Diagnosing the Charge Dynamic Behaviors in Quantum-Dot\nLight-Emitting Diodes by Temperature-Dependent Measurements

Distinguishing\nand understanding the nonradiative recombination\nof charges are crucial for optimizing quantum-dot light-emitting diodes\n(QLEDs). Auger recombination (AR), a well-known nonradiative process,\nis widely recognized to occur in QLEDs. However, it has not yet been\ndirectly observed in a real working QLED. Here, the AR effect is verified\nin the QLED at temperatures of <150 K. At low temperatures, the\nQLED exhibits a unique S-shaped external quantum efficiency (EQE)\nevolution as the driving current density increases. Experimental and\nmodeling results indicate that this S-shaped EQE results from the\nasynchronous changes in the behavior of injection of electrons and\nholes into the quantum-dot emission layer. At low driving voltages,\nboth electron and hole currents are limited by the Fowler–Nordheim\n(F–N) tunneling behavior. The relatively low barrier for electrons\nleads to overwhelming electron injection and seriously imbalanced\ncharges in the quantum dots, triggering the AR process. As the voltage\nincreases, the electron current within the emission layer is no longer\ngoverned by F–N tunneling but limited by space charges. Then,\ncharge injection becomes balanced, and the EQE increases. These results\noffer valuable insights into the charge injection and recombination\nprocesses within QLEDs, as well as implications for device design.