Highly efficient tandem full exciplex orange and warm white OLEDs based on thermally activated delayed fluorescence mechanism

In this manuscript, we demonstrated highly efficient tandem full exciplex orange and warm white organic light emitting diodes (OLEDs) by using 2,4,6-tris(3-(1H-pyrazol-1-yl) phenyl)-1,3,5-triazine (3P-T2T):cesium carbonate (Cs2CO3)/Al/molybdenum trioxide (MoO3) as the charge generation layer. The maximum current efficiency and external quantum efficiency (EQE) of the optimized tandem orange OLEDs are 38.1 cd/A and 14.4%, respectively. We then utilized two primary colors of blue and orange exciplex emitter to achieve highly efficient white emission. The tandem WOLEDs made by stacking two single color OLEDs in series demonstrate a maximum EQE of 9.17%. Meanwhile, the spectra are almost the same under various voltages, with the Commission Internationale de I'Eclairage coordinates of (0.41, 0.44), which change only (+/- 0.003, +/- 0.002) from 6 V to 14 V. We prove that the highly efficient tandem full exciplex orange and white OLEDs are attributed to the thermally activated delayed fluorescence by efficient reverse intersystem crossing. Balanced carriers injection and recombination are responsible for the stable spectra of the white OLEDs. (C) 2014 Elsevier B.V. All rights reserved.