Solution-Processed OLEDs Based on a Bipolar AIE Terpyridine Derivative as a Host

The efficiency of organic light-emitting diodes (OLEDs) with multiple functional components is still limited owing to their complicated design and fabrication process. A postfunctionalization strategy was exploited to develop devices derived from terpyridine derivative bipolar host 4′-(3′,4′,5′-triphenyl-[1,1′:2′,1″-terphenyl]-4-yl)-2,2′:6′,2″-terpyridine to overcome this limitation. The glass transition temperature was up to 176 °C, and the host was favorable for practical OLED devices. The crystallite size of the powder calculated by the modified Scherrer’s method was 102 nm. Furthermore, the ionization potential (IP^PE) of the spin-coated host on the fluorine tin oxide (FTO), which is related to the highest occupied molecular orbital (HOMO), was calculated to be 5.98 eV. Both hole and electron mobilities measured by space charge limit current (SCLC) reveal bipolar transport in the host, with a hole mobility of 1.87 × 10^-4 cm² V^-1 s^-1 and an electron mobility of 6.69 × 10^-5 cm² V^-1 s^-1. Aggregation-induced emission (AIE) phenomena were discussed in detail with field emission scanning electron microscopy (FESEM). In addition, a thermally activated delayed fluorescence (TADF) emitter consisting of 10-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) was considered in a host-guest system. Taking into account the role of the designed and synthesized host, using poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as a hole injection layer (HIL) for cyan OLED solution processing, the maximum luminescence, current, power, and external quantum efficiency (EQE) reached 19,986 cd m^-2, 45.15 cd A^-1, 32.95 lm W^-1, and 22.35%, respectively, for host (70 wt %):DMAC-TRZ as an emitting layer.