Large‐Scale Synthesis of Highly Luminescent Perovskite‐Related CsPb2Br5 Nanoplatelets and Their Fast Anion Exchange

All‐inorganic cesium lead‐halide perovskite nanocrystals have emerged as attractive optoelectronic nanomaterials owing to their stabilities and highly efficient photoluminescence. Herein we report a new type of highly luminescent perovskite‐related CsPb2Br5 nanoplatelets synthesized by a facile precipitation reaction. The layered crystal structure of CsPb2Br5 promoted an anisotropic two‐dimensional (2D) crystal growth during the precipitation process, thus enabling the large‐scale synthesis of CsPb2Br5 nanoplatelets. Fast anion exchange has also been demonstrated in as‐synthesized CsPb2Br5 nanoplatelets to extend their photoluminescence spectra to the entire visible spectral region. The large‐scale synthesis and optical tunability of CsPb2Br5 nanoplatelets will be advantageous in future applications of optoelectronic devices.