Scientists synthesize hafnium-based, vacancy-ordered perovskite nanocrystals by hot injection method

Lead-free vacancy-ordered perovskite Cs₂M⁴⁺X₆ (X=Cl^-, Br^- or I^-) nanocrystals feature low toxicity, high stability and unique optical properties.

In previously reported hot injection methods for synthesizing perovskite nanocrystals, metal halides or metal acetates are often used as metal precursors. However, for many new perovskite nanocrystalline systems, the inability of these two types of metal salts to ionize in organic solvents is an important reason for synthesis failure.

Recently, a research group led by Prof. Han Keli and Prof. Yang Bin from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences discovered that metal acetylacetonates are a suitable type of metal precursor. By using Hf-based, vacancy-ordered perovskite as a model system and hafnium acetylacetonate as a metal source, they synthesized Cs₂HfCl₆ nanocrystals for the first time via hot injection method.

This study was published in Laser & Photonics Reviews on Dec. 13.

Different from previously reported perovskite nanocrystals, the newly synthesized Cs₂HfCl₆ nanocrystal is a defect-intolerant semiconductor.

To mitigate the sub-band gap defect states inside Cs₂HfCl₆ nanocrystals, the researchers proposed a passivation strategy of Sb³⁺ doping, which had not been reported in previous perovskite studies.

Moreover, by using rare earth acetylacetonates, the researchers doped four rare earth ions, including Pr³⁺, Tb³⁺, Eu³⁺, Ho³⁺, into the crystal lattice of the Cs₂HfCl₆ nanocrystal host, and obtained tunable multicolor emissions.

Compared with the previously reported rare-earth-ion-doped perovskite nanocrystal systems, the use of rare earth acetylacetone compounds enabled rare earth element ions to be doped into the nanocrystal lattice under a relatively milder temperature.

"Our study not only provides an effective strategy for regulating the optical properties of vacancy-ordered perovskite nanocrystals, but also enriches the hot-injection synthesis method, which may promote the development of new perovskite nanocrystal systems," said Prof. Han.