Layer-by-layer assembly of poly(3,4-ethylenedioxythiophene):: Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

Ultrathin films of the conducting polymer system PEDOT: PSS, poly(3,4-ethylenedioxythiophene): poly( styrenesulfonate), were fabricated through layer-by-layer assembly with PAH, poly( allylamine hydrochloride). A variety of grades of PEDOT: PSS were used to study the effects of the PEDOT to PSS weight ratio and particle size on the assembly behavior. All systems studied exhibited linear film-growth behavior as indicated by film thickness and UV-vis absorption measurements. Assembly of grades with a relatively small proportion of PEDOT to PSS behaved similarly to PSS/PAH bilayer films fabricated from pristine components. Grades with a higher proportion of PEDOT resulted in thicker bilayers, primarily due to the incorporation of more PEDOT into the film. When compared to their spin-coated analogues, layer-by-layer assembled films incorporated a smaller amount of PEDOT with respect to the PSS. This is highly suggestive of partial decomplexation of the PEDOT from the PSS during the assembly process. Surprisingly, the percent of decomplexation is estimated to be just over 50% for all of the grades studied. That is, slightly less than half of the PEDOT originally present in solution is incorporated into the layer-by-layer film, independent of both the PEDOT: PSS particle size and weight ratio. The combination of this depressed level of PEDOT together with the incorporation of PAH into the film results in the conductivity of the layer-by-layer films being similar to 1 order of magnitude less than that for spin-coated films of the same grade.