The authors would like to acknowledge the &#34;Excilight project&#34; which received funding from H2020-MSCA-ITN-2015/674990.

CAUTION: The following procedure involves the use of different solvents, so proper care must be taken when using them. Please use fume and personal protective equipment (gloves, lab-coat). To ensure the quality of the devices evaporated, it is recommended that all the procedure is done in a clean environment (such as a clean room and/or a glovebox). The safety datasheets must be consulted before the use of each equipment/material.
1. ITO Patterning
<ol>
	<li>Cover uniformly the Indium Tin Oxide (24 x 24 mm2, ITO-coated glass substrates with a sheet resistance of 20 &#937;/cm2 and ITO thickness of 100 nm) substrate with a p-type photoresist using a pipette. Spin-coat it at rate 500 rpm for 5 s followed by 4000 rpm for 45 s.</li>
	<li>Anneal the substrates on a hotplate for at least 5 min at 95 &#176;C. This will ensure that all the remaining solvent evaporates producing a uniform film.</li>
	<li>Place the mask with 4 mm stripes (or the desired pattern) on the resist-coated ITO substrate. Expose to an 8 W 365 nm UV lamp for 50 s.</li>
	<li>Place the ITO substrate into the developer solution (1 part developer: 2 parts deionized (DI) water) for 60 s.</li>
	<li>Carefully rinse the substrate for about 10 s with a wash bottle containing DI water, holding the substrate with tweezers. Dry the remaining water with an air gun.</li>
	<li>Heat the ITO substrate on the hotplate at 95 &#176;C for, at least, 15 min.</li>
	<li>Remove the photoresist from the edges of the substrate and in-between the stripes using a cotton swab soaked with acetone.</li>
	<li>Remove the ITO using a mixture of hydrochloric acid and nitric acid (20:1 v/v), leave it for 5 min at room temperature.</li>
	<li>Rinse with DI water for 10 s and remove the rest of photoresist with acetone.</li>
</ol>
2. Substrate Cleaning
<ol>
	<li>Take two patterned ITO substrates, rinse for about 10 s with acetone and wipe with a non-porous sheet of paper or dry with a Nitrogen gun.</li>
	<li>Using tweezers, fully submerge the substrates into a container with acetone. Put it into an ultrasonic bath (320 W, 37 kHz) for 15 min.</li>
	<li>Now submerge the substrates into a container with isopropyl alcohol (IPA, 2-propanol). Put the container in the ultrasonic bath for another 15 min.</li>
	<li>Remove the container from the ultrasonic bath and then the substrates from the IPA bath and dry with a nitrogen gun. Visually inspect the substrates to see if there are no solid residues or smudges. If there is, repeat from point 2.1.</li>
	<li>Open the flow in the oxygen tank to a rate of around 50 units. Use an oxygen plasma cleaner (100 W, 40 kHz) to clean the ITO substrates for 6 min at a 2.5 L/h oxygen flow being sure the ITO faces upward.</li>
	<li>Remove the substrates from the plasma chamber and attach them to the substrate holder. Two masks will be used: (A) for the evaporation of all organic layers and (B) for the evaporation of aluminum (Figure 1). For simplicity, in this protocol, Mask A is attached to the substrate holder</li>
</ol>
3. Preparation of the Evaporation Chamber
<ol>
	<li>Insert the substrate holder, mask A and mask B, into the evaporation chamber. Depending on the type of the evaporating system, place a substrate holder with mask A on the deposition shelf and mask B on shelf 1.</li>
	<li>Add the organic powder of all different materials used for this device in different aluminum oxide crucibles making sure the surface is covered by it. In this case, add NPB, DPTZ-DBTO2, CBP and TPBi to 4 different 10 mL aluminum oxide crucibles. Add LiF in one 5 mL crucible and aluminum (Al) pieces in a half-full 5 mL boron nitride high-temperature crucible.</li>
	<li>Take into consideration the organic crucible position with respective Quartz Crystal Microbalance (QCM) sensor which will give the real value of thickness. For D-A and G-H system evaporations, a&#160;co-evaporation process needs to be done. Therefore,&#160;to control the co-evaporation process, both DPTZ-DBTO2 and CBP (TADF OLED) or DtBuCz-DBTO2 and TAPC (Exciplex OLED) need to be controlled by different QCMs. In this case, the positions of the respective compounds are presented in Figure 2.</li>
	<li>Close the chamber and initiate the vacuum procedure (also known as pumping down). Wait for the pressure P &#60;1&#183;10-5 mbar to start the evaporation.</li>
</ol>
4. Evaporation of the Organic Layers
NOTE: For all organics, do not exceed the evaporation rate of 2 &#197;/s as this results in increased roughness and decreased&#160;uniformity of the layers. To a certain point, this may result in non-uniform emissions and even shorts.
<ol>
	<li>Turn ON the water flow to provide sufficient cooling of the elements.</li>
	<li>Turn ON the substrate rotation, at 10 rotations per min (rpm), to ensure the deposition of uniform layers.</li>
	<li>Pre-heat the NPB crucible by switching-on the temperature controller of the system and open its&#39; shutter. This can be done using the VTE software at the disposal of the user. Start the evaporation (open deposit shutter) when the rate stabilizes at around 1 &#197;/s. Evaporate a 40 nm thick layer, close the shutter, wait until the crucible cools down to start the next process.</li>
	<li>In a similar fashion to point 4.3., preheat the CBP and DPTZ-DBTO2 and open their shutters for co-evaporation. Depending on the final concentration of the layer, use different rates of compounds.
	<ol>
		<li>For the 10% emissive layer start the evaporation when the rate will stabilize around 2.0 &#197;/s for CBP and 0.22 &#197;/s for DPTZ-DBTO2. Open the depositing shutter when the rate is achieved.</li>
		<li>Evaporate 20 nm thickness layer containing 18 nm of CBP and 2 nm of DPTZ-DBTO2, close the shutter, wait until the crucible cools down to start the next process.</li>
	</ol>
	</li>
	<li>Pre-heat the TPBi and open its shutter. Start the evaporation (open deposit shutter) when the rate stabilizes at around 1 &#197;/s. Evaporate 60 nm thickness layer, close the shutter, wait until the crucible cools down to start the next process.</li>
	<li>Pre-heat the LiF, start the evaporation (open evaporation shutter) when the rate stabilizes at around 0.2 &#197;/s. Do not exceed the evaporation rate of 0.5 &#197;/s. Evaporate 1 nm thickness layer, close the shutter, wait until the crucible cools down to start next process.</li>
	<li>Turn OFF the substrate rotation.</li>
	<li>Replace the mask A on a substrate holder with mask B. If necessary, vent the evaporation chamber. If vented, the chamber must be pumped down before the continuation of the procedure. In this protocol, mask A is placed onto mask B.</li>
	<li>Turn ON the substrate rotation, i.e., 10 rpm.</li>
	<li>Pre-heat the Al, start the evaporation (open deposit shutter) when the rate stabilizes at around 1 &#197;/s. Do not exceed the evaporation rate of 2 &#197;/s. Evaporate 100 nm thickness layer, close the shutter, wait until the crucible cools down.</li>
	<li>Vent and open the chamber. Remove the substrate holder with deposited devices. 
	NOTE: Once evaporated, 4 pixels are obtained with two different sizes as shown in Figure 1: 2x4 and 4x4 cm2. This ensures there is reproducibility when upscaling the devices. The level of defects can also be more visible in the bigger pixels11.</li>
</ol>
5. OLED Encapsulation
NOTE: This section is not mandatory for the analysis of OLEDs though it is highly recommended. To secure their quality, it is also important that this section is done in a controlled environment.
<ol>
	<li>Remove the substrates from the substrate holder. Place them on top of an encapsulation stage with the evaporated films facing forward.</li>
	<li>Prepare the resin tube and dispersing tools. Screw a proper tip to one side of the tube, and a pressure gun to the other side of the tube.</li>
	<li>Apply pressure with the gun to disperse the resin. Draw squares that involve all evaporated pixels (Figure 2).</li>
	<li>Place an encapsulation glass on top of each square of resin.</li>
	<li>UV-cure the substrates with the resin and encapsulation glass for as long as required by the resin manufacturer.</li>
</ol>
6. OLED Characterization
<ol>
	<li>If necessary, clean the ITO stripes not covered by the encapsulation glass with a toothpick using acetone or IPA to remove any organic material deposited before connecting to the measuring unit. This will guarantee that a good ohmic contact between measuring system and electrodes is achieved.</li>
	<li>Calibrate the OLED measurement according to the NIST standards using a pre-calibrated lamp.</li>
	<li>Place the OLED in the integrating sphere, making sure the contacts are placed correctly (Figure 1). Confirm that the anode (+) and cathode (-) are connected to the ITO and Al pads, respectively. Close to the integrating sphere.</li>
	<li>Measure the I-V curve of the device and the obtained luminance and emission spectra at different voltages.
	<ol>
		<li>Apply a voltage between the two terminals and measure the current output. A luminance meter measures the brightness output.</li>
		<li>Using a software and the correct pixel size, calculate the Current Density (J), External Quantum Efficiency (EQE), Power, Wall-plug efficiency, Luminous Flux, Luminous efficiency (&#414;P), Current Efficiency (&#414;L) Luminance (L) and Commission Internationale de L&#39;Eclairage (CIE) coordinates. More information on these values can be found in reference15.</li>
	</ol>
	</li>
	<li>Plot J-V-L, EQE-J, &#414;P-V- &#414;L, EL-&#955; at different voltages and analyse the data. This can be done using a data processing software. For a better understanding, use the following table as a reference on the plotting.</li>
</ol>

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The authors have nothing to disclose.

The present protocol aims to present an effective tool for the patterning, production, encapsulation and characterization of OLEDs based on small molecular-weight TADF-emitting or exciplex-emitting layers. The organic vacuum thermal evaporation allows for the production of thin films (from a few &#197; to hundreds of nm) of both organic and inorganic materials and produce pathways for charge carriers to recombine from which light will be emitted. Although versatile, the device production is fairly limited to the evaporator i.e., the number of organic and inorganic sources available or the possibility of more than one evaporation at the same time (co- and tri-evaporations are very common, particularly in TADF devices). More advanced systems may allow for the evaporation of more than 3 sources at the same time, which may be useful for applications such as white-OLEDs28 for displays and general lighting. Nevertheless, a trade-off between the device complexity and its performance must be met. The multifunctionality of this evaporation procedure also allows doing different studies that go beyond this work. These include effects of layer thickness, dopant concentration, layer functionality or even study the inherent mobilities of new layers. The fine control over the rates of single and co-evaporated layers is also crucial since it allows for the formation of uniform films with controlled precise rations.
It is recommended that all steps of this protocol are done in a controlled environment and, more importantly for the encapsulation, inside a glovebox to avoid any ambient related degradation. Finally, an integrating sphere is most welcomed as it provides for a more detailed electrical and optical analysis. With this mind, all steps from theoretical introduction to production and characterization of TADF-based OLEDs were presented in this protocol highlighting all these different stages allowing the production of stable devices that, when encapsulated, can last for large periods of time.

Organic electronics brings together all fields from chemistry to physics, going through materials science and engineering in order to improve the current technologies towards more efficient and more stable structures and devices. From this, organic light-emitting diodes (OLEDs) is a technology that has shown great improvements over the last few years, both in terms of efficiency and stability1,2. Reports say that the OLED industry for displays may increase from the 16 billion dollars in 2016 to around 40 billion dollars by 2020 and more than 50 billion by 20263. It is also finding its way into general lighting and head-mounted microdisplays for augmented-reality4. Applications like organic sensors for biomedical applications is more of a futuristic application at the moment, given the requirements for both high luminance and stability5. This trend confirms the need for improved device structures that includes more efficient molecules at less expense of natural resources. A better understanding of the inherent processes of the materials used for OLEDs is also of great importance when designing these.
An OLED is a multi-layered organic stack sandwiched between two electrodes, at least one of the latter transparent. Each layer, designed accordingly to their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and their intrinsic mobility, has a specific function (injection, blockage, and transport) in the overall device. The mechanism is based on opposite charge carriers (electrons and holes) travelling across the device where they meet in a specific layer, recombine to form excitons and from the deactivation of these excitons comes the emission of a photon6. This photon will be a characteristic of the layer where the deactivation is taking place7,8,9. So, pending molecular design strategies, different red, green and blue emitters can be synthesized and applied to the stack. Putting them together, white devices can also be produced10,11. The emitting layer of an OLED stack is usually based on the guest-host (G-H) system where the guest is dispersed into the host to avoid quenching of light9 and by-side reactions12.
There are several ways to push molecules to emit light, with thermally-activated delayed fluorescence (TADF) implemented more recently13,14,15. TADF allowed for the increase of the external efficiency of devices from 5% of a typical fluorescence emitter up to 30% by means of triplet harvesting through a small singlet-triplet energy-splitting in a process called reverse intersystem crossing (rISC). There are several ways to form efficient TADF-based OLEDs: one of the most common in literature is the G-H system where the emissive state is formed by a single molecule16,17,18. A second system uses an exciplex emitter formed between an electron donor (D) and an electron acceptor (A) molecules, which are simply called the donor-acceptor (D-A) system15,19,20,21; A small range of TADF materials and devices have been reported, yielding very high external quantum yields14, reaching a values of, for example, 19% EQE22, clearly indicating that very efficient triplet harvesting is occurring and that 100% internal quantum efficiency is possible. In these TADF-based OLEDs, care must be taken when choosing the proper host material as the polarity of the environment can change the charge transfer (CT) state away from the local excited (LE) state, therefore, reducing the TADF mechanism. The procedure to be taken into account is similar to other fluorescent emitters23. Such devices have relatively simple stack structures, typically 3 to 5 organic layers, and without the need of a p-i-n structure24, resulting in ultra-low turn-on voltages of the order of 2.7 V and a maximum thickness of around 130 nm for all organic layers to guarantee a good charge balance.
Apart from the materials&#39; properties, the production of multi-layered stacks can be either be based on vacuum thermal evaporation (VTE) or spin-coating, the former more frequent for small molecules. It requires precise control over the temperature, pressure, environment, rate, and thickness of each layer. For emitting G-H layers, the rates of co-evaporation have to be controlled for the desired ratios to be obtained. Also of extreme importance is the cleaning of the substrates used for OLEDs which can result in non-working devices or uneven emissions throughout the emitting pixel25.
Therefore, this article aims at all steps of preparation, production, and characterization of organic devices and intends to help new specialists on the careful protocol required for high efficiency and evenness of emission. It involves the use of DPTZ-DBTO2 (2,8-Bis(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide) as emitting guest in a TADF G-H system16,26. Similar methods can be also implemented for the formation of an exciplex based D-A systems using DtBuCz-DBTO2 (2,8-Bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide) in TAPC (4,4&#8242;-Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine])15, where the main difference in the procedure is the concentration ratio of the emissive layer but it significantly changes the nature of emission (single molecule CT emission vs exciplex CT emission). The G-H system described here has a single molecule CT emitter and involves the evaporation of 5 layers with 3 organic, and 2 inorganic materials. The device is composed of indium tin oxide (ITO) as the anode, 40 nm of N,N&#8242;-di(1-naphthyl)-N,N&#8242;-diphenyl-(1,1&#8242;-biphenyl)-4,4&#8242;-diamine (NPB) as the hole transport layer (HTL), and a total 20 nm of 4,4&#8242;-bis(N-carbazolyl)-1,1&#8242;-biphenyl (CBP) with 10% of DPTZ-DBTO2 as the emitting layer based on the G-H system. 60 nm of 2,2&#8242;,2&#34;-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi) is then used as the electron transport layer (ETL) and 1 nm of Lithium Floride (LiF) as electron injection layer (EIL). 100 nm of aluminum (Al) finalizes the device as a cathode. A diagram of the whole procedure can be found in Figure 1. The thicknesses of organics were chosen to be similar to other devices used in the literature. The mobility of each layer must be carefully examined as to ensure good carrier balance inside the layer. The operation of LiF is based on a tunnelling effect, i.e., carriers travel through the tunnels of a packed LiF, ensuring a better injection to the transport layers. This means thin layers (between 0.8 and 1.5 nm) are required27. The layer of Al must be thick enough to prevent any oxidation (70 nm is a minimal requirement).

<table>
	<tbody>
		<tr>
			<td>N,N&#8242;-Di(1-naphthyl)-N,N&#8242;-diphenyl-(1,1&#8242;-biphenyl)-4,4&#8242;-diamine</td>
			<td>NPB</td>
			<td>Sigma Aldrich</td>
			<td>556696</td>
			<td>Sublimed grade</td>
		</tr>
		<tr>
			<td>4,4&#8242;-Bis(N-carbazolyl)-1,1&#8242;-biphenyl</td>
			<td>CBP</td>
			<td>Sigma Aldrich</td>
			<td>699195</td>
			<td>Sublimed grade</td>
		</tr>
		<tr>
			<td>2,2&#8242;,2&#34;-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)</td>
			<td>TPBi</td>
			<td>Sigma Aldrich</td>
			<td>806781</td>
			<td>Sublimed grade</td>
		</tr>
		<tr>
			<td>Lithium Floride 99.995%</td>
			<td>LiF</td>
			<td>Sigma Aldrich</td>
			<td>669431</td>
			<td></td>
		</tr>
		<tr>
			<td>Aluminum 99.999%</td>
			<td>Al</td>
			<td>Alfa Aesar</td>
			<td>14445</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetone 99.9%</td>
			<td>Acetone</td>
			<td>Sigma Aldrich</td>
			<td>439126</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropyl alcohol 99.9 %</td>
			<td>IPA</td>
			<td>Sigma Aldrich</td>
			<td>675431</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoresist</td>
			<td></td>
			<td>DOW Electronic Materials</td>
			<td>Microposit S1813</td>
			<td></td>
		</tr>
		<tr>
			<td>Developer</td>
			<td></td>
			<td>DOW Electronic Materials</td>
			<td>Microposit 351</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid 37%</td>
			<td>HCl</td>
			<td>Sigma Aldrich</td>
			<td>435570</td>
			<td></td>
		</tr>
		<tr>
			<td>Nitric acid 70%</td>
			<td>HNO3</td>
			<td>Sigma Aldrich</td>
			<td>258113</td>
			<td></td>
		</tr>
		<tr>
			<td>Encapsulation resin</td>
			<td></td>
			<td>Delo</td>
			<td>Kationbond GE680</td>
			<td></td>
		</tr>
		<tr>
			<td>Encapsulation square glass 15x15mm</td>
			<td></td>
			<td>Agar</td>
			<td>AGL46s15-4&#38;</td>
			<td></td>
		</tr>
		<tr>
			<td>ITO</td>
			<td></td>
			<td>Naranjo Substrates</td>
			<td>Custom made</td>
			<td></td>
		</tr>
	</tbody>
</table>

production and characterization of vacuum deposited organic light emitting diodes

A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex donor-acceptor emitters is presented. With a step-by-step procedure, readers will be able to repeat and produce OLED devices based on simple organic emitters. A patterning procedure allowing the creation of personalized indium tin oxide (ITO) shape is shown. This is followed by the evaporation of all layers, encapsulation and characterization of each individual device. The end goal is to present a procedure that will give the opportunity to repeat the information presented in cited publication but also using different compounds and structures in order to prepare efficient OLEDs.

The data presented in Figure 3 is a good example of the different information one can get by the analysis of this type of OLEDs. From Figure 3a, the turn-on voltage (voltage at which the detector starts detecting light on the device) can be determined. In this case, it is 4 V. Device degradation due to high voltages is seen when luminance decreases substantially (around 13 V). Degradation occurs when carriers injected into the device react with the organic layers resulting in the breaking of bonds and molecules. Also, electrical stress can be associated with device degradation. The maximum luminance of this device is around 17000 cd/m2. From Figure 3b, the maximum E.Q.E. (around 7%) and roll-off, a measure of the device electrical stability, are determined. The roll-off of a device is also defined as the drop in efficiency with the current flowing through it. To compare the roll-off of different devices, the values of EQE at the standard luminance of 100 and 1000 cd/m2 are usually given6. In this case, 6.1 and 5.5%, respectively which represents a drop of 9% and 20% of its maximum value. This represents a poor roll-off. Good values should be between 0 and 5% until high levels of luminance. The other values of efficiency are shown in Figure 3c, as other means of comparison with similar types of devices. Finally, the EL is shown peaking at 573 nm, a typical green-yellow emission (inset of Figure 3d). The EL at different voltages can help giving insights into optical stability i.e., where the emission is taking place. In this case, as this seemingly does not change with the applied voltage, one can assume that the device is optically-stable. Checking the CIE coordinates (inset of Figure 3b with voltage is another way to measure the optical stability.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56593/56593fig1.jpg" /> 
Figure 1: Diagram containing all steps represented in this protocol. All organic layers and LiF are evaporated using mask A. After metallization (evaporation of aluminium), two sets of devices can be produced using mask B: one with 2x4 cm2 and another with 4x4 cm2. The voltage will be applied between the ITO (anode: +) and aluminium (cathode: - ) and a current will be measured. A cross-section of the device structure is also shown. <a href="https://www.jove.com/files/ftp_upload/56593/56593fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56593/56593fig2.jpg" /> 
Figure 2: a) Diagram of the organic low temperature (black) and inorganic high-temperature sources (blue) to be placed in the vacuum chamber. Each material has to be put in the specified source with a specific heating number for the software as they were previously optimized for each material in question. b) QCM sensors arranged throughout the chamber. <a href="https://www.jove.com/files/ftp_upload/56593/56593fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56593/56593fig3.jpg" /> 
Figure 3: a) J-V-L, b) EQE-J, c) &#414;P-V- &#414;L, d) EL-&#955; at different voltages for the device in this study. The CIE coordinates change with voltage is shown on the inset of b) while a photograph of the device is shown in the inset of d). <a href="https://www.jove.com/files/ftp_upload/56593/56593fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Curve</td>
			<td>x</td>
			<td>Scale</td>
			<td>y1</td>
			<td>Scale</td>
			<td>y2</td>
			<td>Scale</td>
		</tr>
		<tr>
			<td>J-V-L</td>
			<td rowspan="2">V</td>
			<td rowspan="2">linear</td>
			<td>J</td>
			<td>log</td>
			<td>L</td>
			<td>log</td>
		</tr>
		<tr>
			<td>&#414;P-V-&#414;L</td>
			<td>&#414;P</td>
			<td>log</td>
			<td>&#414;L</td>
			<td>log</td>
		</tr>
		<tr>
			<td>EQE-J</td>
			<td>J</td>
			<td>log</td>
			<td>EQE</td>
			<td>log</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EL- &#955;</td>
			<td>&#955;</td>
			<td>linear</td>
			<td>EL</td>
			<td>linear</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 1: Considered curves and related scale for the unification of the characterization of OLEDs.

Watch this Scientific Journal Video about Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes at JoVE.com

Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes

A protocol for the production of simple structured organic light-emitting diodes (OLEDs) is presented.

A method for producing simple and efficient thermally-activated delayed fluorescence organic light-emitting diodes (OLEDs) based on guest-host or exciplex ...

production-characterization-vacuum-deposited-organic-light-emitting

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8.8K Views.  Durham University. A protocol for the production of simple structured organic light-emitting diodes (OLEDs) is presented.

Video: Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

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 ...

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Ambient Method for the Production of an Ionically Gated Carbon Nanotube Common Cathode in Tandem Organic Solar Cells

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

A method of fabricating, in ambient conditions, organic photovoltaic tandem devices in a parallel configuration is presented. These devices feature an air-processed, semi-transparent, carbon nanotube common cathode.

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two ...

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

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

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

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active layer which consists of blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated triphenylamine molecules. This white light emission originates from exciplexes formed between PFD and amines in electronically excited states. A device containing PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), Poly(ethylene oxide) and K2CF3SO3 showed white light emission with Commission internationale de l&#39;&#233;clairage (CIE) coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at an applied voltage of 3.5 V. Constant voltage measurements showed that the CIE coordinates of (0.27, 0.37), Ra of 67, and the emission color observed immediately after application of a voltage of 5 V were nearly unchanged and stable after 300 sec.

The authors present a method for fabricating stable white-light-emitting electrochemical cells utilizing emission from exciplexes formed between a blue-emitting fluorene polymer and aromatic amines.

The authors present an approach for fabricating stable white light emission from polymer light-emitting electrochemical cells (PLECs) having an active ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m-2, and a maximum current efficiency of 1.15 cd A-1. The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A protocol is presented for fabricating high-performance, pure blue ZnCdS/ZnS-based quantum dots light-emitting diodes by employing an autoxidized aluminum cathode.

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation ...

Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes

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