“Understanding and Overcoming the Poor Efficiency of QLEDs Utilizing Organic Electron Transport Layers”

Despite their potential advantages over widely used ZnO, the use of organic materials for the electron transport layers (ETLs) in quantum dot light-emitting devices (QLEDs) has been limited by subpar external quantum efficiency (EQE). This work investigates the root causes of this issue and approaches to address them. Contrary to expectations, electron leakage toward the hole transport layer (HTL) is identified as a plays a primary role in limiting the efficiency of these devices. By using a multilayer ETL configuration that includes electron blocking interfaces, electron leakage is reduced, and higher EQE is achieved. Using this approach, a max EQE of ≈10% in green- and red-emitting QLEDs, the highest reported for a green QLED not utilizing a ZnO ETL and among the highest in the case of red QLEDs, has been demonstrated. Tests on electron-only devices as well as transient electroluminescence measurements point to a mechanism where the formation of electron space charges within the organic ETLs may be assisting hole injection in the quantum dot layer, thus helping to reduce leakage. The findings highlight the importance of layer interface engineering and leakage control for achieving higher EQE in QLEDs, and present strategies for the effective utilization of organic ETLs in them.