INTERFERENCE PHENOMENA IN POLYMER LIGHT-EMITTING-DIODES - PHOTOLUMINESCENCE AND MODELING

We report an experimental and theoretical study of the effects of inte rference in polymeric light-emitting diodes (LEDs). These effects art: due to the complex optical structures of the devices, which include m any layers of materials with different refractive indices, and are of considerable importance since they affect spectral distribution and in tensity of the absorption and emission in a significant way. By way of comparison, they can also provide a flexible, noninvasive optical pro be of the electroluminescent processes, such as, for example, the spat ial distribution of the recombination inside the LED. in this paper we analyse single-layer diodes with indium-tin oxide (ITO) and Al electr odes, where poly(p-phenylene vinylene) (PPV) is the luminescent polyme r. We find that photo-induced excitation of the radiative species prod uce different spectral shapes depending on the excitation energy (and hence on the profile of excited chromophores) which we can describe in terms of interference phenomena, The theoretical analysis is conducte d by means of multilayer stack theory and transfer matrix calculations , and takes into account additional quenching effects due to In contam inations from the ITO electrode. The theoretical results are in good a greement with the experiment. (C) 1998 Elsevier Science B.V.