Name: printing fabrication of bulk heterojunction solar cells and in situ morphology characterization
Uploaded: 2017-01-29T14:00:00
Description: Watch this Scientific Journal Video about Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization at JoVE.com

This work was supported by Polymer-Based Materials for Harvesting Solar Energy (PHaSE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under award number DE-SC0001087 and the U.S. Office of Naval Research under contract N00014-15-1-2244. Portions of this research were carried out at beamline 7.3.3 and 11.0.1.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory, which was supported by the DOE, Office of Science, and Office of Basic Energy Sciences.

1. Photon-active Blend Ink Preparation
<ol>
	<li>Weigh 10 mg of DPPBT polymer and 10 mg of PC71BM material (chemical structures shown in Figure 1). Mix them in a 4 ml vial.</li>
	<li>Add 1.5 ml chloroform and 75 &#181;l of 1,2-dichlorobenzene into the mixture.</li>
	<li>Put a small stir bar into the vial, close the vial with a polytetrafluoroethylene (PTFE) cap, and transfer the vial to a hot plate. Stir at ~400 rpm, and heat at ~50 &#176;C overnight before use.</li>
</ol>
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<ol>
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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-Length-Scale+Morphologies+in+PCPDTBT/PCBM+Bulk-Heterojunction+Solar+Cells.">Multi-Length-Scale Morphologies in PCPDTBT/PCBM Bulk-Heterojunction Solar Cells.</a> Adv. Energy Mater. 2 (6), 683-690 (2012).</li><li>Perez, L. 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=Solvent+Additive+Effects+on+Small+Molecule+Crystallization+in+Bulk+Heterojunction+Solar+Cells+Probed+During+Spin+Casting.">Solvent Additive Effects on Small Molecule Crystallization in Bulk Heterojunction Solar Cells Probed During Spin Casting.</a> Adv. Mater. 25 (44), 6380-6384 (2013).</li><li>Lee, J. 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Mater. 24 (29), 3947-3951 (2012).</li><li>Liu, 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=Relating+Chemical+Structure+to+Device+Performance+via+Morphology+Control+in+Diketopyrrolopyrrole-Based+Low+Band+Gap+Polymers.">Relating Chemical Structure to Device Performance via Morphology Control in Diketopyrrolopyrrole-Based Low Band Gap Polymers.</a> J. Am. Chem. Soc. 135 (51), 19248-19259 (2013).</li><li>Liu, 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=Fast+Printing+and+In+Situ+Morphology+Observation+of+Organic+Photovoltaics+Using+Slot-Die+Coating.">Fast Printing and In Situ Morphology Observation of Organic Photovoltaics Using Slot-Die Coating.</a> Adv. Mater. 27 (5), 886-891 (2015).</li></ol>

The method described here focuses on developing a film preparation method that can be easily scaled up in industrial production. Thin film printing and synchrotron morphology characterization are the most critical steps with the protocol. In previous lab scaled OPV research, spin coating is used as the dominant method to fabricate thin film devices. However, this process uses high centrifuge force to spread out BHJ solution, which is quite different from industrial based roll-to-roll fabrication. Thus the knowledge and e...

Organic photovoltaics (OPV) are a promising technology to produce cost-effective renewable energies in the near future.1,2,3 Tremendous efforts have been made to develop photo-active polymers and fabricate high efficiency devices. To date, single layered OPV devices have achieved a &#62;10% power conversion efficiency (PCE). These efficiencies have been achieved on laboratory scale devices using spin coating to generate the film, and translation to larger size scale devices has been fraught with significant reductions in the PCE.4,5 In industry, roll-to-roll (R2R) based thin film coating is used to generate photon active thin films on conductive substrates, which is quite different from typical laboratory-scale processes, particularly in the rate of solvent removal. This is critical since the morphologies are kinetically trapped, resulting from the interplay between multiple kinetic processes, including phase separation, ordering, orientation and solvent evaporation.6,7 This kinetically trapped morphology, though, largely determines the performance of the solar cell devices. Thus, understanding the development of the morphology during the coating process is of high importance for manipulating the morphology so as to optimize performance.
The optimization of the morphology requires understanding the kinetics associated with the ordering of the hole-conducting polymer in solution as solvent is removed;8,9 quantifying the interactions of the polymer with the fullerene-based electron conductor;10,11,12 understanding the roles of additives in defining the morphology;13,14,15 and balancing the relative rates of evaporation of the solvent(s) and additives.16 It has been a challenge to characterize the evolution of the morphology quantitatively in the active layer in an industrially relevant setting. Roll-to-roll processing has been studied for the fabrication of large scale OPV devices.4,17 However, these studies were performed in a manufacturing setting where large quantities of materials are used, effectively limiting studies to commercially available polymers.
In this paper, the technical details of fabricating OPV devices using a mini-slot die coating system are demonstrated. Coating parameters such as film drying kinetics and film thickness control are applicable to larger scale processes, making this study directly related to industry fabrication. Besides, a very small amount of material is used in the mini slot die coating experiment, making this processing applicable to new synthetic materials. In design, this mini-slot die coater can be mounted onto synchrotron end stations, and thus grazing incidence small angle X-ray scattering (GISAXS) and X-ray diffraction (GIXD) can be used to enable real-time studies on the evolution of the morphology over a wide range of length scales at different stages of the film drying process under a range of processing conditions. Information obtained in these studies can be directly transferred to an industrial manufacturing setting. The small amount of materials used enables a rapid screening of a large number of photo-active materials and their mixtures under various processing conditions.
The semi-crystalline diketopyrrolopyrrole and quaterthiophene (DPPBT) based low band conjugated polymer is used as the model donor material, and (6,6)-phenyl C71-butyric acid methyl ester (PC71BM) is used as the electronic acceptor.18,19 It is shown in previous studies that DPPBT:PC71BM blends form large size phase separation when using chloroform as the solvent. A chloroform:1,2-dichlorobenzene solvent mixture can reduce the size of phase separation and thus increase the device performance. The morphology formation during the solvent drying process is investigated in situ by grazing incidence X-ray diffraction and scattering. Solar cell devices fabricated using the mini-slot die coater showed an average PCE of 5.2% using the best solvent mixture conditions,20 which is similar to spin-coating fabricated devices. The mini-slot die coater opens a new route to fabricate solar cell devices in a research laboratory setting that mimics an industrial process, filling a gap in the predicting the viability of these materials in an industrially relevant setting.

<table border="0" cellpadding="0" cellspacing="0" width="787">
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		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">PC71BM</td>
			<td style="width:263px;">Nano-C Inc</td>
			<td style="width:184px;">nano-c-PCBM-SF</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">DPPBT</td>
			<td style="width:263px;">The University of Massachusetts</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">PEDOT:PSS</td>
			<td style="width:263px;">Heraeus</td>
			<td style="width:184px;">P VP Al 4083</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Mucasol Liquid Cleaner</td>
			<td style="width:263px;">Sigma-Aldrich</td>
			<td style="width:184px;">Z637181</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Acetone</td>
			<td style="width:263px;">Sigma-Aldrich</td>
			<td style="width:184px;">270725</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Isopropyl Alcohol</td>
			<td style="width:263px;">BDH</td>
			<td style="width:184px;">BDH1133</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Chloroform</td>
			<td style="width:263px;">Sigma-Aldrich</td>
			<td style="width:184px;">372978&#160;</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">1,2-diChlorobenzene</td>
			<td style="width:263px;">Sigma-Aldrich</td>
			<td style="width:184px;">240664</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Lithium fluoride</td>
			<td style="width:263px;">Sigma-Aldrich</td>
			<td style="width:184px;">669431</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Aluminum</td>
			<td style="width:263px;">Kurt Lesker</td>
			<td style="width:184px;">EVMAL50QXHD</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Glass vials</td>
			<td style="width:263px;">Fisher Scientific</td>
			<td style="width:184px;">03-391-7B</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Ultrasonic Cleaner</td>
			<td style="width:263px;">Cleanosonic</td>
			<td style="width:184px;">Branson 2800</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Oven</td>
			<td style="width:263px;">WVR</td>
			<td style="width:184px;">414005-118</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Cleaning Rack</td>
			<td style="width:263px;">Lawrence Berkeley National Lab</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Shadow Mask</td>
			<td style="width:263px;">Lawrence Berkeley National Lab</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">UV-Ozone Cleaner</td>
			<td style="width:263px;">UVOCS INC</td>
			<td style="width:184px;">T16X16 OES</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Glove Box</td>
			<td style="width:263px;">MBraun</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Evaporator</td>
			<td style="width:263px;">MBraun</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Slot Die Coater</td>
			<td style="width:263px;">Jema Science Inc</td>
			<td style="width:184px;">Custom Made</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Solar Simulator</td>
			<td style="width:263px;">Newport</td>
			<td style="width:184px;">Class ABB</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Spin Coater</td>
			<td style="width:263px;">SCS Equipment</td>
			<td style="width:184px;">SCS G3</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">Hot Plate</td>
			<td style="width:263px;">Thermo Scientific</td>
			<td style="width:184px;">SP131015Q</td>
			<td style="width:149px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:191px;">X-ray Measurement</td>
			<td style="width:263px;">Lawrence Berkeley National Lab</td>
			<td style="width:184px;">Beamline 7.3.3</td>
			<td style="width:149px;"></td>
		</tr>
	</tbody>
</table>

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.

Shown in Figure 3 is the mini-slot die coating system. It consists of one coating machine, one syringe pump and a central control box. The coating machine is the essential part, which is made of a slot die head, one horizontal translational stage, and one vertical translational stage. The slot die head is mounted to the base of a vertical translational motor through a 2-D tilting manipulator. Figure 10a shows the printer main body without mounting the pri...

Watch this Scientific Journal Video about Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization at JoVE.com

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.

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 ...

The overall goal of this experiment is to demonstrate the printing fabrication of organic thin film solar cells and to observe the thin film morphology evolution during solvent evaporation. This method help answer key questions in functional thin films such as in thin film solar cells and polymer coatings. The main advantage of this technique is that industry processing and synchrotron techniques are well merged to demonstrate the fundamental aspect of the material science.The implication of this method help understand the morphology evolution of adjoining thin films, which is crucial in determining the final morphology and device performance. So this technique can give us information in the morphology of thin film organic photovoltaics. It could also give us information in other materials, for example, light-emitting diodes or functional thin film materials.To load the substrate, put the prepared PEDOT:PSS coated indium-tin-oxide substrate onto the base plate of the mini-slot die coater. Using the linear manipulator beneath the substrate plate, adjust the position of the substrate to put it right beneath the printer head. Adjust the head tilting using the two-dimensional tilting manipulator that holds the printing head.Make sure that the head stands vertically on top of the loaded substrate. Tune the head to substrate distance to zero. The vertical motor is coupled with a force sensor.When the printing head is floating, a constant force reading will be obtained from the weight of the printing head and the tilting manipulator assemblies. Once the printer head touches the substrate, the reading will reduce, marking the zero position. Set a head to substrate value to run the experiment.In this experiment, set the head to substrate gap to 100 microns. Next, adjust the linear translational stage motor that will be used to print. Set the 10 millimeter motor position as the starting point, and the 80 millimeter motor position as the end point.Set the printing speed to 10 millimeters per second by using the motor controlling software interface. Set the motor acceleration speed to 100 meters per second. Load the OPV ink into a one milliliter syringe, and mount the syringe to the syringe pump that is connected to the slot die printer.Set the printing parameters in the controlling software. To start the printing experiment, type the starting point position in the position window in the controlling software. This action will move the substrate to the starting point.Start to pump the solution into the slot die head by clicking start in the syringe pump software. Quickly start the translational motor when the solution starts coming out from the printing head. The substrate will move to the end position.Stop the syringe pump and lift the printing head by using the vertical motor. Turn the vacuum off, and take the substrate off the base plate. Load the printed substrate into a vacuum oven for three to five hours to remove residual solvent.Next put a Petri dish beneath the printing head. Pump 10 milliliters of chloroform into the printing head to clean it. Collect the contaminated chloroform solution with the Petri dish.Set up a helium box to suppress air scattering in the x-ray measurement. Mount the mini slot die coater into the helium box. Mount an optical interferometer onto the printing machine to monitor the thickness change over the solvent evaporation.Put the PEDOT:PSS coated wafer substrate onto the substrate holder of the printer, and adjust the head and substrate position as before. Purge the helium box to remove the air. The oxygen level should be less than 0.3%which can be monitored by an oxygen sensor.Align the substrate at the position where the x-ray impinges on the substrate, and set the incidence angle, which is 0.16 degrees in this case. Set the x-ray exposure time in the data acquisition method. Here, use two seconds as the exposure time, followed by three seconds of delay time to avoid server beam damage.Thus, each experiment period is five seconds. Carry out a continuous queue of 100 repeats taking 100 pictures. Name the experiment and choose the data path to save the experimental files.Move the substrate to the starting position by entering the starting position in the motor controlling software. Start the x-ray shutter, and the detector will continuously record diffraction and scattering signals. Next, start the syringe pump to feed solution into the printing head.When the solution begins to eject from the printing head as monitored by a surveillance camera, quickly start the printing process. When the pre-chosen measurement position is reached, the two-dimensional detector will capture the scattering signal from the solution. Film thickness will be monitored by an interferometer.Thus, the thin film morphology evolution will be recorded. Lift up the printer head and clean the head when the experiment is done. Shown here is an ITO substrate coated with conjugated polymer PCBM blends.The film is quite smooth visually. The beginning and end of the coated film is not always uniform due to the formed meniscus and the drying from the edges. The freshly coated substrate is eventually loaded into shadow masks.The mask is loaded into an evaporator to deposit the cathode thin layer. Shown here is a completed device after the cathode layer deposition. The device performance is measured using a solar simulator under 100 milliwatts per square centimeter.Here is a representative current voltage curve of a mini-slot die coated device. An average power conversion efficient of 5.2%is achieved for slot die coated devices, which is close to that achieved by spin coating. This figure represents a typical in situ grazing incidence small angle scattering experiment during solvent drying.The time evolution is color coded. In the earlier stage of drying where an excess of solvent existed, a red scattering curve is seen and the blends mixed well. A scattering peak gradually developed at around 0.02 inverse angstroms, indicating approximately 60 nanometers of phase separation.This information, when coupled with in situ x-ray diffraction results, reveals the kinetics of polymer crystallization and phase separation. Once mastered this technique can be done in about five minutes if conducted properly. While attempted these experiments, it is important to remember that for each material system we have to find the ideal condition.This has to be optimized for every experiment. This method paved the way for the researchers in thin film solar cells to explore the structure and property relationship in industrial manufacturing. After watching this video, you should have a very good understanding of how to conduct an in situ printing experiment at a synchrotron beamline.

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Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

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 ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

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 ...

Morphology Control for Fully Printable Organic&#8211;Inorganic Bulk-heterojunction Solar Cells Based on a Ti-alkoxide and Semiconducting Polymer

The photoactive layer of a typical organic thin-film bulk-heterojunction (BHJ) solar cell commonly uses fullerene derivatives as the electron-accepting material. However, fullerene derivatives are air-sensitive; therefore, air-stable material is needed as an alternative. In the present study, we propose and describe the properties of Ti-alkoxide as an alternative electron-accepting material to fullerene derivatives to create highly air-stable BHJ solar cells. It is well-known that controlling the morphology in the photoactive layer, which is constructed with fullerene derivatives as the electron acceptor, is important for obtaining a high overall efficiency through the solvent method. The conventional solvent method is useful for high-solubility materials, such as fullerene derivatives. However, for Ti-alkoxides, the conventional solvent method is insufficient, because they only dissolve in specific solvents. Here, we demonstrate a new approach to morphology control that uses the molecular bulkiness of Ti-alkoxides without the conventional solvent method. That is, this method is one approach to obtain highly efficient, air-stable, organic-inorganic bulk-heterojunction solar cells.

A method for fully printable, fullerene-free, highly air-stable, bulk-heterojunction solar cells based on Ti alkoxides as the electron acceptor and the electron-donating polymer fabrication is described here. Moreover, a method for controlling the morphology of the photoactive layer through the molecular bulkiness of the Ti-alkoxide units is reported.

The photoactive layer of a typical organic thin-film bulk-heterojunction (BHJ) solar cell commonly uses fullerene derivatives as the electron-accepting ...

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 ...

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 ...

Developing High Performance GaP/Si Heterojunction Solar Cells

To improve the efficiency of Si-based solar cells beyond their Shockley-Queisser limit, the optimal path is to integrate them with III-V-based solar cells. In this work, we present high performance GaP/Si heterojunction solar cells with a high Si minority-carrier lifetime and high crystal quality of epitaxial GaP layers. It is shown that by applying phosphorus (P)-diffusion layers into the Si substrate and a SiNx layer, the Si minority-carrier lifetime can be well-maintained during the GaP growth in the molecular beam epitaxy (MBE). By controlling the growth conditions, the high crystal quality of GaP was grown on the P-rich Si surface. The film quality is characterized by atomic force microscopy and high-resolution x-ray diffraction. In addition, MoOx was implemented as a hole-selective contact that led to a significant increase in the short-circuit current density. The achieved high device performance of the GaP/Si heterojunction solar cells establishes a path for further enhancement of the performance of Si-based photovoltaic devices.

Here, we present a protocol to develop high-performance GaP/Si heterojunction solar cells with a high Si minority-carrier lifetime.

To improve the efficiency of Si-based solar cells beyond their Shockley-Queisser limit, the optimal path is to integrate them with III-V-based solar ...