Renewing Halogen Substitution Strategy for the Rational Design of High‐Curie Temperature Metal‐Free Molecular Antiferroelectrics

Metal‐free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high‐curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high‐Tc molecular AFEs of the halogen‐substituted phenethylammonium bromides (x‐PEAB, x = H/F/Cl/Br), resembling the binary stator‐rotator system. Strikingly, the p‐site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br‐PEAB, on par with the record‐high Tc values for molecular AFEs. As a typical case, the member 4‐fluorophenethylammonium bromide (F‐PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F‐PEAB also exhibits a high energy storage efficiency (η) of 83.6% even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high‐Tc AFEs for energy storage devices.