Lead halide perovskites have drawn extensive attention over recent decades owing to their advantages of high absorption coefficient, large carrier diffusion lengths, and superior photoelectric properties, which make them as promising candidates for solar cells, light-emitting diodes, photodetectors and lasers. However, their toxicity and instability as big issues need to be solved for further commercialization. So far, many efforts have been made to explore low- or non-toxic elements to replace lead, including tin (Sn), bismuth (Bi), silver (Ag), indium (In), antimony (Sb), germanium (Ge), and copper (Cu). Among these rising lead-free perovskite materials, all inorganic copper-based perovskites benefit from low cost and earth-abundant. In the previous reports, a limited number of synthetic methods have been used to fabricate copper based inorganic perovskites, and there are some problems in these methods, such as energy consumption, time consuming and solvent consuming, which is not accord with the concept of environment-friendly development.

Dr. Bingkun Chen who comes from a research group of Beijing Institute of Technology developed a facile dry ball milling method (preparation method of green and energy saving, which was identified by IUPAC as one of 10 world-changing technologies) to synthesize lead-free Cs₃Cu₂X₅ (X=I, Cl) zero dimensional perovskites with photoluminescence quantum yield (PL QY) up to 60%. Dry ball milling method not only avoid the use of solvents, but also achieve high yield in a relatively short time by controlling raw materials. The as-synthesized Cs₃Cu₂I₅ and Cs₃Cu₂Cl₅ lead-free perovskite powders have good thermal stability, photostability and air stability. Furthermore, UV pumped phosphor converted light-emitting diodes were obtained by using Cs₃Cu₂I₅ and Cs₃Cu₂Cl₅ as phosphors. The research results are published in Photonics Research, Vol. 8, Issue 6, 2020 (Lingling Xie, Bingkun Chen, Fa Zhang, et al. Highly luminescent and stable lead-free cesium copper halide perovskite powders for UV-pumped phosphor-converted light-emitting diodes[J]. Photonics Research, 2020, 8(6): 06000768).

Future work will focus on the synthetic technology, photoluminescence mechanism and applications in the field of optoelectronic devices in order to fully explore and realize Cs₃Cu₂X₅ perovskites.

Prof. Yongtian Wang from the Beijing Institute of Technology believes that this method not only provides copper based lead-free perovskite, but also develops a new material preparation technology, which avoids the solubility limitation of insoluble reactants and the limitation of water sensitive reactants, and paves the way for materials that cannot be obtained by other methods.

The blue emissive Cs₃Cu₂I₅ and green emissive Cs₃Cu₂Cl₅ synthesized by dry milling method were used as phosphors to prepare UV pumped phosphor converted light-emitting diodes.