Study on the Transient Electroluminescence of Phosphorescent OLEDs

Abstract

We have studied the turn-off dynamics of phosphorescent organic light-emitting diodes (OLEDs) by investigating the temperature, pulse width, and voltage dependences of the radiative triplet lifetime with the dispersive parameter gamma, calculated from the second luminescence of the transient electro-luminescence. This behavior is caused by the redistribution and recombination of electrons and holes accumulated near the interfaces. The lifetime increases with increasing carrier density and with decreasing temperature. This is due to the decrease in the hopping and the triplet-triplet annihilation rates. The experimental data satisfy the relationship between the dispersive parameter gamma and temperature T, gamma - 1 proportional to exp(-A/T), with a constant A.