Bottom emission QLED

The performance of the QLEDs depends primarily on the PLQY of the active layer, charge injection efficiency through the CTLs, and light extraction efficiency. Here we talk about the bottom emission architecture of QLEDs. A binary blend of QDs is used as active layer in the QLEDs. Zinc oxide (ZnO) as ETL and 1,2-ethanedithiol (EDT) capped lead sulphide (PbS) QDs as HTL leads to band alignment as in the picture. 

The inherent long chain oleic acid ligands on the QDs were exchanged with short chain ligands via solid state ligand exchange process. By doing this on multiple layers  (layer-by-layer), we can control the thickness of the layers.

By tuning different properties such as ZnO annealing temperature, EML thickness, step injection of electrons, a record external quantum efficiency of 15% and maximum radiance of 30 W·sr⁻¹·m⁻². However, the thick glass substrate limits the light extraction efficiency limiting the performance, which can be improved by top emission.