Light-Emitting Diodes with Cd-Free Quantum Dots Embedded in a Carrier Transport Matrix Grown by a Wet Process

Quantum dot light-emitting diodes (QLEDs) are promising next-generation display devices due to their stable inorganic components, sharp emission peaks, and simple device structures. Although Cd-based QLEDs exhibit good device performance, Cd-free devices are expected to be developed for reducing negative environmental impact. Cd-free QDs are ready to be oxidized. We therefore propose a procedure for fabrication of QLEDs, in which the interparticle space of the QD layer is gradually filled with an inorganic carrier transport material (ZnS) by the successive ionic layer adsorption and reaction (SILAR) method. Since organic ligands of the QDs are removed and the QDs are embedded in the inorganic matrix in the SILAR process, QDs are protected from the oxidizing environment by the matrix. This room-temperature process would not cause significant damage to the underlayers. The SILAR process was optimized through replacement of the countercation of the anionic precursor (S2-) with a larger one (from Na+ to K+) and doping the matrix with Mg2+ for suppressing nonradiative leak currents. As a result, the external quantum efficiency of the QLED device was improved by a factor of 2.1, and the device lifetime was extended by more than 80 times in comparison with the device fabricated without the SILAR process.