First evidences of the flexoelectric responses of PEDOT-PSS polymers

National audienceThe project concerns the field of electroactive polymer films intended to ensure a mechanical to electrical energy conversion. The transduction mechanism considered is the flexoelectric effect, which corresponds to the appearance of an electric polarization induced by a deformation gradient (equal to the curvature) This effect that is different from piezoelectricity is present in all the dielectric (insulator) solids [1]. However, a recent study [2] about flexoelectric effect in oxide thin films revealed a three orders of magnitude enhancement of the effective flexoelectric coefficient accompanied by a large increase in the dielectric constant, after the insulating oxide has been reduced to a semi-conducting sample. Thus, the main objective of the present study is to explore the flexoelectric responses of organic (semi)-conductor films. As a first step films of poly (3, 4-ethylenedioxythiophene- poly (styrene sulfonate) (PEDOT-PSS) have been studied. PEDOT-PSS is a classical conducting polymer used in the elaboration of optoelectronic devices [3].In this way, various commercially available PEDOT-PSS polymer solutions have been deposited by drop casting on stainless steel substrates with different volumes leading to varied polymer thicknesses (µm range). Polymer films were covered with aluminum top electrodes up to 100 nm in thickness using a metal evaporator) and the complex permittivity and conductivity were measured to possibly establish a correlation with the flexoelectric coefficient. This latter has been obtained by current output and deflections measurements of bending cantilever-shaped samples using the lab setup showed in fig.1.1.Merupo, V.I., et al., Flexoelectric response in soft polyurethane films and their use for large curvature sensing. Journal of Applied Physics, 2017. 122(14): p. 144101.2. J. Narvaez, F. Vasquez-Sancho, and G. Catalan, Enhanced flexoelectric-like response in oxide semiconductors. Nature, Sep. 2016. 538: p. 219.3.Kirchmeyer, S. and K. Reuter, Scientific importance, properties and growing applications of poly(3,4-ethylenedioxythiophene). Journal of Materials Chemistry, 2005. 15(21): p. 2077-2088