Piezoelectric Paper Energy Harvesters Based on Microwave-Assisted Grown ZnO Rods

The growing energy demand, combined with the rising volume of e-waste, demands an urgent search for sustainable energy-harvesting devices. Among the several energy sources, mechanical energy is the most explored due to its abundance. In this context, piezoelectric energy harvesters have great potential, as they leverage the synergy between tribo- and piezoelectric effects to convert mechanical into electrical energy with high efficiency. Herein, the potential of sustainable materials to produce paper-based energy harvesters is explored. Specifically, paper is used as both active layer and substrate and the response of devices based on this material in different forms (pristine, embedded with matrices of cellulose derivatives and embedded with composites of hydrothermally synthesized one-dimensional zinc oxide—ZnO—particles and polymeric matrices) is evaluated. Different architectures were studied, namely the active layer sandwiched between two commercial electrodes and devices based on paper substrates with screen-printed silver electrodes. Among these, a maximum output of (3.5 ± 0.8) V was obtained with devices based on Whatman paper embedded with ZnO/ethylcellulose nanocomposites sandwiched between commercial electrodes, and the same active layer with screen-printed electrodes yielded an output voltage of (0.29 ± 0.01) V, for an impact force of 10 N. The present results thus represent a promising avenue for the development of sustainable devices, paving the way for eco-friendly, cost-effective and versatile energy-harvesting technologies.