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Using atomic-scale imaging and in-situ thermal analysis, the authors uncover a hierarchical herringbone network of polar walls embedded within the nominally non-polar halide perovskite CsPbBr3. Both ferroelastic twin walls and antiphase boundaries exhibit localized broken inversion symmetry and assemble via a sequential phase-transition pathway fundamentally distinct from standard oxide perovskites. These topologically protected, symmetry-broken nano-interfaces offer a structural explanation for anomalous carrier transport and polarization dynamics in metal halide semiconductors.
Nominally non-polar CsPbBr3 harbors an internal network of polar domain walls, revealing a hidden topological architecture that can govern charge transport in halide perovskite optoelectronics.
Domain walls in ferroic materials can host nanoscale functionalities absent from the periodic crystal, offering new opportunities to control electronic transport and polarization in semiconductor devices. Metal halide perovskites demonstrate important photophysical properties; however, their ferroic properties remain unclear. Here we discover a hierarchical herringbone network of polar walls within the non-polar halide perovskite CsPbBr3 comprising ferroelastic twin walls and antiphase walls. Atomic-scale imaging reveals that both wall types comprise nanoscale regions whose inversion-symmetry is broken compared to the surrounding bulk lattice. In-situ heating experiments show that these interfaces form sequentially during symmetry-lowering phase transitions, revealing a different formation pathway compared with'conventional'oxide perovskites. These polar nano-walls, together with their enclosed topology, may impact carrier transport. This reveals a previously unrecognized structural motif in CsPbBr3, providing new insights into their photophysical and optoelectronic behavior.