Single-component light-emitting electrochemical cell with improved stability

We report a single-component polymeric light-emitting electrochemical cell with $\mathrm{poly}{\text{[9,9}}^{\prime }-\mathrm{bis}{\text{[6}}^{″}\mathrm{-(N,N,N-}\mathrm{trimethylammonium})\mathrm{hexyl}]\mathrm{fluorene}\mathrm{-alt-co-}\mathrm{phenylene}]\mathrm{bromide}$ $({\mathrm{PFN}}^{+}{\mathrm{Br}}^{-})$ as the active material. Indium tin ${\mathrm{oxide/PFN}}^{+}{\mathrm{Br}}^{-}/\mathrm{aluminum}$ sandwich structures demonstrate a low and thickness-independent turn-on voltage (2.9 V) for blue light emission. Thermophysical characterization shows that ${\mathrm{PFN}}^{+}{\mathrm{Br}}^{-}$ 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 $\mathrm{p–i–n}$ 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.