CAREER: Photonic spectrum splitting with nanocrystal luminophores

太阳是地球上最丰富的潜在可持续能源。捕捉太阳光线并将能量转化为电能的太阳能电池？S可以通过光子学来改进太阳能电池，光子学使用先进的材料来引导光通过设备。该项目将开发包含纳米晶体-聚合物复合材料的光子结构，将太阳光谱分裂并集中成其组成波长，然后将集中的特定波长引导到能够最好地将这些波长能量转化为电能的半导体材料。通过这些工艺的结合，可以提高太阳能转换的整体效率。拟议的研究目标是那些可以很容易地用现有的太阳能电池制造工艺实施的设计，也可以整合到建筑物的建筑特征中。这些光子材料还可能在医疗诊断、固态照明和显示技术的生物成像中找到其他应用。除研究活动外，该项目还有广泛的教育目标，旨在通过基于项目的太阳能学习，鼓励妇女和代表性不足的少数群体进入STEM职业生涯。该项目将解决太阳能光伏将阳光转化为电力的根本挑战--宽广的太阳光谱与半导体之间的不匹配，半导体只能在其带隙能量附近的波长有效地转换光。在传统的多结太阳能电池中，光必须通过一堆半导体层来传输，这些半导体层旨在捕获一部分太阳光谱。光通过该堆的传输会导致吸收损失，从而降低理论上可获得的太阳能转换效率。将太阳光谱分成几个分量波长，并将这些波长指向邻近的半导体，而不是堆叠在一起，可以减少损失，提高太阳能转换效率。拟议研究的总体目标是开发一种高效的光谱分裂系统，利用将光子结构与发光纳米晶体-聚合物复合材料相结合的光学材料来增强太阳能的收集。为此，拟议的研究试图从根本上了解这些纳米复合材料与各种用于捕光的光子结构之间的相互作用。该研究计划有三个主要目标。第一个目标是考虑提高基于纳米复合发光聚光器的太阳光谱分裂效率的光子路径。例如，通过在发光聚光器中加入布拉格反射镜等捕光元件，可以提高发光体的量子产率。第二个目标将通过调节发光纳米晶体-聚合物复合材料的性能来解决损耗机制。例如，由高折射率和低折射率交替的纳米晶体-聚合物复合材料组成的光子晶体可以减少发光聚光器内的损耗。在第三个目标中，光子纳米晶体-聚合物复合材料将被集成到单结太阳能光伏电池中，作为发光集中器，提供可控的发射角度，减少吸收损失，并提高辐射衰减率。通过单结装置建立的设计原则将用于开发多结太阳能电池的光谱分裂和集中系统，该电池使用具有不同带隙的纳米晶体发光体获取更大比例的太阳光谱。理论方法将把纳米尺度的特性和光子结构与其作为波导的性能联系起来，这种波导可以接收漫反射的阳光，并将其引导到邻近的太阳能电池。这些信息将被用来预测单结和多结太阳能电池的效率上限。实验工作将包括纳米晶体-聚合物复合材料的合成，复合材料纳米结构与光学响应的关联，以及光子结构的制造。光学光谱学和电子显微镜将被用来表征聚光器内部的光传播。拟议的研究与教育活动相结合，这些活动侧重于在教育和外联平台上以项目为基础学习太阳能，包括编写介绍性讲座和实验室课程材料，为本科生女性创建一个方案，让她们了解太阳能和相关可持续能源系统的本科生研究机会，以及面向K-12学生的外联活动，强调工程学在实现社会目标方面的作用。

The sun represents the most abundant potential source of sustainable energy on earth. Solar cells that capture the sun?s rays and convert this energy into electricity can potentially be improved through the science of photonics, which uses advanced materials to guide the light pathway through the device. This project will develop photonic structures which contain nanocrystal-polymer composite materials that split and concentrate the solar spectrum into its component wavelengths, and then direct the concentrated specific wavelengths to semiconductor materials that are best able to convert these wavelength energies into electricity. Through the combination of these processes, the overall efficiency for solar energy conversion can be increased. The proposed research targets designs that can be readily implemented with existing solar cell fabrication processes and could also be integrated into architectural features for buildings. These photonic materials may also find other applications in biological imaging for medical diagnostics, solid-state lighting, and display technology. This project also has broad educational goals coupled to the research activities, aimed at encouraging women and underrepresented minorities into STEM careers through project-based learning about solar energy.This project will address a fundamental challenge in solar photovoltaic conversion of sunlight to electricity - the mismatch between the broad solar spectrum and semiconductors that only efficiently convert light at wavelengths near their bandgap energy. In conventional multi-junction solar cells, the light must transfer through a stack of semiconductor layers designed to capture a portion of the solar spectrum. The transfer of light through this stack results in absorption losses that lower the theoretically-attainable solar energy conversion efficiency. The splitting of the solar spectrum into component wavelengths and the direction of these wavelengths to adjacent semiconductors, as opposed to within a stack, can reduce losses and improve solar energy conversion efficiency. The overall goal of the proposed research is to develop an efficient spectrum splitting system for enhancing solar energy harvesting using optical materials that combine photonic structures with luminescent nanocrystal-polymer composite materials. Towards this end, the proposed research seeks to gain a fundamental understanding of the interaction of these nanocomposite materials with various photonic structures for harvesting of light. The research plan has three primary objectives. The first objective is to consider photonic routes for enhancing the efficiency of solar spectrum splitting based on nanocomposite luminescent concentrators. For example, by incorporating light trapping elements such as Bragg mirrors into luminescent concentrators, luminophore quantum yield can be increased. The second objective will address loss mechanisms by tuning the properties of luminescent nanocrystal-polymer composite materials. For example, a photonic crystal consisting of alternating high index and low index nanocrystal-polymer composites could reduce losses within the luminescent concentrator. In the third objective, photonic nanocrystal-polymer composite materials will be integrated into single-junction solar photovoltaic cells to serve as luminescent concentrators that provide controlled angles of emission, reduced absorption loss, and enhanced radiative decay rate. The design principles established through the single-junction device will be used to develop a spectrum splitting and concentrating system for multi-junction solar cells that harvest a larger fraction of the solar spectrum using nanocrystal luminophores engineered with different bandgaps. Theoretical approaches will link nanoscale properties and photonic structures to their performance as waveguides that accept diffuse sunlight and direct it to adjacent solar cells. This information will used to predict the upper limits of efficiency for single and multi-junction solar cells. Experimental work will include synthesis of nanocrystal-polymer composites, correlation of the composite nanostructure to optical response, and fabrication of photonic structures. Optical spectroscopy and electron microscopy will be used to characterize the light propagation inside the concentrators. The proposed research is integrated with educational activities that focus on project-based learning about solar energy across educational and outreach platforms, including the development of introductory lecture and laboratory coursework materials, the creation of a program for undergraduate women to learn about undergraduate research opportunities in solar and related sustainable energy systems, and outreach to K-12 students that emphasizes the role of engineering in addressing societal goals.