YCl-Substituted CsPbI Perovskite Nanorods for Efficient Red-Light-Emitting Diodes.

Cesium lead iodide (CsPbI) perovskite nanocrystals (NCs) are a promising material for red-light-emitting diodes (LEDs) due to their excellent color purity and high luminous efficiency. However, small-sized CsPbI colloidal NCs, such as nanocubes, used in LEDs suffer from confinement effects, negatively impacting their photoluminescence quantum yield (PLQY) and overall efficiency. Here, we introduced YCl into the CsPbI perovskite, which formed anisotropic, one-dimensional (1D) nanorods. This was achieved by taking advantage of the difference in bond energies among iodide and chloride ions, which caused YCl to promote the anisotropic growth of CsPbI NCs. The addition of YCl significantly improved the PLQY by passivating nonradiative recombination rates. The resulting YCl-substituted CsPbI nanorods were applied to the emissive layer in LEDs, and we achieved an external quantum efficiency of ~3.16%, which is 1.86-fold higher than the pristine CsPbI NCs (1.69%) based LED. Notably, the ratio of horizontal transition dipole moments (TDMs) in the anisotropic YCl:CsPbI nanorods was found to be 75%, which is higher than the isotropically-oriented TDMs in CsPbI nanocrystals (67%). This increased the TDM ratio and led to higher light outcoupling efficiency in nanorod-based LEDs. Overall, the results suggest that YCl-substituted CsPbI nanorods could be promising for achieving high-performance perovskite LEDs.