Spontaneous anion-exchange synthesis of optically active mixed-valence Cs2Au2I6perovskites from layered CsAuCl4perovskites
Cs2Au2I6, a lead-free photovoltaic material, has been synthesizedviacontrolled and systematic addition of hydroiodic acid (HI) to CsAuCl4. X-ray diffraction studies suggest the formation of Cs2Au2I6when a threshold concentration of HI is added to CsAuCl4. The final compound shows good stability against light, oxygen and moisture and at temperatures up to 140 °C without any phase degradation. The stability of Cs2Au2I6is also confirmed by its high negative formation energy and the convex hull diagram constructed using Density Functional Theory (DFT). Absorption studies suggest an abrupt band shift from 2.31 eV to 1.06 eV when HI concentration reaches the threshold limit (~100 μl). A sharp absorption edge was found for Cs2Au2I6with an Urbach energy of 59 meV, indicating lower structural disorder and higher crystallinity.
Studies of Mixed-valence States in Three-dimensional Halogen-bridged Gold Compounds, Cs2AuIAuIIIX6 (X = Cl, Br or I). Part 2. X-Ray Photoelectron Spectroscopic Study
The mixed-valence states in Cs2AuIAuIIIX6 (X = Cl, Br or I) were systematically studied by X-ray photoelectron spectroscopy of the Au 4f region for the first time.The gold valence states in halogeno complexes of AuI and Au