Spectrally Tunable and Stable Electroluminescence Enabled by Rubidium Doping of CsPbBr₃ Nanocrystals

Abstract Perovskite nanocrystals exhibit high photoluminescence quantum yields (PLQYs) and tunable bandgaps from ultraviolet to infrared. However, blue perovskite light‐emitting diodes (LEDs) suffer from color instability under applied bias. Developing narrow‐bandwidth deep‐blue emitters will maximize the color gamut of display technologies. Mixed anion approaches suffer from halide segregation that leads to their spectral instability. Here instead, a mixed cation strategy is employed whereby Rb⁺ is directly incorporated during synthesis into CsPbBr₃ nanocrystals. Blue‐emitting perovskite quantum dots (QDs) with stable photoluminescence, PLQYs greater than 60%, tunable emission from 460 to 500 nm, and narrow emission linewidths (<25 nm) are reported. The strategy retains a pure bromine crystal structure resulting in color‐pure stable electroluminescence at operating voltages of up to 10 V, peak external quantum efficiencies (EQEs) of 0.87% and 0.11% for sky‐blue (490 nm), and deep‐blue (464 nm) devices. The sky‐blue devices exhibit the highest combined luminance of 93 cd m⁻² at an EQE of 0.75%, the best reported to date of perovskite QD LEDs.