Conjugated polymer field-effect transistors (FETs) and light-emitting diodes (LEDs) form the basis of new ultra-thin, flexible display technologies. The performance of such devices is critically dependent on the structure of polymer-polymer interfaces. Neutron reflection (NR) has been used to study a number of different types of buried polymer-polymer interfaces to understand how different deposition methods and thermal processing procedures affect device performance. Careful thermal processing allows the roughness of the polymer interfaces found in an LED to be systematically controlled over the range 1 nm - 5 nm (as measured using NR). Increased roughness is strongly correlated with enhancement of the photoluminescence, which can only be explained if significant molecular-level mixing occurs between the two polymers at the interface. In a related study we controlled the roughness at a conjugated polymer / insulating polymer interface by varying solvent quality. This allows us to correlate charge mobility in FETs with the competing effects of interfacial roughness and the molecular packing within the conjugated polymer layer.

SS Chang (Swansea University), AB Rodríguez (University of Sheffield), AM Higgins (Swansea University), C Liu (University of Cambridge), M Geoghegan (University of Sheffield), H Sirringhaus (University of Cambridge), F Cousin (CEA Saclay), R Dalgliesh (ISIS), Y Deng (University of Cambridge)

Research date: December 2008