EAGER:TDM Solar Cells: Research on CdSe-Si tandem junction cells

摘要：项目非技术描述利用光伏技术将太阳能转化为电能是一项重要的技术，在减缓全球变暖方面具有巨大的潜力。目前，光伏太阳能系统的成本主要是与系统相关的成本，如结构成本、现场布线以及化学封装材料和玻璃的成本。为了显著降低太阳能光伏技术的总成本，需要将转换效率从目前的~15%-20%提高到30%，因为大多数系统的成本随着效率的增加而成比例地降低。实现这种更高效率的唯一方法是使用串联结太阳能电池，该电池由两种材料组成，一种具有高带隙，另一种具有较低的带隙。在这个项目中，我们将研究无机材料CdSe的基本性质，然后用这种材料制造太阳能电池，然后将这种材料制造的电池与硅制造的电池结合起来，制造概念验证串联结太阳能电池。该项目将涉及研究生和本科生的研究培训，包括女科学家。对社会的好处是显著降低了太阳能转换技术的成本，从而加快了太阳能在国家电网中的部署。该项目是爱荷华州立大学和锡拉丘兹大学的联合项目。项目技术描述：CdSe是一种有趣的新材料，具有带隙(~1.72 eV)，处于用硅制造串联电池所需的范围内。但人们对这种材料的电子性质知之甚少，也没有用这种材料制造出任何高效率的电池。该项目的一个基本目标是研究这种材料的薄膜的电子性能，然后在这种材料中制造概念验证太阳能电池。要研究的性质包括掺杂浓度、电子和空穴的迁移率、深缺陷密度和复合现象、少数载流子扩散长度、电子亲和势和带边能量。将使用结构、电子和光学测量技术来测量相关性能。我们将使用多源蒸发技术来沉积CdSe薄膜。除了研究这些基本的电子性质外，我们还将使用合适的异质结来制作概念验证器件。此外，我们将使用CdSe和Si之间的隧道结来制造概念验证串联电池。我们的目标是证明使用这种新材料系统确实可以制造串联结电池。在CdSe和c-Si电池上都将使用适当的重掺杂接触层，以形成有效的隧道结来连接这两个电池。其目标是在串联单元中获得~1.5V的开路电压，以及高填充系数，从而证明串联结的概念是可行的。该项目的智力价值在于系统地研究了一种稳定的无机材料体系制造高效太阳能电池的潜力。

Abstract:Non-technical description of the projectThe conversion of solar energy into electricity using photovoltaic (PV) technology is an important technology with significant potential for reducing global warming. Currently, the costs of the PV solar energy system are dominated by systems related costs, such as structural costs, field wiring and the costs of chemical encapsulant materials and glass. In order to significantly reduce the total costs of solar PV technology, the conversion efficiency needs to be increased from the current ~15-20% to 30%, because most of the systems costs reduce proportionately with an increase inefficiency. The only way to achieve such higher efficiencies is to use a tandem junction solar cell, comprising two materials, one with a high bandgap and one with a lower bandgap. In this project, we will investigate the fundamental properties of an inorganic material, CdSe, then make solar cells in this material, and then make proof-of-concept tandem junction solar cells by combining cells made in this material with cells made in Si. The project will involve the research training of graduate and undergraduate students, including women scientists. The advantage to society is a significant lowering of the cost of solar energy conversion technology, thereby accelerating the deployment of solar energy into the nation's grid. The project is a joint project between Iowa State University and Syracuse University.Technical description of the project:CdSe is an interesting new material with a bandgap (~1.72 eV) which is in the range needed to make tandem cells with Si. But not much is known about the electronic properties of this material, nor have any high efficiency cells been made in this material. A fundamental objective of this project is to study electronic properties of thin films of this material and then make proof-of-concept solar cells in the material. Among the properties to be studied will be doping concentration, mobility of electrons and holes, deep defect densities and recombination phenomena, minority carrier diffusion lengths, electron affinities and energies of band edges. Structural, electronic and optical measurement techniques will be used to measure the relevant properties. CdSe films will be deposited using multi-source evaporation techniques.In addition to studying these fundamental electronic properties, we will make proof-of-concept devices using appropriate heterojunctions. In addition, we will make proof-of-concept tandem cells using tunnel junctions between CdSe and Si. The objective is to demonstrate that one can indeed make tandem junction cells using this new material system. Appropriate heavily doped contact layers will be used on both CdSe and c-Si cells to make efficient tunnel junctions to connect the two cells. The goal is to obtain an open-circuit voltage of ~1.5V in a tandem cell, and also a high fill factor, thereby demonstrating that the tandem junction concept works. The intellectual merit of the project lies in systematically investigating the potential of a stable, inorganic material system for making high efficiency solar cells.