Room‐Temperature Direct Synthesis of Tetragonal β‐CsPbI3 Nanocrystals

Abstract Phase engineering of CsPbI 3 nanocrystals (NCs) is a priority for their optoelectronic applications. So far, the scalable and room‐temperature direct synthesis of black phase CsPbI 3 NCs remains an enormous challenge because of the thermal unequilibrium‐induced phase transition. Herein the direct synthesis is reported of metastable β‐CsPbI 3 NCs in gram‐scale at room‐temperature in seconds via spontaneous crystallization. The obtained β‐CsPbI 3 NCs exhibit good monodispersity, narrow‐band far‐red emission (716 nm, FWHM = 38 nm) as well as a high photoluminescence quantum yield of 62%. The crystallization dynamics of β‐CsPbI 3 NCs are revealed through in situ UV–vis absorption and photoluminescence spectra analysis. Finally, a photon‐to‐photon conversion indirect X‐ray detector based on the phase‐stable NCs/polystyrene film is preliminarily demonstrated. This scalable and low‐cost preparation of high‐quality metastable β‐CsPbI 3 NCs will pave the way for their future commercial applications in novel optoelectronic devices.