Improved electroluminescent performances of europium-complex based devices by doping into electron-transporting/hole-blocking host

High-efficiency, pure red organic light-emitting devices were fabricated by doping a europium-complex Eu(DBM)(3)pyzphen (DBM=dibenzoylmethane, pyzphen=pyrazino[2,3-f][1,10]phenanthroline) into 4,7-diphenyl-1,10-phenanthroline as emission layer. A maximum current efficiency of 5.1 cd/A at the current density of 1.2 mA/cm(2) and a maximum luminance of 1400 cd/m(2) were obtained from a 25 wt % Eu(DBM)(3)pyzphen doped device. High efficiencies were maintained at high current densities and high luminance. For example, at the current density of 10 mA/cm(2), the efficiency reached 3.8 cd/A. It means that the efficiency roll-off, a major obstacle to the development of Eu-complex ogranic light-emitting devices, was greatly alleviated. The mechanisms behind the improvement are discussed.