Giant Reversible Piezoelectricity from Symmetry-Governed Stochastic Dipole Hopping

Organic–inorganic hybrid perovskites with giant piezoelectric responses, exemplified by TMCM-CdCl${}_3$, represent a promising platform for flexible and environmentally friendly electromechanical materials. However, the microscopic origin of such exceptional performance in this weakly polar system has remained elusive. Here, using deep-learning-assisted large-scale molecular dynamics simulations, we resolve this paradox by reproducing the experimentally measured piezoelectric coefficient $d_{33}\approx 220$~pC/N, and demonstrating that the giant response arises from the collective contribution of multiple intrinsic components, particularly the shear component $d_{15}$. This effect does not stem from conventional polarization rotation or phase switching, but instead originates from stochastic 120${}^{\circ }$ in-plane rotational hopping of a small fraction of organic cations. This discrete hopping mechanism is governed by the local C${}_3$-symmetric halogen-bonding network between the host framework and the guest cation. The Arrhenius-type temperature dependence of $d_{15}$ further confirms the role of thermally activated dipole hopping. This work provides a clear pathway to enhance piezoelectric performance of hybrid materials through rational engineering of host–guest interactions.