Designing Surface Plasmon Enhanced Thin-Film Solar Cells for Enhanced Absorption
Efficiency
Background: The looming energy crisis and climate change provides one of the greatest engineering challenges to the world today. With rising costs of fuel and harmful impacts of fossil fuels on the environment, there is an increasing need for alternative energy resources. One of the leading alternate energy sources is solar power, or photovoltaics. However, because of the high costs of producing silicon wafers for solar cells, photovoltaics are not yet a viable solution to combating climate change or solving the world’s energy crisis. To decrease costs of crystalline silicon solar cells, research has increased on thin-film solar cells. Although thin-film solar cells can be produced at a significantly lower cost, their absorption of near-bandgap light is ineffective [1]. Therefore, trapping of light and other methods to maximize absorption efficiency becomes a research point of interest. There are two basic mechanisms to enhance the photocurrent by metal nanoparticles: (1) light scattering of the nanostructures and (2) near-field concentration of light [1].
Problem Definition: Although it has been proven that solar cells can be enhanced by surface plasmons, the optimum configuration of nanostructures has not been determined to maximize the absorption efficiency. Because the geometry of nanostructure greatly determines its response and characteristics [2], a thorough study of shapes and distributions of the particles is needed to optimize thin-film solar cells. The implementation of metal nanostructures on thin-film solar cells has utilized the property of light scattering by the nanostructures to increase absorption.
However, coupling of two nanoparticles together forming nano-antennas could enhance the absorption by the mechanism of near-field concentration of light [2]. By combining these two mechanisms and developing guidelines for the optimum configuration of nanostructures, the absorption of the thin-film solar cells should increase in efficiency and therefore make them an affordable and practical alternate energy source.
Goals: The main objective for this research is to develop guidelines for the design of plasmon enhanced thin-film solar cells to achieve the optimum absorption efficiency of the solar cell. To accomplish this objective, the following key issues will be researched and tested: (1) Study the effects of the geometry and orientation of the nanostructures above the substrate, (2) Investigate the optimum distance between the nanostructures and the top of the substrate and also the distribution of the nanostructures, (3) Investigate the effects and applications of the near-field concentration of light by the nano-antennas on the solar cell, (4) Develop sophisticated fabrication techniques for the application of the nano-antennas on the solar cell, and (5) Measure the absorption efficiency using near and far field techniques.
Methodology: I will first conduct a literature review on the increased absorption due to light scattering. Following the initial research, I will then develop computer models to simulate the different geometries and configurations of the nanostructures. Computer models will also be used to initially test the effects of the thickness of the dielectric and the distribution of the nanostructures. Commercial computer models, such as Ansoft HFSS, could be essential for the initial investigation. Through my undergraduate research next semester, I will develop the background knowledge of how to use these types of computer programs. Next, the near-field responses of nano-antennas will be researched and tested by both computer simulations and by laboratory experiments. With the design of a specific geometry determined, fabrication will

ensue to verify the computer simulations. Once the research is complete on the specific parameters, the next step will be to determine an efficient way to fabricate the entire system. To do this,
I will investigate current fabrication methods for plasmon enhanced solar cells, namely thermal evaporation and electron-beam lithography, and develop new methods of fabrication. After the physical models are prepared, I will then conclude the research by measuring the absorption efficiency of the solar cell in the lab. Figure 1. Plasmon Enhanced
Solar Cell
Specifics: For my graduate career, I have researched many graduate programs and have determined that working for Dr. Adrienne Stiff-Roberts in the Electrical Engineering program at
Duke University is the best fit for my interests. Dr. Stiff-Roberts’ specialties include nanomaterial manufacturing and characterization as well as semiconductor photonic devices, and she is currently researching the field of enhanced solar cells. Her lab in the Fitzpatrick Center for Interdisciplinary Engineering, Medicine, and Applied Sciences houses equipment to determine the structural, optical, and electrical characterization of nanomaterials and hybrid nanomaterial heterostructures, which is imperative for measuring the absorption efficiency of the developed solar cells. I plan to take courses such as Quantum Mechanics, Semiconductor
Physics, Optoelectronic Devices, and Computational Electromagnetics. Physics courses such as
Quantum Optics and Atomic Physics and Spectroscopy will also help with my proposed research. This project will span several disciplines; it will be beneficial to create a partnership with the other departments in order to maximize the resources available.
Anticipated Outcomes: Upon receiving my PhD degree, I plan to apply my graduate research experience to work on solar cells and new technologies associated with solar energy. Ultimately,
I would like to be a part of the movement to expand the use of solar energy in order to help curb the impending energy crisis and climate change. This research will allow me to become involved with the current efforts to make solar energy affordable and to help serve the cause of finding better energy alternatives.
Intellectual Merit: This research can drastically improve the efficiency of thin-film solar cell and make it a practical alternative energy option. If thin-film solar cells can be made effectively and cheaply, their applications can extend to parts of the world that traditional wafer solar cells cannot. Affordability of the thin-film solar cells can also make photovoltaics competitive with fossil fuel energy and become a part of the solution to the world’s energy crisis.
The characterization of the parameters for nano-antennas and the fabrication techniques will not be limited just for solar cell applications; they can be extended to other potential uses for nano-antennas, such as bio-sensing, infrared detection, high resolution microscopy and lithography. Being able to communicate the proposed research outcomes is critical to disseminate research results to others.
References:
[1] Catchpole, K.R. and Poleman, A. “Plasmonic Solar Cells.” Optics Express, Vol. 16, No. 26,
17 December 2008.
[2] Maier, Stefan Alexander. Plasmonics Fundamentals and Applications. Springer. New York,
NY. 2007