Rod-shaped thiocyanate-induced abnormal band gap broadening in SCN^- doped CsPbBr₃ perovskite nanocrystals

In this work, the pseudohalide thiocyanate has been demonstrated as a promising alternative to the halide anion to engineer optoelectronic properties of inorganic/organic hybrid perovskites because it exhibits better chemical stability than the halide anion. Previous reports have suggested that the ionic radii and electronegativity of SCN^- is close to that of I^-; the SCN^- doped CH₃NH₃PbI₃ exhibited similar optical properties as pure CH₃NH₃PbI₃. Consequently, it was expected that doping of CsPbBr₃ perovskite with SCN^- would result in band gap narrowing. Interestingly, the photoluminescent all-inorganic CsPbBr₃ perovskite nanocrystals exhibit an abnormal blue shift in optical properties and improvement of the crystallinity when successfully doped by SCN^-. Combined experimental and theoretical investigations revealed that doping of the CsPbBr₃ perovskite with the rod-like SCN^- anion introduced disorder in the crystal lattice, leading to its expansion, and impacted the electronic structure of the perovskite with band gap broadening.