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 a giant piezoelectric coefficient of ≈211  pC/N and demonstrating that it 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° 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 Letter provides a clear pathway to enhance piezoelectric performance of hybrid materials through rational engineering of host-guest interactions.