Transient and DC electroluminescence of some new conjugated polymers

Electroluminescence (EL) of thin and thick polymer films sandwiched between ITO and aluminum electrode was studied under DC or rectangular pulsed voltage. Results are reported for two conjugated ladder type modifications of PPP (having similar band structure properties as PPV) and a non-conjugated polymer consisting of peryelene units. Thermal annealing improves the device properties. The luminescence versus current density follows a power law with exponents between 1.3 and 2 depending on the substance. We have observed a new type of transient EL in organic LED devices with low capacity, namely, sharp peaks of luminescence at the falling and rising edge of the square wave of the applied voltage. The threshold voltage for this type of transient EL is significantly smaller compared to the forward bias of the DC luminescence.