Structure−property correlations of two electroactive polymer bilayers fabricated by different methods are investigated using neutron reflectivity to probe the buried polymer/polymer interfaces. Both bilayers utilize electropolymerized poly(2,2‘-bithiophene) as an inner, mediating layer, while the outer layer consists of either electropolymerized polypyrrole or electroprecipitated polyxylylviologen, respectively. These devices have very different current−potential behaviors, which neutron reflectivity shows is a consequence of the fabrication method and the resulting polymer/polymer interfacial structure. The polybithiophene/polypyrrole film is found to be of composite structure while polybithiophene/polyxylylviologen forms a film comprised of segregated polymer layers.