Carrier Dynamics in Quantum Dot Solar Cells and Infrared Detectors

摘要：摘要标题：“Understanding the enhancement mechanisms of optical energy conversion efficiency in solar cells based on confinement by quantum dots“非技术性：光伏是一种技术，允许将来自太阳的大量辐射能量转化为电能，最终可以使用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进行。尽管Si太阳能电池是公认的清洁能源，但仍需要提高其目前的转换效率。实现这一目标的新材料和新方法已经出现。一种有吸引力的方法是基于使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。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地转换太阳能。后一种方法的优点是更简单，不需要复杂的生长过程。这可能是制造太阳能电池的一种非常便宜的方法。另一方面，这种方法尚未显示出其潜力。不同的实验研究提出了理解这种方法的潜力和局限性的目标。所提出的方法涉及更好地理解这些结构中的光吸收，以便设计基于量子点的非常高效的太阳能电池。如果成功，该项目将对该国清洁和高效的能源转换产生重大影响。技术：基于p-n结的光伏器件是最成熟的太阳能收集技术。该提案旨在开发基于中间带概念的新型高效GaAs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。中间带太阳能电池的概念已经伴随我们超过15年。不幸的是，这些太阳能电池到目前为止表现出的有限转换效率为18%或更低，这在很大程度上与研究人员未能证明具有与导带费米能量分离的明确定义的中间带费米能量的中间带太阳能电池的事实有关。为了阐明这一主题，提出了一些以前没有尝试过的中间带太阳能电池的关键测量。特别地，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，以及该过程是否基于顺序光子吸收或由于同时的双光子吸收。这将回答一个问题，即中间带太阳能电池是否可以实现良好定义的中间带费米能量，从导带费米能量分离。如果使用中间带太阳能电池的概念不能达到显著更高的效率，这意味着该概念基本上是有缺陷的，则需要对此进行调查，并提供最终答案并给出明确的解释。此外，由于这些太阳能电池的物理学与描述红外探测器中光子吸收的物理学相似，这种新的理解也将有助于更好地理解量子点红外光电探测器（QDIP）的操作。两个量子点太阳能电池将研究不同的带隙，以优化预测的转换效率的中间带太阳能电池。

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.