Cs_1–xRb_xPbCl₃ and Cs_1–xRb_xPbBr₃ Solid Solutions: Understanding Octahedral Tilting in Lead Halide Perovskites

Abstract

The structures of the lead halide perovskites CsPbCl3 and CsPbBr3 have been determined from X-ray powder diffraction data to be orthorhombic with Pnma space group symmetry. Their structures are distorted from the cubic structure of their hybrid analogs, CH3NH3PbX3 (X = Cl, Br), by tilts of the octahedra (Glazer tilt system a – b + a –). Substitution of the smaller Rb+ for Cs+ increases the octahedral tilting distortion and eventually destabilizes the perovskite structure altogether. To understand this behavior, bond valence parameters appropriate for use in chloride and bromide perovskites have been determined for Cs+, Rb+, and Pb2+. As the tolerance factor decreases, the band gap increases, by 0.15 eV in Cs1–x Rb x PbCl3 and 0.20 eV in Cs1–x Rb x PbBr3, upon going from x = 0 to x = 0.6. The band gap shows a linear dependence on tolerance factor, particularly for the Cs1–x Rb x PbBr3 system. Comparison with the cubic perovskites CH3NH3PbCl3 and CH3NH3PbBr3 shows that the band gaps of the methylammonium perovskites are anomalously large for APbX3 perovskites with a cubic structure. This comparison suggests that the local symmetry of CH3NH3PbCl3 and CH3NH3PbBr3 deviate significantly from the cubic symmetry of the average structure.

Stabilizing RbPbBr3 Perovskite Nanocrystals through Cs+ Substitution

“…A single crystal of orthorhombic RbPbBr 3 was first prepared at 310 °C by Cola et al., but it can hardly be synthesized at room temperature . The PXRD patterns in Figure b clearly demonstrate that our obtained NCs adopt an orthorhombic structure, which is consistent with a previous report on the Rb 1− x Cs x PbBr 3 bulk analogue . It is worth noting that the diffraction peaks of the Rb 1− x Cs x PbBr 3 NCs are slightly shifted to lower 2 θ values compared with the standard orthorhombic RbPbBr 3 pattern, and the shift becomes more obvious when increasing the amount of Cs + (Figure c), which can probably be ascribed to the incorporation of the larger Cs + into the lattice.…”

“…[18] The PXRD patterns in Figure 2b clearly demonstrate that our obtained NCs adopt an orthorhombic structure, which is consistent with aprevious report on the Rb 1Àx Cs x PbBr 3 bulk analogue. [19] It is worth notingt hat the diffraction peaks of the Rb 1Àx Cs x PbBr 3 NCs are slightly shifted to lower 2q values compared with the standard orthorhombic RbPbBr 3 pattern, and the shiftb ecomes more obviousw hen increasing the amount of Cs + (Figure 2c), which can probablyb ea scribed to the incorporation of the larger Cs + into the lattice.T his result echoeswellt he EDS mapping results in that Cs + is successfully incorporated into the NCs.…”

“…The redshift of the band gap with increasing amount of Cs + may originate from the tilt of the [PbBr 6 ]o ctahedron when al arger cation is incorporated at the As ite. [19,23] The PL quantum yield (PLQY) for the 30 %C s, 40 %C sa nd 50 %C s NCs was determinedt ob e28 %, 44 %a nd 61 %r espectively. (Table 2).…”

Dry Mechanochemical Synthesis of Highly Luminescent, Blue and Green Hybrid Perovskite Solids

“…The structural characterization (Figure c) showed again a high degree of conversion and crystallinity for the entire series of compounds, with an expected shift to larger angles upon substitution with the smaller cesium cation. The different intensity of the main diffraction peaks between hybrid and fully inorganic perovskites ( y = 1) agrees with the slightly different orientation of the unit cell . The concentration of Cs + in this perovskite series was confirmed by XPS (Figure S7 and Table S1, Supporting Information).…”

Metal Doping/Alloying of Cesium Lead Halide Perovskite Nanocrystals and their Applications in Light‐Emitting Diodes with Enhanced Efficiency and Stability

“…In contrast to the claimed more stable lattice structure of the Rb‐doped CsPbX 3 NCs, Linaburg et al . performed theoretical simulation and concluded that the Rb‐doped perovskites are likely to form unstable crystal structure . Considering the very small difference in the HRTEM and the XRD results, further investigation on the change to the crystal lattice and the materials stability of Rb‐doped CsPbX 3 NCs are still needed.…”