Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

The overall goal of this work is to fabricate a photoanode for dye-sensitized solar cells with improved performance using electrospinning. Nanomaterials are great. They show chemical and physical properties that you cannot find in the corresponding bulk materials.

However, if you try to make a device using nanomaterials, this become, can become quite difficult. In this video, we show how to fabricate one-dimensional inorganic nanofibres, and using them for a solar cell device. The directionality in the nanofibres causes the devices to have a much better performance compared with devices that just use nanocrystalline materials.

To make the precursor solution, place 10 milliliters of absolute ethanol, one milliliter of glacial acetic acid, five grams of Titanium(II)oxide, and one gram of PVP into a sample vial. Mix the solution until it has become homogeneous and no bubbles can be observed. In order to obtain a one-dimensional nanoarchitecture, we're going to use electrospinning.

A simple yet rather clever technique which allows us to obtain nanofibres with several micrometers in length and only few hundred nanometers in diameter. To prepare the needle used for the electrospinning process, cut the tip of a 21 gauge needle and sand it down using moderate grade sandpaper until the tip is completely flat. Load the precursor solution into the syringe and place it on the syringe pump.

Wrap the collector plate with aluminum foil and place the protective shield around the setup. The distance between the needle and the collector plate should be 20 centimeters. Connect the collector to the ground and the needle to the power source.

Set the flow rate of the syringe pump to one milliliter per hour, and begin pumping. As soon as some solution appears on the tip of the needle, turn on the high voltage source and set it to 15 kilovolts. At this point, fibers are going to collect on the plate.

This can be left running for as long as necessary to achieve the desired thickness of the fiber mat. After the spinning is completed, turn off the high voltage source and remove the foil from the collector plate. Letting the fibers rest overnight makes it easier to peel them off the collector plate.

Place the peeled off fibers in a crucible and place them in a furnace with a temperature ramp of five degrees per minute, up to 500 degrees for two hours to remove the PVP and produce pure TiO2 nanofibres. Fabrication of the photoanode requires that the position of a light-scattering layer consisting of titanium dioxide nanofibres on top of a blocking layer made of commercially available titanium dioxide nanoparticles. This is essential for preventing charge accumulation with a substrate.

Start by adding 500 milligrams of titanium dioxide nanoparticles to 20 mils of ethanol in a round-bottom flask. In a separate flask, mix 500 milligrams of the electrospun titanium dioxide nanofibres with another 20 mils of ethanol. Sonicate the solutions for two hours using a bath sonicator.

Once uniform mixtures are obtained, add 2 mils of terpineol to each flask, and sonicate for another 15 minutes. Finally, evaporate the solvent using a rotary evaporator to obtain the slurries. Using a diamond glass cutter, cut an FTO slide into a two by two centimeter square.

Place adhesive tape on the glass slide, leaving a 0.4 square centimeter area, exposing the center. Deposit a few drops of the titanium dioxide nanoparticle slurry on the center of the glass slide. Use a razor blade to spread the slurry evenly on the exposed area.

Once a uniform coating is achieved, carefully remove the adhesive tape. Photoanodes are then placed in a furnace and centered at 500 degrees for two hours. Repeat the process on the same glass slide, this time using the nanofibre slurry to deposit the light scattering layer.

The composite photoanode is again centered at 500 degrees for two hours. To characterize our nanofibres, we are going to use SEM and XRD, and then to test the performance of our nanofibres, we are going to implement them in a dye-sensitized solar cell. To prepare the sample for scanning electron microscoping, attach a strip of adhesive carbon tape on the microscope stub.

And then carefully place a small quantity of nanofibres on the tape. Mount the stub onto a sample holder and lower it into the exchange chamber of the instrument. Set up the instrument conditions and parameters accordingly.

Collect images of the sample, making sure that they display the overall morphology of the material. The SEM images show that the fibers are porous in structure and have a high aspect ratio. To prepare the material for X-ray diffraction characterization, gently grind some nanofibres into a fine powder and spread them evenly on an XRD stage.

Load the sample into the diffractometer. Set up the acquisition parameters and start collecting the data. The diffractogram shows a series of peaks corresponding to the anatase phase of titanium dioxide.

To prepare the solar cell, first treat the TiO2 photoanodes with an aqueous solution of TiCl4 at 75 degrees C for 45 minutes. After treatment, wash the photoanodes with the ionized water. Dry them, and insensitize them in a solution of Ruthenizer N719 and absolute ethanol for 24 hours under dark conditions.

The sensitized photoanodes will wash with ethanol to remove excess dye molecules from the TiO2 photoanode surface. Sealing film is used as a thermoplastic gasket between the counter electrode and the photoanodes. Counter electrodes of platinum-coated FTO are used for all solar cells.

The assembled solar cells are heated to 100 degrees C for 15 minutes to seal the gasket. A redox mediator is added to the internal space of the solar cells by vacuum filling. J-V curves are acquired using a Keithley 2400 Digital SourceMeter under a 100 milowatt per centimeter square illumination from a xenon arc source passed through an AM 1.5 G filter.

The illumination plane for the light source is calibrated with a monocrystalline silicon reference cell. In this video, we have shown you how to fabricate a dye-sensitized solar cells using inorganic nanofibres. On top of this application, there are many other possibilities.

For example, batteries, transparent electrodes, active filters, and others. If you want to know more details, please have a look at our publications. I hope you enjoyed and learned from this video, and please contact us if you've got question or want to give any feedback.