Perovskites are a class of materials with useful properties for different optoelectronic applications, such as LEDs and sensors. However, the high lead content of the common CsPbBr₃ type and its limited stability both pose challenges for real-world applications. Cs₄PbBr₆ perovskites show green emission and have attracted attention as an alternative to CsPbBr₃ due to their enhanced stability and reduced lead content. However, the synthesis of Cs₄PbBr₆ usually requires complex procedures, a variety of ligands, or a combination of solvents.

Cuncheng Li, University of Jinan, China, Haibo Zeng, Nanjing University of Science and Technology, China, and colleagues have developed an environmentally friendly, single-solvent, ligand-free route for the gram-scale synthesis of Cs₄PbBr₆ perovskite solids. The team combined lead bromide and cesium bromide in N,N‐dimethylformamide (DMF) under ambient conditions. Over 10 g ligand-free Cs₄PbBr₆ perovskite solids could be obtained after simply evaporating the solvent.

The solvent vapor can be recovered and reused. This process eliminates the potential environmental harm caused by using organic solvents. The product has strong photoluminescence, a high photoluminescence quantum yield, and a reversible fluorescent response towards heat and light.

• Single-Solvent, Ligand-Free, Gram-cale Synthesis of Cs₄PbBr₆ Perovskite Solids with Robust Green Photoluminescence,
  Yunwei Wei, Ruijia Sun, Yuehua Li, Yuhai Zhang, Yizhong Lu, Xiaoming Li, Guozhu Chen, Bingqiang Cao, Cuncheng Li, Haibo Zeng,
  ChemNanoMat 2019.
  https://doi.org/10.1002/cnma.201900604