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

0854313 Yang知识分子的优点：由于通过Stranski-Krastanov（S-K）生长模式的自组装量子点（SAQD）的缺陷和低光吸收，基于中间带（IB）的第三代太阳能电池实现超过60%的预期效率一直是困难的。用S-K模式制备的SAQD的性质是尺寸和位置的随机性。这种随机性加宽了p结和n结之间形成的IB结构，这降低了给定光谱处的吸收，从而降低了效率。将SAQD应用于太阳能电池的另一个问题是当SAQD的堆叠超过约20层时难以实现高点浓度的无缺陷层。为了克服与尺寸和位置控制相关的问题以及SAQD堆叠中的缺陷，本项目将开发低成本和直接原位图案化工艺，以指导用于高效太阳能电池的均匀尺寸的多层SAQD的自组装。高功率激光脉冲的干涉照射将用于在表面上产生热调制，以在表面上产生无缺陷、均匀和有序的纳米级图案。原子理解将追求的图案化过程和堆叠SAQD超过50层。使用真空扫描隧道显微镜（STM）的原子优化将提供按比例放大所需尺寸和形状的SAQD阵列的方法。特别是，该项目将研究尺寸和周期性如何影响SAQD形成的IBs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，以便图案化和生长过程最大化基于QD的太阳能电池的效率。获得的洞察力将用于制造基于SAQD的太阳能电池，目标效率超过50%。广泛的影响：要以0.02美元/千瓦时的价格发电，太阳能电池效率超过50%至关重要。当与聚光器设计一起使用时，所开发的高效太阳能电池将对社会产生巨大影响。此外，该项目将推进对纳米级热处理的理解，以在各种基板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接受太阳能电池设计和制造过程的培训。这将通过将它们暴露在使用STM的图案化原子研究的前沿研究，IB太阳能电池的光学特性以及分子束外延和脉冲激光沉积等异质外延生长技术来实现。太阳能电池和量子尺寸效应的演示将通过在泻湖举行的年度物理日的公开演示来提高公众对太阳能和纳米科学与工程的理解。该项目得到了工程局CBET部门的可持续能源计划和材料研究部门的电子/光子材料计划的支持数学和物理科学理事会的主席

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.