Nenosecond electroluminescence (EL) spikes at the voltage turn-off from a small molecular organic light-emitting device (OLED)

Abstract

Nanosecond EL spikes observed when multilayer blue 4,4'-bis(2,2'-diphenyl vinyl)-1,1-biphenyl (DPVBi)/AlO x /Al-based OLEDs are excited by rectangular voltage pulses are described. The spikes occur at the voltage tum-off and exceed the cw brightness by up to x10, Time-resolved CCD images show that the uniform emission from most of the OLED surface decays with a single constant τ 1 = 13 ± 3 ns. In the brighter areas of increased electron injection such as cathode edges and morphological defects, a second slower decay time 20 ns < τ 2 < 1 μs is observed, apparently due to release of carriers from localized trap states in the organic/cathode interface. At a bias of 10 V the amplitude of the spike is found to peak at a pulse duration of -20 μs.