Theoretical Investigation of the Role of Mixed A⁺ Cations in the Structure, Stability, and Electronic Properties of Perovskite Alloys

Abstract

Experimental studies have demonstrated the importance of the combination of different chemical species at the A-, B-, or X-sites in metal-halide ABX3 perovskites to improve the performance of perovskite solar cells (PSCs). However, from our understanding, further efforts at the atomistic scale are required to unveil the role of alloying in PSCs. Here, we performed a density functional theory investigation on perovskite alloy materials, namely, Cs x MA1–x PbI3, MA x FA1–x Sn0.50Pb0.50I3, and MA x FA1–x PbBr2.50I0.50 (x = 0.00, 0.25, 0.50, 0.75, 1.00). Equilibrium orthorhombic supercell structures were obtained for all systems with distorted octahedral environments, in which the magnitude depends on the chemical species. Besides, energetically stable crystals, in comparison with the parent structures, were found only for Cs x MA1–x PbI3, even though the remaining alloys presented stronger bonds. Furthermore, we addressed the role of the spin–orbit coupling effects to the electronic structure, which was critical to estimate the power conversion efficiency (PCE) with radiative recombinations, e.g., a PCE exceeding 23% was obtained. From our analyses, alloys with Cs content stood out as the best photovoltaic material.

Contrasting the stability, octahedral distortions, and optoelectronic properties of 3D MABX3 and 2D (BA)2(MA)B2X7 (B = Ge, Sn, Pb; X = Cl, Br, I) perovskites

“…The 3D and 2D organic–inorganic perovskites have a rich chemical environment, with a variety of intermolecular interactions and bonds, such as hydrogen bonds, halide bonds, ionic bonds, Lewis acid–base interactions and van der Waals interactions. 79 However, these different interactions differ in their strengths, and, for a suitable comparison between the energetic stability of the 3D and 2D perovskites, it is useful to perform cohesive energy decomposition, 26 which provides insights into the interaction between each part of the system and also allows access to the stability factors for organic–inorganic perovskites.…”

“…Current studies are mainly being developed to improve solar harvesting performance by constructing solar cells with different combinations at the A or A′ sites, 22,23 metal cation alloys, 24,25 or even mixed species of halide anions, 26 which, aiming for high solar cell efficiencies, can tune properties such as energy band gap and current density. 23,27,28 Most of these investigations are experimental, suggesting a deep theoretical understanding of the stabilization mechanisms that result in better stability of 2D perovskites.…”

Cubic-to-hexagonal structural phase transition in metal halide compounds: a DFT study

“…Before performing the optimization process, all super-cubic structures included local distortions by means of displacements of the halogen atoms and A-site cations, considering also an aleatory conguration of the organic cations. 25 A similar optimization procedure was employed for these structures (Section 2.1), with the main difference that the stress-tensor had only one component, since the cubic symmetry was preserved throughout the relaxation process.…”

“…[21][22][23][24] Since then, several mixtures have been synthesized to achieve either an improvement on the durability of the material or an enhancement of the opto-electronic properties; [17][18][19] as a consequence, the term "perovskite alloy" has been coined. 17,19,25 In this context, we carried out a DFT study on the APbX 3 MHCs, with A = FA, MA, and Cs, and X = I, Br, and Cl, to study the inuence of the chemical species on the cubic-to-hexagonal phase transition. The structures used to model such a transition were extracted from the work of Chen et al 4 mentioned above for FAPbI 3 .…”

Charting the Irreversible Degradation Modes of Low Bandgap Pb‐Sn Perovskite Compositions for De‐Risking Practical Industrial Development

“…While the role of the A‐site cation is often described as that of a spacer ion with an effective ionic radius that satisfies the tolerance criteria for forming the perovskite crystal structure, this is an oversimplification. In addition to stabilizing the desired crystallographic phase, [ 18,20–22 ] certain choices of the A‐site cation can also suppress ion migration, [ 21,23–26 ] minimize halide segregation, [ 27–29 ] induce octahedral distortions, [ 30–32 ] and improve structural cohesion, [ 33,34 ] as well as charge transport properties. [ 35–37 ] The shape, size, and chemical nature of the A‐site ions can induce local and global lattice deformations that either promote or suppress the formation of defects.…”