Stabilization of Quantum-Confined Anisotropic CsPbI₃ Nanoplatelets by Solid-Phase Metal Iodide Crude Reaction for Color-Pure Red Emission

Quantum-confined CsPbI3 perovskite nanoplatelets (NPLs) are highly desirable for optoelectronic applications owing to their anisotropic electronic properties that substantially boost the light outcoupling efficiency in light-emitting diodes (LEDs). However, the structural instability of the emissive CsPbI₃ phases makes it degrade rapidly to the non-emissive δ-phase under ambient conditions. Here, the study presents a synthetic approach to produce spectrally stable CsPbI₃ nanoplatelets (NPLs) through solid-phase crude reactions with metal iodide powders, MI₂ (M²⁺ = Mn²⁺ or Zn²⁺). The synthesized NPLs exhibit narrow and color-pure red emission with high photoluminescence (PL) quantum yields (QYs, ηPL) of up to 85%. Systematic investigations into the surface chemistry of NPLs reveal that metal iodide treatment stabilizes anisotropic CsPbI₃ NPLs via surface passivation with metal and halide ions, substantially hindering from the formation of non-emissive yellow phase. The anisotropic NPLs display signatures of spontaneous self-assembly in spin-casted films, which yield strong emission anisotropy, with up to 82% of the transition dipoles being horizontally oriented with respect to the substrate, as revealed by the back focal plane (BFP) imaging. The results presented here shed light on solid-phase approaches for the preparation of quantum-confined nanocrystals (NCs) with desirable geometry, which boost the light outcoupling efficiency in LEDs.