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Topological textures of ferroelectric polarizations have promise as alternative devices for future information technology. A polarization rotation inevitably deviates from the stable orientation in axial ferroelectrics, but local energy losses compromise the global symmetry, resulting in a distorted shape of the topological vortex or inhibiting the vortex. Easy planar isotropy helps to promote rotating structures and, accordingly, to facilitate access to nontrivial textures. Here, we investigate the domain structure of an epitaxial thin film of bismuth tungsten oxide (Bi2WO6) grown on a (001) SrTiO3substrate. By using angle-resolved piezoresponse force microscopy and scanning transmission electron microscopy, we find the existence of a hidden phase with ⟨100⟩-oriented ferroelectric polarizations in the middle of the four variant ⟨110⟩-oriented polarization domains, which assists in the formation of flux closure domains. The results suggest that this material is one step closer to becoming an isotropic two-dimensional polar material.

Organotin halide perovskites are developed as an appropriate substitute to replace highly toxic lead-based hybrid perovskites, which are a major concern for the environment as well as for human health. However, instability of the lead-free Sn-based perovskites under ambient conditions has hindered their wider utility in device applications. In this study, we report a predominantly stable lead-free methylammonium tin bromide (MASnBr3) perovskite that has air stability over 120 days without passivation under ambient conditions. Further, the feasibility of this predominant air-stable MASnBr3perovskite for use in the harvesting of mechanical energy is described with the fabrication of an ecofriendly, flexible, and cost-effective piezoelectric generator (PEG) using MASnBr3–polydimethylsiloxane composite films. The fabricated PEG exhibits high performance along with good mechanical durability and long-term stability. This flexible device reveals a high piezoelectric output voltage of ∼18.8 V, current density of ∼13.76 μA/cm2, and power density of ∼74.52 μW/cm2under a periodic applied pressure of 0.5 MPa. Further, the ability of PEG to scavenge energy from various easily accessible biomechanical movements is demonstrated. The energy generated from PEG by finger tapping is stored in a capacitor and is used to power both a stopwatch and a commercial light-emitting diode. These findings offer a new insight to achieve long-term air-stable Sn-based hybrid perovskites, demonstrating the feasibility of using organotin halide perovskites to realize highly efficient, ecofriendly, mechanical energy harvesters with a wide range of utility that includes wearable and portable electronics as well as biomedical devices.

An environmentally-friendly lead-free methylammonium tin iodide (MASnI3) perovskite is successfully synthesized using a facile approach of an antisolvent-assisted collision technique (ACT) under room ambient conditions, which results stability within 24 h under ambient room conditions. The phase transition of MASnI3from tetragonal to cubic is first observed at ~ 30 °C. Polycrystalline MASnI3films reveal a high dielectric constant of ~ 65 at 100 kHz, a low-leakage current density of 7 × 10−7A cm−2at 50 kV cm−1, well-developed P-E hysteresis loops, and a high piezoelectric coefficient (d33) of 20.8 pm V−1. The MASnI3piezoelectric nanogenerator (PENG) shows an output voltage of ~ 3.8 V and an output current density of 0.35 μA cm−2. To enhance the piezoelectric output performance, the MASnI3films are composited with an environmentally friendly PVDF polymer that had a porous structure. The PVDF-MASnI3composite based-PENG reveals a maximum output voltage of ~ 12.0 V and current density of ~ 4.0 μA cm−2. A green light-emitting diode (LED) using the PVDF-MASnI3PENGs is instantly lighted without need of a storage device, and long-term stability of the composite PENGs is validated for 90 days. This simple and cost-effective solution process is feasible for the fabrication of large-scale, high-performance, and environmental-friendly PENGs based on lead-free organic-inorganic perovskites to extensively implicate in medical and biomechanical applications.

We report a high-performance flexible piezoelectric generator (PEG) that was based on organic-inorganic lead halide perovskite materials and is operated by controlling the dielectric constant via the partial substitution of Pb2+with Fe2+in MAPbI3. The partial replacement of Pb2+with Fe2+improved both the morphology and crystallinity of MAPb1-xFexI3(0.01 ≤ x ≤ 0.50) films that undergo a tetragonal-cubic phase transition above an incorporated concentration of Fe2+(x > 0.07). In addition, the phase transition temperatures of MAPb1-xFexI3(0.01 ≤ x ≤ 0.07) films linearly decreased as a function of incorporated concentration, which resulted in a transition temperature for MAPb1-xFexI3(x = 0.07) of ~ 45.5 ± 1.5 °C. The dielectric properties as a function of incorporated concentration at room temperature suggested that MAPb1-xFexI3(x = 0.07) exhibited a dielectric constant of ~107 and a dissipation factor of 0.02 at 100 kHz. The MAPb1-xFexI3(x = 0.07) films exhibited a low leakage current density of ~ 10−6at a high applied electric field of 40 kV/cm, and the resultant remanent polarization from saturated ferroelectric P-E hysteresis loops was ~ 1.6 µC/cm2. The MAPb1-xFexI3(x = 0.07) flexible PEG improved output performance by ~ 7.29 V and current density by ~ 0.88 µA/cm2after poling at 30 kV/cm. This was sufficient to instantly light a commercial light-emitting diode (LED) without a storage device. This approach provides a framework that enhances the output performance of organic-inorganic metal halide perovskite materials-based piezoelectric energy harvesters, which could help pave the road to viable, self-powered, wearable electronics.