Ultrathin broadband solar absorbers for UV and UV-NIR based on a scalable plasmonic metamaterial

在联合实验和理论方法中，我们将研究可扩展的等离子体超材料，用于在紫外线范围或从紫外线到近红外线的整个范围内作为宽带太阳能吸收剂的应用。本超材料由高度填充的颗粒等离子体纳米复合材料组成，其具有宽的粒度分布，沉积在涂覆有介电间隔层的反射金属膜上。我们的概念是基于量身定制的长度尺度，成分和其他参数的不均匀性。特别地，它结合了单个纳米颗粒的等离子体吸收的巨大加宽，这是由于跨颗粒之间的纳米间隙的强近场耦合与其他加宽效应。对于UV-NIR吸收剂，这些范围从不同等离子体纳米颗粒的组合到合金纳米颗粒中的阻尼和纳米级粗糙度到量子力学阻尼现象。对于UV吸收剂，将仅采用不同尺寸和形状的Al颗粒。我们的目标是分别在UV范围和从UV到NIR范围内实现宽带吸收，同时在IR范围内具有低发射率，对光偏振和入射角不敏感。该纳米复合材料是通过气相沉积涉及高速率气体聚集团簇源和磁控溅射。簇源阿利亚允许通过独立控制纳米颗粒填充因子和尺寸分布来精确定制纳米结构。与其他纳米结构的等离子体吸收剂相比，纳米结构在沉积期间通过自组织形成，并且不需要光刻技术。因此，该方法适合于大规模制造。我们的最终目标是在恶劣的环境条件下保持稳健性和热稳定性。使用团簇源，我们计划探索将不同材料的纳米颗粒和合金纳米颗粒结合在一起的独特潜力。通过理论分析和模拟计算，获得了吸收体的设计参数，如粒子填充因子、粒径分布、介质间隔层厚度等。该分析包括多重散射形式主义，大规模模拟的基础上，时域有限差分法，和有限元法，以获得光吸收后的纳米复合材料的温度分布。模拟的输入参数将由各种表征技术提供，包括紫外-可见光谱和光谱椭圆偏振法。我们已经在初步的实验工作中证明了我们的概念的一般可行性。虽然本申请的重点显然是对宽带等离子体吸收剂的基本理解，但我们期望我们的结果与太阳能收集中的未来应用高度相关。

In a joint experimental and theoretical approach, we will investigate scalable plasmonic metamaterials for applications as ultrathin broadband solar absorbers either in the UV range or in the entire range from UV to NIR. The present metamaterials consist of highly filled particulate plasmonic nanocomposites with a broad particle size distribution that are deposited on a reflective metallic film coated with a dielectric spacer layer. Our concept is based on tailored inhomogeneities in lengths scales, composition, and other parameters. In particular, it combines the huge broadening of the plasmonic absorption of the individual nanoparticles due to strong near field coupling across the nanogaps between the particles with other broadening effects. For the UV-NIR absorbers, these range from the combination of different plasmonic nanoparticles to damping in alloy nanoparticles and nanoscale roughness to quantum mechanical damping phenomena. For the UV absorbers, only Al particles of different size and shapes will be employed. We aim for broadband absorption in the UV range and from the UV to the NIR range, respectively, with simultaneous low emittance in the IR range and insensitivity to light polarization and incidence angle. The nanocomposites are fabricated by vapor phase deposition involving high-rate gas aggregation cluster sources and magnetron sputtering. The cluster sources, inter alia, allow precise tailoring of the nanostructure through independent control of the nanoparticle filing factor and size distribution. In contrast to other nanostructured plasmonic absorbers, the nanostructure forms during deposition by self-organization and does not require lithography techniques. The method thus lends itself to large-scale fabrication. We finally aim for robustness against harsh environmental conditions and thermal stability. Using cluster sources, we plan to explore the unique potential of combining nanoparticles of different materials and alloy nanoparticles. The design parameters of the absorber such as particle filing factor, size distribution, thickness of the dielectric spacer etc. will be obtained from theoretical analysis and simulations. The analysis includes a multiple scattering formalism, large scale simulations based on finite difference time domain method, and a finite element method to obtain the temperature profiles of the nanocomposites upon absorption of light. The input parameters for the simulations will be provided by various characterization techniques including UV-vis spectroscopy and spectroscopic ellipsometry. We already demonstrated the general feasibility of our concept in preliminary experimental work. While the focus of the present application is clearly on fundamental understanding of the broadband plasmonic absorbers, we expect our results to be highly relevant for future applications in solar energy harvesting.