How cation nature controls the bandgap and bulk Rashba splitting of halide perovskites

Abstract

Because of instability issues presented by metal halide perovskites based on methylammonium (MA), its replacement to (Formula presented.) has emerged as an alternative to improve the materials' durability. However, the impact of this replacement on electronic properties, especially gap energy and bulk Rashba splitting remains unclear since electrostatic interactions from organic cations can play a crucial role. Through first-principles calculations, we investigated how organic/inorganic cations impact the electronic properties of (Formula presented.) and (Formula presented.) perovskites. Although at high temperatures the organic cation can assume spherical-like configurations due to its rotation into the cages, our results provide a complete electronic mechanism to show, from a chemical perspective based on ab initio calculations at (Formula presented.), how the (Formula presented.) dipoles suppression can reduce the (Formula presented.) gap energy by promoting a degeneracy breaking in the electronic states from the (Formula presented.) framework, while the dipole moment reinforcement is crucial to align theory (Formula presented.) experiment, increasing the bulk Rashba splitting through higher (Formula presented.) off-centering motifs. The lack of permanent dipole moment in (Formula presented.) results in (Formula presented.) polymorphs with a pronounced (Formula presented.) on-centering-like feature, which causes suppression in their respective bulk Rashba effect.