Bipolar iridium dendrimers containing carbazolyl dendron and 1,2,4-triazole unit for solution-processed saturated red electrophosphorescence

Two solution-processable, carbazole-based iridium dendrimers (Ir-1 and Ir-2) were synthesized and characterized. The presence of carbazolyl substituent on the cyclometallated ligand resulted in improved solubility, good control over intermolecular interactions, and improved hole transport properties. The triazole ancillary ligand led to improved electron transport properties. When the dendrimers were employed as host-free light-emitting layers in the OLEDs, the devices exhibited a low turn-on voltage of 5.4 V. The maximal external quantum efficiencies and luminous efficiency of the devices obtained from Ir-1 and Ir-2 were 5.1% and 3.3 cd A−1 and 7.9% and 4.4 cd A−1, respectively, both with saturated red emission (CIE coordinates, 0.663, 0.332). The devices have a structure of indium tin oxide/poly(3,4-ethylenedioxythiophene)/dendrimer/1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene/cesium fluoride/aluminum. Given ease of synthesis and good device performance, these iridium dendrimers can be used to fully exploit the potential of low-cost OLEDs, leading to more applications in high-efficiency OLEDs.

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