Halide Tunablility Leads to Enhanced Biomechanical Energy Harvesting in Lead-Free Cs₂SnX₆-PVDF Composites

The main challenges impeding the widespread use of organic-inorganiclead halide perovskites in modern-day technological devices are theirlong-term instability and lead contamination. Among other environmentallyconvivial and sustainable alternatives, Cs2SnX6 (X = Cl, Br, and I) compounds have shown promise as ambient-stable,lead-free materials for energy harvesting, and optoelectronic applications.Additionally, they have demonstrated tremendous potential for thefabrication of self-powered nanogenerators in conjunction with piezoelectricpolymers like polyvinylidene-fluoride (PVDF). We report on the fabricationof composites constituting solvothermally synthesized Cs2SnX6 nanostructures and PVDF. The electroactive phasesin PVDF were boosted by the incorporation of Cs2SnX6, leading to enhanced piezoelectricity in the composites.First-principles density functional theory (DFT) studies were carriedout to understand the interfacial interaction between the Cs2SnX6 and PVDF, which unravels the mechanism of physisorptionbetween the perovskite and PVDF, leading to enhanced piezoresponse.The halide ions in the inorganic Cs2SnX6 perovskiteswere varied systematically, and the piezoelectric behaviors of therespective piezoelectric nanogenerators (PENGs) were investigated.Further, the dielectric properties of these halide perovskite-basedhybrids are quantified, and their piezoresponse amplitude, piezoelectricoutput signals, and charging capacity are also evaluated. Out of theseveral films fabricated, the optimized Cs2SnI6_PVDF film shows a piezoelectric coefficient (d (33)) value of & SIM;200 pm V-1 and a remanentpolarization of & SIM;0.74 & mu;C cm(-2) estimatedfrom piezoresponse force microscopy and polarization hysteresis loopmeasurement, respectively. The optimized Cs2SnI6_PVDF-based device produced an instantaneous output voltage of & SIM;167V, a current of & SIM;5.0 & mu;A, and a power of & SIM;835 & mu;Wacross a 5 M & omega; resistor when subjected to periodic vertical compression.The output voltage of this device is used to charge a capacitor witha 10 & mu;F capacitance up to 2.2 V, which is then used to powersome commercial LEDs. In addition to being used as a pressure sensor,the device is employed to monitor human physiological activities.The device demonstrates excellent operational durability over a spanof several months in an ambient environment vouching for its exceptionalpotential in application to mechanical energy harvesting and pressuresensing applications.