A lead-free flexible structure for piezoelectric power generation

Here, we demonstrate a fully-flexible piezoelectric hybrid structure composed of sodium niobate nanocubes and polyvinylidene fluoride. Hydrothermally-grown sodium niobate nanocubes show an orthorhombic crystal structure with Pmc21 symmetry, and polyvinylidene fluoride is electrically poled for the β-phase, each of those represents piezoelectricity. Hybrid devices were electrically tested in two different modes by applying forces parallel to the in-plane and the out-of-plane directions of the piezoelectric layer. Our device shows an output voltage, current, and power density of 2.9 V, 68 nA, and 4.4 μWcm−3, respectively, at a pushing force of 5 kgf and a frequency of 1 Hz. The output power generation also shows a linear relation with the applied force over a wide range of 1–5 kgf. This implies our flexible hybrid piezoelectric structure can be adapted to various mechanical environments. Our unique structure should open up various application areas of piezoelectric materials such as touch sensors, flexible energy harvesters and eco-friendly piezoelectric actuators.