Ordered Array of Uniformly Sized Quantum Dots for High Efficiency Solar Cells

知识优势：由于自组装量子点（SAQD）通过Stranski-Krastanov （S-K）生长模式存在缺陷和低光吸收，因此基于中间带（IB）的第三代太阳能电池实现超过60%的预测效率一直很困难。S-K模式制备的SAQDs具有大小和位置的随机性。这种随机性扩大了p结和n结之间形成的IB结构，从而降低了给定光谱下的吸收，降低了效率。在太阳能电池中应用saqd的另一个问题是，当saqd的堆叠超过20层时，难以实现无缺陷的高浓度点层。为了克服与尺寸和位置控制相关的问题，以及saqd堆栈的缺陷，本项目将开发低成本和直接的原位图图化工艺，以指导用于高效太阳能电池的均匀尺寸，多堆叠saqd的自组装。高功率激光脉冲的干涉照射将在表面上产生热调制，从而在表面上产生无缺陷、均匀有序的纳米尺度图案。将对图案过程和50层以上的saqd叠加进行原子性的理解。原子优化，使用真空扫描隧道显微镜（STM），将提供放大所需尺寸和形状的saqd阵列的方法。特别是，该项目将研究大小和周期性如何影响由saqd形成的ib的电子结构。原位光学表征将用于分析光学缺陷，IB结构与QD阵列的性质（如尺寸和密度）之间的相关性，以便图像化和生长过程最大化基于QD的太阳能电池的效率。获得的见解将用于制造目标效率超过50%的基于saqd的太阳能电池。广泛影响：要以每千瓦时0.02美元的价格发电，太阳能电池效率超过50%至关重要。高效太阳能电池与聚光器设计结合使用，将对社会产生巨大的影响。此外，该项目将促进对纳米尺度热工艺的理解，以在各种基材上生产无缺陷的高质量纳米线和纳米点。学生将通过研究型教育在太阳能电池的设计和制造过程中接受培训。这将通过让他们接触到使用STM的图像化的原子研究，IB太阳能电池的光学特性以及异质外延生长技术（如分子束外延和脉冲激光沉积）的前沿研究来实现。太阳能电池和量子尺寸效应的演示将通过泻湖年度物理日的公开演示来增强公众对太阳能和纳米尺度科学和工程的理解。该项目得到了工程局CBET部门可持续性能源计划和数学与物理科学理事会材料研究部（DMR）电子/光子材料计划的支持。

0854313YangIntellectual merit: Achieving the predicted efficiency over 60% from the third generation solar cells based on Intermediate Band (IB) has been troublesome due to the defects and low light absorption by Self-Assembled Quantum Dots (SAQD) via the Stranski-Krastanov (S-K) growth mode. The nature of the SAQDs fabricated by the S-K mode is randomness in size and position. This randomness broadens the IB structure formed between p- and n-junctions, which reduces the absorption at a given spectrum, reducing the efficiency. Another problem in applying SAQDs for solar cells is the difficulty in realizing defect-free layers of high concentration of dots when the stacking of SAQDs is more than ~20 layers. In order to overcome the problems related with controls of size and site, and the defects in the SAQD-stacks, this project will develop low cost and direct in-situ patterning processes to guide the self-assembly of uniformly sized, multi-stacked SAQDs for high efficiency solar cells. Interferential irradiation of high power laser pulses will be employed to create thermal modulations on surface in order to produce defect-free, uniform and ordered nanoscale patterns on surfaces. Atomistic understanding will be pursued on the patterning processes and the stacking SAQDs more than 50 layers. The atomistic optimization, using in-vacuum Scanning Tunneling Microscopy (STM), will provide ways to scale-up the arrays of desired sizes and shapes of SAQDs. In particular, the project will study how the size and periodicity influence the electronic structure of IBs formed by SAQDs. In-situ optical characterizations will be used to analyze optical defects, the correlation between IB structure and the properties of QD arrays such as size and density so that the patterning and growth processes maximize the efficiency of QD-based solar cells. Gained insight will be used to fabricate SAQD-based solar cells with target efficiency over 50%. Broad impact: To generate electricity at $0.02/kWh, solar cells efficiency over 50% are crucial. When used with concentrator designs, the developed high efficiency solar cells will have huge impact on society. Also the project will advance understanding on nanoscale thermal processes to produce defect-free high quality nano lines and dots on various substrates. Students will be trained in design and fabrication processes of solar cells through research based education. This will be accomplished by exposing them to the cutting edge research on atomistic studies on the patterning using STM, the optical properties of IB solar cells, and heteroepitaxial growth techniques such as Molecular Beam Epitaxy and Pulsed Laser Deposition. Demonstrations of the solar cells and quantum size effects will be used to enhance public understanding on solar energy and nanoscale science and engineering through public demonstrations in annual Physics Day in Lagoon.This project was supported by the Energy for Sustainability Program of the CBET Division of the Engineering Directorate and the Electronic/Photonic Materials Program of the Division of Materials Research (DMR) of the Mathematical and Physical Sciences Directorate.