Carrier Dynamics in Quantum Dot Solar Cells and Infrared Detectors

摘要：摘要标题：“了解基于量子点约束的太阳能电池光能转换效率的增强机制”非技术：光伏是一种将太阳的丰富辐射能转换为电能的技术，最终可以通过智能电网基础设施广泛分布。这可以在对环境的负面影响最小的情况下完成。尽管硅太阳能电池是一种公认的清洁能源，但其目前的转换效率仍有待提高。实现这一目标的新材料和新方法已经出现。利用具有不同带隙的不同材料来提高现有太阳能电池的转换效率是一种很有吸引力的方法。另一种方法是基于使用被称为量子点的受限纳米结构来高效率地转换太阳能。后一种方法的优点是更简单，不需要复杂的增长过程。这可能是一种非常便宜的制造太阳能电池的方法。另一方面，这种方法尚未显示出其潜力。为了了解这种方法的潜力和局限性，提出了不同的实验研究。提出的方法包括努力更好地理解这些结构中的光吸收，以便设计基于量子点的高效太阳能电池。如果成功，该项目将对该国的清洁和高效能源转换产生重大影响。技术：基于p-n结的光伏器件是太阳能收集技术中最成熟的技术。本提案旨在开发基于中间带概念的新型高效砷化镓量子点太阳能电池。这些电池具有与3结太阳能电池一样高效的潜力，但复杂性要低得多。中间波段太阳能电池的概念已经伴随我们超过15年。不幸的是，到目前为止，这些太阳能电池的转换效率只有18%或更低。这在很大程度上与研究人员未能证明具有明确定义的中间带费米能量的中间带太阳能电池有关，该中间带费米能量与导带费米能量分离。为了阐明这一主题，提出了一些以前没有尝试过的中间波段太阳能电池的关键测量方法。特别是，提出了使用不同波长的两个光源的双光子测量，以了解是否可以测量双光子吸收，以及该过程是基于顺序光子吸收还是由于同时双光子吸收。这将回答中间带太阳能电池是否可以实现具有明确定义的中间带费米能量，脱离导带费米能量的问题。如果使用中间波段太阳能电池的概念不能达到更高的效率，这意味着这个概念基本上是有缺陷的，这需要进行调查，并提供一个明确的解释。此外，由于这些太阳能电池的物理性质与红外探测器中描述光子吸收的物理性质相似，这种新的认识也将有助于更好地理解量子点红外光电探测器（qdip）的操作。研究了两种不同带隙的量子点太阳能电池，以优化中间带太阳能电池的预测转换效率。

Abstract:Abstract Title: "Understanding the enhancement mechanisms of optical energy conversion efficiency in solar cells based on confinement by quantum dots"Nontechnical:Photovoltaic is a technology that permits the conversion of abundant radiative energy from the sun to electrical energy which can ultimately be widely distributed using a smart electrical grid infrastructure. This can be done with a minimum negative impact on the environment. In spite of being a well-established clean source of energy, there is a need for improving the present conversion efficiency of Si solar cells. New materials and new approaches to achieve this goal have emerged. One appealing approach is based on using different materials with different bandgap to enhance the conversion efficiency of present solar cells. Another approach is based on using confined nanostructures, called quantum dots, to convert solar energy with high efficiency. This latter approach has the advantage of being simpler and does not require complex growth processes. This might be a very inexpensive approach to making solar cells. On the other hand, this approach has not yet demonstrated its potential. Different experimental studies are proposed with the goal of understanding the potential and limitations of this approach. The proposed approach involves an effort toward a better understanding of light absorption in these structures in order to design very efficient solar cells based on quantum dots. If successful, this project will have a major impact on clean and efficient energy conversion in this country.Technical:Photovoltaic devices based on p-n junction are the most mature technology for solar-energy harvesting. This proposal seeks to develop new highly efficient GaAs quantum dot solar cells based on the intermediate band concept. These cells have the potential of being as efficient as 3-junction solar cells but at a much lower level of complexity. The concept of intermediate band solar cells has been with us for more than 15 years. Unfortunately, these solar cells have so far demonstrated a limited conversion efficiency of 18 % or less. This is in large part related to the fact that researchers have not been able to demonstrate an intermediate band solar cell with a well-defined intermediate band Fermi energy, detached from the conduction band Fermi energy. Some key measurements on intermediate band solar cells that have not been attempted before are proposed in order to shed light on this topic. In particular, two-photon measurements using two optical sources of different wavelengths are proposed to understand if a 2-photon absorption can be measured and if the process is based on sequential photons absorption or due to simultaneous two-photon absorption. This will answer the question if intermediate band solar cells can be realized with well-defined intermediate band Fermi energy, detached from the conduction band Fermi energy. If substantially higher efficiencies cannot be reached using the concept of intermediate band solar cells, implying that the concept is basically flawed, this needs to be investigated and a final answer has to be provided with a clear explanation. Additionally, since the physics of these solar cells is similar to the physics describing photon absorption in IR-detectors, this new understanding will also lead to a better understanding of the operation of quantum dot infrared photodetectors (QDIPs). Two quantum dot solar cells will be studied with different bandgaps to optimize the predicted conversion efficiency of intermediate band solar cells.