In situ Surface Reconstruction in Pure Water by Ice‐Confined Freeze‐Thaw Strategy for High‐Performance Core–Shell Structural Perovskite Nanocrystals

Constructing core–shell structure is recognized as an effective approach for the conventional colloidal semiconductor nanocrystals (NCs) to improve their stability and optical performance in optoelectronic applications. It is, however, still a challenge to develop green manufacture for core–shell lead halide perovskite NCs (PeNCs). Herein, an ice‐confined freeze‐thaw strategy using pure water solvent is devised, which results in the surface reconstruction of CsPbBr3 PeNCs thereby formatting the CsPb2Br5 shell on the CsPbBr3 core to achieve core–shell CsPbBr3@CsPb2Br5. The in situ formation of the CsPb2Br5 shell is attributed to the transformation of the intermediate polyhedral structure with the help of amphiphilic 4‐dodecylbenzene sulfonic acid ligand in the precursor solution. The PeNCs show ultrahigh photoluminescence quantum yield of 95%, remarkable stability and humidity‐resistance. Moreover, both light‐emitting diodes and stretchable fluorescence hydrogels based on the PeNCs exhibit a boosted optical performance and excellent operation stability. The organic solvent‐free and recyclability of this strategy pave a novel way to the environmentally friendly and large‐scale manufacture of high‐quality PeNCs for optoelectronic application. The ice‐confined freeze‐thaw strategy is devised to achieve core–shell CsPbBr3@CsPb2Br5 PeNCs through surface reconstruction. The as‐prepared core–shell PeNCs show high photoluminescence quantum yield of 95%, remarkable stability, and recyclability.