A room-temperature antiferroelectric in hybrid perovskite enables highly efficient energy storage at low electric fields.

Molecular antiferroelectrics (AFEs) have taken a booming position in the miniaturization of energy storage devices due to their low critical electric fields. However, regarding intrinsic competitions between dipolar interaction and steric hindrance, it is a challenge to exploit room-temperature molecular AFEs with high energy storage efficiency. Here, we present a new 2D hybrid perovskite-type AFE, (i-BA) 2 (FA)Pb 2 Br 7 (1), which shows ultrahigh energy storage efficiencies at room temperature. Most strikingly, the typical double P - E hysteresis loops afford an ultrahigh storage efficiency up to ∼91% at low critical electric fields ( E cr = 41 kV cm -1 ); this E cr value is much lower than those of state-of-the-art AFE oxides, revealing the potential of 1 for miniaturized energy-storage devices. In terms of the energy storage mechanism, the dynamic ordering and antiparallel reorientation of organic cations trigger its AFE-type phase transition at 303 K, thus giving a large spontaneous electric polarization of ∼3.7 μC cm -2 , while the increasement of steric hindrance of the organic branched-chain i-BA + spacer cations stabilizes its antipolar sublattices. To the best of our knowledge, this exploration of achieving ultrahigh energy storage efficiency at such a low critical electric field is unprecedented in the AFE family, which paves a pathway for miniaturized energy storage applications.