Magic-size nanoclusters as low-temperature precursors to nanocrystal and bulk semiconductor films

在这个项目中进行的研究推进了半导体纳米科学在太阳能技术中的潜在应用。由于大气中的二氧化碳（CO2）水平目前威胁着全球生态系统和人类福祉，清洁能源技术的发展是一项重大的社会需求。Buhro教授正在提供新的方法来制备更高效的太阳能电池和经济、可扩展的半导体加工，这是广泛使用太阳能电力所必需的。该项目的一个方面是开发具有优化结构的半导体纳米晶体薄膜，用于太阳能电池的太阳能吸收层中的电荷传输。这可能会提高电池的性能。这种策略的关键是纳米晶体的形状，它们是板状或带状的，并且紧密地堆叠在一起。这些形状能够远距离传输电荷。该项目的第二个方面是利用溶液化学技术低温沉积半导体薄膜。太阳能电力广泛应用的一个主要缺点是，利用目前的气相和真空技术制造太阳能电池的半导体组件的成本很高。Buhro教授正在为开发更经济的基于解决方案的处理方法做出贡献。该项目的两个方面都依赖于所谓的“神奇大小的半导体纳米团簇”作为关键的化学中间体和前体。神奇大小的纳米团簇是小而离散的分子单元，与目标半导体相具有相同的组成，并且在低温下从溶液中产生晶体半导体。通过提高传输电荷的能力和半导体薄膜制造的经济性，这项研究可能会产生广泛的社会影响，因为它促进了太阳能技术的可用性和实用性。此外，Buhro教授还是一大批女性博士科学家的导师。他致力于通过在入门课程中加入主动学习策略来留住STEM领域的女性。在这个研究项目中，圣路易斯华盛顿大学的William Buhro教授得到了大分子、超分子和纳米化学（MSN）项目的支持，利用化学计量学的神奇尺寸的半导体纳米团簇和平面（2D）、胶体半导体纳米晶体来推进低温、基于溶液的半导体加工和纳米晶体太阳能电池。固态量子点（QD）太阳能电池已经成为第三代光伏技术，有望实现经济、可扩展的生产，并具有实际应用所需的太阳能转换性能。平面（2D）半导体纳米晶体（量子带和量子片）具有与胶体量子点相当的光学特性和界面特性。它们还具有至少一个扩展长度维度。Buhro教授现在正在研究它们在纳米晶体太阳能吸收层中的应用。二维纳米晶体薄膜的结构由面向三维的捆绑半有序畴组成。相对于量子点而言，更大的横向纳米晶体尺寸有望增加载流子的平均自由程并最小化跳变。整个薄膜结构可以提供在所有三个维度上渗透的传导途径。这些材料可以减少载流子复合，提高太阳能电池的光子转换效率。这个项目的第二个组成部分是分子半导体油墨。用于半导体制造的理想分子墨水应该具有与目标半导体相匹配的化学计量学，动力学不稳定的配体，以及低温半导体结晶的能力。为此，Buhro教授正在研究新分离的、化学计量学上神奇大小的II-VI纳米团簇。利用这种纳米团簇作为低温前体来制备大块多晶半导体薄膜的策略正在研究中。完成这些化学计量的、胺钝化的、神奇大小的II-VI纳米团簇的结构表征，以及探索它们的化学反应性和物理性质的努力也在进行中。该项目的研究有望从根本上推进半导体纳米科学，影响太阳能技术。此外，Buhro教授还指导了大量女性博士科学家，并正在努力通过将主动学习策略纳入STEM入门课程来留住女性。

The research pursued in this project advances semiconductor nanoscience for potential use in solar-energy technologies. As atmospheric carbon dioxide (CO2) levels currently threaten the global ecosystem and human well-being, the development of clean-energy technologies is a major societal necessity. Professor Buhro is providing new methods to prepare more-efficient solar cells and the economical, scalable semiconductor processing required for widespread access to solar electricity. One aspect of the project is to develop semiconductor-nanocrystal films having optimized structures for charge transport in the solar-absorber layers of solar cells. This may increase the performance of the cells. The key to this strategy is the shape of the nanocrystals, which are plate-like or ribbon-like, and stack together compactly. These shapes are capable of transporting charge over large distances. A second aspect of the project is the low-temperature deposition of semiconductor films using solution chemistry. A major drawback to the wider implementation of solar electricity is the high cost of making the semiconductor components of solar cells by the current gas-phase and vacuum-based technologies. Professor Buhro is contributing to the development of much more economical solution-based processing methods. Both aspects of the project rely on so-called "magic-size semiconductor nanoclusters" as key chemical intermediates and precursors. The magic-size nanoclusters are small, discrete molecular units that have the same compositions as the target semiconductor phases, and that produce crystalline semiconductors from solution at low temperatures. By increasing the ability to transport charge and the economy of semiconductor-film fabrication, this research may have broad societal impact as it promotes the availability and practicality of solar-energy technology. Additionally, Professor Buhro is a mentor to a large number female Ph.D. scientists. He works to retain women in STEM fields by incorporating active-learning strategies in introductory courses.In this research project, Professor William Buhro of Washington University in St. Louis is supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) program to employ stoichiometric magic-size semiconductor nanoclusters and flat (2D), colloidal semiconductor nanocrystals in the advancement of low-temperature, solution-based semiconductor processing and nanocrystal solar cells. Solid-state quantum-dot (QD) solar cells have emerged as a third-generation photovoltaic technology that promises economical, scalable production, and the necessary solar-conversion performance for real-world application. Flat (2D) semiconductor nanocrystals (quantum belts and quantum platelets) have optical properties and interfacial characteristics comparable to colloidal quantum dots. They also have at least one extended length dimension. Professor Buhro is now investigating their use in nanocrystal solar-absorber layers. The architectures of 2D-nanocrystal films consist of bundled semi-ordered domains oriented in three dimensions. The larger lateral nanocrystal dimensions relative to QDs are expected to increase the carrier mean free paths and minimize hopping. The overall film architecture may provide conduction pathways percolating in all three dimensions. These materials may minimizing carrier recombination and increasing the photon-conversion efficiencies of solar cells. A second component of this project addresses molecular semiconductor inks. Ideal molecular inks for semiconductor fabrication should possess stoichiometries matched to the target semiconductor, kinetically labile ligands, and the capacity for low-temperature semiconductor crystallization. Professor Buhro is investigating the newly isolated, stoichiometric magic-size II-VI nanoclusters for this purpose. Strategies for employing such nanoclusters as low-temperature precursors to bulk, polycrystalline semiconductor films are under study. Efforts to complete the structural characterization of these stoichiometric, amine-passivated, magic-size II-VI nanoclusters, and to explore their chemical reactivities and physical properties are also underway. The research pursued in this project is expected to fundamentally advance semiconductor nanoscience impacting solar-energy technologies. Additionally, Professor Buhro mentors a large number female Ph.D. scientists, and is working to retain women by incorporating active-learning strategies into introductory STEM courses.