Using Neutron Scattering to Elucidate the Thermodynamics of Conjugated Polymer:Fullerene Nanocomposites

技术摘要：在这项研究计划中，中子散射将用于确定共轭聚合物：富勒烯薄膜混合物作为聚合物和富勒烯结构，热处理，表面结构和溶剂的函数的可溶解性，相图，相分离结构，界面特性和垂直相分离。共轭聚合物（CP）被选为本研究的重点，因为它们是一类很有前途的材料，用于太阳能转化为电能。大多数研究创建CP纳米复合材料，测量其光伏（PV）性能，然后试图根据观察到的形态特征来确定PV活性和形态之间的关系。 不存在对形态的先验控制。拟议的研究计划的目的是提供热力学信息，将提供方法来控制形成所得的CP：富勒烯形态的基础上已知的表面和/或界面能，和聚合物：富勒烯，聚合物：溶剂，和富勒烯：溶剂的相互作用。然后，这些知识将用于调整系统中的相互作用，以制造具有目标结构的有源层。 PV活性与完全表征的目标形态的相关性代表了在有机光致发光中如何优化纳米级形态和光伏活性的范式转变。中子散射和反射率将是该项目的主要工具，因为质子化聚合物和富勒烯之间的中子散射长度密度的巨大差异奇异地允许聚合物：富勒烯系统的组装，界面结构，形态和组成的有效和彻底的表征。此外，实验的设计，使实验技术，分析和解释将适用于聚合物纳米复合材料，无论聚合物结构和纳米颗粒的大小，形状或构成。因此，本研究计划的完成将提供方法来发展的基本热力学和物理学的理解，支配的形成和结构的广泛的聚合物纳米复合材料。非技术摘要： 太阳能直接转换为电力是解决美国和整个世界的能源需求所面临的巨大挑战的有前途的方法，因为只有太阳能可以以环境清洁（即，零碳排放）过程。然而，目前太阳能的转换比其他常用能源贵5-10倍。需要通过基础性、变革性研究实现重大创新，以提高太阳能转换效率并降低成本。拟议的研究计划旨在满足这一需求，因为它的完成将提供合理设计和生产下一代更高效和更具成本效益的光伏电池所需的关键基础信息。 此外，这项工作的更广泛的影响将来自公立高中学生的经验，当他们在大学研究实验室度过一个夏天，为这个项目做出贡献，获得动手实验室经验和大学的特殊准备。在ORNL和NIST的中子设施完成实验将产生进一步的影响，参加该项目的学生将在多用户设施中获得实践经验，以确保这些国家设施的持续健康。该项目还将进一步发展EPSCOR州田纳西州的可持续研究基础设施，并将实施以确保代表性不足的群体参与这项研究。

TECHNICAL SUMMARY:In this research program, neutron scattering will be utilized to determine the miscibility, phase diagram, phase-separated structure, interfacial characteristics, and vertical phase separation of conjugated polymer:fullerene thin film mixtures as a function of polymer and fullerene structure, thermal processing, surface structure, and solvent. Conjugated polymers (CPs) are chosen as the focus of this study as they are a promising class of materials for use in the conversion of solar energy to electricity. Most studies create the CP nanocomposite, measure its photovoltaic (PV) properties and then attempt to ascertain the relationship between the PV activity and morphology based on the observed morphological features. There exists no a priori control of the morphology. The proposed research program is designed to supply thermodynamic information that will provide methods to control the formation of resultant CP:fullerene morphologies based on known surface and/or interfacial energies, and polymer:fullerene, polymer:solvent, and fullerene:solvent interactions. This knowledge will then be used to tune the interactions in the system to fabricate active layers with targeted structures. Correlation of PV activity to the fully characterized targeted morphology represents a paradigm shift in how the nanoscale morphology and photovoltaic activity are optimized in organic photovoltaics. Neutron scattering and reflectivity will be the primary tools in this project, as the large difference in neutron scattering length density between protonated polymers and fullerenes singularly allows the efficient and thorough characterization of the assembly, interfacial structure, morphology, and composition of polymer:fullerene systems. Moreover, the experiments are designed such that the experimental techniques, analyses, and interpretations will be applicable to polymer nanocomposites regardless of polymer structure and nanoparticle size, shape or constitution. Therefore, the completion of this research program will provide methods to develop an understanding of the fundamental thermodynamics and physics that govern the formation and structure of a broad range of polymer nanocomposites.NON-TECHNICAL SUMMARY: The direct conversion of solar energy to electricity is a promising method to solve the grand challenges facing the energy needs of the US and the world at large, as only solar energy can deliver the required power in an environmentally clean (i.e., zero carbon emission) process. However, the conversion of solar energy is currently 5-10 times more expensive than other commonly used energy sources. Major innovations made possible through fundamental, transformative research will be required to improve the efficiency of solar energy conversion and reduce its cost. The proposed research program is designed to meet this need, as its completion will provide critical fundamental information that is needed to rationally design and produce the next generation of more efficient and cost-effective photovoltaic cells. Additionally, broader impacts of this work will come from the experience of public High School students when they spend a summer in a university research lab contributing to this project obtaining hands-on laboratory experience and exceptional preparation for college. Further impact will result from the completion of experiments at the neutron facilities at ORNL and NIST where the students participating in this project will acquire hands-on experience in a multi-user facility to insure the continued health of these National facilities. This project will also further develop the sustainable research infrastructure in Tennessee, an EPSCOR state, and will be implemented to ensure the participation of underrepresented groups in this research.