Highly efficient Ag–In–Zn–S quantum dot light-emitting diodes with a hole-spacing interlayer

Although much effort has been made to the cadmium-free quantum dot light emitting diodes (QLEDs), it is still a big challenge to achieve an efficient eco-friendly QLED. Here, an extremely efficient QLED based on Ag–In–Zn–S QDs is constructed with the insertion of an 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) hole-spacing interlayer. The electrical properties of single carrier devices demonstrate the TPBi blocks the hole injection, leading to a more balanced charge injection in the device. Transient electroluminescence measurements confirm that the hole accumulation adjacent QDs is dramatically suppressed after the insertion of TPBi, hence limiting the interactions between excitons and holes. Consequently, the peak current (power) efficiency of 6.0 cd/A (6.5 lm/W) is achieved. To the best of our knowledge, this is the record efficiency for the Ag–In–Zn–S QLEDs reported to date. We anticipate this work will provide a new route for optimizing the performance of Cd-free QLEDs.