Optical and Structural Property Tuning in Physical Vapor Deposited Bismuth Halides Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1).

Crystalline films of lead-free all-inorganic Cs3Bi2X9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs3Bi2I9 to 2.64 eV for Cs3Bi2Br9. X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts.