Hybrid Organic-Inorganic Quantum Dot Superlattices for Photovoltaics

非技术概述半导体量子点（QD）膜是下一代太阳能电池的重要新兴材料类别，但是基于QD膜的电池的效率部分地受到QD的不良空间有序性的限制。该项目的重点是开发高度有序和导电的量子点薄膜作为一类新的电子材料。在电子和光子材料计划以及材料研究部门的固态和材料化学计划的支持下，加州大学欧文分校（UCI）的研究人员将制造这些新材料，并研究有序在电荷传输中的作用，目标是证明量子点薄膜中电荷传输的极大改善。该项目将促进对功能性纳米级系统中运输的理解，包括空间和能量秩序在集体中尺度现象出现中的作用，例如依赖于纳米级构件之间强电子相互作用的带形成。该项目将产生对量子点自组装，界面物理和电荷扩散长度的新见解，并产生一类模块化的有机-无机混合量子点晶体，其传输特性适用于各种量子点技术，包括太阳能电池。这种通过溶液自组装制成的量子点太阳能电池可以降低太阳能发电的成本，并促进全球太阳能的部署，特别有利于发展中社区。该项目还将使K-12材料科学推广工作成为UCI/查普曼大学联合数学，工程，科学成就（梅萨）计划（http：//mesa.eng.uci.edu/）的一部分。研究人员将开发一个动手QD量子物理学梅萨计划，学生可以帮助合成QD，并通过光谱学和电子显微镜探索它们的特性。该联合计划为橙子县和洛杉矶县的约1，600名小学、初中和高中学生提供服务，重点是促进STEM教育，并为来自历史上参与高等教育水平较低背景的低收入学生提供学术充实。此外，一些本科生将参加这项研究，每年夏天的一部分，NSF资助的化学REU和UCI加州联盟少数民族参与（CAMP）夏季研究programmes.Technical总结PbX（X = S，Se，或Te）量子点（QD）薄膜代表了一个重要的新兴类的吸收层的下一代光伏（PV）。在过去的几年里，通过用短的有机分子或无机离子取代所制备的PbX量子点上的长的电绝缘油酸配体，在量子点光伏中取得了显着的进展。不幸的是，这些配体处理破坏了量子点薄膜中的中程和长程有序。部分地作为结果，电荷传输限于顺序声子辅助隧穿，导致低载流子迁移率、短载流子扩散长度和来自QD器件的有限光电流。一个令人兴奋的前景是将量子点组装成电子耦合的导电超晶格（量子点的晶体），其中可以通过畴离域态或布洛赫型扩展态（迷你带）进行输运。量子点超晶格中的微带输运可以产生更大的载流子迁移率和扩散长度。在电子和光子材料计划以及材料研究部门的固态和材料化学计划的支持下，加州大学欧文分校的研究人员将用共轭有机“分子线”取代PbX QD的油酸配体，以制造一类由量子点与分子线互连组成的新型导电PbX QD混合超晶格纳米复合材料（HSN）。分子线将提供优异的超晶格有序性、可调谐的HOMO和LUMO能级、经由势垒降低的强电子耦合、以及有利于超晶格结晶和共配体吸附以钝化表面态的大的QD间间距。超晶格顺序对电荷传输，载流子迁移率和扩散长度的影响将使用一系列的电气和光谱技术进行研究。该项目的主要基本目标是阐明超晶格效应增强量子点薄膜中载流子迁移率和扩散长度的程度和机制，而主要应用目标是制造少数载流子扩散长度至少为1000 nm的HSN，这将使量子点光伏的电荷收集和转换效率接近完美。

NON-TECHNICAL SUMMARYFilms of semiconductor quantum dots (QDs) are an important emerging class of materials for next-generation solar cells, but the efficiency of cells based on QD films is limited in part by the poor spatial order of the QDs. This project focuses on the development of highly-ordered and electrically-conductive QD films as a new class of electronic materials. With support from both the Electronic and Photonic Materials Program and the Solid State and Materials Chemistry Program in the Division of Materials Research, researchers at the University of California, Irvine (UCI) will make these new materials and study the role of order in charge transport, with the goal of demonstrating greatly improved charge transport in QD films. The project will advance the understanding of transport in functional nanoscale systems, including the role of spatial and energetic order in the emergence of collective mesoscale phenomena such as band formation that depend on strong electronic interactions between nanoscale building blocks. The project will yield new insights into QD self-assembly, interfacial physics, and charge diffusion length, and result in a class of modular, organic-inorganic hybrid QD crystals with transport properties suitable for a variety of QD technologies, including solar cells. Such QD solar cells made by self-assembly from solution can lower the cost of solar electricity and promote solar energy deployment worldwide, with particular benefits to developing communities. The project will also enable a K-12 materials science outreach effort as part of the UCI/Chapman University joint Mathematics, Engineering, Science Achievement (MESA) Program (http://mesa.eng.uci.edu/). The researchers will develop a hands-on QD photophysics MESA program in which students help synthesize QDs and explore their characterization by spectroscopy and electron microscopy. This joint program serves approximately 1,600 elementary, middle and high school students in Orange and Los Angeles Counties, and focuses on promoting STEM education and providing academic enrichment to low-income students from backgrounds with historically low levels of participation in higher education. In addition, several undergraduate students will participate in this research each summer as part of the NSF-funded Chemistry REU and the UCI California Alliance for Minority Participation (CAMP) summer research programs.TECHNICAL SUMMARYPbX (X = S, Se, or Te) quantum dot (QD) thin films represent an important emerging class of absorber layers for next-generation photovoltaics (PV). Remarkable progress has been made in QD PV over the past several years by replacing the long, electrically insulating oleate ligands on as-made PbX QDs with short organic molecules or inorganic ions. Unfortunately, these ligand treatments destroy medium and long range order in the QD films. Partly as a consequence, charge transport is limited to sequential phonon-assisted tunneling, resulting in low carrier mobility, short carrier diffusion lengths, and limited photocurrent from QD devices. One exciting prospect is to assemble QDs into electronically coupled, conductive superlattices (crystals of QDs) in which transport can occur via domain-delocalized states or Bloch-type extended states (mini-bands). Mini-band transport in QD superlattices could yield much larger carrier mobility and diffusion length. With support from both the Electronic and Photonic Materials Program and the Solid State and Materials Chemistry Program in the Division of Materials Research, researchers at the University of California, Irvine will replace the oleate ligands of PbX QDs with conjugated organic "molecular wires" to fabricate a new class of conductive PbX QD hybrid superlattice nanocomposites (HSNs) composed of QDs interconnected with molecular wires. The molecular wires will provide excellent superlattice order, tunable HOMO and LUMO levels, strong electronic coupling via barrier lowering, and large inter-QD spacing that is favorable for superlattice crystallization and the adsorption of co-ligands to passivate surface states. The impact of superlattice order on charge transport, carrier mobility, and diffusion length will be studied using an array of electrical and spectroscopic techniques. The main fundamental goal of the project is to elucidate the degree to which and the mechanisms by which superlattice effects enhance carrier mobility and diffusion length in QD films, while the main applied goal is to make HSNs with minority carrier diffusion lengths of at least 1000 nm, which would enable nearly perfect charge collection and very high conversion efficiency from QD PV.