Interfacial structure in conjugated polymers:: Characterization and control of the interface between poly(9,9-dioctylfluorene) and poly(9,9-dioctylfluorene-alt-benzothiadiazole)

Specular neutron reflectivity and nuclear reaction analysis (NRA) are used to measure the interfacial width between poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) in a 500 nm bilayer. Annealing at temperatures up to 280 degrees C allows us to vary this width over a large range, from similar to 1 nm to greater than 30 nm. Approximate calculations using the predictions of self-consistent field theory (SCFT) for both Gaussian and semiflexible chains suggest that in the liquid-liquid regime the Gaussian results of SCFT are valid for this system. We also demonstrate the ability to control the interfacial width in 100 nm bilayers, on both silicon and indium tin oxide (ITO). The procedure of "preannealing" the F8 and F8BT layers, before bringing them together to make a bilayer, allows us to independently control the interfacial width and the properties of the bulk of these 100 nm films.