Nanostructured Unsubstituted Polythiophene Films Deposited Using Oxidative Chemical Vapor Deposition: Hopping Conduction and Thermal Stability

Abstract Unsubstituted polythiophene (PT), a promising material that is challenging to process into thin films due to its intrinsic insolubility, can be synthesized and deposited using unique oxidative chemical vapor deposition (oCVD) at room temperature. The conduction mechanism of nanostructured oCVD PT thin films is illuminated through the investigation of in situ conductivity measurements. It is identified that the 3D variable range hopping process governs the transport of charge carriers in oCVD PT thin films with an activation energy of ≈48 meV regardless of doping concentrations. It is also reported that the thermal stability of oCVD PT largely relies on the doping concentration of the material; oCVD PT demonstrates excellent thermal stability at temperatures up to 160 °C with carrier density values lower than ≈1 × 10¹⁷ cm⁻³, while higher doping leads to a reduction in conductivity at T >≈ 100 °C due to electron–hole recombination. X‐ray photoelectron spectroscopy analyses on the change in the concentrations of dopant anions (Cl⁻ and FeCl₄⁻) support the suggested mechanisms.