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>
<p class="jove_tit...

<ol>
	<li>Brabec, C. 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=Polymer-Fullerene+Bulk-Heterojunction+Solar+Cells.">Polymer-Fullerene Bulk-Heterojunction Solar Cells.</a> Adv. Mater. 22 (34), 3839-3856 (2010).</li><li>Thompson, B. C., Fr&#233;chet, J. M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer-Fullerene+Composite+Solar+Cells.">Polymer-Fullerene Composite Solar Cells.</a> Angew. Chem. Int. Ed. 47 (1), 58-77 (2008).</li><li>G&#252;nes, S., Neugebauer, H., Sariciftci, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conjugated+Polymer-Based+Organic+Solar+Cells.">Conjugated Polymer-Based Organic Solar Cells.</a> Chem. Rev. 107 (4), 1324-1338 (2007).</li><li>Krebs, F. 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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">
	<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...

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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10.1K vistas.  Lawrence Berkeley National Laboratory. 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 implicat...