High-performance all-solution-processed inverted quantum dot light-emitting diodes enabled by water treatment

All-solution-processed inverted quantum dot (QD) light-emitting diodes (QLEDs) with transparent bottom cathodes can be directly connected to the n-type thin-film transistors, offering a feasible solution for low-cost active matrix-driven QD displays. However, the subsequent solution-deposition of the hole-transporting layer destroys the underneath QD films, resulting in largely deteriorated device performance. Various strategies have been implemented to prevent QD film from dissolution, but all at a heavy cost of device performance suffering from either reduced efficiency or increased driving voltage. Here, a facile and effective water-treatment approach for QD film to fabricate inverted QLEDs through all solution processing is reported. The water treatment substitutes the long-chain oleate ligands with hydroxyl groups, resulting in significantly improved non-polar solvent resistance of the QD films. Importantly, the QD films reserve their excellent photoluminescence efficiency after water treatment. With the water-treated QD film as the emissive layer, all-solution-processed inverted red QLED with a peak external quantum efficiency of 19.6%, a turn-on voltage of 1.8 V, and a T-50 operational lifetime of 150,000 h at 100 cd.m(-2) was achieved. Furthermore, efficient and low-voltage-driven green and blue QLEDs can also be prepared with this method. This work provides a feasible strategy for the fabrication of high-performance all-solution-processed inverted QLEDs, paving the way toward achieving QLEDs by all ink-jet printing.