Wall Effect for Film Formation on Thermoelectric Properties of Poly(3,4-Ethylenedioxythiophene)/poly 4-Styrenesulfonate (PEDOT/PSS) Films

Previously, when poly(3,4-ethylenedioxythiophene)/poly 4-styrenesulfonate PEDOT/PSS films were treated with an organic solvent just once, a power factor (PF) of 60 μW/mK² or less was achieved. In the present study, we found a unique and simple film formation process that improves Seebeck coefficients for free-standing thick films (~5μm), utilizing a wall during immersing the PEDOT/PSS in MeOH, followed by drying at 130-180°C. Exactly, this process increased the Seebeck coefficient to over 30 μV/K compared to the 21 μV/K of flat PEDOT/PSS films formed on a glass substrate without a wall. Using this simple process, we obtained a maximum PF of 126 μW/mK². X-ray diffraction analysis revealed that widening of the (100) interplanar spacing, while maintaining a narrow (010) spacing, was associated with simultaneous increases in electrical conductivity and the Seebeck coefficient. By assuming energy filtering between PEDOT particles with different work functions, we modeled the Seebeck coefficient and conductivity by varying the fractions of three phases: a conductive phase, a much higher-conductivity phase with a higher work function capable of energy filtering, and a low-conductivity phase with a low Seebeck coefficient. The calculated results were consistent with the experimental results.