Understanding the Instability of the Halide Perovskite CsPbI₃ through Temperature‐Dependent Structural Analysis

Abstract

Despite the tremendous interest in halide perovskite solar cells, the structural reasons that cause the all‐inorganic perovskite CsPbI3 to be unstable at room temperature remain mysterious, especially since many tolerance‐factor‐based approaches predict CsPbI3 should be stable as a perovskite. Here single‐crystal X‐ray diffraction and X‐ray pair distribution function (PDF) measurements characterize bulk perovskite CsPbI3 from 100 to 295 K to elucidate its thermodynamic instability. While Cs occupies a single site from 100 to 150 K, it splits between two sites from 175 to 295 K with the second site having a lower effective coordination number, which, along with other structural parameters, suggests that Cs rattles in its coordination polyhedron. PDF measurements reveal that on the length scale of the unit cell, the PbI octahedra concurrently become greatly distorted, with one of the IPbI angles approaching 82° compared to the ideal 90°. The rattling of Cs, low number of CsI contacts, and high degree of octahedral distortion cause the instability of perovskite‐phase CsPbI3. These results reveal the limitations of tolerance factors in predicting perovskite stability and provide detailed structural information that suggests methods to engineer stable CsPbI3‐based solar cells.

New accurate molecular dynamics potential function to model the phase transformation of cesium lead triiodide perovskite (CsPbI3)

“…Whereas the least deviations occur at Cs-Cs and I-I peaks with a deviation of $0.01 A. In fact, the new proposed Hybrid EABC results in Pb-I bond lengths of $3.05 A which agrees with experimental ndings reported by Straus et al 50 with an error of less than 1%. Also, it proves that the change in lattice parameters with temperature must originate from tilting in the octahedra of Pb-I.…”

“…This agrees with the ndings in ref. 50 that Cs cations become distorted, occupy two positions and rattle within the structure causing the instability of CsPbI 3 at ambient conditions. At 600 K, the increase in volume which is observed from the increase in the scattered positions along the X-axis indicates the transition into a cubic crystal structure and it would be discussed in more detail in the phase transformation section.…”

CsPbI3 nanocrystal films: towards higher stability and efficiency

“…This indicates that the functional black α-CsPbI 3 phase is entropically favored. [33][34][35][36] Theoretical calculations further prove that vibrational instabilities exist, induced by octahedral tilting in their high-temperature cubic phase from lattice-dynamics calculations. 32 Investigation of single-crystal γ-CsPbI 3 indicates that the rattling of the Cs cation, lower coordination of the Cs site, and local octahedral distortion contribute to the thermodynamic instability at room temperature.…”

“…32 Investigation of single-crystal γ-CsPbI 3 indicates that the rattling of the Cs cation, lower coordination of the Cs site, and local octahedral distortion contribute to the thermodynamic instability at room temperature. 35…”

Enhanced Light Absorption by Facile Patterning of Nano-grating on Mesoporous TiO2 Photoelectrode for Cesium Lead Halide Perovskite Solar Cells

“…However, the black α-phase CsPbI 3 suffers from severe instability and easily degrades to a nonperovskite yellow δ-phase CsPbI 3 (E g = 2.82 eV), even at room temperature. These are the major issues that delimit the fabrication of solar cell devices using CsPbI 3 [13,14]. On the other hand, the CsPbBr 3…”