The authors would like to acknowledge the support in part from the Ministry of Economic Affairs and the Ministry of Science and Technology, Taiwan, via Grants MEA 104-EC-17-A-07-S3-012, MOST 104-2119-M-007-012, and MOST 103-2923-E-007-003-MY3.

NOTE: All the materials used are non-carcinogenic, non-flammable, and non-toxic.
1. Fabrication of Blue-hazard-free Candlelight OLED
<ol>
	<li>Dry process
	<ol>
		<li>Take a glass slide as a substrate to be coated with a 125 nm indium tin oxide (ITO) anode layer. Wash the substrate with 200 mL (50 mL of liquid detergent and 150 mL of deionized water) of soap solution. Rinse the substrate with deionized water. Dry the substrate with a nitrogen jet spray.</li>
		<li>Put the substrate on a glass slide holder and dip the slide holder in acetone solution in a beaker. Put the beaker in an ultrasonic bath. Sonicate the substrate at 50 &#176;C for 10 min.</li>
		<li>Transfer the slide holder with the substrate to isopropanol solution in a beaker and again sonicate at 60 &#176;C for 10 min.</li>
		<li>Take out the substrate from the beaker and put it in the UV/ozone slot for 10 min to dry. Clean the surface completely.</li>
		<li>Break the vacuum of the thermal evaporator chamber by closing the valve of the high vacuum and opening the valve of nitrogen gas to the chamber.</li>
		<li>Load the cleaned substrate in the chamber on the rotating substrate holder. For each layer that will be deposited, load 100 mg of each required organic material, 3 mg of lithium fluoride (LiF), and a 224 mg aluminum (Al) ingot into the crucible inside the chamber.</li>
		<li>Close the door of the chamber and wait for a high vacuum of 5&#215;10-6 Torr. Once the high vacuum has been reached inside the chamber, start the deposition of the organic layers onto the substrate with ITO.
		<ol>
			<li>Deposit a 5 nm hole injection layer at a deposition rate of 0.8-1 &#197;/s.</li>
			<li>Deposit a 25 nm transport layer at a deposition rate of 1-1.5 &#197;/s.</li>
			<li>Deposit a 30 nm emissive layer (8 wt.% green dye and 0.85 wt.% deep-red dye doped in 20 mg of a specified host) at a deposition rate of 1-1.5 &#197;/s.</li>
			<li>Deposit a 30 nm electron transport layer at a deposition rate of 1-1.5 &#197;/s.</li>
			<li>Deposit a 20 nm layer of electron transport co-evaporate with electron injection material at a deposition rate of 1-1.5 &#197;/s.</li>
			<li>Deposit a 1-nm electron injection layer of LiF at a deposition rate of 0.3-0.4 &#197;/s.</li>
			<li>Deposit a 100-nm cathode layer of Al at a deposition rate of 10-15 &#197;/s.</li>
		</ol>
		</li>
		<li>Turn off the current controller and wait 10 min under high vacuum. Close the valve for high vacuum and open the valve for nitrogen gas to the chamber to break the high vacuum.</li>
		<li>Move the fabricated OLED device from the chamber to the atmosphere, and then transfer it to a glove box with an encapsulation machine under a nitrogen atmosphere.</li>
		<li>Encapsulate the fabricated OLED device with a top cover made of glass by using glue and then dry the glue by putting the device in UV radiation box for 110 s.</li>
		<li>Eject out the encapsulated OLED device from the glove box and transfer it to the darkroom for measurements.</li>
	</ol>
	</li>
	<li>Wet process
	<ol>
		<li>Clean the ITO-coated substrate by using the aforementioned cleaning procedures from steps 1.1.2 to 1.1.4.</li>
		<li>Take an aqueous solution of PEDOT: PSS (stored at 4 &#176;C) to deposit the hole injection layer. Filter the solution in a vial by using a 25-mm diameter filter consisting of a nylon fabric with a pore size of 0.45 &#181;m.</li>
		<li>In a vial, prepare the hole transport layer solution of 3,6-bis(4-vinylphenyl)-9-ethylcarbazole (VPEC)30 dissolved in chlorobenzene solvent in the ratio of 3 mg:1,000 &#181;L. Sonicate the solution for 30 min in the ultrasonic bath and filter the sonicated solution in a vial with a 15-mm diameter filter consisting of a nylon fabric with a pore size of 0.45 &#181;m.</li>
		<li>Prepare a solution for the emissive layer.
		<ol>
			<li>Take 5 mg of the specified host material and dissolve it in tetrahydrofuran (THF) in a ratio of 10 mg:1,000 &#181;L. Sonicate the host-solution at 50 &#176;C for 30 min.</li>
			<li>Take 1 mg of each of the required guest materials and dissolve them in THF in a ratio of 1 mg:1,000 &#181;L. Sonicate the guest-solution at 50 &#176;C for 30 min.</li>
			<li>Filter each solution separately in vials with a 15 mm diameter filter consisting of a nylon fabric with a pore size of 0.45 &#181;m.</li>
			<li>Mix the guest-solution into the host-solution according to the given weight percent (3 wt.% of yellow dye, 6 wt.% of orange-dye, and 12.5 wt.% of green dye), doping for the emissive layer.</li>
		</ol>
		</li>
		<li>Transfer the vials of PEDOT: PSS, VPEC, and emissive layer solutions along with pre-cleaned substrate and pipette them into the glove box.</li>
		<li>Start coating the layers onto the substrate with ITO in the following sequence under a nitrogen atmosphere: the hole injection layer, hole transport layer, and emissive layer.
		<ol>
			<li>Deposit a 35 nm hole injection layer by spin-coating a 750 &#181;L solution of PEDOT: PSS at 4,000 revolutions per min (rpm) for 20 s.</li>
			<li>Dry the PEDOT: PSS layer at 120 &#176;C for 40 min to remove residual solvent.</li>
			<li>Deposit a 10-nm hole transport layer by spin-coating a 400 &#181;L solution of VPEC at 3,000 rpm for 20 s.</li>
			<li>Bake the layer at 120 &#176;C for 20 min to remove residual solvent.</li>
			<li>Heat the layer at 230 &#176;C for 40 min for a crosslinking reaction to occur before depositing the emissive layer30.</li>
			<li>Deposit a 20 nm emissive layer by spin-coating a 400-&#181;L solution at 2,500 rpm for 20 min.</li>
		</ol>
		</li>
		<li>Eject out the spin-coated substrate from the glove box to the atmosphere and transfer it to the thermal evaporator chamber for the further deposition of layers. Break the vacuum of the thermal evaporator chamber by closing the valve of the high vacuum and open the valve of the nitrogen gas to the chamber.</li>
		<li>Load the substrate in the chamber on the rotating substrate holder. Load the 45 mg of TPBi, 3 mg of LiF, and a 224 mg Al ingot into the crucible inside the chamber for the layers that will be deposited. Deposit the layers onto the substrate with the emissive layer in the following sequence.
		<ol>
			<li>Deposit a 32 nm electron transport layer of TPBi at a deposition rate of 1-1.5 &#197;/s.</li>
			<li>Deposit a 1 nm electron injection layer of LiF at a deposition rate of 0.3-0.4 &#197;/s.</li>
			<li>Deposit a 100-nm cathode layer of Al at a deposition rate of 10-15 &#197;/s.</li>
		</ol>
		</li>
		<li>Turn off the current controller and wait 10 min under the high vacuum. Follow the aforementioned procedures from steps 1.1.8 to 1.1.11 to complete the encapsulated OLED device.</li>
	</ol>
	</li>
	<li>Calculation of the retina-permissible exposure limit &#34;t&#34;:
	<ol>
		<li>Measure the EL spectrum of the lighting device by using a spectroradiometer. The resulting EL spectrum is shown in Figure 1a.</li>
		<li>Measure the EL spectrum data (intensity versus wavelength) at a CCT.</li>
		<li>Convert the EL spectrum data to spectral radiance E&#955; (normalized intensity versus wavelength). Change the spectrum to the format shown in Figure 1b.</li>
		<li>Use the spectral data from the blue light-weighted function for measuring the retinal hazard from lighting source (i.e., draw the blue light hazard function B(&#955;) with respect to the wavelength)28. The resulting plot is shown in Figure 1c.</li>
		<li>Calculate the value of the radiance (EB) of a given light source by using the spectral radiance E&#955; and blue-hazard function B(&#955;) corresponding to each wavelength.</li>
		<li>Put the values of E&#955; and B(&#955;) from the abovementioned plots into the following formula: 
		<img alt="Equation 1" src="/files/ftp_upload/54644/54644equation1.jpg" />&#160; .....(1)</li>
		<li>Get the numerical value of EB in W m-2.</li>
		<li>Put the value of EB in the maximum permissible retinal exposure limit &#34;t&#34; formula: 
		<img alt="Equation 2" src="/files/ftp_upload/54644/54644equation2.jpg" /> .....(2)</li>
		<li>Acquire the exposure limit &#34;t&#34; with respect to the CCT of a given light source.</li>
	</ol>
	</li>
	<li>Calculation for melatonin suppression sensitivity:
	<ol>
		<li>Measure the EL spectrum of a given lighting device by using spectroradiometer. The resulting spectrum is shown in Figure 2a.</li>
		<li>Get the melatonin suppression power per quantum, SPQ, from the programmed data29. For a given monochromatic light &#955;, express the SPQ as follows: 
		SPQ (&#955;) = 10 (&#955;r-&#955;)/C&#160; &#8230;&#8230;&#8230;&#8230;. (3) 
		The values of SPQ (&#955;) with respect to wavelength are given in Table 1, and the respective graph is shown in Figure 2b.</li>
		<li>Use the photopic luminosity function V (&#955;) to convert SPQ (&#955;) into the melatonin suppression power per lux, SLC (&#955;), in order to give it a practical meaning. The values of V (&#955;) with respect to the wavelength are given in Table 2, and the respective graph is shown in Figure 2c.</li>
		<li>Express the correlated melatonin suppression power, SLC (&#955;), for a polychromatic light, as follows:29 
		SLC (&#955;) = &#8747;&#955;SPQ(&#955;)SI(&#955;)d&#955;/&#8747; V(&#955;)SI(&#955;)d&#955;&#160; &#8230;&#8230;&#8230;&#8230;&#8230;.. (4)</li>
		<li>Put the values of the intensity SI (&#955;) from the EL spectrum of a given light source along with the values of SPQ (&#955;) and V(&#955;) with respect to the wavelength in the above formula and calculate the SLC (&#955;) as follows: 
		SLC (&#955;) = 
		<img alt="Equation 3" src="/files/ftp_upload/54644/54644equation3.jpg" /></li>
		<li>Retrieve a numerical value of SLC (&#955;) in lx-1 from the above calculation. For example, by putting the SI (&#955;) from the EL spectrum of the given candlelight OLED with a CCT of 1,940 K, the melatonin suppression power is: 
		SLC (&#955;) = 90 lx-1</li>
		<li>Choose a reference light to calculate the relative melatonin suppression sensitivity of a given light source. The reference light can be a wavelength of 460 or 480 nm. Here, we choose a blue light of 480 nm as the reference light.</li>
		<li>Calculate the SLC (&#955;) for the reference blue light (480 nm) by using the abovementioned formula. 
		SLC (480 nm) = 3,445 lx-1</li>
		<li>Divide the SLC (&#955;) of a given light source by the SLC (480 nm) and multiply the quotient by 100 to get the melatonin suppression sensitivity percentage (%) of a given light relative to the reference blue light. 
		Relative melatonin suppression sensitivity = <img alt="Equation 4" src="/files/ftp_upload/54644/54644equation4.jpg" /> &#215;100 % &#8230;&#8230;&#8230;.... (5) 
		NOTE: For example, relative melatonin suppression sensitivity = <img alt="Equation 5" src="/files/ftp_upload/54644/54644equation5.jpg" />&#215;100% = 2.61%. Thus, the given candlelight OLED shows a melatonin suppression sensitivity of 2.61% relative to that of the 480-nm blue light.</li>
	</ol>
	</li>
</ol>

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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-power+flexible+organic+light-emitting+diode+display+device.">Low-power flexible organic light-emitting diode display device.</a> Adv. Mater. 23, 3511-3516 (2011).</li><li>Kaake, L. G., Barbara, P. F., Zhu, X. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intrinsic+charge+trapping+in+organic+and+polymeric+semiconductors:+a+physical+chemistry+perspective.">Intrinsic charge trapping in organic and polymeric semiconductors: a physical chemistry perspective.</a> J. Phys. Chem. Lett. 1 (3), 628-635 (2010).</li><li>Yersin, H., Rausch, A. F., Czerwieniec, R., Hofbeck, T., Fischer, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+triplet+state+of+organo-transition+metal+compounds.+Triplet+harvesting+and+singlet+harvesting+for+efficient+OLEDs.">The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs.</a> Coord. Chem. Rev. 255, 2622-2652 (2011).</li><li>Jou, J. H., Kumar, S., Agarwal, A., Lia, T. H., Sahoo, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Approaches+for+fabricating+high+efficiency+organic+light+emitting+diodes.">Approaches for fabricating high efficiency organic light emitting diodes.</a> J. Mater. Chem. C. 3, 2974-3002 (2015).</li><li>Volz, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Auto-catalysed+crosslinking+for+next-generation+OLED-design.">Auto-catalysed crosslinking for next-generation OLED-design.</a> J. Mater. Chem. 22, 20786-20790 (2012).</li><li>Furuta, P. T., Deng, L., Garon, S., Thompson, M. E., Frechet, J. M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum+functionalized+random+copolymers+for+use+in+solution-processible,+efficient,+near-white+organic+light-emitting+diodes.">Platinum functionalized random copolymers for use in solution-processible, efficient, near-white organic light-emitting diodes.</a> J. Am. Chem. Soc. 126 (47), 15388-15389 (2004).</li><li>Biwu, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+thermally+cross-linkable+polymer+and+its+application+as+a+hole-transporting+layer+for+solution+processed+multilayer+organic+light+emitting+diodes.">New thermally cross-linkable polymer and its application as a hole-transporting layer for solution processed multilayer organic light emitting diodes.</a> Chem. Mater. 19, 4827-4832 (2007).</li></ol>

We have nothing to disclose.

The most critical steps in the fabrication of OLED devices are: 1) cleaning the glass substrate, 2) selecting the appropriate solvent, 3) dissolving the organic materials, 4) uniformly forming the film via spin-coating in the wet process, and 5) controlling the deposition rate and thickness of the organic layer during the thermal evaporation. Initially, cleaning the ITO anode coated substrate is a crucial step to achieve high efficiency. The glass substrate is cleaned with soap solution to remove greasy spots or layers. Then, it is ultra-sonicated in acetone, followed by isopropanol, to eradicate dirt particles from the anode layer. UV/ozone treatment is given to the substrate before depositing any layer on the ITO. UV/ozone treatment not only dries the substrate, but it also increases the surface oxygen and thus enhances the work function of ITO35. It can reduce the hole injection barrier to facilitate more hole transport.
Subsequently, organic layers are deposited on the ITO anode by two separate methods, namely the dry process and the wet process. For the candlelight OLED fabricated with the dry process, all organic molecules are evaporated under high vacuum and deposited successively on the ITO layer. In this process, temperature is increased gradually step by step, and the organic materials are deposited at a certain temperature. It prevents non-uniformity of the thin film and allows for precise layer thickness. Dry-processed candlelight OLED devices are ultra-clean and free from any non-emissive spots. Nevertheless, this process is limited to producing large-area films and is cost-ineffective due to a large consumption of organic materials. On the other hand, the wet process includes spin-coating, inkjet printing, and screen printing of polymer and organic materials, a cost-effective, large-area, and mass-manufacturing procedure for the creation of OLED devices36-38.
For wet-processed candlelight OLEDs, hole injection, hole transporting, and emissive layers are spin-coated at a specified rpm and duration. It is a fast deposition technique, which allows for continuous production. Major challenges in the wet process are the selection of solvent and the prevention of undesirable blending of subsequently coated organic layers. Some organic materials do not dissolve properly in the organic solvent due to a polarity mismatch. Organic solvents also dissolve precast organic layers, resulting in morphological and compositional defects39,40. To avoid such difficulties, we baked the hole injection layer of a conducting polymer, PEDOT:PSS, to make a more hydrophilic surface before coating the hole transport layer. After that, a hole transport layer of VPEC is spin-coated and again baked at 120 &#176;C for 20 min to make it thermally stable and to avoid the presence of residual solvent. Furthermore, the VPEC layer is heated to 230 &#176;C for crosslinking30 the hole transporting layer. Accordingly, the emissive layer is spin-coated onto the hole transporting layer to circumvent any morphological defects. The electron transport layer and cathode layer are deposited via thermal evaporation under high vacuum.
Earlier-reported candlelight-style OLED devices were fabricated by a dry process18,21. These devices were composed of a complex architecture, like double emissive layers and an additional carrier modulation layer18,21,22. In this study, we have modified the OLED device architecture and avoided complexity by using a single emissive layer. The reported blue-hazard-free candlelight OLEDs are also fabricated without using any blue or sky-blue emitters. The EL spectrum of OLED devices can be arbitrarily formed. Dry- and wet-processed OLED devices exhibited differently shaped emission spectra with low CCT values. These spectra showed different effects from the perspective of maximum exposure limit and melatonin suppression sensitivity (Table 3).
The dry process allows the vapor deposition of small molecules and oligomers in the multiple layer architecture. Additionally, the dry process develops various ways to achieve high efficiency. Also, the multiple-layered architecture enables the lower carrier-injection barrier, balanced carrier-injection to emissive layer, and effective recombination zone to facilitate more carriers to recombine40. However, the dry process has some issues, such as the limited thermal stability of the organic molecules, the low throughput due to the need of a high-vacuum fabrication condition, and the material wastage due to the low material utilization rate in deposition, etc.
In contrast, the wet process is more favorable to reduce the production cost and to achieve high efficiency. Low-cost polymeric materials are promising for multiple-layer, wet-processed OLEDs. Their efficiency is comparatively lower than vacuum-deposited, small molecule organic materials. In the wet process, efficiency can be improved by utilizing a combination of successive polymer and small molecule layers. Generally, the employment of a polymeric hole transport layer with high triplet energy is able to stabilize the prior spin-coated hole injection film and also to confine the excitons generated in the emissive layer. Small-molecule organic materials with high glass transition temperatures are not crystalized during spin-coating and uphold the film integrity. Additionally, high triplet energy small molecules can be used as an effective host material to facilitate a host-to-guest energy transfer mechanism. Wet-process fabrication of OLEDs also has some restrictions due to the solubility issue of its materials. Nowadays, to stabilize the multiple layer architecture in the wet process, many approaches have been developed that maintain the solubility from polar to non-polar solvents42,43,44. The wet process enables the devices to be fabricated in large areas and roll-to-roll with high throughput. The wet process offers more design freedom for disruptive characteristics, such as flexibility, transparency, and ultra-thinness. The wet process can be a promising technology for OLED lighting.

Nowadays, lighting sources like LED and CFL are abundantly used for indoor and outdoor illumination, partly for energy-saving reasons. However, these lights are rich in blue emission, showing a higher tendency to cause blue-hazards. LED and CFL emit a spectrum enriched with blue light, leading to irreversible damage to retinal cells1,2,3,4. Blue light or intense white light with high CCT suppresses the secretion of melatonin, an oncostatic hormone, which may disrupt the circadian rhythm5,6 and sleeping behavior7,8. Melatonin, an essential hormone for the circadian rhythm, is synthesized in the pineal gland9. A high level of melatonin is observed during the dark period during the 24-h light-dark cycle10. However, intensive light at night suppresses its synthesis and disrupts the circadian rhythm11. Melatonin suppression due to overexposure to bright lights at night can be a risk factor for breast cancer in women12,13,14. Besides these hazards, blue light interrupts the activities of nocturnal amphibians and can be threatening to ecological protection. It has also been reported that LED lighting in museums is discoloring the actual colors of oil paintings painted by Van Gogh and C&#233;zanne15,16.
Thus, a blue-emission free and low CCT candle-like organic LED (OLED) can be a good substitute for LED and CFL. Candles emit a blue-hazard-free and low CCT (1,914 K) illumination, as well as a high-quality (high color rendering index, CRI) emission spectrum. However, most of the electricity-driven lighting devices emit intense blue light with a comparatively high CCT. For example, the lowest CCT is about 2,300 K for incandescent bulbs, while it is 3,000 or 5,000 K for warm or cold white fluorescent tubes and LED luminaires. So far, low CCT OLEDs nearly free of the blue emission have been fabricated for human-friendly lighting. In 2012, Jou&#39;s group reported a physiologically friendly, dry-processed, single emissive layer OLED with a CCT of 1,773 K and a power efficiency of 11.9 lm/W17. The device exhibited a much lower CCT as compared to the incandescent bulb (2,300 K), while its power efficiency was not acceptable from an energy-saving point of view. They reported another dry-processed candlelight-style OLED by using double emissive layers along with a carrier modulation layer18. It exhibited a low CCT of 1,970 K and a power efficiency of 24 lm/W. Later on, a dry-processed OLED consisting of three emissive layers along with a carrier modulation layer was reported19. Its power efficiency was from 21 to 3 lm/W and varied with the CCT, which ranged from 2,500 K to 1,900 K. In 2014, Hu et al. reported a dry-processed hybrid OLED with double emissive layers separated by an interlayer, which showed a high power efficiency of 54.6 lm/W and a low CCT of 1,910 K20. Recently, Jou&#39;s group has fabricated a high-efficiency candlelight-style OLED by employing double emissive layers21. It exhibited a high power efficiency of 85.4 lm/W with a CCT of 2,279 K. Until now, all efforts have been made to develop high efficiency, low CCT candlelight-style OLED devices by utilizing dry processes and complicated device architectures17,18,19,20,21,22. Devising a candlelight OLED with wet-process feasibility while simultaneously having a low CCT, a high power efficiency, and a high light quality is a challenge. No study has been developed to describe the emission spectrum sensitivity of a given light source with respect to the blue light. The quality of light at night can be decided/improved to minimize the suppression of melatonin secretion.
There are some reported models that calculate the amount of suppression. Firstly, Brainard et al.23 and Thapan et al.24 reported the spectral sensitivity by using monochromatic light. Later on, the effect of polychromatic light on melatonin suppression was described25,26. The latter is adopted in this study, since most of the commercially available luminaires or novel lighting sources are polychromatic and span over the entire visible range (i.e., from deep red to violet).
In this work, we present comprehensive protocols for the fabrication of blue-hazard-free candlelight OLEDs via dry and wet processes. In both processes, the device architecture is simplified by employing a single emissive layer without any carrier modulation layers. The electroluminescent (EL) spectrum of the fabricated OLED is analyzed for the retinal exposure limit and for the level of melatonin secretion suppression. A maximum exposure limit of emitted light to the retina is calculated by using the theoretical aspect that was reported by the International Electrotechnical Commission (IEC) 62471 standard27,28. The maximum exposure limit &#34;t&#34; is calculated by using the emission spectrum of each OLED at the brightness of 100 and 500 lx, sufficient for home and office illumination, respectively. All related calculation steps are sequentially given in the protocol section. Further, the effect of lighting on the melatonin suppression sensitivity is calculated by following the equations of the action spectrum of melatonin suppression29. The calculation is done by following the steps given in the protocol section. The calculated values of the maximum exposure limit &#34;t&#34; and the melatonin suppression sensitivity (%) with respect to CCT are given in Table 3.

<table><tbody><tr><td>ITO glass</td><td>Lumtech</td><td></td><td>84% transparency</td></tr><tr><td>poly(3,4-ethylenedioxythiophene) - poly(styrenesulfonate) (PEDOT/PSS)</td><td>UniRegion Bio-Tech</td><td></td><td>Stored at 4 &amp;deg;C, HOMO (eV) = -4.9, LUMO (eV) = -3.3</td></tr><tr><td>4,4,4-tris(N-carbazolyl)triphenylamine (TCTA)</td><td>E-Ray Optoelectronics Technology co., Ltd</td><td></td><td>Non-toxic, HOMO (eV) = -5.7, LUMO (eV) = -2.3</td></tr><tr><td>tris(2-phenyl-pyridine) (Ir(ppy)&lt;sub&gt;3&lt;/sub&gt;)</td><td>E-Ray Optoelectronics Technology co., Ltd</td><td></td><td>Non-toxic, HOMO (eV) = -5.6, LUMO (eV) = -3.9</td></tr><tr><td>1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi)</td><td>Luminescence Technology corp.</td><td></td><td>Non-toxic, HOMO (eV) = -6.2, LUMO (eV) = -2.7</td></tr><tr><td>iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N,C 2&amp;rsquo;)acetylacetonate (PO-01)</td><td>Luminescence Technology corp.</td><td></td><td>Non-toxic, HOMO (eV) = -5.1, LUMO (eV) = -2.7</td></tr><tr><td>tris(2-phenylquinoline)iridium(III) (Ir(2-phq)&lt;sub&gt;3&lt;/sub&gt;)</td><td>E-Ray Optoelectronics</td><td></td><td>Non-toxic, HOMO (eV) = -5.1, LUMO (eV) = -2.8</td></tr><tr><td>LiF</td><td>Echo chemicals</td><td></td><td>99.98%</td></tr><tr><td>Aluminium ingot (Al)</td><td>Guv team International pvt. ltd</td><td></td><td>100.00%</td></tr><tr><td>Acetone</td><td>Echo chemicals</td><td></td><td>99.90%</td></tr><tr><td>2-Propanol</td><td>Echo chemicals</td><td></td><td>99.90%</td></tr><tr><td>Hole-injection material, WHI-001</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -9.8, LUMO (eV) = -5.6</td></tr><tr><td>Hole-transport material, WHI-215</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -5.4, LUMO (eV) = -2.5</td></tr><tr><td>host material, WPH-401</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -5.8, LUMO (eV) = -2.7</td></tr><tr><td>Electron-injection material, WIT-651</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -5.8, LUMO (eV) = -3.1</td></tr><tr><td>Electron-transpot material, WET-603</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -5.9, LUMO (eV) = -2.6</td></tr><tr><td>Green dye, WPGD-832</td><td>WAN HSIANG precision machinery co., Ltd</td><td></td><td>non-toxic, HOMO (eV) = -5.8, LUMO (eV) = -3.1</td></tr><tr><td>Deep-red dye, PER 53</td><td>E-Ray Optoelectronics Technology co., Ltd</td><td></td><td>non toxic, HOMO (eV) = -5.1, LUMO (eV) = -2.4</td></tr></tbody></table>

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.

Watch this Scientific Journal Video about Blue-hazard-free Candlelight OLED at JoVE.com

Blue-hazard-free Candlelight OLED

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 ...

Nanyang Technological University

Research

JoVE Journal

Engineering

9.3K Views.  National Tsing Hua University. We present a protocol for the fabrication of a blue-hazard-free candlelight organic light emitting diode (OLED) for eye protection and melatonin secretion.

Video: Blue-hazard-free Candlelight OLED

Fluorescent Paper Strips for the Detection of Diesel Adulteration with Smartphone Read-out

Three fluorescent molecular rotors of 4-dimethylamino-4-nitrostilbene (4-DNS) were investigated for their potential use as viscosity probes to indicate the content of kerosene in diesel/kerosene blends, a wide-spread activity to adulterate fuel. In solvents with low viscosity, the dyes rapidly deactivate via a so-called twisted intramolecular charge transfer state, efficiently quenching the fluorescence. Measurements of diesel/kerosene blends revealed a good linear correlation between the decrease in fluorescence and the increase of the fraction of the less viscous kerosene in diesel/kerosene blends. Immobilization of the hydroxy derivative 4-DNS-OH in cellulose paper yielded test strips that preserve the fluorescent indicator&#39;s behavior. Combination of the strips with a reader based on a smartphone and a controlling app allowed to create a simple field test. The method can reliably detect the presence of kerosene in diesel from 7 to 100%, outperforming present standard methods for diesel adulteration.

Here, we present a protocol to detect the adulteration of diesel with kerosene using test strips coated with a fluorescent viscosity probe together with a smartphone-based analysis system.

Three fluorescent molecular rotors of 4-dimethylamino-4-nitrostilbene (4-DNS) were investigated for their potential use as viscosity probes to indicate ...

Environment

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 ...

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 ...

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 ...

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% ...

Quantitative Characterization of Bioink Properties for Continuous DLP Printing

Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing parameters of digital light processing (DLP). However, the acquisition of working curves wastes materials and requires high formability of materials, which are not suitable for biomaterials. In addition, the reduction of cell activity due to multiple exposures and the failure of structural formation due to repeated positioning are both unavoidable problems in conventional DLP bioprinting. This work introduces a new method of obtaining the working curve and the improvement process of continuous DLP printing technology based on such a working curve. This method of obtaining the working curve is based on the absorbance and photorheological properties of the biomaterials, which do not depend on the formability of the biomaterials. The continuous DLP printing process, obtained from improving the printing process by analyzing the working curve, increases the printing efficiency more than tenfold and greatly improves the activity and functionality of cells, which is beneficial to the development of tissue engineering.

Author Spotlight: Quantitative Characterization of Liquid Photosensitive Bioink Properties for Continuous Digital Light Processing Based Printing  

This study uses temperature and material composition to control the yield stress properties of yield stress fluids. The solid-like state of the ink can protect the printing structure, and the liquid-like state can continuously fill the printing position, realizing the digital light processing 3D printing of extremely soft bioinks.

Precise printing fabrication of bioinks is a prerequisite for tissue engineering; the Jacobs working curve is the tool to determine the precise printing ...

Bioengineering

Advanced Cardiac Rhythm Management by Applying Optogenetic Multi-Site Photostimulation in Murine Hearts

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is currently the only treatment for life-threatening ventricular fibrillation. However, defibrillation may have side-effects, including intolerable pain, tissue damage, and worsening of prognosis, indicating a significant medical need for the development of more gentle cardiac rhythm management strategies. Besides energy-reducing electrical approaches, cardiac optogenetics was introduced as a powerful tool to influence cardiac activity using light-sensitive membrane ion channels and light pulses. In the present study, a robust and valid method for successful photostimulation of Langendorff perfused intact murine hearts will be described based on multi-site pacing applying a 3 x 3 array of micro light-emitting diodes (micro-LED). Simultaneous optical mapping of epicardial membrane voltage waves allows the investigation of the effects of region-specific stimulation and evaluates the newly induced cardiac activity directly on-site. The obtained results show that the efficacy of defibrillation is strongly dependent on the parameters chosen for photostimulation during a cardiac arrhythmia. It will be demonstrated that the illuminated area of the heart plays a crucial role for termination success as well as how the targeted control of cardiac activity during illumination for modifying arrhythmia patterns can be achieved. In summary, this technique provides a possibility to optimize the on-site mechanism manipulation on the way to real-time feedback control of cardiac rhythm and, regarding the region specificity, new approaches in reducing the potential harm to the cardiac system compared to the usage of non-specific electrical shock applications.

This work reports a method for controlling the cardiac rhythm of intact murine hearts of transgenic channelrhodopsin-2 (ChR2) mice using local photostimulation with a micro-LED array and simultaneous optical mapping of epicardial membrane potential.

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is ...