The Curious Out-of-Plane Conductivity of PEDOT:PSS

For its application as transparent conductor in light‐emitting diodes and photovoltaic cells, both the in‐plane and out‐of‐plane conductivity of PEDOT:PSS are important. However, studies into the conductivity of PEDOT:PSS rarely address the out‐of‐plane conductivity and those that do, report widely varying results. Here a systematic study of the out‐of‐plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. To this end, the PEDOT:PSS is enclosed in small interconnects between metallic contacts. An unexpected, but strong dependence of the conductivity on interconnect diameter is observed for PEDOT:PSS formulations without high boiling solvent. The change in conductivity correlates with a diameter dependent change in PEDOT:PSS layer thickness. It is suggested that the order of magnitude variation in out‐of‐plane conductivity with only a 3‐4‐fold layer thickness variation can quantitatively be explained on basis of a percolating cluster model. Reported measurements of the anisotropy in the conductivity of spin coated films of PEDOT:PSS vary widely. A systematic study of the out‐of‐plane charge transport in thin films of PEDOT:PSS with varying PSS content is presented. It is suggested that the orders of magnitude change in anisotropy can be quantitatively explained on the basis of a percolating cluster model.