Efficient, visible organic light-emitting diodes utilizing a single polymer layer doped with quantum dots

We demonstrate organic light-emitting diodes (OLEDs) using a single active layer consisting of CdSe/ZnS quantum dots (QDs) dispersed in poly (9,9-dioctylfluorene) (PFO). The diodes have an external quantum efficiency of similar to 0.5% and reach 0.1 A/cm(2) at 6.5 V. These results are comparable to complex, multilayer QD OLEDs. Built-in potential measurements show that the QD valence levels are shifted to lower binding energy when compared to quantum confinement based estimates, and are close to PFO valence levels. Devices using red and green QDs emit predominantly from the QDs but the spectrum of blue QDs is perturbed by interactions with PFO. (C) 2008 American Institute of Physics.