Polymer-based electronics have attracted huge interest due to their wide applicability to light emitting diodes, field effect transistors and photovoltaics. The aim of our experiments is to understand the link between the processing history of the device, its nanoscale interfacial structure and the photophysics at the interface to the final device performance. Here we propose to extend our previous neutron reflectivity studies of conjugated polymer interfaces to a hole transport TFB layer and a light emitting layer. We will use neutron reflectivity to characterise the interfacial width between the light emitting polymer layers of either F8BT or F8 and a deuterated version of TFB for various thermal processing conditions. This interface is of crucial importance since it strongly affects the injection and the recombination of charge in LED devices.