Controlling charge separation and recombination rates in CdSe/ZnS type I core-shell quantum dots by shell thicknesses.
Controlling charge separation and recombination rates in CdSe/ZnS type I core-shell quantum dots by shell thicknesses.
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DOI：
10.1021/ja106710m
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发表时间：
2010-10
影响因子：
15
通讯作者：
Haiming Zhu;Nianhui Song;T. Lian
中科院分区：
文献类型：
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作者：
Haiming Zhu;Nianhui Song;T. Lian
与单纯的核/壳量子点相比，第一类核/壳量子点(QD)可以提高QD敏化太阳能电池的稳定性和转换效率。为了了解壳层厚度对太阳电池性能的影响，研究了壳层厚度对界面电荷分离和复合动力学的影响。用时间分辨的暂态吸收光谱测量了吸附了邻苯二酚分子(作为电子受体)的CdSe/ZnS I型核壳量子点的这些动力学性质。结果表明，电荷分离和复合速率随壳层厚度(D)呈指数下降，k(D)=k(0)e(-βd)，指数衰减因子β分别为0.35±0.03per和0.91±0.14per；模型计算表明，这些趋势可以归因于量子点表面的1s电子和空穴密度随壳层厚度的指数减小。电荷复合速率的急剧下降是由于硫化锌壳层中的空穴有效质量(比电子大)造成的。这一发现提出了通过控制壳层材料的厚度和性质来优化电荷分离产率和寿命的可能方法。
Type I core/shell quantum dots (QDs) have been shown to improve the stability and conversion efficiency of QD-sensitized solar cells compared to core only QDs. To understand how the shell thickness affects the solar cell performance, its effects on interfacial charge separation and recombination kinetics are investigated. These kinetics are measured in CdSe/ZnS type I core/shell QDs adsorbed with anthroquinone molecules (as electron acceptor) by time-resolved transient absorption spectroscopy. We show that the charge separation and recombination rates decrease exponentially with the shell thickness (d), k(d) = k(0)e(-βd), with exponential decay factors β of 0.35 ± 0.03 per Å and 0.91 ± 0.14 per Å, respectively. Model calculations show that these trends can be attributed to the exponential decrease of the 1S electron and hole densities at the QD surface with the shell thickness. The much steeper decrease in charge recombination rate results from a larger hole effective mass (than electron) in the ZnS shell. This finding suggests possible ways of optimizing the charge separation yield and lifetime by controlling the thickness and nature of the shell materials.