A(2)AgCrBr(6) (A = K, Rb, Cs) and Cs(2)AgCrX(6)(X = Cl, I) Double Perovskites: A Transition-Metal-Based Semiconducting Material Series with Remarkable Optics

With an interest to quest for transition metal-based halogenated double perovskites AB′B″X(6) as high performance semiconducting materials for optoelectronics, this study theoretically examined the electronic structures, stability, electronic (density of states and band structures), transport (effective masses of charge carriers), and optical properties (dielectric function and absorption coefficients, etc.) of the series A(2)AgCrBr(6) (A = K, Rb, Cs) using SCAN + rVV10. Our results showed that A(2)AgCrBr(6) (A = Rb, Cs), but not K(2)AgCrBr(6), has a stable perovskite structure, which was revealed using various traditionally recommended geometry-based indices. Despite this reservation, all the three systems were shown to have similar band structures, density of states, and carrier effective masses of conducting holes and electrons, as well as the nature of the real and imaginary parts of their dielectric function, absorption coefficient, refractive index, and photoconductivity spectra. The small changes observed in any specific property of the series A(2)AgCrBr(6) were due to the changes in the lattice properties driven by alkali substitution at the A site. A comparison with the corresponding properties of Cs(2)AgCrX(6) (X = Cl, I) suggested that halogen substitution at the X-site can not only significantly shift the position of the onset of optical absorption found of the dielectric function, absorption coefficient and refractive spectra of Cs(2)AgCrCl(6) and Cs(2)AgCrI(6) toward the high- and low-energy infrared regions, respectively; but that it is also responsible in modifying their stability, electronic, transport, and optical absorption preferences. The large value of the high frequency dielectric constants—together with the appreciable magnitude of absorption coefficients and refractive indices, small values of effective masses of conducting electrons and holes, and the indirect nature of the bandgap transitions, among others—suggested that cubic A(2)AgCrBr(6) (A = Rb, Cs) and Cs(2)AgCrCl(6) may likely be a set of optoelectronic materials for subsequent experimental characterizations.