By using two modes of excitation, optical excitation and current excitation, we have clarified the device physics in operation of multilayer organic light-emitting diodes utilizing poly(methylphenylsilane) as a hole transporting material, focusing on the dynamics of charge carriers injected from electrodes and of excitons generated by the charge carrier recombination.

SIMS depth profiling experiments have been used to elucidate the layered structure, the impurity distribution, and current induced changes in polymeric light emitting diodes (LEDs). In the first investigated system (ITO/PPV/Al), a poly-p-phenylene-vinylene (PPV) layer has been deposited onto an indium/tin oxide (ITO) glass support, and covered by an aluminium top electrode. A well defined aluminium oxide interlayer has been found in between the polymer and the Al overlayer. Furthermore, an enrichment of chlorine has been detected at both electrode-polymer interfaces, a residue from the polymer preparation process. This observation points to a chemical reaction between the electrodes and elimination products that are liberated during the thermal decomposition of the polymer precursor. In the second system, three different polymeric layers have been spin-coated onto an ITO substrate, i.e. a pure poly-methylphenylsilane (PMPS) layer, a second PMPS layer doped with an organic dye, and finally a polystyrene (PS) layer containing an oxadiazole derivative. By the addition of a bromine containing label into the first layer, it can be shown that the two PMPS layers have been diffusing into each other, whereas the PMPS and the PS regions have remained well separated. As found with the single layer devices, the formation of an interfacial oxide layer between the PS layer and the Al top electrode has been observed. Investigations of driven multilayer LEDs have provided evidence for drastic current-induced degradation effects.

We have investigated the optical and electrical properties of polysilane-based multilayer electroluminescent (EL) devices, utilizing poly(methylphenylsilane) (PMPS) as the hole transporting material, in order to elucidate the mechanism of EL emission in these devices. The EL devices which we fabricated have two or three functional organic layers. These layers are composed of a PMPS layer as well as a 3-(2′-Benzothiazolyl)-7-diethylaminocoumarin (Coumarin 6) doped polystyrene (PS) layer and/or a tris-(8-hydroxyquinoline) aluminum (Alq3) layer. An indium-tin-oxide-coated glass and an Al electrode were used as the hole and the electron injecting electrode, respectively. On the basis of a combined analysis of the basic characteristics of these devices, photoexcited fluorescence spectra and decay curves as well as the band diagram of these devices, we concluded that the recombination of charge carriers and the EL emission in the three-layer device occur both in the Coumarin 6:PS and the evaporated Alq3 layers.

The fabrication of high‐efficiency light‐emitting diodes (LEDs) based on sublimed molecular films has attracted much attention in the search for materials for application in large‐area flat‐panel displays. Here, multilayered LEDs based on poly(methylphenylsilane), PMPS, as the hole transporting material are reported (see Figure). In contrast to polyphenylenevinylene, PMPS films exhibit a high effective mobility of holes, making the material suitable for fast switching applications. magnified image