Single-component light-emitting electrochemical cell with improved stability

We report a single-component polymeric light-emitting electrochemical cell with poly[9,9'-bis[6"-(N, N, N-trimethylammonium)hexyl]fluorene-alt-co-phenylene]bromide (PFN+Br-) as the active material. Indium tin oxide/PFN+Br-/aluminum sandwich structures demonstrate a low and thickness-independent turn-on voltage (2.9 V) for blue light emission. Thermophysical characterization shows that PFN+Br- is in a metastable amorphous phase after spin casting, but that crystallization takes place at elevated temperatures. With this information at hand, we allowed devices to turn-on via ionic redistribution (and the formation of a p-i-n junction) in the amorphous phase, and then stabilized this desired configuration through crystallization. We find significantly improved lifetimes and relatively fast turn-on times for these single-component devices operating at room temperature. (C) 2003 American Institute of Physics.