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

Generally, the properties of CsPbX 3 (X = Cl, Br, I) are closely related to their morphology, size, composition and phase. Black phase (α, β, or γ) CsPbI 3 easily transforms to yellow phase (δ) CsPbI 3 accompanied by optical performance decay at room temperature. A temperature-dependent phase transition is a routine process for bulk CsPbI 3, whereas there is a lack of an effective method to control the phase of CsPbI 3 nanocrystals. It is still interesting and challenging to control the morphology and phase transition of black phase CsPbI 3 . 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-CsPbI 3 nanorods (NRs) could be obtained due to F – preferential adsorption on the γ-CsPbI 3 (220) crystal plane to inhibit its growth and allow preferential growth orientation perpendicular to the γ-CsPbI 3 (202) crystal plane. Benefiting from Pb–F bond passivation and the hydrophobic phenyl group of ligands, γ-CsPbI 3 NRs exhibited good water resistance and crystal phase stability. Furthermore, a high-quality γ-CsPbI 3 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-CsPbI 3 NR film could meet the needs of practical applications.