Eco-friendly water-synthesis of lead-free Cs2AgBiBr6 perovskites

The synthesis of lead-free Cs2AgBiBr6 perovskite is a huge challenge within the framework of the new emergent full-inorganic materials, with the aim of being employed as sensitive layers for a new generation of solar cells and/or optoelectronic devices. Here we report an innovative eco-friendly method for the preparation of Cs2AgBiBr6 perovskite, obtained both by "wet" and "dry" CsBr, AgBr, and BiBr3 precursor salts, in a fully hydro-solution liquid process, free of chemical solvents. Cs2AgBiBr6 powders and Cs2AgBiBr6 lead-free perovskite nanocrystal films have been realised and investigated for electronic, structural, and optical properties. X-ray diffraction revealed that powders and/or perovskite films obtained in a water bath belong to the cubic phase, symmetry group Fm-3m, as revealed by scanning electron microscopy as tetrahedral nanocrystal morphology. Energy gaps of about 2.10 and 2.60 eV are evidenced by synchrotron radiation valence band photoemission spectroscopy, photo-/cathodo-luminescence, and optical measurements. Core levels x-ray photoemission and synchrotron radiation x-ray fluorescence spectroscopies give insights on Cs2AgBiBr6 perovskite formation in water-process solution.