Structure of films of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) crosslinked with glycerol

We show that films of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) crosslinked with glycerol function well as hole injection layers for light-emitting diodes even after immersion in water. Neutron reflectometry, X-ray photoelectron spectroscopy, and nuclear reaction analysis are used to characterise the structure of these layers. The glycerol at a moderate concentration of 5% (w/v) provides the best performance when used as a part of a light-emitting diode, but larger quantities impact adversely on device quality. Glycerol is shown to be present in considerable quantities in the film, at ∼13% by volume at the surface. No significant surface segregation of any component is observed in these films, although poly(3,4-ethylene dioxythiophene) is absent from the surface.