In this study, we propose on-demand multi-color microfluidic organic light-emitting diodes (microfluidic OLEDs) using fluorescent guest emitter-doped liquid organic semiconductors. We use 1-pyrenebutyric acid 2-ethylhexyl ester (PLQ) not only for a greenish-blue liquid emitter, but also for a liquid host. 5,12-Diphenyltetracene (DPT), 5,6,11,12-tetraphenyltetracene (rubrene), and tetraphenyldibenzoperiflanthene (DBP) are doped into PLQ to obtain green, yellow, and red liquid emitters, respectively. Single-micrometer-thick SU-8-based microchannels sandwiched between an indium tin oxide (ITO) anode and a 3-aminopropyltriethoxysilane (APTES)-modified ITO cathode are fabricated on a glass substrate using photolithography and heterogeneous bonding techniques, and emitting layers are formed on-demand by simply injecting liquid emitters into the target microchannels. The microfluidic OLEDs with liquid emitters successfully exhibited multi-color electroluminescence (EL) emissions. Furthermore, the maximum luminance reached 26.0 cd/m2 at 61 V for 2.5-μm-thick microfluidic OLED with PLQ, and the decreased EL luminance was recovered by replacing the degraded emitting layer with a fresh liquid emitter. We expect that on-demand multi-color EL emissions and refreshable luminance features of the proposed microfluidic OLEDs will be highly promising technologies for future long-life light-emitting device applications.
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