EAGER: TDM solar cells: Bifacial III-V nanowire array on silicon tandem solar cells

翻译后摘要：非技术：传统的国家的最先进的串联结光伏太阳能电池，由多个子电池的III-V族化合物半导体，能够转换入射辐射从太阳到电力具有更高的效率比所有其他类型的太阳能电池。这些器件的高性能部分地由于使用高质量单晶III-V材料而实现，并且部分地由于共同允许吸收宽带太阳光谱范围的多个子电池的耦合而实现。然而，开发III-V族串联结器件所需的材料和制造成本对于在大规模地面消费应用中的使用而言过高。因此，世界上性能最高的太阳能电池仅限于在利基市场中使用，如地面高浓度和空间电力应用。一个高风险，高回报的探索性研究路径，旨在提供一个非传统的，但可能是变革性的纳米技术使能的解决方案所面临的最先进的串联结太阳能电池的上述消费者市场渗透的挑战。该项目旨在通过将由垂直纳米线阵列组成的III-V子电池单片集成到中央硅子电池中，从而大幅降低制造成本，同时消除主要的III-V衬底成本驱动因素，同时将III-V晶体生长量与传统技术相比减少高达95%。EAGER项目的更广泛意义在于可能实现低成本和高效率的可再生能源创新，提供更大的国家能源独立性和清洁电力。这项研究还影响和推进物理学，纳米材料生长和表征，纳米电子学和光电子学领域的科学和工程基础知识。直接预期的社会影响包括推广活动，促进科学，技术，工程和数学的概念，向公众，培训高技能劳动力的新成员，并直接纳入高中，本科和研究生来自代表性不足的社区。技术：该EAGER项目的技术方法依赖于通过金属有机化学气相沉积在薄化的Si（1.1 eV）子电池的顶面上选择性区域异质外延GaAsP（1.75 eV）纳米线阵列。双面，三种不同的材料，串联结器件通过背面InGaAs（0.5 eV）纳米线阵列的单片集成形成。包括顶表面阵列和背表面阵列的垂直纳米线将包含径向分段的p-i-n结，并且将经由外延隧道结串联连接到中心Si子电池。这种设计能够吸收宽带入射太阳能以及太阳辐射。标准的晶格匹配的限制，克服了通过应变松弛沿着纳米线自由表面。因此，实现了理想的光谱匹配，而不需要渐变缓冲层或位错调解策略。使用具有同轴p-i-n结几何形状的垂直纳米线阵列允许关键优点，包括在不使用抗反射涂层的情况下在垂直和倾斜入射下对太阳辐照度的接近统一吸收，光子吸收和载流子收集方向的解耦，以及外延体积的95%的显著减少。器件参数的严格建模将与广泛的材料表征和性能相关性实验迭代耦合，以在单纳米线和集成阵列水平上优化III-V子电池结构。这项工作的最终目标是演示一种功能性双面、三种不同材料、基于纳米线的串联结太阳能电池，其太阳能转换效率为30%或更高。

Abstract:Non-Technical:Conventional state-of-the-art tandem junction photovoltaic solar cells, composed of multiple sub-cells of III-V compound semiconductors, are capable of converting incident radiation from the Sun to electricity with greater efficiency than all other types of solar cells. The high performance of these devices is enabled in part due to the use of high quality monocrystalline III-V materials and in part due to the coupling of multiple sub-cells that collectively allow for absorption of a broadband solar spectral range. However, the materials and manufacturing costs required for the development of III-V tandem junction devices is prohibitively high for use in wide-scale terrestrial consumer applications. As a consequence, the world's highest performance solar cells are limited to use in niche markets such as terrestrial high concentration and space power applications. A high-risk, high-payoff exploratory research path is proposed here that aims to provide an unconventional, yet potentially transformative nanotechnology-enabled solution to the above consumer market penetration challenges faced by state-of-the-art tandem junction solar cells. The project aims to dramatically reduce manufacturing costs by monolithically integrating III-V sub-cell composed of vertical nanowire arrays to a central silicon sub-cell, thereby simultaneously eliminating the primary III-V substrate cost-driver while cutting III-V crystal growth volumes by up to 95% compared to conventional technologies. The broader significance of this EAGER project lies in the potential realization of a low-cost and high-efficiency renewable energy innovation that provides greater national energy independence and clean power. This research also impacts and advances fundamental knowledge in science and engineering in the fields of physics, nanomaterials growth and characterization, nanoelectronics, and optoelectronics. Immediate anticipated societal impacts include outreach activities that promote science, technology, engineering, and mathematics concepts to the general public, training new members of a highly-skilled workforce, and direct inclusion of high school, undergraduate, and graduate students from under-represented communities. Technical:The technical approach of this EAGER project relies on selective-area heteroepitaxy of a GaAsP (1.75 eV) nanowire array on the top surface of a thinned Si (1.1 eV) sub-cell by metal-organic chemical vapor deposition. A bifacial, three dissimilar materials, tandem junction device is formed via monolithic integration of a back-side InGaAs (0.5 eV) nanowire array. The vertical nanowires comprising the top- and back-surface arrays will contain radially-segmented p-i-n junctions and will be serially connected to the central Si sub-cell via epitaxial tunnel junctions. This design enables absorption of broadband incident solar energy as well as albedo radiation. Standard lattice-matching constraints are overcome via strain relaxation along nanowire free surfaces. Therefore, ideal spectral matching is realized without a need for graded buffer layers or dislocation mediation strategies. Use of vertical nanowire arrays with coaxial p-i-n junction geometries permits key advantages, including near-unity absorption of solar irradiance at normal and tilted incidence without the use of anti-reflection coatings, decoupling of photon absorption and carrier collection directions, and dramatic reduction of 95% in epitaxial volumes. Rigorous modeling of device parameters will be iteratively coupled with extensive materials characterization and property correlation experiments for optimization of III-V sub-cell structure on the single nanowire and ensemble array levels. The ultimate target of this work is demonstration of a functional bifacial, three dissimilar materials, nanowire-based tandem junction solar cell with one Sun power conversion efficiency of 30% or better.