DC and transient electroluminescence of some new conjugated polymers

Summary form only given. Electroluminescence (EL) of polymer films sandwiched between ITO and aluminum electrodes is reported for several polymers including ladder type modifications of PPP, a partially conjugated polymer based on polyimide and PPV. The EL was studied as a function of film thickness under DC or rectangular pulsed voltage. The emphasis here is on the basic understanding of the EL characteristics as a function of the polymer properties (mobility, gap, etc.) and the metal/ polymer contact. We found that after annealing of the cells the EL versus the current density follows a power law with exponent between 1.3 and 2 depending on the type of polymer. Attempts to understand the I versus V curves by conventional models for Schottky and/or tunneling barriers gives significantly lower barrier heights. For cells with thick polymer films we have observed short EL pulses upon applying a rectangular voltage pulse even far below the threshold voltage; the shape of the EL peaks is proportional to the first derivative of the voltage pulse. These features may be explained by simple models. This work was supported by a research fund donated by VW.