Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Solution-Processable Highly Conductive Spinel Structure CuCo 2 O 4 Hole Injection Layer.

Charge imbalance in quantum-dot light-emitting diodes (QLEDs) causes emission degradation. Therefore, many studies focused on improving hole injection into the QLEDs-emitting layer owing to lower hole conductivity compared to electron conductivity. Herein, CuCo 2 O 4 has a relatively higher hole conductivity than other binary oxides and can induce an improved charge balance. As the annealing temperature decreases, the valence band maximum (VBM) of CuCo 2 O 4 shifts away from the Fermi energy level (E F ), resulting in an enhanced hole injection through better energy level alignment with hole transport layer. The maximum luminance and current efficiency of the CuCo 2 O 4 hole injection layer (HIL) of the QLED were measured as 93,607 cd/m 2 and 11.14 cd/A, respectively, resulting in a 656% improvement in luminous performance of QLEDs compared to conventional metal oxide HIL-based QLEDs. These results demonstrate that the electrical properties of CuCo 2 O 4 can be improved by adjusting the annealing temperature, suggesting that solution-processed spinel can be applied in various optoelectronic devices.