Enhanced efficiency in organic photovoltaic cells using engineered plasmonic nanostructures

题目：利用工程等离子体纳米结构提高有机光伏电池的效率知识产权有机光伏电池（opv）有可能重新定义太阳能转换的成本。有机半导体因其与高通量处理方法的兼容性而具有吸引力，但已证明的功率转换效率仅为7%左右。提出的研究概述了一种利用纳米结构金属电极的表面等离子体来克服opv典型的低吸收效率的新方法。由于OPV材料中的吸收会导致激子的形成，因此光电流的产生需要激子解离成其组成的载流子。这个过程通常发生在给电子(D)和接受电子(a)材料之间的异质结上。挑战在于激子的扩散长度通常比光学吸收长度短，因此需要使用薄的活性层来有效地收集和解离激子。这项工作将薄膜opv与等离子体电极集成在一起，允许亚波长限制和光场的共振增强，以提高吸收和功率转换效率。薄OPV与工程等离子体电极的结合为激子-等离子体耦合的高可调性和控制提供了潜力，从而实现了高效率。在提出的研究中，将引入从纳米结构等离子体电极提供光场增强的新架构，以最大限度地提高薄opv中的光吸收，并允许有效地收集激子和载流子。将进行广泛的计算建模，以确定等离子体opv的最佳设计规则。使用连续的、纳米图案的金属薄膜是有吸引力的，因为与金属纳米颗粒相比，场增强的范围更长（~200 nm），增强了整个活性OPV层的吸收。此外，这些连续的薄膜可以同时作为电极，这是金属纳米颗粒不可能的。对于等离子体电极的高通量制造，将采用模板剥离法。利用成熟的硅制造技术，将制造出各种纳米模板。沉积在模板上的金属膜将在界面处形成光滑的表面，可以使用弹性冲压件将其从基板上剥离，并使用冷焊直接转移到完整的OPV电池的顶部。该方案将为等离子体opv的制造提供前所未有的灵活性，因为顶部和底部电极可以独立的纳米图案，在大面积上具有高吞吐量。在这项工作中提出的opv也将利用分级供体-受体异质结（GHJs）。GHJ的使用是有吸引力的，因为它平衡了对有效激子扩散（大界面面积）和有效电荷收集（梯度传输途径）的需求。ghj的生长也是可调的，通过一系列的组成来研究等离子体opv的设计如何受到空间D-A组成的影响。更广泛的影响与此项目相关的研究生将在可再生能源有机光伏器件的背景下获得纳米制造，等离子体学和分子光物理学的跨学科知识。现有的本科生研究机会将通过与明尼苏达大学UROP计划和美国国家科学基金会REU计划的持续关系得到加强。对于K-12教育，多个高中研究人员将在夏季期间通过可再生能源项目的夏季研究集群在PIs实验室接受主持和指导。这些活动将辅以计划，通过校园讲习班和为行业参与者举办的年度实践实验室短期课程，向行业传播拟议工作的成果。最后,?和科学家坐在一起？在每年四月为期一周的纳米日活动期间，将通过拟议的推广计划在明尼苏达科学博物馆组织会议。

Institution: University of Minnesota-Twin CitiesTitle: Enhanced efficiency in organic photovoltaic cells using engineered plasmonic nanostructuresIntellectual MeritOrganic photovoltaic cells (OPVs) have the potential to redefine the cost of solar energy conversion. Organic semiconductors are attractive due to their compatibility with high throughput processing methods, but demonstrated power conversion efficiencies are only around 7%. The proposed research outlines a new approach to overcome the low absorption efficiency typical in OPVs by exploiting surface plasmons in nanostructured metallic electrodes. Since absorption in OPV materials leads to exciton formation, photocurrent generation requires the dissociation of excitons into their constituent charge carriers. This process usually occurs at a hetero-junction between electron donating (D) and accepting (A) materials. The challenge lies in the fact that the exciton diffusion length is typically shorter than the optical absorption length, necessitating the use of thin active layers to efficiently collect and dissociate excitons. This work integrates thin film OPVs with plasmonic electrodes, permitting sub-wavelength confinement and resonant enhancement of the optical field, to increase the absorption and power conversion efficiencies. The combination of a thin OPV with engineered plasmonic electrodes offers the potential for a high level of tunability and control over the exciton-plasmon coupling to realize high efficiency. In the proposed research, novel architectures that offer optical field enhancement from nanostructured plasmonic electrodes will be introduced to maximize optical absorption in thin OPVs and permit the efficient harvesting of excitons and charge carriers. Extensive computational modeling will be performed to identify optimal design rules for plasmonic OPVs. The use of continuous, nanopatterned metal films is attractive, since the field enhancement is longer range (~200 nm) compared with metallic nanoparticles, enhancing absorption throughout the active OPV layers. Furthermore, these continuous films can concurrently function as electrodes, which is not possible with metallic nanoparticles. For high-throughput fabrication of plasmonic electrodes, a template-stripping method will be used. Using mature silicon fabrication technology, a variety of nano-patterned templates will be fabricated. A metal film deposited on the template will form a smooth surface at the interface, which it can be peeled off of the substrate using an elastomeric stamp and directly transferred to the top of a completed OPV cell using cold welding. This scheme will provide unprecedented flexibility in the fabrication of plasmonic OPVs, since the top and bottom electrodes can be independently nano-patterned with high throughput over large areas. The OPVs proposed in this work will also utilize graded donor-acceptor heterojunctions (GHJs). The use of a GHJ is attractive because it balances the need for efficient exciton diffusion (large interface area) with efficient charge collection (graded pathways for transport). The growth of GHJs is also tunable, enabling a range of compositions through which to examine how the design of plasmonic OPVs is impacted by the spatial D-A composition.Broader ImpactsGraduate students associated with this project will acquire an interdisciplinary spectrum of knowledge in nanofabrication, plasmonics, and molecular photophysics in the context of organic photovoltaic devices for renewable energy. Existing undergraduate research opportunities will be enhanced through continuing relationships with the University of Minnesota UROP program and the NSF REU program. For K-12 education, multiple high school researchers will be hosted and mentored in the PIs laboratory during the summer through the Summer Research Cluster in Renewable Energy program. These activities will be complemented by plans to disseminate results from the proposed work to industry via on-campus workshops and annual hands-on lab short courses for industry participants. Finally, ?Sit with a Scientist? sessions at the Science Museum of Minnesota will be organized through the proposed outreach plan during the one week-long NanoDays event in April of each year.