Quantum Confinement-Tunable Ultrafast Charge Transfer at the PbS Quantum Dot and Phenyl-C61-butyric Acid Methyl Ester Interface
Quantum Confinement-Tunable Ultrafast Charge Transfer at the PbS Quantum Dot and Phenyl-C61-butyric Acid Methyl Ester Interface
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DOI：
10.1021/ja413254g
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发表时间：
2014-05-14
影响因子：
15
通讯作者：
Mohammed, Omar F.
中科院分区：
文献类型：
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作者：
El-Ballouli, Ala'a O.;Alarousu, Erkki;Mohammed, Omar F.
量子点(QD)太阳能电池已经成为现有光伏技术的有前途的低成本替代品。在这里，我们使用飞秒宽带暂态吸收(TA)光谱和稳态光致发光猝灭测量相结合的方法研究了PbS量子点和苯基-C-61-丁酸甲酯(PCBM)界面上的电荷转移和分离。我们分析了四种不同量子点尺寸的PbS量子点/PCBM界面的超快电子注入和电荷分离，以及它们与PCBM浓度的关系。结果表明，受量子尺寸效应调节的能带排列是有效的电子注入和电荷分离过程的关键因素。更具体地说，稳态和时间分辨数据表明，只有禁带宽度大于i eV的小尺寸PbS量子点才能在光吸收时将电子转移到PCBM。我们发现，这些趋势是由于量子点的尺寸分布导致了11类界面带排列的结果。瞬时吸收数据表明，对于具有实现第二类对齐的带隙的量子点，从光激发的PbS量子点到PCBM的电子注入发生在我们120 fS的时间分辨率内，而在较小带隙的量子点样品中观察到的几乎所有信号都是由尺寸分布中的大带隙异常值引起的。综上所述，我们的结果清楚地表明，通过设计量子点的尺寸分布，量子点界面上的电荷转移速率可以被调节几个数量级。本文的工作将对太阳能转换量子点接口的设计和理解起到推动作用。
Quantum dot (QD) solar cells have emerged as promising low-cost alternatives to existing photovoltaic technologies. Here, we investigate charge transfer and separation at PbS QDs and phenyl-C-61-butyric acid methyl ester (PCBM) interfaces using a combination of femtosecond broadband transient absorption (TA) spectroscopy and steady-state photoluminescence quenching measurements. We analyzed ultrafast electron injection and charge separation at PbS QD/PCBM interfaces for four different QD sizes and as a function of PCBM concentration. The results reveal that the energy band alignment, tuned by the quantum size effect, is the key element for efficient electron injection and charge separation processes. More specifically, the steady-state and time-resolved data demonstrate that only small-sized PbS QDs with a bandgap larger than I eV can transfer electrons to PCBM upon light absorption. We show that these trends result from the formation of a type-11 interface band alignment, as a consequence of the size distribution of the QDs. Transient absorption data indicate that electron injection from photoexcited PbS QDs to PCBM occurs within our temporal resolution of 120 fs for QDs with bandgaps that achieve type-II alignment, while virtually all signals observed in smaller bandgap QD samples result from large bandgap outliers in the size distribution. Taken together, our results clearly demonstrate that charge transfer rates at QD interfaces can be tuned by several orders of magnitude by engineering the QD size distribution. The work presented here will advance both the design and the understanding of QD interfaces for solar energy conversion.