Metal‐halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal‐free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light‐weight, and low‐cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal‐free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal‐halide, metal‐free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal‐free perovskites are highlighted for their future developments.
Smart fabrics that can harvest ambient energy and provide diverse sensing functionality via triboelectric effects have evoked great interest for next‐generation healthcare electronics. Herein, a novel borophene/ecoflex nanocomposite is developed as a promising triboelectric material with tailorability, durability, mechanical stability, and flexibility. The addition of borophene nanosheets enables the borophene/ecoflex nanocomposite to exhibit tunable surface triboelectricity investigated by Kelvin probe force microscopy. The borophene/ecoflex nanocomposite is further fabricated into a fabric‐based triboelectric nanogenerator (B‐TENG) for mechanical energy harvesting, medical assistive system, and wound healing applications. The durability of B‐TENG provides consistent output performance even after severe deformation treatments, such as folding, stretching, twisting, and washing procedures. Moreover, the B‐TENG is integrated into a smart keyboard configuration combined with a robotic system to perform an upper‐limb medical assistive interface. Furthermore, the B‐TENG is also applied as an active gait phase sensing system for instantaneous lower‐limb gait phase visualization. Most importantly, the B‐TENG can be regarded as a self‐powered in vitro electrical stimulation device to conduct continuous wound monitoring and therapy. The as‐designed B‐TENG not only demonstrates great potential for multifunctional self‐powered healthcare sensors, but also for the promising advancements toward wearable medical assistive and therapeutic systems.
Single crystal metal-free halide perovskites have received great attention in recent years owing to their excellent piezoelectric and ferroelectric properties. However, the nanotoxicity and piezoelectricity within the nanoscale of such materials have yet been reported for the demonstration of practical applications. In this work, the observation of intrinsic piezoelectricity in metal-free perovskite (MDABCO-NH 4 I 3 ) films using piezoresponse force microscopy (PFM) is reported. A cytotoxicity test is also performed on MDABCO-NH 4 I 3 to evaluate its low-toxic nature. The as-synthesized MDABCO-NH 4 I 3 is further integrated into a piezoelectric nanogenerator (PENG). The MDABCO-NH 4 I 3 -based PENG (MN-PENG) exhibits optimal output voltage and current of 15.9 V and 54.5 nA, respectively. In addition, the MN-PENG can serve as a self-powered strain sensor for human-machine interface applications or be adopted in in vitro electrical stimulation devices. This work demonstrates a path of perovskite-based PENG with high performance, low toxicity, and multifunctionality for future advanced wearable sensors and portable therapeutic systems.
One of the most interesting structural features of multiwall carbon onions (MWCNOs) and nanotubes (MWCNTs) is the excellent chemical stability, which allows in-situ encapsulation of chosen magnetic materials of interest...
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