EFFECTS OF DOPING IN POLYMER LIGHT-EMITTING-DIODES

We observed a dramatic improvement in the performance of polymer light-emitting diodes (LEDs) upon light doping of the organic layer. The LEDs betrayed symmetrical electrical and light-emission characteristics. Their turn-on voltage is lower and their external quantum and power conversion efficiencies are higher by nearly an order of magnitude when compared with devices that utilized a nominally undoped organic layer. We attributed these results to the modification of the tunneling barrier in metal-polymer-metal junctions due to the presence of an induced polarization electric field associated with the ionized dopant counterions and charged polymer chains. (C) 1995 American Institute of Physics.