Name: fabrication of white light-emitting electrochemical cells with stable emission from exciplexes
Uploaded: 2016-11-15T13:00:00.000+00:00
Duration: 5 min 51 s
Description: Watch this Scientific Journal Video about Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes at JoVE.com

This work was partially supported by a Grant-in-Aid for Scientific Research (No. 24225003). This work was supported financially by the JX Nippon Oil &#38; Energy Corporation.

1. Preparation of Active Layer Solutions
<ol>
	<li>Active layer solution for the amine doped PFD devices 
	NOTE: The PFD, 4,4&#39;,4&#39;&#39;-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), 9,9-dimethyl-N,N&#39;-di(1-naphthyl)-N,N&#39;-diphenyl-9H-fluorene-2,7-diamine (DMFL-NPB), Poly(ethylene oxide) (PEO), were used as received. The potassium trifluoromethanesulfonate (K2CF3SO3) was dried under vacuum at 200 &#176;C for 1 hr prior to use.
	<ol>
		<li>For the devices having a PFD:amine ratio of 1:0.25, dissolve 10 mg of PFD and 2.5 mg of the aromatic amine in 1 ml of chloroform and stir for 1 hr at 40 &#176;C. For those having a PFD:amine ratio of 1:1, use 10 mg of the aromatic amine.</li>
		<li>Separately, dissolve 10 mg of PEO in 1 ml of cyclohexanone and stir for 1 hr at 60 &#176;C, and dissolve 2.5 mg of potassium trifluoromethanesulfonate (KCF3SO3) in 1 ml of cyclohexanone and stir for 1 hr at 40 &#176;C.</li>
		<li>Add 0.78 ml of the PEO solution and 0.147 ml of the KCF3SO3 solution to the PFD solution using micropipettes. Stir the mixed solution for 4 hr at 40 &#176;C.</li>
		<li>Filter the mixed solution using a membrane filter prior to spin coating.</li>
	</ol>
	</li>
	<li>Active layer solution for the undoped PFD device
	<ol>
		<li>For the undoped PFD device, dissolve 10 mg of PFD in 1 ml of chloroform and stir for 1 hr at 40 &#176;C. The steps which follow are the same as those described previously for the amine doped PFDs in 1.1.2 - 1.1.4.</li>
	</ol>
	</li>
</ol>
2. Fabrication of LEC Devices
NOTE: Fabrication process of LEC devices is summarized in Figure 1.
<ol>
	<li>Ultrasonically clean patterned indium-tin oxide (ITO) glass substrates with diluted detergent, followed by ionized water, acetone and 2-propanol using a desktop ultrasonic bath (38 kHz) for 3 min for each step. Finally, remove the solvent using an N2 blower.</li>
	<li>Treat the substrates with UV/O3 for 3 min using a UV/O3 treating unit according to manufacturer&#39;s protocol. Perform the active layer coating process under an inert atmosphere in a glove box.</li>
	<li>Set a cleaned substrate on the head of a spin coater. Dispense around 100 &#181;l of the active layer solution using a micropipette. Spin the substrate as follows: 800 rpm for 60 sec, increase the rate to 1,000 rpm over 3 sec, then spin at 1,000 rpm for 10 sec. The active layer thickness will be around 150 nm.</li>
	<li>Dry the coated substrates in the glove box overnight.</li>
	<li>Wipe off excess polymer to ensure a proper electrode connection and encapsulation.</li>
	<li>Place the substrates on an evaporation holder for deposition of aluminum. Load the holder in the evaporation chamber, and thermally deposit a 100 nm layer of aluminum at an evaporation rate of 0.4 nm/sec through a stainless steel evaporation mask, which has 3 mm wide openings for depositing the aluminum counter electrodes.</li>
	<li>When deposition is complete, transfer the devices to a glove box under an inert atmosphere. Apply a bead of UV curable epoxy resin in the shape of a rectangle using a dispenser. Place a cover glass (15 mm x 12 mm x 0.7 mm-thick) on the resin to encapsulate the device (see Figure 1).</li>
	<li>Cure the resin using UV radiation (cumulative dose: 6,000 mJ/cm2, wavelength: 365 nm) from a UV-LED light source.</li>
</ol>
3. Characterization
<ol>
	<li>J-V-L measurements 
	NOTE: The current density (J)-voltage (V)-luminance (L) (J-V-L) characteristics and Commission Internationale de l&#39;Eclairage (CIE) coordinates were measured using a spectral photo detector equipped with a DC voltage current source monitor. The measurement system is controlled by a PC with a custom control software for data acquisition. The system was calibrated following manufacturer&#39;s protocol and measurements were performed in the dark under a black curtain.
	<ol>
		<li>Connect the terminals to the contacts of the device with alligator clips. Place the device on the measurement stage.</li>
		<li>Run the control software for data acquisition. The system controls the applied voltage and current over time and collects the emission spectra by the spectrometer through an optical fiber.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Pei, Q., Yu, G., Zhang, C., Yang, Y., Heeger, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer+light-emitting+electrochemical+cells.">Polymer light-emitting electrochemical cells.</a> Science. 269 (5227), 1086-1088 (1995).</li><li>Sun, Q., Li, Y., Pei, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polymer+light-emitting+electrochemical+cells+for+high-efficiency+low-voltage+electroluminescent+devices.">Polymer light-emitting electrochemical cells for high-efficiency low-voltage electroluminescent devices.</a> J. Disp. Technol. 3 (2), 211-224 (2007).</li><li>Meier, S. B., 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=Light-emitting+electrochemical+cells:+recent+progress+and+future+prospects.">Light-emitting electrochemical cells: recent progress and future prospects.</a> Mater. Today. 17 (5), 217-223 (2014).</li><li>Edman, L., 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=Single-component+light-emitting+electrochemical+cell+fabricated+from+cationic+polyfluorene:+Effect+of+film+morphology+on+device+performance.">Single-component light-emitting electrochemical cell fabricated from cationic polyfluorene: Effect of film morphology on device performance.</a> J. Appl. 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Photonics. 7 (10), 817-824 (2013).</li><li>Yang, Y., Pei, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+blue-green+and+white+light-emitting+electrochemical+cells+based+on+poly+9,+9-bis+(3,+6-dioxaheptyl)-fluorene-2,+7-diyl.">Efficient blue-green and white light-emitting electrochemical cells based on poly 9, 9-bis (3, 6-dioxaheptyl)-fluorene-2, 7-diyl.</a> J. Appl. Phys. 81 (7), 3294-3298 (1997).</li><li>Tang, S., Buchholz, H. A., Edman, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=White+Light+from+a+Light-Emitting+Electrochemical+Cell:+Controlling+the+Energy-Transfer+in+a+Conjugated+Polymer/Triplet-Emitter+Blend.">White Light from a Light-Emitting Electrochemical Cell: Controlling the Energy-Transfer in a Conjugated Polymer/Triplet-Emitter Blend.</a> ACS Appl. Mater. Iterfaces. 7 (46), 25955-25960 (2015).</li><li>Nishikitani, Y., Takizawa, D., Nishide, H., Uchida, S., Nishimura, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=White+Polymer+Light-Emitting+Electrochemical+Cells+Fabricated+Using+Energy+Donor+and+Acceptor+Fluorescent+&#960;-Conjugated+Polymers+Based+on+Concepts+of+Band-Structure+Engineering.">White Polymer Light-Emitting Electrochemical Cells Fabricated Using Energy Donor and Acceptor Fluorescent &#960;-Conjugated Polymers Based on Concepts of Band-Structure Engineering.</a> J. Phys. Chem. C. 119 (52), 28701-28710 (2015).</li><li>Sun, M., Zhong, C., Li, F., Cao, Y., Pei, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Fluorene&#8722;+Oxadiazole+Copolymer+for+White+Light-Emitting+Electrochemical+Cells.">A Fluorene&#8722; Oxadiazole Copolymer for White Light-Emitting Electrochemical Cells.</a> Macromolecules. 43 (4), 1714-1718 (2010).</li><li>Tang, S., Pan, J., Buchholz, H., Edman, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=White+Light-Emitting+Electrochemical+Cell.">White Light-Emitting Electrochemical Cell.</a> ACS Appl. Mater. Interfaces. 3 (9), 3384-3388 (2011).</li><li>Tang, S., Pan, J., Buchholz, H. A., Edman, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=White+light+from+a+single-emitter+light-emitting+electrochemical+cell.">White light from a single-emitter light-emitting electrochemical cell.</a> J. Am. Chem. Soc. 135 (9), 3647-3652 (2013).</li><li>Nishikitani, Y., 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=White+polymer+light-emitting+electrochemical+cells+using+emission+from+exciplexes+with+long+intermolecular+distances+formed+between+polyfluorene+and+&#960;-conjugated+amine+molecules.">White polymer light-emitting electrochemical cells using emission from exciplexes with long intermolecular distances formed between polyfluorene and &#960;-conjugated amine molecules.</a> J. Appl. Phys. 118 (22), 225501 (2015).</li><li>Tang, S., Mindemark, J., Araujo, C. M. G., Brandell, D., Edman, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identifying+Key+Properties+of+Electrolytes+for+Light-Emitting+Electrochemical+Cells.">Identifying Key Properties of Electrolytes for Light-Emitting Electrochemical Cells.</a> Chem. Mater. 26 (17), 5083-5088 (2014).</li></ol>

The authors have nothing to disclose.

The LEC has an active layer containing hydrophobic PFD and aromatic amines, and hydrophilic polyethylene oxide and KCF3SO3. Because these materials have very different solubilities, careful preparation of the spin coating solution is critical to avoid incomplete solvation. Each must be first dissolved separately and completely in solvents with sufficient solvating ability, then the solutions are mixed together to form a uniform mixture. Balancing the exciton and exciplex emissions is key to obtaining white emission. Therefore, the amounts of PFD and amines must be precisely measured.
In LECs it is also important to control the phase-separation morphology of the active layer. The authors tried using other ion conducting polymers such as trimethylolpropane ethoxylate (TMPE-OH)16 instead of PEO, but the device fabricated with TMPE-OH did not function as an LEC. The hydrophobic materials (PFD and aromatic amines) and the hydrophilic polymer electrolyte tend to phase-separate, meaning that materials must be selected carefully.
The UV-light used to cure the resin may damage the active layer material. Therefore, the UV-light is shined from the aluminum deposited side through a glass cover to avoid unnecessary exposure.
Compared to methods in which multiple light-emitting materials are used,10-14 the method described above has a major advantage in that white light emission can be obtained through just the addition of simple compounds such as aromatic amines. To produce high CRI white light, it will be necessary to obtain broader band emissions with a spectrum closer to sunlight. Because exciplexes generally produce broadband emissions, finding better combinations of blue light-emitting polymers and amines should make it possible to achieve these higher CRIs.
Figure 5 shows time evolution of luminance, current density, CIE coordinates and efficacy of the 2-TNATA-doped LEC applied at a constant voltage of 5 V. Figure 4b shows the typical behavior of an LEC, such as increasing luminance and current density and changes in efficacy during the first 30 seconds of operation.
The authors have thus demonstrated the fabrication procedure for PLECs with white light emission utilizing exciplex emissions originating from PFD and amines. The authors have also shown the stability of this white light emission, a property which is especially important for large area lighting applications.

Research and development of polymer light-emitting electrochemical cells (PLECs) have expanded in recent years.1-15 PLECs are similar to organic light-emitting diodes (OLEDs) in that both are surface emitting organic devices and are expected to find their way into future lighting applications. OLEDs are already on the market, but the cost is still high, one reason being that OLEDs need a complicated device structure with multiple layers. In contrast, PLECs have a very simple device structure which consists of a single active layer (emitting layer) between a pair of electrodes. This means that PLECs are suited to mass production processes such as roll-to-roll printing and coating. 
A PLEC has an active layer consisting of a fluorescent &#960;-conjugated polymer (FCP). The FCP can be electrochemically doped with a polymer electrolyte (a mixture of an ion conducting polymer and a salt). The FCP is p-doped on the anode side and n-doped on the cathode side during operation, and generates excitons which emit light between the p- and n-doped regions. Therefore, the emission color reflects the exciton emission (=fluorescence) wavelength of the FCP.
Stable white light emission is important for lighting applications, and color mixing techniques which employ two or more emitters have been widely used to achieve this.10-14 Recently, we presented a different approach for obtaining stable white light emission, using an active layer which contains blue-fluorescent poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and &#960;-conjugated aromatic amines15. This white light emission comes from exciplexes formed between PFD and amine molecules in excited states. Exciplex emission has a broader spectrum compared to the exciton emission from the PDF and/or amines, which gives it a color close to that of natural light. This translates to a higher color rendering index (CRI), which is preferable for lighting applications.
In this article, the authors describe the procedure used to fabricate the exciplex based LECs and show the stability of their white light emission.

<table><tbody><tr><td>Poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD)</td><td>Aldrich</td><td>571660</td><td></td></tr><tr><td>4,4&amp;rsquo;,4&amp;rsquo;&amp;rsquo;-Tris[2-naphthyl(phenyl)amino] triphenylamine (2-TNATA)</td><td>Aldrich</td><td>768669</td><td></td></tr><tr><td>9,9-Dimethyl-&lt;em&gt;N,N&amp;rsquo;&lt;/em&gt;-di(1-naphthyl)-&lt;em&gt;N,N&amp;rsquo;&lt;/em&gt;-diphenyl-9H-fluorene-2,7-diamine (DMFL-NPB)</td><td>Aldrich</td><td></td><td></td></tr><tr><td>Poly(ethylene oxide) (PEO)</td><td>Aldrich</td><td>182028</td><td></td></tr><tr><td>Potassium tirifluoromethansulfonate (KCF&lt;sub&gt;3&lt;/sub&gt;SO&lt;sub&gt;3&lt;/sub&gt;)</td><td>Aldrich</td><td>422843</td><td>dried under vacuum at 200 &amp;deg;C for 2&amp;nbsp;hr prior to use</td></tr><tr><td>Chloroform</td><td>Kanto Chemical Co.</td><td>08097-25</td><td>dehydrated</td></tr><tr><td>Cyclohexanone</td><td>Kanto Chemical Co.</td><td>07555-00</td><td></td></tr><tr><td>SCAT 20-X (detergent)</td><td>Daiichi Kogyo Seiyaku</td><td></td><td>diluted with water</td></tr><tr><td>Acetone</td><td>Kanto Chemical Co.</td><td>01866-25</td><td>Electronic grage</td></tr><tr><td>2-propanol</td><td>Kanto Chemical Co.</td><td>32439-75</td><td>Electronic grage</td></tr><tr><td>13 mm GD/X Disposable Filter Device PVDF Filter Media, Polypropylene Housing</td><td>Whatman</td><td>6872-1304</td><td></td></tr><tr><td>UV/O&lt;sub&gt;3&lt;/sub&gt; Treating Unit</td><td>SEN Lights Co.</td><td>SSP16-110</td><td></td></tr><tr><td>Spectral Photo Detector</td><td>Otsuka Electronics</td><td>MCPD 9800</td><td></td></tr><tr><td>Voltage Current Source Monitor</td><td>ADCMT</td><td>6241A</td><td></td></tr><tr><td>Evaporation Mask</td><td>Tokyo Process Service Co., Ltd.</td><td>NA</td><td>The evaporation mask was wet-etched to create openings for patterned deposition of aluminum. The size of the mask is 100 mm x 100 mm x 0.2&amp;nbsp;mm-thick.</td></tr></tbody></table>

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 electroluminescence (EL) spectra were used to calculate the CIE coordinates and CRI values (Figures 2, 4, 5). Photographic images of the emitting devices were collected to verify the whiteness of the emission (Figure 3).
The EL spectra of the amine doped PFD devices and the undoped PFD device are shown in Figure 2. The undoped PFD device showed blue emission that corresponds to PFD exciton emission. Meanwhile, the 2-TNATA and the DMFL-NPB doped devices showed longer wavelength emissions compared to the undoped PFD device. The emissions from the amine doped devices originated from exciplexes formed between the PFD and amines in electronically excited states.
The 2-TNATA and the DMFL-NPB doped devices showed white light emission as seen in the color photographs of the emitting devices (Figure 3). The changes in the CIE coordinates of the amine doped devices (doping ratios of PFD:amine = 1:0.25 and 1:1) are shown in Figure 4. The 2-TNATA doped device (PFD:2-TNATA = 1:0.25) showed CIE coordinates of (0.33, 0.43) and a Color Rendering Index (CRI) of Ra = 73 at Vturn-on = 3.5 V (Vturn-on is defined as the voltage required to produce a luminance of over 1 cd/cm2 during a voltage sweep measurement) and the DMFL-NPB doped device with the same ratio of PFD:DMFL-NPB (1:0.25) showed CIE coordinates of x = 0.23, y = 0.33, and a CRI of Ra = 54 at Vturn-on = 3.5 V. The emission color of the DMFL-NPB doped device was slightly blue shifted compared to that of the 2-TNATA doped device. This is due to a difference in the exciplex forming abilities of the amines with the PFD, with 2-TNATA having a greater ability to form exciplexes than DMFL-NPB.15
Figure 5 shows the changes in current density, luminance and CIE coordinates of the 2-TNATA doped device when a constant voltage of 5 V was applied. Immediately after applying the voltage, the device showed CIE coordinates of (0.27, 0.37) and a Ra of 67, and the emission color was almost unchanged and stable after 300 sec.
<img alt="Figure 1" src="/files/ftp_upload/54628/54628fig1.jpg" /> 
Figure 1. Fabrication process of LEC device. <a href="http://cloudflare.jove.com/files/ftp_upload/54628/54628fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54628/54628fig2.jpg" /> 
Figure 2. EL emission spectra of PLECs, 2-TNATA doped, DMFL-NPB doped and undoped devices. <a href="http://cloudflare.jove.com/files/ftp_upload/54628/54628fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54628/54628fig3.jpg" /> 
Figure 3. Photograph of light emission from the amine doped devices. Doping ratio of PFD:amine = 1:1. a) 2-TNATA doped device. b) DMFL-NPB doped device (scale bars: 5 mm). <a href="http://cloudflare.jove.com/files/ftp_upload/54628/54628fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/54628/54628fig4.jpg" /> 
Figure 4. Changes in CIE coordinates of the 2-TNATA and the DMFL-NPD doped devices with increasing voltage. a) Devices with doping ratio of PFD:amine = 1:1. b) Devices with doping ratio of PFD:amine = 1:0.25. <a href="http://cloudflare.jove.com/files/ftp_upload/54628/54628fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54628/54628fig5.jpg" /> 
Figure 5. Temporal evolution of a) CIE coordinates, luminance and current, and b) efficacy, luminance, and current of the 2-TNATA doped PLECs. <a href="http://cloudflare.jove.com/files/ftp_upload/54628/54628fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Fabrication of White Light-emitting Electrochemical Cells with Stable Emission from Exciplexes at JoVE.com

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

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 ...

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Nanyang Technological University

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8.0K Views.  JX Nippon Oil & Energy Corporation. 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.

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

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

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Chemistry

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 ...

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.

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 ...

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 ...

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

Preparing a Celadonite Electron Source and Estimating Its Brightness

The electron celadonite source described here performs well in a low-energy electron point-source projection microscope in long-range imaging. It presents major advantages compared to sharp metal tips. Its robustness affords a lifetime of months and it can be used under relatively high pressure. The celadonite crystal is deposited at the apex of a carbon fiber, maintained itself in a coaxial structure ensuring a spherical beam shape and easy mechanical positioning to align the source, the object and the electron-optical system axis. There is a single crystal deposition via generation of celadonite-containing water droplets with a micropipette. Scanning electron microscopy observation can be performed to verify the deposition. However, this adds steps and therefore increases the risk of damaging the source. Thus, after preparation, the source is usually inserted directly under vacuum in the projection microscope. A first high voltage supply provides the kick-off needed to start the electron emission. The field emission process involved is then measured: it has already been observed for dozens of electron sources prepared in this way. The brightness is under-estimated through an over-estimation of source size, intensity at one energy and cone angle measured in a projection system.

The article presents a protocol to prepare a celadonite source and estimate its brightness for use in a long-range imaging low-energy electron point-source projection microscope.

The electron celadonite source described here performs well in a low-energy electron point-source projection microscope in long-range imaging. It presents ...

Development of Efficient OLEDs from Solution Deposition

The use of highly efficient organic emitters based on the thermally activated delayed fluorescence (TADF) concept is interesting due to their 100% internal quantum efficiency. Presented here is a solution deposition method for the fabrication of efficient organic light-emitting diodes (OLEDs) based on a TADF emitter in a simple device structure. This fast, low-cost, and efficient process can be used for all OLED emissive layers that follow the host-guest concept. The fundamental steps are described along with necessary information for further reproduction. The goal to establish a general protocol that can be easily adapted for principal organic emitters currently under study and development.

Presented here is a protocol for the fabrication of efficient, simple, solution-deposited organic light-emitting diodes with low roll-off.

The use of highly efficient organic emitters based on the thermally activated delayed fluorescence (TADF) concept is interesting due to their 100% ...

Hydrothermal Synthesis of Persistent Luminescent Nanoparticles

Synthesis of Persistent Luminescent Nanoparticles for Rewritable Displays and Illumination Applications

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ceased. PLNPs have been widely used across various domains, including information displays, data encryption, biological imaging, and artistic decoration with sustained and vivid luminosity, providing boundless possibilities for a variety of innovative technology and artistic projects. This protocol focuses on an experimental procedure for the hydrothermal synthesis of PLNPs. The successful synthesis of enduring luminescent nanomaterials with Mn2+ or Cr3+ serving as a luminescent center in Zn2GeO4: Mn (ZGO: Mn) or ZnGa2O4: Cr highlights the universality of this synthetic method. On the other hand, the optical properties of ZGO: Mn can be changed by adjusting the pH of precursor solutions, demonstrating the tunability of the protocol. When charged with ultraviolet (UV) at a wavelength of 365 nm for 3 min and then stopped, PLNPs exhibit the remarkable capacity to generate afterglow efficiently and consistently, which makes them ideal for making two-dimensional rewritable displays and three-dimensional transparent, luminous artworks. This protocol outlined in this paper provides a feasible method for the synthesis of persistent luminescent nanoparticles for further illumination and imaging applications, opening up novel prospects for the fields of science and art.

Author Spotlight: Advancing Bioimaging and Therapy with Functional Nanomaterials

A protocol is presented for the synthesis of persistent luminescent nanomaterials (PLNPs) and their potential applications in rewritable displays and artistic processing utilizing the afterglow effect under ultraviolet light (365 nm) irradiation.

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ...

Measuring Electron Transfer Activity in Shewanella oneidensis Using OECTs

Translating Extracellular Electron Transfer Activities with Organic Electrochemical Transistors

Extracellular electron transfer (EET) is a process through which certain microorganisms can transfer electrons across their cell membranes to external electron acceptors, linking cellular metabolism to their environment. While Geobacter and Shewanella have been the primary models for EET research, emerging studies reveal that EET-active species are also associated with fermentation and the human gut microbiome. Leveraging the ability of EET to bridge biological and electronic systems, we present a protocol for using organic electrochemical transistors (OECTs) to translate microbial EET activity into easily detectable electrical signals. This system enables the use of cellular responses to external stimuli for biosensing and biocomputing applications. Specifically, we demonstrated the de-doping of the p-type poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) channel in the OECT is driven by cellular EET from Shewanella oneidensis. By transcriptionally controlling EET flux by genetic circuits, we establish the biosensing capability of this hybrid OECT system to detect chemical stimuli, such as inducer molecules. Furthermore, we introduce plasmid-based Boolean logic gates within the cells, allowing them to process environmental signals and drive current changes in the OECTs, further demonstrating the biocomputing potential of these devices. This method provides a novel interface between biological systems and electronics, enabling future high-throughput screening, biosensing, and biocomputing applications.

Here, we present a protocol for using organic electrochemical transistors (OECTs) to translate extracellular electron transfer (EET) activity in Shewanella oneidensis into electrical signals. The hybrid OECT system provides enhanced robustness, sensitivity, and potential for rapid, high-throughput testing, making it an effective tool for EET measurements.

Extracellular electron transfer (EET) is a process through which certain microorganisms can transfer electrons across their cell membranes to external ...