Monthly Archives: September 2016

Adding flexibility to solar energy

USC Wrigley Institute

By Betsy Melenbrink

Hi folks! My name is Betsy and I am a 2016 WIES Sonosky Fellow starting the fourth year of my chemistry Ph.D. program at the University of Southern California. My graduate research is on solar energy, specifically polymer solar cells.

What is a polymer solar cell? Well, solar panels are increasing in popularity, and each panel is made up of many cells. A lot of schools, businesses, and houses now have shiny grey panels on their roofs. These solar panels are primarily made from silicon, an inorganic semiconductor, which is great at moving electrical charges through itself, but not very good at absorbing sunlight. This means that the panels must be manufactured to be very thick to absorb more light, a process which is very expensive and energy-intensive, and results in heavy, brittle panels. Alternatively, we can make organic semiconductors from primarily carbon-based molecules. Polymers are just long chains of these molecules strung together. The semiconducting polymers are great at absorbing sunlight, which means they can be incorporated into lightweight, flexible solar panels, and they can be manufactured very cheaply.

Screen Shot 2016-08-15 at 3.19.09 PM

A) Silicon solar panels (figure taken from B) Flexible organic solar device (figure taken from

However, polymer solar cells currently have a few pitfalls as well. They are not yet as efficient at converting sunlight into electricity as silicon, and they do not have as long of a working lifetime. This is due to the fact that organic molecules can break down under intense sunlight and they can also move around in the thin film as it is heated by the sun. Both of these processes mean that the solar panel will lose its ability to convert sunlight into electricity as it ages.

My research aims to change the chemistry of the semiconducting polymers to make them more stable so that polymer solar cells will last longer. On a typical day, I make and purify monomers, a name that we use for the individual molecules that I later connect into long chains as polymers. I use typical organic chemistry methods for purification, such as extraction, column chromatography, and recrystallization.

Screen Shot 2016-08-15 at 3.19.45 PM

A) An extraction to isolate a monomer. B) Shiny crystals obtained from a recrystallization. C) Separating out monomers using column chromatography

When my monomers are pure, I connect them together into long chain polymers. Even if my monomers are colorless, the resulting polymer is often very colorful, as in Image A below. After the polymers have been purified I subject them to a number of tests to determine their chemical structure, their molecular weight (how long the polymer chain is), how the polymers crystallize, and their electrochemical behavior (how much energy it takes to add or subtract an electron). Following all of this characterization, I can test the polymer performance in solar cells.

Screen Shot 2016-08-15 at 3.20.12 PM

A) Leftover vials showing remains of colorful polymers. B) Purifying a colorful polymer using a soxhlet extractor. C) Betsy aligning a solar cell below the solar simulator – a lamp that imitates sunlight.

I am hoping to create solar devices that not only work immediately after they are made (as we usually test them), but also days, weeks, months, or even years afterward. By extending the working lifetime of these solar cells, I can help make the technology more viable as an alternative to silicon solar panels.

Betsy is a PhD student in the USC Department of Chemistry, in the research group of Dr. Barry Thompson. Her dissertation research focuses on development of lightweight flexible single-layer solar cells.

Back to WIES Blog home page

Finding markers of human impacts on marine environments

USC Wrigley Institute

By: Megan Hall

For the first time in four years, I didn’t spend the summer on Catalina Island at Wrigley Marine Science Center. Instead, I was thrilled to be spending my time in the lab on the mainland as a Norma and Jerol Sonosky Fellow. After many years of field sampling, wet lab experiments, and preparations, I was finally able to get to the heart of my research goals and delve into my large datasets for clues about how climate change will affect coastal water pollution.


Me preparing samples to be sequenced.

A central theme of my research has been updating water quality testing methods for copper. Copper is a common pollutant in urban regions, entering coastal waters via storm water runoff and antifouling paint on the hulls of boats. Regulations on copper in marine ecosystems have long been determined by live testing with mussels. Very young mussels (0-3 days old) are especially vulnerable to pollution, and abnormal patterns in their development can be indicative of problematic copper levels in coastal waters.

Screen Shot 2016-08-15 at 12.22.16 PM

Normal (left), and abnormal/developmentally delayed mussels (right), after exposure to copper

While pollution is still a major problem, concerns about climate change and ocean acidification have also escalated in recent years. Scientists are trying to understand how ocean acidification may interact with other existing stressors, and the implications for water quality could be great. For the past several years, I’ve been investigating gene expression in young mussels as a new and potentially more sensitive indicator of copper exposure. This summer, I am trying to understand what these genetic biomarkers could reveal about mussels’ ability to handle combined stressors as the ocean changes.

An organism’s gene expression is highly responsive to environmental changes, so expression is a good indicator of what kinds of stress an animal is experiencing. Using next generation sequencing, researchers can look at expression changes for almost every gene in the animal’s genome. Sequencing can reveal large-scale shifts in expression of many genes, as well as changes in expression of a single gene of interest. I will both look at these larger patterns and try to tease out some important genes that could be used as biomarkers in water quality tests.


An example of a gene expression profile produced by next generation sequencing. Color differences indicate genes (rows) that change with different environmental conditions (columns).

After conducting experiments, extracting RNA, and preparing Illumina sequencing libraries, I’ve just started to dig in to the wealth of data I now have available. So far, I’ve seen that gene expression in mussels exposed to both simulated ocean acidification and copper is quite different than expression in mussels exposed to copper alone. And most interestingly, ocean acidification actually seems to be reducing the toxicity of copper to young mussels! As I continue to explore the expression data, I hope to get some clues about what could be causing this unexpected result.

Previously a WIES Fellow at Catalina Island, Megan is a 2016 WIES Sonosky Fellow. She is currently finishing her PhD work in the research group of USC Professor Dr. Andrew Gracey to assume a position as a Knauss Marine Policy Fellow in Washington DC in January 2017. 

Back to WIES Blog home page