Probing Carrier Physics in Quantum Dot-Based Solar Cells

Jacob examining machine


Engineering and Applied Sciences


Professor of Electrical And Systems Engineering, Professor of Materials Science and Engineering

Project Summary

This summer, I worked in Prof. Cherie Kagan’s lab in SEAS.  I worked under the mentorship of a Ph.D. student, Eric Wong, on his research concerning quantum dot (QD) solar cells.  We aim to better understand the physics of carrier transport in PbS QD-based solar cells by measuring the density of trap states in PbS QD solids using two admittance-based techniques: drive-level capacitance profiling (DLCP) and thermal admittance spectroscopy (TAS).  Eric has been working on a paper concerning the application of these techniques to QDs that are directly synthesized as PbS; my research this summer focused on QDs that are originally synthesized as CdS, before cation exchange is used to create PbS QDs.  We would like to note any difference in the trap states of these two materials.

However, before we could perform the DLCP and TAS measurements, we needed to optimize the procedure for making solar cells with our cation exchanged QDs.  The procedure that works best with the Eric’s original QDs does not necessarily work best with the cation exchanged QDs.  Much of my work this summer focused on varying parameters in the fabrication process of the cells to see which produced the best cells.  We did take two sets of admittance measurements on my cells; while we could not get the information about trap states that we desired, we were able to estimate the location of the Fermi level in our PbS layer and we learned about the effects of air exposure on our cells.  Finally, I did some work to help Eric with his first paper.  This was a good experience, because working on a slightly different project exposed to me to experimental methods that I would not have used working on just my project this summer.

Of course, this experience was a great opportunity to learn about science and engineering.  Through the reading and thinking necessary to truly understand the project, I learned concepts that will surely be useful down the line.  Similarly, through experimental work I learned laboratory techniques that may also come in handy at some future point in my life as a scientist and/or engineer. 

However, perhaps more importantly than these nitty gritty scientific details, I learned at least in part what it’s like to do research in a lab.  Right now, all I really know about what I want to do after college is that I want to involve science and engineering in some way; other than that, I have no idea.  Since I have to get some idea of this in the next few years, it is really important for me to get real-world experience in different situations.  This experience allowed me to see what it would be like to do research at a university full-time. The jury is still out on whether or not I actually want to do that: I can certainly see myself doing research as a grad student after college, but I do not at the moment feel like it is something I absolutely want to do. After my research this summer, though, I can approach this question with a little more understanding.