Lead-Free Ruddlesden–Popper Double Perovskites for High-Performance and Stable Piezoelectric Sensors

Halide perovskites possess excellent piezoelectric properties, but the toxicity and instability of lead-based systems limit their practical use. Lead-free halide perovskites have emerged as promising alternatives, although their performance remains inferior to that of lead-based counterparts. For example, the halide double perovskite Cs₂AgBiBr₆ offers good air and moisture stabilities but exhibits poor piezoelectric response due to its centrosymmetric structure (space group Fm3̅m). Here, we demonstrated piezoelectricity in low-dimensional lead-free halide double perovskites by introducing barrier molecules within the Ruddlesden–Popper framework to enhance symmetry breaking. Three different organic barriers were employed with the 2D perovskite, while incorporating phenylethylammonium showed the strongest performance. This quasi-2D structure achieved an outstanding piezoelectric coefficient (d₃₃) of 41.04 pm/V, significantly surpassing the 3D Cs₂AgBiBr₆. A piezoelectric pressure sensor fabricated from this material exhibited excellent output linearity, a sensitivity of 23.63 mV/kPa over the range of 2.5–10 kPa, and a rapid response time of ∼28 ms, comparable to conventional PZT-based devices. In addition, these sensors exhibit excellent operational stability for up to 90 days under 70% relative humidity. These results establish low-dimensional, lead-free halide double perovskites as a potential class of high-performance piezoelectric materials, opening pathways toward sustainable, flexible, and soft-sensing technologies.