Lifetime studies of light-emitting diode structures incorporating polymeric Langmuir-Blodgett films

The operating lifetimes of light-emitting diode structures incorporating po ly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV) Langmuir-B lodgett films are reported. To remove the moisture from the organic layer, a number of post-deposition treatments have been investigated prior to the deposition of the metal top contact. The best external quantum efficiency w as found for an indium-tin oxide/MEH-PPV/aluminium structure dried in high vacuum. However, this device possessed a relatively short lifetime. Experim ents at constant current and constant voltage revealed that annealing at an elevated temperature could enhance the lifetime. Further improvements were found for devices in which a lithium fluoride layer (approximate to 2 nm) was sandwiched between the aluminium electrode and the polymer layer, and b y encapsulating the device with adhesive tape. (C) 2001 Elsevier Science B. V. All rights reserved.