Remarkably enhanced piezoelectric and ferroelectric characteristics of Er: ZnO upon graphene addition for wearable self-powered piezoelectric sensors

Flexible Er-ZnO/PDMS and Er-GO/ZnO/PDMS nanogenerators with high energy harvesting performance were developed. The output voltage and current density of Er-doped ZnO, Er-doped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanocomposites-based piezoelectric harvesters were (70 V, 1.85 mu Acm(-2)), (80 V, 2.16 mu Acm(-2)) and (100 V, 2.47 mu Acm(-2)), respectively. The Er-doped GO/ZnO wearable sensor showed output voltages of 4 V and 9 V by bending the human wrist and elbow, respectively. In addition, a remarkable improvement of the remnant polarization (Pr) and a favourable reduction of the coercive field (Ec) were achieved for Er-doped ZnO and Er-doped GO/ZnO nanocomposites. The corresponding values of Pr and Ec for pure ZnO, Er-doped ZnO, Erdoped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanostructures were (0.06 mu C/cm(2), 6.50 kV/cm), (8.75 mu C/cm(2), 4.74 kV/cm), (13.25 mu C/cm(2), 3.98 kV/cm) and (8.913 mu C/cm(2), 3.54 kV/cm), respectively. The enhanced piezoelectric and ferroelectric properties of Er-doped ZnO and Er-doped GO/ZnO nanocomposites make them futuristic hybrids with immense potential for designing pressure biosensors, mechanical energy harvesters and environmentally friendly ferroelectric-based memory devices.