Bandgap and Photoluminescence Tunability of Lead‐Free Cs₃Bi₂(Br,I)₉ Solid Solution Compounds

Lead-free halide perovskites of Cs3Bi2X9 (X=Br, I) are successfully hybridized into solid solution compounds. This task is not easy because the end members, X = Br and I, have different crystallographic (electronic) structures – trigonal (direct gap) and hexagonal (indirect gap), respectively – but hydrothermal synthesis crushes the difficulty. Very significantly, the obtained solid solutions of halide perovskites Cs3Bi2(Br,I)9 have a direct or weak-indirect transition in the electronic band structure and can emit tunable photoluminescence in the visible region. For further details see article number 2300241 by Tomokatsu Hayakawa and co-workers. This article is part of the Special Section “Materials for Energy Conversion Systems: Fundamentals, Designs, and Applications” – see Guest Editorial by Maria Rita Cicconi, Tomokatsu Hayakawa, Brahim Dkhil, and Marin Alexe (article number 2400251).