Investigations on the Effect of Halide Dopants on the Piezo Response of ZnO-Based Flexible Energy Harvesters

In this letter, we present a unique method to improve the output performance of ZnO-based flexible piezoenergy harvesters (FPEHs). Halide dopants (Cl, Br) are infused into ZnO nanorods (NRs) to increase lattice distortion along the c-axis. This facilitates charge separation, which improves the output performance of halide-doped ZnO FPEHs. This technique confirmed that the size and concentration of the dopants have a significant impact on lattice distortion along the c-axis in halogen-doped ZnO NRs. By doping the halide elements, the lattice distortion along the ZnO c-axis could be tuned from a contractive to an elastic state. This modulation was driven by the variation in ionic size and doping concentration of halide elements, which yielded an enhancement in the performance of ZnO FPEHs. The pristine ZnO NRs exhibited an output voltage of 2.24 V and a current of 272.68 nA, yielding a maximum power of 610.8 nW. In contrast, ZnO:Cl NRs demonstrated a piezoelectric voltage of 3.41 V and a piezoelectric current density of 323.43 nA/cm², reaching a peak power output of 1.1 µW. ZnO:Br NRs exhibited an even higher piezoelectric voltage of 4.55 V and a current of 367.79 nA, achieving a maximum power of 1.67 µW. Further enhancement in piezoelectric performance was observed when the NaBr doping concentration was increased to 20 mM, resulting in a piezovoltage of 4.84 V, a piezoelectric current of 447.63 nA, and a peak power of 2.17 µW. This approach of inducing the lattice distortion via halide dopants could be applied to design piezoelectric devices with improved efficiency at a low cost.