Nanosecond electroluminescence spikes from multilayer blue 4,4 '-bis(2,2 '-diphenyl vinyl)-1,1 '-biphenyl (DPVBi) organic light-emitting devices

Nanosecond electroluminescence (EL) spikes observed at the voltage turn-off when multilayer blue DPVBi-based organic light-emitting devices (OLEDs) ar e excited by rectangular voltage pulses are described. The spikes exceed th e cw brightness by up to an order of magnitude. Time-resolved images of the devices demonstrate that the emission from most of the sample surface deca ys with a single time constant tau (1) = 13 +/- 3 ns. This decay is attribu ted to recombination of charges, which accumulate at the interface of the e lectron and hole transporting layers, possibly at intrinsic trapping sites. In areas of increased electron injection and EL such as cathode edges and morphological defects, a second slower decay time 20 ns < tau (2) < 1 ?s is observed, apparently due to release of carriers from localized trap states in the organic/cathode interface. Only marginal variations in tau (1) are found between bright and dim areas of the devices. At a bias of 10 V, the a mplitude of the spike is found to peak at a pulse duration of similar to 20 mus. (C) 2001 Elsevier Science B.V. All rights reserved.