Lead halide hybrid perovskite single crystals have been grown using antisolvent vapor-assisted crystallization. The chemical composition and structural model of the crystals have been established using nuclear magnetic resonance and single crystal x-ray diffraction, leading to the formula $\mathrm{F}{\mathrm{A}}_{0.9}\mathrm{M}{\mathrm{A}}_{0.1}\mathrm{Pb}{\mathrm{I}}_{2.23}{\mathrm{Br}}_{0.77}$. The hexagonal crystallographic structure with $P{6}_3$/mmc space group has been confirmed by transmission electron microscope study. Through a detailed analysis of the single crystal XRD data, the locations of $\mathrm{F}{\mathrm{A}}^{+}$ and $\mathrm{M}{\mathrm{A}}^{+}$ in the unit cell have been identified, and the off-centering of ${\mathrm{Pb}}^{2+}$ on the octahedral sites has been unveiled, probably due to the Pauli repulsion of the lone pair. This material is a wide-gap semiconductor with $E_g$ = 2.27 eV and demonstrates photoluminescence activity. The thermal conductivity is disorder-dominated with an extremely low value of $0.17\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ from about 75 K up to 325 K. The present investigation on $\mathrm{F}{\mathrm{A}}_{0.9}\mathrm{M}{\mathrm{A}}_{0.1}\mathrm{Pb}{\mathrm{I}}_{2.23}{\mathrm{Br}}_{0.77}$ single crystal demonstrates that low values of thermal conductivities are obtained in this hexagonal family of hybrid halide perovskites, with mixed cationic and anionic disorder.

• Received 4 July 2023
• Revised 18 October 2023
• Accepted 25 January 2024

DOI:https://doi.org/10.1103/PhysRevMaterials.8.025403