Luminous efficiency enhancement in blue phosphorescent organic light-emitting diodes with an electron confinement layers

This study reports the results of blue phosphorescent organic light emitting diodes (PHOLEDs) employing an electron confinement layer (ECL), tris-(phenylpyrazole)iridium (Ir(ppz)3) and a hole confinement layer (HCl), 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene (TPBi). The electrical and optical characteristics of PHOLEDs with different emissive layers, including current density, luminance, and luminous efficiency, were analyzed. The thickness of the individual emissive layer was optimized, however, and the total thickness of the emitting region was kept constant at 300Å. This work reveals that the effective electron confinement, due to a large energy level offset between the electron confinement and emitting layers, helps to improve hole–electron current balance in the emitting region. The maximum external quantum efficiency of 23.40% at 1500cd/m2 was achieved for PHOLEDs with an ECL, which is 60% higher than the structural identical control device without ECL.