We fabricated long-lived multilayer organic light-emitting diodes (OLEDs), in which a 0.75 nm thick hole-injection layer of molybdenum oxide (MoO3) and a 5 nm thick mixed layer at an organic/organic heterojunction interface were embedded. The use of the MoO3 layer and of the mixed layer enhanced carrier injection at anode/organic and organic/organic heterojunction interfaces, resulting in a marked decrease in driving voltage and an increase in power conversion efficiency in the OLEDs. We observed about a factor of 9 improvement in the operational lifetime of the OLEDs by using the MoO3 layer and the mixed layer as well. We assume that the lifetime improvement originates from the suppression of a thermally induced electrochemical degradation process of organic emitting molecules due to the reduction in the probability of the generation of Joule heat.
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