Case Study for Electronic Spectroscopy
Instructions
Please use the prompts below as a way to structure your analysis of this case study. You will be presented with a multi-faceted chemical or material problem that you need to solve using spectroscopic techniques that we have covered in this course. After being given hypothetical data, observations, and measurements, you will describe how you will formulate and test hypotheses to better understand this system or analyte.
Think of this as if you have a new research problem, you work for a company on a new project or are advising regulators on how to monitor a new environmental problem. The way that the case studies will be assessed is described in the syllabus. Please write your responses to the prompts by replacing the text below. Your final analysis should be comprehensive, rely on peer review literature when necessary, and should be no more than five pages.
Background
Photovoltaic (PV) solar cells are devices that convert solar energy into electricity. Generally, they are constructed to be robust to the elements because they are outside, and must have resilient and transparent housings. Inside of the housing is an active material, this active material absorbs external photons and converts them into electricity. The active material can be composed of many materials, including organic dyes, quantum dots, and solid-state semiconductors. Below this is an opaque mirror and electronics that direct the electricity elsewhere for commercial or residential use. Because they are placed outside, they must have housings that are both durable and see-through, and they are often built to be resistant to the effects of the environment. An active material may be found inside the housing; this active material is responsible for absorbing photons from the environment and converting them into electricity. It is possible for the active material to be made up of a wide variety of components, such as quantum dots, organic dyes, and solid-state semiconductors. Below this is a dark mirror and some electronic components that route the flow of electricity to another location, where it can be used for either business or domestic purposes.
A textile business has had PVs that provide power for their looms for about ten years. Recently, they realized that the efficiency of their PVs has decreased by about 0.5% per year. When they first installed them, they were at 15% efficiency, now they are reduced to 5%. After bringing in an inspector, it is now clear that there are contaminants and adsorbates—dirt, soot, pollutants, etc.—that are covering the glass housing. They now believe that these adsorbates are a significant contributor to the efficiency decrease over time.
Analysis
What physical processes mediated by the adsorbates could influence the performance of the PV? Explain how these processes would decrease the efficiency.
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Cleaning the glass surface of the PV increases the efficiency by 5.0%. However, upon closer inspection, this increase is entirely due to increased absorption of the active material in the orange and red parts of the spectrum. What does this tell us about the physical properties of the adsorbates? How would you quantitatively relate the amount of the adsorbates to the changes in efficiency?
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You are concerned that the surface of the PV will be contaminated again, reducing the efficiency over time. New exterior coating technology, however, can limit the adhesion of adsorbates on the glass surface. What is important about the optical properties of this coating within the context of the PV? Explain what properties are important and how you would measure them.
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You are tasked with designing a new active material. Often, it is best to make the active material as thin as possible to efficiently collect the electrons that it generates. What intrinsic optical property could you maximize in the active material to increase absorption? How could you measure it? Think about this within the context of the path length and Beer’s Law.
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While the cleaning process recovering 5% of the efficiency, the PV system is still operating at 5% below its initial capacity. To determine why the inspectors disassembled one of the PVs to determine how well the active material is functioning. How could you analyze the optical properties of this material? What are some important quantities or figures of merit you would try to measure? Explain.
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