White light electroluminescence in zinc sulfide: polyflourene blends

We document white light emission from ZnS:Cu–PFO blend in the device structure involving indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS)/ZnS–poly(9,9‐dioctylfluorene) (PFO)/Al layers, with varying ZnS:Cu dopant concentrations in the PFO matrix. We observe that with the increase in the ZnS:Cu dopant concentration in PFO from 1 to 10 wt%, the turn‐on‐voltage shifts from 7 V to 4 V. Initial brightness of the device with 1 wt% doping is 30 cd/m2 at 7 V and 40 cd/m2 at 9 V. For a 10‐wt% ZnS:Cu–PFO blend, luminescence up to 25 cd/m2 at 4 V is achieved. The broad spectral feature in electroluminescence is attributed to the partial energy transfer from PFO to ZnS:Cu, due to π–π*, n–π*, and CT–(π–π*) transitions arising out of polyfluorene–polyfluorenone chromophores. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)