Development of porous ZnO thin films for enhancing piezoelectric nanogenerators and force sensors

The applications of piezoelectric nanogenerators (PENGs) as a sustainable power source for portable electronic devices are still limited due to low voltage output ranging from mini- to several volts. In this study, we first develop a porous ZnO structure by annealing (650–950 °C) sputtered ZnO thin film. The porous ZnO thin film enables a significant enhancement in the output voltage of primitive PENG (up to 3 mV), i.e., by 7.5 times than that of pristine ZnO (0.4 mV). Concurrently, the introduction of pores in ZnO thin films leads to a 6.9-fold enhancement in the sensitivity of piezotronic force sensor compared to the pristine one. These excellent performances are further supported by up to two-fold enhancement in the piezoelectric coefficient (2.62 pm/V) than that of pristine ZnO (1.12 pm/V). Herein, we conducted transmission electron microscopy characterizations and found that this phenomenon can be ascribed to the lattice contraction in the c-direction induced by the pores. The diffusion-controlled pore formation mechanism is elucidated. [Display omitted] •Investigation of porous ZnO thin film based piezotronic pressure sensorand piezoelectric nanogenerator.•Large boost in sensitivity of pressure sensor and output voltage in piezoelectric nanogenerator.•Piezoelectric coefficient is increased from 1.03 pm/V in pristine ZnO to 2.57 pm/V for porous ZnO thin film.•C-axis lattice contraction caused from pores are scrutinized through extensive TEM works.•Detail pore formation mechanism is illustrated.