Stable Lead‐Free Blue‐Emitting Cs3Cu2Br5 Single Crystal with Self‐Trap Exciton Emission for Optoelectronics

Owing to their excellent photoelectric properties, perovskite materials have broad application prospects; however, the toxicity of Pb limits the application of Pb‐based perovskite materials. To overcome this problem, Pb‐free perovskite materials are prepared by replacing Pb with nontoxic elements including Ge and Sn; nevertheless, the stabilities of these materials are low. Herein, single crystals of nontoxic Cu(I)‐based ternary metal halide (Cs 3 Cu 2 Br 5 ) with outstanding stabilities and self‐trapped excition (STE) emission are constructed by an antisolvent method for the first time; these crystals exhibit central blue emission at 458 nm and large Stokes shifts. Photoluminescence (PL) intensities of the single crystals remain above 96.9% of their initial intensities when these crystals are exposed to an atmospheric environment for 90 days. Moreover, the stabilities of the Cs 3 Cu 2 Br 5 single crystals are investigated by temperature‐dependent PL spectroscopy, which suggests a considerable exciton binding energy of 503 meV, and derivative thermogravimetric analysis, which indicate that the temperature of complete decomposition of Cs 3 Cu 2 Br 5 is above 930 °C. Furthermore, a new class of white light‐emitting diodes with an ultrahigh color rendering index of 97.8 and satisfactory performance is produced using the Cs 3 Cu 2 Br 5 single crystals. The study demonstrates significant potentials of Cu(I)‐based single crystals in the field of optoelectronics.