Thermally Cross-Linkable Host Materials for Solution-Processed OLEDs: Synthesis, Characterization, and Optoelectronic Properties

A series of cross-linkable bipolar host materials containing carbazole (donor, D) and 1,2,4-triazole (acceptor, A) were designed and synthesized. The host materials with styryl groups can be thermally cross-linked by curing at 172-190 degrees C without any polymerization initiator. Excellent solvent resistance was observed for all the host materials, which is beneficial for the preparation of subsequent functional layers by solution processes. The highest occupied molecular orbital energy levels of 5.55, 5.58 and 5.54 eV are estimated for these host materials, which indicates low injection barrier from the hole transport layer. A current efficiency of 15.3 cd A(-1) and an external quantum efficiency of 4.6 % were achieved for solution-processed Ir(mppy)(3)-based OLEDs by using the cross-linkable host material.