White emission from organic light emitting diodes based on energy down-convertion mechanisms

Balanced white electroluminescence (EL) emission from binary organic blends was achieved via intermolecular down-convertion processes: the exciplex and the Foerster transfer mechanisms. This was obtained by combining a low electronic affinity (EA) molecule, a diamine derivative (TPD), with two high electronic affinity substituted oligothiophenes having high and low ionization potential (IP), respectively. Both the energy down-convertion mechanisms were exploited in two single active-layer organic light emitting devices, showing stable white emission, independent of the applied voltage.