All-Inorganic Lead-Free Cs₂PdX₆ (X = Br, I) Perovskite Nanocrystals with Single Unit Cell Thickness and High Stability

The cesium lead halide perovskite nanocrystal (NC) has shown admirable potential in promising optoelectronic applications. However, the notorious toxicity of lead severely hinders its further commercialization. Herein, we report facile synthesis of a lead-free Cs2PdBr6 perovskite NC without the assistance of long-chain organic ligand. Such Cs2PdBr6 NCs with an average particle diameter of 2.8 nm and thickness of 1–2 unit cells possess a narrow bandgap of 1.69 eV and outstanding stability toward light, humidity, and heat, which enables it to be a promising photoelectrical material. The charge carrier dynamics are also analyzed via time-resolved photoluminescence decay and transient absorption spectroscopy to guide forthcoming material optimizations. Lastly, a fast anion-exchange method is adopted to prepare the Cs2PdI6 NC. Overall, this work inspires an eminent prototype to synthesize ingenious lead-free, narrow-bandgap, and stable perovskite NCs.