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.
Highlights
White organic light-emitting diodes (WOLEDs) have attracted much attentions for the generation of red, green, blue, and white (RGBW)-based displays as well as lighting applications because of their advantages such as plane-emission, large-scale, light-weight, and flexibility[1,2,3,4,5,6,7]
An electro-microfluidic device, which consisted of a single-μ m-thick and 1000- to 1500-μ m-wide negative photoresist SU-8 microchannels, was fabricated on a glass substrate using microelectromechanical systems (MEMS) process and a heterogeneous bonding technique through the use of self-assembled monolayers (SAMs). 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ), which is one of the pyrene-based liquid organic semiconductors (LOSs), was injected into microchannels sandwiched between transparent anode and cathode pairs without a vacuum process to form the liquid emitting layers
We revealed the refreshable luminance characteristics of the microfluidic OLED via reinjection of fresh liquid emitters into the light-emitting pixels, indicating that deteriorated liquids were replaced with new liquids using microfluidic technologies
Summary
Naofumi Kobayashi1,*, Takashi Kasahara1,*, Tomohiko Edura[2], Juro Oshima[3], Ryoichi Ishimatsu[4], Miho Tsuwaki[1], Toshihiko Imato[4], Shuichi Shoji1 & Jun Mizuno[5]. In order to form the liquid white light-emitting layer, the greenish-blue and yellow liquid emitters were alternately injected into the integrated microchannels. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ), which is one of the pyrene-based LOSs, was injected into microchannels sandwiched between transparent anode and cathode pairs without a vacuum process to form the liquid emitting layers. Since our previous microfluidic OLED had shallow microchannels with an aspect ratio (microchannel thickness/width) of 0.004 to 0.006, GOPTS-SAM was formed only on the SU-8 layer of the anode substrate to prevent conjugations between the ITO anode and cathode during the bonding process[14] Both the SU-8 microchannels and ITO anodes were modified with GOPTS-SAM because the aspect ratio of the microfluidic WOLED consisting of 60-μ m-wide and 6-μ m-thick microchannels is two orders higher than that of the previous device. Electroluminescent characteristics of PLQ and TBRb-doped PLQ were measured with the 6-μ m-thick and 1000-μ m-wide electro-microfluidic device, which was fabricated with the same process as that of the microfluidic WOLED
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