| Abstract: | To fully exploit the properties of light‐emitting polymers (LEPs) in electroluminescent applications, it is of paramount importance to develop efficient electrical contacts. An ideal electrode is highly conductive, stable, provides a low barrier to carrier injection, and does not degrade the LEP upon contact. It is difficult to find a single homogeneous material that satisfies all of these requirements. Hence, contact optimization has often required the development of multilayer structures. In particular, indium tin oxide covered by a film of poly(ethylene‐dioxythiophene):poly(styrene sulfonic acid) {ITO/PEDOT:PSS} has become a favorite combination for the transparent anode, and heterostructures of LiF and CsF with metals (Al and Ca) have proven to be efficient electron‐injecting contacts. Here we review our progress in the understanding of the operation of light‐emitting diodes incorporating such contacts, in particular by gauging the materials' energy‐level lineup via electroabsorption measurements. Among the series of LEDs investigated, using a high‐energy‐gap blue polyfuorene polymer, CsF/Ca/Al and LiF/Ca/Al electrodes lead to the best improvements in electron injection. The most promising performance for applications, where a high luminance (～1600 cd/m2 at 5 V) is also accompanied by a high maximum efficiency (～3 lm/W), was obtained with LiF/Ca/Al cathodes and ITO/PEDOT:PSS anodes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2649–2664, 2003 |
