるようなプロセスを採用することができ、陽極の抵抗値を下げる上で大きなメリットがある。また、カラーフィルターや色変換層は陽極形成後に形成されるため、高温プロセスの採用による劣化を心配する必要がない。図４に、▲２▼の構成を例示する。なお、ここで、色変換層としては、蛍光性色素を含有する透明性ポリマーからなり、ＥＬ発光色を蛍光により別の色に変換するものであることが好ましい。
【００６３】
また、▲２▼や▲３▼の構成で、多くの画素を構成させた態様においては、基板上に陽極以外の補助配線やＴＦＴ（Thin Film Transister）が形成されるため、基板方向に光を取り出すと、補助配線やＴＦＴが光を遮断し、光取り出しの開口率が落ち、結果としてディスプレイの輝度が小さくなり、画質が落ちるという欠点がある。本発明を用いれば基板とは逆の方向に光の取り出しができるが、この場合には光が遮断されず光取り出しの開口率が落ちない。
【００６４】
▲４▼や▲６▼の構成においては、画素がオフのときに黒色に見えるので、入射外光が反射せず、ディスプレイのコントラストが向上するという利点がある。図５に、▲４▼の構成を例示する。
▲５▼や▲７▼の構成においては、種々の背景色や図柄を採用することができ、画素がオフのときにも装飾性に優れるディスプレイとすることができる。図６に、▲７▼の構成を例示する。
【００６５】
なお、前記▲２▼〜▲７▼の構成において、色変換層、カラーフィルター、黒色光吸収層及び背景色形成層は、必ずしも電極に密着する必要はなく、中間層を介在させてもよいし、その効果が発現される限り、図４に示すように離して設置してもよい。ただし、色変換層やカラーフィルターは光取り出し方向に設置される必要があり、黒色光吸収層や背景色形成層は光取り出し方向とは逆方向に設置される必要がある。
【００６６】
【実施例】
以下、本発明の実施例について説明する。
〔実施例１〕
＜有機ＥＬ素子の作製＞
２５ｍｍ×７５ｍｍ×１ｍｍのガラス基板上に、ＩＴＯを１００ｎｍの膜厚で製膜したもの（ジオマティックス社製）を基板上に導電性薄膜（陽極）が成膜してあるものとして使用した。次に、これをイソプロピルアルコール中に浸漬し、超音波洗浄を行った後、サムコインターナショナル製の紫外線照射機ＵＶ−３００を用いて紫外線とオゾンとを併用して３０分間洗浄した。
【００６７】
次いで、このＩＴＯ薄膜付きガラス基板を、市販の真空蒸着装置の中に入れ、この装置に設置されている基板ホルダーに取り付け、真空槽を５×１０^-4Ｐａまで減圧した。なお、あらかじめ真空蒸着装置の抵抗加熱ボートには、Ｃｕ配位のフタロシアニン（以下、ＣｕＰｃと略記する。）、Ｎ，Ｎ’−ビス（３−メチルフェニル）−Ｎ，Ｎ’−ジフェニル−（１，１’−ビフェニル）−４，４’−ジアミン（以下、ＴＰＤと略記する。）及び８−キノリノールアルミニウム錯体（アルミニウムトリスオキシン、以下、Ａｌｑと略記する。）をそれぞれ２００ｍｇずつ入れ、また抵抗加熱フィラメントにはアルミニウム−リチウム合金（Ｌｉ含量：２重量％）を入れておいた。これらのボートおよびフィラメントを順次加熱することにより、それぞれの成分を蒸着した。
【００６８】
まず、正孔注入輸送層としてＣｕＰｃをＩＴＯ薄膜付きガラス基板に２５ｎｍ蒸着し、次に第２の正孔注入輸送層としてＴＰＤを４０ｎｍ蒸着し、更に発光層としてＡｌｑを６０ｎｍ蒸着した。次に、形成された積層体の上にマスクを設置し、アルミニウム−リチウム合金を７ｎｍ蒸着して電子注入電極層を形成させた。
【００６９】
次に、上記真空蒸着装置に連結されている別の真空槽の基板ホルダーに基板を移送しセットした。なお、この間真空度は保たれたままである。上記、別の真空槽はＤＣマグネトロンスパッタリングによりＩｎ−Ｚｎ−Ｏ系酸化物膜を形成できるように設備されている。Ｉｎ−Ｚｎ−Ｏ系酸化物膜を形成させるためのターゲットは、Ｉｎ₂ Ｏ₃ とＺｎＯとからなる焼結体であり、Ｉｎの原子比〔Ｉｎ／（Ｉｎ＋Ｚｎ）〕は０．６７である。この真空槽のアルゴンガスと酸素ガスの混合ガス（体積比で１０００：２．８）を３×１０^-1Ｐａとなるまで導入し、スパッタリング出力を２０Ｗ、基板温度を室温に設定して膜厚１００ｎｍの非晶質透明導電膜を形成させた。なお、Ｉｎ−Ｚｎ−Ｏ系酸化物膜が非晶質であることは、ＩＴＯ薄膜が蒸着されていないガラス基板を用いて上記と同様の方法により積層体を形成し、Ｘ線回折により確認した。
【００７０】
次に、雰囲気ガスをアルゴンとし、その圧力を３×１０^-1Ｐａとし、スパッタリング出力を１０Ｗ、基板温度を室温に設定してＤＣマグネトロンスパッタリングにより、銀（Ａｇ）を５ｎｍ積層した。
その後更に、上記と同じ条件によりＩｎ−Ｚｎ−Ｏ系酸化物膜を１００ｎｍ積層し、有機ＥＬ素子を作製した。
【００７１】
＜光透過率および面抵抗値の評価＞
前記した素子の作製方法と同様の方法を用いて、ＩＴＯ薄膜付きガラス基板上に直接、電子注入電極層、非晶質透明導電膜、銀薄膜、Ｉｎ−Ｚｎ−Ｏ系酸化物膜を積層した積層体を作成し、分光光度計を用いて波長４６０ｎｍの光の透過率を計測したところ、６０％と高透明のものであった。
更に、前記した素子の作製方法と同様の方法を用いて、ガラス基板上に直接、非晶質透明導電膜と銀薄膜を積層し、その上にＩｎ−Ｚｎ−Ｏ系酸化物膜を積層して、この酸化物膜表面の面抵抗値を、三菱油化社製のロレスタＦＰを用いて測定したところ、１０Ω／□であった。
【００７２】
＜有機ＥＬ素子の評価＞
次に、ＩＴＯ薄膜を陽極とし、Ｉｎ−Ｚｎ−Ｏ系酸化物膜から電極リードを取り、両薄膜間に電圧を７Ｖ印加したところ、２．８ｍＡ／ｃｍ² の電流密度となり、陰極側より観測したところ、６０ｃｄ／ｍ² の発光があった。発光は、Ａｌｑより生じた緑色発光であった。
更に、この素子を大気中、７０％ＲＨ（相対湿度）の雰囲気に１００時間放置したところ、無発光点は肉眼では観測されず、素子の発光性能も維持されていた。
【００７３】
〔比較例１〕
＜有機ＥＬ素子の作製＞
実施例１と同様の方法により有機ＥＬ素子を作製した。ただし、電子注入電極層の上に非晶質透明導電膜、銀薄膜、Ｉｎ−Ｚｎ−Ｏ系酸化物膜からなる三層の薄膜を形成させる代わりに、市販のＩＴＯターゲットを用いて、２００ｎｍの一層のＩＴＯ膜を形成させた。このＩＴＯ膜を形成させる際の、雰囲気ガスとその圧力、およびスパッタリング方法および出力も実施例１と同様にした。
【００７４】
＜光透過率および面抵抗値の評価＞
前記した素子の作製方法と同様の方法を用いて、ＩＴＯ薄膜付きガラス基板上に直接、電子注入電極層およびＩＴＯ膜を形成させた積層体を作製し、実施例１と同様にして光の透過率を測定したところ８０％であった。
更に、前記した素子の作製方法と同様の方法を用いて、ガラス基板上に直接、ＩＴＯ膜を積層して、その表面の面抵抗値を、実施例１と同様の方法で測定したところ、１３０Ω／□であった。
【００７５】
＜有機ＥＬ素子の評価＞
次に、この有機ＥＬ素子に電圧を８Ｖ印加したところ、４ｍＡ／ｃｍ² の電流密度となり、非晶質透明導電膜側より観測したところ、６０ｃｄ／ｍ² の発光があった。発光は、Ａｌｑより生じた緑色発光であった。この素子を大気中、７０％ＲＨの雰囲気に１００時間放置したところ、無発光点は肉眼で無数確認され、発光欠陥が多いことが確認された。
【００７６】
以上の結果より、実施例１の有機ＥＬ素子は、陰極の透明性が高く、かつ陰極が低抵抗であるため発光効率が高く、更に最外層および電子注入電極層に接する層を構成するＩｎ−Ｚｎ−Ｏ薄膜が非晶質であるため、耐久性に優れ、発光欠陥が生じにくいことが確認された。ところで、電子注入電極層の酸化により発光欠陥が生じることが知られている。本発明の有機ＥＬ素子では、最外層および電子注入電極層に接する層として非晶質透明導電膜が形成され、この透明導電膜には結晶粒界が存在しないため、酸素や水分の侵入が防止され前記の結果となったものと考えられる。
一方、比較例１は陰極の透明性は高いものの、陰極の抵抗値が高いため発光効率に劣ることが確認された。
【００７７】
〔実施例２〕
＜有機ＥＬ素子の作製＞
実施例１において、最後に形成したＩｎ−Ｚｎ−Ｏ系酸化物薄膜に代えて、ＩＴＯ薄膜を、ＤＣマグネトロンスパッタリングにより膜厚１００ｎｍとなるように形成させた以外は、実施例１と同様の方法により有機ＥＬ素子を作製した。
ＩＴＯ薄膜は、ＩＴＯターゲットをアルゴンガスと酸素ガスの混合ガス（体積比で１０００：２．８）を３×１０^-1Ｐａとなるまで導入し、スパッタリング出力を２０Ｗ、基板温度を室温に設定して膜厚１００ｎｍの薄膜を形成させた。
＜光透過率および面抵抗値の評価＞
前記した素子の作製方法と同様の方法を用いて、ＩＴＯ薄膜付きのガラス基板上に直接、電子注入電極層、非晶質透明導電膜、銀薄膜、ＩＴＯ膜を積層した積層体を作成し、波長４６０ｎｍの光の透過率を計測したところ、８０％と高透明のものであった。
更に、前記した素子の作製方法と同様の方法を用いて、ガラス基板上に直接、非晶質透明導電膜と銀薄膜を積層し、その上にＩＴＯ膜を積層して、このＩＴＯ膜表面の面抵抗値を、実施例１と同様にして測定したところ、５Ω／□であった。
【００７８】
＜有機ＥＬ素子の評価＞
次に、ガラス基板に直接積層されたＩＴＯ薄膜を陽極とし、最後に積層したＩＴＯ膜から電極リードを取り、両薄膜間に電圧を６Ｖ印加したところ、２．５ｍＡ／ｃｍ² の電流密度となり、陰極側より観測したところ、６０ｃｄ／ｍ² の発光があった。発光は、Ａｌｑより生じた緑色発光であった。
更に、この素子を大気中、７０％ＲＨ（相対湿度）の雰囲気に１００時間放置したところ、無発光点は肉眼では観測されず、素子の発光性能も維持されていた。
【００７９】
［実施例３］
＜有機ＥＬ素子の作製＞
実施例１において、最初に形成したＩｎ−Ｚｎ−Ｏ酸化物薄膜の膜厚を２００ｎｍとするとともに、最後に形成したＩｎ−Ｚｎ−Ｏ酸化物薄膜に代えて、ＴｉＯ₂ を用い、ＲＦマグネトロンスパッタリングにより膜厚１００ｎｍの薄膜を形成させた以外は、実施例１と同様の方法により有機ＥＬ素子を作製した。
ＴｉＯ₂ 薄膜の形成の際には、雰囲気ガスとしてアルゴンガスを３×１０^-1Ｐａとなるまで導入し、スパッタリング出力を２０Ｗ、基板温度を室温に設定して膜厚１００ｎｍの薄膜を形成させた。
【００８０】
＜光透過率および面抵抗値の評価＞
前記した素子の作製方法と同様の方法を用いて、ＩＴＯ薄膜付きガラス基板上に直接、電子注入電極層、非晶質透明導電膜、銀薄膜、ＴｉＯ₂ 薄膜を積層した積層体を作成し、波長４６０ｎｍの光の透過率を計測したところ、８５％と高透明のものであった。
更に、前記した素子の作製方法と同様の方法を用いて、ガラス基板上に直接、非晶質透明導電膜と銀薄膜を積層し、銀薄膜表面の面抵抗値を、実施例１と同様にして測定したところ、１０Ω／□であった。
【００８１】
＜有機ＥＬ素子の評価＞
次に、ＩＴＯ薄膜を陽極とし、銀薄膜から電極リードを取り、両薄膜間に電圧を７Ｖ印加したところ、３．０ｍＡ／ｃｍ² の電流密度となり、陰極側より観測したところ、８０ｃｄ／ｍ² の発光があった。発光は、Ａｌｑより生じた緑色発光であった。
【００８２】
更に、この素子を大気中、７０％ＲＨ（相対湿度）の雰囲気に１００時間放置したところ、無発光点は肉眼では観測されず、素子の発光性能も維持されていた。
以上の結果より、実施例２，３の有機ＥＬ素子は、陰極の透明性が高く、かつ陰極が低抵抗であるため発光効率が高く、更に電子注入電極層に接する層を構成するＩｎ−Ｚｎ−Ｏ薄膜が非晶質であるため、耐久性に優れ、発光欠陥が生じにくいことが確認された。
【００８３】
【発明の効果】
本発明の第１の目的を達成する有機ＥＬ素子は、低抵抗かつ高透明の陰極を有するため、発光を効率よく素子の両面から取り出すことができるとともに、高精細な表示装置に利用した場合にも、輝度ムラの発生が少なく、駆動時の応答の遅れが小さい。
【００８４】
本発明の第２の目的を達成する有機ＥＬ素子は、第１の目的を達成するとともに、陰極のテーパーエッチング加工ができるため、高精細な有機ＥＬ発光装置の作製が容易である。また、本発明の第２の目的を達成する有機ＥＬ素子は、耐久性（耐湿熱性）に優れる。
本発明の有機ＥＬ素子は以上のような効果を有するため、たとえば情報機器のディスプレイなどに好適に用いられる。
【図面の簡単な説明】
【図１】 本発明の有機ＥＬ素子の一例の構成を示す断面図である。
【図２】 本発明の有機ＥＬ素子において、断面テーパー状の非晶質透明導電膜を採用した場合の一例を示す断面図である。
【図３】 本発明の有機ＥＬ素子において、島状電子注入域が、非晶質透明導電膜と有機層との界面に存在する場合の一例を示す断面図である。
【図４】 本発明の有機ＥＬ素子の利用態様の一例を単純化して示したものであって、非晶質透明導電膜の外側にカラーフィルターを付加した構成を示す断面図である。
【図５】 本発明の有機ＥＬ素子の利用態様の一例を単純化して示したものであって、非晶質透明導電膜の外側に黒色吸収層を備えた構成を示す断面図である。
【図６】 本発明の有機ＥＬ素子の利用態様の一例を単純化して示したものであって、透明陽極の外側に背景色形成層を備えた構成を示す断面図である。
【符号の説明】
１：基板
２：陽極
３：有機層
４：電子注入電極層
５：透明導電膜
６：金属薄膜
７：透明薄膜層
８：島状注入域
９：カラーフィルター
１０：黒色光吸収層
１１：背景色形成層[0001]
[Industrial application fields]
The present invention relates to an organic electroluminescence element that can be used for a transparent light emitting element or the like because light emission can be taken out from the cathode side of the element, and can also be used as a high-definition display device.
[0002]
[Prior art]
Since the electroluminescence element using electroluminescence (hereinafter abbreviated as EL element) has high visibility due to self-emission and is a complete solid element, it has characteristics such as excellent impact resistance. The use as a light emitting element in various display devices has attracted attention.
[0003]
EL elements include inorganic EL elements that use inorganic compounds as light-emitting materials and organic EL elements that use organic compounds. Of these, organic EL elements can be easily reduced in size so that the applied voltage can be significantly reduced. Therefore, research on practical application as a next-generation display element has been actively conducted.
The configuration of the organic EL element is basically the configuration of anode / light emitting layer / cathode, and a configuration in which a transparent anode is laminated on a substrate using a glass plate or the like is usually employed. In this case, the emitted light is extracted to the substrate side.
[0004]
By the way, in recent years, an attempt has been made to extract light emission to the cathode side by making the cathode transparent.
(A) A transparent light emitting device can be manufactured.
(A) By adopting an arbitrary color as the background color of the light emitting element, a colorful display can be obtained even when light is not emitted. When black is used as the background color, the contrast during light emission is improved.
(C) When a color filter or a color conversion layer is used, these can be placed on the light emitting element. For this reason, an element can be manufactured without considering these layers. As an advantage, for example, the substrate temperature can be increased when the anode is formed, thereby reducing the resistance value of the anode.
[0005]
On the other hand, in recent years, display devices (displays) using organic EL elements tend to be high definition and large. For high definition, it is desired that the pixels be several hundred μm square or less. In this case, the scanning electrode lines and signal electrode lines constituting the display become thinner, and the resistance increases accordingly. If the scanning electrode line or the signal electrode line has a high resistance, there is a problem that a voltage drop due to wiring or a delay in response during driving is caused. In other words, the voltage drop causes uneven brightness in the display, and the delay in response during driving is difficult to display a fast-moving screen when manufacturing a high-definition display. there were.
The scanning electrode line and the signal electrode line are connected to the lower electrode and the counter electrode that constitute the organic EL element. For this reason, it has been required to reduce the resistance value of the anode or cathode constituting the lower electrode or the counter electrode.
[0006]
In JP-A-8-185984, a first electrode layer made of a transparent conductive layer, an ultrathin electron injection metal layer, and a second electrode layer made of a transparent conductive layer formed thereon are provided. A transparent organic EL element is disclosed. However, the technical idea of reducing the resistance of the electrode layer is not disclosed.
Further, the cathode disclosed in this publication is composed of only one transparent conductive layer, and specific examples of substances constituting this layer include ITO (indium tin oxide), SnO. ₂ Only is disclosed. By the way, these substances cannot be crystallized to such an extent that the X-ray diffraction peak disappears, and are essentially crystalline. For this reason, when laminating to a substrate through an organic layer, when the substrate temperature is set to room temperature to near 100 ° C. in order to prevent damage to the organic layer, a transparent conductive layer having a high resistivity is formed (ITO). Then 1 × 10 ^-3 It becomes about Ω · cm or more. ).
[0007]
[Problems to be solved by the invention]
When such an organic EL element using a cathode composed of only a single crystalline transparent conductive layer is used in a high-definition display device, a voltage drop occurs in the wiring line of the transparent conductive layer, resulting in ineffective emission. Since it is considered that uniformity occurs, there is a limit to the use of organic EL elements. ITO and SnO ₂ Since it is essentially crystalline, moisture and oxygen are more likely to enter from the grain boundaries. For this reason, the electron injection metal layer laminated | stacked adjacently tends to receive deterioration, As a result, a light emission defect arises or it becomes impossible to light-emit, etc., and the further improvement of durability was desired.
[0008]
Further, in the case of the above crystalline transparent conductive layer, it is possible to employ so-called taper etching in which an etching pattern having a trapezoidal cross section is formed by etching in a patterning step when manufacturing an organic EL display device having an XY matrix structure. Therefore, it may be difficult to manufacture a high-definition display device.
[0009]
A first object of the present invention is to provide an organic EL element that solves the above-described problems of the prior art and that can emit light from the cathode side of the element and can be used in a high-definition display device.
A second object of the present invention is to provide an organic EL element that achieves the first object and is easy to manufacture a high-definition display device and excellent in durability (moisture heat resistance).
[0010]
[Means for Solving the Problems]
As a result of intensive research to solve the above problems, the present inventors have a low-resistance and high-transparency cathode by disposing a low-resistance metal thin film outside the transparent conductive film constituting the cathode. It discovered that an organic EL element was obtained. The present invention has been completed based on such knowledge.
[0011]
That is, the gist of the present invention is as follows.
[1]. An organic electroluminescence device in which an organic layer including an organic light emitting layer is sandwiched between an anode and a cathode, the electron injecting electrode layer, a transparent conductive film, and a resistivity of 1 × 10 from the side where the cathode contacts the organic layer ^-Five An organic electroluminescence device in which a metal thin film of Ω · cm or less is laminated in this order and a transparent thin film layer is formed on the outer side of the cathode, wherein the transparent conductive film is indium (In), zinc (Zn) An amorphous transparent conductive film formed using an oxide made of oxygen (O). The light transmittance of the layer composed of the cathode and the transparent thin film layer is 60% or more. An organic electroluminescence device characterized by comprising:
[2]. [1] The electron injection electrode layer is formed in an ultrathin film using one or more selected from an electron injecting metal, an alloy, and an alkaline earth metal oxide. The organic electroluminescent element of description.
[3]. [1], wherein the electron injecting electrode layer is a mixed layer of one or more selected from an electron injecting metal, an alloy and an alkaline earth metal oxide and an electron transporting organic substance The organic electroluminescent element of description.
[4]. The organic electroluminescence device as described in [1] above, wherein the electron injection electrode layer comprises an island-shaped electron injection region.
[5]. The organic electroluminescent device according to [1], wherein the cathode and the anode form an XY matrix, and the transparent conductive film is formed in a trapezoidal cross section (tapered shape).
[6]. shadow The organic electroluminescence device as described in [1] above, wherein the surface resistance value of the layer comprising the electrode and the transparent thin film layer or the cathode is 10 Ω / □ or less.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
As an organic EL device capable of achieving the first object of the present invention, an organic layer including an organic light emitting layer is sandwiched between an anode and a cathode, and an electron injection electrode is formed from the side where the cathode contacts the organic layer. Layer, transparent conductive film, resistivity 1 × 10 ^-Five A structure in which metal thin films of Ω · cm or less are laminated in this order and a transparent thin film layer is formed outside the cathode can be employed. This element configuration can be schematically represented by, for example, FIG. First, each element and the transparent thin film layer which comprise the cathode of this organic EL element are demonstrated.
[0013]
<Metal thin film>
The metal thin film is used to lower the surface resistance value of the cathode and is thinned to such an extent that light can be transmitted. 1 × 10 resistivity that can be used in the present invention ^-Five Examples of the metal used as the material for the metal thin film of Ω · cm or less include silver (Ag), gold (Au), aluminum (Al), ruthenium (Lu), nickel (Ni), platinum (Pt) and the like. Can do. Among these, Ag, Au, and Pt, which have a low resistivity and are easily thinned, are preferable, and Ag is particularly preferable.
The feature of the present invention is that the transparency of the cathode is improved. For this reason, it is preferable that the light transmittance of a metal thin film layer shall be 70 to 90%. For this purpose, the film thickness is preferably 2 to 20 nm, particularly preferably 2 to 10 nm.
[0014]
Examples of the method for forming this layer include a resistance heating vapor deposition method, an electron beam vapor deposition method, a sputtering method such as an RF magnetron or a DC magnetron, which are usually used for the production of a thin film. Among these, when an organic layer, an electron injection electrode layer, a transparent conductive layer, or the like is formed prior to the formation of this layer, a resistance heating evaporation method or a DC magnetron that has little thermal influence on these layers. It is preferable to use a helicon sputtering method which is a kind of sputtering, and a resistance heating vapor deposition method is particularly preferable. In this case, since the transparent conductive film to be described later is preferably formed by a sputtering method, it is preferable to select a forming means as appropriate in consideration of the advantages of sharing the apparatus and process.
[0015]
In the organic EL device having this configuration, the electrode lead wire is taken from the metal thin film or the transparent thin film layer formed on the outside thereof, and is passed through the metal thin film, the transparent conductive film, and the electron injection electrode layer to the organic layer. Electrons are injected.
[0016]
<Transparent conductive film>
The transparent conductive film that can be used in the present invention is an ITO film or SnO in the case of adopting a structure in which the metal thin film is laminated. ₂ A crystalline transparent conductive film such as a film may be used, but it is preferable that the resistivity of the layer itself is also low. Specifically, the resistivity is 5 × 10. ^-Four It is preferable that it is below Ω · cm.
[0017]
Examples of such a transparent conductive film include an amorphous transparent conductive film. As a material of such an amorphous transparent conductive film, an In—Zn—O-based oxide film is preferable. Here, the In—Zn—O-based oxide film is a transparent conductive film made of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements. The atomic ratio [In / (In + Zn)] of In is preferably 0.45 to 0.90. This is because the conductivity may be low outside this range. The atomic ratio [In / (In + Zn)] of In is particularly preferably 0.50 to 0.90 and more preferably 0.70 to 0.85 in terms of conductivity.
[0018]
The amorphous oxide may substantially contain only In and Zn as main cation elements, and may contain one or more third elements having a valence of at least positive trivalence. It may be a thing. Specific examples of the third element include tin (Sn), aluminum (Al), antimony (Sb), gallium (Ga), germanium (Ge), and titanium (Ti), but the conductivity is improved. In particular, those containing Sn are particularly preferable. The content of the third element is preferably such that the atomic ratio [(total third element) / (In + Zn + (total third element)]) of the total amount is 0.2 or less. If the ratio exceeds 0.2, the conductivity may be lowered due to ion scattering, and the particularly preferable atomic ratio of the total amount of the third element is 0.1 or less. Since the crystallized material is less conductive than the amorphous one, it is preferable to use an amorphous transparent conductive film also from this point.
[0019]
The oxide described above can be used as a transparent conductive film by forming a thin film. The film thickness at this time is preferably about 3 to 3000 nm. If the thickness is less than 3 nm, the electrical conductivity tends to be insufficient, and if it exceeds 3000 nm, the light transmission is reduced, or the organic EL element is intentionally or unavoidably deformed after the process of manufacturing the organic EL element or after manufacturing. Cracks and the like are likely to occur in the transparent conductive film. A particularly preferable film thickness of the transparent conductive film is 5 to 1000 nm, and a more preferable film thickness is 10 to 800 nm.
[0020]
In the organic EL device of the present invention, when a cathode is formed on a substrate via an anode and an organic layer, a transparent conductive film (oxide film) is formed on the electron injection electrode layer. As a method of forming the transparent conductive film, in addition to the sputtering method, a chemical vapor deposition method, a sol-gel method, an ion plating method, or the like can be adopted. However, from the viewpoint of simplicity and thermal effects on the organic layer, sputtering is possible. The method is preferred. In this case, care must be taken so that the organic layer is not damaged by the plasma generated during sputtering. In addition, since the heat resistance of the organic layer is low, the temperature of the substrate is preferably 200 ° C. or lower.
[0021]
The sputtering method may be RF or DC magnetron sputtering, reactive sputtering, ECR sputtering, or ion beam sputtering. The composition of the sputtering target to be used and the sputtering conditions are appropriately selected according to the composition of the transparent conductive film to be formed. In order to avoid the thermal influence as described above, it is preferable to use helicon sputtering which is a kind of magnetron sputtering.
[0022]
When an In—Zn—O based transparent conductive film is formed by RF or DC magnetron sputtering or helicon sputtering, it is preferable to use the following sputtering targets (i) to (ii).
(I) A sintered compact target made of a composition of indium oxide and zinc oxide, having an indium atomic ratio of a predetermined value.
Here, “the atomic ratio of indium is a predetermined one” means that the In atomic ratio [In / (In + Zn)] in the finally obtained film is a desired value within the range of 0.45 to 0.90. This means that the atomic ratio of the sintered compact target is approximately 0.50 to 0.90. The sintered body target may be a sintered body made of a mixture of indium oxide and zinc oxide, or In ₂ O _Three It may be a sintered body substantially consisting of one or more hexagonal layered compounds represented by (ZnO) m (m = 2 to 20), or In ₂ O _Three One or more hexagonal layered compounds represented by (ZnO) m (m = 2 to 20) and In ₂ O _Three And / or a sintered body substantially composed of ZnO. In the above formula representing the hexagonal layered compound, m is limited to 2 to 20 because m does not become a hexagonal layered compound outside the above range.
[0023]
(Ii) A sputtering target comprising an oxide disk and one or more oxide tablets arranged on the disk.
The oxide-based disk may consist essentially of indium oxide or zinc oxide. ₂ O _Three It may be a sintered body substantially consisting of one or more hexagonal layered compounds represented by (ZnO) m (m = 2 to 20), or In ₂ O _Three One or more hexagonal layered compounds represented by (ZnO) m (m = 2 to 20) and In ₂ O _Three And / or a sintered body substantially composed of ZnO. Moreover, as an oxide type tablet, the thing similar to the said oxide type disc can be used. The composition and usage ratio of the oxide-based disk and the oxide-based tablet are desired values within the range where the atomic ratio [In / (In + Zn)] of In in the finally obtained film is 0.45 to 0.80. As appropriate.
[0024]
Any of the sputtering targets (i) to (ii) preferably have a purity of 98% or more. If it is less than 98%, due to the presence of impurities, the heat and humidity resistance (durability) of the resulting film may decrease, the conductivity may decrease, and the light transmission may decrease. More preferable purity is 99% or more, and further preferable purity is 99.9% or more.
[0025]
Moreover, when using a sintered compact target, it is preferable that the relative density of this target shall be 70% or more. When the relative density is less than 70%, the film formation rate and the film quality are likely to decrease. A more preferable relative density is 85% or more, and still more preferably 90% or more.
[0026]
Sputtering conditions in the case of providing a transparent conductive film by a sputtering method are difficult to define unconditionally because it varies depending on the direct sputtering method, the composition of the sputtering target, the characteristics of the apparatus used, etc., but DC magnetron sputtering. For example, it is preferable to set as follows.
The degree of vacuum and target applied voltage during sputtering are preferably set as follows. The degree of vacuum during sputtering is 1.3 × 10 ^-2 ~ 6.7 × 10 ⁰ About Pa, more preferably 1.7 × 10 ^-2 ~ 1.3 × 10 ⁰ About Pa, more preferably 4.0 × 10 ^-2 ~ 6.7 × 10 ^-1 It is about Pa. The applied voltage of the target is preferably 200 to 700V. Vacuum degree during sputtering is 1.3 × 10 ^-2 Less than Pa (1.3 × 10 ^-2 The pressure is lower than Pa), the stability of the plasma is poor, 6.7 × 10 ⁰ Higher than Pa (6.7 × 10 ⁰ If the pressure is higher than Pa), the applied voltage to the sputtering target cannot be increased. On the other hand, if the target applied voltage is less than 200 V, it may be difficult to obtain a good quality thin film, or the film forming speed may be limited.
[0027]
As the atmospheric gas, a mixed gas of an inert gas such as argon gas and oxygen gas is preferable. When argon gas is used as the inert gas, the mixing ratio (volume ratio) between the argon gas and oxygen gas is approximately 1: 1 to 99.99: 0.01, preferably 9: 1 to 99.9: 0. .1. Outside this range, a film with low resistance and high light transmittance may not be obtained.
[0028]
The substrate temperature is appropriately selected within the range of temperatures at which the organic layer does not deform or deteriorate due to heat, depending on the heat resistance of the organic layer. If the substrate temperature is lower than room temperature, an additional cooling device is required, which increases the manufacturing cost. Further, as the substrate temperature is heated to a higher temperature, the manufacturing cost increases. For this reason, it is preferable to set it as room temperature-200 degreeC.
The target transparent conductive film can be provided on the organic layer by performing DC magnetron sputtering under the conditions as described above using the sputtering targets such as (i) to (ii) described above.
[0029]
In the organic EL device that achieves the second object of the present invention, it is necessary to use an amorphous transparent conductive film as the transparent conductive film constituting the cathode. The material, film thickness, formation method and the like of this amorphous transparent conductive film are the same as described above.
[0030]
In a display device using an organic EL element, an anode and a cathode that are generally formed in a linear shape are configured in an XY matrix, and a pixel is formed in the intersection area. Therefore, in order to enable high-definition display, it is necessary to form electrodes (anode and cathode) thinly. Specifically, after an electrode is formed into a thin film, it is patterned into a line by etching or the like to produce an electrode. In this case, if adjacent electrodes come into contact with each other, formation of pixels is hindered, which is not preferable.
[0031]
In such high-definition patterning, when an amorphous transparent conductive film, particularly an amorphous transparent conductive film manufactured using an In—Zn—O-based oxide, is used, the cross section is trapezoidal (tapered). In the case of laminating on the substrate from the anode side, it is possible to suppress the occurrence of step breakage in the metal thin film formed on the substrate. Fabrication is possible. Further, when an organic EL element is produced by laminating on the substrate from the cathode side, it is possible to suppress the occurrence of step breakage in the organic layer laminated on the cathode and the anode laminated thereon.
[0032]
As a method for etching the transparent conductive film into a taper shape, dry etching is preferable, and processing is performed so that the angle (θ) formed between the bottom surface and the side surface of the transparent conductive film formed in a line shape is 30 to 60 degrees. It is preferable to do this. As the etching gas, for example, a mixed gas of methane and hydrogen chloride can be used.
An example of a schematic representation of an organic EL element obtained by processing a transparent conductive film into a tapered shape is shown in FIG.
[0033]
<Electron injection electrode layer>
Next, the electron injection electrode layer will be described. An electron injection electrode layer is a layer of an electrode that can favorably inject electrons into an organic layer including a light emitting layer. In order to obtain a transparent light-emitting element, the light transmittance is preferably 80% or more. For this purpose, it is desirable that the film thickness is an ultrathin film having a thickness of about 0.5 to 20 nm.
[0034]
As the electron injection electrode layer, for example, a metal (electron injection metal) having a work function of 3.8 eV or less, for example, Mg, Ca, Ba, Sr, Li, Yb, Eu, Y, Sc, or the like is used. A layer having a thickness of 1 nm to 20 nm. In this case, a configuration that gives a light transmittance of 60% or more is particularly preferable.
As another preferred example, an electron injecting electrode layer using an alloy (electron injecting alloy) of the metal having a work function of 3.8 eV or less (may be plural kinds) and a metal having a work function of 4.0 eV or more. Can be mentioned. As such an alloy, an alloy capable of forming an electron injection electrode layer is sufficient. For example, an aluminum-lithium alloy, a magnesium-aluminum alloy, an indium-lithium alloy, a lead-lithium alloy, a bismuth-lithium alloy, Examples thereof include a tin-lithium alloy, an aluminum-calcium alloy, an aluminum-barium alloy, and an aluminum-scandium alloy. Also in this case, it is preferable that the film thickness is 1 nm to 20 nm, and it is particularly preferable that the layer give a light transmittance of 60% or more.
[0035]
When the electron injection electrode layer is formed using the metal or alloy, a resistance heating vapor deposition method is preferably used. In this case, it is preferable to set the substrate temperature between 10 to 100 ° C. and the deposition rate between 0.05 to 20 nm / second.
In particular, when an alloy is vapor-deposited, the vapor deposition can be performed by separately setting the vapor deposition rates of the two metals using a binary vapor deposition method. In this case, the deposition rate of Li, Ba, Ca, Sc, Mg, etc. is set between 0.01 and 0.1 nm / second, and the deposition rate of the base metal such as Al is set between 1 and 10 nm / second. Then, it is possible to employ a technique of vapor deposition at the same time. Moreover, when vapor-depositing an alloy, a single vapor deposition method can also be used. In this case, vapor deposition pellets or granules in which a base metal is charged with an electron injectable metal at a desired ratio in advance are placed on a resistance heating boat or filament, and heat vapor deposited.
[0036]
Still another preferred form is an ultrathin film having a film thickness of 0.1 nm to 10 nm, which is a thin-film electron-injecting alkaline earth metal oxide. Examples of the alkaline earth metal oxide include BaO, SrO, CaO, and a mixture thereof. _x Sr _1-x O (0 <x <1) or Ba _x Ca _1-x O (0 <x <1) can be mentioned as a preferable one.
[0037]
As a method for forming the alkaline earth metal oxide layer, oxygen is introduced into the vacuum chamber while the alkaline earth metal is deposited by resistance heating vapor deposition, and the degree of vacuum is set to 10%. ^-3 -10 ^-Four A method of vapor deposition while reacting oxygen and alkaline earth is preferable. Alternatively, a method of forming an alkaline earth metal oxide film by an electron beam evaporation method can be employed.
Note that the electron injecting electrode layer can be formed using not only one type but also two or more types of the electron injecting metal, alloy, and alkaline earth metal oxide described above.
[0038]
As still another preferred example, the electron injection electrode layer may be a mixed layer of an electron injecting metal, alloy, or alkaline earth metal oxide and an electron transporting compound.
Examples of the electron injecting metal, alloy, and alkaline earth metal oxide include the metal, alloy, and alkaline earth metal oxide described above. Moreover, not only 1 type but 2 or more types can also be used for these. On the other hand, the electron-transmitting compound may be any compound that transmits electrons, and as a preferable compound, a chelated oxinoid compound can be exemplified, and a more preferable compound is represented by the following formula.
[0039]
[Chemical 1]

[0040]
(In the formula, Me represents a metal, and n is an integer of 1 to 3. Z independently represents an atom that completes a nucleus having at least two condensed aromatic rings in each case.)
The metal in the formula may be a 1 to 3 valent metal capable of forming a chelate, such as an alkali metal such as lithium, sodium or potassium, an alkaline earth metal such as magnesium or calcium, or boron or aluminum. And trivalent metals such as Z represents an atom that completes a heterocyclic nucleus having at least two fused aromatic rings. Examples of the heterocyclic nucleus in which Z is completed include an azole ring and an azine ring.
[0041]
Examples of the useful chelated oxinoid compound include aluminum trisoxin, magnesium bisoxin, bis [benzo (f) -8-quinolinol] zinc, bis (2-methyl-8-quinolinolato) aluminum oxide, indium trisoxin, aluminum tris. (5-methyloxin), lithium oxine, gallium trisoxine, calcium bis (5-chlorooxin), poly [zinc (II) -bis (8-hydroxy-5-quinolinonyl) methane], dilithium ependridione, etc. Is mentioned.
[0042]
The mixing ratio (weight ratio) of the electron injecting metal, alloy, alkaline earth metal oxide, and electron transporting compound is preferably 100: 1 to 1: 2.
The mixed layer of the electron injecting metal or alloy and the electron transporting compound is preferably formed by a binary co-evaporation method. The substrate temperature may be set between 10 and 100 ° C.
[0043]
Yet another preferred example is a configuration in which the electron injection electrode layer is an island-shaped electron injection region. Here, the island shape means that an electron injecting compound layer is formed discontinuously as shown in FIG. 3, for example, and this layer does not cover the surface of the organic layer.
The island-shaped electron injection region is, for example, formed by discontinuously forming a low work function metal having a work function of 3.8 eV or less, an oxide, a metal boride, a metal nitride, a metal silicide, and the like in an island shape. Although there is no restriction | limiting in particular about a shape and a magnitude | size, It is a fine particle form or a crystalline form, and a thing with a magnitude | size of about 0.5 nm-5 micrometers is preferable.
[0044]
Further, this electron injection region does not indicate a thin film shape, nor does it indicate a state of isolated atom dispersion. The low work function metal or compound is in a state of being dispersed in a particulate form on the conductive thin film or in the organic compound layer. By such dispersion, the area in contact with the organic compound layer is increased, and the electron injecting property is increased.
As the metal and alloy having a low work function constituting the island-shaped electron injection region, those having a work function of 3.8 eV or less are preferable, and examples thereof include the metals and alloys described above. Further, as the low work function oxide, an alkali metal or alkaline earth metal oxide is preferable, and CaO, BaO, SrO and the like are particularly preferable, and a solid solution of these with other metal oxides is also preferable. Can be mentioned. Further, examples of the low work function metal boride and metal nitride include, for example, rare earth borides, rare earth silicides, and TiN.
[0045]
As a method for forming the island-shaped electron injection region, a resistance heating vapor deposition method or an electron beam vapor deposition method can be employed. In the latter case, a high melting point metal boride, metal nitride or oxide is discontinuously formed in an island shape by electron beam evaporation.
In the organic EL device of the present invention, in the case of a cathode including an electron injection electrode layer and an amorphous transparent conductive film, the electron injection electrode layer that is easily deteriorated is protected by the amorphous transparent conductive film. The injection electrode layer can be made thin, and as a result, there is an advantage that a transparent cathode can be suitably formed.
[0046]
In the organic EL device of the present invention, usually, a configuration in which an anode is laminated on a substrate and an organic layer is laminated thereon is employed. Form. Although the formation method is as described above, there is a sputtering method as another preferable method. When using this technique, care must be taken not to damage the organic layer by the plasma.
[0047]
<Transparent thin film layer>
In the cathode having the above-described configuration, the outermost layer is a metal thin film, and thus a layer for protecting it is necessary. Since the first object of the present invention is to obtain a light-transmitting cathode, this layer needs to have light-transmitting properties.
As such a layer, a known thin film made of glass or plastic can be used. However, when an organic EL device is produced by laminating on the substrate from the anode side, a transparent dielectric thin film is formed on the metal thin film. Alternatively, it is preferable to form a transparent conductive film. In the case of using a dielectric thin film, there is an advantage that a transparent protective film having an improved light transmittance due to the refractive index can be formed.
[0048]
As a transparent dielectric thin film, for example, TiO ₂ A crystalline thin film such as can be used. In addition, as the transparent conductive film, for example, ITO, SnO ₂ For example, a crystalline thin film such as In-Zn-O can be used. In particular, the use of an amorphous transparent conductive film is preferable from the viewpoint of improving durability, which is the second object of the present invention. In this layer, conductivity is not essential. For this reason, when a transparent dielectric thin film is used, the lead is taken from a metal thin film.
As a method for forming this layer, RF magnetron sputtering, particularly helicon sputtering is preferably used.
[0049]
<Light transmittance and surface resistance>
In the organic EL device that achieves the first object of the present invention, an organic layer including an organic light emitting layer is sandwiched between an anode and a cathode, and a transparent thin film layer is formed outside the cathode. An element configuration in which the light transmittance of the layer composed of the cathode and the transparent thin film layer is 60% or more, and the surface resistance value of the layer composed of the cathode and the transparent thin film layer or the cathode is 10 Ω / □ or less. Can be adopted.
As a cathode satisfying this configuration, for example, a cathode having the above configuration can be preferably cited. The transparent thin film layer is the same as described above.
[0050]
The light transmittance defined here is a light transmittance from a layer (for example, an electron injection electrode layer) in contact with an organic layer constituting the organic EL element to a transparent thin film formed outside the cathode.
The light transmittance may be 60% or more at any wavelength in the visible light range (380 to 700 nm). As a method for measuring the light transmittance, a known spectrophotometer may be used. Moreover, it is not necessary to produce only a layer composed of a cathode and a transparent thin film layer formed on the outside thereof and measure the light transmittance. If the light transmittance including other layers is 60% or more, this layer It can be said that the light transmittance is 60% or more.
[0051]
The sheet resistance value (Ω / □) specified here is a value measured by the four-point probe method. Specifically, on an insulating substrate (for example, a glass substrate), a film having the same configuration as that of the cathode of the organic EL element and a transparent thin film layer formed on the outside thereof, or a film having the same configuration as the cathode And the surface resistance value of the surface of the transparent thin film layer formed on the cathode or outside thereof is measured by a four-probe method. At this time, a layer from which the electrode lead is taken out is selected as a layer for measuring the sheet resistance value. That is, when the electrode lead is taken out from the cathode, the surface resistance of the cathode is measured, and when the electrode lead is taken out from the transparent thin film layer formed outside the cathode, the surface resistance of the transparent thin film layer is measured. Thus, the measured sheet resistance value is the sheet resistance value defined by the present invention.
[0052]
However, in the case where the cathode includes an electron injection electrode layer, the layers excluding the layer are stacked in the same order as in the actual device configuration, and the sheet resistance is measured. Specifically, for example, in the case of an EL element that takes out electrode leads from a transparent thin film layer, a transparent conductive film, a metal thin film, and a transparent thin film layer are laminated in this order on a support substrate (usually glass). The sheet resistance of the surface of the layer is defined as the sheet resistance value of the present invention. In this case, when the electrode lead is taken out from the metal thin film, the surface resistance of the surface of the metal thin film is set to the surface resistance value of the present invention.
[0053]
<Organic layer>
In the organic EL device of the present invention, the organic layer interposed between the anode and the cathode includes at least an organic light emitting layer. The organic layer may be a layer composed only of an organic light emitting layer, or may have a multilayer structure in which a hole injection transport layer and the like are laminated together with the organic light emitting layer.
[0054]
In this organic EL device, the light emitting layer is (1) a function capable of injecting holes through an anode or a hole transport layer when an electric field is applied, and injecting electrons from an electron injection electrode layer, (2) Transport function to move injected charges (electrons and holes) by the force of electric field; (3) Provides a light-emitting function that provides a field for recombination of electrons and holes inside the light-emitting layer and connects it to light emission ing. There is no restriction | limiting in particular about the kind of luminescent material used for this light emitting layer, The well-known thing in a conventional organic EL element can be used.
[0055]
The hole injecting and transporting layer is a layer made of a hole transfer compound and has a function of transmitting holes injected from the anode to the light emitting layer. By interposing between them, many holes are injected into the light emitting layer with a lower electric field. In addition, the electrons injected from the electron injection layer into the light emitting layer are accumulated near the interface in the light emitting layer due to an electron barrier existing at the interface between the light emitting layer and the hole injecting and transporting layer. And an EL element with excellent light emitting performance is obtained. There is no restriction | limiting in particular about the hole transfer compound used for this hole injection transport layer, A well-known thing can be used as a hole transfer compound in a conventional organic EL element. The hole injecting and transporting layer can be not only a single layer but also a multilayer.
[0056]
<Anode>
The anode is not particularly limited as long as it has a work function of 4.8 eV or more. A metal having a work function of 4.8 eV or more, a transparent conductive film (conductive oxide film), or a combination thereof is preferable. The anode is not necessarily transparent and may be coated with a black carbon layer or the like.
[0057]
Examples of suitable metals include Au, Pt, Ni, and Pd. Examples of conductive oxides include In—Zn—O, In—Sn—O, ZnO—Al, and Zn—Sn—. O can be mentioned. Examples of the stacked body include a stacked body of Au and In—Zn—O, a stacked body of Pt and In—Zn—O, and a stacked body of In—Sn—O and Pt.
[0058]
In addition, since the anode only needs to have a work function of 4.8 eV or more at the interface with the organic layer, the anode may have two layers and a conductive film having a work function of 4.8 eV or less may be used on the side not in contact with the organic layer. Good. In this case, a metal such as Al, Ta, or W, an alloy such as an Al alloy, a Ta—W alloy, or the like can be used. Also, doped conductive polymers such as doped polyaniline and doped polyphenylene vinylene, amorphous semiconductors such as α-Si, α-SiC, α-C, μC-Si, μC-SiC, etc. Microcrystals can also be preferably used. Furthermore, Cr is a black semiconductive oxide. ₂ O _Three , Pr ₂ O _Five , NiO, Mn ₂ O _Five , MnO ₂ Etc. can be used.
[0059]
The thickness of the anode is preferably about 50 to 300 nm. If the film thickness is less than 50 nm, the resistance value may become too high. On the other hand, when the thickness exceeds 300 nm, a step formed at the end where the anode is patterned in the organic EL element may cause the upper film, for example, the organic layer or the cathode, to be disconnected or disconnected.
[0060]
<Configuration of organic EL element>
In the organic EL device of the present invention, an organic layer including an organic light emitting layer is interposed between an anode and a cathode. The cathode is composed of an electron injection electrode layer, a transparent conductive film, and a metal thin film. A structure in which the injection electrode layer is in contact with the organic layer and a transparent thin film layer is formed on the outside of the cathode, or an organic layer including an organic light emitting layer is sandwiched between the anode and the cathode and formed on the cathode and the outside thereof If the light transmittance of the layer composed of the transparent thin film is 60% or more and the surface resistance value of the layer composed of the cathode and the transparent thin film layer or the cathode is 10Ω / □ or less, The first object of the invention can be achieved. In addition, the second object of the present invention can be achieved by employing an amorphous transparent conductive film as the transparent conductive film in the organic EL element.
[0061]
Furthermore, other configurations can be added to provide various functions. Below, the structure using the organic EL element of this invention is illustrated.
(1) Transparent anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film
(2) Anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film / color filter
(3) Anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film / color conversion layer
(4) Transparent anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film / black light absorbing layer
(5) Transparent anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film / background color forming layer
(6) Black light absorbing layer / transparent anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film
(7) Background color forming layer / transparent anode / organic layer / electron injection electrode layer / amorphous transparent conductive film / metal thin film / transparent conductive film
In the case of the configuration (1), since both electrodes are transparent, a transparent display element is formed.
[0062]
In the case of the constructions (2) and (3), the anode is formed on the support substrate and the emitted light can be taken out in the opposite direction to the support substrate, so there is no need to form the anode on the color filter or color conversion layer. . Therefore, a process in which the substrate temperature is 150 ° C. or higher can be adopted when forming the anode, which is a great advantage in reducing the resistance value of the anode. In addition, since the color filter and the color conversion layer are formed after forming the anode, there is no need to worry about deterioration due to the adoption of a high temperature process. FIG. 4 illustrates the configuration of (2). Here, it is preferable that the color conversion layer is made of a transparent polymer containing a fluorescent pigment and converts the EL emission color into another color by fluorescence.
[0063]
Further, in the embodiment in which a large number of pixels are configured with the configurations of (2) and (3), auxiliary wiring other than the anode and TFT (Thin Film Transistor) are formed on the substrate, so that light is directed toward the substrate. When extracted, the auxiliary wiring and the TFT block light, and the aperture ratio for extracting light is lowered. As a result, the luminance of the display is reduced and the image quality is lowered. If the present invention is used, light can be extracted in the direction opposite to that of the substrate, but in this case, the light is not blocked and the aperture ratio of the light extraction does not decrease.
[0064]
In the configurations of (4) and (6), when the pixel is off, it looks black, so that there is an advantage that the incident external light is not reflected and the contrast of the display is improved. FIG. 5 illustrates the configuration (4).
In the configurations of (5) and (7), various background colors and patterns can be adopted, and a display having excellent decorativeness can be obtained even when the pixels are off. FIG. 6 illustrates the configuration of (7).
[0065]
In the structures (2) to (7), the color conversion layer, the color filter, the black light absorption layer, and the background color forming layer are not necessarily in close contact with the electrode, and an intermediate layer may be interposed. As long as the effect is expressed, they may be set apart as shown in FIG. However, the color conversion layer and the color filter need to be installed in the light extraction direction, and the black light absorption layer and the background color formation layer need to be installed in the direction opposite to the light extraction direction.
[0066]
【Example】
Examples of the present invention will be described below.
[Example 1]
<Production of organic EL element>
A glass substrate (25 mm × 75 mm × 1 mm) on which ITO was formed to a thickness of 100 nm (manufactured by Geomatics) was used as a conductive thin film (anode) formed on the substrate. Next, this was immersed in isopropyl alcohol, subjected to ultrasonic cleaning, and then cleaned for 30 minutes using ultraviolet rays and ozone in combination using an ultraviolet irradiator UV-300 manufactured by Samco International.
[0067]
Next, the glass substrate with the ITO thin film is placed in a commercially available vacuum deposition apparatus, attached to a substrate holder installed in the apparatus, and the vacuum chamber is 5 × 10 5. ^-Four The pressure was reduced to Pa. Note that a resistance-coating boat of a vacuum evaporation apparatus is previously provided with Cu-coordinated phthalocyanine (hereinafter abbreviated as CuPc), N, N′-bis (3-methylphenyl) -N, N′-diphenyl- (1 , 1′-biphenyl) -4,4′-diamine (hereinafter abbreviated as TPD) and 8-quinolinol aluminum complex (aluminum trisoxine, hereinafter abbreviated as Alq), 200 mg each, and resistance heating An aluminum-lithium alloy (Li content: 2% by weight) was placed in the filament. These boats and filaments were sequentially heated to deposit each component.
[0068]
First, CuPc was deposited on a glass substrate with an ITO thin film as a hole injection transport layer by 25 nm, then TPD was deposited as a second hole injection transport layer by 40 nm, and Alq was deposited as a light emitting layer by 60 nm. Next, a mask was placed on the formed laminate, and an aluminum-lithium alloy was evaporated to 7 nm to form an electron injection electrode layer.
[0069]
Next, the substrate was transferred and set in a substrate holder of another vacuum chamber connected to the vacuum deposition apparatus. During this time, the degree of vacuum remains maintained. The other vacuum chamber is equipped so that an In—Zn—O-based oxide film can be formed by DC magnetron sputtering. The target for forming the In—Zn—O-based oxide film is In ₂ O _Three And ZnO, and the In atomic ratio [In / (In + Zn)] is 0.67. A mixed gas (1000: 2.8 in volume ratio) of argon gas and oxygen gas in this vacuum chamber was 3 × 10 ^-1 It introduced until it became Pa, the sputtering output was set to 20 W, the substrate temperature was set to room temperature, and the amorphous transparent conductive film with a film thickness of 100 nm was formed. Note that the fact that the In—Zn—O-based oxide film was amorphous was confirmed by X-ray diffraction after forming a laminate by the same method as described above using a glass substrate on which no ITO thin film was deposited. .
[0070]
Next, the atmosphere gas is argon and the pressure is 3 × 10. ^-1 The sputtering power was set to 10 W, the substrate temperature was set to room temperature, and silver (Ag) was laminated to 5 nm by DC magnetron sputtering.
Thereafter, an In—Zn—O-based oxide film was further deposited to a thickness of 100 nm under the same conditions as described above, and an organic EL element was manufactured.
[0071]
<Evaluation of light transmittance and surface resistance>
An electron injection electrode layer, an amorphous transparent conductive film, a silver thin film, and an In—Zn—O-based oxide film were laminated directly on a glass substrate with an ITO thin film using a method similar to the method for manufacturing the element described above. When a laminate was prepared and the transmittance of light having a wavelength of 460 nm was measured using a spectrophotometer, it was highly transparent at 60%.
Further, using a method similar to the above-described device manufacturing method, an amorphous transparent conductive film and a silver thin film are laminated directly on a glass substrate, and an In—Zn—O-based oxide film is laminated thereon. The surface resistance value of the oxide film surface was measured using a Loresta FP manufactured by Mitsubishi Oil Chemical Co., Ltd. and found to be 10Ω / □.
[0072]
<Evaluation of organic EL element>
Next, when the ITO thin film was used as an anode, an electrode lead was taken from the In—Zn—O-based oxide film, and a voltage of 7 V was applied between the two thin films, 2.8 mA / cm. ² Of 60 cd / m when observed from the cathode side. ² There was luminescence. The light emission was green light emission generated from Alq.
Furthermore, when this device was left in the atmosphere at 70% RH (relative humidity) for 100 hours, no light emitting point was observed with the naked eye, and the light emitting performance of the device was maintained.
[0073]
[Comparative Example 1]
<Production of organic EL element>
An organic EL element was produced by the same method as in Example 1. However, instead of forming a three-layer thin film consisting of an amorphous transparent conductive film, a silver thin film, and an In—Zn—O-based oxide film on the electron injection electrode layer, a commercially available ITO target was used, A single ITO film was formed. Atmospheric gas and its pressure, sputtering method and output when forming this ITO film were also the same as in Example 1.
[0074]
<Evaluation of light transmittance and surface resistance>
Using a method similar to the above-described device manufacturing method, a laminate in which an electron injection electrode layer and an ITO film are formed directly on a glass substrate with an ITO thin film is manufactured, and light is transmitted in the same manner as in Example 1. When the rate was measured, it was 80%.
Further, using the same method as the above-described device manufacturing method, an ITO film was directly laminated on a glass substrate, and the surface resistance value of the surface was measured by the same method as in Example 1. / □.
[0075]
<Evaluation of organic EL element>
Next, when a voltage of 8 V was applied to the organic EL element, 4 mA / cm ² The current density was 60 cd / m when observed from the amorphous transparent conductive film side. ² There was luminescence. The light emission was green light emission generated from Alq. When this device was allowed to stand in the atmosphere of 70% RH for 100 hours in the air, innumerable non-light emitting points were confirmed with the naked eye, and it was confirmed that there were many light emitting defects.
[0076]
From the above results, the organic EL device of Example 1 has a high transparency of the cathode and a high resistance because the cathode has a low resistance, and further, an In − layer constituting the outermost layer and the layer in contact with the electron injection electrode layer. Since the Zn—O thin film was amorphous, it was confirmed that it was excellent in durability and light emitting defects were hardly generated. By the way, it is known that a light emitting defect is caused by oxidation of the electron injection electrode layer. In the organic EL device of the present invention, an amorphous transparent conductive film is formed as a layer in contact with the outermost layer and the electron injection electrode layer, and since there is no crystal grain boundary in this transparent conductive film, entry of oxygen and moisture is prevented. It is thought that the above result was obtained.
On the other hand, it was confirmed that Comparative Example 1 was inferior in luminous efficiency because the cathode had high transparency, but the cathode had high resistance.
[0077]
[Example 2]
<Production of organic EL element>
In Example 1, instead of the last formed In—Zn—O-based oxide thin film, the same method as in Example 1 except that the ITO thin film was formed to a thickness of 100 nm by DC magnetron sputtering. Thus, an organic EL element was produced.
For the ITO thin film, the ITO target is a mixed gas of argon gas and oxygen gas (1000: 2.8 in volume ratio) 3 × 10 ^-1 It introduced until it became Pa, the sputtering output was set to 20 W, the substrate temperature was set to room temperature, and the thin film with a film thickness of 100 nm was formed.
<Evaluation of light transmittance and surface resistance>
Using a method similar to the method for producing the element described above, a laminate in which an electron injection electrode layer, an amorphous transparent conductive film, a silver thin film, and an ITO film are laminated directly on a glass substrate with an ITO thin film is created. When the transmittance of light having a wavelength of 460 nm was measured, it was highly transparent at 80%.
Further, by using the same method as the above-described device manufacturing method, an amorphous transparent conductive film and a silver thin film are laminated directly on a glass substrate, and an ITO film is laminated thereon. When the sheet resistance value was measured in the same manner as in Example 1, it was 5Ω / □.
[0078]
<Evaluation of organic EL element>
Next, the ITO thin film directly laminated on the glass substrate was used as the anode, the electrode lead was taken from the last laminated ITO film, and a voltage of 6 V was applied between the two thin films to obtain 2.5 mA / cm. ² Of 60 cd / m when observed from the cathode side. ² There was luminescence. The light emission was green light emission generated from Alq.
Furthermore, when this device was left in the atmosphere at 70% RH (relative humidity) for 100 hours, no light emitting point was observed with the naked eye, and the light emitting performance of the device was maintained.
[0079]
[Example 3]
<Production of organic EL element>
In Example 1, the thickness of the first formed In—Zn—O oxide thin film was set to 200 nm, and instead of the last formed In—Zn—O oxide thin film, TiO 2 was used. ₂ An organic EL element was produced by the same method as in Example 1 except that a thin film having a thickness of 100 nm was formed by RF magnetron sputtering.
TiO ₂ In forming the thin film, argon gas is used as an atmosphere gas at 3 × 10 ^-1 It introduced until it became Pa, the sputtering output was set to 20 W, the substrate temperature was set to room temperature, and the thin film with a film thickness of 100 nm was formed.
[0080]
<Evaluation of light transmittance and surface resistance>
Using the same method as the above-described device fabrication method, an electron injection electrode layer, an amorphous transparent conductive film, a silver thin film, TiO, directly on a glass substrate with an ITO thin film. ₂ When a laminated body in which thin films were laminated was prepared and the transmittance of light having a wavelength of 460 nm was measured, it was highly transparent at 85%.
Further, using the same method as the above-described device manufacturing method, an amorphous transparent conductive film and a silver thin film are laminated directly on a glass substrate, and the surface resistance value on the surface of the silver thin film is set in the same manner as in Example 1. The measured value was 10Ω / □.
[0081]
<Evaluation of organic EL element>
Next, the ITO thin film was used as the anode, the electrode lead was taken from the silver thin film, and a voltage of 7 V was applied between the two thin films. ² Of 80 cd / m when observed from the cathode side. ² There was luminescence. The light emission was green light emission generated from Alq.
[0082]
Furthermore, when this device was left in the atmosphere at 70% RH (relative humidity) for 100 hours, no light emitting point was observed with the naked eye, and the light emitting performance of the device was maintained.
From the above results, the organic EL elements of Examples 2 and 3 have high light-emitting efficiency because the cathode has high transparency and the cathode has low resistance, and further, In—Zn that forms a layer in contact with the electron injection electrode layer. Since the —O thin film was amorphous, it was confirmed that it was excellent in durability and luminescent defects were hardly generated.
[0083]
【The invention's effect】
The organic EL device that achieves the first object of the present invention has a low resistance and highly transparent cathode, so that the light emission can be efficiently taken out from both sides of the device, and when used in a high-definition display device. However, the occurrence of uneven brightness is small and the response delay during driving is small.
[0084]
Since the organic EL element that achieves the second object of the present invention achieves the first object and can be subjected to taper etching of the cathode, it is easy to produce a high-definition organic EL light-emitting device. Moreover, the organic EL element which achieves the second object of the present invention is excellent in durability (moisture heat resistance).
Since the organic EL element of the present invention has the effects as described above, it is suitably used for, for example, a display of information equipment.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of an example of an organic EL element of the present invention.
FIG. 2 is a cross-sectional view showing an example where an amorphous transparent conductive film having a tapered cross section is employed in the organic EL element of the present invention.
FIG. 3 is a cross-sectional view showing an example where an island-shaped electron injection region is present at the interface between an amorphous transparent conductive film and an organic layer in the organic EL device of the present invention.
FIG. 4 is a simplified cross-sectional view showing an example of a usage mode of an organic EL element according to the present invention, in which a color filter is added to the outside of an amorphous transparent conductive film.
FIG. 5 is a simplified cross-sectional view showing an example of a usage mode of an organic EL element of the present invention, and is a cross-sectional view showing a configuration in which a black absorption layer is provided outside an amorphous transparent conductive film.
FIG. 6 is a simplified cross-sectional view showing an example of a utilization mode of the organic EL element of the present invention, and is a configuration including a background color forming layer outside a transparent anode.
[Explanation of symbols]
1: Substrate
2: Anode
3: Organic layer
4: Electron injection electrode layer
5: Transparent conductive film
6: Metal thin film
7: Transparent thin film layer
8: Island-like injection area
9: Color filter
10: Black light absorption layer
11: Background color forming layer

Claims (6)

An organic electroluminescence device in which an organic layer including an organic light emitting layer is sandwiched between an anode and a cathode, the electron injecting electrode layer, a transparent conductive film, and a resistivity of 1 × 10 from the side where the cathode contacts the organic layer ^An organic electroluminescence device in which a metal thin film of ^-5 Ω · cm or less is laminated in this order, and a transparent thin film layer is formed outside the cathode,
The transparent conductive film of indium (In), zinc (Zn), an oxide consisting of oxygen (O), in Ri formed amorphous transparent conductive film Der comprising,
The organic electroluminescent device light transmission layer of the cathode transparent thin film layer, characterized in der Rukoto 60%.   The electron injection electrode layer is formed in an ultrathin film using one or more selected from an electron injecting metal, an alloy, and an alkaline earth metal oxide. The organic electroluminescent element of description.   2. The electron injecting electrode layer is a mixed layer of one or more selected from an electron injecting metal, an alloy, and an alkaline earth metal oxide and an electron transporting organic substance. Organic electroluminescence element.   2. The organic electroluminescence device according to claim 1, wherein the electron injection electrode layer comprises an island-shaped electron injection region.   The organic electroluminescence device according to claim 1, wherein the cathode and the anode form an XY matrix, and the transparent conductive film is formed in a trapezoidal cross section (tapered shape). The organic electroluminescent device according to claim 1, wherein the sheet resistance of the layer or cathode made from the the negative pole transparent thin film layer is 10 [Omega / □ or less.

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