Twistionics in halide perovskites

Ion migration is a fundamental instability in halide perovskites, critically constraining their practical development in optoelectronic applications. Here we introduce twistionics, a twist-angle engineering strategy, to modulate ionic transport in halide perovskites. Through low-dose in situ aberration-corrected scanning transmission electron microscopy, we directly visualize the twist-angle-dependent ion diffusion in CsPbBr 3 -CsPbCl 3 heterostructures. Our observations uncover a two-step migration pathway: formation of interfacial diffusion channels followed by their lateral growth to achieve complete interdiffusion. In lattice-aligned heterostructures, interfacial van der Waals (vdW) interactions facilitate the formation of diffusion channels and promote ion interdiffusion. Critically, introducing a twist angle disrupts interlayer registry, weakens vdW coupling, and dramatically suppresses cross-interface ion migration by reducing the density and continuity of diffusion channels. The resulting 28°-twisted heterostructures exhibit improved structural integrity and prolonged operational stability in photodetectors. These findings establish twist engineering as a powerful strategy for stabilizing perovskite devices and pave the way for regulating ion transport in the emerging field of twistionics.