Name: well-aligned vertically oriented zno nanorod arrays and their application in inverted small molecule solar cells
Uploaded: 2018-04-25T12:30:00
Description: Watch this Scientific Journal Video about Well-aligned Vertically Oriented ZnO Nanorod Arrays and their Application in Inverted Small Molecule Solar Cells at JoVE.com

The authors would like to thank the National Science Council of China for the financial support of this research under Contract No. MOST 106-2221-E-239-035, and MOST 106-2119-M-033-00.

1. Growth of AZO Sputtered Seed Layer on ITO Substrate
<ol>
	<li>Stick 4 anti-corrosion tape pieces (0.3 x 1.5 cm) on one side of the indium tin oxide (ITO) substrate to form a square (1.5 x 1.5 cm). Put the ITO into hydrochloric acid for 15 min to etch the exposed area of ITO.</li>
	<li>Remove the tape and clean the sample using a sonicator; sonicate with deionized (DI) water, acetone, ethanol, and isopropanol in turn for 30 min each. Blow-dry the patterned ITO with a compressed nitrogen gun.</li>
	<li>Attach the clea...

<ol>
	<li>Dou, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tandem+polymer+solar+cells+featuring+a+spectrally+matched+low-bandgap+polymer.">Tandem polymer solar cells featuring a spectrally matched low-bandgap polymer.</a> Nat. Photonics. 6 (3), 180-185 (2012).</li><li>You, J., 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=Metal+Oxide+Nanoparticles+as+an+Electron-Transport+Layer+in+High+Performance+and+Stable+Inverted+Polymer+Solar+Cells.">Metal Oxide Nanoparticles as an Electron-Transport Layer in High Performance and Stable Inverted Polymer Solar Cells.</a> Adv. Mater. 24 (38), 5267-5272 (2012).</li><li>Dou, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+Investigation+of+Benzodithiophene-+and+Diketopyrrolopyrrole-Based+Low-Bandgap+Polymers+Designed+for+Single+Junction+and+Tandem+Polymer+Solar+Cells.">Systematic Investigation of Benzodithiophene- and Diketopyrrolopyrrole-Based Low-Bandgap Polymers Designed for Single Junction and Tandem Polymer Solar Cells.</a> J. Am. Chem. Soc. 134 (24), 10071-10079 (2012).</li><li>Li, G., Zhu, R., Yang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer+solar+cells.">Polymer solar cells.</a> Nat. Photonics. 6 (3), 153-161 (2012).</li><li>You, J., 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=A+polymer+tandem+solar+cell+with+10.6%+power+conversion+efficiency.">A polymer tandem solar cell with 10.6% power conversion efficiency.</a> Nat. Commun. 4, 1446 (2013).</li><li>Chen, J. D., 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=Single-Junction+Polymer+Solar+Cells+Exceeding+10%+Power+Conversion+Efficiency.">Single-Junction Polymer Solar Cells Exceeding 10% Power Conversion Efficiency.</a> Adv. Mater. 27 (6), 1035-1041 (2015).</li><li>Zhang, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developing+high-performance+small+molecule+organic+solar+cells+via+a+large+planar+structure+and+an+electron-withdrawing+central+unit.">Developing high-performance small molecule organic solar cells via a large planar structure and an electron-withdrawing central unit.</a> Chem. Commun. 53, 451-454 (2017).</li><li>Zhou, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conductive+Conjugated+Polyelectrolyte+as+Hole-Transporting+Layer+for+Organic+Bulk+Heterojunction+Solar+Cells.">Conductive Conjugated Polyelectrolyte as Hole-Transporting Layer for Organic Bulk Heterojunction Solar Cells.</a> Adv. Mater. 26 (5), 780-785 (2014).</li><li>Lin, M. Y., 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=Enhance+the+light-harvesting+capability+of+the+ITO-free+inverted+small+molecule+solar+cell+by+ZnO+nanorods.">Enhance the light-harvesting capability of the ITO-free inverted small molecule solar cell by ZnO nanorods.</a> Opt. Express. 24 (16), 17910-17915 (2016).</li><li>Liu, Y., 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=Solution-processed+small-molecule+solar+cells:+breaking+the+10%+power+conversion+efficiency.">Solution-processed small-molecule solar cells: breaking the 10% power conversion efficiency.</a> Sci. Rep. 3, 3356 (2013).</li><li>Farahat, M. E., 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=Toward+environmentally+compatible+molecular+solar+cells+processed+from+halogen-free+solvents.">Toward environmentally compatible molecular solar cells processed from halogen-free solvents.</a> J. Mater. Chem. A Mater. Energy Sustain. 4 (19), 7341-7351 (2016).</li><li>Lin, M. Y., 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=Plasmonic+ITO-free+polymer+solar+cell.">Plasmonic ITO-free polymer solar cell.</a> Opt. Express. 22 (S2), A438-A445 (2014).</li><li>Donato, 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=RF+sputtered+ZnO-ITO+films+for+high+temperature+CO+sensors.">RF sputtered ZnO-ITO films for high temperature CO sensors.</a> Thin Solid Films. 517 (22), 6184-6187 (2009).</li><li>Lin, M. Y., 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=Sol-gel+processed+CuOx+thin+film+as+an+anode+interlayer+for+inverted+polymer+solar+cells.">Sol-gel processed CuOx thin film as an anode interlayer for inverted polymer solar cells.</a> Org. Electron. 11 (11), 1828-1834 (2010).</li><li>Vandewal, K., 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=On+the+origin+of+the+open-circuit+voltage+of+polymer-fullerene+solar+cells.">On the origin of the open-circuit voltage of polymer-fullerene solar cells.</a> Nat. Mater. 8, 904-909 (2009).</li><li>Sharma, R., 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=X-ray+diffraction:+a+powerful+method+of+characterizing+nanomaterials.">X-ray diffraction: a powerful method of characterizing nanomaterials.</a> Recent Research in Science and Technology. 4 (8), 77-79 (2012).</li><li>Huggett, J. M., Shaw, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Field+emission+scanning+electron+microscopy+a+high-resolution+technique+for+the+study+of+clay+minerals+in+sediments.">Field emission scanning electron microscopy a high-resolution technique for the study of clay minerals in sediments.</a> Clay Miner. 32, 197-203 (1997).</li><li>Lou, S., 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=Laser+beam+homogenizing+system+design+for+photoluminescence.">Laser beam homogenizing system design for photoluminescence.</a> Appl. Opt. 53 (21), 4637-4644 (2014).</li><li>Huang, J. S., Lin, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influences+of+ZnO+sol-gel+thin+film+characteristics+on+ZnO+nanowire+arrays+prepared+at+low+temperature+using+all+solution-based+processing.">Influences of ZnO sol-gel thin film characteristics on ZnO nanowire arrays prepared at low temperature using all solution-based processing.</a> J. Appl. Phys. 103, 014304 (2008).</li><li>Leung, S. F., 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=Light+Management+with+Nanostructures+for+Optoelectronic+Devices.">Light Management with Nanostructures for Optoelectronic Devices.</a> J. Phys. Chem. Lett. 5, 1479-1495 (2014).</li><li>Lee, C. Y., 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=White-light+electroluminescence+from+ZnO+nanorods/polyfluorene+by+solution-based+growth.">White-light electroluminescence from ZnO nanorods/polyfluorene by solution-based growth.</a> Nanotechology. 20 (42), (2009).</li></ol>

By utilizing the NRs interlayer, both the Jsc and the FF of the devices can be improved. However, the surface roughness of NRs will also influence the subsequent processes. Thus, the orientation and the surface morphology of the NRs should be carefully manipulated. For a long time, the sol-gel processed ETL such as TiO2 and ZnO were commonly used in PSCs due to their simple procedures. However, the crystallization of sol-gel processed layers is generally of the amorphous type, and the surface morpho...

Organic photovoltaic (OPV) devices have recently undergone remarkable developments in the application of renewable energy sources. Such organic devices have many advantages, including solution-process compatibility, low cost, light weight, flexibility, etc.1,2,3,4,5 Up until now, polymer solar cells (PSCs) with a PCE of more than 10% have been developed by utilizing the conjugated polymers blended with PC71BM6. Compared to polymer-based PSCs, small molecule-based OPVs (SM-OPVs) have attracted more attention when it comes to fabricating OPVs due to their several distinct advantages, including well-defined chemical structures, facile synthesis and purification, and generally higher open-circuit voltages (Voc)7,8,9. At present, a 2-D structure conjugated small molecule SMPV1 (2,6-Bis[2,5-bis(3-octylrhodanine)-(3,3-dioctyl-2,2&#39;:5,2&#39;&#39;-terthiophene)]-4,8-bis((5-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b&#39;]dithiophene) with BDT-T (benzo[1,2-b:4,5-b&#39;]dithiophene) as the core unit and 3-octylrodanine as the electron-withdrawing end-group10 has been designed and used to blend with PC71BM for promising sustainable OPVs application. The PCE of conventional small molecule solar cells (SM-OPVs) based on SMPV1 blended with PC71BM has reached more than 8.0%10,11.
In the past, PSCs could be enhanced and optimized simply by adjusting the thickness of the active layer. However, unlike PSCs, SM-OPVs in general have a shorter diffusion length, which greatly limits the thickness of the active layer. Hence, to further increase the short current density (Jsc) of SM-OPVs, utilizing the nano-structure12 or NRs9 to improve optical absorption of SM-OPVs became necessary.
Among these methods, the anti-reflection NRs structure is generally effective for light harvesting of the active layer over a broad range of wavelengths; therefore, knowing how to grow well-aligned vertically oriented zinc oxide (ZnO) NRs is very critical. The surface roughness of the seed layer below the ZnO NRs layer has a great influence on the orientation of the NR arrays; therefore, in order to deposit well-oriented NRs, the crystallization of the seed layer needs to be precisely controlled9.
In this work, the AZO films are prepared by theRadio-Frequency (RF) sputtering technique. Compared with other techniques, RF sputtering is known to be an efficient technology that is transferable to industry for it is a reliable deposition technique, which allows the synthesis of high purity, uniform, smooth, and self-sustainable AZO thin films to grow over large area substrates. Utilizing the RF sputtering deposition enables the forming of high quality AZO films that exhibit high crystallization with reduced roughness of surface. Therefore, in the subsequent growth layer, the orientations of the NRs are highly aligned, even more so when compared to ZnO films prepared by the sol-gel method. Using this technique, the PCE of the inverted small molecule solar cells based on well-aligned vertically oriented ZnO NR arrays can reach 6.01%.

<table>
	<tbody>
		<tr>
			<td>AZO target</td>
			<td>Ultimate Materials Technology Co., Ltd.</td>
			<td>none</td>
			<td>AZO (2 wt% Al2O3 in ZnO) , 3&#8221;&#968;x 3mmt 
			+ 3mmt Cu B/P + Bonding</td>
		</tr>
		<tr>
			<td>SMPV1</td>
			<td>Luminescence Technology Corp.</td>
			<td>1651168-29-4</td>
			<td>2,6-Bis[2,5-bis(3-octylrhodanine)-(3,3-dioctyl-2,2&#39;:5,2&#39;&#39;-terthiophene)]-4,8-bis((5-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b&#39;]dithiophene</td>
		</tr>
		<tr>
			<td>RF sputtering system</td>
			<td>Kao Duen Technology Co., Ltd</td>
			<td>none</td>
			<td>http://www.kaoduen.com.tw/index.php?action=product</td>
		</tr>
		<tr>
			<td>Zinc Acetate Dihydrate</td>
			<td>J. T. Baker</td>
			<td>5970456</td>
			<td>4.39 g</td>
		</tr>
		<tr>
			<td>Monoethanolamine</td>
			<td>J. T. Baker</td>
			<td>141435</td>
			<td>1.22 g</td>
		</tr>
		<tr>
			<td>2-methoxyethanol</td>
			<td>Sigma-Aldrich</td>
			<td>109864</td>
			<td>40 mL</td>
		</tr>
		<tr>
			<td>Zinc Nitrate Hexahydrate</td>
			<td>J. T. Baker</td>
			<td>10196186</td>
			<td>1.49 g</td>
		</tr>
		<tr>
			<td>Hexamethylenetetramine</td>
			<td>Sigma-Aldrich</td>
			<td>100-97-0</td>
			<td>0.7 g</td>
		</tr>
		<tr>
			<td>Indium tin oxide (ITO)</td>
			<td>RiTdisplay</td>
			<td>none</td>
			<td>coated glass substrates (&#60;10 &#937; sq&#8211;1)</td>
		</tr>
		<tr>
			<td>AFM</td>
			<td>Veeco</td>
			<td>Innova SPM</td>
			<td></td>
		</tr>
		<tr>
			<td>SEM</td>
			<td>FEI</td>
			<td>Nova 200 NanoSEM</td>
			<td>operation voltage: 10 kV</td>
		</tr>
		<tr>
			<td>XRD</td>
			<td>Bruker</td>
			<td>D8 X-ray diffractometer</td>
			<td>2&#952; range: 10&#8211;90 &#176;; step size: 0.008 &#176;</td>
		</tr>
		<tr>
			<td>PL</td>
			<td>Horiba</td>
			<td>Jobin-Yvon HR800</td>
			<td>excitation source: 325 nm UV Laser 20 mW</td>
		</tr>
		<tr>
			<td>solar simulator</td>
			<td>Newport</td>
			<td>91192A</td>
			<td>AM 1.5G</td>
		</tr>
		<tr>
			<td>Precision Semiconductor Parameter Analyzer</td>
			<td>Keysight Technologies</td>
			<td>Agilent 4156C</td>
			<td>sweep from -1 to +1 V</td>
		</tr>
		<tr>
			<td>toluene</td>
			<td>Sigma-Aldrich</td>
			<td>108-88-3</td>
			<td>1 mL</td>
		</tr>
		<tr>
			<td>PC71BM</td>
			<td>Sigma-Aldrich</td>
			<td>609771-63-3</td>
			<td>11.25 mg</td>
		</tr>
		<tr>
			<td>Thermal evaporation system</td>
			<td>Kao Duen Technology Co., Ltd</td>
			<td>Kao Duen PVD System</td>
			<td>http://www.kaoduen.com.tw/index.php?action=product</td>
		</tr>
		<tr>
			<td>HCl</td>
			<td>Sigma-Aldrich</td>
			<td>7647-01-0</td>
			<td></td>
		</tr>
		<tr>
			<td>MoO3</td>
			<td>Alfa Aesar</td>
			<td>1313-27-5</td>
			<td>99.50%</td>
		</tr>
		<tr>
			<td>silver ingot</td>
			<td>ADMAT Inc.</td>
			<td>none</td>
			<td>100.00%</td>
		</tr>
		<tr>
			<td>Thin Film Deposition Controller</td>
			<td>INFICON</td>
			<td>XTC</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-corrosion tape (Polyimide Film)</td>
			<td>3M Taiwan Corporation</td>
			<td>none</td>
			<td>http://solutions.3m.com.tw/wps/portal/3M/zh_TW/InsulatingTape/home/product/Polyimide/</td>
		</tr>
		<tr>
			<td>spin-coater</td>
			<td>Chemat Technology, Inc</td>
			<td>KW-4A</td>
			<td>http://www.chemat.com/chematscientific/KW-4A.aspx</td>
		</tr>
	</tbody>
</table>

well-aligned vertically oriented zno nanorod arrays and their application in inverted small molecule solar cells

This manuscript describes how to design and fabricate efficient inverted solar cells, which are based on a two-dimensional conjugated small molecule (SMPV1) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), by utilizing ZnO nanorods (NRs) grown on a high quality Al-doped ZnO (AZO) seed layer. The inverted SMPV1:PC71BM solar cells with ZnO NRs that grew on both a sputtered and sol-gel processed AZO seed layer are fabricated. Compared with the AZO thin film prepared by the sol-gel method, the sputtered AZO thin film exhibits better crystallization and lower surface roughness, according to X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. The orientation of the ZnO NRs grown on a sputtered AZO seed layer shows better vertical alignment, which is beneficial for the deposition of the subsequent active layer, forming better surface morphologies. Generally, the surface morphology of the active layer mainly dominates the fill factor (FF) of the devices. Consequently, the well-aligned ZnO NRs can be used to improve the carrier collection of the active layer and to increase the FF of the solar cells. Moreover, as an anti-reflection structure, it can also be utilized to enhance the light harvesting of the absorption layer, with the power conversion efficiency (PCE) of solar cells reaching 6.01%, higher than the sol-gel based solar cells with an efficiency of 4.74%.

The layered structure of the devices consisted of an ITO substrate/AZO (40 nm)/ZnO NRs layer, SMPV1:PC71BM (80 nm)/MoO3 (5 nm)/Ag (150 nm) as shown in Figure 1. In general, the AZO or ZnO seed layer is widely used to function as the electron transport layer (ETL) in PSCs devices. Apart from PSCs, SM-OPVs usually have a shorter active layer, limited by the shorter diffusion length8. Hence, to further improve the li...

Watch this Scientific Journal Video about Well-aligned Vertically Oriented ZnO Nanorod Arrays and their Application in Inverted Small Molecule Solar Cells at JoVE.com

Well-aligned Vertically Oriented ZnO Nanorod Arrays and their Application in Inverted Small Molecule Solar Cells

This manuscript describes how to design and fabricate efficient inverted SMPV1:PC71BM solar cells with ZnO nanorods (NRs) grown on a high quality Al-doped ZnO (AZO) seed layer. The well-aligned vertically oriented ZnO NRs exhibit high crystalline properties. The power conversion efficiency of solar cells can reach 6.01%.

This manuscript describes how to design and fabricate efficient inverted solar cells, which are based on a two-dimensional conjugated small molecule ...

The overall goal of this research is to observe the optical and electrical effects of small molecular solar cells using well-aligned vertically oriented zinc oxide nanorods. Demonstrating the NR growth procedure will be Shang-Hsuan Wu, a research assistant from our lab. A PhD candidate, Widhya Budiawan, will demonstrate device fabrication and measurement.This method can help answer key questions in the energy harvesting field such as how to increase efficiency of cells and organic photovoltaic devices. The main advantage of this technique is that the process is very low-cost and very compatible with most of the electronic devices. Gather the materials to prepare the substrates.There should be a sonicator and sources of deionized water, acetone, ethanol, and isopropanol. Also have anti-corrosion tape and a hydrochloric acid bath. Obtain a substrate and begin work.This idium tin oxide substrate measures approximately 1.5 centimeters squared. Apply anti-corrosion tape to form a square on one of its sides. At this point, put the substrate into hydrochloric acid to etch it.After 15 minutes, retrieve the substrate. Before proceeding, remove the anti-corrosion tape from the substrate. Then put the substrate into a beaker of deionized water.Move the beaker to a sonicator and begin sonication. After 30 minutes.

well-aligned-vertically-oriented-zno-nanorod-arrays-their-application

Research

JoVE Journal

Engineering

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.
Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4.
To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO2 films. In this configuration, photoinduced electrons are injected into TiO2 and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer6. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells7.

A general strategy for the development of charge-separating semiconductor nanocrystal composites deployable for solar energy production is presented. We show that assembly of donor-acceptor nanocrystal domains in a single nanoparticle geometry gives rise to a photocatalytic function, while bulk-heterojunctions of donor-acceptor nanocrystal films can be used for photovoltaic energy conversion.

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

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 ...

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we ...

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 ...

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 ...