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

Hybrid organic, halide, and divalent metal double perovskites K(Sn, Se, Te)Br 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 KSeBr and KSnBr deviated from the experimental values by 4.3% and 3.1%, respectively. The elastic constants of K(Sn, Se, Te)Br were significantly smaller due to their larger reticular distances, lower Coulomb forces, and reduced hardness. The high dynamic lattice anharmonicity of K(Sn, Se, Te)Br reduced their electronic conductivity, providing a practical advantage in the presence of a thermoelectric field. K(Se, Te)Br were predicted to have indirect bandgaps of X-L nature, while KSnBr exhibited a direct - bandgap. The power conversion efficiency (PCE) for photovoltaic devices with K(Sn, Se, Te)Br 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.