In recent years, there has been an unprecedented rise in the research of halide perovskites because of their important optoelectronic applications, including photovoltaic cells, light-emitting diodes, photodetectors and lasers. The most pressing question concerns the stability of these materials. Here faster degradation and PL quenching are observed at higher iodine content for mixed-halide perovskite CsPb(Br_xI_1−x)₃ nanocrystals, and a simple yet effective method is reported to significantly enhance their stability. After selective etching with acetone, surface iodine is partially etched away to form a bromine-rich surface passivation layer on mixed-halide perovskite nanocrystals. This passivation layer remarkably stabilizes the nanocrystals, making their PL intensity improved by almost three orders of magnitude. It is expected that a similar passivation layer can also be applied to various other kinds of perovskite materials with poor stability issues.

Assembling different materials into one optical fiber to realize multifunctional all-fiber devices is always a challenging task, mainly because the process is not compatible with current microfabrication technology. Although various devices have been proposed to achieve “all-fiber” optoelectronic functions, most of these devices cannot connect seamlessly with the mainstream optical fiber system (silica): this is a serious impairment to their further implementation in practical applications. Here, we present an integration approach that directly combines low-dimensional optoelectronic materials (${\text{CsPbBr}}_3$ nanocrystals and graphene) onto the facet of a standard silica fiber to construct a high-performance photodetector, which can detect light with a power as low as ${10}^{-11}\mathrm{W}$ with photoresponsivity as high as $2\times {10}^4\mathrm{A}/\mathbf{W}$. Moreover, it has an extraordinary light–matter interaction path beneficial to enhancing light absorption and realizing self-passivation and protection. Because of its compatibility with current established optical fiber systems, this technique could provide a highly versatile, reproducible, and low-cost method to integrate novel zero-, one-, and two-dimensional materials and deliver more sophisticated functionalities.