CAREER: Transparent, passivating, and carrier-selective heterojunction contacts for silicon and cadmium telluride solar cells

非技术：这个CAREER项目旨在提高太阳能电池将太阳光转化为电能的效率。该项目将探索太阳能电池电接触的材料科学和物理学。这样做，它将促进对这些接触如何限制细胞操作的理解。每个太阳能电池必须完成两个过程：将光转化为受激电子，并以电流的形式提取这些电子。前一种工艺通过半导体吸收材料进行；后者由两个电触点组成，吸收器夹在两个电触点之间。尽管太阳能电池已被大量生产，目前其发电量占美国总用电量的1%，但仍有一些基本问题没有得到解答。研究界还不知道是什么特性决定了一种材料是否能产生良好的电接触，也不知道如何快速找到并制造出具有理想特性的材料。该项目将通过对现有模型系统的测量和模拟的结合，以及利用由此产生的理解来开发新接触的实验，为这些问题提供答案。该项目的成功将为太阳能电池的效率提高10-15%奠定基础，将太阳能发电的成本降低到每千瓦时3美分以下。反过来，预计这将加速太阳能的部署，到2030年，美国17%的电力来自太阳能，而不是在一切照旧的情况下预计的5%。除了这些科学、环境和社会影响外，该项目还将通过为期一周的“太阳能电池101”实践课程，为美国目前的26万个太阳能工作岗位培训社区学院、本科生和研究生。在课程中，他们将从头到尾制作电池和模块。技术方面：许多光伏（PV）技术已经达到了具有低非辐射复合率的吸收材料，因此可以支持接近详细平衡极限的电池电压，但没有技术开发出相对理想的透明电接触，使吸收表面钝化，并有选择地从吸收体中提取电子或空穴。该项目针对阻碍异质结接触理解和技术快速发展的关键问题，使用(1)将载流子选择层、包含这些层的触点和包含这些触点的PV电池的性质联系在一起的表征套件，以及(2)使用干簇喷涂的新沉积技术，以实现接触层化学计量的密切控制，而不会溅射损坏。这两种平台将应用于晶体硅和碲化镉光伏电池作为模型系统，因为这些技术具有现成的高质量吸收剂（这使得对触点功能的解释更加明显），可用于分析这些材料的先前开发的触点集合，但理想的触点尚未发现。该项目在理解和技术上的任何进步都将产生巨大的研究和商业影响。在研究了最先进的现有触点的潜在物理特性后，该项目将继续沉积和测试迄今为止尚未开发的载流子选择层，包括宽带隙、重掺杂、非晶或多晶III-V材料。这项研究将解决27%效率的硅光伏电池和25%效率的碲化镉电池的关键障碍——良好的接触。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical:This CAREER project aims to increase the efficiency of conversion of sunlight into electricity by solar cells. The project will explore the materials science and physics of electrical contacts to solar cells. In so doing, it will advance the understanding of how these contacts limit the operation of the cells. Every solar cell must perform two processes: convert light into excited electrons and extract those electrons in the form of current. The former process is performed by a semiconductor absorber material; the latter by two electrical contacts between which the absorber is sandwiched. Although solar cells are mass manufactured and now generate 1% of the electricity consumed in the U.S., there are still fundamental questions that are unanswered. The research community does not yet understand which properties determine if a material will make an excellent electrical contact and how to quickly find and make materials with the desired properties. This project will provide answers to these questions with a combination of measurements and simulations applied to existing model systems, as well as experiments to use the resulting understanding to develop new contacts. Success in the project will lay the groundwork for solar cells that are 10-15% more efficient than today's cells, reducing the cost of solar electricity generation to below 3 cents per kilowatt-hour. This, in turn, is predicted to accelerate the deployment of solar energy, resulting in 17% of U.S. electricity being generated by solar in 2030 instead of the 5% projected in a business-as-usual scenario. In addition to these scientific, environmental, and societal impacts, this project will also train community college, undergraduate, and graduate students for the 260,000 solar jobs presently in the US through a week-long, hands-on "Solar Cell 101" course in which they make cells and modules from start to finish.Technical:Many photovoltaic (PV) technologies have arrived at absorber materials that have low non-radiative recombination rates and thus could support cell voltages approaching the detailed-balance limit, but no technology has developed comparatively ideal electrical contacts that are transparent, that passivate the absorber surface, and that selectively extract electrons or holes from the absorber. This project targets key questions that inhibit rapid progress in heterojunction contact understanding and technology using (1) a characterization suite that links together the properties of carrier-selective layers, contacts containing those layers, and PV cells containing those contacts, and (2) a new deposition technique using dry-cluster spraying to enable intimate control of the stoichiometry of contact layers without sputter damage. These two platforms will be applied to crystalline silicon and cadmium telluride PV cells as model systems, as these technologies have readily available high-quality absorbers (which makes interpretation of the function of the contacts more apparent), a collection of previously developed contacts for these materials is available for analysis but ideal contacts have yet to be discovered, and any advances in understanding and technology resulting from the project will have large research and commercial impact. After studying the underlying physics of state-of-the-art existing contacts, the project will progress to depositing and testing heretofore unexplored carrier-selective layers, including wide-bandgap, heavily doped, amorphous or polycrystalline III-V materials. This research will address the critical impediment--excellent contacts--to 27%-efficient silicon PV cells and 25%-efficient cadmium telluride cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.