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.