Name: production and characterization of vacuum deposited organic light emitting diodes
Uploaded: 2018-11-16T12:30:00.000+00:00
Duration: 7 min 44 s
Description: Watch this Scientific Journal Video about Production and Characterization of Vacuum Deposited Organic Light Emitting Diodes at JoVE.com

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

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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

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

Chemistry

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 ...

Blue-hazard-free Candlelight OLED

A candlelight-style organic light emitting diode (OLED) is a human-friendly type of lighting because it is blue-hazard-free and has a low correlated color temperature (CCT) illumination. The low CCT lighting is deprived of high-energy blue radiation, and it can be used for a longer duration before causing retinal damage. This work presents the comprehensive protocols for the fabrication of blue-hazard-free candlelight OLEDs. The emission spectrum of the OLED was characterized by the maximum exposure time limit of the retina and the melatonin suppression sensitivity. The devices can be fabricated using dry and wet processes. The dry-processed OLED resulted in a CCT of 1,940 K and exhibited a maximum retinal exposure limit of 1,287 s at a brightness of 500 lx. It showed 2.61% melatonin suppression sensitivity relative to 480 nm blue light. The wet-processed OLED, where the spin coating is used to deposit hole injection, hole transport, and emissive layers, making fabrication fast and economical, produced a CCT of 1,922 K and showed a maximum retinal exposure limit of 7,092 at a brightness of 500 lx. The achieved relative melatonin suppression sensitivity of 1.05% is 86% and 96% less than that of the light emitting diode (LED) and compact fluorescent lamp (CFL), respectively. Wet-processed blue-hazard-free candlelight OLED exhibited a power efficiency of 30 lm/W, which is 2 times that of the incandescent bulb and 300 times that of the candle.

We present a protocol for the fabrication of a blue-hazard-free candlelight organic light emitting diode (OLED) for eye protection and melatonin secretion.

A candlelight-style organic light emitting diode (OLED) is a human-friendly type of lighting because it is blue-hazard-free and has a low correlated color ...

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and 2,8-bis(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide (compound 5) using Buchwald-Hartwig cross-coupling reaction conditions. In addition, we demonstrate a scaled-up synthesis of all non-commercially available starting materials that are required for the amination cross-coupling reaction. In the present article, we provide the detailed synthetic procedures for all of the described compounds, alongside their spectral characterization. This work shows the possibility to produce organic molecules for optoelectronic applications on a large scale, which facilitates their implementation into real world devices.

Scale-up synthesis of highly efficient thermally activated delayed fluorescence emitters is described in the presented article.

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and ...

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables the acquisition of photoluminescence spectra covering the time regime from nanoseconds up to 0.1 s. This enables us to follow the changes in the intensity (decay) and emission of the spectra over time. Using this method, it is possible to study diverse photophysical phenomena, such as the emission of phosphorescence, and the contributions of prompt and delayed fluorescence in molecules showing thermally activated delayed fluorescence (TADF). Remarkably, all spectra and decays are obtained in a single experiment. This can be done for solids (thin film, powder, crystal) and liquid samples, where the only limitations are the spectral sensitivity of the camera and the excitation wavelength (532 nm, 355 nm, 337 nm, and 266 nm). This technique is, thus, very important when investigating the excited state dynamics in organic emitters for their application in organic light-emitting diodes and other areas where triplet harvesting is of paramount importance. Since triplet states are strongly quenched by oxygen, emitters with efficient TADF luminescence, or those showing room temperature phosphorescence (RTP), must be correctly prepared in order to remove any dissolved oxygen from solutions and films. Otherwise, no long-lived emission will be observed. The method of degassing solid samples as presented in this work is basic and simple, but the degassing of liquid samples creates additional difficulties and is particularly interesting. A method of minimizing solvent loss and changing the sample concentration, while still enabling to remove oxygen in a very efficient and a repeatable manner, is presented in this work.

Here, we present a method of the spectroscopic characterization of organic molecules by means of time-resolved photoluminescence spectroscopy on the nanosecond-to-millisecond timescale in oxygen-free conditions. Methods to efficiently remove oxygen from the samples and, thus, limit luminescence quenching are also described.

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables ...

Using Cyclic Voltammetry, UV-Vis-NIR, and EPR Spectroelectrochemistry to Analyze Organic Compounds

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance (EPR) or ultraviolet-visible and near-infrared (UV-Vis-NIR) spectroscopies, we obtain useful information such as electron affinity, ionization potential, band-gap energies, the type of charge carriers, and degradation information that can be used to synthesize stable organic electronic devices. In this study, we present electrochemical and spectroelectrochemical methods to analyze the processes occurring in active layers of an organic device as well as the generated charge carriers.

In this article, we describe electrochemical, electron paramagnetic resonance, and ultraviolet-visible and near-infrared spectroelectrochemical methods to analyze organic compounds for application in organic electronics.

Cyclic voltammetry (CV) is a technique used in the analysis of organic compounds. When this technique is combined with electron paramagnetic resonance ...

A 3D-printed Chamber for Organic Optoelectronic Device Degradation Testing

In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, using 3D-printing. As these types of devices are sensitive to moisture and oxygen, such a chamber can aid researchers in characterizing the electronic and stability properties. The chamber is intended to be used as a temporary, reusable, and stable environment with controlled properties (including humidity, gas introduction, and temperature). It can be used to protect air-sensitive materials or to expose them to contaminants in a controlled way for degradation studies. To characterize the properties of the chamber, we outline a simple procedure to determine the water vapor transmission rate (WVTR) using relative humidity as measured by a standard humidity sensor. This standard operating procedure, using a 50% infill density of polylactic acid (PLA), results in a chamber that can be used for weeks without any significant loss of device properties. The versatility and ease of use of the chamber allows it to be adapted to any characterization condition that requires a compact-controlled atmosphere.

Here, we present a protocol for the design, manufacture, and use of a simple, versatile 3D-printed and controlled atmospheric chamber for the optical and electrical characterization of air-sensitive organic optoelectronic devices.

In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, ...

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 ...

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 ...