Professor Kanata Takuji of Kansai University and the joint research and development team of JNC Petrochemical Co., Ltd., a subsidiary of JNC Corporation, have successfully developed a blue light-emitting material for organic display panels with color purity exceeding quantum dots and LEDs . As a new display technology to replace the liquid crystal display, the organic EL (OLED) display is gradually being promoted. However, organic light-emitting materials have the disadvantage of low color purity (wide emission spectrum).
Need to develop OLED display luminescent materials with excellent color purity and luminous efficiency;
Using the characteristics of nitrogen and boron flexibly, we have successfully developed an organic series of blue light-emitting materials (ν-DABNA) with a color purity exceeding that of gallium nitride (Gallium) series LEDs and cadmium (Cadmium) series quantum dots.
It is expected to achieve high color gamut, high brightness, low power consumption, and blue light reduction for organic EL displays.
If the color purity is low, when it is applied to the display screen, it is necessary to use the optical filter (Filter) to remove unnecessary colors from the luminescence spectrum (Spectre) and improve the color purity. As a result, the brightness and luminous efficiency of the display screen will be large The amplitude is reduced. In addition, the improvement of color purity through filters is still limited. Therefore, there is a problem that it is difficult to improve the color gamut of the display screen, and it is necessary to develop a luminescent material with higher color purity.
Professor Hatada and his R & D team introduced 2 boron and 4 nitrogen at the appropriate positions of the luminescent molecules, plus the effect of the resonance effect, successfully controlled the cause of the broad luminescence spectrum-that is, stretching vibration, and successfully developed Organic blue light emitting material (v-DABNA) with a color purity that exceeds the gallium nitride (Gallium) series LEDs and cadmium (Cadmium) series quantum dots.
The R & D team successfully developed DABNA in 2016, which is the prototype of ν-DABNA (Prototype), and successfully applied it to the organic EL display of high-end smartphones. The color purity and luminous power of ν-DABNA developed this time far exceed that of DABNA, and it is expected to achieve high color gamut, high brightness, low power consumption, and blue light reduction of organic EL displays.
The research and development achievements were published on the online breaking report of the British science magazine "Nature Photonics" on July 15, 2019 (UK time).
Research background and process:
Compared with the liquid crystal display, the organic EL (OLED) display has excellent contrast (Contrast), no viewing angle restrictions, fast response and other advantages, and has a wide range of applications in smartphones, TVs, and industrial displays. As light-emitting materials for organic EL displays, fluorescent materials, phosphorescent materials, and thermally activated delayed fluorescence (TADF) materials can be used as organic series of light-emitting materials. However, there are full width at half width Half Maxima) is larger and has lower color purity.
In general, the light emission of the display is to display a variety of colors by mixing the three primary colors of red, green, and blue. If the color purity is low, there may be a problem that the color cannot be reproduced. The picture quality (color reproducibility) will also decrease. Organic EL displays sold on the market generally remove unnecessary light from the emission spectrum through an optical filter (Filter) to improve color purity (that is, reduce the width of the spectrum) before use. At this time, if the width of the original spectrum is wider, the proportion of the removed light will also increase, which will cause a problem that the brightness and luminous efficiency of the display will be greatly reduced. Moreover, the color purity improved by the filter is limited, so there is also a problem that it is difficult to improve the color gamut of the display screen, so it is urgent to develop a luminescent material with higher color purity. In addition, against this background, as a technology to replace organic EL, micro-LEDs using gallium nitride series (Diode) (LED) and QD-OLEDs using cadmium series quantum dots R & D is in full swing.
research content:
Professor Hatada and his research team have developed an organic series blue light-emitting material (v-DABNA) with extremely high color purity (refer to the right picture below). Hitherto, as the blue light-emitting material of organic EL, an inducer of polycyclic aromatic hydrocarbons (Pyrene) and perylene (Perylene) having high luminous efficiency has been used. , But it brings about the problem that the full width at half maxima (Full Width at Half Maxima) is about 40nm (refer to the left picture below). Luminescence, when the singlet state (S1) to the ground state (S0) transition (S1 → S0 migration, equivalent to the electron migration from LUMO to HOMO), the electron density between carbon atoms changes great. Due to the migration of S1 → S0, if the density between carbon atoms becomes larger, the activity force between carbon atoms will also change, although it will also be accompanied by the expansion and contraction vibration of the carbon-carbon combination, according to the energy of the vibration (Energy) ( 1300-1700cm-1), the width of the emission spectrum increases. On the other hand, with regard to v-DABNA, due to the multiple resonance effects of boron and nitrogen, HOMO and LUMO are locally distributed on different carbon atoms, because there are almost no electrons between the carbon atoms generated by S1 → S0 migration The density changes, so there is no stretching vibration (refer to the right picture). Although the migration of S1 → S0 will produce a torsional (torsional) vibration of the entire molecule, the energy of the vibration (Energy) is extremely small (~ 20cm-1), so it shows an extremely narrow half-peak width of 14-18nm Luminescence spectrum. In addition, v-DABNA has excellent TADF characteristics, in terms of practical brightness (300cdm-2), it has a 30% external quantum luminous efficiency far exceeding the conventional blue particles.
Future direction:
The v-DABNA developed this time has both the color purity and the highest level of power that exceed the gallium nitride series LED and Cadmium series quantum dots. Therefore, it is expected to achieve high color gamut and high brightness of organic EL displays Reduction, low power consumption, and blue light reduction. In addition, regarding the display screens on the market, how to improve the performance of the blue luminescence element is its "Bottle Neck". To this end, by rationally optimizing the element structure and production process, it is expected that the cost of the display screen can be reduced in the future. Through the molecular design established by this research, more luminescent materials with excellent characteristics will be developed in the future.
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