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>
2. ITO and Wafer Substrate Cleaning and Preparation
<ol>
	<li>Load pre-patterned indium tin oxide (ITO) glass substrate (1 inch by 3 inches, with half removed ITO) or silicon wafer into a Teflon cleaning rack and put the rack into a glass container (Figure 2). Add dilute detergent solution (300 ml, 1% universal detergent solution) into the glass container and put the glass container into sonicator and sonicate for 15 min.</li>
	<li>Remove the detergent and rinse the ITO glass with deionized (DI) water a couple of times. Then add 300 ml DI water into the container, and put the glass container into sonicator for another 15 minutes.</li>
	<li>Remove the water from the container. Add 300 ml acetone into the container, and sonicate for 15 min.</li>
	<li>Remove the acetone. Add 300 ml 2-isopranol into the glass container, and then sonicate for 15 min.</li>
	<li>Move the cleaning rack out into an oven. Set the oven temperature to 100 &#176;C, and wait 3-5 hr until the ITO glass is completely dried.</li>
	<li>Take out cleaned substrates. Transfer them into an UV-ozone cleaner or oxygen plasma cleaner. Use high-powered UV-ozone or plasma to clean them for ~15 min according to manufacturer&#39;s protocol.</li>
	<li>Put the cleaned substrate onto a spin-coater, add 150 &#181;l poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) solution onto the cleaned substrate, and spin coat at 3,000 rpm to coat a ~30 nm thick PEDOT:PSS (PEDOT:PSS 4083) thin film onto either the ITO glass or silicon wafers.</li>
	<li>Take off spin coated substrates. Transfer the fresh coated substrates onto a heating plate and anneal at 150 &#176;C for 15 min.</li>
</ol>
3. Active Layer Printing
<ol>
	<li>Load substrate. Put the PEDOT:PSS coated ITO substrate onto the base plate of mini slot die coater. Turn on the vacuum pump that is connected to the vacuum chuck of the slot die coater to hold the substrate tightly. (See Figure 3 to locate different components.)</li>
	<li>Adjust the position of substrate to put it right beneath printer head. This can be done by using the linear manipulator beneath the substrate plate.</li>
	<li>Adjust the head tilting using the 2-D tilting manipulator that holds the printing head. Make sure that the head stands vertically on top of the loaded substrate. Note that in this process, the printing head can be lowered close to the substrate. Use the gap between printing head and substrate to show whether the head is tilted or not. This will be extremely useful when a wafer substrate is used, since a minor image of printing head will show up and it will be much easier to check the tilting.</li>
	<li>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 printing head and tilting manipulator assemblies). Once printer head touches substrate, the reading will reduce, marking the zero position. See Figure 4 for the step distance setting. Use jog mode in tuning the distance. 
	NOTE: The vertical manipulator translational plate is connected to its base using springs and the spring constant varies slightly. Thus small changes in force sensor are inevitable during the experiment.</li>
	<li>Set a head-to-substrate value to run the experiment. In this experiment, set the head to substrate gap to 100 &#181;m.</li>
	<li>Adjust the linear translational stage motor that will be used to print. Find the starting point and end point. Record these values. The travel distance of the linear motor is 100 mm. Here, set 10 mm motor position as the starting point and 80 mm motor position as the end point.</li>
	<li>Set the printing speed to 10 mm/sec by using the motor controlling software interface (Figure 4b). Set the motor acceleration speed to 100 m/sec.
	<ol>
		<li>If the motor does not work properly or the software has an error, please restart the software and click &#34;enable&#34; and then &#34;home&#34; in the software interface. Note that during printing process, the printing head remains fixed and the substrate moves to dispense the solution and mimic the industrial printing process.</li>
	</ol>
	</li>
	<li>Load DPPBT:PCBM solution (room temperature) into 1 ml syringe and mount the syringe to the syringe pump that is connected to the slot die printer. Set the printing parameters in controlling software (syringe diameter and solution feeding speed, 0.3 ml/min in this case).</li>
	<li>Start the printing experiment.
	<ol>
		<li>Move the substrate to the starting point by typing the starting point position in the position window in controlling software. See Figure 4c for details.</li>
		<li>Start to pump solution into slot die head by clicking the start in the syringe pump software. Alternatively, manually operate the syringe pump. For each coating, around ~100 &#181;l of solution will be used. Normally, use 300 &#181;l solution for first time printing and use ~100 &#181;l solution for repeated printing.</li>
		<li>Quickly start the translational motor when the solution starts coming out from the printing head, and the substrate will move to the end position. Please note this is a critical step. Preload the translational motor ending position into the position window, and click enter to start the motor movement.</li>
		<li>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. Note that the dead volume for this printing head is 250 &#181;l, and thus filling the first time takes more than 250 &#181;l of solution.</li>
		<li>Load the printed substrate into a vacuum oven for 3-5 hr to remove residual solvent.</li>
		<li>Put a Petri dish beneath the printing head. Pump 10 ml chloroform into the printing head to clean the head. Collect the contaminated chloroform solution with the Petri dish. Use cotton swabs to clean the printing head while pumping the cleaning solution. After each coating run, clean the printing head, especially when a different solution is used. 
		NOTE: The DPPBT:PCBM solution shows a dark green color. When the cleaning is complete, no color can be seen from the chloroform solvent.</li>
	</ol>
	</li>
</ol>
4. Cathode Electrode Deposition
<ol>
	<li>Load the active layer coated substrate onto shadow masks (Figure 5) and mount the mask into the evaporation chamber.</li>
	<li>Put two thermal evaporation boats in between the electrode studs (Figure 6a). Load one boat with LiF salt (barely covering the boat, ~0.2 g) and one boat with aluminum metal (4 pellets).</li>
	<li>Close the evaporation chamber and pump down the evaporation chamber to about 2 x 10-6 Torr.</li>
	<li>Set the chamber to deposit 1 nm of LiF followed by 100 nm of aluminum. In the current case, use 20% power for LiF deposition and use 26% power for Al deposition. Shown in Figure 6b is the evaporator control interface of the system used in this study.</li>
	<li>Stop evacuation pumps and fill the chamber with nitrogen gas. When pressure returns to atmosphere pressure, take the substrates out.</li>
</ol>
5. Photovoltaic Performance Measurement
<ol>
	<li>Prepare a glass slide that is half the width of the ITO glass that is used in device fabrication. Carry out this step in a glove box. Paste epoxy glue to one side of the glass substrate, and cover the device area using the epoxy glue coated glass slides (see Figure 11 for sample device). When the epoxy has cured, the device will be fully sealed.</li>
	<li>Start the solar simulation lamp and set to AM 1.5 radiation with 100 mW/cm2. Stabilize the lamp for about 15 min before measurement. Shown in Figure 7 is the PV measurement system used in this study.</li>
	<li>Mount the device under the solar simulator at the instrument suggested distance. Connect the anode and the cathode to the measurement circuit. Record a current-voltage curve using an electrical multimeter using manufacturer&#39;s protocol.</li>
	<li>Determine the performance of the device as follows: 
	Jsc: short circuit current, the maximum current that a solar cell device can deliver; 
	Voc: open circuit voltage, the maximum voltage that a solar cell device can deliver; 
	FF: fill factor, the maximum area in I-V curve divided by Jsc* Voc; 
	PCE: power conversion efficiency, Jsc* Voc*FF/(100mW/cm2).</li>
</ol>
6. Synchrotron X-ray Measurement
<ol>
	<li>Set up a helium box to suppress air scattering in the X-ray measurement. Mount the mini-slot die coater into the helium box. Shown in Figure 8 is the experiment setup of grazing incidence X-ray diffraction experiments using a helium box at Advanced Light Source.</li>
	<li>Mount an optical interferometer onto the printing machine to monitor the thickness change over the solvent evaporation. In this experiment, use an UVX model (e.g., Filmetrix F20). The materials that are used in this experiment have strong light absorption from 300-900 nm wavelength.
	<ol>
		<li>Use a source lamp of optical interferometer that avoids material absorption. Use an 1,100-1,700 nm wavelength lamp in this experiment. Pre-calibrate the instrument before experiment following its operation procedures.</li>
	</ol>
	</li>
	<li>Put the PEDOT:PSS coated wafer substrate onto substrate holder of the printer and adjust the head and substrate position following step 3.2-3.5. Turn on the vacuum pump and make sure that the wafer substrate sticks to the substrate holder tightly.</li>
	<li>Purge the helium box to remove air. Note that oxygen level should be less than 0.3 v%, which can be monitored by oxygen sensor.</li>
	<li>Align the substrate at the position where the X-ray impinges on the substrate (the end position in printing), and set the incidence angle, 0.16&#176; in this case. Align according to beam-line protocol.</li>
	<li>Set the X-ray exposure time and data acquisition method. Here, use 2 sec as the exposure time, and followed by 3 sec of delay time (to avoid server beam damage). Thus each experiment period will be 5 sec. Carry out a continuous queue of 100 repeats; thus take 100 pictures.</li>
	<li>Name the experiment and choose the data path to save experimental files. Shown in Figure 9 is the Advanced Light Source beamline 7.3.3 user interface where the above-mentioned settings can be easily located.</li>
	<li>Move the substrate to the starting position by entering the starting position in motor controlling software. Start the X-ray shutter and the detector will continuously record diffraction/scattering signals.</li>
	<li>Start the syringe pump to feed solution into printing head. When the solution begins to eject from the printing head (monitored by a surveillance camera), quickly start the printing process. 
	NOTE: When the pre-chosen measurement position is reached, 2-D detector will capture the scattering signal from solution. Film thickness will be monitored by interferometer. Thus the thin film morphology evolution will be recorded.</li>
	<li>Lift up the printer head and clean the head when experiment is done.</li>
</ol>

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The authors have nothing to disclose.

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">
	<colgroup>
		<col />
		<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...

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

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 ...

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10.2K Views.  Lawrence Berkeley National Laboratory. 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.

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

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 ...

Patterning via Optical Saturable Transitions - Fabrication and Characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

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 ...

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 ...