Understanding the charge dynamics in the quantum-dot light-emitting diodes (QLEDs) is essential to further improve their performance. Here we demonstrate that the holes can be stored for over 30 ms in QLEDs based Cd-based quantum dot (QD) emission layer. This ultralong-term hole storage is examined by inserting an electron-capturing unit (ECU) in the hole-transport layer. Through superimposing a negative offset voltage during transient electroluminescence measurements, the electrons captured by the ECU were transported back to the QDs, where holes are stored during the typical operation for the QLED. Then, excitons are formed and electroluminescence signal is detected. We found that the electroluminescence signal can be detected until 30 ms after turning off the driving voltage for the QLED. Given the limited electron capturing time in the ECU, this should be the lower limit for hole storage time. It is abnormal and unanticipated for the QLEDs based on the ZnO electron-transport layer, for which electrons are widely considered as the majority charge carriers. We believe our results can offer significant insights into the working mechanism and degradation of the QLEDs.

中文翻译：

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量子点发光二极管中的电荷存储行为


了解量子点发光二极管 （QLED） 中的电荷动力学对于进一步提高其性能至关重要。在这里，我们证明了空穴可以在基于 QLED 的基于 Cd 的量子点 （QD） 发射层中存储超过 30 毫秒。通过在空穴传输层中插入电子捕获单元 （ECU） 来检查这种超长期空穴存储。通过在瞬态电致发光测量期间叠加负偏移电压，ECU 捕获的电子被传输回 QD，在 QLED 的典型操作期间，QD 会在那里存储空穴。然后，形成激子并检测电致发光信号。我们发现，在关闭 QLED 的驱动电压后 30 ms 内可以检测到电致发光信号。鉴于 ECU 中的电子捕获时间有限，这应该是空穴存储时间的下限。对于基于 ZnO 电子传输层的 QLED 来说，这是不正常的和意想不到的，其中电子被广泛认为是大多数电荷载流子。我们相信我们的结果可以为 QLED 的工作机制和退化提供重要的见解。