EAGER: Enhanced Solar Energy Conversion by Ultra-slow Photon Sub-diffusion in Aperiodic Media

渴望：通过减缓光子纳米结构中的扩散来增强太阳能转换非技术描述：太阳能光伏（PV）是可再生能源技术中增长最快的领域。在部署系统中使用的大多数现代太阳能电池是由晶体硅（Si）或薄膜半导体材料制成的。晶体硅电池在将太阳光转化为电能方面效率更高，但通常具有较高的制造成本。另一方面，薄膜材料通常具有较低的转换效率，但更简单，制造成本更低。材料成本的增加和硅太阳能工业需求的增长推动了吸收电池厚度的急剧减少。然而，由于吸收长度小，薄膜太阳能电池的转换效率有限，为了在全球市场上具有竞争力，需要大幅提高转换效率。这项EAGER研究将通过开发一种新的光子引导方法来提高厚度小于100nm的Si层的光学吸收，从而解决薄膜PV太阳能转换的基本挑战。我们雄心勃勃的目标将通过设计、制造和测试一种新型光子纳米结构来实现，这种结构能够通过设计减缓光扩散来捕获太阳辐射。PI预计，这个EAGER项目的影响将分布在整个太阳能产业和集成硅光电子领域。特别是，该研究将创造新的器件原理，也可用于提高集成在平面芯片上的光电探测器和光学传感器的性能。该项目的教育活动旨在将可持续能源主题和纳米光子学研究整合到研究生，本科生，高中生以及高中教师的教育中。技术描述：这个探索性EAGER项目的具体目标是创建、设计和制造一种新颖的纳米光子驱动方法，以有效地将入射辐射耦合到亚波长半导体薄膜中，并在宽波长和入射角范围内显著提高其光子吸收率，而不考虑偏振。与成熟的光子晶体、随机纹理表面或光栅增强的太阳能电池不同，它们受偏振敏感性的影响，需要小范围的入射方向，并且依赖于吸收介质中光子路径长度的有限增加，这种新策略建立在一个根本不同的光子传输机制上，称为对数光子亚扩散。该方法首次将介电纳米结构中的超低（即对数）光子输运现象与非周期系统中的各向同性散射相结合，以便在不依赖光子窄带共振激发的情况下实现高效的光伏太阳能转换。超低异常光子扩散机制将利用磁控溅射和标准纳米光刻技术制造的Si和SiN纳米结构，在设计的非周期图案覆盖的大面积上进行设计，这些图案在薄膜多晶硅和非晶硅电池的活性区域上产生相关的光子走行。虽然将重点放在Si上，以方便集成，成本效益和技术可扩展性，但这一概念同样可以应用于替代半导体材料平台，例如第三代太阳能电池材料。利用亚扩散光子异常在工程非周期光子介质中具有独特的性能优势，如非谐振工作，光子扩散长度可调，对入射角和偏振不敏感。这项研究是跨学科的，具有潜在的变革性，因为它基于一种全新的、可调谐的超薄膜光伏器件光子机制，创造了亚扩散太阳能转换器。

EAGER: Enhancing Solar Energy Conversion by Slowing Diffusion in Photonic NanostructuresNontechnical Description: Solar Photovoltaics (PV) is the fastest growing sector among renewable energy technologies. Most modern solar cells utilized in deployed systems are made from either crystalline silicon (Si) or thin-film semiconductor materials. Crystalline Si cells are more efficient at converting sunlight to electricity, but generally feature higher manufacturing costs. On the other hand, thin-film materials typically have lower conversion efficiencies but are simpler and less costly to manufacture. The increasing materials cost and the growing demands of the Si solar industry have driven a dramatic reduction of the absorbing cell thickness. However, due to their small absorption length, thin-film solar cells have a limited conversion efficiency that needs to be substantially increased in order to become competitive on the global market. This EAGER research will address the fundamental challenges of thin-film PV solar energy conversion by developing a novel photonics-led approach that boosts the optical absorption in Si layers with thickness less than 100nm. Our ambitious goal will be accomplished by designing, fabricating and testing a novel class of photonic nanostructures that are capable of trapping solar radiation by slowing down optical diffusion by design. The PI anticipates that the impact of this EAGER program will be distributed across the solar energy industry and in the field of integrated silicon optoelectronics. In particular, the research will create novel device principles that can also be used to improve the performances of photodetectors and optical sensors integrated on planar chips. The educational activities of this project are designed to integrate sustainable energy topics and nanophotonics research into the education of graduate, undergraduate, and high school students, as well as high school teachers. Technical Description: The specific objective of this exploratory EAGER project is to create, design and engineer a novel nanophotonic-driven approach to efficiently couple incident radiation into sub-wavelength semiconductors films and dramatically enhance their photon absorption rate, irrespective of polarization, over a broad range of wavelengths and incident angles. Differently from well-established photonic crystals, randomly textured surfaces or grating-enhanced solar cells, which suffer from polarization sensitivity, require a small range of incident directions, and rely on limited increase of the photon path length within the absorbing medium, this novel strategy builds on a fundamentally different photon transport mechanism, known as logarithmic photon sub-diffusion. This approach combines for the first time ultraslow (i.e., logarithmic) photon transport phenomena in dielectric nanostructures with isotropic scattering in aperiodic systems in order to achieve efficient PV solar energy conversion without relying on the excitation of photonic narrowband resonances. The ultraslow anomalous photon diffusion regime will be engineered using Si and SiN nanostructures fabricated by magnetron sputtering and standard nanolithography over large areas covered by designed aperiodic patterns that create correlated photon walks across the active regions of thin-film poly-Si and a-Si cells. While focusing the efforts on Si for ease of integration, cost-effectiveness and technological scalability, this concept can similarly be applied to alternative semiconductor material platforms as well, such as third-generation solar cells materials. Leveraging sub-diffusive photon anomaly in engineered aperiodic photonic media offers unique performance advantages, such as non-resonant operation, tunable photon diffusion length, insensitivity to incident angles and polarization. This research is interdisciplinary and potentially transformative as it creates sub-diffusive solar energy converters based on a completely novel and tunable photonic mechanism for ultra-thin film PV devices.