Synthesis And Optoelectronic Properties Of Electrophosphorescent Materials Based On Cationic Iridium Complexes And Broad Bandgap Polymers Host

In recent years, organic and polymer light-emitting diods (OLED and PLED) based on phosphorescent iridium complex have been achieved great attention due to their potential for achieving 100% internal emission. But most progress has been made in neutral complex; reports about cationic iridium complexes are rare. Compared with neutral complex, light-emitting electrochemical cells (LECs) based on cationic iridium complexes possess several advantages, for example, simple device structure with single emissive layer, low cost fabrication based on solution-process and no need to use air-sensitive metal to facilitate electron injection, etc. Since the emissive layer contains mobile ions, thus when external voltage is applied, ions will redistribute and lead to redox near the electrodes, creating in-situ formation of p-i-n junction in the device. As a result of ohmic contact with each electrode, charge carrier injection barrier height for electron and hole is minimized. Therefore, device can operate at very low voltage with balanced charge injection and transport, thus can potentially lead to high power efficiency with very low turn-on voltage.In this paper, novel sky-blue and blue-green emitting cationic iridium complexes with triazole-pyridine as the ancillary ligand were prepared and characterized. The emission of these cationic iridium complexes can be tuned and blue-shifted by using triazole-pyridine ancillary ligand. Upon the incorporation of cyanogen group in the side alkyl chain of the ancillary ligand, the device efficiencies were significantly improved. Single layer LECs based on C1 and C2 show a high luminous efficiency of 2.6 cd/A with CIE coordinate of (0.21, 0.33), and a LE of 6.8 cd/A with a CIE coordinate of (0.31, 0.53), respectively.The new bipolar polymers derived from carbazole and pyridine units with high triplet energy level were prepared by metal-free, superacid-catalyzed polyhydroxyalkylation. The polymers shows good thermal stability with high glass transition temperature of 210 ?C for P1, 185 ?C for P2 and 110 ?C for P3 and broad bandgap exceed 3.3 eV estimated from the onset of the absorption spectra. Efficient green phosphorescent PLEDs are realized by using these polymers as host and iridium complexes Ir(mppy)3 as guest. The maximum luminous efficiency was 4.4 cd/A obtained using P2 as the host in the single-layer devices without blending any other electron-transporting materials.