Systematic Study of the Synthesis of Monodisperse CsPbI 3 Perovskite Nanoplatelets for Efficient Color‐Pure Light Emitting Diodes

Abstract Metal halide perovskite nanoplatelets (NPls) possess ultra‐narrow photoluminescence (PL) bands tunable over the entire visible spectral range, which makes them promising for utilization in light‐emitting diodes (LEDs) with spectrally pure emission colors. This calls for development of synthetic methods toward perovskite NPls with a high degree of control over both their thickness and lateral dimensions. A general strategy is developed to obtain such monodisperse CsPbI 3 NPls through the control over the halide‐to‐lead ratio during heating‐up reaction. The excess of iodine precursor changes the chemical equilibrium, thus yielding monodisperse (3 monolayers in thickness) CsPbI 3 NPls whose PL width constitutes ≈22 nm, while the lateral dimensions of NPls are determined by choice of precursor and by the reaction temperature. Postsynthetic cation exchange on the A‐site of the perovskite lattice allows for the tuning of the PL peak position, while simultaneous removal of the excess ligands and the surface passivation allows for improvement of the PL quantum yield to 96% and ensures superior stability of optical properties upon storage. Electroluminescent LEDs with the peak values are fabricated for the external quantum efficiency and luminance being 9.45% and 29800 cd m −2 , respectively, and a narrow (≈26 nm) electroluminescence peak at 601 nm.