Limits...
Microfluidic White Organic Light-Emitting Diode Based on Integrated Patterns of Greenish-Blue and Yellow Solvent-Free Liquid Emitters.

Kobayashi N, Kasahara T, Edura T, Oshima J, Ishimatsu R, Tsuwaki M, Imato T, Shoji S, Mizuno J - Sci Rep (2015)

Bottom Line: The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V.A white emission with Commission Internationale de l'Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light.The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.

ABSTRACT
We demonstrated a novel microfluidic white organic light-emitting diode (microfluidic WOLED) based on integrated sub-100-μm-wide microchannels. Single-μm-thick SU-8-based microchannels, which were sandwiched between indium tin oxide (ITO) anode and cathode pairs, were fabricated by photolithography and heterogeneous bonding technologies. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ) was used as a solvent-free greenish-blue liquid emitter, while 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb)-doped PLQ was applied as a yellow liquid emitter. In order to form the liquid white light-emitting layer, the greenish-blue and yellow liquid emitters were alternately injected into the integrated microchannels. The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V. A white emission with Commission Internationale de l'Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light. The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting.

No MeSH data available.


(a) PL spectrum of PLQ and 2wt% TBRb-doped PLQ, and absorption spectrum of 33.3 μM TBRb. (b) EL spectra of PLQ and 2wt% TBRb-doped PLQ with the microfluidic OLED. Inset: EL emissions of PLQ and TBRb-doped PLQ, and the sum of EL spectra of PLQ and 2wt% TBRb-doped PLQ under an applied voltage of 100 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4594091&req=5

f3: (a) PL spectrum of PLQ and 2wt% TBRb-doped PLQ, and absorption spectrum of 33.3 μM TBRb. (b) EL spectra of PLQ and 2wt% TBRb-doped PLQ with the microfluidic OLED. Inset: EL emissions of PLQ and TBRb-doped PLQ, and the sum of EL spectra of PLQ and 2wt% TBRb-doped PLQ under an applied voltage of 100 V.

Mentions: Figure 3(a) shows the absorption spectrum of 33.3 μM TBRb and the PL spectra of PLQ and TBRb-doped PLQ. An excitation wavelength of 365 nm was used for the PL measurements because the host PLQ has a strong UV absorption wavelength at less than 377 nm151622. TBRb showed an absorption spectrum ranging from 400 nm to 570 nm. The PL emission of PLQ has a peak wavelength of 500 nm, and its spectrum overlaps with the absorption spectrum of TBRb. Although the host PLQ was selectively excited, TBRb-doped PLQ exhibited a peak PL wavelength of 560 nm. This result suggests that the Förster resonance energy transfer (FRET), which only allows for singlet-singlet energy transfer23, occurred from PLQ to TBRb. Figure 3(b) shows the EL spectra and photographic images of EL emissions. Greenish-blue and yellow EL emissions were confirmed from the 1000-μm-wide electro-microfluidic device with PLQ and TBRb-doped PLQ, respectively. In the case of PLQ, similar to the PL spectrum [Fig. 3(a)], an emission maximum at 500 nm and broad emission ranging from 420 nm to 650 nm were observed. The lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level of PLQ are 2.6 eV and 5.8 eV, respectively1522. The work-function values of the GOPTS-modified ITO and APTES-modified ITO are 4.70 eV and 4.55 eV, respectively15. The EL emission confirms that the holes and electrons were injected from the GOPTS-modified ITO anode and APTES-modified ITO cathode, respectively, and then the excitons of PLQ were produced by the recombination of the holes and electrons. The electro-microfluidic device with TBRb-doped PLQ showed a broad emission ranging from 520 nm to 750 nm. The obtained EL emission maximum of TBRb-doped PLQ is identical to the PL emission maximum [Fig. 3(a)]. Although the emission attributed to the host PLQ was observed at approximately 500 nm in the PL spectrum, this emission was not clearly observed in the EL spectrum. The LUMO level and HOMO level of TBRb are reported to be located at 3.2 eV and 5.4 eV, respectively1718. It was found that the HOMO-LUMO level of TBRb is within the HOMO-LUMO gap of the host PLQ. Therefore, the obtained EL spectrum suggests that the excitons of TBRb were generated not only by the FRET from the host to the guest but also by direct recombination of the electrons and holes which were trapped in the guest emitters2425. From the EL spectrum measurements, TBRb-doped PLQ was found to be useful for the yellow liquid emitter. In addition, the sum of the EL spectra of PLQ and TBRb-doped PLQ is shown in the inset of Fig. 4(b). White EL emission, which has a broad spectrum ranging from 420 nm to 750 nm, would be produced by the simultaneous EL emissions of PLQ and TBRb-doped PLQ from the integrated microchannels. It was also found that the emission intensity of TBRb-doped PLQ is higher than that of PLQ at the same driving voltage of 100 V. PLQY of 10 μM PLQ and 18 μM TBRb were measured to be 69% and 74%, respectively. This result indicates that the enhancement in TBRb-doped system can be explained by the PLQY values. Thus, PLQ was found to be useful as the liquid host for a highly fluorescent yellow dopant of TBRb. From these results, the generation of warm-white light can be expected to be obtained by the proposed microfluidic WOLED having the same size of PLQ and TBRb-doped PLQ patterns.


Microfluidic White Organic Light-Emitting Diode Based on Integrated Patterns of Greenish-Blue and Yellow Solvent-Free Liquid Emitters.

Kobayashi N, Kasahara T, Edura T, Oshima J, Ishimatsu R, Tsuwaki M, Imato T, Shoji S, Mizuno J - Sci Rep (2015)

(a) PL spectrum of PLQ and 2wt% TBRb-doped PLQ, and absorption spectrum of 33.3 μM TBRb. (b) EL spectra of PLQ and 2wt% TBRb-doped PLQ with the microfluidic OLED. Inset: EL emissions of PLQ and TBRb-doped PLQ, and the sum of EL spectra of PLQ and 2wt% TBRb-doped PLQ under an applied voltage of 100 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594091&req=5

f3: (a) PL spectrum of PLQ and 2wt% TBRb-doped PLQ, and absorption spectrum of 33.3 μM TBRb. (b) EL spectra of PLQ and 2wt% TBRb-doped PLQ with the microfluidic OLED. Inset: EL emissions of PLQ and TBRb-doped PLQ, and the sum of EL spectra of PLQ and 2wt% TBRb-doped PLQ under an applied voltage of 100 V.
Mentions: Figure 3(a) shows the absorption spectrum of 33.3 μM TBRb and the PL spectra of PLQ and TBRb-doped PLQ. An excitation wavelength of 365 nm was used for the PL measurements because the host PLQ has a strong UV absorption wavelength at less than 377 nm151622. TBRb showed an absorption spectrum ranging from 400 nm to 570 nm. The PL emission of PLQ has a peak wavelength of 500 nm, and its spectrum overlaps with the absorption spectrum of TBRb. Although the host PLQ was selectively excited, TBRb-doped PLQ exhibited a peak PL wavelength of 560 nm. This result suggests that the Förster resonance energy transfer (FRET), which only allows for singlet-singlet energy transfer23, occurred from PLQ to TBRb. Figure 3(b) shows the EL spectra and photographic images of EL emissions. Greenish-blue and yellow EL emissions were confirmed from the 1000-μm-wide electro-microfluidic device with PLQ and TBRb-doped PLQ, respectively. In the case of PLQ, similar to the PL spectrum [Fig. 3(a)], an emission maximum at 500 nm and broad emission ranging from 420 nm to 650 nm were observed. The lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level of PLQ are 2.6 eV and 5.8 eV, respectively1522. The work-function values of the GOPTS-modified ITO and APTES-modified ITO are 4.70 eV and 4.55 eV, respectively15. The EL emission confirms that the holes and electrons were injected from the GOPTS-modified ITO anode and APTES-modified ITO cathode, respectively, and then the excitons of PLQ were produced by the recombination of the holes and electrons. The electro-microfluidic device with TBRb-doped PLQ showed a broad emission ranging from 520 nm to 750 nm. The obtained EL emission maximum of TBRb-doped PLQ is identical to the PL emission maximum [Fig. 3(a)]. Although the emission attributed to the host PLQ was observed at approximately 500 nm in the PL spectrum, this emission was not clearly observed in the EL spectrum. The LUMO level and HOMO level of TBRb are reported to be located at 3.2 eV and 5.4 eV, respectively1718. It was found that the HOMO-LUMO level of TBRb is within the HOMO-LUMO gap of the host PLQ. Therefore, the obtained EL spectrum suggests that the excitons of TBRb were generated not only by the FRET from the host to the guest but also by direct recombination of the electrons and holes which were trapped in the guest emitters2425. From the EL spectrum measurements, TBRb-doped PLQ was found to be useful for the yellow liquid emitter. In addition, the sum of the EL spectra of PLQ and TBRb-doped PLQ is shown in the inset of Fig. 4(b). White EL emission, which has a broad spectrum ranging from 420 nm to 750 nm, would be produced by the simultaneous EL emissions of PLQ and TBRb-doped PLQ from the integrated microchannels. It was also found that the emission intensity of TBRb-doped PLQ is higher than that of PLQ at the same driving voltage of 100 V. PLQY of 10 μM PLQ and 18 μM TBRb were measured to be 69% and 74%, respectively. This result indicates that the enhancement in TBRb-doped system can be explained by the PLQY values. Thus, PLQ was found to be useful as the liquid host for a highly fluorescent yellow dopant of TBRb. From these results, the generation of warm-white light can be expected to be obtained by the proposed microfluidic WOLED having the same size of PLQ and TBRb-doped PLQ patterns.

Bottom Line: The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V.A white emission with Commission Internationale de l'Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light.The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Science and Engineering, Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan.

ABSTRACT
We demonstrated a novel microfluidic white organic light-emitting diode (microfluidic WOLED) based on integrated sub-100-μm-wide microchannels. Single-μm-thick SU-8-based microchannels, which were sandwiched between indium tin oxide (ITO) anode and cathode pairs, were fabricated by photolithography and heterogeneous bonding technologies. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ) was used as a solvent-free greenish-blue liquid emitter, while 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb)-doped PLQ was applied as a yellow liquid emitter. In order to form the liquid white light-emitting layer, the greenish-blue and yellow liquid emitters were alternately injected into the integrated microchannels. The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V. A white emission with Commission Internationale de l'Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light. The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting.

No MeSH data available.