Dipole–dipole-interaction-assisted self-assembly of quantum dots for highly efficient light-emitting diodes

The external quantum efficiency of state-of-the-art quantum dot light-emitting diodes is limited by the low photon out-coupling efficiency. Light-emitting diodes using oriented nanostructures such as nanorods, nanoplatelets and dot-in-disc nanocrystals favour photon out-coupling; however, their internal quantum efficiency is often compromised and thus achieving a net gain has proved challenging. Here we report isotropic-shaped quantum dots featuring a mixed-crystallographic structure composed of wurtzite and zinc blende phases. The wurtzite phase promotes dipole–dipole interactions that orient quantum dots in solution-processed films, whereas the zinc blende phase helps lift the electronic state degeneracy to enable directional light emission. These combined features improve photon out-coupling without compromising internal quantum efficiency. Fabricated light-emitting diodes exhibit an external quantum efficiency of 35.6% and can be continuously operated with an initial brightness of 1,000 cd m^–2 for 4.5 years with a minimal performance loss of about 5%.