Microscopic Origin of Piezoelectricity in Lead-Free Halide Perovskite: Application in Nanogenerator Design

In this work, we report a lead-free hybrid halide perovskite system with a very high piezoelectric charge density for applications in nanogenerators. We use materials engineering by incorporation of formamidinium tin iodide, FASnI3, in a soft polymer (polyvinylidene fluoride, PVDF) matrix and demonstrate high-performance large-area flexible piezoelectric nanogenerators. This is achieved by using self-poled thin films of a FASnI3:PVDF nanocomposite. The fabricated devices show an output voltage up to ∼23 V and power density of 35.05 mW cm–2 across a 1 MΩ resistor, under a periodic vertical compression, with a release pressure of ∼0.1 MPa. Measured values of the local piezoelectric coefficient (d33) of these films reach up to 73 pm/V. We provide the microscopic mechanism using first-principles calculations, which suggest that a soft elastic nature and soft polar optic phonons are responsible for the high piezoelectric response of FASnI3. Our studies open up a route to high-performance nanogenerators using a lead-free organic–inorganic halide perovskite family of materials.