Perovskite nanocrystals, e.g., nanoplatelets made from CsPbBr₃, can be used as luminescent materials. However, the photoluminescence quantum yields for the emission of blue light are significantly lower than the quantum yields for red- and green-emitting materials. This hampers the development of displays, which need red, green, and blue emitters. Synthesizing blue luminescent CsPbBr₃ nanoplatelets with a low number of defects, for example, is challenging. The defects reduce the quantum yield.

Xiaoming Li, Haibo Zeng, Nanjing University of Science and Technology, China, and colleagues have reduced the density of surface defects in CsPbBr₃ by adding excess HBr before nucleation. This favors the formation of intact PbBr₆^4– octahedrons and prevents the formation of defect structures with missing Br^– ions during the fast nucleation process. The amount of HBr had to be carefully adjusted. Diluted HBr led to smaller nanocrystals with broad emissions, while too much HBr destroyed the PbBr₆^4– octahedrons and the formed nanoplatelets.

Using this approach, quantum yields of 96 % were achieved for a sharp blue emission from CsPbBr₃ nanoplatelets. The team used the synthesized nanoplatelets to fabricate blue light-emitting diodes (LEDs) and found high external quantum efficiencies. According to the researchers, these results could be a basis for the development of displays based on next-generation perovskite nanocrystals.

• In-situ Passivation of PbBr₆^4- Octahedrons towards Blue Luminescent CsPbBr₃ Nanoplatelets with Near 100% Absolute Quantum Yield,
  Ye Wu, Changting Wei, Xiaoming Li, Yuelei Li, Shuangchen Qiu, Wei Shen, Bo Cai, Zhiguo Sun, Dandan Yang, Zhengtao Deng, Haibo Zeng,
  ACS Energy Lett. 2018.
  https://doi.org/10.1021/acsenergylett.8b01025