Large Curvature Sensors Based on Flexoelectric Effect in PEDOT:PSS Polymer Films

This paper presents the flexoelectric effect in semiconducting polymeric blend (poly(3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT:PSS)) films. Flexoelectricity can be considered as an alternative transduction mechanism to the piezoelectricity to directly detect curvature. It is simply defined as the coupling between the strain gradient and polarization in solid dielectrics and semiconductors. In this study, flexoelectricity in PEDOT:PSS films works on the basis of electrical energy generation induced by dynamic bending. Of particular interest is the phenomenon of polarity change during bending, i.e., the reversal of the polarization direction. In this paper, the procedure to obtain free-standing PEDOT:PSS polymer films for mechanical/electrical bending conversion based on the flexoelectric effect is presented. Here, we report the flexoelectric characterization of 30-μm-thick flexible films of PEDOT:PSS encapsulated between two polyethylene terephthalate (PET) sheets. This characterization reveals a much higher transverse flexoelectric coefficient than those recently reported in the literature for free-standing PEDOT:PSS films with a coefficient that reaches 76 μC/m at 0.5 Hz. It was also demonstrated that it was possible to determine the curvature of the sample up to 62 m –1 through signal acquisition of the current and thus the possibility of using the encapsulated PEDOT:PSS films as a large curvature sensor. Their efficiency in converting a strain gradient into electrical energy, combined with their robustness and flexibility, may open a promising route toward organic semiconductors-based curvature sensors and ambient mechanical energy harvesting devices with large effective flexoelectric coefficients.