Room Temperature Synthesis of Stable, Printable Cs₃Cu₂X₅ (X = I, Br/I, Br, Br/Cl, Cl) Colloidal Nanocrystals with Near-Unity Quantum Yield Green Emitters (X = Cl)

Lead halide perovskite nanocrystals (NCs) have shown remarkable properties for emission applications, but their toxicity and instability are a hindrance to many commercial uses. Herein, we report the synthesis of lead-free all-inorganic Cs3Cu2X5 (X = I, Br/I, Br, Br/Cl, Cl) colloidal nanocrystals as members of the metal–metal halide family of materials. These nanocrystals have uniform sizes less than 10 nm in diameter and show excellent optical properties, including composition-tunable emission spectra over the spectral region of 440–530 nm; high photoluminescence quantum yields of ∼100, 20, and 30% for X = Cl, Br, and I, respectively; and large effective Stokes shifts of over 100 nm for all species. Nanocrystals are synthesized by a room temperature, antisolvent method, but the precursors and ligands are also shown to be effective in hot -injection synthesis. Pure- and mixed-halide materials show tunable emission with the halide concentration, with a large fwhm of 80–110 nm due to a widely reported exciton self-trapping emission mechanism. Notably, the Cu3Cu2Cl5 NCs exhibit a near-unity quantum yield with an emission at 520 nm, high crystallinity, and good stability. These materials can be processed and maintained in adequately stable dispersions to enable inkjet printing of these materials into arbitrary patterns. These results indicate that cesium copper chloride NCs may have great potential for the future display or lighting applications.