Semiconductor behavior of halide perovskites AGeX3 (A = K, Rb and Cs; X = F, Cl and Br): first-principles calculations

The structural, elastic and optoelectronic properties for cubic halide perovskites AGeX3 (A = K, Rb and Cs, X = F, Cl and Br) have been successfully studied in this paper, using the density functional theory with the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE). The modified Becke–Johnson (mBJ-GGA) potential approximation was used to describe the band structure more accurately. The calculated band structure from mBJ gives appropriate optoelectronic properties of these materials. Band structure calculations reveal a semiconducting behavior with a direct band gap at the R-point in the reciprocal lattice space, with values lying between 0.79 and 2.87 eV. The compounds of interest are mechanically stable, anisotropic and ductile in nature. The optical properties indicate that these compounds can be used in various optoelectronic devices operating in the visible and ultraviolet energies. To the best of our knowledge, this is the first quantitative theoretical prediction of the elastic, electronic and optical properties for these compounds which still awaits experimental confirmation.