First used
commercially in the automotive industry, electrophoretic deposition (EPD) is an
established, scalable method for applying coatings to conductive substrates via
an applied electric field. When paired with colloidal semiconductor
nanocrystals, EPD is an environmentally and economically advantageous method
for large-scale manufacturing of photovoltaic cells due to its reduced waste
and higher throughput compared to alternative methods. However, EPD typically
uses high voltages in order to increase the electrostatic force and rate of
deposition. This is problematic for semiconductor nanocrystals as high voltages
may damage the depositing nanocrystals. Our research focuses on engineering the
surface properties of copper zinc tin sulfide nanocrystals and the EPD bath
composition in order to lower the process voltage, thus preserving the
semiconductor. A new reactor was designed and implemented in order to directly
observe the deposition process in situ. An automated amperometry apparatus was
made to quantitatively measure the current that goes toward depositing the
films during EPD. Theoretically, this current directly corresponds to the
number of nanocrystals deposited. Therefore, by integrating the recorded
current and comparing it against film thickness, we quantified the efficiency
and the presence of additional electrochemical side-reactions that accompany
the EPD process.
