Stability enhancement of Cs₃Cu₂I₅ powder with high blue emission realized by Na⁺ doping strategy

Cesium copper iodide compound (Cs₃Cu₂I₅) is in a blossoming status owing to its advantages of high photoluminescence quantum yield (PL QY), non-toxicity and low-cost, which holds great potential in optoelectronic applications. The issue of long-term stability of Cs₃Cu₂I₅ should be concerned before its commercialization. Herein, we fabricate ultra-stable Cs₃Cu₂I₅ powder by adopting Na ⁺ ions doping strategy, achieving great improvements in the air-, photo- and thermal stabilities, and the PL intensity enhancement is also obtained possibly due to the formation of a stronger chemical interaction between Cu⁺ and I⁻ ions upon Na⁺ doping, which potentially helps to stabilize both Cu⁺ cations and I⁻ anions by restraining the diffusion of these ions and prevent Cu⁺ from oxidizing into Cu²⁺ from the X-ray photoelectron spectroscopy (XPS) results. We find that Cs₃Cu₂I₅: Na with the doping concentration of 7.4% displays the best performance, its air-, photo-, and thermal stabilities exhibit great improvements. In addition, the PL intensity of Cs₃Cu₂I₅: 7.4% Na powder gets significantly enhanced by 17.4% compared with the undoped Cs₃Cu₂I₅ powder. Moreover, the performance of the UV pumped phosphor converted LEDs (pc-LEDs) based on Cs₃Cu₂I₅: 7.4% Na powder as phosphor also slightly improved compared with the undoped Cs₃Cu₂I₅ based device. Above all, this work is expected to promote the commercialization process of copper-based compounds with excellent stabilities and high emission.