SGER: Initiated Chemical Vapor Deposition Synthesis and Design of Polymers for Alternative Energies

CBET-0820608LauThis Small Grant for Exploratory Research（SGER）project is aimed to develop a new design and synthesis methodology based on initiated chemical vapor deposition（iCVD）to make semiconductor，conjugated polymers for using in solar cells with enhanced efficiency and performance.在基于本体异质结聚合物的太阳能电池中，低效率归因于聚合物的高带隙，导致与太阳光谱的失配，并且由于结构和形态缺陷，聚合物中的电荷产生和传输通常较差。在使用无机纳米晶体二氧化钛的混合系统中，无论是否有染料敏化，聚合物对中孔二氧化钛的填充不良都阻碍了太阳能电池的效率。这些问题中的一些源于使用基于液体的处理方法来形成太阳能电池堆中的共轭聚合物薄膜。由于未改性的共辄聚合物通常是难处理的和不溶性的，在这些聚合物上添加增溶侧链诱导溶解性并因此诱导可加工性。然而，侧基的添加可能导致结晶度、形态和稳定性的不期望的变化，并导致聚合物的降解。此外，聚合物性质通常对溶剂的选择和溶剂去除的条件敏感。iCVD依赖于使用蒸汽形式的单体和热活化引发剂/催化剂在表面上直接聚合固体聚合物薄膜。通过避开液相，不需要溶剂，因此iCVD获得了显著的加工自由度，不仅使未改性的共轭聚合物易于处理，而且还开辟了设计新颖材料的可能性，否则由于溶剂限制或不相容性，这些材料在液相中是无法获得的。此外，在没有宏观尺度相分离和由不利溶剂相互作用引起的分层的问题的情况下，iCVD作为一种无溶剂加工技术被期望能够实现共轭聚合物和其反向连接之间的不同相的紧密的纳米级混合。具体的研究目标是（1）证明使用iCVD对于选定的单体和共聚单体的列表的共轭聚合物的合成，其将具有作为太阳能电池材料的可行特性;以及（2）通过集成iCVD和加工技术如热蒸发和旋涂来证明施主相和受主相之间的紧密接触以产生异质结，类似于通过利用CVD和其他处理技术成功应用于微电子制造的范例。更广泛的影响：该计划的动机是需要发现替代能源解决方案，以减少我们对化石燃料的依赖，保护我们的环境免受其破坏性影响，并实现更可持续的地球。由于太阳能仍然是一种未开发的资源，该计划是旨在推动这种替代能源技术发展的第一步。除此之外，这项工作中设计良好的共轭聚合物可以在柔性电子产品，有机发光二极管（OLED）器件和生物医学中找到应用。该计划将通过指导高中和本科学生从德雷克塞尔？有许多外展计划;通过与地区高中建立越来越密切的关系，提供实践机会来测试太阳能电池的长期稳定性，以此向学生介绍负责任的技术。该计划旨在积极从少数民族和代表性不足的群体中招募人员。研究结果将被传播，并预计将发芽多学科研究，因为适用性和多功能性的iCVD方法。

CBET-0820608LauThis Small Grant for Exploratory Research (SGER) project is aimed at developing a new design and synthesis methodology based on initiated chemical vapor deposition (iCVD) to make semiconducting, conjugated polymers for use in solar cells with enhanced efficiency and performance.Intellectual merit: In bulk heterojunction polymer-based solar cells, inefficiencies are attributed to the high band gap of polymers leading to a mismatch with the solar spectrum, and generally poor charge generation and transport in the polymer due to structural and morphological defects. In hybrid systems using inorganic, nanocrystalline titania, with or without dye sensitization, solar cell efficiency has been hampered by the poor filling of the mesoporous titania with the polymer. Some of these issues stem from using liquid-based processing methods to form the conjugated polymer thin films in the solar cell stack. Since unmodified conjugated polymers are typically intractable and insoluble, addition of solubilizing side chains on these polymers induce solubility and therefore processability. However, addition of side groups may result in undesirable changes in crystallinity, morphology and stability and lead to degradation of the polymer. Further, polymer properties are often sensitive to the choice of solvent and the conditions for solvent removal. iCVD relies on the direct polymerization of a solid polymer thin film on a surface using monomers and thermally activated initiators/catalysts in the vapor form. By circumventing the liquid-phase, there is no requirement for solvents, and therefore iCVD gains significant processing freedom, not only in making unmodified conjugated polymers tractable, but also opening up the possibility of designing novel materials which would otherwise have been unattainable in the liquid phase due to solvent constraints or incompatibilities. Further, without the issues of macroscale phase separation and demixing from adverse solvent interactions, iCVD as a solventless processing technique is expected to enable intimate, nanoscale mixing of dissimilar phases between the conjugated polymer and its counter-junction.The specific research objectives are (1) to demonstrate the synthesis of conjugated polymers using iCVD for a selected list of monomers and co-monomers, which will have viable properties as solar cell materials; and (2) to demonstrate the tight contact between the donor and acceptor phases by integrating iCVD and processing techniques like thermal evaporation and spin coating to produce the heterojunctions, similar to the paradigm that has been successfully applied in microelectronics fabrication through the utilization of CVD and other processing techniques.Broader impact: This program is motivated by the need to discover alternative energy solutions to reduce our dependency on fossil fuel, protect our environment from its damaging effects, and enable a more sustainable Earth. With solar energy remaining a largely untapped resource, this program is a first step that aims to fuel the technological development of this alternative energy. Beyond this, well-designed conjugated polymers from this work could find applications in flexible electronics, organic light-emitting diode (OLED) devices, and biomedicine. This program will integrate a strong educational component through mentoring high school and undergraduate students from Drexel?s many outreach programs; by growing relationships with area high schools to provide hands-on opportunities to test the long term stability of solar cells as a way to inform students of responsible technology. This program aims to actively recruit from minority and underrepresented groups. Research results will be disseminated and are expected to germinate multidisciplinary research because of the applicability and versatility of the iCVD approach.