Zeng Shijia, Li Zhenbo, Tan Wenjiang, Si Jinhai, Li Yuren, Hou Xun
Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Shaanxi Key Laboratory of Information Photonic Technique, School of Electronics Science and Engineering, Xi'an Jiaotong University, 28 Xianning Road, Xi'an 710049, China.
Nanomaterials (Basel). 2022 Oct 28;12(21):3817. doi: 10.3390/nano12213817.
The excellent performance of InP/ZnSe/ZnS core/shell/shell quantum dots (CSS-QDs) in light-emitting diodes benefits from the introduction of a ZnSe midshell. Understanding the changes of ultrafast carrier dynamics caused by the ZnSe midshell is important for their optoelectronic applications. Herein, we have compared the ultrafast carrier dynamics in CSS-QDs and InP/ZnS core/shell QDs (CS-QDs) using femtosecond transient absorption spectroscopy. The results show that the ZnSe midshell intensifies the electron delocalization and prolongs the in-band relaxation time of electrons from 238 fs to 350 fs, and that of holes from hundreds of femtoseconds to 1.6 ps. We also found that the trapping time caused by deep defects increased from 25.6 ps to 76 ps, and there were significantly reduced defect emissions in CSS-QDs. Moreover, the ZnSe midshell leads to a significantly increased density of higher-energy hole states above the valence band-edge, which may reduce the probability of Auger recombination caused by the positive trion. This work enhances our understanding of the excellent performance of the CSS-QDs applied to light-emitting diodes, and is likely to be helpful for the further optimization and design of optoelectronic devices based on the CSS-QDs.
InP/ZnSe/ZnS核/壳/壳量子点（CSS-QDs）在发光二极管中的优异性能得益于ZnSe中间壳层的引入。了解由ZnSe中间壳层引起的超快载流子动力学变化对于其光电应用至关重要。在此，我们使用飞秒瞬态吸收光谱法比较了CSS-QDs和InP/ZnS核/壳量子点（CS-QDs）中的超快载流子动力学。结果表明，ZnSe中间壳层增强了电子离域，并将电子的带内弛豫时间从238飞秒延长至350飞秒，空穴的带内弛豫时间从数百飞秒延长至1.6皮秒。我们还发现，由深缺陷引起的俘获时间从25.6皮秒增加到76皮秒，并且CSS-QDs中的缺陷发射显著减少。此外，ZnSe中间壳层导致价带边缘以上高能空穴态的密度显著增加，这可能降低由正三激子引起的俄歇复合概率。这项工作增进了我们对应用于发光二极管的CSS-QDs优异性能的理解，并且可能有助于基于CSS-QDs的光电器件的进一步优化和设计。
