Carrier transport and high-efficiency electroluminescence properties of copolymer thin films

A novel copolymer with moieties capable of charge transport and electroluminescence was synthesized. The drift mobilities of electron and hole in the spin-coated films of the copolymer on silicon substrate have been determined by the time-of-flight technique. The shape of the photo-current curves obtained for the transport of both electron and hole is typical for dispersive transport in organic polymers. Under an electrical field strength of 5.0 x 10(5) V/cm, the drift mobility of electron and hole is 4.78 x 10(-6) and 3.46 x 10(-6) cm(2)/V s, respectively. A high-efficiency electroluminescent device with the bi-layer structure of ITO/copolymer/2-(4-biphenylyl)-5-(4-tert-butylphenl)-1,3,4-oxadiazole (PBD) /LiF/Al was fabricated. The device emitted a bright blue-green light peaking at wavelength of 496 nm, originating from copolymer with a maximum current efficiency of 10 cd/A and a maximum luminescence efficiency of 2.9 lm/W at the DC drive voltage of 12 V. (C) 2000 Elsevier Science S.A. All rights reserved.