Lead halide perovskite nanocrystals (PNCs) are emerging as promising light emitters to be actively explored for high color purity and efficient light-emitting diodes. However, the most reported lead halide perovskite nanocrystal light-emitting diodes (PNCLEDs) encountered issues of emission line width broadening and operation voltage elevating caused by the quantum confinement effect. Here, we report a new type of PNCLED using large-size CsPbBr3 PNCs overly exceeding the Bohr exciton diameter, achieving ultranarrow emission line width and rapid brightness rise around the turn-on voltage. We adopt calcium-tributylphosphine oxide hybrid ligand passivation to produce highly dispersed large-size colloidal CsPbBr3 PNCs with a weak size confinement effect and also high photoluminescence quantum yield (∼85%). Utilizing these large-size PNCs as emitters, we manifest that the detrimental effects caused by the quantum confinement effect can be avoided in the device, thereby realizing the highest color purity in green PNCLED, with a narrow full width at half-maximum of 16.4 nm and a high corrected maximum external quantum efficiency of 17.85%. Moreover, the operation half-life time of the large-size PNCLED is 5-fold of that based on smaller-size PNCs. Our work provides a new avenue for improving the performance of PNCLEDs based on unconventional large-size effects.

Lead halide perovskite nanocrystals (LHP NCs) are regarded as promising emitters for next-generation ultrahigh-definition displays due to their high color purity and wide color gamut. Recently, the external quantum efficiency (EQE) of LHP NC based light-emitting diodes (PNC LEDs) has been rapidly improved to a level required by practical applications. However, the poor operational stability of the device, caused by halide ion migration at the grain boundary of LHP NC thin films, remains a great challenge. Herein, we report a resurfacing strategy via pseudohalogen ions to mitigate detrimental halide ion migration, aiming to stabilize PNC LEDs. We employ a thiocyanate solution processed post-treatment method to efficiently resurface CsPbBr3 NCs and demonstrate that the thiocyanate ions can effectively inhibit bromide ion migration in LHP NC thin films. Owing to thiocyanate resurfacing, we fabricated LEDs with a high EQE of 17.3%, a maximum brightness of 48000 cd m–2, and an excellent operation half-life time.