Ligand-Assisted Breaking Crystal Symmetry to Achieve Stable γ-CsPbI₃ Nanorods with Strong Polarization Response

Generally, the properties of CsPbX3 (X = Cl, Br, I) are closely related to their morphology, size, composition and phase. Black phase (α, β, or γ) CsPbI3 easily transforms to yellow phase (δ) CsPbI3 accompanied by optical performance decay at room temperature. A temperature-dependent phase transition is a routine process for bulk CsPbI3, whereas there is a lack of an effective method to control the phase of CsPbI3 nanocrystals. It is still interesting and challenging to control the morphology and phase transition of black phase CsPbI3. Herein, we proposed a ligand-assisted strategy of breaking crystal symmetry via a short Pb–F bond to simultaneously achieve a phase transition and an nisotropic morphology. High-quality γ-CsPbI3 nanorods (NRs) could be obtained due to F– preferential adsorption on the γ-CsPbI3 (220) crystal plane to inhibit its growth and allow preferential growth orientation perpendicular to the γ-CsPbI3 (202) crystal plane. Benefiting from Pb–F bond passivation and the hydrophobic phenyl group of ligands, γ-CsPbI3 NRs exhibited good water resistance and crystal phase stability. Furthermore, a high-quality γ-CsPbI3 NR film was assembled with a strong emission anisotropy polarization degree of up to 0.63 and the demo experiment of polarization imaging confirmed that the γ-CsPbI3 NR film could meet the needs of practical applications.