Opportunity
Wearable electronics demand power sources that are flexible, lightweight, high-capacity, durable, and comfortable for daily use. These power sources enable applications in electronic skins, self-powered sensing, and physiological health monitoring. Although batteries and supercapacitors offer stability and efficiency, their lifespan, rigidity, size, encapsulation, and safety concerns limit their use. Triboelectric nanogenerators (TENGs) provide a promising solution for self-powered technology by harvesting mechanical energy from raindrops, wind, tidal energy, and human movements such as running, walking, and finger bending. The output performance of TENGs is highly influenced by the inherent properties of the triboelectric materials. Polyvinylidene fluoride (PVDF) and its copolymers like PVDF-HFP are used for their mechanical flexibility, biocompatibility, chemical stability, and electronegativity. Electrospinning these polymers into fibrous membranes enhances breathability and wearability while promoting the formation of the highly polarized β-phase, which acts as the working dipole to improve TENG performance. Conventional strategies to increase β-phase content involve blending with carbon nanotubes, metal nanoparticles, graphene, or semiconducting perovskites. However, most existing studies focus on lead-based halide perovskites, which are toxic to human health and the environment. Moreover, nanofillers often lead to nonuniform dispersion and mixed anisotropic crystallinity containing different phases (α, β, and γ), causing charge loss at crystal interfaces and limiting performance improvement. Therefore, increasing β-phase content and controlling its uniaxial orientation remains a critical challenge. There is a need for improved TENGs that address these issues.
Technology
The patent discloses core-shell nanofibers comprising a core of Cs₂InCl₅(H₂O) perovskite nanocrystals and a shell of an electroactive polymer such as PVDF-HFP. These nanofibers are fabricated by a one-step electrospinning-assisted self-assembly strategy. The lead-free Cs₂InCl₅(H₂O) acts as an inducer, promoting β-phase-enhanced and self-aligned nanocrystals along the uniaxial fiber direction. This enables the transformation of the nonpolar α-phase, which has randomly oriented dipoles, into a polarized β-phase with uniform dipoles oriented by the fiber direction. The interface interaction, investigated by experimental measurements and molecular dynamics, reveals that hydrogen bonds form between the hydroxyl groups of Cs₂InCl₅(H₂O) and the fluorine moieties of PVDF-HFP. This hydrogen bond network induces automatically well-aligned dipoles and stabilizes the β-phase. Under the electric field during electrospinning, the O–H bonds and –F groups become oppositely charged, forming stable directional O–H···F hydrogen bonds. The interacting network emerges to form the core, while non-interacting PVDF-HFP migrates to the surface due to its low surface energy, forming a continuous shell. The constant tensile force uniaxially stretches the polymer chains, further enhancing dipole alignment. The resulting CIC@HFP nanofibers exhibit an electroactive phase content of up to 81.25%, significantly higher than pure PVDF-HFP (65.9%). A TENG fabricated using these nanofibers with nylon 6,6 as the opposite triboelectric layer achieves an output voltage of 681 V, output current of 53.1 μA, and peak power density of 6.94 W m⁻², the highest reported output voltage among halide-perovskite-based TENGs. The device also demonstrates excellent mechanical durability, with no performance decay after 10,000 cycles.
Advantages
- Lead-free and biocompatible perovskite nanocrystals avoid toxicity concerns.
- One-step electrospinning method is simple and scalable.
- Core-shell structure protects humidity-sensitive perovskite nanocrystals, achieving good humidity resistance.
- High β-phase content (up to 81.25%) dramatically enhances triboelectric output.
- Uniaxial orientation of dipoles minimizes charge loss at crystal interfaces.
- Superior mechanical properties (breaking strength 14.2 MPa) and breathability (WVTR >18.0 kg m⁻² d⁻¹).
- Excellent long-term cyclic stability (no decay after 10,000 cycles).
- Biocompatible and suitable for wearable applications.
Applications
- Biomechanical energy harvesting (e.g., walking, finger bending, wrist and elbow movements).
- Self-powered physiological monitoring (e.g., breathing, swallowing, joint motion detection).
- Powering portable electronics (e.g., LEDs, stopwatches, calculators).
- Wearable self-powered sensing systems for health monitoring.
- Environmental energy harvesting (e.g., raindrops, wind, tidal energy).
