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

摘要

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 tri-azole 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-ethylenedioxythio phene)/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.