Suppression of phase separation through blending of electron transporting materials in polymer electrophosphorescent devices

Herein, we report the concentration effect of an electron transporting material, 1,3-bis ((4-tert-butyl-phenyl)-1,3,4-oxidiazolyl) phenylene (OXD-7), on the performance of polymer electrophosphorescent devices. From the phase mode images of atomic force microscopy, we observed that phase separation between the host material and the triplet dopants was suppressed in the photoactive film while the concentration of OXD-7 was increased. Correspondingly, the single-layer blue light-emitting device with the best external quantum efficiency of 7.9% was achieved. We attributed the device enhancement to the improved compatibility between the host and the phosphorescent molecules after the addition of OXD-7 molecules.