Efficient Green Phosphorescent Organic Light Emitting Diode using Iridium Complex

Abstract

We report here the fabrication and characterization of an efficient green phosphorescent organic light emitting diodes (PhOLED) using phosphorescent iridium complex, tris(2-phenylpyridine) iridium (III) (Ir(ppy)₃). Ir(ppy)₃ is an organic phosphorescent material, which emits green light via both the singlet as well as triplet exciton relaxation. To avoid triplet-triplet annihilation and for efficient light emission, the phosphorescent emitters should be doped in a suitable host material which has band-gap larger than the doped guest material and the band gap of the guest should lie within the band-gap of the host. We optimally doped phosphorescent Ir(ppy)₃ into a fluorescent 4,4'-bis(9-carbazolyl) biphenyl (CBP) host and used it as the emitter to prepare PhOLEDs. The PhOLED exhibited green electroluminescence (EL) in the range ~ 480-650 nm with EL peak at 550 nm along with a shoulder at 510 nm. The Commission Internationale de-I’eclairage (CIE) colour coordinate of the device was measured to be (0.25, 0.60). The current density vs voltage vs luminescence (J-V-L) characteristics of the device led us to calculate its current efficiency, which was found to be 28.9 cd/A at 7V. The efficiency of PhOLED decreased with increment in the applied voltage beyond 7 V and has been attributed to the triplet-triplet annihilation due to high injected current densities.