Piezoresistive Sensors from Bithiophene-fulleropyrrolidine Bisadducts Thin-Films

The phenomenon of piezoresistivity in materials is based on the separation of conductive domains triggered by mechanical strains, resulting in a variation of the electrical resistance.1 This property is at the core of sensors for wearable electronics, e-skins, human motion detectors and machine learning devices.2 Fundamental requirements include lightness, good transparency, high flexibility and sensitivity to tiny deformations. However, the fabrication of a system integrating all these features is challenging. Herein, we show a semitransparent piezoresistive sensor realized by an electropolymerized bithiophene‐fulleropyrrolidine bisadduct onto ITO/PET3 (see Figure 1a). The good outcome of the electrodeposition was confirmed by cyclic voltammetry and optical techniques. AFM investigation highlights a thin-film morphology characterized by a network of nanosized globular grains, wherein the grain-to-grain separation depends on the bending strain (see Figure 1b). The resulting discontinuity triggers piezoresistive mechanism, in accordance with reported models.4 The ΔR/R0 variation of the piezoresistive device is measured by a motorized hinge as a function of the bending angle in the range 0°-90°, showing good detection repeatability, high sensitivity at small bending angles (10°‐30°) and saturation at angles > 40°. Preliminary tests carried out with a different fulleropyrrolidine bisadduct will be shown. The polymeric piezoresistive sensors shown in this work are a first step towards the applications of fullerene-based materials in bending sensors.