Lead-free soft hybrid materials for piezoelectric sensors: A paradigm shift from toxic lead-based ceramics to sustainable electronics

The development of piezoelectric materials has significantly transformed modern electronic and sensing technologies, and their use has extended from extremely precise actuators to wearable self-powering devices. But the problem is that these materials are commonly made out of lead-based ceramics, and for example, lead zirconate titanate (PZT) contains 60% of lead. Such materials entail great risks to the environment and people's health. This extensive paper elaborates on the evolution of lead-free soft hybrid piezoelectric materials with special emphasis on bismuth iodide-based organic-inorganic hybrids that can be a safe choice of the electronic sensor market of tomorrow. The latest breakthrough research demonstrates that owing to a well-planned halogen bonding between the organic and the inorganic components of the material, there occurs a slight structural instability which in turn opens the way to the improved piezoelectric performance thus making the piezoelectric coefficients comparable to those of commercial PZT with zero toxic lead content (d 3 3 =161.5 pm/V). This review connects developments in sensing mechanisms, material chemistry, crystal engineering, wearable electronics, energy harvesting, and medical implants.