Colloidal nanoplatelets (NPLs) are an emerging semiconductor nanocrystal in the display community due to their ultranarrow emission linewidth. Herein, an ultrapure green emitting nanocrystal light‐emitting diode (LED) based on four‐monolayer CdSe/CdS core/crown NPLs is developed. By applying the nonstacked nanoplates, the nonradiative energy transfer in the NPLs film is successfully suppressed. The nonstacked NPL‐LEDs with pure green emission of 521.5 nm exhibit a low turn‐on voltage of 2.1 V, a maximum luminance of 22 400 cd m−2, a peak external quantum efficiency (EQE) of 2.16%, which is a sixfold enhancement comparing to the stacked NPL‐LED (EQE = 0.34%). This work demonstrates the potential of core/crown NPLs for ultrawide color gamut displays.

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Improving the stability of inkjet‐printed quantum dot light emitting diodes (QLEDs) is critical for the technology to become commercially viable. The major obstacle is the compromise between the printability of the ink system and the functionality of the carrier transport layers. Here, a ternary ink system consisting of octane, 1‐cyclohexyl‐ethanol, and n‐butyl acetate is reported, which solves the erosion between the printed quantum dot ink and the underneath hole transport layer. A gradient vacuum post‐treatment is developed to accompany the ternary ink system with gradient vacuum pressures, which is helpful in forming a uniform printing layer. Based on both technologies, the inkjet‐printed R/G/B QLEDS are fabricated with high resolution patterns, showing high efficiencies and stabilities. The external quantum efficiency of R/G/B devices is 19.3%, 18.0%, and 4.4%, respectively. Correspondingly, the half operating lifetime is up to 25 178 h @ 1000 cd m−2, 20 655 h @ 1000 cd m−2, and 46 h @ 100 cd m−2, respectively. The improvements in the ink engineering and post‐treatment in this study have taken the efficiency and stability of the devices to a higher level and confirm the application prospects of printed QLEDs in the display industry.