Electronic structures and optical properties of (Ph4P)MX2 (M = Cu, Ag; X = Cl, Br)

In recent years, all inorganic copper(I) halides have emerged as an exciting new class of optical materials that demonstrate high-efficiency photoluminescence (PL) properties. Here, we report the synthesis and characterization of a series of hybrid copper(I) and silver(I) halides (Ph4P)MX2 (M ​= ​Cu, Ag; X ​= ​Cl, Br) containing tetraphenylphosphonium (Ph4P+) cation as the organic component. Addressing one of the shortcomings of all-inorganic copper(I) halides, inclusion of the bulky organic Ph4P+ cation improves the stability of the hybrid compounds; (Ph4P)MX2 show no sign of degradation upon long-term ambient air exposure. The compounds are found to exhibit unusually weak light emission properties for Cu(I) and Ag(I) halides. Our combined experimental and density-functional theory (DFT) studies attribute the contrasting optical properties of these compounds to their unique crystal and electronic structures. This work provides new materials design perspectives to explore low cost and low toxicity metal halides for light emission applications.