Silicon Metal-Insulator-Semiconductor Photovoltaics with Atomic Layer Deposited Interfacial Layers

太阳代表着地球上最丰富的潜在可持续能源。用于发电的太阳能电池需要吸收太阳能量并将其光子转化为电子的材料，这一过程被称为光伏发电。降低太阳能光伏能源转换系统的每瓦成本是一个长期的目标，它可以使太阳能得到更广泛的采用。特别是，薄膜太阳能电池可以比晶体硅基太阳能电池更便宜，如果能找到高太阳能转换效率的材料特性的正确组合。该项目的目标是研究薄膜太阳能光伏电池的新层状结构，这种结构有可能提供低成本的加工和高太阳能转换效率。这些新的层状结构，基于电子材料的金属-绝缘体-半导体三明治，在各自的材料边界上具有行为，可能有利于改变太阳能电池的整体电子结构和性能，从而提高性能。这项研究的创新之处在于，将采用先进的技术，以原子级的精度将这些层一层一层地沉积在一起，这样就可以更仔细、更深入地研究这些特性。与该项目相关的教育活动包括与当地科学中心合作开发社区外展计划，以及制作视频，以动画形式展示光伏设备操作背后的物理效果。本研究的总体目标是确定在金属-绝缘体-半导体光伏（PV）背景下，通过插入介电隧道层诱导势垒高度改变和其他界面电子变化的潜在机制。金属-绝缘体-半导体结构将通过薄膜沉积和界面修饰技术制造，从而实现前所未有的界面控制水平。这种水平的控制将使研究固定电荷的基本行为、分子表面功能化、原子层沉积（ALD）化学、氢处理和MIS结构中的ALD双层成为可能。这些现象对势垒高度和与改进光伏器件有关的界面电子图形的具体影响将被量化。不同金属氧化物双层中的偶极子也将用于控制势垒高度。通过改变固定电荷密度和绝缘体厚度的实验研究了固定电荷对电子性能的影响，并将实验结果与理论模拟结果进行了比较。分子表面功能化和界面上的氢提供了额外的合成控制，它们最小化界面电子缺陷的能力将被确定。通过比较电子测量、低能离子散射和光电子能谱测量，将阐明层混合、偶极子强度和界面陷阱密度之间的关键关系。因此，该研究将促进对潜在物理机制的基本理解，同时改善新一代金属-绝缘体-半导体薄膜太阳能光伏器件的能量转换数字。

The sun represents the most abundant potential source of sustainable energy on earth. Solar cells for producing electricity require materials that absorb the sun's energy and convert its photons to electrons, a process called photovoltaics. Lowering the cost per watt for solar photovoltaic energy conversion systems is a long-standing goal that could enable more widespread adoption of solar energy. In particular, thin-film solar cells can be made cheaper than crystalline silicon-based solar cells if the right combination of material properties for high solar energy conversion efficiency can be found. The goal of this project is to investigate new layered structures for thin-film solar photovoltaics that potentially offer both low-cost processing and high solar energy conversion efficiency. These new layered structures, based on a metal-insulator-semiconductor sandwich of electronic materials, have behavior at their respective material boundaries that may favorably change the overall electronic structure and properties of the solar cell, resulting in improved performance. The innovative aspect of this research is that advanced techniques will be used to deposit these layers on top of one another with atomic level precision so that these properties can be more carefully and insightfully studied. The educational activities associated with this project include the development of a community outreach program with a local science center and the production of videos that animate the effects of physics behind the operation of photovoltaic devices.The overall goal of this research is to identify the underlying mechanisms that induce barrier height modifications and other interfacial electronic changes by insertion of dielectric tunnel layers in the context of metal-insulator-semiconductor photovoltaics (PV). Metal-insulator-semiconductor structures will be fabricated by film deposition and interface modification techniques that allow for an unprecedented level of interfacial control. This level of control will enable investigation of the fundamental behavior of fixed charges, molecular surface functionalization, atomic layer deposition (ALD) chemistry, hydrogen treatment, and ALD bilayers in MIS structures. The specific influence of these phenomena on barrier heights and interfacial electronic figures of merit relevant for improving PV devices will be quantified. Dipoles within bilayers of dissimilar metal oxides will also be used to control barrier heights. The impact of fixed charge on electronic properties will be investigated by varying fixed charge density and insulator thickness experimentally, and comparing these experimental results with theoretical simulations. Molecular surface functionalization and hydrogen at interfaces provide additional synthetic control, and their ability to minimize interfacial electronic defects will be determined. By comparing electronic measurements, low-energy ion scattering, and photoelectron spectroscopy measurements, critical relationships between layer mixing, dipole strength, and interface trap densities will be elucidated. Thus, the research will advance fundamental understanding of the underlying physical mechanisms while improving energy conversion figures of merit in a new generation of metal-insulator-semiconductor, thin-film solar PV devices.