Peeling back the effect of quantum dot shell thickness on blue QLEDs

The lagging performance of blue quantum-dot light-emitting diodes (QLEDs) behind other colors limits QLED-based applications. While researchers know that the shell thickness of blue quantum dots affects their charge-injection properties, which partially determine QLED performance, they do not understand the process.

Zhang et al. used transient electroluminescence measurements to study blue quantum dots with different shell thicknesses as the emitting layers of QLEDs. Analyzing the transient electroluminescence spectrum allowed them to examine how shell thickness affects both the electron and hole injection processes.

The authors found shell thickness influences the injection of electrons more than the injection of holes. A thick shell dampens the electron injection, which balances charge injection and enhances QLED efficiency.

The transient electroluminescence technique allowed them to distinguish shell thickness’s effect on electrical properties from its effect on optical properties, which routine density-voltage-luminance measurements cannot do. The authors believe this technology could be extended to other electroluminescent devices, such as QLEDs of other colors and halide perovskite-based light-emitting diodes.

“Our present work confirms two things,” said author Wenyu Ji. “One is that transient electroluminescence is a feasible and powerful technology to investigate the charge dynamics of the electroluminescent devices. The other is that the effect of the shells outside the quantum dots on the charge injection is verified, which is significant to design and optimize the QLEDs.”

With the results from this work, the authors fabricated a blue QLED with an ideal shell thickness of about 1.5 nanometers that featured a record current efficiency. They are currently investigating how quantum dot shells influence device lifetime in the hopes of eventually producing efficient and stable blue QLEDs.

Source: “Unraveling the effect of shell thickness on charge injection in blue quantum-dot light-emitting diodes,” by Huimin Zhang, Qilin Yuan, Ting Wang, Xulan Xue, Yuan Yuan, Hanzhuang Zhang, Mi Zhou, and Wenyu Ji, Applied Physics Letters (2021). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0068934 .