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

• Published in: Journal of computational chemistry 2023-05, Vol.44 (14), p.1395-1403
• Main Authors: Araujo, Luis Octavio, Rêgo, Celso R. C., Wenzel, W., Silveira, Danilo N., Piotrowski, Maurício J., Sabino, Fernando P., Pramudya, Yohanes, Guedes‐Sobrinho, Diego
• Format: Article
• Language: English
• Subjects: bulk Rashba effect; Cations; dipole moment; Dipole moments; Electron states; Energy gap; gap energy; High temperature; Ions; Mathematical analysis; metal halide perovskites; Metal halides; Perovskites; Splitting
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.27094

Because of instability issues presented by metal halide perovskites based on methylammonium (MA), its replacement to Cs 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 MAPbI3 and CsPbI3 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 0K, how the MA dipoles suppression can reduce the MAPbI3 gap energy by promoting a degeneracy breaking in the electronic states from the PbI3 framework, while the dipole moment reinforcement is crucial to align theory ↔ experiment, increasing the bulk Rashba splitting through higher Pb off‐centering motifs. The lack of permanent dipole moment in Cs results in CsPbI3 polymorphs with a pronounced Pb on‐centering‐like feature, which causes suppression in their respective bulk Rashba effect. Through first‐principles calculations, we showed how organic/inorganic cations impact the electronic properties of MAPbI3 and CsPbI3 perovskites. We found that the suppression of MA dipole moments can close MAPbI3 gap energy, while their reinforcement is crucial to increase the bulk Rashba effect in representative polymorphs. However, the Pb on‐centering‐like structures from CsPbI3 cause the suppression of the bulk Rashba effect, with their corresponding octahedral tilts leading to the opening of their band gap.