Ultralong Compositional\nGradient Perovskite Nanowires\nFabricated by Source-Limiting Anion Exchange

Anion exchange in halide perovskites offers prospective\napproaches\nto band gap engineering for miniaturized and integrated optoelectronic\ndevices. However, the band engineering at the nanoscale is uncontrollable\ndue to the rapid and random exchange nature in the liquid or gas phase.\nHere, we report a source-limiting mechanism in solid-state anion exchange\nbetween low-dimensional perovskites, which readily gives access to\nultralong compositional gradient nanowires (NWs) with lengths of up\nto 100 μm. The exchanged NWs remain single-crystalline with\nintact morphology, while the halogen content exhibits an apparent\ngradient distribution, leading to a tapered energy band profile along\na NW. In the dynamic study of anion behavior, it is shown that the\nspatial stoichiometric composition can be precisely tuned following\nFick’s law of diffusion. In addition, self-powered, spectrally\nresolved photodetectors incorporating multiple detection units within\na single gradient NW are demonstrated. This work provides a feasible\nstrategy for the realization of perovskite-based ultracompact optoelectronics,\nimaging sensors, and other miniaturized semiconductor devices.