Enhancing the Performance of Quantum-Dot Light-Emitting Diodes by Postmetallization Annealing.

The effect of postannealing on the device characteristics is systematically investigated. The external quantum efficiency (EQE) of blue quantum-dot light-emitting diodes (QLEDs) is significantly improved from 5.22 to 9.81% after postannealing. Similar results are obtained in green and red QLEDs, whose EQEs are enhanced from 11.47 and 13.60 to 15.57 and 16.59%, respectively. The annealed devices also exhibit a larger current density. The origin of efficiency improvement is thoroughly investigated. Our finding indicates that postannealing promotes the interfacial reaction of Al and ZnMgO and consequently leads to the metallization of the AlZnMgO contact and the formation of the AlO interlayer. Because of the metallization of AlZnMgO, the contact resistance is effectively reduced, and thus the electron injection is enhanced. On the other hand, the formation of the AlO interlayer can effectively suppress the quenching of excitons by the metal electrode. Because of the enhancement of electron injection and suppression of exciton quenching, the annealed blue, green, and red QLEDs exhibit a 1.9-, a 1.3-, and a 1.2-fold efficiency improvement, respectively. We envision the results offer a simple yet effective method to enhance the charge injection and the efficiency of QLED devices, which would promote the practical application of QLEDs.