High-temperature workable flexible piezoelectric energy harvester comprising thermally stable (K,Na)NbO₃-based ceramic and polyimide composites

Composite-based piezoelectric devices have been widely investigated to realize a semi-permanent power supplier or self-powered sensors with high flexibility; however, their working temperatures are mostly restricted below 200 °C. Herein, we report high-temperature and flexible composite-based piezoelectric energy harvesters (f-PEHs) comprising lead-free (K,Na)NbO₃ (KNN)-based ceramic dispersants and polyimide matrix. The KNN-based ceramics with different BiScO₃ (BS) compositions of 0.0025 and 0.01 were synthesized via a solid-state reaction and characterized under high-temperature conditions. Thereafter, the output voltage, current signals, and effective power of f-PEHs with 0.0025BS- and 0.01BS-doped KNN-based particles were measured at the temperature range from room temperature (RT) to 300 °C. The 0.0025BS KNN-adopted f-PEH not only generated 130% higher output voltage (∼4 V) and 137% higher current (∼0.24 μA) than the device with 0.01BS-doped KNN at RT, but also has superior electrical outputs compared to those harvested from the 0.01BS KNN-adopted f-PEH over all temperature ranges. These measurement results corresponded well with the trend of change in piezoelectric voltage constants and piezoelectric figure of merit characterized from ceramic discs, respectively. Moreover, theoretical and quantitative analyses using finite element method simulations proved that 0.0025BS is more suitable for the fabrication of high-temperature f-PEH compared to 0.01BS. This work can serve as a guide for developing a fully flexible and high-temperature workable f-PEH to realize self-powered sensor systems in high-temperature environments.