Name: integrating a triplet-triplet annihilation up-conversion system to enhance dye-sensitized solar cell response to sub-bandgap light
Uploaded: 2014-09-12T15:00:00
Description: Watch this Scientific Journal Video about Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light at JoVE.com

A.N. acknowledges contributions from the Australian Renewable Energy Agency (ARENA) and the Australian National Fabrication Facility (ANFF). This research project is funded by the Australian Solar Institute (6-F020 and A-023), with contributions from The New South Wales Government and the University of Sydney. Aspects of this research were supported under Australian Research Council&#8217;s Discovery Projects funding scheme (DP110103300). Equipment was purchased with support from the Australian Research Council (LE0668257).

1. DSC Fabrication
1.1. Working Electrode Preparation
<ol>
	<li>Clean one whole sheet of F:SnO2 coated glass (110 mm &#215; 110 mm &#215; 2.3 mm, &#60;8 &#937;/&#9633;) by sonication sequentially in soapy water, then acetone and finally ethanol (10 min each).</li>
	<li>Deposit a dense layer of TiO2 following the steps below:
	<ol>
		<li>Dry glass using compressed air and heat glass to 450 &#176;C on hotplate (conductive side up).</li>
		<li>Dilute Titanium diisopropoxide b...

<ol>
	<li>O'Regan, B., Gr&#228;tzel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+low-cost,+high-efficiency+solar-cell+based+on+dye-sensitized+colloidal+TiO2+films.">A low-cost, high-efficiency solar-cell based on dye-sensitized colloidal TiO2 films.</a> Nature. 353, 737-740 (1991).</li><li>Gr&#228;tzel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoelectrochemical+cells.">Photoelectrochemical cells.</a> Nature. 414 (6861), 338-344 (2001).</li><li>Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L., Pettersson, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dye-Sensitized+Solar+Cells.">Dye-Sensitized Solar Cells.</a> Chem. Rev. 110 (11), 6595-6663 (2010).</li><li>Tayebjee, M. J. Y., Hirst, L. 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Mater. 9 (1), 31-35 (2010).</li><li>Nattestad, A., 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=Dye-Sensitized+Solar+Cell+with+Integrated+Triplet-Triplet+Annihilation+Upconversion+System.">Dye-Sensitized Solar Cell with Integrated Triplet-Triplet Annihilation Upconversion System.</a> J. Phys. Chem. Lett. 4 (12), 2073-2078 (2013).</li><li>Liu, M., Lu, Y., Xie, Z. B., Chow, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancing+Near-Infrared+Solar+Cell+Response+Using+Upconverting+Transparent+Ceramics.">Enhancing Near-Infrared Solar Cell Response Using Upconverting Transparent Ceramics.</a> Sol. Energ. Mat. Sol. C. 95, 800-803 (2011).</li><li>Shan, G. B., Demopolous, G. 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This protocol provides a means to achieve photon up-conversion enhanced DSC and detail on how to correctly measure such a device. The FoM allows for the simple calculation of anticipated &#916;JSC improvements to be expected at different light intensities, including at 1 sun. The values shown here are invariant with light intensity (inset of Figure 4), as per expectation when the system is below its saturation threshold33. With the FoM, we can standardize the enhancement effect of T...

Dye-sensitized solar cells (DSCs) have been proclaimed as a promising concept in affordable solar energy collection1-3. In spite of this enthusiasm, widespread commercialization has yet to occur. A number of reasons have been put forward for this, with one pressing issue being the relatively high energy of the absorption onset, limiting the achievable light harvesting efficiency of these devices4. Although this can be overcome, lowering the absorption onset is typically accompanied by a drop in open circuit voltage, which disproportionately erodes any gains in current density5, 6.
The general operation of DSCs involves electron transfer from a photoexcited dye to a semiconductor (typically TiO2), followed by the regeneration of the oxidized dye by a redox mediator. Both these processes appear to require substantial driving forces (potential) in order to proceed with high efficiency7. With such significant inherent losses, it becomes obvious that the optimal absorption onset for these devices is reasonably high in energy. Similar problems exist for organic photovoltaics (OPV), due once again to the large chemical driving forces required for effective charge separation. Accordingly, predictions of upper solar-to-electric conversion efficiency limits to single junction devices based on both of these technologies involve absorbers with wide (effective) band gaps4.
In order to overcome the light harvesting issue raised above, a number of approaches have been taken. This includes the &#8216;third generation&#8217;8 approaches of tandem structures9, 10 and photon upconversion11-14.
Recently11 we reported an integrated device composed of a DSC working and counter electrode, with a triplet-triplet annihilation based up-conversion (TTA-UC) system incorporated into the structure. This TTA-UC element was able to harvest red light transmitted through the active layer and chemically convert it (as described in detail below) to higher energy photons which could be absorbed by the active layer of the DSC and generate photocurrent. There are two important points to note about this system. Firstly, TTA-UC has many prospective advantages over other photon upconversion systems11; secondly it demonstrates a feasible architecture (proof-of-principle) for the incorporation of TTA-UC, which had been lacking from the TTA-UC literature up to that point.
The process of TTA-UC15-24 involves the excitation of &#8216;sensitizer&#8217; molecules, in this case Pd porphyrins, by light with energy below the device onset energy. The singlet-excited sensitizers undergo rapid intersystem crossing to the lowest-energy triplet state. From there, they can transfer energy to a ground-state triplet-accepting &#8216;emitter&#8217; species such as rubrene, as long as the transfer is allowed by free energy25. The first triplet state of rubrene (T1) is greater than half the energy of its first excited singlet state (S1) but less than half the energy of T2, meaning that an encounter complex of two triplet-excited rubrenes can annihilate to give one singlet excited emitter molecule (and the other in the ground state) with a fairly high probability. Other states, statistically predicted, are most likely energetically inaccessible for rubrene26. The singlet excited rubrene molecule can then emit a photon (as per fluorescence) with energy sufficient to excite the dye on the working electrode of the DSC. This process is shown in Animation 1.
TTA-UC offers a number of advantages compared to other UC systems, such as a broad absorption range and incoherent nature27, 28, making it an attractive option for coupling with DSC (as well as OPV). TTA-UC has been demonstrated operating at relatively low light intensities and in diffuse lighting conditions. Both DSC and OPV are most efficient in the low light intensity regime. Solar concentration is expensive and only justifiable for high efficiency, high cost devices. The relatively high performance of TTA-UC systems in low intensity lighting conditions is attributable to the process involving sensitizer chromophores with strong, broad absorption bands in concert with long-lived triplet states which are capable of diffusing in order to come into contact with interacting species. In addition, TTA-UC has been found to have high intrinsic efficiency from a kinetic study26.
Although TTA-UC operates at low light intensity, there is still a quadratic relationship between incident light intensity and emitted light (at least at low light intensities). This is due to the bimolecular nature of the process. To account for this and the varied experimental conditions (particularly light intensity) reported by different groups, a figure of merit (FoM) system should be employed to meter the performance enhancement offered by upconversion. This FoM has been defined as &#916;JSC/&#664;, where &#916;JSC is the increase in short circuit current (usually determined by integration of the Incident Photon to Charge Carrier Efficiency, IPCE, with and without the upconversion effect) and &#664; is the effective solar concentration (based on the photon flux in the relevant region, that is the Q-band absorption of the sensitizer)229.
Herein, a protocol for producing and correctly characterizing an integrated DSC-TTA-UC device is reported, paying special attention to potential pitfalls in device testing. It is hoped that this will serve as a basis for further work in this field.

<table border="0" cellpadding="0" cellspacing="0" width="1100">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Name of Material/ Equipment</td>
			<td style="width:200px;">Company</td>
			<td style="width:160px;">Catalog Number</td>
			<td style="width:245px;">Comments/Description</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:495px;">(tetrakis(3,5-di-tert-butylphenyl)-6&#8217;-amino-7&#8217;-nitro-tetrakisquinoxalino[2,3-b&#39;7,8-b&#39;&#39;12,13-b&#39;&#39;&#39;17,18-b&#39;&#39;&#39;&#39;-porphyrinato) palladium(II))</td>
			<td style="width:200px;">in house</td>
			<td style="width:160px;">in house</td>
			<td>Chem. Commun., 4851&#8211;4853 (2007)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1,2-dimethyl-3-propylimidazolium iodide</td>
			<td style="width:200px;">Solaronix</td>
			<td style="width:160px;">33150</td>
			<td>Material warning: Irritant</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">405 nm longpass filter</td>
			<td style="width:200px;">Semrock</td>
			<td>BLP01-405R-25</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">670 nm laser</td>
			<td style="width:200px;">Thorlabs</td>
			<td>LDS5 + CPS198</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Acetone</td>
			<td style="width:200px;">Chemsupply</td>
			<td style="width:160px;">AA008-20L-P</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Acetonitrile</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">271004</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Alumina</td>
			<td style="width:200px;">Alfa Aesar</td>
			<td style="width:160px;">12733</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Alumina</td>
			<td style="width:200px;">Leeco</td>
			<td style="width:160px;">810-782</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Back filling chamber</td>
			<td style="width:200px;">Sistema</td>
			<td style="width:160px;">1303</td>
			<td>Kilip it round, modified</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Benzene</td>
			<td style="width:200px;">Scharlau</td>
			<td style="width:160px;">BE0033</td>
			<td>Material warning: Toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">BNC cable</td>
			<td style="width:200px;">Jaycar</td>
			<td style="width:160px;">RG- 59U</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Cerasolzer</td>
			<td style="width:200px;">MBR</td>
			<td style="width:160px;">CS186</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Chopper wheel</td>
			<td style="width:200px;">Thorlabs</td>
			<td>MC1000A</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Control software</td>
			<td style="width:200px;">in house</td>
			<td style="width:160px;">in house</td>
			<td>Written in LabVIEW</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Current Amplifier</td>
			<td>Standford Research&#160;</td>
			<td style="width:160px;">SR 570</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">D149 dye</td>
			<td style="width:200px;">1m</td>
			<td style="width:160px;">OSO149</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Dental burr</td>
			<td style="width:200px;">Priority dental supplies</td>
			<td style="width:160px;">835.104.008</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Detergent</td>
			<td style="width:200px;">Palmolive</td>
			<td style="width:160px;">Original</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Diamond wheel</td>
			<td style="width:200px;">Frameco</td>
			<td style="width:160px;">14220</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Drill</td>
			<td style="width:200px;">Dremmel</td>
			<td style="width:160px;">220</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Dynamic dignal acquisition device</td>
			<td>National Instruments</td>
			<td style="width:160px;">USB-4431</td>
			<td>Analog to Digital</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Ethanol</td>
			<td style="width:200px;">Univar</td>
			<td style="width:160px;">214</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:495px;">F:SnO2 glass</td>
			<td style="width:200px;">Hartford</td>
			<td style="width:160px;">TEC8</td>
			<td>2.3mm, &#60; 8 &#937;/&#9633;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Glovebox</td>
			<td style="width:200px;">IT systems</td>
			<td style="width:160px;">-</td>
			<td>-</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:495px;">H2PtCl6</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">334472</td>
			<td>Material warning: corrosive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Hot melt adhesive gasket</td>
			<td style="width:200px;">Solaronix</td>
			<td style="width:160px;">Meltronic 1170-25</td>
			<td style="width:245px;">Surlyn</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Hot melt adhesive gasket</td>
			<td style="width:200px;">Solaronix</td>
			<td style="width:160px;">Meltronix 1170-60</td>
			<td style="width:245px;">Surlyn</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Hotplate</td>
			<td style="width:200px;">Harry Gestigkeit</td>
			<td style="width:160px;">PR 5 3T / PZ28-3T</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Hotplate</td>
			<td style="width:200px;">IKA</td>
			<td style="width:160px;">RCT basic</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Image analysis software</td>
			<td style="width:200px;">National Institutes for Health</td>
			<td style="width:160px;">Image-J</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Iodine</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">326143</td>
			<td>Material warning: corrosive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Laser engraver</td>
			<td style="width:200px;">Universal Laser Systems</td>
			<td style="width:160px;">PLS6WM</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Liquid Nitrogen</td>
			<td style="width:200px;">Air Liquide</td>
			<td style="width:160px;"></td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Lithium Iodide</td>
			<td style="width:200px;">Aldrich</td>
			<td style="width:160px;">518018</td>
			<td>Material warning: toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Methoxypropionitrile</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">65290</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Mirror</td>
			<td style="width:200px;">Thorlabs</td>
			<td style="width:160px;">PF10-03-P01</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Mirror mount</td>
			<td style="width:200px;">Thorlabs</td>
			<td style="width:160px;">KM100</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Monochromator</td>
			<td style="width:200px;">Spectral Products&#160;</td>
			<td>CM110</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Neutral density filters</td>
			<td style="width:200px;">Edmund Industrial Optics</td>
			<td style="width:160px;">64-352</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Parabolic mirror</td>
			<td style="width:200px;">Newport</td>
			<td style="width:160px;">50329AL, 50338AL</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Photodiode</td>
			<td>Newport</td>
			<td>918D-UV-OD3</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Power meter</td>
			<td>Newport</td>
			<td style="width:160px;">1936-C</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Rubrene</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">551112</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Semi-automatic screen printer</td>
			<td style="width:200px;">Keywell</td>
			<td style="width:160px;">KY-500FH</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Spray pyrolyser</td>
			<td style="width:200px;">Glaskeller</td>
			<td style="width:160px;">-</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Tape</td>
			<td style="width:200px;">3M</td>
			<td style="width:160px;">Magic Tape</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Terminal block</td>
			<td style="width:200px;">Jaycar</td>
			<td>HM3194</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">tert-Butanol</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">360538</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">TiCl4</td>
			<td style="width:200px;">Sigma</td>
			<td style="width:160px;">89545</td>
			<td>Material warning: corrosive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Tile</td>
			<td style="width:200px;">Johnson tiles</td>
			<td style="width:160px;">-</td>
			<td>-</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:495px;">Tile cutter</td>
			<td style="width:200px;">DTA</td>
			<td style="width:160px;">DTA-310</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">TiO2 paste</td>
			<td style="width:200px;">Dyesol</td>
			<td style="width:160px;">NR18-T</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Titanium diisopropoxide bis(acetylacetonate) (75% in isopropanol)</td>
			<td style="width:200px;">Aldrich</td>
			<td style="width:160px;">325252</td>
			<td>Material warning: Flammable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Ultrasonic soldering iron</td>
			<td style="width:200px;">MBR</td>
			<td style="width:160px;">USS-9200</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">UV cure epoxy</td>
			<td style="width:200px;">Dymax</td>
			<td style="width:160px;">425</td>
			<td>Material warning: Irritant</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">UV cure system</td>
			<td style="width:200px;">Dymax</td>
			<td style="width:160px;">BlueWave 50</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UV Visible Spectrophotometer</td>
			<td style="width:200px;">Varian Cary</td>
			<td style="width:160px;">1E</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Vacuum cuvette</td>
			<td style="width:200px;">Custom made</td>
			<td style="width:160px;">Custom made</td>
			<td>-</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:495px;">Vacuum pump</td>
			<td style="width:200px;">N/A</td>
			<td style="width:160px;">Rotary backed diffusion pump</td>
			<td>-</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Wipes</td>
			<td style="width:200px;">Kimtech</td>
			<td style="width:160px;">34120KC</td>
			<td>Kimwipes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:495px;">Xe lamp</td>
			<td>Energetiq&#160;</td>
			<td style="width:160px;">LDLSTM EQ-1500</td>
			<td style="width:245px;">White light source</td>
		</tr>
	</tbody>
</table>

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.

Figures 3A - D display enhancement responses measured under different measurement conditions, with the effects discussed in more detail below. From the raw current density enhancements it should be clear that the results in Figure 4A and 4B are attributable to upconversion, with the peak current enhancement and IPCE enhancement matching well with the absorption spectrum of the sensitizer, attenuated by transmission through the active layer of the DSC.</p...

Watch this Scientific Journal Video about Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light at JoVE.com

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

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 ...

integrating-triplet-triplet-annihilation-up-conversion-system-to

Research

JoVE Journal

Engineering

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach.
The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles.
To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 &mu;m thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint.
To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23&deg;C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only.
Introduction
Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested.
Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10.
The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only.

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To ...

Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped crystallites. Neutrons are passed through two well defined regions of magnetic field; one before and one after the sample. The two magnetic field regions have opposite polarity and are tuned such that neutrons travelling through both regions, without being perturbed, will undergo the same number of precessions in opposing directions. In this case the neutron precession in the second arm is said to &#34;echo&#34; the first, and the original polarization of the beam is preserved. If the neutron interacts with a sample and scatters elastically the path through the second arm is not the same as the first and the original polarization is not recovered. Depolarization of the neutron beam is a highly sensitive probe at very small angles (&#60;50&#160;&#956;rad) but still allows a high intensity, divergent beam to be used. The decrease in polarization of the beam reflected from the sample as compared to that from the reference sample can be directly related to structure within the sample.
In comparison to scattering observed in neutron reflection measurements the SERGIS signals are often weak and are unlikely to be observed if the in-plane structures within the sample under investigation are dilute, disordered, small in size and polydisperse or the neutron scattering contrast is low. Therefore, good results will most likely be obtained using the SERGIS technique if the sample being measured consist of thin films on a flat substrate and contain scattering features that contains a high density of moderately sized features (30 nm to 5 &#181;m) which scatter neutrons strongly or the features are arranged on a lattice. An advantage of the SERGIS technique is that it can probe structures in the plane of the sample.

Progress has been made in utilizing spin echo resolved grazing incidence scattering (SERGIS) as a neutron scattering technique to probe the length-scales in irregular samples. Crystallites of [6,6]-phenyl-C61-butyric acid methyl ester have been probed using the SERGIS technique and the results confirmed by optical and atomic force microscopy.

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data ...

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 ...

A System to Create Stable Nanoparticle Aerosols from Nanopowders

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring minimal amounts of test materials (min. 200 mg), for studying powder aerosolization behavior and aerosol properties. The aerosolization procedure follows the concept of the fluidized-bed process, but occurs in the modified volume of a V-shaped aerosol generator. The airborne particle number concentration is adjustable by controlling the air flow rate. The system supplied stable aerosol generation rates and particle size distributions over long periods (0.5-2 hr and possibly longer), which are important, for example, to study aerosol behavior, but also for toxicological studies. Strict adherence to the operating procedures during the aerosolization experiments ensures the generation of reproducible test results. The critical steps in the standard protocol are the preparation of the material and setup, and the aerosolization operations themselves. The system can be used for experiments requiring stable aerosol concentrations and may also be an alternative method for testing dustiness. The controlled aerosolization made possible with this setup occurs using energy inputs (may be characterized by aerosolization air velocity) that are within the ranges commonly found in occupational environments where nanomaterial powders are handled. This setup and its operating protocol are thus helpful for human exposure and risk assessment.

We designed and developed an effective nanopowder aerosolization setup and operating protocol. The system generated nanoparticle aerosols with stable number concentrations and size distributions for long durations, requiring only small quantities of test material (min. 200 mg).

Nanoparticle aerosols released from nanopowders in workplaces are associated with human exposure and health risks. We developed a novel system, requiring ...

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 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 ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is composed of two materials, a plastic and an elastomer, whose dispersion characteristics (refractive index variation with wavelength) are different. We first designed the lens geometry and then used ray-tracing simulation, based on the Monte Carlo method, to analyze its performance from the point of view of both optical efficiency and the maximum attainable concentration. Afterwards, ADG Fresnel lens prototypes were manufactured using a simple and reliable method. It consists of a prior injection of plastic parts and a consecutive lamination, together with the elastomer and a glass substrate to fabricate the parquet of ADG Fresnel lenses. The accuracy of the manufactured lens profile is examined using an optical microscope while its optical performance is evaluated using a solar simulator for concentrator photovoltaic systems. The simulator is composed of a xenon flash lamp whose emitted light is reflected by a parabolic mirror. The collimated light has a spectral distribution and an angular aperture similar to the real Sun. We were able to assess the optical performance of the ADG Fresnel lenses by taking photographs of the irradiance spot cast by the lens using a charge-coupled device (CCD) camera and measuring the photocurrent generated by several types of multi junction (MJ) solar cells, which have been previously characterized at a solar simulator for concentrator solar cells. These measurements have demonstrated the achromatic behavior of ADG Fresnel lenses and, as a consequence, the suitability of the modelling and manufacturing methods.

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass ADG Fresnel Lens for Concentrating Photovoltaics

The achromatic doublet on glass (ADG) Fresnel lens makes use of two materials with differing dispersion to reduce chromatic aberration and increase attainable concentration. In this paper, a protocol for the complete characterization of the ADG Fresnel lens is presented.