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 highperformance large-area flexible piezoelectric nanogenerators. This is achieved by using self-poled thin films of a FASnI 3 :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 (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 nanogenerators using a lead-free organic−inorganic halide perovskite family of materials.