Observation of piezoelectricity in a lead-free Cs2AgBiBr6 perovskite: a new entrant in the energy harvesting arena

Halide perovskite materials have recently been recognised as powerful ferroelectric and piezoelectric materials with applications in the energy harvesting arena, but their experimental proof is very limited. We achieved strong intrinsic piezoelectricity in the lead-free inorganic double perovskite Cs₂AgBiBr₆ at room temperature and utilized it for mechanical energy harvesting, with a piezoelectric co-efficient (d₃₃) of 12.7 pC N^-1. Hysteresis loop and structural analyses offered further validation for the substantial ferroelectric features of the as-synthesised double perovskite. Density functional theory (DFT) calculations revealed the presence of anharmonic phonon soft modes in tetragonal Cs₂AgBiBr₆ due to dynamic instability, which resulted in piezoelectricity. Under an optimal pressure of ≈25 kPa, a Cs₂AgBiBr₆ thin film-based piezoelectric nanogenerator device delivered instantaneous output values of ≈45 V and ≈200 nA. The strain-sensitive responses of the device were also exemplified to identify specific body motions from the detected instantaneous output values. The energy obtained from the device is shown to be effective for capacitor charging and commercial light-emitting diode (LED) lighting. Our study provides significant insights into the dielectric behaviour of materials as well as piezo- and ferroelectric behaviours, which are crucial for the development of modern electronic and energy harvesting devices.