Highly efficient, solution-processed orange–red phosphorescent OLEDs by using new iridium phosphor with thieno[3,2-c]pyridine derivative as cyclometalating ligand

Abstract

A new orange iridium phosphor of (EtPy)2Ir(acac) with thieno[3,2-c]pyridine derivative as cyclometalating ligand was designed and synthesized. The combination of thieno[3,2-c]pyridine with rigid fluorene moiety enlarged the π conjugation of ligand, and consequently caused the peak emission of (EtPy)2Ir(acac) red-shift to 588nm. By using (EtPy)2Ir(acac) as the orange phosphor, the fully solution-processed PhOLEDs were fabricated with the following device configuration: ITO/PEDOT:PSS/PVK: PBD: (EtPy)2Ir(acac)/CsF/Al. With PEDOT:PSS 8000 as the hole-injecting material, the orange device achieved a maximum current efficiency of 13.4cdA−1, a maximum power efficiency of 5.9lmW−1 and a maximum external quantum efficiency (EQE) of 11.2% with a CIE coordinate of (0.62, 0.38) that falls into the orange–red region. Moreover, at high luminance of 1000cdm−2, the device still remained high current efficiency of 8.7cdA−1 and EQE of 7.3%. To the best of our knowledge, these efficiencies were among the highest ever reported for solution-processed orange–red PhOLEDs.