Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Am Chem Soc. 2010 Oct 27;132(42):15038-45. doi: 10.1021/ja106710m.
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.
I 型核壳量子点 (QD) 已被证明可提高 QD 敏化太阳能电池的稳定性和转化效率，优于仅含核的 QD。为了了解壳层厚度如何影响太阳能电池的性能，研究了其对界面电荷分离和复合动力学的影响。通过时间分辨瞬态吸收光谱，在吸附有蒽醌分子（作为电子受体）的 CdSe/ZnS 型 I 核壳 QD 中测量这些动力学。结果表明，电荷分离和复合速率随壳层厚度 (d) 呈指数衰减，k(d) = k(0)e(-βd)，其中指数衰减因子 β 分别为 0.35 ± 0.03 和 0.91 ± 0.14 每 Å。模型计算表明，这些趋势可归因于壳层厚度引起的 QD 表面 1S 电子和空穴密度的指数衰减。电荷复合速率的急剧下降是由于 ZnS 壳层中的空穴有效质量（大于电子）较大。这一发现表明，通过控制壳层材料的厚度和性质，可以优化电荷分离产率和寿命。
