By: Laura Estergreen

Hello everyone! My name is Laura Estergreen and I am a fourth-year graduate student in pursuit of my PhD in chemistry, and a 2018 Wrigley Sonosky Fellow.

I often spend my days in a dark room working away at a laser table or on my computer fitting and interpreting data. In my field I use lasers as a means of measuring the electronic properties of certain materials in hope of understanding how the molecular structure of a light-absorbing dye will affect the properties upon absorption of light.

How does this help with bettering our environment?

Many of you have probably seen those solar farms where there are a bunch of large, bulky silicon solar cells lined up in a row absorbing sun light. One of the issues with silicon solar cells is that they aren’t very good at absorbing light, so they have to be made very thick and crystallin in order to be of any benefit. The issue with this is that there is a lack of flexibility as to where these cells can be mounted due to their necessary size as well as the importance in the angle of incident sunlight at the solar cell’s surface. The manufacturing process alone has a very negative impact on our environment.

So what do we do? In my research project, in collaboration with the Mark Thompson group where the dyes we study are synthesized, we are working to develop organic solar cells (OSC’s). Small molecules have the benefit of being highly absorbing and therefore can be made into thin, flexible films. Perhaps you have seen those colorful windows on buildings? Those are little OSC’s. Currently they aren’t very efficient, much less than the silicon solar cells. However, the environmental impact on manufacturing and mounting OSC’s is significantly less than silicon. However, there is an underlying complexity in the process of light absorption towards charge generation and there are many pathways that can take away from a device’s efficiency. So, when in doubt, turn to biology to see how it has managed to maximize charge generation from sunlight.

Example of some dyes in solution I’ve been studying.

My research specifically focuses on a process that readily occurs in biology as an initial step in photosynthesis. It is called “Symmetry Breaking Charge Transfer” (SBCT). In biology, SBCT is a process in which an identical pair of light absorbing molecules are linked together and couple to make the process of separating charges more efficient. After absorption of sunlight this “special pair” undergoes SBCT, allowing for further charge transport to participating enzymes and proteins, resulting in the synthesis of oxygen and sugar. In OSC’s we want to use SBCT to design dyes where an identical pair are linked together to mimic SBCT. This, in principle will not only give selectivity to the site at which charge transfer occurs in a device, but will also make the process more efficient.

The image on the left is white light which we use to probe our experiments; the image on the right is the dispersed white light where all of the colors are separated.

In my lab, we use ultrafast laser pulses to measure these excited state processes since we are looking at lifetimes of excited electrons, and those time scales are super duper fast. We use femtosecond lasers, where one femtosecond is a quadrillionth of a second (10-15 seconds), in order to resolve these superfast processes. This allows us to shed light (no pun intended) on the complex excited landscape of these dyes, to gain further knowledge towards producing highly efficient light absorbing dyes. This is done in hopes of making organic solar cells competitive with silicon solar cells and eventually a beneficial alternative to fossil fuels.