A Benchtop Guide to Quantum Dot Solar Cell Fabrication

A Benchtop Guide to Quantum Dot Solar Cell Fabrication


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.

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