Shear Piezoelectricity and Electromechanical Conversion for a Pair of Chiral Hybrid Metal Halides with Reversible Phase Transition

Organic-inorganic hybrid metal halide piezoelectrics have gathered considerable interests due to its excellent piezoelectric output performance and remarkable structural flexibility, making them suitable for smart integrated application such as wearable devices and implantable medical instruments. However, constructing the multifunctional piezoelectrics still face great challenge. Here, a pair of zero-dimensional chiral hybrid metal halide piezoelectrics, R-/S- MPCoCl4 (R-/S- MP = 2-methylpiperazine), are reported and studied their piezoelectric energy harvesting and human motion sensing properties. Density functional theory (DFT) calculations demonstrate that this chiral piezoelectric material possesses relatively low elastic modulus (E = 11.2-20.9 GPa) and high piezoelectric constant (10.5 pC·N-1). Subsequently, R-/S- MPCoCl4/PBAT (PBAT = poly(butylene adipate-co-terephthalate) piezoelectric thin-film devices prepared via composite processing exhibit outstanding piezoelectric output performance. The piezoelectric device with 10 wt.% R-/S- MPCoCl4 content shows optimal output properties, achieving an open-circuit voltage of 7.9 V and power density of 0.1 µW·cm-2, while maintaining stable performance after 4500 cycles. Furthermore, the device shows highly sensitive sensing capabilities for human movements, enabling real-time detection of subtle mechanical signals. These chiral hybrid metal halides, leveraging the synergistic advantages of flexibility and piezoelectric performance, show significant application potential in intelligent wearable systems and biomedical sensors.