Dual optimization strategies to achieve low roll-off and stable quantum dot light-emitting diodes

Quantum dot (QD) based light-emitting diode devices (QLEDs) attracted significant academic interest due to their outstanding color saturation and convenient solution-based manufacturing processes. Currently, the external quantum efficiency (EQE) of red, green, and blue QLEDs reached their own theoretical limits. However, there was still a common phenomenon of roll-off existed in QLEDs. In this work, QLEDs with an ultra low roll-off were realized via simple carrier injection regulation strategy in achieving carrier recombination balance and exhibited excellent repeatability. By modifying quantum dots and electron transport layer (ETL), the champion device with the peak EQE of 15.2 %, and a current efficiency (CE) of 63.4 cd/A was successfully fabricated, which were 1.9 and 2.0 times greater than those of the control devices, respectively. The devices delivered a peak brightness of 266,778 cd/m2, and the EQE remained at 15.0 % at a brightness of 50,000 cd/m2, staying above 14 % within the range of 3000 to 200,000 cd/m2. At a voltage of 10 V, the peak EQE of the optimized devices decreased by only 7.6 % when compared with their optimum value of EQEs, while the EQE of the control device declined by 26.6 %. Finally, analysis of 40 different batches of devices revealed an average EQE of 14.3 %, demonstrating that this strategy exhibited good repeatability. This approach provided a convenient means to regulate carrier injection and further elucidated the relationship between roll-off and carrier injection balance in QLEDs, proposing a strategy to enhance their performance and simultaneously mitigate roll-off.