This research project is supported by Australian Research Council through the linkage grant with CSG Solar Pty. Ltd. Jing Rao acknowledges her University of NSW Vice-Chancellor Postdoctoral Fellowship. SEM images were taken by Jongsung Park using the equipment provided by the Electron Microscopy Unit of the University of NSW.

1. Fabrication of polycrystalline silicon solar cells (Animation 3)
<ol>
 <li>Silicon film deposition
 <ol class="lalpha">
 <li>Prepare the e-beam evaporation tool by baking it out at ~100 &deg;C overnight to reach the base pressure of &lt;3E-8 Torr. Preset the sample heater to the 150 &deg;C standby temperature.</li>
 <li>Use a substrate made of 5x5 cm2 (or 10 x10 cm2) substrate borosilicate glass (Schott Borofloat33), 1.1 or 3.3 mm thick, coated with ~80 nm of silicon nitride (prepared by PECVD from N2 and SiH4 mixture).</li>
 <li>Blow the surface of the substrate with dry nitrogen to remove dust and place it into a sample holder. Vent the load lock, load the sample, pump the load-lock down to the pressure &lt;1E5 Torr, and transfer the sample to the main chamber. Start the heater to the set-point of 250 &deg;C. Pump for about 20 min when the pressure reaches 8E-8 Torr or lower.</li>
 <li>Check that the dopant source and the silicon source shutters are closed. Preset dopant source temperatures to standby temperatures, i.e. the phosphorous source temperature at 700 &deg;C and boron source temperature at 1250 &deg;C. Start e-gun and melt silicon in a crucible by slowly increasing the e-gun current.</li>
 <li>When the required current is reached (from previous calibration: this current can vary depending of the e-gun and the Si source conditions) evaporate silicon layers doped with the required concentrations of P and B: 35 nm emitter at 1E20 cm-3 of P; 2~3 &mu;m absorber at 5E15 cm-3 of B; 100 nm back-surface field (BSF) at 4E19 cm-3 of B. The exact dopant concentrations are achieved by matching certain Si deposition rates, as measured by Quartz Crystal Monitor (QCM), with certain dopant source temperatures, using relationships established from SIMS calibration.</li>
 <li>After evaporation is done switch the heater off, cool down the sample for ~10 min. Transfer the sample to the load-lock, close the gate-valve, vent the load lock and unload the sample with the silicon film.</li>
 </ol>
 </li>
 <li>Silicon crystallisation 
 If the sample is 10x10 cm2, it can be cut into four 5x5 cm2 cell size pieces prior to crystallisation. Place a deposited silicon film on glass (Si film up) on a holder made of roughened and silicon nitride coated Schott Robax glass (to avoid sticking). Load into a nitrogen purged oven preheated to 200-300 &deg;C. Ramp up the temperature up to 600 &deg;C at 3~5 &deg;C/min and anneal for 30 hr. Turn of the oven heater and let oven cool down naturally to ~200 &deg;C (2~3 hr) before unloading the sample. The sample can have a concave shape due to silicon shrinkage during crystallisation. It will flatten during the following rapid thermal processing.</li>
 <li>Dopant activation and defect annealing (RTA) 
 Place the sample with the crystallised film on a holder made of pyrolytic graphite and load to a rapid thermal processor purged with argon. Ramp the temperature up to 600 &deg;C at 1 &deg;C/s, then up to 1000 &deg;C at 20 &deg;C/s, hold for 1 min then cool down naturally to ~100 &deg;C and unload.</li>
 <li>Surface oxide removal 
 Immediately prior to hydrogenation the surface oxide formed on silicon film during crystallisation and RTA must be removed to ensure that the bare silicon film surface is exposed to hydrogen. Immerse the annealed sample into 5% HF solution until the silicon surface turns hydrophobic (30~100 s). Rinse with deionised water and dry with a nitrogen gun.</li>
 <li>Defect passivation 
 Load the sample into a vacuum chamber equipped with the remote hydrogen plasma source. Pump down to &lt;1E-4 Torr, heat up the sample up to ~620 &deg;C, turn on the argon/hydrogen mixture flow (50:150 sccm), set pressure 50-100 mTorr, start the plasma source at 3.5 kW of the microwave power and continue the process for ~10 min. Turn the heater off while maintaining the plasma for another 10-15 min until the temperature falls down below 350 &deg;C before turning the plasma off and stopping the gas flow. Unload the sample when the temperature is below 200 &deg;C.</li>
 <li>Cell metallisation 
 Cell metallisation is conducted in a series of consecutive photolithographic patterning, Al film deposition and etching steps which are described in details in11. The final cell looks like shown in the last slide of ANIMATION 3. A close-up view of the metallised cell is shown in Fig 1.</li>
 <li>Measure EQE of the metallised cell.</li>
</ol>
2. Fabrication of the Plasmonic Ag Nanoparticle (Animation 4)
<ol>
 <li>Blow the metallised cell surface with dry nitrogen to remove dust and load the sample into a thermal evaporator containing a W boat filled with Ag granules (0.3-0.5 g). Pump down the evaporator chamber to the base pressure of 2~3E-5 Torr. Program QCM with parameters for Ag: Density 10.50 and Z ratio 0.529.</li>
 <li>Ensure that the sample shutter is closed, turn the W boat heater on and increase the current slowly enough to avoid pressure rise above 8E-5 Torr until Ag granules melt (as observed through a view-port). After pressure stabilises set the current to the set point corresponding the Ag deposition rate of 0.1-0.2 &Aring;/s (from calibration) and open the shutter to start the deposition process.</li>
 <li>Monitor the growing Ag film thickness using QCM and close the shutter when the thickness of 14 nm is reached. Allow the W boat cool down for about 15 min, unload the sample. The film should be annealed to form nanoparticles as soon after deposition as possible to avoid Ag oxidation.</li>
 <li>A cell with a freshly deposited Ag film is placed into a nitrogen purged oven preheated to 230 0.1-0.2 &deg;C, annealed for 50 min, and then unloaded. Note the change in surface appearance due to nanoparticles. Scanning electron microscopy image of Ag nanoparticles is shown in Fig. 2.</li>
 <li>Measure EQE of the cell with the nanoparticle array.</li>
</ol>
3. Fabrication of the Rear Reflector
The rear reflector consists of ~300 nm thick MgF2 (RI 1.38) dielectric cladding with a coat of a commercial white ceiling paint (Dulux).
<ol>
 <li>Before fabricating the rear reflector the cell contacts have to be protected by applying a black marker ink on them, which allows exposing the contacts from under the dielectric by a lift-off process.</li>
 <li>Use nitrogen gun to blow the sample with NP array and painted contacts to remove dust. Use modest nitrogen pressure and exercise care not to blow the nanoparticles away. Place the sample into the thermal evaporator containing a W boat filled with MgF2 pieces. Pump down the evaporator to pressure of 2~3E-5 Torr. Set QCM parameters for MgF2: Density 3.05 and Z ratio 0.637.</li>
 <li>Ensure that the sample shutter is closed, turn on the boat heater and slowly increase the current to avoid excessive pressure rise until MgF2 melts as seen through a view-port. After the pressure stabilises set the current to the set point corresponding the MgF2 deposition rate of 0.3 nm/s and open the sample shutter.</li>
 <li>Monitor the deposited thickness using QCM and close the shutter when 300 nm is reached.</li>
 <li>Turn off the heater. Allow the W boat to cool down for about 15 min, unload the sample. Note the change in the cell appearance with the MgF2 cladding.</li>
 <li>To remove the ink mask from the cell contacts immerse the cell with the dielectric cladding into acetone. Wait until the dielectric above the ink starts cracking and lifting off. Keep the cell in acetone until all the ink with the dielectric is removed and the metal contacts are fully exposed. Remove the sample from acetone, rinse with fresh acetone and dry with nitrogen gun.</li>
 <li>Apply a layer of a white paint (Dulux One-Coat ceiling paint) with a fine soft brush on the whole cell surface carefully avoiding the metal contacts. The paint layer has to be thick enough to be completely opaque (~&gt;0.5 mm), so that no light can be seen when looking through the painted cell at the bright light source. Let paint dry for a day.</li>
 <li>Measure EQE of the cell with the white paint rear reflector.</li>
</ol>
4. Representative Results
The solar cell short-circuit current is calculated by integrating the EQE curve over the standard global solar spectrum (air mass 1.5). Both the cell current and its enhancement due to light-trapping depend on the cell absorber layer thickness: the current itself is higher for thicker cells but the current enhancement is higher for thinner devices, see Table 1 for the respective data and Animation 5 for EQE curves. The original 2 &mu;m thick cells, without light-trapping, have Jsc measured at step 1.7.) of ~15 mA/cm2. After fabrication of a nanoparticle array, Jsc increases up to about 20 mA/cm2, which is 32% enhancement. It is slightly better than the enhancement effect of 25-30% by the rear diffuse reflector only. After adding the rear diffuse reflector on the MgF2 cladding to the cell with the plasmonic nanoparticle array, the Jsc is increased further to 22.3 mA/cm2, or about 45% enhancement. Note that for the 3 &mu;m thick cell all currents are higher, up to 25.7 mA/cm2 while the relative enhancement is slightly lower, 42%: light-trapping has a relatively larger effect in thinner devices.
<table border="1">
 <tbody>
 <tr>
 <td>Cell thickness:</td>
 <td colspan="2">2 &mu;m</td>
 <td colspan="2">3 &mu;m</td>
 </tr>
 <tr>
 <td>&nbsp;</td>
 <td>Jsc, mA/cm2</td>
 <td>+%</td>
 <td>Jsc, mA/cm2</td>
 <td>+%</td>
 </tr>
 <tr>
 <td>original cell</td>
 <td>15.4</td>
 <td>&nbsp;</td>
 <td>18.1</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Rear diffuse reflector (R)</td>
 <td>20.1</td>
 <td>30.5</td>
 <td>21.5</td>
 <td>18.8</td>
 </tr>
 <tr>
 <td>Nanoparticles (NP)</td>
 <td>20.3</td>
 <td>31.8</td>
 <td>21.9</td>
 <td>21.0</td>
 </tr>
 <tr>
 <td>NP/MgF2/R</td>
 <td>22.3</td>
 <td>45.3</td>
 <td>25.7</td>
 <td>42.0</td>
 </tr>
 </tbody>
</table>
Table 1. Plasmonic cell short-circuit current and its enhancement compared to original cell.
<img alt="Figure 1" src="/files/ftp_upload/4092/4092fig1.jpg" /> 
Figure 1. Close-up view of poly-Si thin-film solar cell with metallisation grid.
<img alt="Figure 2" src="/files/ftp_upload/4092/4092fig2.jpg" /> 
Figure 2. Scanning electron microscopy image of Ag nanoparticles on the silicon surface.
<img alt="Figure 3" src="/files/ftp_upload/4092/4092fig3.jpg" /> 
Figure 3. A schematic view of a plasmonic crystalline silicon thin-film solar cell (not to scale).
<img alt="Figure 4" src="/files/ftp_upload/4092/4092fig4.jpg" /> 
Figure 4. External quantum efficiency and short-circuit current for the polycrystalline silicon thin-film cells with diffuse reflector and plasmonic nanoparticles: dashed-black - original 2 &mu;m thick cell without light-trapping, Jsc 15.36 mA/cm2; blue - cell with diffuse paint reflector, Jsc 20.08 mA/cm2; red - cell with plasmonic Ag nanoparticles, Jsc 20.31 mA/cm2; green - cell with nanoparticles, MgF2, and diffuse paint reflector, Jsc 22.32 mA/cm2. Purple - 3 &mu;m thick cell (on 3 mm thick glass) with nanoparticles, MgF2, and diffuse reflector, Jsc 25.7 mA/cm2 (note lower blue response due to unintentional differences in the AR layers and the emitter thickness). Solid black - 2 &mu;m thick textured cell prepared by plasma enhanced chemical vapor deposition (on 3 mm thick glass), Jsc 26.4 mA/cm2, shown for comparison.
Animation 1. <a href="https://www.jove.com/files/ftp_upload/4092/4092animation1.pptx" target="_blank"> Click here to view Animation</a>.
Animation 2. <a href="https://www.jove.com/files/ftp_upload/4092/4092animation2.pptx" target="_blank"> Click here to view Animation</a>.
Animation 3. <a href="https://www.jove.com/files/ftp_upload/4092/4092animation3.pptx" target="_blank"> Click here to view Animation</a>.
Animation 4. <a href="https://www.jove.com/files/ftp_upload/4092/4092animation4.pptx" target="_blank"> Click here to view Animation</a>.
Animation 5. <a href="https://www.jove.com/files/ftp_upload/4092/4092animation5.pptx" target="_blank"> Click here to view Animation</a>.

<ol>
	<li>Henley, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kerf-free+wafering.">Kerf-free wafering.</a> , 1184-1192 (2010).</li><li>Kunz, O., Wong, J., Janssens, J., Bauer, J., Breitenstein, O., Aberle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shunting+problems+due+to+sub-micron+pinholes+in+evaporated+solid-phase+crystallised+poly-Si+thin-film+solar+cells+on+glass.">Shunting problems due to sub-micron pinholes in evaporated solid-phase crystallised poly-Si thin-film solar cells on glass.</a> Progress Photovoilt.: Res. Appl. 17, 35-46 (2009).</li><li>Kunz, O., Ouyang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=5%+Efficient+evaporated+solid-phase+crystallised+polycrystalline+silicon+solar+cells.">5% Efficient evaporated solid-phase crystallised polycrystalline silicon solar cells.</a> Progress Photovolt.: Res. Appl. 17, 567-573 (2009).</li><li>Van Nieuwenhuysen, K., Payo, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epitaxially+grown+emitters+for+thin+film+silicon+solar+cells+result+in+16%+efficiency.">Epitaxially grown emitters for thin film silicon solar cells result in 16% efficiency.</a> Thin Solid Films. 518, S80-S82 (2008).</li><li>Lee, B. G., Stradin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-trapping+by+a+dielectric+nanoparticle+back+reflector+in+film+silicon+solar+cells.">Light-trapping by a dielectric nanoparticle back reflector in film silicon solar cells.</a> Appl. Phys. Lett. 99, 064101 (2011).</li><li>Catchpole, K. R., Polman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmonic+solar+cells.">Plasmonic solar cells.</a> Optics Express. 16, 21793-21800 (2008).</li><li>Ouyang, Z., Zhao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoparticle+enhanced+light-trapping+in+thin-film+silicon+solar+cells.">Nanoparticle enhanced light-trapping in thin-film silicon solar cells.</a> Progress Photovolt.: Res. Appl. 19, 917-926 (2011).</li><li>Catchpole, K. R., Polman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+principle+for+particle+plasmon+enhanced+solar+cells.">Design principle for particle plasmon enhanced solar cells.</a> Appl. Phys. Lett. 93, 191113 (2008).</li><li>Beck, F. J., Mokkapati, S., Polman, A., Catchpole, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Asymmetry+in+photocurrent+enhancement+by+plasmonic+nanoparticle+arrays+located+on+the+front+or+on+the+rear+of+solar+cells.">Asymmetry in photocurrent enhancement by plasmonic nanoparticle arrays located on the front or on the rear of solar cells.</a> Appl. Phys. Lett. 96, 033113 (2008).</li><li>Beck, F. J., Verhagen, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resonant+SPP+modes+supported+bt+discrete+metal+nanoparticles+on+high+index+substrates.">Resonant SPP modes supported bt discrete metal nanoparticles on high index substrates.</a> Optics Express. 19, 146-156 (2010).</li><li>Kunz, O., Ouyang, Z., al, a. t. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=5%+Efficient+evaporated+solid-phase+crystallised+polycrystalline+silicon+thin-film+solar+cells.">5% Efficient evaporated solid-phase crystallised polycrystalline silicon thin-film solar cells.</a> Progress Photovolt. 17, 567-573 (2009).</li><li>Keevers, M. J., Young, T. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=10%+Efficient+CSG+minimodules.">10% Efficient CSG minimodules.</a> , 1783-1790 (2007).</li></ol>

No conflicts of interest declared.

Evaporated polycrystalline silicon solar cells and the light-scattering plasmonic nanoparticles are ideal partners for light-trapping. Such cells are planar, hence they cannot rely on light-scattering from textured surfaces, nor can plasmonic nanoparticles be easily formed on textured surfaces. The cells have only one, rear surface with directly exposed silicon, which also happens to be the best nanoparticle location for most effective plasmonic light-scattering. Moreover, the easiest method for nanoparticle formation by...

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Silver granular</td>
 <td>Sigma-Aldrich</td>
 <td>303372</td>
 <td>99.99%</td>
 </tr>
 <tr>
 <td>MgF2, random crystals, optical grade</td>
 <td>Sigma-Aldrich</td>
 <td>378836</td>
 <td>&gt;=99.99%</td>
 </tr>
 <tr>
 <td>Dulux one-coat ceiling paint</td>
 <td>Dulux</td>
 <td>&nbsp;</td>
 <td>R&gt;90% 
 (500-1100 nm)</td>
 </tr>
 </tbody>
</table>

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.

Watch this Scientific Journal Video about Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping at JoVE.com

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

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 ...

polycrystalline-silicon-thin-film-solar-cells-with-plasmonic-enhanced

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18.7K Views.  University of New South Wales. 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.

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

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

We describe a nanomoulding technique which  allows low-cost nanoscale patterning of functional materials, materials stacks  and full devices. Nanomoulding ...

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 oC. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 oC. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance.
For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 oC by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application.

We offered a method to directly synthesize high c-axis (0002) ZnO thin film by plasma enhanced chemical vapor deposition. The as-synthesized ZnO thin film combined with Pt interdigitated electrode was used as sensing layer for ultraviolet photodetector, showing a high performance through a combination of its good responsivity and reliability.

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto ...

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 ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

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 ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Monovalent Cation Doping of CH3NH3PbI3 for Efficient Perovskite Solar Cells

Here, we present a protocol to adjust the properties of solution-processed CH3NH3PbI3 through the incorporation of monovalent cation additives in order to achieve highly efficient perovskite solar cells.

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical ...

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 ...

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction of degradation mechanisms and prevention of module field failure can consequently decrease investment risks as well as increase the electricity yield. An improved knowledge level can for these reasons significantly decrease the total costs of PV electricity. 
In order to better understand and minimize the degradation of PV modules, the occurring degradation mechanisms and conditions should be identified. This should preferably happen under combined stresses, since modules in the field are also simultaneously exposed to multiple stress factors. Therefore, two 'Combined Stress test with in situ measurement' setups have been designed and constructed. These setups allow the simultaneous use of humidity, temperature, illumination, and electrical biases as independently controlled stress factors on solar cells and minimodules. The setups also allow real-time monitoring of the electrical properties of these samples. This protocol presents these setups and describes the experimental possibilities. Moreover, results obtained with these setups are also presented: various examples about the influence of both deposition and degradation conditions on the stability of thin film Cu(In,Ga)Se2 (CIGS) as well as Cu2ZnSnSe4 (CZTS) solar cells are described. Results on the temperature dependency of CIGS solar cells are also presented.

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for CuIn,GaSe2 Solar Cells

Two &#39;Combined Stress test with in situ measurement&#39; setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...