Blue-hazard-free Candlelight OLED

Summary

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

Abstract

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.

Introduction

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 cells^1,2,3,4. Blue light or intense white light with high CCT suppresses the secretion of melatonin, an oncostatic hormone, which may disrupt the circadian rhythm^5,6....

Protocol

NOTE: All the materials used are non-carcinogenic, non-flammable, and non-toxic.

1. Fabrication of Blue-hazard-free Candlelight OLED

1. Dry process
   1. 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.
   2. 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 °C for 10 min.....

Results

The current-voltage-luminance characteristics of the resulting candlelight OLEDs are measured by using an electrometer together with a 100 A luminance meter. The emission areas are 9 mm² for all of the resulting dry-processed devices and are 25 mm² for wet-processed devices. Here, we used a 125 nm ITO-coated glass substrate with a sheet resistance of 15 Ω/sq as an anode. It has a transparency greater than 84% (Table 4). All the OLED devices consistin.......

Discussion

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. .......

Materials

List of materials used in this article

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