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

作者：Vasilopoulou Maria^*; Papadimitropoulos George; Palilis Leonidas C; Georgiadou Dimitra G; Argitis Panagiotis; Kennou Stella; Kostis Ioannis; Vourdas Nikolaos; Stathopoulos Nikolaos A; Davazoglou Dimitris

来源：Organic Electronics, 2012, 13(5): 796-806.

DOI：10.1016/j.orgel.2012.01.008

• Transition metal oxides
• Reduced metal oxides
• Metallic suboxides
• Organic light emitting diodes
• Efficient hole injection

In this work we demonstrate the unique hole injection and transport properties of a substoichiometric tungsten oxide with precise stoichiometry, in particular WO2.5, 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%26apos;s reduction. These states greatly facilitate hole injection and charge generation/electron extraction enabling the demonstration of extremely efficient hole only devices. WO2.5 films exhibit metallic-like conductivity and, thus, can also enhance charge transport at both anode and cathode interfaces. Electroluminescent devices using WO2.5 as both, hole and electron injection layer, and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1%26apos;,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.

• 出版日期2012-5