Sb‐Substituted Cs<sub>2</sub>AgBiBr<sub>6</sub>—As Much As It Could Be?—Influence of Synthesis Methods on Sb‐Substitution Level in Cs<sub>2</sub>AgBiBr<sub>6</sub>
Songhak Yoon, Bastian Fett, Alexander Frebel, Sina Kroisl, Bettina Herbig, Marc Widenmeyer, Benjamin Balke, Gerhard Sextl, Karl Mandel, Anke Weidenkaff
Abstract
Sb‐substituted Cs 2 AgBiBr 6 single crystals and powders are synthesized by various wet‐chemical routes as well as by solvent‐free mechanochemical synthesis. Phase purity and resulting optical properties of differently synthesized Sb‐substituted Cs 2 AgBiBr 6 absorbers are investigated and compared. X‐ray diffraction confirms that Sb substitution results in an apparent single‐phase formation with a unit cell shrinkage up to a certain substitution limit, which varies depending on the synthesis routes. Questions about the phase identification determined by X‐ray diffraction are raised and thoroughly investigated by Raman spectroscopy. UV–vis spectroscopy reveals that Sb 3+ substitution induces a reduction in the optical bandgap of Cs 2 AgBiBr 6 , whereas octahedral factor calculations provide that SbBr 6 octahedra can be hardly stable in a Cs 2 AgBiBr 6 double perovskite. The experimental results of the occurrence and evolution of Raman bands and theoretical calculations of the structural stability of SbBr 6 octahedra in Cs 2 AgBiBr 6 unambiguously raise doubts about the Sb‐substitution feasibility in Cs 2 AgBiBr 6 , and a general substitution strategy in Cs 2 AgBiBr 6 is discussed.