Hi, I'm Joe Manser, a graduate student in the Camont Lab at the University of Notre
Dame. Hi, I'm a postdoc at the University of Notre Dame. Today we are going to show
you step by step how to assemble a liquid junction quantum dot solar cell. The
first step in our cell assembly is to cut the optically transparent electrode to the
appropriate size. Next, we test our electrode for conductivity. The backside is insulating,
while the working side is conductive as indicated by the multimeter. We then wash our electrode
in a surfactin solution using an ultrasonicater. This is followed by rinsing with deionized
water and ethanol. The electrode is then submerged in an ethanol bath and subjected to a second
round of sonication. The scanning electron micrograph shows the various layers of our
working electrode. The Compact TIO2 is the think black layer just on the surface of the
electrode and is shown between the two orange arrows. This layer prevents short circuiting
in our liquid junction solar cell. To deposit this layer, we use an aqueous solution of
titanium tetrachloride, poured over the surface of the electrode. Then, treat at 70 degrees celsius
to form titanium dioxide. After heating, the electrode is rinsed with deionized water and
ethanol. Next we apply the active TIO2 Layer to our working electrode. This mesapore support
provides a framework for depositing our quantum dot light absorbers. Active TIO2 areas are
marked out using a tape template and cast by a doctor blade technique. Using this simple
technique, we can simultaneously prepare multiple active areas. The electrode is then heated
to 80 degrees celsius, followed by a kneeling at 500 degrees celsius. The final tier in
our photo anode is the scattering TIO2 Layer. This layer provides backscatter photons for
our quantum dot light absorbers in our active area. Again we use the doctor blade technique
to cast this film, marking a spot slightly bigger than our active area. The electrode
is again heated to 80 degrees celsius, followed by a treatment at 500 degrees celsius. Just
before depositing our solar sensitizer, our photo anode is treated a second time with
titanium tetrachloride, to increase the surface area and improve quantum dot deposition. Individual
solar cells are then cut from the optically transparent electrode. Electrophloretic deposition
allows us to deposit pre-synthesized colloidal quantum dots onto our photo anode. After submerging
the electrode into the quantum dot solution, we use high voltage to drive the particles
into the TIO2 network. Looking through the front side of our solar cell, we can see the
brightly colored active area. This is because the majority of particles have been driven through
the scattering layer and now reside in the mesoporous TIO2 support. Using EPD, we
can deposit various sized quantum dots to tune the visible absorption of our solar cell,
making what we call rainbow solar cells. To perform SILAR, we submerged our TIO2 film
into a cation solution followed by rinsing and submersion into an anion solution. Using
custom built instruments and software developed in our lab, we have automated this process
to increase our solar cell throughput. During the first cycle of SILAR, we can see the white
unsensitized electrodes, and after five cycles we can see the characteristic yellow color
of cadmium sulfide. After sensitizing our TIO2 films, we deposit a zinc sulfide blocking
layer using SILAR. This layer prevents back SILAR transfer from our sensitizer and TIO2
particles into our liquid electrolyte. For our counter electrodes, we use a copper RGO
composite material cast on a fluorine dote tin oxide electrode. The counter electrodes
are then placed in a vacuum oven at 110 degrees celsius overnight. A para-film spacer is melted
on the surface of the electrode, and the copper RGO composite material is allowed to react
with the polysulfide electrolyte to form copper sulfide RGO. First, several drops of electrolyte
are placed on the counter electrode. Then, the cell is sandwiched and held together using
binder clips. The final step is to solder indium contex on the working and counter electrodes.
After connecting the cell to the potentials stat we are ready to test it using our solar
simulator. Using software, we can monitor the photocurrent response of our solar cell.
Upon illumination, the quantum dots absorb light and generate charged carriers that then
can be used to do useful work. In summary, we have created a simple yet effective device
for harnessing solar energy using only straightforward benchtop techniques. Such transformative
technologies have the potential to play key roles in meeting our future energy demand.