UNS: Fundamental studies of charge transfer states at organic donor-acceptor interfaces for photovoltaics

PI：Alberto Salleo提案编号：1510481太阳代表着地球上最丰富的可持续能源的潜在来源。 使用有机导电聚合物将光转化为电的太阳能电池-有机光伏（OPV）器件-为可再生电力生产提供了一条潜在的低成本路线。 然而，为了达到与其他太阳能光伏技术同等的水平，有机太阳能电池必须将其功率转换效率提高到目前的10.5%世界纪录。 这种低功率输出的主要原因是将太阳的光子转换成电子的有机聚合物与接受所产生的电子的纳米结构碳之间的电荷转移在这两种材料的界面处不能有效地工作。 这项拟议的研究将通过先进的光谱分析技术在分子水平上对这一过程进行基本的科学理解。 拟议的教育活动包括为材料科学课程开发在线视频，以及一个本科生项目，该项目使用研究中开发的光谱方法来表征斯坦福大学康托艺术中心的文物。本研究的目标是在分子水平上对有机聚合物基光伏（OPV）器件中供体-受体界面的结构-性质关系有一个基本的了解。 OPV中的基本光电流产生机制涉及分裂紧密结合的电子-空穴对。 在形成分离的电荷之前，从光吸收聚合物供体分子到电子受体分子（通常为富勒烯或类似的纳米结构碳）的电子转移产生电荷转移状态，其中电子和空穴形式上在两个不同的分子上，但仍然能够跨越供体-受体界面相互作用。 OPV的太阳能转换效率是由于低电压产生，这与电荷转移态的能量直接相关，并且假设电荷转移态的无序可能是因果因素。 为了更好地理解这个过程，模型材料将被用来系统地测量分子取向如何影响电荷转移态的能量。 为此，傅立叶变换光电流光谱将测量产生的光电流，和纳米级电致发光技术将开发空间映射的电荷转移状态，并将其关联到众所周知的供体-受体界面配置。 稀释的三元共混物，其中两个相互混溶的富勒烯与低浓度的供体聚合物共混，将作为模型材料，以研究组成和结构的无序如何影响电荷转移态的能量。使用不同程度的聚合供体的补充研究将提供有关该过程对聚合物聚集和结晶度的依赖性的信息。 总的来说，这些研究将建立施主-受主界面的结构-性质关系，并为材料和界面设计提出新的方法，以提高OPV器件的电压和功率转换效率。 这些基础知识也可以提供关于如何改进用于预测有机聚合物基光电材料的性能和性质的理论工具的见解。 对OPV器件的研究将用于为斯坦福大学的有机半导体课程开发在线视频材料。 该项目还将涉及本科生与斯坦福大学的康托艺术中心合作，使用拟议研究中开发的技术对文物进行光谱表征。

PI: Alberto SalleoProposal Number: 1510481The sun represents the most abundant potential source of sustainable energy on earth. Solar cells that use organic conducting polymers to convert light to electricity - organic photovoltaic (OPV) devices - offer a potentially low-cost route for renewable electricity production. However, in order to achieve parity with other solar photovoltaic technologies, organic solar cells must increase their power conversion efficiency past the current 10.5% world record. A principal reason for this low power output is that the electric charge transfer between the organic polymer that converts the sun's photons into electrons, and the nanostructured carbon which accepts the generated electron, does not work efficiently at the interface of these two materials. This proposed research will develop a fundamental scientific understanding of this process at the molecular level through advanced spectroscopic analysis techniques. The proposed educational activities include development of online videos for material science courses, and an undergraduate student project to use the spectroscopic methods developed in the research to characterize artifacts at the Cantor Arts Center at Stanford University. The goal of this research is to develop a fundamental understanding of the structure-property relationships for the donor-acceptor interface in organic polymer based photovoltaic (OPV) devices at the molecular level. The fundamental photocurrent generation mechanism in OPV involves splitting a tightly-bound electron-hole pair. Prior to the formation of separated charges, the electron transfer from the light absorbing polymer donor molecule to the electron acceptor molecule, typically fullerene or similar nanostructured carbon, generates a charge transfer state, where the electron and hole are formally on two different molecules and yet are still able to interact across the donor-acceptor interface. The solar energy conversion efficiency of OPV is due to low voltage generation, which is directly linked to energy of the charge transfer state, and it is hypothesized the disorder of the charge transfer state may be a causal factor. To better understand this process, model materials will be used to measure systematically how molecular orientation affects the energy of the charge transfer state. Towards this end, Fourier transform photocurrent spectroscopy will measure generated photocurrent, and a nanoscale electroluminescence technique will be developed to map the charge transfer state spatially and correlate it to well-known donor-acceptor interface configurations. Dilute ternary blends, where two mutually miscible fullerenes are blended with a low concentration of a donor polymer, will serve as model materials to investigate how compositional and structural disorder affects the energy of the charge transfer state. Complementary studies using donors with different degrees of aggregation will provide information on the dependence of this process on polymer aggregation and crystallinity. Overall, these studies will establish the structure-property relationships of the donor-acceptor interface and suggest new approaches for materials and interface design to increase voltage and power conversion efficiency of OPV devices. This fundamental knowledge may also provide insights on how to refine theoretical tools used to predict the performance and properties of organic polymer based optoelectronic materials. Research on OPV devices will be used to develop online video materials for an organic semiconductors course at Stanford University. The project will also involve undergraduate students to work with the Cantor Arts Center at Stanford University to spectroscopically characterize artifacts using the techniques developed in the proposed research.