Relativistic DFT-1/2 Calculations Combined with a Statistical Approach for Electronic and Optical Properties of Mixed Metal Hybrid Perovskites

Abstract

We overcome the great theoretical computational challenge of mixed perovskites, providing a rigorous and efficient model by including quasiparticle, spin−orbit coupling, and disorder effects. As a benchmark, we consider the mixed MAPb 1−x Sn x I 3 perovskites. The calculations are based on the generalized quasichemical approach and the DFT-1/2 approximated quasiparticle correction. Both cubic and tetragonal structures are investigated. By mapping the entire range of compositions, we correctly describe the bowing-like behavior for the energy gaps with 1.24 eV as the minimum value at x = 0.70, in very good agreement with the experimental data. Furthermore, while the tetragonal alloy reaches the maximum absorbance with a limit for the red shift at x = 1.0, the cubic alloy sets a maximum absorbance/red shift for the optimal composition at x = 0.70.

Atomistic Origins of Enhanced Band Gap, Miscibility, and Oxidation Resistance in α-CsPb1–xSnxI3 Mixed Perovskite

“…The calculations consider both the standard DFT approach and the DFT-1/2 quasiparticle correction to the PBE functional. DFT-1/2 is a correction approach , to the well-known underestimation in band gap of DFT that has shown to be successful in numerous perovskite systems. − It consists of adapting the Kohn–Sham potential by removing the self-energy potential associated with the half-electron from the valence band maximum V S,VBM and then adding the same term for the half-electron in the conduction band minimum V S,CBM Equation is approximated by neglecting the CBM term. To prevent the potential from diverging due to the periodic charge disbalance, the correction term is multiplied by a trimming function of the form where CUT is a system-dependent length parameter obtained variationally, as described elsewhere. , For the unit cell calculations, we obtain values of 3.20 and 3.05 au for the corrections of the I p orbital in CsPbI 3 and CsSnI 3 , respectively.…”

Bulk Rashba Effect Splitting and Suppression in Polymorphs of Metal Iodine Perovskites

“…20 Additionally, given the importance of the relativistic aspects of Pb in typical OIHP polymorphs, searching for substituents for the heavy and toxic lead using cleaner metals, such as Sn and Ge, sets an additional debate about the relationship between bulk Rashba and SOC effects. 21,22 This Letter shows how polymorphism affects the bulk Rashba splitting for MAPbI 3 , MASnI 3 , MAGeI 3 , and MASiI 3 in all 3D perovskite structures, i.e., cubic, tetragonal, and orthorhombic. Standard density functional theory (DFT) leads to a good bandgap description for OIHP; however, this is just an artificial effect.…”

“…From that, and by using effective models, Zheng et al found that the long recombination time of the charge carriers is due to the slower transition rate thanks to the mismatch of spin and momentum due to the Rashba effect . Additionally, given the importance of the relativistic aspects of Pb in typical OIHP polymorphs, searching for substituents for the heavy and toxic lead using cleaner metals, such as Sn and Ge, sets an additional debate about the relationship between bulk Rashba and SOC effects. , …”

Fundamentals of tin iodide perovskites: a promising route to highly efficient, lead-free solar cells

“…The VPSIC approach used in this work was shown to be of accuracy similar to the very popular hybrid HSE hybrid functional, 67,68 albeit substantially less computationally demanding. An interesting alternative is represented by the DFT-1/2 method, 69 which was recently used for stannates, [70][71][72] and can be considered a simplied version of the VPSIC (a comparison of these two approaches can be found in ref. 73).…”