EAPSI: Moving Toward High-Efficiency, Cost-Effective Tandem Solar Cells through Real-time Study of Novel Substrate Preparation

为了满足日益增长的社会的需要，由太阳能产生的清洁、丰富的电力有着巨大的希望。为了扩大这种强大的能源，太阳能转换效率必须最大化，而制造成本必须最小化。串联太阳能电池技术的优化有能力对当前商业规模的太阳能研究和生产造成有益的破坏，从而产生更高的效率，更低的成本。串联太阳能电池的特点是一堆半导体材料。这种独特的结构可以吸收比单一材料更多的阳光。化学表面预处理技术旨在减少硅（Si）衬底表面制备的热量和时间预算，从而生长具有优化和成本效益的光收集配置的磷化铟镓/硅（InGaP/Si）串联太阳能电池。硅已经是一种相对便宜且易于制造的半导体材料，它能有效地收集较长波长的太阳光。简化高质量磷化铟镓（可以收集更高波长的光）在Si上的生长，将使这种串联太阳能电池技术在工业应用中更具可扩展性。这项研究将与东京大学集成光子学研究所的Masakazu Sugiyama博士合作进行。几十年来，人们一直在硅上研究磷化镓（GaP）的金属有机气相外延（MOVPE）生长，目的是提供一个合适的表面来生长高质量的磷化铟镓（InGaP），以实现具有1.7 eV/ 1.1 eV配置的InGaP/Si串联太阳能电池，以优化阳光吸收。很少有研究人员能够在硅衬底上生产具有低位错密度的GaP薄膜，特别是器件效率降低的反相边界（APB）缺陷。硅表面制备涉及气相蚀刻和表面钝化是非平衡过程，因此非常依赖于时间。如果没有实时分析，重要的动态过程可能会被误解和忽略。反射各向异性光谱（RAS）技术提供的实时数据极大地促进了无apb GaP薄膜生长的Si（100）表面制备的最新进展。这项研究将深入研究RAS，因为它可以对正在制备的Si（100）二聚体表面和随后的GaP逐层外延生长进行现场、实时的表面敏感分析。该奖项由美国国家科学基金会和日本科学促进会（JSPS）共同资助，隶属于东亚和太平洋暑期研究所项目，支持美国研究生的暑期研究。

To meet the needs of a growing society, the clean, abundant power produced by solar energy holds tremendous promise. To scale up this powerful energy source, solar conversion efficiency must be maximized while manufacturing cost must be minimized. Optimization of tandem solar cell technology has the ability to cause a beneficial disruption in current commercial-scale solar energy research and production, resulting in higher efficiency, lower cost power. Tandem solar cells feature a stack of semiconductor materials. This unique configuration enables the absorption of more sunlight than one just material alone. Chemical surface pretreatment techniques will aim to reduce the thermal and time budget of the preparation of Silicon (Si) substrate surfaces in order to grow Indium Gallium Phosphide/Silicon (InGaP/Si) tandem solar cells with an optimized and cost-effective light-collecting configuration. Silicon is already a relatively cheap and very manufacturable semiconductor material which is efficient at collecting longer wavelength sunlight. Simplifying the growth on top of Si of high-quality indium gallium phosphide (which collects higher wavelength light) will make this tandem solar cell technology more scalable to industrial applications. This research will be conducted in collaboration with Dr. Masakazu Sugiyama of the Integrated Photonics Institute at the University of Tokyo.Metalorganic vapor phase epitaxy (MOVPE) growth of Gallium Phosphide (GaP) on silicon has been studied for several decades with the goal of providing a suitable surface with which to grow high-quality indium gallium phosphide (InGaP) in order to achieve InGaP/Si tandem solar cells with a 1.7 eV/ 1.1 eV configuration for optimized sunlight absorption. Few researchers have been able to produce GaP films with low dislocation densities, notably device-efficiency degrading anti-phase boundary (APB) defects, on silicon substrates. Silicon surface preparation involving vapor etching and surface passivation are non-equilibrium processes and are thus very dependent upon time. Without real-time analysis, important dynamic processes can be misunderstood and overlooked. Recent advancements in Si(100) surface preparation for APB-free GaP thin film growth has been greatly facilitated by real-time data provided by reflectance anisotropy spectroscopy (RAS) techniques. This study will be an in-depth look at RAS as it enables in-situ, real-time surface-sensitive analysis of the Si(100) dimerized surface undergoing preparation and subsequent GaP layer-by-layer epitaxial growth. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science (JSPS).