Hole migration enables efficient and ultra-bright green quantum dot LEDs

Quantum dots are promising candidates for more efficient and brighter light-emitting diodes in display and lighting applications. However, due to low carrier concentrations and strong confinement, the electroluminescence efficiency and brightness are hindered by low exciton formation rate, i.e. the probability of electrons meeting holes. Here, we demonstrate that the weak hole confinement, induced inter-dot hole diffusion in quantum dots with large CdZnSe cores and thin ZnS shells, allows more efficient exciton formation. As a result, we achieve a peak external quantum efficiency of 30.7%, a maximum luminance exceeding 1.9 million cd m-2 in green quantum dot light-emitting diodes. Moreover, efficient utilization of carriers depresses the Joule heat generation, allowing us to achieve a T95 operational lifetime (time for the luminance to decrease to 95% of the initial value) of 21,900 hours at 1000 cd m−2. Zhang et al. report green-emitting colloidal quantum dots with a large CdZnSe core and a thin ZnS shell, enabling the weak hole confinement for efficient exciton formation. LEDs with efficiency of 30.7%, peak luminance of 1.9 million nits, and T95 of 21,900 h at 1,000 nits are achieved.