Light-emitting devices with a photoluminescent quinquethiophene derivativeas an emitting material

Electrical and electroluminescence measurements were carried out on single- and double-layer light emitting devices where a functionalized quinquethio phene, having a high photoluminescence quantum yield in its solid state (si milar to 11%), was used as the emitting molecule. The thiophene derivative was used together with N,N'-dipheny-N,N'-bis(3-metylphenyl)-1,1'-biphenyl-4 ,4'-diamine (TPD), the well-studied hole injecting and transporting molecul e, and with Alq(3) as the electron transporting and emitting material. The deposition techniques for the device construction were both vacuum sublimat ion of the pure compounds and spinning of the concentrated solutions of pur e or mixed compounds. Electroluminescence spectra show that the thiophene d erivative is the only emitting species when put together with TPD, both in the single- and double-layer devices. Its orange emission is mixed with the green Alq(3) emission in the double layer devices where a vacuum-deposited Alq(3) layer is in contact with the cathode, the orange/green intensity ra tio being dependent on the applied voltage. These light emitting devices ar e characterized by an extremely low onset voltage (2 Volt) and a fairly goo d electroluminescence external quantum efficiency (EQE = 0.7%). (C) 2000 El sevier Science S.A. AU rights reserved.