Efficient energy transfer in organic thin films by ultra-high vacuum evaporation

The energy transfer in organics, aiming to optimise the performance of many. LED devices, has been exploited with two suitable oligomers deposited either in multi layered or in co-evaporated films by ultra high vacuum evaporation. We have chosen two components displaying the appropriate absorption/emission windows, in fact the emission maximum of the first, a thienyl-fluorene derivative, is centred in the region where the absorption of the second, tetrahexylsexithiophene, is intense, hence guaranteeing a complete Foerster transfer even at low content of the latter. Optical microscopy investigations together with XRD analysis allowed us to get in sight onto both the structure orientation and the morphology of the film components. The optical aspects of this thin layers, 15-30 nm thick, are also discussed and compared with the mono-component films obtained in the same conditions. LED prototypes were prepared and compared with analogous devices obtained by spin-coating technique. The intimate structure/morphology can readily account for the better performance of LED devices obtained by high-vacuum evaporation. (C) 2004 Elsevier B.V. All rights reserved.