Kinetic Monte Carlo modeling of the efficiency roll-off in a multilayer white organic light-emitting device

M. Mesta, H. van Eersel, R. Coehoorn and P. A. Bobbert

Appl. Phys. Lett. 108 (2016) 133301

Triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) in organic light-emitting devices(OLEDs) lead to a roll-off of the internal quantum efficiency (IQE) with increasing current density J. We employ a kinetic Monte Carlo modeling study using Bumblebee to analyze the measured IQE and color balance as a function of J in a multilayer hybrid white OLED that combines fluorescent blue with phosphorescent green and red emission. We investigate two models for TTA and TPQ involving the phosphorescent green and red emitters: short-range nearest-neighbor quenching and long-range Förster-type quenching. Short-range quenching predicts roll-off to occur at much higher J than measured. Taking long-range quenching with Förster radii for TTA and TPQ equal to twice the Förster radii for exciton transfer leads to a fair description of the measured IQE-J curve, with the major contribution to the roll-off coming from TPQ. The measured decrease of the ratio of phosphorescent to fluorescent component of the emitted light with increasing J is correctly predicted. A proper description of the J-dependence of the ratio of red and green phosphorescent emission needs further model refinements.