JP3556258B2 - Organic thin film EL device having a plurality of carrier injection layers - Google Patents

Description

【００１１】
【表１−（２）】

【００１２】
【表１−（３）】

【００１３】
【表１−（４）】

【００１４】
ホール注入輸送層材料としては、これまでホール輸送層材料として従来公知の材料をすべて利用することができるが、好ましくは、少なくとも２つの芳香族３級アミンを含み、好ましくは、芳香族３級アミンがモノアリールアミン、ジアリールアミン、トリアリールアミンである。代表的な有用な芳香族３級アミンして、ＵＳＰ Ｎｏ．４，１７５，９６０、ＵＳＰ Ｎｏ．４，５３９，５０７、特開昭６３−２６４６９２号、特開平４−３０８６８８号によって開示されている化合物を利用することができる。また、ＵＳＰ Ｎｏ．４，７２０，４３２に開示されているポリフィリン誘導体（フタロシアニン類）も有用な化合物である。以下表２に有用なホール注入輸送層材料の具体例を示す。また、ホール注入輸送層を複数の層から構成する場合、前記式（ＩＩ）を満足する積層順が耐久性向上に好ましい。
【００１５】
【表２−（１）】

【００１６】
【表２−（２）】

ＨＴＬ９ 鉄フタロシアニン
ＨＴＬ１０ 塩化インジウムフタロシアニン
ＨＴＬ１１ 塩化バナジルフタロシアニン
ＨＴＬ１２ マグネシウムフタロシアニン
ＨＴＬ１３ ニッケルフタロシアニン
ＨＴＬ１４ 亜鉛フタロシアニン
ＨＴＬ１５ フリーメタルナフタロシアニン
ＨＴＬ１６ 銅ナフタロシアニン
ＨＴＬ１７ 鉄ナフタロシアニン
ＨＴＬ１８ 銅フタロシアニン
ＨＴＬ１９ フリーメタルフタロシアニン
ＨＴＬ２０ チタニルフタロシアニン
【００１７】
電子注入輸送層材料としては、これまで電子輸送層材料として使用されてきた従来公知の材料をすべて利用することができる。１つの好ましい電子注入輸送材料は、電子輸送能の発現ユニットであるオキサジアゾール環を少なくとも１つ以上含む化合物である。さらに、耐久性を向上させるには、オキサジアゾール環を２個以上含む化合物が好ましい。代表的な有用なオキサジアゾール化合物は、Ａｐｐｌ．Ｐｈｙｓ．Ｌｅｔｔ５５，１４８９（１９８９）および日本化学会誌１５４０（１９９１）に開示されている。
以下表３に有用なオキサジアゾール化合物の具体例を示す。
【００１８】
【表３−（１）】

【００１９】
【表３−（２）】

【００２０】
【表３−（３）】

【００２１】
【表３−（４）】

【００２２】
【表３−（５）】

【００２３】
さらに、本発明の積層ＥＬ素子の電子注入輸送層に使用するために特に好ましい有機物質は８−ヒドロキシキノリンのキレートを含めた金属キレート化オキシノイド化合物である。
具体例として以下表４のものを挙げることができる。
【００２４】
【表４−（１）】
ＥＴＬ２９ アルミニウムトリスオキシン

ＥＴＬ３０ マグネシウムビスオキシン
ＥＴＬ３１ ビス（ベンゾ−８−キノリノール）亜鉛
ＥＴＬ３２ 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
ＥＴＬ３３ インジウムトリスオキシン
ＥＴＬ３４ アルミニウムトリス（５−メチルオキシン）
ＥＴＬ３５ リチウムオキシン
ＥＴＬ３６ ガリウムトリスオキシン
ＥＴＬ３７ カルシウムビス（５−クロロオキシン）
ＥＴＬ３８ ポリ（亜鉛（ＩＩ）−ビス（８−ヒドロキシ−５−キノリノニル）メタン）
ＥＴＬ３９ ジリチウムエピンドリジオン
【００２５】
【表４−（２）】

【００２６】
また、ＵＳＰ５，１５１，６２９及びＵＳＰ５，１５０，００６記載のビス型金属キレート化オキシノイド化合物も電子注入輸送層材料として好ましい。
さらに、他の好ましい電子注入輸送層材料としては、１，４ジフェニルブタジエンおよびテトラフェニルブタジエンのようなブタジエン誘導体、クマリン誘導体、ビススチリルベンゼン誘導体、ビススチリルアントラセン誘導体、ベンズオキサゾール誘導体、オキサジアゾール誘導体、オキサゾール誘導体、チアジアゾール誘導体、ナフタルイミド誘導体、ペリレンテトラカルボン酸ジイミド誘導体、キナクリドン誘導体等を挙げることができる。
以下表５に具体的化合物を挙げる。
【００２７】
【表５】

【００２８】
以上に有用な電子注入輸送材料の具体例を示してきたが、電子注入輸送層を複数の層から構成する場合、前記式（Ｉ）を満足する積層順が耐久性向上の観点から好ましい。
そして、本発明においては、第１電子注入輸送層の材料として、アルミニウムトリスオキシン（上記ＥＴＬ２９）を用いることを特徴とする。
【００２９】
本発明における有機薄膜ＥＬ素子は、以上で説明した有機化合物を真空蒸着法、溶液塗布法等により、有機化合物層全体で０．５μｍより薄い厚み、好ましくは１０００Å以下、さらに好ましくは、各有機層を１００Å〜１０００Åの厚みに薄膜化することにより有機化合物多層を形成し、陽極及び陰極で狭持することにより構成される。また、構成有機化合物が著しく薄膜形成能に富む場合、１００Å以下の膜厚において層を形成することも可能である。
また、本発明の有機薄層ＥＬ素子は、各隣接する有機層間および電極と有機層間が明確な界面を持たず、混合した混合領域を形成した構造のものであってもよい。
【００３０】
以下、図面に沿って本発明をさらに詳細に説明する。
図１は、陽極／ホール注入輸送層／発光層／電子注入輸送層／陰極を順次設けたものである。（但、ホール注入輸送層と電子注入輸送層の少なくとも一方が２層以上の層からなる。）
図２は、陽極／発光層／電子注入輸送層／陰極を順次設けたものである。（但、電子注入輸送層が少なくとも２層以上の層からなる。）
【００３１】
本発明の有機薄膜ＥＬ素子はＥＬ素子に電気的に電圧を印加し発光させるものであるが、わずかなピンホールによって短絡をおこし、素子として機能しなくなる場合もあるので、有機層の形成には薄膜形成性に優れた化合物を併用することが望ましい。さらにこのような薄膜形成性に優れた化合物とポリマー結合剤を組み合わせて発光層を形成することもできる。この場合に使用できるポリマー結合剤としては、ポリスチレン、ポリビニルトルエン、ポリ−Ｎ−ビニルカルバゾール、ポリメチルメタクリレート、ポリメチルアクリレート、ポリエステル、ポリカーボネート、ポリアミド等が挙げることができる。
【００３２】
陽極材料としては、ニッケル、金、白金、パラジウムやこれらの合金あるいは酸化スズ（ＳｎＯ_２）、酸化スズ−インジウム（ＩＴＯ）、ヨウ化銅などの仕事関数の大きな金属やそれらの合金、化合物、更にはポリ（３−メチルチオフェン）、ポリピロール、ポリアリーレンビニレン等の導電性ポリマーなどを用いることができる。一方、陰極材料としては、仕事関数の小さな銀、スズ、鉛、マグネシウム、マンガン、アルミニウム、或はこれらの合金が用いられる。陽極および陰極として用いる材料のうち少なくとも一方は、素子の発光波長領域において十分透明であることが望ましい。具体的には８０％以上の光透過率を有することが望ましい。
【００３３】
本発明においては、透明陽極を透明基板上に形成し、図１〜図３のような構成とすることが望ましいが、場合によっては、その逆構成をとっても良い。また、透明基板としては、ガラス、プラスチックフィルム等が使用できる。
また、本発明においては、このようにして得られたＥＬ素子の安定性の向上、特に大気中の水分に対する保護のために、別に保護層を設けたり、素子全体をセル中にいれ、シリコンオイル等を封入するようにしてもよい。
【００３４】
【実施例】
以下実施例に基づいて、本発明をより具体的に説明する。
【００３５】
実施例１（電子注入輸送層が２層から形成される場合）
ＩＴＯ（インジウム錫酸化物：シート抵抗２０Ω／□）基板を順次、中性洗剤、アセトン、イソプロピルアルコールで超音波洗浄した。そして煮沸したイソプロピルアルコールにＩＴＯ基板を５分間浸漬し、加熱乾燥した。
ホール注入輸送層材料ＨＴＬ１を１０^−６ｔｏｒｒの真空下でアルミナるつぼを加熱することにより４００Å蒸着した。次に、発光層材料ＥＭＬ１を１５０Å蒸着した。次に、第２電子注入輸送層ＥＴＬ１を２００Å、さらに第１電子注入輸送層ＥＴＬ２９を３００Å蒸着し、最後に１０：１の原子比のＭｇＡｇ電極を２０００Å蒸着した。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において駆動電圧８．９Ｖ、発光輝度６２０ｃｄ／ｍ^２を示した。その後、６０分経過後、６６８ｃｄ／ｍ^２、１０時間経過後でも４３０ｃｄ／ｍ^２の高輝度を維持した。発光スペクトルは４７５ｎｍを中心とした青色発光であった。
このとき、第２電子注入輸送層の電子親和力は２．１４ｅＶ、第１電子注入輸送層の電子親和力は３．０ｅＶ、陰極の仕事関数は３．５０ｅＶであり、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（３．０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （ＩＩＩ）
【００３６】
比較例１（電子注入輸送層が単層から形成される場合）
第１電子注入輸送層ＥＴＬ２９を省略した以外、実施例１と同様にＥＬ素子を作成した。ただし、第２電子注入輸送層の膜厚を５００Åとした。この場合、電圧印加直後、３０ｍＡ／ｃｍ^２の定電流下で５２０ｃｄ／ｍ^２の発光輝度、駆動電圧１０Ｖが観測された。ところが、１時間経過後では２７０ｃｄ／ｍ^２、１０時間経過後では発光輝度４３ｃｄ／ｍ^２と第２電子注入輸送層を省略した場合、耐久性が著しく劣っていた。また、初期駆動電圧も実施例１に比べ１．１Ｖ高い値を示した。このことから、複数の電子注入輸送層が存在する場合、耐久性の向上及び駆動電圧の低下に効果があることがわかる。
【００３７】
実施例２（ホール注入輸送層及び電子注入輸送層がそれぞれ２層から形成される場合）
第１ホール注入輸送層として膜厚２５０Åの銅フタロシアニン（ＨＴＬ１８）（ＣｕＰｃ）を陽極と、第２ホール注入輸送層（ＨＴＬ１）の界面に挿入した以外は実施例１と同様にＥＬ素子を作成した。ただし、第２ホール注入輸送層の膜厚を２００Åとした。
この場合、電圧印加直後、定電流下において、発光輝度４９２ｃｄ／ｍ^２、駆動電圧５．３Ｖが観測され、１０時間経過後においても２６０ｃｄ／ｍ^２の高輝度が観測され、耐久性に富むＥＬ素子であった。このことより、ホール注入輸送層と電子注入輸送層を複数層から形成することにより、著しく駆動電圧を低下させることが可能となることがわかる。
この構成において、陽極であるＩＴＯ電極のイオン化ポテンシャルはｌｐａ＝４．５３ｅＶ、第１ホール注入輸送層のイオン化ポテンシャルはｌｐｈ１＝４．９７ｅＶ、第２ホール注入輸送層のイオン化ポテンシャルはｌｐｈ２＝５．０８ｅＶであり、請求項１記載の関係式を満足する。
Ｉｐａ（４．５３ｅＶ）＜ｌｐｈ１（４．９７ｅＶ）＜ｌｐｈ２（５．０８ｅＶ） （ＩＩＩ）
【００３８】
実施例３（第１電子注入輸送層にキナクリドンを用いた場合）
ホール注入輸送層にトリフェニルアミン誘導体ＨＴＬ２、第１電子注入輸送層にキナクリドン誘導体ＥＴＬ４７を用いた以外は実施例１と同様にＥＬ素子を作成した。この場合、電圧印加直後、３０ｍＡ／ｃｍ^２の定電流下で、２５０ｃｄ／ｍ^２の発光輝度、駆動電圧１１Ｖが観測され、１０時間経過後においても１００ｃｄ／ｍ^２の発光輝度が観測された。キナクリドン化合物の電子親和力は２．６０ｅＶと見積もられ、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（２．６０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （Ｖ）
【００３９】
実施例４（第１電子注入輸送層にナフタルイミド誘導体を用いた場合）
ホール注入輸送層にトリフェニルアミン誘導体ＨＴＬ３、第１電子注入輸送層にナフタルイミド誘導体ＥＴＬ４５を用いた以外は実施例１と同様にＥＬ素子を作成した。この場合、電圧印加直後、３０ｍＡ／ｃｍ^２の定電流下で、３２８ｃｄ／ｍ^２の発光輝度、駆動電圧９Ｖが観測された。１時間経過後においては５２８ｃｄ／ｍ^２の発光輝度が観測され、１０時間経過後でも１００ｃｄ／ｍ^２以上の発光輝度が観測された。このナフタルイミド化合物の電子親和力は２．７０ｅＶと見積もられ、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（２．７０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （ＶＩ）
【００４０】
比較例２
実施例１と同様にＥＬ素子を作成した。ただし、第１電子注入輸送層に下記ペリレン誘導体（ＰＶ）を用いた。この場合、印加電圧２０Ｖにおいても微弱なＥＬ発光しか観察されず、極めて発光効率の悪い素子であった。また、この素子を３０ｍＡ／ｃｍ^２の定電流下で耐久試験を行なったところ、１時間以内に輝度が半減してしまい、極めて耐久性に劣る素子であった。
この場合、第１、第２電子注入輸送層の電子親和力と陰極の仕事関数の関係は
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（４．３０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （Ｖ）
であり、請求項１記載の関係式を満足せず、（Ｉ）の関係式を満足する陰極と電子注入輸送層の電子的性質の関係が耐久性の向上に重要であることを示している。
【化２６】

【００４１】
実施例５〜８
実施例１と同様にＥＬ素子を作成した。以下の表７に層構成材料及び耐久特性について示す。
【００４２】
【表７】

これらの素子は、実施例１と同様に陰極と第１及び第２電子注入輸送層との間に請求項１記載の関係式を満足する。
【００４３】
実施例９（パルス駆動）
実施例１と同様にＥＬ素子を作成した。ただし、有機層の膜厚を以下のように設定した。
第１ホール注入輸送層 ＨＴＬ１ ４００Å
発光層 ＥＭＬ１ １５０Å
第２電子注入輸送層 ＥＴＬ６ ２００Å
第１電子注入輸送層 ＥＴＬ２９ ３００Å
このようにして作成したＥＬ素子をピーク電流値３０ｍＡ／ｃｍ^２、周波数１００Ｈｚの矩形波で駆動したところ、初期輝度８５ｃｄ／ｍ^２、駆動電圧６．２Ｖを示した。その後、２０１時間経過後においても９７ｃｄ／ｍ^２の発光輝度（駆動電圧８．６Ｖ）を維持しており、極めて耐久性に富むＥＬ素子であった。
【００４４】
実施例１０
実施例２と同様にＥＬ素子を作成した。ただし、第２電子注入輸送層にＥＴＬ２０を用いた。この場合、電圧印加直後、３０ｍＡ／ｃｍ^２の定電流下において発光輝度６０ｃｄ／ｍ^２、駆動電圧６．２Ｖを示し、１７０時間経過後においても初期輝度を維持しており、極めて耐久性に富む結果が得られた。この場合もＥＴＬ２０層の電子親和力は２．５ｅＶと見積もられ、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（２．５０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （ＶＩＩＩ）
【００４５】
実施例１１（電子注入輸送層が３層から形成される場合）
ＩＴＯ（インジウム錫酸化物：シート抵抗２０Ω／□）基板を順次、中性洗剤、アセトン、イソプロピルアルコールで超音波洗浄した。そして、煮沸したイソプロピルアルコールにＩＴＯ基板を５分間浸漬し、加熱乾燥した。
ホール注入輸送層材料ＨＴＬ１を１０^−６ｔｏｒｒの真空下でアルミナるつぼを加熱することにより４００Å蒸着した。次に発光層材料ＥＭＬ１を１５０Å蒸着した。次に、第３電子注入輸送層ＥＴＬ１を１５０Å、第２電子注入輸送層ＥＴＬ６を１５０Å、さらに第１電子注入輸送層ＥＴＬ２９を２５０Å蒸着し、最後に１０：１の原子比のＭｇＡｇ電極を２０００Å蒸着した。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において、駆動電圧７．６Ｖ、発光輝度５１０ｃｄ／ｍ^２、を示した。その後、６０分経過後６１０ｃｄ／ｍ^２、１０時間経過後でも４２０ｃｄ／ｍ^２の高輝度を維持した。
このとき、第３電子注入輸送層の電子親和力は２．１４ｅＶ、第２電子注入輸送層の電子親和力は２．５０ｅＶ、第１電子注入輸送層の電子親和力は３．０ｅＶ、陰極の仕事関数は３．５０ｅＶであり、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（３．０ｅＶ）＞Ｅａｅ２（２．５０ｅＶ）＞Ｅａｅ３（２．１４ｅＶ） （ＩＸ）
【００４６】
実施例１２
第１ホール注入輸送層として銅フタロシアニン（ＣｕＰｃ）（ＨＴＬ１８）を２００Å、第２ホール注入輸送層としてＨＴＬ１を２００Å用いた以外は実施例１１と同様にＥＬ素子を作成した。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において、駆動電圧６．６Ｖ、発光輝度４９０ｃｄ／ｍ^２、を示した。その後、１０時間経過後でも４００ｃｄ／ｍ^２以上の高輝度を維持した。この場合、銅フタロシアニンを挿入することにより、実施例１１に比べ駆動電圧の低下を図ることができた。
【００４７】
実施例１３
実施例１１と同様に基板の洗浄を行った後、第１ホール注入輸送層として銅フタロシアニン（ＣｕＰｃ）（ＨＴＬ１８）を２００Å、第２ホール注入輸送層としてＨＴＬ１を１５０Å、第３ホール注入輸送層ＨＴＬ２を１５０Å、発光層ＥＭＬ１を１５０Å、第２電子注入輸送層ＥＴＬ１を２００Å、第１電子注入輸送層ＥＴＬ２９を３００Å蒸着し、最後にＭｇＡｇ合金電極を形成した。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において、駆動電圧６．４Ｖ、発光輝度５３０ｃｄ／ｍ^２、を示した。その後、６０分経過後５６０ｃｄ／ｍ^２、１０時間経過後でも４６０ｃｄ／ｍ^２の高輝度を維持した。
この素子において、第２電子注入輸送層の電子親和力は２．１４ｅＶ、第１電子注入輸送層の電子親和力は３．０ｅＶ、陰極の仕事関数は３．５ｅＶであり、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（３．０ｅＶ）＞Ｅａｅ２（２．１４ｅＶ） （Ｘ）
また、第１ホール注入輸送層のイオン化ポテンシャルは４．９７ｅＶ、第２ホール注入輸送層のイオン化ポテンシャルは５．０８ｅＶ、第３ホール注入輸送層のイオン化ポテンシャルは５．３２ｅＶであり、請求項２記載の関係式を満足する。
ｌｐａ（４．５３ｅＶ）＜ｌｐｈ１（４．９７ｅＶ）＜ｌｐｈ２（５．０８ｅＶ）＜ｌｐｈ３（５．３２ｅＶ） （ＸＩ）
【００４８】
比較例３
実施例１３と同様にＥＬ素子の作成を行った。ただし、第１電子注入輸送層にＥＴＬ１（２００Å）を第２電子注入輸送層にＥＴＬ２９（３００Å）を用い、積層順を変えた。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において、駆動電圧８．４Ｖ、発光輝度５１７ｃｄ／ｍ^２、を示したが、１０時間経過後も１００ｃｄ／ｍ^２以下の発光輝度しか得られず耐久性に劣る結果であった。さらに、実施例１３においては４７５ｎｍを中心とした青色のＥＬ発光であったが、積層順を逆にした場合は、第２電子注入輸送層からのＥＬ発光も観察され、５１５ｎｍを中心とした緑色発光であった。
この素子において、第１電子注入輸送層の電子親和力は２．１４ｅＶ、第２電子注入輸送層の電子親和力は３．０ｅＶ、陰極の仕事関数は３．５ｅＶであり、請求項１記載の関係式を満足しない。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（２．１４ｅＶ）＞Ｅａｅ２（３．０ｅＶ） （ＸＩＩ）
【００４９】
実施例１４
実施例１１と同様に基板の処理を行った後、第１ホール注入輸送層として銅フタロシアニン（ＣｕＰｃ）（ＨＴＬ１８）を１０^−６ｔｏｒｒの真空下でアルミナるつぼを加熱することにより２００Å蒸着した。さらに、第２ホール注入輸送層としてＨＴＬ１を１５０Å、第３ホール注入輸送層としてＨＴＬ２を１５０Å蒸着した。次に、発光層材料ＥＭＬ１を１５０Å蒸着した。第３電子注入輸送層ＥＴＬ１を１５０Å、第２電子注入輸送層ＥＴＬ６を１５０Å、さらに第１電子注入輸送層ＥＴＬ２９を２５０Å蒸着し、最後に１０：１の原子比のＭｇＡｇ電極を２０００Å蒸着した。
このようにして作成したＥＬ素子は電圧印加直後、３０ｍＡ／ｃｍ^２の電流密度において、駆動電圧７．１Ｖ、発光輝度５２３ｃｄ／ｍ^２を示した。その後、１０時間経過後でも４８０ｃｄ／ｍ^２の高輝度を維持した。
この場合、第３電子注入輸送層の電子親和力は２．１４ｅＶ、第２電子注入輸送層の電子親和力は３．０ｅＶ、陰極の仕事関数は３．５０ｅＶであり、請求項１記載の関係式を満足する。
Ｉｐｃ（３．５０ｅＶ）＞Ｅａｅ１（３．０ｅＶ）＞Ｅａｅ２（２．５０ｅＶ）＞Ｅａｅ３（２．１４ｅＶ） （ＸＩＩＩ）また、第１ホール注入輸送層のイオン化ポテンシャルは４．９７ｅＶ、第２ホール注入輸送層のイオン化ポテンシャルは５．０８ｅＶ、第３ホール注入輸送層のイオン化ポテンシャルは５．３２ｅＶであり、請求項２記載の関係式を満足する。
Ｉｐａ（４．５３ｅＶ）＜ｌｐｈ１（４．９７）ｅＶ）＜ｌｐｈ２（５．０８ｅＶ）＜ｌｐｈ３（５．３２ｅＶ） （ＸＩＶ）
【００５０】
実施例１５〜２２
実施例１と同様にＥＬ素子の作成を行った。以下の表８に層構成材料及び耐久特性について示す。
なお、これらの素子は、陰極と第１及び第２電子注入輸送層との間には請求項１記載の関係式を満足する。
【００５１】
【表８】

【００５２】
【発明の効果】
本発明の有機薄膜ＥＬ素子は、電界印加により発光層に注入された荷電キャリヤー（電子とホール）の再結合により電気エネルギーを直接光エネルギーに変換でき、従来の白熱灯、蛍光灯、あるいは無機化合物のＥＬ等と異なり、また無機化合物の発光ダイオードでは実現困難であった青色発光の実現を可能にしたものであり、有機薄膜ＥＬ素子において発光層と電極間のホール注入輸送層と電子注入輸送層の両方もしくは何れかを複数層とすることにより、耐久性の向上を図ることが可能となる。
【図面の簡単な説明】
【図１】本発明に係わる有機薄膜ＥＬ素子の模式断面図である。
【図２】本発明に係わる他の有機薄膜ＥＬ素子の模式断面図である。[0001]
[Industrial applications]
The present invention relates to an organic thin-film EL device having a light-emitting layer made of a light-emitting organic compound and capable of directly converting electric energy into light energy by recombination of charged carriers (electrons and holes) injected into the light-emitting layer by applying an electric field. .
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the diversification and space saving of information devices, there has been an increasing need for a flat display element having lower power consumption and less space occupation area than a CRT. As such a flat display element, there are a liquid crystal, a plasma display and the like. In particular, recently, an organic thin film EL element which is self-luminous, has a clear display, and can be driven at a low DC voltage has been increasingly expected.
[0003]
As the element structure of the organic thin film EL element, Kodak C.I. W. Tang et al. (A structure in which a hole transporting layer and an electron transporting light emitting layer are formed between an anode and a cathode (SH-A structure)) (JP-A-59-194393, Appl. Phys. Lett. 51, 913 (1987)), a structure proposed by a group of Kyushu University (SH-B) in which a hole transporting light emitting layer and an electron transporting layer are formed between an anode and a cathode (USP No. 5, 085947, JP-A-2-25092, Appl. Phys. Lett. 55, 1489 (1989)) or a three-layer structure (a hole transport layer, a light emitting layer and an electron transport layer are formed between an anode and a cathode). (DH structure) (Appl. Phys. Lett. 57, 531 (1990)) By using these three types of element structures, initially, 1000 cd / m²High-luminance EL light emission ranging from blue to red is obtained.
[0004]
C. W. It has been reported that an element having an SH-A structure proposed by Tang et al. Exhibits excellent durability by using a triphenyldiamine derivative for the hole transport layer and tris (8-quinolinol) aluminum for the light emitting layer. In the case of this device structure, since there is no electron transport layer having a hole blocking function, a delicate injection balance is disrupted when continuous driving is performed for a long time, and a light-emitting site (carrier recombination site) is expanded, thereby essentially deteriorating. There is a problem that occurs.
Also in the case of the SH-B structure, since there is no hole transporting layer having an electron blocking ability, the light emitting site is expanded as in the case of the SH-A structure, and as a more serious problem, particularly, the crystallization of the electron transporting layer is continuous. There is a problem that it is generated by driving and the element is deteriorated.
In the DH structure, since the light emitting site is restricted by the hole transport layer and the electron transport layer, the light emitting site is not expanded and essentially does not deteriorate with time. Due to various factors (such as formation of space charge) caused by crystallization of the layer, there is a major problem in the durability of the device.
[0005]
As one attempt to improve durability, C.I. W. Tang et al. Have a three-layer structure in which a hole injection layer is inserted into an SH-A structure (Japanese Patent Application Laid-Open No. 63-295693), thereby improving the durability by lowering the hole injection barrier from the anode to the hole transport layer and the light emitting layer. Reports that it is possible. As described above, it has been found that in order to improve the durability of the device, a detailed material design for the hole and electron injection process is required. Although the study on the hole injection process has been started slightly as described above, the electronic design guidelines for the constituent materials have not been sufficiently clarified yet. On the other hand, no detailed study has been made on the electron injection process.
[0006]
[Problems to be solved by the invention]
The present invention provides an organic thin film having a particularly low durability while lowering the device driving voltage by inserting a plurality of carrier injection layers at one or both of the interface between the anode and the light emitting layer and the interface between the cathode and the light emitting layer. An EL element is provided.
[0007]
[Means for Solving the Problems]
According to the present invention, in an organic thin-film EL device composed of an anode / hole injection / transport layer / light emitting layer / electron injection / transport layer / cathode, at least one of the hole injection / transport layer and the electron injection / transport layer is a layer having two or more layers. Consisting of
Each of the electron affinity values Eae1, Eae2,... Eaen of the plurality of electron injecting and transporting layers (where n means that the electron injecting and transporting layer is composed of n layers, 1, 2,. N represents the order from the cathode side) satisfies the relationship between the work function value (Ipc) of the cathode and the following equation (I),
And the ionization potentials Iph1, Iph2,... Iphm of each of the plurality of hole injection / transport layers (where m means that the hole injection / transport layer is composed of m layers, 1, 2,. M indicates the order from the anode side) satisfies the relationship between the work function value (Ipa) of the anode and the following equation (II).The material of the first electron injection transport layer was aluminum trisoxine.An organic thin film EL device is provided,
Ipc ≧ Eae1 ≧ Eae2 ≧ ... ≧ Eaen (I)
Ipa ≦ Iph1 ≦ Iph2 ≦... ≦ Iphm (II)
Also,In an organic thin-film EL device comprising an anode / light-emitting layer / electron injection / transport layer / cathode, the electron injection / transport layer is composed of at least two or more layers, and the electron affinity value Eae1 of each of the plurality of electron injection / transport layers is provided. , Eae2,... Eaen (where n means that the electron injection / transport layer is composed of n layers, and 1, 2,... N means the order from the cathode side). Satisfies the relationship between the work function value (Ipc) and the following equation (I).The material of the first electron injection transport layer was aluminum trisoxine.An organic thin film EL device is provided,
Ipc ≧ Eae1 ≧ Eae2 ≧ ... ≧ Eaen (I)
Further, the thickness of each of the hole injection / transport layer and / or the electron injection / transport layer formed of one layer or a plurality of layers is 1000 ° or less.RecordIs provided.
[0008]
The present inventors have conducted intensive studies on the hole injection process and the electron injection process and found that a plurality of carrier injection layers are inserted at one or both of the interface between the anode and the light emitting layer and the interface between the cathode and the light emitting layer. As a result, the present inventors have found that an organic thin film EL element having excellent durability can be achieved, and have completed the present invention.
In the case of a conventional EL device, a hole injection barrier from the anode to the light-emitting layer and an electron injection barrier from the cathode to the light-emitting layer are large, causing crystallization of the organic layer by Joule heat, which has a problem in durability. In particular, regarding the electron injection process, there is a problem in that a conventional electron transport layer in which one layer is inserted has a large electron injection barrier.
In the present invention, a plurality of carrier injection / transport layers, that is, a plurality of hole injection / transport layers (layers for injecting / transporting holes from the anode to the light-emitting layer) and / or a plurality of electron injection / transport layers (electrons from the cathode to the light-emitting layer). ), The carrier injection barrier can be significantly reduced, and the driving voltage can be reduced and the durability can be improved. Further, in order to improve the durability, each carrier injection / transport layer, that is, a plurality of electron injection / transport layers and a plurality of hole injection / transport layers, is required to have the electronic state represented by the above formulas (I) and (II). It is more desirable to satisfy the following.
[0009]
Preferred materials for forming the multilayer EL device will be described below.
As the light emitting layer material, a substance which has strong fluorescence in a solid and forms a dense film in a thin film of 500 ° or less is preferable. All conventionally known materials that have been used for the light emitting layer of the organic EL device can be applied to the EL device of the present invention. Metal chelated oxinoid compounds (8-hydroxyquinoline metal complexes) (JP-A-59-194393, JP-A-63-295695), butadiene derivatives such as 1,4-diphenylbutadiene and tetraphenylbutadiene, coumarin derivatives, Benzoxazole derivatives, oxadiazole derivatives, oxazole derivatives, thiadiazole derivatives, styrylamine derivatives, bisstyrylbenzene derivatives (JP-A-2-247277), tristyrylbenzene derivatives (JP-A-3-296595), bisstyrylanthracene derivatives ( JP-A-3-163186), perinone derivatives, aminopyrene derivatives, etc.,as well asThe bis-metal chelated oxinoid compounds described in US Pat. Nos. 5,151,629 and 5,150,006 are excellent light emitting layer materials.
Table 1 below shows specific examples of useful light emitting layer materials.
[0010]
[Table 1- (1)]

[0011]
[Table 1- (2)]

[0012]
[Table 1- (3)]

[0013]
[Table 1- (4)]

[0014]
As the hole injecting / transporting layer material, any of conventionally known materials as the hole injecting / transporting layer material can be used, but it preferably contains at least two aromatic tertiary amines, and preferably contains at least two aromatic tertiary amines. Is a monoarylamine, a diarylamine, or a triarylamine. Representative useful aromatic tertiary amines include USP No. 4,175,960, USP No. 4,539,507, JP-A-63-264692 and JP-A-4-308688 can be used. In addition, USP No. The porphyrin derivatives (phthalocyanines) disclosed in 4,720,432 are also useful compounds. Table 2 below shows specific examples of useful hole injection transport layer materials. When the hole injecting and transporting layer is composed of a plurality of layers, a stacking order satisfying the above formula (II) is preferable for improving durability.
[0015]
[Table 2- (1)]

[0016]
[Table 2- (2)]

HTL9 Iron phthalocyanine
HTL10 Indium chloride phthalocyanine
HTL11 Vanadyl phthalocyanine chloride
HTL12 Magnesium phthalocyanine
HTL13 Nickel phthalocyanine
HTL14 Zinc phthalocyanine
HTL15 Free Metal Naphthalocyanine
HTL16 Copper naphthalocyanine
HTL17 Iron naphthalocyanine
HTL18 Copper phthalocyanine
HTL19 Free Metal Phthalocyanine
HTL20 titanyl phthalocyanine
[0017]
As the material for the electron injecting and transporting layer, all conventionally known materials which have been used as the material for the electron transporting layer can be used. One preferred electron injecting and transporting material is a compound containing at least one oxadiazole ring, which is a unit exhibiting electron transporting ability. Further, in order to improve durability, a compound containing two or more oxadiazole rings is preferable. Representative useful oxadiazole compounds are described in Appl. Phys. Lett 55, 1489 (1989) and The Chemical Society of Japan 1540 (1991).
Table 3 below shows specific examples of useful oxadiazole compounds.
[0018]
[Table 3- (1)]

[0019]
[Table 3- (2)]

[0020]
[Table 3- (3)]

[0021]
[Table 3- (4)]

[0022]
[Table 3- (5)]

[0023]
Further, particularly preferred organic materials for use in the electron injecting and transporting layer of the stacked EL device of the present invention are metal chelated oxinoid compounds, including chelates of 8-hydroxyquinoline.
Specific examples include those shown in Table 4 below.
[0024]
[Table 4- (1)]
ETL29 Aluminum Trisoxin

ETL30 magnesium bisoxin
ETL31 bis (benzo-8-quinolinol) zinc
ETL32 bis (2-methyl-8-quinolinolate) aluminum oxide
ETL33 Indium trisoxin
ETL34 Aluminum Tris (5-methyloxin)
ETL35 Lithium oxine
ETL36 Gallium trisoxin
ETL37 calcium bis (5-chlorooxin)
ETL38 poly (zinc (II) -bis (8-hydroxy-5-quinolinonyl) methane)
ETL39 dilithium epidridione
[0025]
[Table 4- (2)]

[0026]
Further, bis-type metal chelated oxinoid compounds described in US Pat. No. 5,151,629 and US Pat. No. 5,150,006 are also preferable as the material for the electron injecting and transporting layer.
Further, other preferred electron injecting and transporting layer materials include butadiene derivatives such as 1,4 diphenylbutadiene and tetraphenylbutadiene, coumarin derivatives, bisstyrylbenzene derivatives, bisstyrylanthracene derivatives, benzoxazole derivatives, oxadiazole derivatives, Oxazole derivatives, thiadiazole derivatives, naphthalimide derivatives, perylenetetracarboxylic diimide derivatives, quinacridone derivatives and the like can be mentioned.
Table 5 shows specific compounds.
[0027]
[Table 5]

[0028]
Although specific examples of useful electron injecting and transporting materials have been described above, when the electron injecting and transporting layer is composed of a plurality of layers, the order of lamination satisfying the formula (I) is preferable from the viewpoint of improving durability.
The present invention is characterized in that aluminum trisoxine (ETL29) is used as a material for the first electron injection / transport layer.
[0029]
The organic thin-film EL device of the present invention is obtained by applying the organic compound described above by a vacuum evaporation method, a solution coating method, or the like, to a thickness of less than 0.5 μm in the entire organic compound layer, preferably 1000 ° or less, more preferably, Is formed into a thin film having a thickness of 100 to 1,000 mm to form an organic compound multilayer, which is sandwiched between an anode and a cathode. When the constituent organic compound has a remarkably rich ability to form a thin film, it is possible to form a layer with a thickness of 100 ° or less.
Further, the organic thin-layer EL device of the present invention may have a structure in which each adjacent organic layer and each electrode and the organic layer do not have a clear interface, and a mixed mixed region is formed.
[0030]
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 shows a structure in which an anode / a hole injection / transport layer / a light emitting layer / an electron injection / transport layer / a cathode are sequentially provided. (However, at least one of the hole injection transport layer and the electron injection transport layer is composed of two or more layers.)
Figure2Shows a structure in which an anode / a light-emitting layer / an electron injection / transport layer / a cathode are sequentially provided. (However, the electron injection transport layer is composed of at least two or more layers.)
[0031]
The organic thin-film EL element of the present invention applies an electric voltage to the EL element to emit light.However, a short circuit may occur due to a slight pinhole, and the element may not function as an element. It is desirable to use a compound having excellent thin film forming properties in combination. Furthermore, the light emitting layer can be formed by combining such a compound having excellent thin film forming properties and a polymer binder. Examples of the polymer binder that can be used in this case include polystyrene, polyvinyl toluene, poly-N-vinyl carbazole, polymethyl methacrylate, polymethyl acrylate, polyester, polycarbonate, and polyamide.
[0032]
As the anode material, nickel, gold, platinum, palladium, alloys thereof, or tin oxide (SnO)₂), A metal having a large work function such as tin-indium oxide (ITO) or copper iodide, or an alloy or compound thereof, or a conductive polymer such as poly (3-methylthiophene), polypyrrole, or polyarylenevinylene. be able to. On the other hand, as the cathode material, silver, tin, lead, magnesium, manganese, aluminum, or an alloy thereof having a small work function is used. It is desirable that at least one of the materials used as the anode and the cathode is sufficiently transparent in the emission wavelength region of the device. Specifically, it is desirable to have a light transmittance of 80% or more.
[0033]
In the present invention, it is desirable that the transparent anode is formed on a transparent substrate and has a configuration as shown in FIGS. 1 to 3. However, in some cases, the reverse configuration may be adopted. Further, as the transparent substrate, glass, plastic film, or the like can be used.
In the present invention, in order to improve the stability of the EL device thus obtained, particularly to protect against moisture in the air, a separate protective layer may be provided, or the entire device may be placed in a cell, Etc. may be enclosed.
[0034]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
[0035]
Example 1 (when the electron injection transport layer is formed from two layers)
An ITO (indium tin oxide: sheet resistance: 20Ω / □) substrate was sequentially ultrasonically cleaned with a neutral detergent, acetone, and isopropyl alcohol. Then, the ITO substrate was immersed in boiled isopropyl alcohol for 5 minutes and dried by heating.
The hole injection transport layer material HTL1 is 10^-6The alumina crucible was vapor-deposited at 400 ° C. under a torr vacuum. Next, the light emitting layer material EML1 was deposited at 150 °. Next, the second electron injection / transport layer ETL1 was deposited at 200 °, the first electron injection / transport layer ETL29 was further deposited at 300 °, and finally a MgAg electrode having an atomic ratio of 10: 1 was deposited at 2000 °.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 8.9 V and a light emission luminance of 620 cd / m²showed that. Then, after a lapse of 60 minutes, 668 cd / m²430 cd / m even after 10 hours²High brightness was maintained. The emission spectrum was blue emission centered at 475 nm.
At this time, the electron affinity of the second electron injection / transport layer is 2.14 eV, the electron affinity of the first electron injection / transport layer is 3.0 eV, and the work function of the cathode is 3.50 eV. To be satisfied.
Ipc (3.50 eV)> Eae1 (3.0 eV)> Eae2 (2.14 eV) (III)
[0036]
Comparative Example 1 (when the electron injection transport layer is formed from a single layer)
An EL device was produced in the same manner as in Example 1, except that the first electron injection / transport layer ETL29 was omitted. However, the thickness of the second electron injection transport layer was set to 500 °. In this case, immediately after voltage application, 30 mA / cm²520 cd / m under constant current of²And a driving voltage of 10 V were observed. However, after one hour, 270 cd / m²After 10 hours, the emission luminance is 43 cd / m.²When the second electron injection transport layer was omitted, the durability was remarkably inferior. Further, the initial drive voltage also showed a value higher by 1.1 V than that of Example 1. This indicates that the presence of a plurality of electron injecting and transporting layers is effective in improving durability and lowering driving voltage.
[0037]
Example 2 (when the hole injection transport layer and the electron injection transport layer are each formed of two layers)
An EL element was prepared in the same manner as in Example 1, except that copper phthalocyanine (HTL18) (CuPc) having a thickness of 250 ° was inserted at the interface between the anode and the second hole injection / transport layer (HTL1) as the first hole injection / transport layer. . However, the thickness of the second hole injection / transport layer was set to 200 °.
In this case, immediately after the voltage was applied, the light emission luminance was 492 cd / m 2 under a constant current.², A driving voltage of 5.3 V was observed, and 260 cd / m²Was observed, and the EL device was highly durable. This indicates that the drive voltage can be significantly reduced by forming the hole injection transport layer and the electron injection transport layer from a plurality of layers.
In this configuration, the ionization potential of the ITO electrode serving as the anode is lpa = 4.53 eV, the ionization potential of the first hole injection / transport layer is lph1 = 4.97 eV, and the ionization potential of the second hole injection / transport layer is lph2 = 5.08 eV. Which satisfies the relational expression of claim 1.
Ipa (4.53 eV) <lph1 (4.97 eV) <lph2 (5.08 eV) (III)
[0038]
Example 3 (when quinacridone is used for the first electron injection / transport layer)
An EL device was prepared in the same manner as in Example 1, except that the triphenylamine derivative HTL2 was used for the hole injection / transport layer and the quinacridone derivative ETL47 was used for the first electron injection / transport layer. In this case, immediately after voltage application, 30 mA / cm²Under constant current of 250 cd / m²And a driving voltage of 11 V were observed. Even after 10 hours, 100 cd / m²Was observed. The electron affinity of the quinacridone compound is estimated to be 2.60 eV, which satisfies the relational expression of claim 1.
Ipc (3.50 eV)> Eae1 (2.60 eV)> Eae2 (2.14 eV) (V)
[0039]
Example 4 (when a naphthalimide derivative is used for the first electron injection / transport layer)
An EL device was prepared in the same manner as in Example 1, except that the triphenylamine derivative HTL3 was used for the hole injection / transport layer and the naphthalimide derivative ETL45 was used for the first electron injection / transport layer. In this case, immediately after voltage application, 30 mA / cm²328 cd / m under the constant current of²And a driving voltage of 9 V were observed. 528 cd / m after 1 hour²Is observed, and 100 cd / m is observed even after 10 hours.²The above emission luminance was observed. The electron affinity of this naphthalimide compound is estimated to be 2.70 eV, which satisfies the relational expression of claim 1.
Ipc (3.50 eV)> Eae1 (2.70 eV)> Eae2 (2.14 eV) (VI)
[0040]
Comparative Example 2
An EL element was produced in the same manner as in Example 1. However, the following perylene derivative (PV) was used for the first electron injection transport layer. In this case, only weak EL emission was observed even at an applied voltage of 20 V, and the device was extremely poor in luminous efficiency. Further, this device was set to 30 mA / cm.²When a durability test was conducted under a constant current of, the luminance was reduced by half within one hour, and the device was extremely poor in durability.
In this case, the relationship between the electron affinity of the first and second electron injection / transport layers and the work function of the cathode is
Ipc (3.50 eV)> Eae1 (4.30 eV)> Eae2 (2.14 eV) (V)
This indicates that the relationship between the electronic properties of the cathode and the electron injection / transport layer that does not satisfy the relational expression of claim 1 and satisfies the relational expression (I) is important for improving the durability. .
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[0041]
Examples 5 to 8
An EL element was produced in the same manner as in Example 1. Table 7 below shows the layer constituting materials and the durability characteristics.
[0042]
[Table 7]

These devices satisfy the relational expression of claim 1 between the cathode and the first and second electron injection / transport layers as in the first embodiment.
[0043]
Example 9 (pulse drive)
An EL element was produced in the same manner as in Example 1. However, the thickness of the organic layer was set as follows.
First hole injection / transport layer HTL1 400Å
Emitting layer EML1 150Å
Second electron injection transport layer ETL6 200６
First electron injection transport layer ETL29 300２９
The EL device thus prepared was subjected to a peak current value of 30 mA / cm.²When driven by a rectangular wave having a frequency of 100 Hz, the initial luminance was 85 cd / m 2.², And a driving voltage of 6.2 V. After that, even after 201 hours, 97 cd / m²And the EL device was extremely durable.
[0044]
Example 10
An EL device was prepared in the same manner as in Example 2. However, the ETL is used for the second electron injection / transport layer.20Was used. In this case, immediately after voltage application, 30 mA / cm²Under a constant current of 60 cd / m², The driving voltage was 6.2 V, and the initial luminance was maintained even after 170 hours had elapsed, and a result with extremely high durability was obtained. Also in this case, the electron affinity of the ETL 20 layer is estimated to be 2.5 eV, which satisfies the relational expression of claim 1.
Ipc (3.50 eV)> Eae1 (2.50 eV)> Eae2 (2.14 eV) (VIII)
[0045]
Example 11 (when the electron injection transport layer is formed from three layers)
An ITO (indium tin oxide: sheet resistance: 20Ω / □) substrate was sequentially ultrasonically cleaned with a neutral detergent, acetone, and isopropyl alcohol. Then, the ITO substrate was immersed in boiled isopropyl alcohol for 5 minutes and dried by heating.
The hole injection transport layer material HTL1 is 10^-6The alumina crucible was heated at 400 ° C. under a torr vacuum to deposit 400 °. Next, the light emitting layer material EML1 was deposited at 150 °. Next, the third electron injection / transport layer ETL1 is deposited at 150 °, the second electron injection / transport layer ETL6 is deposited at 150 °, and the first electron injection / transport layer ETL29 is deposited at 250 °. Finally, a MgAg electrode having an atomic ratio of 10: 1 is deposited at 2000 °. did.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 7.6 V, a driving voltage of 7.6 V and a light emission luminance of 510 cd / m²,showed that. Then, after lapse of 60 minutes, 610 cd / m²420 cd / m even after 10 hours²High brightness was maintained.
At this time, the electron affinity of the third electron injection transport layer is 2.14 eV, the electron affinity of the second electron injection transport layer is 2.50 eV, the electron affinity of the first electron injection transport layer is 3.0 eV, and the work function of the cathode is 3.55 eV, which satisfies the relational expression of claim 1.
Ipc (3.50 eV)> Eae1 (3.0 eV)> Eae2 (2.50 eV)> Eae3 (2.14 eV) (IX)
[0046]
Example 12
An EL device was produced in the same manner as in Example 11, except that copper phthalocyanine (CuPc) (HTL18) was used as the first hole injection / transport layer at 200 ° and HTL1 was used at 200 ° as the second hole injection / transport layer.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 6.6 V, a driving voltage of 6.6 V and a light emission luminance of 490 cd / m²,showed that. After that, 400 cd / m even after 10 hours²The above high brightness was maintained. In this case, by inserting copper phthalocyanine, the drive voltage could be reduced as compared with Example 11.
[0047]
Example 13
After the substrate was washed in the same manner as in Example 11, copper phthalocyanine (CuPc) (HTL18) was used as the first hole injection / transport layer at 200 °, HTL1 was used as the second hole injection / transport layer at 150 °, and the third hole injection / transport layer HTL2 was used. Was deposited at 150 °, the light emitting layer EML1 was deposited at 150 °, the second electron injection / transport layer ETL1 was deposited at 200 °, and the first electron injection / transport layer ETL29 was deposited at 300 °. Finally, an MgAg alloy electrode was formed.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 6.4 V, a driving voltage of 6.4 V and a light emission luminance of 530 cd / m²,showed that. Then, after 60 minutes, 560 cd / m²460 cd / m even after 10 hours²High brightness was maintained.
2. The relational expression according to claim 1, wherein in the device, the electron affinity of the second electron injection / transport layer is 2.14 eV, the electron affinity of the first electron injection / transport layer is 3.0 eV, and the work function of the cathode is 3.5 eV. To be satisfied.
Ipc (3.50 eV)> Eae1 (3.0 eV)> Eae2 (2.14 eV) (X)
The ionization potential of the first hole injection / transport layer is 4.97 eV, the ionization potential of the second hole injection / transport layer is 5.08 eV, and the ionization potential of the third hole injection / transport layer is 5.32 eV. Satisfies the relational expression.
lpa (4.53 eV) <lph1 (4.97 eV) <lph2 (5.08 eV) <lph3 (5.32 eV) (XI)
[0048]
Comparative Example 3
An EL element was produced in the same manner as in Example 13. However, ETL1 (200 °) was used for the first electron injection / transport layer, and ETL29 (300 °) was used for the second electron injection / transport layer, and the stacking order was changed.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 8.4 V, a driving voltage of 8.4 V and a light emission luminance of 517 cd / m², But 100 cd / m after 10 hours.²Only the following emission luminance was obtained, resulting in poor durability. Furthermore, in Example 13, blue EL emission was centered at 475 nm, but when the stacking order was reversed, EL emission from the second electron injection transport layer was also observed, and green emission centered at 515 nm was observed. It was luminescence.
2. The relational expression according to claim 1, wherein the first electron injection / transport layer has an electron affinity of 2.14 eV, the second electron injection / transport layer has an electron affinity of 3.0 eV, and the cathode has a work function of 3.5 eV. Not satisfied.
Ipc (3.50 eV)> Eae1 (2.14 eV)> Eae2 (3.0 eV) (XII)
[0049]
Example 14
After processing the substrate in the same manner as in Example 11, copper phthalocyanine (CuPc) (HTL18) was used as the first hole injection / transport layer.^-6The alumina crucible was deposited at 200 ° by heating under a torr vacuum. Further, HTL1 was deposited at 150 ° as a second hole injection / transport layer, and HTL2 was deposited at 150 ° as a third hole injection / transport layer. Next, the light emitting layer material EML1 was deposited at 150 °. The third electron injection / transport layer ETL1 was deposited at 150 °, the second electron injection / transport layer ETL6 was deposited at 150 °, the first electron injection / transport layer ETL29 was deposited at 250 °, and finally a MgAg electrode having an atomic ratio of 10: 1 was deposited at 2000 °.
Immediately after the voltage was applied, the EL device thus fabricated was 30 mA / cm.²At a current density of 7.1 V, a driving voltage of 7.1 V and a light emission luminance of 523 cd / m²showed that. 480 cd / m after 10 hours²High brightness was maintained.
In this case, the third electron injection / transport layer has an electron affinity of 2.14 eV, the second electron injection / transport layer has an electron affinity of 3.0 eV, and the cathode has a work function of 3.50 eV. To be satisfied.
Ipc (3.50 eV)> Eae1 (3.0 eV)> Eae2 (2.50 eV)> Eae3 (2.14 eV) (XIII) The ionization potential of the first hole injection / transport layer is 4.97 eV, and the second hole injection is The ionization potential of the transport layer is 5.08 eV, and the ionization potential of the third hole injection / transport layer is 5.32 eV, which satisfies the relational expression of claim 2.
Ipa (4.53 eV) <lph1 (4.97) eV) <lph2 (5.08 eV) <lph3 (5.32 eV) (XIV)
[0050]
Examples 15 to 22
An EL element was prepared in the same manner as in Example 1. Table 8 below shows the layer constituting materials and the durability characteristics.
These devices satisfy the relational expression of claim 1 between the cathode and the first and second electron injection / transport layers.
[0051]
[Table 8]

[0052]
【The invention's effect】
The organic thin-film EL device of the present invention can directly convert electric energy into light energy by recombination of charged carriers (electrons and holes) injected into the light-emitting layer by applying an electric field, and can use conventional incandescent lamps, fluorescent lamps, or inorganic compounds. Unlike the EL of the above, it is possible to realize blue light emission, which was difficult to achieve with a light emitting diode of an inorganic compound. In an organic thin film EL device, a hole injection transport layer and an electron injection transport layer between a light emitting layer and an electrode are provided. By making both or any of them into a plurality of layers, it is possible to improve the durability.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an organic thin film EL device according to the present invention.
FIG. 2 is a schematic sectional view of another organic thin film EL device according to the present invention.

Claims (3)

At the anode / hole injecting and transporting layer / light emitting layer / an organic thin film EL element formed from the electron injection transport layer / cathode, the electron injecting and transporting layer is composed of two or more layers,
Each of the electron affinity values Eae1, Eae2,... Eaen of the plurality of electron injecting and transporting layers (where n means that the electron injecting and transporting layer is composed of n layers, 1, 2,. N means the order from the cathode side) satisfies the relationship between the work function value (Ipc) of the cathode and the following equation (I),
When the hole injection / transport layer has a plurality of layers, the values of the ionization potentials Iph1, Iph2,... Iphm of the plurality of hole injection / transport layers (where m is an m number of hole injection / transport layers) , M means the order from the side of the anode)), the value of the work function (Ipa) of the anode and the following equation (II) are satisfied, and the first electron An organic thin-film EL device wherein the material of the injection / transport layer is aluminum trisoxine and the material of the light-emitting layer is an aminopyrene derivative .
Ipc ≧ Eae1 ≧ Eae2 ≧ ... ≧ Eaen (I)
Ipa ≦ Iph1 ≦ Iph2 ≦... ≦ Iphm (II) In an organic thin-film EL device comprising an anode / light-emitting layer / electron injection / transport layer / cathode, the electron injection / transport layer is composed of two or more layers , and the electron affinity value Eae1 of each of the plurality of electron injection / transport layers. , Eae2,... Eaen (where n means that the electron injection / transport layer is composed of n layers, and 1, 2,... N means the order from the cathode side). Characterized in that the first electron injection / transport layer is made of aluminum trisoxin and the light emitting layer is made of an aminopyrene derivative , which satisfies the relationship of the work function value (Ipc) with the following formula (I). EL element.
Ipc ≧ Eae1 ≧ Eae2 ≧ ... ≧ Eaen (I) 2. The organic thin film EL device according to claim 1 , wherein the thickness of each of the hole injection transport layer and / or the electron injection transport layer formed of one layer or a plurality of layers is 1000 ° or less.

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