Efficient alternating current electroluminescence of CBP: Ir(ppy)3 in the tandem devices with ladder barrier layers

Abstract

In this paper, alternating current-driven organic light-emitting diodes (AC-OLEDs) with different structures are reported, which can be driven under forward and reverse biases by using a bipolar functionality emission layer of CBP: Ir(ppy)3. The maximum current efficiencies (CEs) under forward and reverse DC biases of prepared symmetric devices with ladder barrier layers are 9.6 and 13.6 cd A−1, respectively. The mechanism and the reason for efficiency improvement are discussed by changing the thickness of barrier layers from 0, 5, 7.5 to 10 nm respectively. The differences in EL spectra of different devices are explained by FDTD simulation. The distance from the metal electrode to the light source influences the light extraction, which results in the spectrum difference for devices with different thicknesses of ladder barriers or working under different biases. The current density decreases along with the increasing thickness of barrier layers, and the highest current efficiency is achieved when the thickness is 7.5 nm. Then an effective method to further develop AC-driven tandem devices is proposed.