Collaborative Research: Ultrafast Carrier Dynamics in Semiconductor Nanocrystal Solar Cells

合作研究：半导体纳米晶体太阳能电池中的超快载流子动力学

• 批准号: 1335821
• 负责人: Christopher Murray
• 金额: $ 23万
• 依托单位: University of Pennsylvania
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1335821&HistoricalAwards=false
• 关键词: Collaborative; Research; Ultrafast; Carrier; Dynamics

PI: Baxter, Jason / Murray, ChristopherProposal Number: 1333649 / 1335821Institution: Drexel University / University of PennsylvaniaTitle: Collaborative Research: Ultrafast Carrier Dynamics in Semiconductor Nanocrystal Solar CellsClose-packed arrays of semiconductor nanocrystals (NCs), or quantum dots, are ideal systems for fundamental investigations of photo-induced charge and energy transfer in interacting quantum-confined materials. The materials, diameters, and arrangement of the NCs can be used to tune the inter-NC coupling to exploit both the properties of the individual NCs and the long-range effects of the solid. The emergent optical, electronic, and thermal properties of NC superlattices may lead to transformational improvements in applications including photovoltaics, photonics, and thermoelectrics.The broad objectives of this proposal are (1) to understand ultrafast charge carrier generation, separation, recombination, and transport phenomena in semiconductor nanocrystal superlattices, and (2) to control these fundamental photophysical processes to improve solar cell performance. Specifically, we will investigate films of CdSe, CdTe, and Cu2ZnSnS4 (CZTS) NCs. CdSe and CdTe NCs are excellent model systems because their synthesis and optical properties are well-understood, enabling fundamental ultrafast studies of carrier dynamics in glassy arrays and ordered superlattices of a single monodisperse NC species, as well as binary NC superlattices. CZTS NCs provide an exciting new direction for high efficiency photovoltaics made from non-toxic, earth-abundant elements. The PIs will refine the synthesis of monodisperse CZTS NCs to enable meaningful ultrafast spectroscopic characterization.This approach centers on time-resolved terahertz spectroscopy (TRTS) and femtosecond visible/infrared transient absorption (TA) to probe intraband and interband transitions, respectively. THz spectroscopy is an ideal, non-contact probe of electronic materials because the THz frequency regime (0.1 - 3 THz) brackets typical carrier scattering rates in semiconductors. THz spectroscopy is unique in its abilities to distinguish between excitons and free carriers and to measure their dynamics on sub-picosecond to nanosecond time scales, providing an excellent complement to our steady-state field effect transistor (FET) measurements. Pump-probe TRTS and TA are ideal techniques to investigate the dynamics of interfacial charge transfer, recombination, and inter-NC transport of photoexcited carriers on their natural time and energy scales.This work will advance our understanding of the physical phenomena that govern ultrafast exciton and free carrier dynamics in NCs and NC superlattices. Specific studies will include: (1) Determining mechanisms of charge transport in NC superlattices, e.g. by extended states or by activated hopping; (2) Measuring dynamics of inter-NC coupling, interfacial charge transfer, and long-range charge transport in superlattices of a single monodisperse NC species; (3) Determining the dependence of dynamics and transport mechanisms on NC size, capping ligand, inter-NC spacing, and long range order; (4) Understanding charge separation and transport in binary NC superlattices; and (5) Incorporating good candidate materials into solar cells to demonstrate improvements in efficiency that result from carefully designed NC architectures. This work will address the challenge of maintaining quantum-confined NC photophysics while also enabling long range charge transport necessary for devices. PI Baxter?s expertise in ultrafast spectroscopy and solar cells and PI Murray?s expertise in synthesis of NCs and superlattices make the team well-equipped to carry out this work.The understanding of fundamental photophysical processes such as interfacial charge transfer, recombination, and inter-NC transport in NC superlattices developed here can be applied to create high-efficiency NC solar cells. Availability of efficient, low-cost, clean, and sustainable solar cells made from earth-abundant, non-toxic materials would transform the US energy portfolio. This project will result in the education and training of two Ph.D. students and multiple undergraduates. Additionally, PI Baxter is developing new courses on "Fundamentals of Solar Cells" and lab-based "Nanomanufacturing for Energy Applications" for students from both universities. Outreach will extend to K-12 students by the PIs? continued participation in NanoDay@Penn, Philly Materials Day at Drexel, and mentoring local high school teachers through NSF RET and university programs. These programs are particularly beneficial for underrepresented groups since they target students and teachers from the School District of Philadelphia, whose student body is over 80% minorities.

PI：Baxter，Jason/Murray，Christopher Proposal编号：1333649/1335821机构：德雷克塞尔大学/宾夕法尼亚大学标题：合作研究：半导体纳米晶体太阳能电池中的超快载流子动力学紧密堆积的半导体纳米晶体(NC)或量子点阵列，是基础研究相互作用的量子限制材料中光致电荷和能量转移的理想系统。NCS的材料、直径和排列可用于调整NC间的耦合，以利用单个NCS的属性和固体的长期影响。纳米超晶格的光学、电学和热学特性可能会在光伏、光子学和热电学等应用领域带来革命性的改进。这一提议的主要目标是(1)了解半导体纳米晶体超晶格中超快载流子的产生、分离、复合和输运现象，(2)控制这些基本的光物理过程，以提高太阳能电池的性能。具体地说，我们将研究CdSe、CdTe和Cu2ZnSnS4(CZTS)NCS薄膜。Cd Se和Cd Te NCs是很好的模型体系，因为它们的合成和光学性质是众所周知的，使得能够对玻璃阵列和单一单分散NC物种的有序超晶格以及二元NC超晶格中的载流子动力学进行基本的超快研究。CZTS NCS为由无毒、富含地球的元素制造的高效光伏提供了一个令人振奋的新方向。PI将改进单分散CZTS NCS的合成，以实现有意义的超快光谱表征。该方法以时间分辨太赫兹光谱(TRT)和飞秒可见光/红外瞬时吸收(TA)为中心，分别探测带内和带间跃迁。太赫兹光谱学是一种理想的非接触式电子材料探头，因为太赫兹频率(0.1-3太赫兹)包含了半导体中典型的载流子散射率。太赫兹光谱的独特之处在于它能够区分激子和自由载流子，并在亚皮秒到纳秒的时间尺度上测量它们的动力学，为我们的稳态场效应晶体管(FET)测量提供了极好的补充。抽运探测TRT和TA是在自然时间和能量尺度上研究光激载流子界面电荷转移、复合和NC间输运动力学的理想技术。这项工作将加深我们对控制NCS和NC超晶格中超快激子和自由载流子动力学的物理现象的理解。具体研究将包括：(1)确定NC超晶格中的电荷传输机制，例如通过扩展态或激活跳跃；(2)测量单一单分散NC物种的超晶格中NC间耦合、界面电荷转移和远程电荷传输的动力学；(3)确定动力学和传输机制对NC尺寸、封顶配体、NC间间距和长程有序的依赖；(4)了解二元NC超晶格中的电荷分离和传输；以及(5)将良好的候选材料引入太阳能电池，以展示精心设计的NC结构导致的效率提高。这项工作将解决在维持量子受限的NC光物理的同时实现设备所需的远程电荷传输的挑战。皮巴克斯特、S在超快光谱和太阳能电池方面的专业知识，以及皮默里、S在NC和超晶格合成方面的专业知识，使该团队能够很好地完成这项工作。本文发展的对NC超晶格中界面电荷转移、复合和NC间传输等基本光物理过程的理解，可以用于制造高效的NC太阳能电池。由地球上丰富的无毒材料制成的高效、低成本、清洁和可持续的太阳能电池的可获得性将改变美国的能源组合。该项目将教育和培训两名博士生和多名本科生。此外，Pi Baxter正在为两所大学的学生开发新的课程，内容包括“太阳能电池基础”和基于实验室的“用于能源应用的纳米制造”。PIS会将外展服务扩展至K-12学生吗？继续参加NanoDay@Penn，在Drexel的费城材料日，并通过NSF RET和大学项目指导当地高中教师。这些方案对代表性不足的群体特别有利，因为它们针对的是来自费城学区的学生和教师，他们的学生群体中80%以上是少数族裔。