[J. Mater. Chem. C] Ligand-Assisted Solid Phase Synthesis of Mixed-Halide Perovskite Nanocrystals for Color-Pure and Efficient Electroluminescence

Colloidal nanocrystals (NCs) of lead halide perovskites have generated considerable interest in demonstrating their optoelectronic devices, such as light emitting-diodes (LEDs), because of their tunable optical bandgap, narrow spectral width, and high defect tolerance. However, the inhomogeneous halide distribution within individual NCs remains to be a critical challenge in order to obtain color-stable electroluminescence in the mixed-halide systems. Here, we demonstrate a new post-synthetic approach, the ligand-assisted solid phase synthesis (LASPS), to prepare the electroluminescent colloidal NCs of methylammonium (MA) lead halide perovskites, at room temperature. The slow reaction kinetics preserve the morphology, size, and shape in the resulting NCs, whose emission covers the entire visible spectral region with the photoluminescence (PL) quantum yields (QYs) of up to > 90% and the colloidal stability up to several months. Using the prepared mixed-halide NCs, the fabricated LEDs display narrowband electroluminescence (EL) ranging from 476 to 720 nm. The optimized red LEDs exhibit an external quantum efficiency, ηext, of up to 2.65%, together with the CIE 1931 color coordinates of (0.705, 0.290), nearly identical to that for the red primary in the recommendation (rec.) 2020 standard (0.708, 0.292).