Name: electrospinning of photocatalytic electrodes for dye-sensitized solar cells
Uploaded: 2017-06-28T13:00:00.000+00:00
Duration: 9 min 30 s
Description: Watch this Scientific Journal Video about Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells at JoVE.com

The authors have no acknowledgements.

1. Precursor Solution Preparation
NOTE: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in this procedure are harmful and/or toxic to humans. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use the appropriate safety measures and personal protective equipment.
<ol>
	<li>Place 5 g of titanium(IV) n-butoxide, 1 g of polyvinylpyrrolidone (PVP), 1 mL of glacial acetic acid, and 10 mL of absolute ethanol into a sample vial.</li>
	<li>Use a magnetic stirring plate to mix the solution until it has become homogeneous and no bubbles can be observed.</li>
</ol>
2. Electrospinning and Calcination of the Nanofibers
<ol>
	<li>Prepare the needle used for the electrospinning process by cutting off the tip of a 21 G needle and sanding it down using moderate-grade sandpaper until the tip is completely flat.</li>
	<li>Mount the needle on a disposable 10 mL syringe.</li>
	<li>Load some of the precursor solution into the syringe and place it on the syringe pump.</li>
	<li>Wrap the collector plate in aluminum foil and place it directly in front of the needle tip. 
	NOTE: The distance from the needle to the plate should be 20 cm.</li>
	<li>Connect the collector plate to the ground and the needle to the high-voltage power source.</li>
	<li>Place the protective shield around the setup.</li>
	<li>Set the flow rate on the syringe pump to 1 mL/h and begin pumping.</li>
	<li>As soon as some solution appears at the tip of the needle, turn on the high-voltage source and set it to 15 kV. 
	NOTE: At this point, fibers are going to collect on the plate. The setup be left running for as long as necessary to achieve the desired thickness of the fiber mat.</li>
	<li>After the spinning is completed, turn off the high-voltage source and syringe pump. Remove the foil from the collector plate.</li>
	<li>Let the fibers rest overnight and then peel them off the aluminum foil.</li>
	<li>Place the peeled-off fibers in a crucible and place that into a muffle furnace.</li>
	<li>Calcinate the fibers by setting up a temperature ramp of 5&#176;/min up to 500 &#176;C and holding for 2 h to remove the PVP and to produce pure TiO2 nanofibers.</li>
	<li>Once the calcination process is completed, leave the furnace closed until the temperature reaches below 80 &#176;C to avoid any thermal shock, which may damage the fibers.</li>
</ol>
3. Electrode Fabrication
<ol>
	<li>Preparation of the slurries
	<ol>
		<li>Add 500 mg of titanium dioxide paste to 20 mL of ethanol in a round-bottomed flask.</li>
		<li>In a separate flask, mix 500 mg of the electrospun TiO2-NFs with another 20 mL of ethanol.</li>
		<li>Sonicate the solutions for 2 h using a bath sonicator.</li>
		<li>Once uniform mixtures are obtained, add 2 mL of terpineol to each flask and sonicate for another 15 min.</li>
		<li>Evaporate the solvent from both flasks using a rotary evaporator to obtain the slurries.</li>
	</ol>
	</li>
	<li>Doctor blading and sintering
	<ol>
		<li>Using a diamond glass cutter, cut an FTO-conductive glass slide into a 2 cm x 2 cm square.</li>
		<li>Secure the FTO slide to the work area by placing adhesive tape on the glass slide, leaving a 0.4-cm2 area exposed in the center. To avoid an irregular coating, place the tape on two parallel sides first and then on the other two.</li>
		<li>Deposit a few drops of the TiO2-NP slurry on the exposed center of the slide.</li>
		<li>Use a razor blade to spread the slurry evenly over the exposed area.</li>
		<li>Once a uniform coating is achieved, carefully remove the adhesive tape.</li>
		<li>Place the coated slide in a furnace and sinter at 500 &#176;C for 2 h.</li>
		<li>Repeat steps 3.2.2-3.2.6 on the same FTO slide, this time using the TiO2-NF slurry instead of the nanoparticles, to obtain the photoanode.</li>
	</ol>
	</li>
</ol>
4. NF Characterization
<ol>
	<li>SEM characterization
	<ol>
		<li>Prepare the sample for SEM by attaching a strip of adhesive carbon tape to a microscope stub. Carefully place a small quantity of nanofibers on the tape.</li>
		<li>Mount the stub onto a sample holder and load it into the exchange chamber of the instrument.</li>
		<li>Set up the instrument conditions and parameters: set the accelerating voltage to 20 kV and the working distance to 10 mm.</li>
		<li>Collect images of the sample, making sure that they display the overall morphology of the material.</li>
	</ol>
	</li>
	<li>XRD characterization
	<ol>
		<li>Gently grind some nanofibers into a fine powder and spread them evenly on an XRD stage.</li>
		<li>Load the sample into the diffractometer.</li>
		<li>Set up the acquisition parameters: use a start angle of 10&#176;, an end angle of 80&#176;, and a step size of 0.015&#176;.</li>
		<li>Start the acquisition of the XRD data.</li>
	</ol>
	</li>
</ol>
5. Solar-cell Fabrication
<ol>
	<li>Treat the photoanode with an aqueous solution of TiCl4 at 75 &#176;C for 45 min. After treatment, wash it with deionized water and dry it.</li>
	<li>Sensitize the photoanode by submerging it in a 0.5-mM solution of ruthenium dye N719 in absolute ethanol for 24 h under dark conditions.</li>
	<li>Place a sheet of sealing film on top of the sensitized photoanode to serve as a thermoplastic gasket between the photoanode and the counter-electrode.</li>
	<li>Place a Pt-coated FTO counter-electrode with a pre-drilled hole in the center, on top of the sealing film, such that both sides face each other.</li>
	<li>Heat the assembled cell to 100 &#176;C for 15 min to seal the gasket.</li>
	<li>Deposit a few drops of a redox mediator, consisting of a solution of 1-propyl-3-methylimidazolium iodide (0.8 M), iodine (0.1 M), and benzimidazole (0.3 M) in 3-methoxypropionitrile, on top of the pre-drilled hole of the counter-electrode.</li>
	<li>Place the cell in a vacuum desiccator to let the redox mediator fill the internal space of the assembled cell.</li>
</ol>
6. J-V Curve Characterization
<ol>
	<li>Acquire the J-V curves using a digital source meter under 100 mW/cm2 illumination from a xenon-arc source passed through an AM1.5G filter.</li>
</ol>

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J., Laurencin, C. T., Caterson, E. J., Tuan, R. S., Ko, F. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrospun+nanofibrous+structure:+A+novel+scaffold+for+tissue+engineering.">Electrospun nanofibrous structure: A novel scaffold for tissue engineering.</a> J Biomed Mat Res. 60 (4), 613-621 (2002).</li><li>Jia, H., Zhu, G., Vugrinovich, B., Kataphinan, W., Reneker, D. H., Wang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enzyme-Carrying+Polymeric+Nanofibers+Prepared+via+Electrospinning+for+Use+as+Unique+Biocatalysts.">Enzyme-Carrying Polymeric Nanofibers Prepared via Electrospinning for Use as Unique Biocatalysts.</a> Biotechnol Prog. 18 (5), 1027-1032 (2002).</li><li>Mai, L., Xu, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrospun+Ultralong+Hierarchical+Vanadium+Oxide+Nanowires+with+High+Performance+for+Lithium+Ion+Batteries.">Electrospun Ultralong Hierarchical Vanadium Oxide Nanowires with High Performance for Lithium Ion Batteries.</a> Nano Letters. 10 (11), 4750-4755 (2010).</li><li>Cai, J., Niu, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Performance+Supercapacitor+Electrode+Materials+from+Cellulose-Derived+Carbon+Nanofibers.">High-Performance Supercapacitor Electrode Materials from Cellulose-Derived Carbon Nanofibers.</a> ACS Appl Mat Interfaces. 7 (27), 14946-14953 (2015).</li><li>Joshi, P., Zhang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Composite+of+TiO2+nanofibers+and+nanoparticles+for+dye-sensitized+solar+cells+with+significantly+improved+efficiency.">Composite of TiO2 nanofibers and nanoparticles for dye-sensitized solar cells with significantly improved efficiency.</a> Energ Environ Sci. 3 (10), 1507-1510 (2010).</li><li>Macdonald, T. J., Tune, D. D., Dewi, M. R., Gibson, C. T., Shapter, J. G., Nann, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+TiO2+Nanofiber-Carbon+Nanotube-Composite+Photoanode+for+Improved+Efficiency+in+Dye-Sensitized+Solar+Cells.">A TiO2 Nanofiber-Carbon Nanotube-Composite Photoanode for Improved Efficiency in Dye-Sensitized Solar Cells.</a> ChemSusChem. 8 (20), 3396-3400 (2015).</li><li>Teo, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electrospinning parameters and fiber control. , (2015).</li></ol>

The authors have nothing to disclose.

The methods presented in this work describe the fabrication of efficient nanofibrous photoanodes for photocatalytic devices such as DSSCs. Electrospinning is a very versatile technique for the fabrication of nanofibers, but a certain level of skill and knowledge is required to obtain materials with optimal morphologies. One of the most critical aspects to obtaining good nanofibers is the preparation of the precursor solution: there are some key factors, such as the concentration of the carrier polymer and the choice of titanium precursor, that can have a critical impact on the final structure of the material. A low concentration of carrier polymer will lead to the formation of beads or the total absence of a nanofibrous structure. On the other hand, a too-high concentration will excessively increase the viscosity of the solution and lead to an increase of the diameter of the nanofiber, with a consequent loss of surface area and charge mobility. The inorganic precursor needs to be highly soluble and should not react or decompose in the presence of the other components of the solution. It should also calcinate easily into the final material, without leaving any undesired sub-products.
The instrumental parameters (i.e., voltage, tip-to-collector distance, and needle diameter) also have an important effect on the nanofiber morphology. Although a general trend can be observed when changing these conditions using a specific precursor solution, this does not necessarily apply to other solutions, as they may be affected differently by modifications of the electric field and other instrumental conditions17.
Thanks to the versatility of this technique, a wide range of nanomaterials can be fabricated and used in several different applications, such as energy conversion and storage, catalysis, filtration, composite materials, and superhydrophobic surfaces. Furthermore, this method shows significant potential for upscaling, which is a key factor for its use in commercial applications.
The calcination process needs to be performed at a high enough temperature to completely remove the carrier polymer and to promote the crystallization of TiO2, but without disrupting the nanostructure of the material. The calcination temperature also needs to be reached at a relatively slow heating rate to avoid any thermal shock, which might damage the fibers. This also applies to the cooling process: after the heat treatment is finished, the furnace must remain closed until the temperature has reached a safe temperature (&#60;80 &#176;C).
Doctor blading is a simple and quick method that allows one to easily obtain thin-film substrates on flat surfaces. The key factor to obtaining a smooth and uniformly coated surface is the slurry viscosity: if too much dispersant is added to the mixture, the coating will present pores and have an uneven thickness; if too little dispersant is added, the resulting film will likely have cracks on its surface.
Once mastered, this technique can easily be used for any application that requires thin-film deposition for device fabrication.

Dye-sensitized solar cells (DSSCs) are an interesting alternative to silicon-based solar cells1 thanks to their low cost, relatively simple manufacturing process, and ease of large-scale production. Another benefit is their potential to be incorporated into flexible substrates, a distinct advantage over silicon-based solar cells2. A typical DSSC utilizes: (1) a nanoparticulate TiO2 photoanode, sensitized with a dye, as a light-harvesting layer; (2) a Pt-coated FTO, used as a counter electrode; and (3) an electrolyte containing a redox couple, such as I-/I3-, placed between the two electrodes, working as a &#34;hole-conducting medium.&#34;
Although DSSCs have surpassed efficiencies of 15%3, the performance of nanoparticle-based photoanodes is still still hindered by a number of limitations, including slow electron mobility4, poor absorption of low-energy photons5, and charge recombination6. The electron collection efficiency strongly depends upon the rate of electron transport through the TiO2 nanoparticle layer. If the charge diffusion is slow, the probability of recombination with I3- in the electrolyte solution increases, resulting in a loss of efficiency.
It has been shown that replacing nanoparticulate TiO2 with one-dimensional (1D) TiO2 nanoarchitectures can improve charge transport by reducing the scattering of free electrons from the grain boundaries of the interconnected TiO2 nanoparticles7. As 1D nanostructures provide a more direct pathway for charge collection, we can expect that electron transport in nanofibers (NFs) would be significantly faster than in nanoparticles8,9.
Electrospinning is one of the most commonly used methods for the fabrication of fibrous materials with sub-micron diameters10. This technique involves the use of high voltage to induce the ejection of a polymer solution jet through a spinneret. Due to bending instability, this jet is subsequently stretched many times to form continuous nanofibers. In recent years, this technique has been extensively used to fabricate polymeric and inorganic materials, which have been used for numerous and diverse applications, such as tissue engineering11, catalysis12, and as electrode materials for lithium ion batteries13 and supercapacitors14.
The use of electrospun TiO2-NFs as the scattering layer in the photoanode can increase the performance of DSSCs. However, photoanodes with nanofibrous architectures tend to have poor dye absorption due to surface-area limitations. One of the possible solutions to overcome this is to mix NFs and nanoparticles. This has been shown to result in additional scattering layers, improving light absorption and overall efficiency15.
The protocol presented in this video provides a facile method to synthesize ultralong TiO2 nanofibers through a combination of electrospinning and sol-gel techniques, followed by a calcination process. The protocol then illustrates the use of the TiO2-NFs in combination with nanoparticulate TiO2 for the fabrication of a dual-layer photoanode with enhanced light-scattering capability using doctor blading techniques, as well as the subsequent assembly of a DSSC using such a photoanode.

<table><tbody><tr><td>titanium(IV) n-butoxide</td><td>Sigma-Aldrich</td><td>244112</td><td></td></tr><tr><td>Polyvinylpyrrolidone</td><td>Sigma-Aldrich</td><td>437190</td><td></td></tr><tr><td>glacial acetic acid</td><td>Sigma-Aldrich</td><td>A6283</td><td></td></tr><tr><td>Ethanol, absolute</td><td>Fisher Scientific</td><td>E/0650DF/17</td><td></td></tr><tr><td>20 mL Sample vials</td><td>(any)</td><td></td><td>(or larger volume)</td></tr><tr><td>disposable 21G needle</td><td>(any)</td><td></td><td></td></tr><tr><td>P150 grit sandpaper</td><td>(any)</td><td></td><td></td></tr><tr><td>disposable 10mL syringe</td><td>(any)</td><td></td><td>(or larger volume)</td></tr><tr><td>magnetic stirrer + stirring bar</td><td>(any)</td><td></td><td></td></tr><tr><td>PHD 2000 syringe pump</td><td>Harvard Apparatus</td><td>71-2002</td><td>(or any other syringe pump capable of outputting a 1mL/hr flow</td></tr><tr><td>Aluminium foil</td><td>(any)</td><td></td><td></td></tr><tr><td>Stainless steel collector plate</td><td>(custom built)</td><td></td><td></td></tr><tr><td>High Voltage Power Source</td><td>Gamma High Voltage Research, Inc</td><td>ES30P-10W</td><td>(or any other power supply capable of outputting +15 kV</td></tr><tr><td>Polycarbonate protective shield</td><td>(custom built)</td><td></td><td></td></tr><tr><td>Ceramic crucible</td><td>(any)</td><td></td><td></td></tr><tr><td>Muffle furnace</td><td>(any)</td><td></td><td></td></tr><tr><td>Titanium dioxide, nanopowder</td><td>Sigma-Aldrich</td><td>718467</td><td></td></tr><tr><td>50 mL 1-neck round bottom flasks</td><td>(any)</td><td></td><td></td></tr><tr><td>bath sonicator</td><td>(any)</td><td></td><td></td></tr><tr><td>Terpineol</td><td>Sigma-Aldrich</td><td></td><td></td></tr><tr><td>Rotary evaporator</td><td>(any)</td><td></td><td></td></tr><tr><td>FTO glass</td><td>Solaronix</td><td>TCO30-10/LI</td><td></td></tr><tr><td>Adhesive tape</td><td>(any)</td><td></td><td></td></tr><tr><td>razor blade</td><td>(any)</td><td></td><td></td></tr><tr><td>SEM</td><td>JEOL</td><td>6500F</td><td></td></tr><tr><td>XRD</td><td>PANalytical&amp;nbsp;</td><td>X&#039;pert Pro</td><td></td></tr><tr><td>Titanium Tetrachloride</td><td>Sigma-Aldrich</td><td>89545</td><td></td></tr><tr><td>Ruthenizer&amp;nbsp; 535-bisTBA</td><td>Solaronix</td><td>N719</td><td></td></tr><tr><td>sealing film</td><td>Dyesol</td><td>Meltonix 1170-25</td><td></td></tr><tr><td>Pt-coated FTO</td><td>Solaronix</td><td>TCO30-10/LI</td><td></td></tr><tr><td>1-propyl-3-methylimidazolium iodide</td><td>Sigma-Aldrich</td><td>49637</td><td></td></tr><tr><td>Iodine</td><td>Sigma-Aldrich</td><td>207772</td><td></td></tr><tr><td>benzimidazole</td><td>Sigma-Aldrich</td><td>194123</td><td></td></tr><tr><td>3-Methoxypropionitrile</td><td>Sigma-Aldrich</td><td>65290</td><td></td></tr><tr><td>Digital source meter</td><td>Keithley</td><td>2400</td><td></td></tr><tr><td>Solar Simulator</td><td>Abet technologies</td><td>10500</td><td></td></tr></tbody></table>

electrospinning of photocatalytic electrodes for dye-sensitized solar cells

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of electrospun titanium dioxide nanofibers (TiO2-NFs) on top of a blocking layer made of commercially available titanium dioxide nanoparticles (TiO2-NPs). This is achieved by first electrospinning a solution of titanium (IV) butoxide, polyvinylpyrrolidone (PVP), and glacial acetic acid in ethanol to obtain composite PVP/TiO2 nanofibers. These are then calcined at 500 &#176;C to remove the PVP and to obtain pure anatase-phase titania nanofibers. This material is characterized using scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The photoanode is prepared by first creating a blocking layer through the deposition of a TiO2-NPs/terpineol slurry on a fluorine-doped tin oxide (FTO) glass slide using doctor blading techniques. A subsequent thermal treatment is performed at 500 &#176;C. Then, the light-scattering layer is formed by depositing a TiO2-NFs/terpineol slurry on the same slide, using the same technique, and calcinating again at 500 &#176;C. The performance of the photoanode is tested by fabricating a dye-sensitized solar cell and measuring its efficiency through J-V curves under a range of incident light densities, from 0.25-1 Sun.

The TiO2 nanofibers were characterized using SEM, X-ray photoelectron spectroscopy (XPS), and XRD. The nanostructure of the photoanode was characterized using SEM. The performance of the assembled DSSC was tested using a solar simulator and a source measure unit.
The SEM image in Figure 1A shows that the nanofibers synthesized using this protocol have a porous structure and a high aspect ratio. They are up to several micrometers in length and only a few hundred nanometers in diameter. The cross-section in Figure 1B shows three layers: the top layer is the fibrous scattering layer of the TiO2-NF, the second layer is the blocking layer of TiO2-NP paste, and the bottom layer is the FTO substrate. Both layers are approximately 7 &#181;m, resulting in a total film thickness of approximately 14 &#181;m.
The diffractogram in Figure 2 shows a series of peaks corresponding to the anatase phase of titanium dioxide. The sharp peaks in the spectra indicate that the nanofibers are highly crystalline, which is a favorable feature for this type of application. Figure 3 shows the Ti 2p XPS spectrum for TiO2 NF and NP photoelectrodes. TiO2 was verified by the Ti 2p peaks present at binding energies of 465 eV (Ti2p(1/2)) and 459 eV (Ti2p(3/2)).
The J-V curve in Figure 4 shows that under 1-Sun illumination (solid line), The TiO2-NF DSSC achieved a short-circuit current density (JSC) of 8.30 mA/cm2, an open circuit voltage (VOC) of 0.63 V, a fill factor (FF) of 56%, and a power conversion efficiency (PCE) of 2.90%. To investigate further, the dependence of the cell performance on illumination intensity (from 0.25-1 Sun) was measured. The characteristic values are plotted in Figure 5. The JSC increases linearly up to 0.75 Sun (Figure 5A); the slope then increases considerably between 0.75 and 1 Sun. The VOC exhibits a linear increase across the measured range (Figure 5B). In Figure 5C, the FF is stable between 0.25 and 0.75 Sun, but it rapidly decreases up to 1 Sun; this may be due to an increase in charge recombination. Figure 5D shows that, at an incident light intensity of 25 mW/cm2, the DSSC achieves a PCE of 3.7%, indicating higher performance under lower illumination intensities. As a comparison, Figure 6 shows TiO2 NP DSSCs, which achieved a JSC of 6.53 mA/cm2, a VOC of 0.63 V, an FF of 57%, and a PCE of 2.35%.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55309/55309fig1.jpg" /> 
Figure 1: Images of the electrospun TiO2-NFs. (A) High-resolution image of the electrospun TiO2-NFs. (B) Cross-section SEM; the top layer is the light-scattering nanofiber layer, and the bottom layer is the blocking TiO2-NP layer. Figures adapted and reprinted with permission from Macdonald et al.16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55309/55309fig2.jpg" /> 
Figure 2: XRD spectrum of the electrospun TiO2-NFs. The inset shows the selective-area electron diffraction (SAED) pattern indicative of TiO2 in the anatase phase; reprinted with permission from Macdonald et al.16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55309/55309fig3.jpg" /> 
Figure 3: Ti 2p XPS spectrum for TiO2 NF and NP photoelectrodes. The solid red curve shows the spectrum for nanofibers, and the solid black curve shows the spectrum for nanoparticles. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/55309/55309fig4.jpg" /> 
Figure 4: J-V curve under 1-Sun illumination of the DSSC made with TiO2 NFs. (A) The dark current is represented by the dotted line. Reprinted with permission from Macdonald et al.16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/55309/55309fig5.jpg" /> 
Figure 5: Device characterization parameters. (A) JSC, (B) VOC, (C) FF, and (D) PCE as a function of light intensity, from 25 mW/cm2 (0.25 Sun) to 100 mW/cm2 (1 Sun). Reprinted with permission from Macdonald et al.16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/55309/55309fig6.jpg" /> 
Figure 6: J-V curve under 1-Sun illumination of the DSSC made with TiO2-NPs. The curve shows TiO2 NP DSSCs, which achieved a JSC of 6.53 mA/cm2, a VOC of 0.63 V, an FF of 57%, and a PCE of 2.35%. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55309/55309fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells at JoVE.com

Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

The overall goal of this project was to use electrospinning to fabricate a photoanode with improved performance for dye-sensitized solar cells.

This work demonstrates a protocol to fabricate a fiber-based photoanode for dye-sensitized solar cells, consisting of a light-scattering layer made of ...

electrospinning-photocatalytic-electrodes-for-dye-sensitized-solar

Nanyang Technological University

Research

JoVE Journal

Engineering

9.6K Views.  Victoria University of Wellington.  Het algemene doel van dit project was om elektrospinning te gebruiken om een ​​fotoanode te vervaardigen met verbeterde prestaties voor kleurstofgevoeligte zonnecellen. 

Video: Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

Electrospinning Fundamentals: Optimizing Solution and Apparatus Parameters

Electrospun nanofiber scaffolds have been shown to accelerate the maturation, improve the growth, and direct the migration of cells in vitro. Electrospinning is a process in which a charged polymer jet is collected on a grounded collector; a rapidly rotating collector results in aligned nanofibers while stationary collectors result in randomly oriented fiber mats. The polymer jet is formed when an applied electrostatic charge overcomes the surface tension of the solution. There is a minimum concentration for a given polymer, termed the critical entanglement concentration, below which a stable jet cannot be achieved and no nanofibers will form - although nanoparticles may be achieved (electrospray). A stable jet has two domains, a streaming segment and a whipping segment. While the whipping jet is usually invisible to the naked eye, the streaming segment is often visible under appropriate lighting conditions. Observing the length, thickness, consistency and movement of the stream is useful to predict the alignment and morphology of the nanofibers being formed. A short, non-uniform, inconsistent, and/or oscillating stream is indicative of a variety of problems, including poor fiber alignment, beading, splattering, and curlicue or wavy patterns. The stream can be optimized by adjusting the composition of the solution and the configuration of the electrospinning apparatus, thus optimizing the alignment and morphology of the fibers being produced. In this protocol, we present a procedure for setting up a basic electrospinning apparatus, empirically approximating the critical entanglement concentration of a polymer solution and optimizing the electrospinning process. In addition, we discuss some common problems and troubleshooting techniques.

Electrospinning techniques can create a variety of nanofibrous scaffolds for tissue engineering or other applications. We describe here a procedure to optimize the parameters of the electrospinning solution and apparatus to obtain fibers with the desired morphology and alignment. Common problems and troubleshooting techniques are also presented.

Electrospun nanofiber scaffolds have been shown to accelerate the maturation, improve the growth, and direct the migration of cells in vitro. ...

Bioengineering

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents and hence higher efficiencies. Photon up-conversion by way of triplet-triplet annihilation (TTA-UC) is an attractive technique for using these otherwise wasted low energy photons to produce photocurrent, while not interfering with the photoanodic performance in a deleterious manner. Further to this, TTA-UC has a number of features, distinct from other reported photon up-conversion technologies, which renders it particularly suitable for coupling with DSC technology. In this work, a proven high performance TTA-UC system, comprising a palladium porphyrin sensitizer and rubrene emitter, is combined with a high performance DSC (utilizing the organic dye D149) in an integrated device. The device shows an enhanced response to sub-bandgap light over the absorption range of the TTA-UC sub-unit resulting in the highest figure of merit for up-conversion assisted DSC performance to date.

An integrated device, incorporating a dye-sensitized solar cell and triplet-triplet annihilation up-conversion unit was produced, affording enhanced light harvesting, from a wider section of the solar spectrum. Under modest irradiation levels a significantly enhanced response to low energy photons was demonstrated, yielding a record figure of merit for dye-sensitized solar cells.

The poor response of dye-sensitized solar cells (DSCs) to red and infrared light is a significant impediment to the realization of higher photocurrents ...

Postproduction Processing of Electrospun Fibres for Tissue Engineering

Electrospinning is a commonly used and versatile method to produce scaffolds (often biodegradable) for 3D tissue engineering.1, 2, 3 Many tissues in vivo undergo biaxial distension to varying extents such as skin, bladder, pelvic floor and even the hard palate as children grow. In producing scaffolds for these purposes there is a need to develop scaffolds of appropriate biomechanical properties (whether achieved without or with cells) and which are sterile for clinical use. The focus of this paper is not how to establish basic electrospinning parameters (as there is extensive literature on electrospinning) but on how to modify spun scaffolds post production to make them fit for tissue engineering purposes - here thickness, mechanical properties and sterilisation (required for clinical use) are considered and we also describe how cells can be cultured on scaffolds and subjected to biaxial strain to condition them for specific applications.
Electrospinning tends to produce thin sheets; as the electrospinning collector becomes coated with insulating fibres it becomes a poor conductor such that fibres no longer deposit on it. Hence we describe approaches to produce thicker structures by heat or vapour annealing increasing the strength of scaffolds but not necessarily the elasticity. Sequential spinning of scaffolds of different polymers to achieve complex scaffolds is also described. Sterilisation methodologies can adversely affect strength and elasticity of scaffolds. We compare three methods for their effects on the biomechanical properties on electrospun scaffolds of poly lactic-co-glycolic acid (PLGA).
Imaging of cells on scaffolds and assessment of production of extracellular matrix (ECM) proteins by cells on scaffolds is described. Culturing cells on scaffolds in vitro can improve scaffold strength and elasticity but the tissue engineering literature shows that cells often fail to produce appropriate ECM when cultured under static conditions. There are few commercial systems available that allow one to culture cells on scaffolds under dynamic conditioning regimes - one example is the Bose Electroforce 3100 which can be used to exert a conditioning programme on cells in scaffolds held using mechanical grips within a media filled chamber.4 An approach to a budget cell culture bioreactor for controlled distortion in 2 dimensions is described. We show that cells can be induced to produce elastin under these conditions. Finally assessment of the biomechanical properties of processed scaffolds cultured with or without cells is described.

Electrospun scaffolds can be processed post production for tissue engineering applications. Here we describe methods for spinning complex scaffolds (by consecutive spinning), for making thicker scaffolds (by multi-layering using heat or vapour annealing), for achieving sterility (aseptic production or sterilisation post production) and for achieving appropriate biomechanical properties.

Electrospinning is a commonly used and versatile method to produce  scaffolds (often biodegradable) for 3D tissue engineering.1, 2, 3 Many tissues in vivo ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Digital Printing of Titanium Dioxide for Dye Sensitized Solar Cells

Silicon solar cell manufacturing is an expensive and high energy consuming process. In contrast, dye sensitized solar cell production is less environmentally damaging with lower processing temperatures presenting a viable and low cost alternative to conventional production. This paper further enhances these environmental credentials by evaluating the digital printing and therefore additive production route for these cells. This is achieved here by investigating the formation and performance of a metal oxide photoelectrode using nanoparticle sized titanium dioxide. An ink-jettable material was formulated, characterized and printed with a piezoelectric inkjet head to produce a 2.6 &#181;m thick layer. The resultant printed layer was fabricated into a functioning cell with an active area of 0.25 cm2 and a power conversion efficiency of 3.5%. The binder-free formulation resulted in a reduced processing temperature of 250 &#176;C, compatible with flexible polyamide substrates which are stable up to temperatures of 350 &#730;C. The authors are continuing to develop this process route by investigating inkjet printing of other layers within dye sensitized solar cells.

This paper investigates the suitability of inkjet printing for the manufacturing of dye-sensitized solar cells. A binder-free TiO2 nanoparticle ink was formulated and printed onto a FTO glass substrate. The printed layer was fabricated into a cell with an active area of 0.25 cm2 and an efficiency of 3.5%.

Silicon solar cell manufacturing is an expensive and high energy consuming process. In contrast, dye sensitized solar cell production is less ...

Electrospinning Fibrous Polymer Scaffolds for Tissue Engineering and Cell Culture

As the field of tissue engineering evolves, there is a tremendous demand to produce more suitable materials and processing techniques in order to address the requirements (e.g., mechanics and vascularity) of more intricate organs and tissues. Electrospinning is a popular technique to create fibrous scaffolds that mimic the architecture and size scale of the native extracellular matrix. These fibrous scaffolds are also useful as cell culture substrates since the fibers can be used to direct cellular behavior, including stem cell differentiation (see extensive reviews by Mauck et al. and Sill et al. for more information). In this article, we describe the general process of electrospinning polymers and as an example, electrospin a reactive hyaluronic acid capable of crosslinking with light exposure (see Ifkovits et al. for a review on photocrosslinkable materials). We also introduce further processing capabilities such as photopatterning and multi-polymer scaffold formation. Photopatterning can be used to create scaffolds with channels and multi-scale porosity to increase cellular infiltration and tissue distribution. Multi-polymer scaffolds are useful to better tune the properties (mechanics and degradation) of a scaffold, including tailored porosity for cellular infiltration. Furthermore, these techniques can be extended to include a wide array of polymers and reactive macromers to create complex scaffolds that provide the cues necessary for the development of successful tissue engineered constructs.

The process of electrospinning polymers for tissue engineering and cell culture is addressed in this article. Specifically, the electrospinning of photoreactive macromers with additional processing capabilities of photopatterning and multi-polymer electrospinning is described.

As the field of tissue engineering evolves, there is a tremendous demand to produce more suitable materials and processing techniques in order to address ...

Biology

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number of photoactive assemblies have emerged where a photosensitizer and cobaloxime-based H2 production catalysts work in tandem to convert light energy into the H-H chemical bonds. However, the long-term instability of these assemblies and the need for hazardous proton sources have limited their usage. Here, in this work, we have integrated a stilbene-based organic dye into the periphery of a cobaloxime core via a distinct axial pyridine linkage. This strategy allowed us to develop a photosensitizer-catalyst hybrid structure with the same molecular framework. In this article, we have explained the detailed procedure of the synthesis of this hybrid molecule in addition to its comprehensive chemical characterization. The structural and optical studies have exhibited an intense electronic interaction between the cobaloxime core and the organic photosensitizer. The cobaloxime was active for H2 production even in the presence of water as the proton source. Here, we have developed a simple airtight system connected with an online H2 detector for the investigation of the photocatalytic activity by this hybrid complex. This photosensitizer-catalyst dyad present in the experimental setup continuously produced H2 once it was exposed in the natural sunlight. This photocatalytic H2 production by the hybrid complex was observed in aqueous/organic mixture media in the presence of a sacrificial electron donor under complete aerobic conditions. Thus, this photocatalysis measurement system along with the photosensitizer-catalyst dyad provide valuable insight for the development of next generation photocatalytic H2 production devices.

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

We have directly incorporated a stilbene-based organic dye into a cobaloxime core to generate a photosensitizer-catalyst dyad for photocatalytic H2 production. We have also developed a simple experimental setup for evaluating the light-driven H2 production by photocatalytic assemblies.

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number ...

Chemistry

Fully Automated Centrifugal Microfluidic Device for Ultrasensitive Protein Detection from Whole Blood

Enzyme-linked immunosorbent assay (ELISA) is a promising method to detect small amount of proteins in biological samples. The devices providing a platform for reduced sample volume and assay time as well as full automation are required for potential use in point-of-care-diagnostics. Recently, we have demonstrated ultrasensitive detection of serum proteins, C-reactive protein (CRP) and cardiac troponin I (cTnI), utilizing a lab-on-a-disc composed of TiO2 nanofibrous (NF) mats. It showed a large dynamic range with femto molar (fM) detection sensitivity, from a small volume of whole blood in 30 min. The device consists of several components for blood separation, metering, mixing, and washing that are automated for improved sensitivity from low sample volumes. Here, in the video demonstration, we show the experimental protocols and know-how for the fabrication of NFs as well as the disc, their integration and the operation in the following order: processes for preparing TiO2 NF mat; transfer-printing of TiO2 NF mat onto the disc; surface modification for immune-reactions, disc assembly and operation; on-disc detection and representative results for immunoassay. Use of this device enables multiplexed analysis with minimal consumption of samples and reagents. Given the advantages, the device should find use in a wide variety of applications, and prove beneficial in facilitating the analysis of low abundant proteins.

This protocol demonstrates how to achieve femto molar detection sensitivity of proteins in 10 &#181;L of whole blood within 30 min. This can be achieved by using electrospun nanofibrous mats integrated in a lab-on-a-disc, which offers high surface area as well as effective mixing and washing for enhanced signal-to-noise ratio.

Enzyme-linked immunosorbent assay (ELISA) is a promising method to detect small amount of proteins in biological samples. The devices providing a platform ...

High-resolution Patterning Using Two Modes of Electrohydrodynamic Jet: Drop on Demand and Near-field Electrospinning

Electrohydrodynamic (EHD) jet printing has drawn attention in various fields because it can be used as a high-resolution and low-cost direct patterning tool. EHD printing uses a fluidic supplier to maintain the extruded meniscus by pushing the ink out of the nozzle tip. The electric field is then used to pull the meniscus down to the substrate to produce high-resolution patterns. Two modes of EHD printing have been used for fine patterning: continuous near-field electrospinning (NFES) and dot-based drop-on-demand (DOD) EHD printing. According to the printing modes, the requirements for the printing equipment and ink viscosity will differ. Even though two different modes can be implemented with a single EHD printer, the realization methods significantly differ in terms of ink, fluidic system, and driving voltage. Consequently, without a proper understanding of the jetting requirements and limitations, it is difficult to obtain the desired results. The purpose of this paper is to present a guideline so that inexperienced researchers can reduce the trial and error efforts to use the EHD jet for their specific research and development purposes. To demonstrate the fine-patterning implementation, we use Ag nanoparticle ink for the conductive patterning in the protocol. In addition, we also present the generalized printing guidelines that can be used for other types of ink for various fine-patterning applications.

Here, we present a protocol to produce high-resolution conductive patterns using electrohydrodynamic (EHD) jet printing. The protocol includes two modes of EHD jet printing: the continuous near-field electrospinning (NFES) and the dot-based drop-on-demand (DOD) EHD printing.

Electrohydrodynamic (EHD) jet printing has drawn attention in various fields because it can be used as a high-resolution and low-cost direct patterning ...

Vapor Phase Deposition of Electroactive Poly(3,4-ethylenedioxythiophene) onto Electrospun Commodity Polymer Nanofibers

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for applications in water purification, electrocatalysis, and biomedicine. The uniformly white PAN nanofiber mats were cut into 2 cm x 2 cm coupons to ensure consistency. After electrospinning, these nanofibers were coated with an electroactive polymer (EAP) using chemical vapor deposition, with iron (III) chloride (FeCl3) serving as an oxidant for polymerizing 3,4-ethylenedioxythiophene (EDOT) into poly(3,4-ethylenedioxythiophene) (PEDOT). The study examined the impact of different FeCl3 concentrations on PEDOT deposition on the PAN coupons. PEDOT deposition led to an increase in coupon weight. Scanning electron microscopy (SEM) revealed increases in the diameter of the nanofibers treated with increasing FeCl3 oxidant concentration, although higher FeCl3&#160;concentrations caused inter-fiber bridging, implying a concomitant decrease in inter-fiber spacing. Energy dispersive X-ray spectroscopy (EDS) was used to confirm the presence of Fe, Cl, and S in the nanofibers, with sulfur content rising with FeCl3&#160;concentration used, suggesting increased PEDOT deposition efficiency with increasing oxidant concentration. Mechanical testing showed that PEDOT-coated PAN fibers had improved tensile strength and toughness in the hydrated state compared to pure PAN nanofibers. These results highlight the crucial role of FeCl3&#160;concentration in influencing the morphology and properties of PAN-PEDOT composites, enhancing their suitability for applications such as water purification, tissue engineering, biosensing, catalysis, and energy storage.

This paper describes a simple technique for coating electrospun PAN nanofibers with electroactive polymers using vapor deposition. The effects of the oxidant FeCl&#8323; on the deposition of poly(3,4-ethylenedioxythiophene) coatings on PAN were investigated to understand and optimize polymer growth, fiber diameter, and overall mechanical strength of the nanofiber mats.

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for ...

Electrospinning of Photocatalytic Electrodes for Dye-sensitized Solar Cells

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