Competitive Chirality Induction in Two‐dimensional Germanium Iodide Perovskites Enabling Highly Anisotropic Nonlinear Optical Response

Abstract Chiral metal halide perovskites (CMHPs) are a promising class of chiroptical materials with significant potential applications in chiral‐optoelectronic and chiral‐spintronic devices. However, their chirality induction generally stems from the incorporation of chiral ligands, which constitutes compositional diversity and functional versatility. Herein, we report a significant chiral expression resulting from two distinct mechanisms: chirality transfer induced by chiral organic cations and mirror symmetry breaking driven by stereochemically active lone pairs, both contributing to controlled chirality induction. Homochiral germanium iodide perovskites, ( R / S ‐BrMBA) 2 GeI 4 ( R/S is Rectus/Sinister) can be achieved by employing chiral ( R / S )‐BrMBA cations to induce chirality via hydrogen bonding. In contrast, two enantiomorphous helical germanium iodide perovskites, P / M ‐( rac ‐BrMBA) 2 GeI 4 ( P / M is Plus/Minus and rac is racemic), are formed via the co‐assembly of racemic rac ‐BrMBA cations and germanium iodide networks, where chirality arises from spontaneous symmetry breaking induced by the stereochemically active 4s 2 electron pair. Remarkably, benefiting from the inherent chirality, both ( R ‐BrMBA) 2 GeI 4 and P ‐( rac ‐BrMBA) 2 GeI 4 crystals exhibit exceptional anisotropic nonlinear optical properties with large anisotropy factors ( g SHG‐CD ) up to 0.71 and 0.83 and laser damage thresholds of 697.5 and 535.2 GW cm − 2 , surpassing most previously reported CMHPs. This study provides insight into the interplay of chiral organic ligands and inorganic ions in the chiral induction, transfer, and functions of metal halide perovskites.