Spontaneous Formation of Nanofibrillar and Nanoporous Structures in High‐Conductivity Conducting Polymers and Applications for Dye‐Sensitized Solar Cells

High-conductivity and highly electrochemically active poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films with nanofibrillar, nanoporpous, and PEDOT-richer surface structures are spontaneously induced by addition of highly polar, high-boiling-point co-solvent and by repeated solution coating. They are useful as an the effective electrocatalytic layer or a dual-function electrocatalytic/conductive layer in Pt-free/fluorine-doped tin oxide (FTO)-free counter electrodes of dye-sensitized solar cells (DSSCs) and have efficiencies similar to those using Pt/FTO-containing counter electrodes.