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, FASnI(3), 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 FASnI(3):PVDF nano-composite. The fabricated devices show an output voltage up to similar to 23 V and power density of 35.05 mW cm(-2) across a 1 M Omega resistor, under a periodic vertical compression, with a release pressure of , similar to 0.1 MPa. Measured values of the local piezoelectric coefficient (d(33)) 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 FASnI(3). Our studies open up a route to high-performance organic-inorganic halide perovskite family of materials.