Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br I) (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br I) nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.