Stereo‐Active Lone Pairs Induced Giant Polarization in a 2D Ge‐Based Halide Perovskite Antiferroelectric

Abstract Antiferroelectrics, characterized by electrically controlled antipolar‐polar phase transformation, have attracted tremendous attention as a class of promising electroactive materials for assembling electronic devices. The emerging two‐dimensional (2D) halide perovskites with superior compositional diversity offer an ideal platform for exploring electroactive materials, whereas lead‐free antiferroelectric counterparts are still scarcely reported. Herein, for the first time, a new lead‐free 2D germanium iodide perovskite antiferroelectric (i‐BA)₂CsGe₂I₇ (1, i‐BA is iso‐butylammonium) has been presented, which exhibits a high Curie temperature (T_c) up to 403 K. Remarkably, benefiting from the lone pair stereochemical activity in Ge²⁺ induced large structural distortion and Cs⁺ ion off‐center displacement, 1 shows well‐defined double P–E hysteresis loops in a wide temperature range with a giant maximum polarization up to 18.8 µC cm⁻², which achieves a new high record among molecular antiferroelectrics. Moreover, under a low external electric field of 22.5 kV cm⁻¹, the antipolar‐polar phase transformation in 1 affords a recoverable energy storage density W_rec of 0.27 J cm⁻³ and high storage efficiency up to 79.76%. Such lead‐free halide perovskite antiferroelectric with intriguing antiferroelectric behaviors, including high T_c, large polarization and remarkable energy storage properties, is exciting, which provides an alternative candidate for high‐performance antiferroelectrics for environmentally friendly electronic devices.