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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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 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><tbody><tr><td>PC&lt;sub&gt;71&lt;/sub&gt;BM</td><td>Nano-C Inc</td><td>nano-c-PCBM-SF</td><td></td></tr><tr><td>DPPBT</td><td>The University of Massachusetts</td><td>Custom Made</td><td></td></tr><tr><td>PEDOT:PSS</td><td>Heraeus</td><td>P VP Al 4083</td><td></td></tr><tr><td>Mucasol Liquid Cleaner</td><td>Sigma-Aldrich</td><td>Z637181</td><td></td></tr><tr><td>Acetone</td><td>Sigma-Aldrich</td><td>270725</td><td></td></tr><tr><td>Isopropyl Alcohol</td><td>BDH</td><td>BDH1133</td><td></td></tr><tr><td>Chloroform</td><td>Sigma-Aldrich</td><td>372978&amp;nbsp;</td><td></td></tr><tr><td>1,2-dichlorobenzene</td><td>Sigma-Aldrich</td><td>240664</td><td></td></tr><tr><td>Lithium fluoride</td><td>Sigma-Aldrich</td><td>669431</td><td></td></tr><tr><td>Aluminum</td><td>Kurt Lesker</td><td>EVMAL50QXHD</td><td></td></tr><tr><td>Glass vials</td><td>Fisher Scientific</td><td>03-391-7B</td><td></td></tr><tr><td>Ultrasonic Cleaner</td><td>Cleanosonic</td><td>Branson 2800</td><td></td></tr><tr><td>Oven</td><td>WVR</td><td>414005-118</td><td></td></tr><tr><td>Cleaning Rack</td><td>Lawrence Berkeley National Lab</td><td>Custom Made</td><td></td></tr><tr><td>Shadow Mask</td><td>Lawrence Berkeley National Lab</td><td>Custom Made</td><td></td></tr><tr><td>UV-Ozone Cleaner</td><td>UVOCS INC</td><td>T16X16 OES</td><td></td></tr><tr><td>Glove Box</td><td>MBraun</td><td>Custom Made</td><td></td></tr><tr><td>Evaporator</td><td>MBraun</td><td>Custom Made</td><td></td></tr><tr><td>Slot Die Coater</td><td>Jema Science Inc</td><td>Custom Made</td><td></td></tr><tr><td>Solar Simulator</td><td>Newport</td><td>Class ABB</td><td></td></tr><tr><td>Spin Coater</td><td>SCS Equipment</td><td>SCS G3</td><td></td></tr><tr><td>Hot Plate</td><td>Thermo Scientific</td><td>SP131015Q</td><td></td></tr><tr><td>X-ray Measurement</td><td>Lawrence Berkeley National Lab</td><td>Beamline 7.3.3</td><td></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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10.5K Views.  Lawrence Berkeley National Laboratory.  Hier presenteren we een protocol om organische dunne film zonnecellen met behulp van een mini-slot sterven coater en de bijbehorende in-line structuur karakteriseringen met behulp van synchrotronstraling scattering technieken te fabriceren. 

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

Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped crystallites. Neutrons are passed through two well defined regions of magnetic field; one before and one after the sample. The two magnetic field regions have opposite polarity and are tuned such that neutrons travelling through both regions, without being perturbed, will undergo the same number of precessions in opposing directions. In this case the neutron precession in the second arm is said to &#34;echo&#34; the first, and the original polarization of the beam is preserved. If the neutron interacts with a sample and scatters elastically the path through the second arm is not the same as the first and the original polarization is not recovered. Depolarization of the neutron beam is a highly sensitive probe at very small angles (&#60;50&#160;&#956;rad) but still allows a high intensity, divergent beam to be used. The decrease in polarization of the beam reflected from the sample as compared to that from the reference sample can be directly related to structure within the sample.
In comparison to scattering observed in neutron reflection measurements the SERGIS signals are often weak and are unlikely to be observed if the in-plane structures within the sample under investigation are dilute, disordered, small in size and polydisperse or the neutron scattering contrast is low. Therefore, good results will most likely be obtained using the SERGIS technique if the sample being measured consist of thin films on a flat substrate and contain scattering features that contains a high density of moderately sized features (30 nm to 5 &#181;m) which scatter neutrons strongly or the features are arranged on a lattice. An advantage of the SERGIS technique is that it can probe structures in the plane of the sample.

Progress has been made in utilizing spin echo resolved grazing incidence scattering (SERGIS) as a neutron scattering technique to probe the length-scales in irregular samples. Crystallites of [6,6]-phenyl-C61-butyric acid methyl ester have been probed using the SERGIS technique and the results confirmed by optical and atomic force microscopy.

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped ...

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

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

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

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

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 ...

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 ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Influence of Hybrid Perovskite Fabrication Methods on Film Formation, Electronic Structure, and Solar Cell Performance

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to achieve device efficiencies exceeding other thin film device technologies. Yet, large variations in device efficiency and basic physical properties are reported. This is due to unintentional variations during film processing, which have not been sufficiently investigated so far. We therefore conducted an extensive study of the morphology and electronic structure of a large number of CH3NH3PbI3 perovskite where we show how the preparation method as well as the mixing ratio of educts methylammonium iodide and lead(II) iodide impact properties like film formation, crystal structure, density of states, energy levels, and ultimately the solar cell performance.

We present an extensive study on the effects of different fabrication methods for organic/inorganic perovskite thin films by comparing crystal structures, density of states, energy levels, and ultimately the solar cell performance.

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to ...

Chemistry

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 ...

Inkjet Printing All Inorganic Halide Perovskite Inks for Photovoltaic Applications

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are demonstrated. The ink synthesis is based on a simple wet chemical reaction and the inkjet printing protocol is a facile step by step method. The inkjet printed thin films have been characterized by X-ray diffraction, optical absorption spectroscopy, photoluminescent spectroscopy, and electronic transport measurements. X-ray diffraction of the printed quantum dot films indicates a crystal structure consistent with an orthorhombic room temperature phase with (001) orientation. In conjunction with other characterization methods, the X-ray diffraction&#160;measurements show high quality films can be obtained through the inkjet printing method.

A protocol for synthesizing inorganic-lead-halide hybrid perovskite quantum dot inks for inkjet printing and the protocol for preparing and printing the quantum dot inks in an inkjet printer with post characterization techniques are presented.

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are ...

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 ...

In situ Grazing Incidence Small Angle X-ray Scattering on Roll-To-Roll Coating of Organic Solar Cells with Laboratory X-ray Instrumentation

We present an in-house, in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS) experiment, developed to probe the drying kinetics of roll-to-roll slot-die coating of the active layer in organic photovoltaics (OPVs), during deposition. For this demonstration, the focus is on the combination of P3HT:O-IDTBR and P3HT:EH-IDTBR, which have different drying kinetics and device performance, despite their chemical structure only varying slightly by the sidechain of the small molecule acceptor. This article provides a step-by-step guide to perform an in situ GISAXS experiment and demonstrates how to analyze and interpret the results. Usually, performing this type of in situ X-ray experiments to investigate the drying kinetics of the active layer in OPVs relies on access to synchrotrons. However, by using and further developing the method described in this paper, it is possible to perform experiments with a coarse temporal and spatial resolution, on a day-to-day basis to gain fundamental insight in the morphology of drying inks.

This paper is a demonstration and a guideline to perform and analyze in-house (with a laboratory X-ray instrument) in situ GISAXS experiments of drying inks on roll-to-roll slot-die coated, non-fullerene organic photovoltaics.

We present an in-house, in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS) experiment, developed to probe the drying kinetics of roll-to-roll ...

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

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