Center for Advanced Solar Photophysics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
ACS Nano. 2012 Nov 27;6(11):9532-40. doi: 10.1021/nn3043226. Epub 2012 Oct 18.
Carrier multiplication (CM) is the process in which absorption of a single photon produces multiple electron-hole pairs. Here, we evaluate the effect of particle shape on CM efficiency by conducting a comparative study of spherical nanocrystal quantum dots (NQDs) and elongated nanorods (NRs) of PbSe using a time-resolved technique that is based on photon counting in the infrared using a superconducting nanowire single-photon photodetector (SNSPD). Due to its high sensitivity and low noise levels, this technique allows for accurate determination of CM yields, even with the small excitation intensities required for quantitative measurements, and the fairly low emission quantum yields of elongated NR samples. Our measurements indicate an up to ∼60% increase in multiexciton yields in NRs versus NQDs, which is attributed primarily to a decrease in the electron-hole pair creation energy. These findings suggest that shape control is a promising approach for enhancing the CM process. Further, our work demonstrates the effectiveness of the SNSPD technique for the rapid screening of CM performance in infrared nanomaterials.
载流子倍增（CM）是指吸收单个光子产生多个电子-空穴对的过程。在这里，我们通过使用基于超导纳米线单光子光电探测器（SNSPD）在红外光中进行光子计数的时间分辨技术，对球形纳米晶量子点（NQD）和拉长的纳米棒（NR）的 CM 效率进行了对比研究，评估了颗粒形状对 CM 效率的影响。由于其灵敏度高、噪声水平低，即使在进行定量测量所需的小激发强度下，以及拉长的 NR 样品相当低的发射量子产率下，该技术也允许对 CM 产率进行准确的确定。我们的测量表明，NR 中的多激子产率比 NQD 增加了约 60%，这主要归因于电子-空穴对产生能量的降低。这些发现表明，形状控制是增强 CM 过程的一种很有前途的方法。此外，我们的工作还证明了 SNSPD 技术在快速筛选红外纳米材料的 CM 性能方面的有效性。
