Semiconductor Nanowires for Efficient Transport of Energy and Charge

技术摘要：在美国国家科学基金会化学部大分子、超分子和纳米化学项目的资金支持下，一项旨在提高量子线和相关纳米结构的光致发光效率的全面实验研究正在进行中。纳米线在纳米电子学、纳米光子学、太阳能转换等领域具有潜在的应用前景。二维量子约束和量子线中激子和载流子的输运也引起了人们的基本兴趣。这种应用和基础研究要求纳米线很好地钝化，以抑制激子和电荷载流子在表面陷阱中的损失。纳米线或量子线器件的高效性能要求载流子不会不成比例地在表面/界面位置被捕获和重组。光致发光效率提供了表面钝化质量和诱导非辐射重组的陷阱位点的稀缺性的度量。不幸的是，迄今为止报道的纳米线和量子线的光致发光效率很差。然而，CdSe量子带和CdTe量子线的效率最近分别达到了30%和7%。因此，量子线的光致发光效率问题是可以克服的。针对量子点和量子棒的一系列成功策略尚未在量子线上进行试验。因此，该项目的主要目标是合成具有良好钝化表面的量子线和相关纳米结构，能够有效地传输能量和电荷。建议工作的具体目标如下：-将制备和研究各种成分、长度和厚度的量子带。-探索量子线中的核壳策略，包括核壳壳和梯度壳策略。-制备掺杂量子线，研究稀磁性半导体量子线中的带隙缩小和激子磁极化子。-将调查各种有机和无机表面钝化剂，包括金属有机化合物（路易斯酸），以钝化洞阱。非技术总结：将半导体纳米晶体结合到下一代太阳能转换设备中，引起了相当大的兴趣。由半导体纳米结构构建的太阳能电池有望比传统的硅基器件更经济地制造，并具有其他应用优势。太阳能电池的功能是通过捕获光能并将其转化为高能的正电荷和负电荷，然后将其分离并传输到电池中的相反电极。它为电池充电或操作电器提供电能。因此，关键步骤是有效地分离正电荷和负电荷，并将这些电荷有效地传输到电极上。半导体纳米线是用于新的太阳能电池设计的目标，因为它们原则上可以长距离传输能量和电荷，纳米线的整个长度可以跨越电极间的分离。然而，有效的运输将要求电荷不被困在电线的缺陷处。在美国国家科学基金会化学部大分子、超分子和纳米化学项目的资金支持下，该项目将识别并消除这些陷阱位点缺陷，从而使半导体纳米线在太阳能电池、纳米电子学以及用于光探测和产生的小型设备中的应用成为可能。更广泛的影响包括技术进步，以帮助解决国家的能源挑战。PI在培训妇女和代表性不足群体成员方面也有出色的记录，从而增加了该国技术劳动力的多样性。PI正在华盛顿大学共同领导一项努力，以增加科学、技术、工程和数学（STEM）领域的本科女性留用率。

TECHNICAL SUMMARY: A thorough experimental study to improve the photoluminescence efficiencies in quantum wires and related nanostructures is to be undertaken with the financial support from the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry at the National Science Foundation. Nanowires have potential applications in nanoelectronics, nanophotonics, and solar-energy conversion. There is also fundamental interest in 2D quantum confinement and the transport of excitons and charge carriers in quantum wires. Such applications and fundamental studies require that nanowires be well passivated to inhibit the loss of excitons and charge carriers to surface traps. Efficient performance of a nanowire or quantum-wire device requires that carriers not be disproportionately trapped and recombined at surface/interface sites. Photoluminescence efficiencies provide a measure of the quality of surface passivation and the scarcity of trap sites that induce nonradiative recombination. Unfortunately, the photoluminescence efficiencies in nanowires and quantum wires reported to date are poor. However, efficiencies of 30% and 7%, respectively, in CdSe quantum belts and CdTe quantum wires were recently achieved. Therefore, the problem of photoluminescence efficiency in quantum wires is surmountable. A range of successful strategies just emerging for quantum dots and rods have yet to be tried for quantum wires. The primary goal of the project is thus the synthetic achievement of quantum wires and related nanostructures having well-passivated surfaces, capable of the efficient transport of energy and charge.The specific goals of the proposed work are as follows.- Quantum belts of various compositions, lengths, and thicknesses will be prepared and studied.- Core-shell strategies, including core-shell-shell and gradient-shell strategies, in quantum wires will be explored.- Doped quantum wires will be prepared to investigate band-gap-narrowing, and excitonic magnetic polarons in dilute magnetic semiconductor quantum wires.- A wide variety of organic and inorganic surface-passivating agents, including metalloorganic compounds (Lewis acids) will be surveyed to passivate hole traps.NON-TECHNICAL SUMMARY: There is considerable interest in incorporating semiconductor nanocrystals into next-generation devices for solar-energy conversion. Solar cells constructed from semiconductor nanostructures are expected to be fabricated more economically than the traditional silicon-based devices, and to have other application advantages. A solar cell functions by capturing light energy and converting it to energetic positive and negative electric charges, which are then separated and transported to opposite electrodes in the cell. This provides electrical energy for charging a battery, or operating an electrical appliance. The critical steps are thus the efficient separation of the positive and negative charges, and the efficient transport of those charges to the electrodes. Semiconductor nanowires are targeted for use in new solar-cell designs because they can in principle transport energy and charge over long distances, the entire lengths of the nanowires, which can span the inter-electrode separations. However, efficient transport will require that charges not be trapped at defect sites in the wires. With financial support from Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry at the National Science Foundation, this project will identify and eliminate those trap-site defects, enabling the application of semiconductor nanowires in solar cells, nanoelectronics, and in small-scale devices for light detection and generation. The broader impacts include technological advances to assist in addressing the nation's energy challenge. The PI also has an excellent record of training women and members of underrepresented groups, thereby increasing the diversity of the nation's technological work force. The PI is co-leading an effort at Washington University to increase the retention of undergraduate women in science, technology, engineering, and math (STEM) fields.