Spontaneous Octahedral Tilting in the Cubic Inorganic Cesium Halide Perovskites CsSnX₃ and CsPbX₃ (X = F, Cl, Br, I)

Abstract

The local crystal structures of many perovskite-structured materials deviate from the average space group symmetry. We demonstrate, from lattice-dynamics calculations based on quantum chemical force constants, that all the caesium-lead and caesium-tin halide perovskites exhibit vibrational instabilities associated with octahedral titling in their high-temperature cubic phase. Anharmonic double-well potentials are found for zone-boundary phonon modes in all compounds with barriers ranging from 108 to 512 meV. The well depth is correlated with the tolerance factor and the chemistry of the composition, but is not proportional to the imaginary harmonic phonon frequency. We provide quantitative insights into the thermodynamic driving forces and distinguish between dynamic and static disorder based on the potentialenergy landscape. A positive band gap deformation (spectral blueshift) accompanies the structural distortion, with implications for understanding the performance of these materials in applications areas including solar cells and light-emitting diodes.

All‐Inorganic CsPbX3 Perovskite Solar Cells: Progress and Prospects

“…1% for the Cl;however,this is apparently enough to stabilize the room-temperature perovskite forms to orthorhombic for CsPbBr 3 and the unusual monoclinic for CsPbCl 3 .C sPbCl 3 exists in an umber of different phases just above room temperature (for at abulation of the phase relations with temperature of the various CsPbX 3 (and CsSnX 3 ), see Table 1 in Ref. [32].…”

Nature of the octahedral tilting phase transitions in perovskites: A case study of CaMnO3

“…Experimental values at room temperature for the orthorhombic phase [40] are provided for comparison. [44,45]. The depth of the potential well has, for instance, been used as an indicator of the nature of the phase transitions, i.e., deep and shallow wells should correspond to order-disorder and displacive transitions, respectively.…”

Caesium for Perovskite Solar Cells: An Overview

“…Caesium metal halide perovskites (CsBX 3 ), isostructural to perovskite CaTiO 3 and related oxides, consist of a Cs‐based cuboctahedral cavity at the centre of the corner‐sharing lead/tin halide octahedral network . The interaction of Cs + with the halide‐dominated perovskite structure is potentially very different and understanding its effect on the perovskite structure is crucial to improve solar cell performances.…”

“…[1] Caesium metal halide perovskites (CsBX 3 ), isostructuralt o perovskite CaTiO 3 and relatedo xides, consist of aC s-based cuboctahedral cavity at the centre of the corner-sharing lead/ tin halide octahedral network. [142] The interaction of Cs + with the halide-dominated perovskite structure is potentially very different and understanding its effect on the perovskite structure is crucial to improve solar cell performances. First synthesised by Wellse tal., [143] the perovskite CsPbI 3 possessesa ne xcellent combination of band-gap, [144,145] thermal stability,a nd absorption coefficient for photovoltaic applications, [146,147] if compared to the bromide (CsPbBr 3 )a nd chloride (CsPbCl 3 ) counterparts.…”