Sanxia Yin, Shihao Zhang, Weiqi Gao, Zhou Li, Yaonan Xiong, Xin Zhang, Pan Xu, Kun Zheng, Yangfeng Li, Jinhua Hong, Shuchen Zhang, Chao Ma, Lei Liao, Yiliu Wang, Shulin Chen
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 CsPbBr3-CsPbCl3 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.