High performance organic light emitting diodes using substoichiometric tungsten oxide as efficient hole injection layer

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• 作者：Maria Vasilopoulou^a ; ^{mariva@imel.demokritos.gr} ; George Papadimitropoulos^a ; Leonidas C. Palilis^b ; Dimitra G. Georgiadou^a ; Panagiotis Argitis^a ; Stella Kennou^c ; Ioannis Kostis^a ; ^d ; Nikolaos Vourdas^a ; Nikolaos A. Stathopoulos^d ; Dimitris Davazoglou^a
• 关键词：Transition metal oxides ; Reduced metal oxides ; Metallic suboxides ; Organic light emitting diodes ; Efficient hole injection
• 刊名：Organic Electronics
• 出版年：2012
• 期刊代码：137_15661199
• 类别：et
• 出版时间：May, 2012
• 卷：13
• 期：5
• 页码：796-806
• 文件大小：803 K

摘要

In this work we demonstrate the unique hole injection and transport properties of a substoichiometric tungsten oxide with precise stoichiometry, in particular WO_2.5, obtained after the controlled hydrogen reduction during growth of tungsten oxide, using a simple hot-wire vapor deposition technique. We present clear evidence that tungsten suboxide exhibits metallic character and that an almost zero hole injection barrier exists at the anode/polymer interface due to the formation/occupation of electronic gap states near the Fermi level after oxide鈥檚 reduction. These states greatly facilitate hole injection and charge generation/electron extraction enabling the demonstration of extremely efficient hole only devices. WO_2.5 films exhibit metallic-like conductivity and, thus, can also enhance charge transport at both anode and cathode interfaces. Electroluminescent devices using WO_2.5 as both, hole and electron injection layer, and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1鈥?3}-thiadiazole)] (F8BT) as the emissive layer exhibited high efficiencies up to 7 cd/A and 4.5 lm/W, while, stability studies revealed that these devices were extremely stable, since they were operating without encapsulation in air for more than 700 h.