Nanosecond transients in the electroluminescence from multilayer blue organic light-emitting devices based on 4,4(')-bis(2,2(')diphenyl vinyl)-1,1(')-biphenyl

Nanosecond electroluminescence (EL) overshoots observed when multilayer blu e 4,4'-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl (DPVBi)-based organic light-e mitting devices (OLEDs) are excited by rectangular voltage pulses are descr ibed. The overshoots occur at the voltage turn-off and exceed the cw bright ness by up to an order of magnitude. Time-resolved images of the OLEDs demo nstrate that the emission from most of the sample surface decays with a sin gle time constant tau(1)=13 +/- 3 ns. This decay is attributed to recombina tion of charges which accumulate at the interface of the electron and hole transporting layers, possibly at intrinsic trapping sites. In areas of incr eased electron injection and EL, such as cathode edges and morphological de fects, a second slower decay time 20 ns <tau(2)< 1 mu s is observed, appare ntly due to release of carriers from localized trap states in the organic/c athode interface. Only marginal variations in tau(1) are found between brig ht and dim areas of the devices. At a bias of 10 V, the amplitude of the ov ershoot is found to peak at a pulse duration of similar to 20 mu s. Its beh avior is believed to result from increased quenching of singlet excitons by the accumulated charges. (C) 2000 American Institute of Physics. [S0003-69 51(00)02212-9].