Organic–inorganic hexahalometalate-crystal semiconductor K ₂ (Sn, Se, Te)Br ₆ hybrid double perovskites for solar energy applications

Hybrid organic, halide, and divalent metal double perovskites K₂(Sn, Se, Te)Br₆ with cubic structures were computationally evaluated using the generalized-gradient approximation (GGA) and modified Becke-Johnson (mBJ-GGA) functionals. The Goldschmidt tolerance factor, octahedral factor, Helmholtz free energy, and formation energy illustrated the structural, chemical, and thermodynamic stabilities of the studied compounds. The equilibrium lattice constants for K₂SeBr₆ and K₂SnBr₆ deviated from the experimental values by 4.3% and 3.1%, respectively. The elastic constants of K₂(Sn, Se, Te)Br₆ were significantly smaller due to their larger reticular distances, lower Coulomb forces, and reduced hardness. The high dynamic lattice anharmonicity of K₂(Sn, Se, Te)Br₆ reduced their electronic conductivity, providing a practical advantage in the presence of a thermoelectric field. K₂(Se, Te)Br₆ were predicted to have indirect bandgaps of X-L nature, while K₂SnBr₆ exhibited a direct <i>Γ</i>-<i>Γ</i> bandgap. The power conversion efficiency (PCE) for photovoltaic devices with K₂(Sn, Se, Te)Br₆ perovskite compounds as solar absorbers reached 20.51%. Their absorption in the visible region provided an advantage in energy harvesting. The electronic transitions in the studied double perovskites took place between the Br-4p and K-4s orbitals. Thus, these hybrid organic-inorganic halide perovskites proved to be excellent semiconductors for photovoltaic applications and demonstrated optimized photovoltaic efficiency.