Ligand-Assisted Breaking Crystal Symmetry to Achieve Stable -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 (alpha, beta, or gamma) CsPbI3 easilytransforms to yellow phase (delta) CsPbI3 accompaniedby optical performance decay at room temperature. A temperature-dependentphase transition is a routine process for bulk CsPbI3,whereas there is a lack of an effective method to control the phaseof CsPbI3 nanocrystals. It is still interesting and challengingto control the morphology and phase transition of black phase CsPbI3. Herein, we proposed a ligand-assisted strategy of breakingcrystal symmetry via a short Pb-F bond to simultaneously achievea phase transition and an nisotropic morphology. High-quality gamma-CsPbI3 nanorods (NRs) could be obtained due to F- preferential adsorption on the gamma-CsPbI3 (220) crystalplane to inhibit its growth and allow preferential growth orientationperpendicular to the gamma-CsPbI3 (202) crystal plane.Benefiting from Pb-F bond passivation and the hydrophobic phenylgroup of ligands, gamma-CsPbI3 NRs exhibited good waterresistance and crystal phase stability. Furthermore, a high-quality gamma-CsPbI3 NR film was assembled with a strong emissionanisotropy polarization degree of up to 0.63 and the demo experimentof polarization imaging confirmed that the gamma-CsPbI3 NR film could meet the needs of practical applications.