Efficient red electroluminescence from devices having multilayers of a europium complex

Abstract
In order to get red electroluminescence from a europium (Eu) complex with high efficiency, a hole-injection layer was inserted between the Eu-complex layer and an indium–tin–oxide electrode, and a hole-blocking layer was inserted between the Eu-complex and electron-transporting layers. To further improve the efficiency, devices having multiple-stacked Eu-complex (2.5 nm)/hole blocking (2.5 nm) units were fabricated. By stacking six units, the maximal luminance and emission efficiency of the red emission were increased to more than twice that from a device with a single Eu-complex layer.