Summer Summary

Going into summer research this year, I had no idea what to expect. For the past three years, there had been at least one more experienced student to share the work and provide guidance, but this summer I was the only one on my project. Even though I was very nervous at the beginning, it ended up being a great experience because it forced me out of my comfort zone. Since the only other student in the lab was on an entirely different project, I had to become much better at explaining the core concepts involved in my work, while also learning a lot about her art conservation project. I also became better at speaking up and going to my PI with questions when I was unsure about aspects of a new procedure.

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Next Step: Titanium Dioxide

During my last week of research, I started a new phase of my project. After completing the study of the electron transfer dynamics of the dye Rhodamine 560 on glass, I moved on to studying the behavior of this dye on titanium dioxide. While we can learn a lot from the studies of R560 on glass especially when we compare it to other rhodamine dyes on glass, that entire phase of experimentation was just a control for comparison with the results on titanium dioxide. In actual dye-sensitized solar cells, the application of this research, titanium dioxide or some other semiconductor is necessary for the generation of electricity.

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Single Molecule Blinking Traces

At the end of my last post, I mentioned that I had taken a break from trying to measure the fluorescence lifetime of individual molecules of the organic dye Rhodamine 560, since I was unable to get a lifetime curve with a high enough signal to noise ratio at single molecule concentrations. Instead, I returned to a technique called single molecule blinking, which allows us to observe changes in emission intensity while an individual molecule is under continuous excitation.

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Measuring Single Molecule Lifetimes


During the first few weeks of summer research, I’ve been working toward my main goal of studying the behavior of an inexpensive organic dye at the molecular level by integrating two techniques: single molecule spectroscopy (SMS) and time-correlated single photon counting (TCSPC). SMS lets us look at the electron transfer processes happening in individual molecules, which is important because in dye-sensitized solar cells (the eventual application of this research) the environment is heterogeneous, meaning that each molecule undergoes different processes at very different speeds. TCSPC measures fluorescence lifetime decays of individual molecules, and can detect processes that happen in picoseconds, while SMS alone can detect electron transfer events down to only the millisecond timescale.

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Abstract: Understanding Dye-Sensitized Solar Cells

My name is Simran Rohatgi and I am a senior in Dr. Kristin Wustholz’s Physical Chemistry lab. My project deals with understanding how dye-sensitized solar cells (DSSCs) work on the molecular level to harness solar energy and convert it to electricity. Relative to traditional silicon-based solar cells, DSSCs inexpensive and versatile, but they are not as efficient as silicon-based cells and therefore are not widely used. A molecular-level understanding of the electron transfer (ET) processes that take place inside the DSSC may help us understand why they are not as efficient as expected. Once we gain this understanding, scientists may be able to improve the efficiency of DSSCs so that they can begin to play a role in solving the energy crisis facing our planet. This summer, I hope to study DSSC systems using a combination of single molecule (SM) and fluorescence lifetime spectroscopies. SM studies allow us to observe ET processes of individual dye molecules, instead of obtaining averaged data, which would be less valuable due to the heterogeneous nature of the environment inside DSSCs. Additionally, fluorescence lifetime measurements will allow the observation of ET processes down to the picosecond timescale. The molecular-level understanding provided by these combined techniques may help us to explain the plateau in dye-sensitized solar cell (DSSC) efficiency that has been observed in the past decade.