The Effect of A-Cation and X-Anion Substitutions on the Electronic and Structural Properties of AZrX 'Defect' Perovskite Materials: A Theoretical Density Functional Theory Study.

In the present work, nine 'defect' perovskites with the chemical formula AZrX have been studied, where the A-site cations are a methylammonium cation, formamidinium cation, and trimethyl-sulfonium cation and the X-site anions are halogen, X = Cl, Br, and I. We employ periodic DFT calculations using GGA-PBE, MBJ, HSEsol, and HSE06 functionals. All studied compounds exhibit a wide-bandgap energy that ranges from 5.22 eV to 2.11 eV, while for some cases, geometry optimization led to significant structural modification. It was found that the increase in the halogen size resulted in a decrease in the bandgap energy. The choice of the organic A-site cation affects the bandgap as well, which is minimal for the methylammonium cation. Such semiconductors with organic cations may be utilized in optoelectronic devices, given the substantial benefit of solution processability and thin film formation compared to purely inorganic analogs, such as CsZrX.