Enhanced Photon-Electron Conversion in Thin Film Solar Cells by Propagating Surface Plasmons

由于其在太阳能收集方面的巨大潜力，几种类型的薄膜太阳能电池最近引起了人们的极大关注。然而，众所周知的太阳能电池的能量转换效率仍然与理论预期相差甚远。低效率是由于半导体对光的吸收效率低下，以及从半导体向外部负载的载流子提取有限。这两个因素密切相关，这使得解决方案的开发更加困难。利用纳米结构表面等离子体的薄膜太阳能电池的开发将解决这一难题，并有助于进一步实现美国能源安全的目标。鉴于太阳辐射产生的电力仅占美国年总用电量的1%左右，这项研究的成功将通过提供高效的薄膜太阳能电池，为提高美国的能源安全做出贡献。将预期的研究成果与现有和新的课堂课程相结合，也将提高匹兹堡大学纳米科学和可再生能源工程教育的质量。此外，该项目的多学科性质将为本科生和研究生提供机会，使他们有机会接触到超出学科界限的材料和设备的设计、制造和表征的新领域。最后，这个项目的目标是利用薄膜太阳能电池等研究产品来接触代表性不足的群体，这将与匹兹堡大学正在进行的努力相协调，以扩大代表性不足群体在工程教育中的参与。当前与薄膜太阳能电池相关的问题清楚地表明，迫切需要设计一种新的纳米结构，以增强薄膜半导体中的光吸收和载流子输运。一个很有前途的方法是利用共振现象，如表面等离子体。然而，目前流行的等离子体金属纳米粒子在薄膜太阳能电池应用中存在一些缺陷。在本项目中，将利用一维光子晶体/金属薄膜界面上的传播表面等离子体来规避金属纳米粒子的问题。新的纳米结构将在不增加半导体薄膜厚度（即降低载流子收集效率）的情况下提高光收集效率。本项目的目标是利用光子晶体等离子体纳米结构制造一种新型的结型薄膜太阳能电池，并探索传播表面等离子体之间的物理相互作用，太阳光调制和载流子/激子的产生。研究的进展将对薄膜太阳能电池在表面等离子体影响下的光子-激子转换产生根本性的认识。为此，纳米结构光子晶体将被设计成在可见光范围内激发与入射太阳光相互作用的表面等离子体。此外，对光-物质相互作用和纳米结构的辐射特性的基本理解将被追求。这个项目的智力意义在于为高效混合太阳能电池提供了新的方向。关于表面等离子体辅助光吸收调谐的知识将促进不受光吸收和载流子输运之间权衡限制的新型光伏电池的发展。

Several types of thin film solar cells have recently drawn a great amount of attention, due to its huge potential in solar energy harvesting. However, the energy conversion efficiency of the well-known solar cells is still far from the theoretical expectation. The low efficiency is due to inefficient light absorption by the semiconductor and limited carrier extraction from the semiconductor to the external load. These two factors are closely related, which makes the development of a solution more difficult. Development of the thin film solar cells using the surface plasmons of the nanostructures will address this difficult problem and contribute to furthering the goal of energy security of the US. Given that the electricity produced from solar radiation is only about 1% of the total annual electricity consumed in the US, the success of this research will contribute to increasing US's energy security by providing highly efficient thin film solar cells. The integration of the anticipated research accomplishments with existing and new classroom courses will also improve the quality of engineering education on nanoscience and renewable energy at the University of Pittsburgh. In addition, the multi-disciplinary nature of the project will provide undergraduate and graduate students with the opportunity to be exposed to new frontiers in design, fabrication and characterizations of materials and devices, beyond the boundaries of their disciplines. Finally, this project will be aimed at using research products such as thin film solar cells to reach underrepresented groups, which will be coordinated with on-going efforts of the University of Pittsburgh to expand the participation of underrepresented groups in engineering education. Current problems associated with the thin film solar cells clearly show a strong need for design of a new nanostructure that can enhance the light absorption and carrier transport in the thin film semiconductor. One very promising way is to exploit resonance phenomenon, such as surface plasmons. However, popular plasmonic metal nanoparticles have several drawbacks to be implemented to the thin film solar cells. In this project, a propagating surface plasmon on 1-dimensional photonic crystal/metal thin film interface will be used to circumvent the problems of the metal nanoparticles. The new nanostructure will increase the light harvesting efficiency without increasing the thickness of the semiconductor film (i.e. decreasing the carrier collection efficiency). The objective of this project is to fabricate a new junction-type thin film solar cell employing the photonic crystal based plasmonic nanostructure and to explore the physical interactions among propagating surface plasmons, solar light modulation, and carrier/exciton generation. Progress of the research will create the fundamental understanding of the photon-exciton conversion under the influence of the surface plasmons for the thin film solar cells. For this purpose, the nanostructured photonic crystal will be designed to excite the surface plasmons that interact with incoming solar light in a visible range. In addition, basic understanding of light-matter interactions and radiative properties of nanostructures will be pursued. The intellectual significance of this project is that new directions for highly efficient hybrid solar cells will be provided. Knowledge on surface-plasmon-assisted tuning of the light absorption will facilitate a new class of photovoltaics which is not limited by the tradeoff between light absorption and carrier transport.