High-performance tandem CdSe/ZnS quantum-dot light-emitting diodes with a double-layer interconnecting layer composed of thermally evaporated and sputtered metal oxides

High-performance tandem quantum-dot light-emitting diodes (QLEDs) are needed for practical next-generation displays. This study designed a high-performance interconnecting layer (ICL) that combines QLED units into tandem QLEDs and demonstrated its effectiveness. The ICLs were designed for charge generation, for interconnecting QLEDs, and for protecting the underlayers from damage during upper-layer fabrication. Using the ICLs with a first layer of thermally evaporated WO3 and a second layer of sputtered SnO2 or zinc tin oxide, the required roles of the ICL were fulfilled. The current efficiencies of tandem QLEDs using a double-layer ICL were about triple those of a single QLED, an improvement from 26 cd/A for a single QLED to 82 cd/A for a tandem QLED connecting two QLED units. This current efficiency was much higher than previously reported values for tandem QLEDs connecting QLED units with CdSe/ZnS green quantum dots and ZnO electron-transport layers. The method presented here will contribute to the practical application of QLEDs for large TVs and light-illumination devices.