A novel charged iridium complex for organic light emitting diode (OLED) application

This research report the synthesis and characterizations of new charged iridium (III) complexes for organic light emitting diodes (OLEDs). The materials were designed with bis(4-alkoxyphenyl) substituted 4,5-diazafluorene derivatives as bulky N^N ligands. The electroluminescent properties with the complexes as emitters were studied, and the OLED performances with complexes as emitters were assessed in three parts. In the first part, the complexes with different C^N ligands (Co2F, Coppy, and Cothio) were used for color tuning with OLED structures: ITO/PEDPT:PSS/complex/TPBi/LiF/Al. The emission colors showed green, yellow, and orange with the Commission International De L’Elairage coordination of (0.28, 0.54), (0.50, 0.49), and (0.50, 0.40), respectively. The Coppy showed the highest OLED performance with current and power efficiency at 1.37 cd/A and 0.39 lm/W respectively. In the second part, the complexes with varied side chains on N^N ligands (Coppy, C6ppy, C8ppy, and isoC8ppy) were used for the efficient host-guest OLEDs. Results showed that the complexes had no significant effects on the photophysical and electrochemical properties. The device with the configuration of ITO/PEDOT:PSS/PVK:complex/TPBi/LiF/Al showed similar color at CIE coordination of (0.48, 0.50). The device based on the n-octyl chain, namely C8ppy, showed the highest maximum current and power efficiency of 11.37 cd/A and 2.94 Im/W, respectively. In the third part, the ITO/PEDPT:PSS/PVK:complex (10:5 by weight)/Al structures were fabricated for the OLEDs performance study. Results found that the device with long alkyl chains showed longer stabilities than the short methyl group.