Color Tuning in Cesium Lead Halide Nanocrystals via A‑Site Substitution as an Alternative Method for Achieving Spectrally Stable Blue Perovskite Nanocrystal Light-Emitting Diodes

Blue-emitting lead halide perovskite nanocrystals (NCs) continue to exhibit unstable emission spectra, resulting from halide migration effects that hinder the performance of blue NC light-emitting diodes (NC-LEDs). One method to avoid halide mixing while still attaining deeper blue emission with improved stability is to incorporate rubidium into the mixture of A-site ions. Here, we explore the impact of varying the amount of rubidium doping in lead halide perovskite NCs. Our findings indicate that the rubidium-doping ratio influences the number of defects in the perovskite NCs, ultimately affecting the degree of blue shift we observe and the resulting performance of the NC-LEDs. Additionally, this study presents a modified room-temperature, open-air synthesis of sky-blue perovskite Cs_xRb_1–xPbBr₃ NCs with 0 to 45% Rb-alloying. The synthesized NCs have sizes ranging from 13.0 to 15.6 nm, and their emission can be adjusted from 515 to 496 nm with an observed full width at half-maximum of between 19 and 26 nm. These NCs also demonstrate a high photoluminescence quantum yield ranging from 94.5 to 69.7%. The NC-LEDs fabricated from these NCs showed stable spectra, a maximum external quantum efficiency (EQE) of 11.0% with a peak luminescence of 32,300 cd/m² at 508 nm for green emission, and a maximum EQE of 5.9% with a peak luminescence of 21,700 cd/m² at 496 nm for sky-blue emission. These results highlight the potential of Rb-alloying lead halide perovskite NCs for developing efficient and spectrally stable blue perovskite NC-LEDs.