Paul Kim
DAAD Summer Report
I agree that my report and accompanying pictures may be used by the DAAD in
printed materials, presentations, and on websites in order to inform funding
organizations, sponsors, and students about the RISE program.
This summer, I traveled to Germany in order to conduct research at the University of
Konstanz. I was offered an opportunity by the DAAD RISE (Research Internships in
Science and Engineering) program to work with the Hybrid Nanostructures Group at the
University, headed by Professor Lukas Schmidt-Mende. The RISE program provided me
the funds to live in Germany and pay for housing and food. Over the 10 weeks I lived in
Germany, I fully immersed myself in both the German culture and my laboratory work.
My area of research pushes the boundaries of solar energy. One of the greatest challenges
facing the world today is the search for renewable and clean energy. Fossil fuels, while
highly consumed and useful, produce deleterious chemicals and gases that damage
ecosystems and the atmosphere. Solar energy is one of the most promising solutions to
this energy crisis. Solar cells absorb light from the sun and use the energy to generate
current. Modern solar cells can achieve efficiencies in the range of 30%, but are limited
by their costs and difficulty in production. My research with the Hybrid Nanostructures
Group sough to solve this issue by attempting to replace the typical solar cells with
organic or hybrid solar cells. While the solar cells currently in production use metallic
materials like silicon, cadmium, and tellurium, using organic materials would reduce the
prices and make the cells easier to mass produce. A hybrid solar cell makes use of both
metallic and organic components to create a solar cell that is not only cheap but will
produce a high enough efficiency to be considered commercially competitive.
These hybrid solar cells will use an organic material to absorb light and inject electrons
into a metallic or semiconducting film. The electrons, separated from the organic
material, can then be used as current. In order to do so, the electron must reach the
electrode without undergoing recombination: in recombination, the electron does not get
to the electrode, returns to the organic material, and current is not generated. There is a
certain distance the electron can travel through the semiconducting film before it
recombines. When there is too much recombination, the efficiency of the solar cell
significantly falls. My research aims to ensure that the electron is able to reach the
electrode to create current. I used silver nanowires to help improve the mobility of the
electrons. The silver nanowires were coated with a zinc oxide semiconducting film, so
the electrons would be injected into the zinc oxide and then transfer to the nanowire.
Silver nanowires have exceptional conductivity, making them ideal structures to shuttle
electrons to the electrodes. In addition, the nanowire length is ideal for the distance the
electron can travel before succumbing to recombination. The nanowires would improve
the transportation of the electrons and reduce the effects of recombination on the solar
cell. As a result, the hybrid solar cells should achieve higher efficiencies.
At first, I needed to learn the necessary skills before constructing solar cells that would
yield any notable efficiency values. My first few weeks were spent following my mentor
and other lab group members as they created an organic solar cell from scratch and then
characterized the cells to determine their abilities. Once I had become familiar with the
techniques, my primary responsibility became to optimize this procedure. I took each step
of the solar cell creation process and sought to find the best conditions that would result
in the best efficiency at the end. Afterwards, I tackled the issue of implementing the
silver nanowires into the solar cells. Another summer student would grow the silver
nanowires, and I would then construct the cells using the grown silver nanowires.
Although I did not have enough time to optimize solar cell construction with the silver
nanowires, I was able to achieve efficiencies of around 1.5%. While not yet competitive
with the reference cells, which could achieve efficiencies of 2.8%, my work
demonstrated the potential for the implementation of silver nanowires to increase solar
cell efficiency.
For me, a typical day doing research at the university went smoothly and was always well
organized. I would arrive around 8:45 in the morning and grab a chocolate muffin to start
my day. I would speak with my PhD student about my duties for the day. Usually we
would spend some time discussing the previous days result and use that information to
determine the parameters or cells tested that day. Then I would spend the morning doing
most of my spin coating, which is how I could prepare the semiconducting and polymer
films. While I ate lunch, I would use the evaporator to deposit layers of tungsten oxide
and silver onto my solar cells. In the afternoon, I would characterize my solar cells.
Sometimes members of the lab would bring in cakes or snacks to share while we all
congregated to chat and relax. After compiling my data and discussing my results with
my PhD student, I head home to prepare for dinner. I noticed that my coworkers and even
the city itself were efficient. The buses almost always ran on time and my coworkers
always worked around an online schedule when using shared instruments. It let me
carefully plan out my day and allowed me to get the most work completed everyday.
The highlights of my day were whenever I got the opportunity to stray from my planned
schedule. Impromptu hangouts after work, events in the university itself, and especially
the times I assisted in baking cakes for our lab group were some of my fondest memories
of my time in Germany. Konstanz was a great place to work for me personally because it
was smaller in terms of population and seemed quieter than when I visited cities like
Munich. The city itself felt very relaxing and I often enjoyed spending time near the river
without having to worry about too many loud noises or too many people. Having lived in
a city built around highways, the lack of cars in Konstanz was impressive and an
interesting break from what I usually see. If I were to live in Germany again, I would
definitely return to Konstanz.
The fellowship has given me great perspective on my own career goals. While I still want
to explore research in the industry next summer, I realized that I am very comfortable
conducting research in an academic setting. In addition, I feel more comfortable about the
possibility of working in another country as opposed to staying in the United States.
While this wasn’t the first time I’ve lived on my own, it was my first time staying abroad
for so long on my own. I had the chance to learn some German, cook my own meals, and
travel around Europe. Whether I was touring the city of Heidelberg or having a picnic in
Oppenau, I was constantly learning and exposing myself to German culture while
simultaneously picking up skills to help me live more independently. Even if I don’t
travel abroad in my future career, I’ve been able to practice skills in Konstanz that I will
be able to use no matter where I live. At the very least I can cook currywurst if I need to
prepare my own meal. Before coming to Germany, I was nervous about traveling, eating,
and feeling lonely. Now, I feel confident that if I got sent to any country, I could figure
almost any situation out. It’s been a growing experience and I’ll definitely look into some
international opportunities when I apply for graduate schools and jobs.
I want to express my sincere gratitude towards the sponsors of the RISE program and the
DAAD. It was an eye-opening experience to travel to a country I have never visited and
learn so much about the culture while still pursuing a topic that I care deeply about. None
of this could have been possible without their help. Thank you very much!