Flexible organic piezoelectric nanogenerator with high power density and excellent ferroelectric and memristor characteristics

Abstract

Organic materials have attracted huge interest over inorganic materials for their low toxicity, high flexibility, low cost, and appreciable ferroelectric and piezoelectric properties. Herein, we investigated the case of a single-component azobenzene derivative, which exists in polymorphic forms with non-centrosymmetric (polar) and centrosymmetric space groups. The polar form exhibited a low coercive field (6.5 kV/cm) and a high spontaneous polarization (9.7 μC/cm²), comparable to that estimated via quantum chemical calculation. Its unprecedented resistive switching behavior at a low operation voltage and a stable retention time up to 4500 s confirms its memristor characteristics. Further, this lightweight material exhibited an excellent piezoelectric coefficient of 66.5 pm/V, and the fabrication of a highly flexible piezoelectric nanogenerator yielded a high maximum output voltage of ~5.7 V and a peak power density of 2.48 µW/cm2. The device charging using a 22 µF capacitor resulted in storage of charge and energy as high as ~40.5 µC and ~37 µJ, respectively, within 35 seconds. Further, this material exhibited a low bandgap of 1.94 eV, suggesting its photovoltaic characteristics. These excellent figures of merit suggest that this azobenzene with multifunctional properties is an exceptional memory and energy harvester, and it may find applications in next-generation low-power smart electronic devices.